Biomedical subjects

R K McNamara

Publications and source records attributed to R K McNamara.

At least 19 recordsLinked to original sources

PubMed2006

C57BL/6J mice exhibit reduced dopamine D3 receptor-mediated locomotor-inhibitory function relative to DBA/2J mice.

Previous reports have identified greater sensitivity to the locomotor-stimulating, sensitizing, and reinforcing effects of amphetamine in inbred C57BL/6J mice relative to inbred DBA/2J mice. The dopamine D3 receptor (D3R) plays an inhibitory role in the regulation of rodent locomotor activity, and exerts inhibitory opposition to D1 receptor (D1R)-mediated signaling. Based on these observations, we investigated D3R expression and D3R-mediated locomotor-inhibitory function, as well as D1R binding and D1R-mediated locomotor-stimulating function, in C57BL/6J and DBA/2J mice. C57BL/6J mice exhibited lower D3R binding density (-32%) in the ventral striatum (nucleus accumbens/islands of Calleja), lower D3R mRNA expression (-26%) in the substantia nigra/ventral tegmentum, and greater D3R mRNA expression (+40%) in the hippocampus, relative to DBA/2J mice. There were no strain differences in DR3 mRNA expression in the ventral striatum or prefrontal cortex, nor were there differences in D1R binding in the ventral striatum. Behaviorally, C57BL/6J mice were less sensitive to the locomotor-inhibitory effect of the D3R agonist PD128907 (10 microg/kg), and more sensitive to the locomotor-stimulating effects of novelty, amphetamine (1 mg/kg), and the D1R-like agonist +/- -1-phenyl-2,3,4,5-tetrahydro-(1H)-3-benzazepine-7,8,-diol hydrochloride (SKF38393) (5-20 mg/kg) than DBA/2J mice. While the selective D3R antagonist N-(4-[4-{2,3-dichlorphenyl}-1 piperazinyl]butyl)-2-fluorenylcarboxamide (NGB 2904) (0.01-1.0 mg/kg) augmented novelty-, amphetamine-, and SKF38393-induced locomotor activity in DBA/2J mice, it reduced novelty-induced locomotor activity in C57BL/6J mice. Collectively, these results demonstrate that C57BL/6J mice exhibit less D3R-mediated inhibitory function relative to DBA/2J mice, and suggest that reduced D3R-mediated inhibitory function may contribute to heightened sensitivity to the locomotor-stimulating effects of amphetamine in the C57BL/6J mouse strain. Furthermore, these data demonstrate that comparisons between C57BL/6J and DBA/2J mouse strains provide a model for elucidating the molecular determinants of genetic influence on D3R function.

2,3,4,5-Tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-ben↗

PubMed2000

Differential regulation of primary protein kinase C substrate (MARCKS, MLP, GAP-43, RC3) mRNAs in the hippocampus during kainic acid-induced seizures and synaptic reorganization.

In the mature hippocampus, kainic acid seizures lead to excitotoxic cell death and synaptic reorganization in which granule cell axons (mossy fibers) form ectopic synapses on granule cell dendrites. In the present study, we examined the expression of four major, developmentally regulated protein kinase C (PKC) substrates (MARCKS, MLP, GAP-43, RC3), which have different subcellular and regional localizations in the hippocampus at several time points (6 hr, 12 hr, 18 hr, 24 hr, 48 hr, 5 days, or 15 days) following kainic acid seizures using in situ hybridization. Consistent with previous reports, following kainate seizures, GAP-43 mRNA expression exhibited a delayed and protracted elevation in the granule cell layer, which peaked at 24 hr, whereas expression in fields CA1 and CA3 remained relatively unchanged. Conversely, RC3 mRNA expression exhibited a delayed reduction in the granule cell layer that was maximal at 18 hr, as well as a reduction CA1 at 48 hr, whereas CA3 levels did not change. MARCKS mRNA expression in the granule cell layer and CA1 remained stable following kainate, although an elevation was observed in subfield CA3c at 12 hr. Similarly, MLP mRNA expression did not change in the granule cell layer or CA1 following kainate but exhibited a protracted elevation in subfields CA3b,c beginning at 6 hr post-kainate. Collectively these data demonstrate that different PKC substrate mRNAs exhibit unique expression profiles and regulation in the different cell fields of the mature hippocampus following kainic acid seizures and during subsequent synaptic reorganization. The expression profiles following kainate seizures bear resemblance to those observed during postnatal hippocampal development, which may indicate the recruitment of common regulatory mechanisms.

Animals↗

PubMed2000

Facial motor neuron regeneration induces a unique spatial and temporal pattern of myristoylated alanine-rich C kinase substrate expression.

We have previously shown that the myristoylated alanine-rich C kinase substrate, a primary protein kinase C substrate in brain that binds and cross-links filamentous actin, is enriched in neuronal growth cones and is developmentally regulated in brain. Here we examined myristoylated alanine-rich C kinase substrate expression in the facial motor nucleus during axonal regeneration following facial nerve axotomy or facial nerve resection lesions, which impede regeneration, or following motor neuron degeneration induced by the retrograde neurotoxin ricin. For comparative purposes, the protein kinase C substrates myristoylated alanine-rich C kinase substrate-like protein and growth-associated protein-43 were examined in parallel. Myristoylated alanine-rich C kinase substrate messenger RNA exhibited a robust increase in both neurons and non-neuronal cells in the facial motor nucleus beginning four days after axotomy, peaked at seven days (2.5-fold), and declined back to baseline levels by 40 days. Myristoylated alanine-rich C kinase substrate protein similarly exhibited a twofold elevation in the facial motor nucleus determined four and 14 days post-axotomy. Following nerve resection, myristoylated alanine-rich C kinase substrate messenger RNA levels increased at seven days and returned to baseline levels by 40 days. Unlike myristoylated alanine-rich C kinase substrate messenger RNA, myristoylated alanine-rich C kinase substrate-like messenger RNA levels did not increase in the facial motor nucleus at any time point following nerve axotomy or resection, whereas growth-associated protein-43 messenger RNA exhibited a rapid (one day) and prolonged (40 days) elevation in facial motor nucleus neurons following either nerve axotomy or resection. Ricin-induced degeneration of facial motor neurons elevated myristoylated alanine-rich C kinase substrate and myristoylated alanine-rich C kinase substrate-like messenger RNAs in both microglia (lectin-positive) and astrocytes (glial fibrillary acidic protein-positive).Collectively, these data demonstrate that myristoylated alanine-rich C kinase substrate exhibits a unique expression profile in the facial motor nucleus following facial nerve lesions, and it is proposed that myristoylated alanine-rich C kinase substrate may serve to mediate actin-membrane cytoskeletal plasticity in both neurons and glial cells in response to protein kinaseC-mediated signaling during nerve regeneration and degeneration.

Animals↗

PubMed1999

Generation of aberrant sprouting in the adult rat brain by GAP-43 somatic gene transfer.

The expression of GAP-43 was modulated genetically in the adult rat nigrostriatal or septohippocampal pathway using recombinant adeno-associated virus (rAAV) vectors incorporating the neuron specific enolase (NSE) promoter and either a rat GAP-43 cDNA or the corresponding antisense sequence. Bicistronic expression of green fluorescent protein (GFP) enabled us to evaluate transduced neurons selectively. Single injections of rAAV into the substantia nigra pars compacta (SNc) transduced both dopaminergic and non-dopaminergic neurons stably for the 3-month duration of the study. Transduction with the GAP-43 vector in this region: (1) increased GAP-43 mRNA levels 2-fold compared to controls; (2) led to GAP-43 immunoreactivity in neuronal perikarya, axons, and dendrites that was not observed otherwise; and (3) resulted in GAP-43/ GFP-positive axons that were traced to the striatum where they formed clusters of aberrant nets. The GAP-43 antisense vector, in contrast, decreased neuropil GAP-43 immunoreactivity compared to controls in the SNc. In septum, injections of the GAP-43 expressing vector also caused aberrant clusters of GAP-43 labelled fibers in terminal fields, i.e., fornix and hippocampus, that were not observed in control tissues. It therefore appears that rAAV vectors provide a novel approach for modulating intraneuronal GAP-43 expression in the adult brain.

Afferent Pathways↗

PubMed1999

Impaired learning and memory and altered hippocampal neurodevelopment resulting from interleukin-2 gene deletion.

Interleukin-2 (IL-2), the protypical T cell growth factor and immunoregulatory cytokine produced by lymphocytes, has been implicated as a brain neurotrophic factor and neuromodulator. The consequences of the absence of endogenous IL-2 on brain development and function were unknown. Brain IL-2 receptors are enriched in the hippocampal formation, an area critical for the acquisition and consolidation of spatial learning and memory. Thus, we tested the hypothesis that mice lacking IL-2 would exhibit alterations in hippocampal-dependent learning and neurodevelopment. Compared with C57BL/6-IL-2+/+ wild-type mice, we observed that C57BL/6-IL-2-/- gene knockout mice had markedly impaired spatial learning and memory in the Morris water maze. No significant deficits in parameters of learning and memory performance were found in severe combined immunodeficient (SCID) mice (C57BL/6scid), however, suggesting that the impaired spatial learning and memory exhibited by IL-2 knockout mice is not attributable to generalized immunodeficiency resulting from the absence of endogenous IL-2. Examination of other domains of behavioral performance showed that the IL-2 knockout and wildtype mice did not differ in measures of fearfulness or locomotor activity in an elevated plus maze, or in reflexive startle responses to auditory stimuli--although prepulse inhibition of acoustic startle (PPI) was increased significantly in IL-2 knockout mice. The spatial learning and memory impairment in IL-2 knockout mice was accompanied by reductions in hippocampal infrapyramidal mossy neuronal fiber length, a factor shown previously to correlate positively with spatial learning ability. These findings indicate that, in addition to being a pivotal cytokine in immune regulation, IL-2 may play a role in the development and regulation of brain neurons involved in spatial learning and memory.

Acoustic Stimulation↗

PubMed1999

Differential subcellular redistribution of protein kinase C isozymes in the rat hippocampus induced by kainic acid.

Protein kinase C (PKC) consists of a family of Ca2+/phospholipid-dependent isozymes that has been implicated in the delayed neurotoxic effects of glutamate in vitro. In the present study, we assessed the effect of the glutamate analogue kainic acid (KA) on the subcellular expression of PKC isozymes in the hippocampus (HPC) in the period preceding (0.5, 1.5, 12, and 24 h) and during (120 h) hippocampal necrosis using western blot analysis and PKC isozyme-specific antibodies. Before subcellular fractionation (cytosol + membrane), hippocampi were microdissected into "HPC" (fields CA1-CA3) and "dentate gyrus" (DG; granule cells + hilus) regions. Four general patterns of alterations in PKC isozyme expression/distribution were observed following KA treatment. The first pattern was a relative stability in expression following KA treatment and was most apparent for cytosol PKCalpha (HPC + DG) and membrane (HPC) and cytosol (DG) PKCbetaII. The second pattern, observed with PKCgamma and PKCepsilon, was characterized by an initial increase in expression in both membrane and cytosolic fractions before seizure activity (0.5 h) followed by a gradual decrease until significant reductions are observed by 120 h. The third pattern, exhibited by PKCdelta, involved an apparent translocation, increasing in the membrane and decreasing in the cytosol, followed by down-regulation in both fractions and subsequent recovery. The fourth pattern was observed with PKCzeta only and entailed a significant reduction in expression before and during limbic motor seizures followed by a dramatic fivefold increase in the membrane fraction during the period of hippocampal necrosis (120 h). Although these patterns did not segregate according to conventional PKC isozyme classifications, they do indicate dynamic isozyme-specific regulation by KA. The subcellular redistribution of PKC isozymes may contribute to the histopathological sequelae produced by KA in the hippocampus and may model the pathogenesis associated with diseases involving glutamate-induced neurotoxicity.

Animals↗

PubMed1999

Expression of the myristoylated alanine-rich C kinase substrate (MARCKS) and MARCKS-related protein (MRP) in the prefrontal cortex and hippocampus of suicide victims.

BACKGROUND: Although suicide is a leading cause of death in the United States and represents a significant public health threat, little is known about the neurobiological or molecular factors that contribute to its pathophysiology. A number of studies now indicate that lithium has considerable efficacy in the prevention of suicide in patients with affective disorders, and accumulating evidence indicates that protein kinase C (PKC) and its substrates, in particular the myristoylated alanine-rich C kinase substrate (MARCKS), are primary targets of chronic lithium treatment. We therefore hypothesized that a dysregulation in MARCKS expression in key brain regions could contribute to the pathophysiology associated with suicide. To address this, we examined MARCKS, as well as the closely related MARCKS-related protein (MRP), mRNA expression in the hippocampus and dorsolateral prefrontal cortex of suicide victims and normal controls. METHOD: MARCKS and MRP mRNA expression was assessed by quantitative in situ hybridization histochemistry performed on postmortem hippocampal and dorsolateral prefrontal cortex sections from suicide (N = 9) and normal control (N = 10) brains. RESULTS: In the normal hippocampus, both MARCKS and MRP mRNA expression were highest in the granule cell layer and low-moderate in CA1, CA3, and hilus. A high level of MRP mRNA expression was also observed in the white matter of the fimbria/fornix. Neither MARCKS nor MRP mRNA expression levels differed significantly in the granule cell layer, CA3, hilus, or CA1 in suicide victims relative to normal controls (1-way ANOVA, p > .05). In the normal prefrontal cortex, MARCKS was expressed exclusively in gray matter (layers I-VI), whereas MRP was expressed in both gray and white matter. Neither MARCKS nor MRP mRNA expression levels in the gray and white matter regions of the dorsal prefrontal cortex differed between suicides and normal controls (1-way ANOVA, p > .05). CONCLUSION: The present findings are the first to demonstrate the expression and distribution of MARCKS and MRP in the human hippocampus and dorsolateral prefrontal cortex, and their expression pattern within these regions bears strong resemblance to those observed in the adult rat brain. Comparison of MARCKS and MRP mRNA expression in the hippocampus and prefrontal cortex of suicide victims and normal controls indicates that these 2 mRNAs are not differentially regulated in these regions. However, differences in MARCKS and MRP protein expression and function cannot be ruled out by the present findings.

Adult↗

PubMed1999

Differential changes in the phosphorylation of the protein kinase C substrates myristoylated alanine-rich C kinase substrate and growth-associated protein-43/B-50 following Schaffer collateral long-term potentiation and long-term depression.

Activation of protein kinase C (PKC) is one of the biochemical pathways thought to be activated during activity-dependent synaptic plasticity in the brain, and long-term potentiation (LTP) and long-term depression (LTD) are two of the most extensively studied models of synaptic plasticity. Here we have examined changes in the in situ phosphorylation level of two major PKC substrates, myristoylated alanine-rich C kinase substrate (MARCKS) and growth-associated protein (GAP)-43/B-50, after pharmacological stimulation or induction of LTP or LTD in the CA1 field of the hippocampus. We find that direct PKC activation with phorbol esters, K+-induced depolarization, and activation of metabotropic glutamate receptors increase the in situ phosphorylation of both MARCKS and GAP-43/B-50. The induction of LTP increased the in situ phosphorylation of both MARCKS and GAP-43/B-50 at 10 min following high-frequency stimulation, but only GAP-43/B-50 phosphorylation remained elevated 60 min after LTP induction. Furthermore, blockade of LTP induction with the NMDA receptor antagonist D-2-amino-5-phosphonopentanoic acid prevented elevations in GAP-43/B-50 phosphorylation but did not prevent the elevation in MARCKS phosphorylation 10 min following LTP induction. The induction of LTD resulted in a reduction in GAP-43/B-50 phosphorylation but did not affect MARCKS phosphorylation. Together these findings show that activity-dependent synaptic plasticity elicits PKC-mediated phosphorylation of substrate proteins in a highly selective and coordinated manner and demonstrate the compartmentalization of PKC-substrate interactions. Key Words: Protein kinase C-Myristoylated alanine-rich C kinase substrate-Growth-associated protein-43-Long-term potentiation-Long-term depression-(RS)-alpha-Methyl-4-carboxyphenylglycine-D-2-Amino-5-ph osphonopentanoic acid-Glutamate.

Enzyme Activation↗

PubMed1998

Effect of reduced myristoylated alanine-rich C kinase substrate expression on hippocampal mossy fiber development and spatial learning in mutant mice: transgenic rescue and interactions with gene background.

The myristoylated alanine-rich C kinase substrate (MARCKS) is a prominent protein kinase C (PKC) substrate in brain that is expressed highly in hippocampal granule cells and their axons, the mossy fibers. Here, we examined hippocampal infrapyramidal mossy fiber (IP-MF) limb length and spatial learning in heterozygous Macs mutant mice that exhibit an approximately 50% reduction in MARCKS expression relative to wild-type controls. On a 129B6(N3) background, the Macs mutation produced IP-MF hyperplasia, a significant increase in hippocampal PKCepsilon expression, and proficient spatial learning relative to wild-type controls. However, wild-type 129B6(N3) mice exhibited phenotypic characteristics resembling inbred 129Sv mice, including IP-MF hypoplasia relative to inbred C57BL/6J mice and impaired spatial-reversal learning, suggesting a significant contribution of 129Sv background genes to wild-type and possibly mutant phenotypes. Indeed, when these mice were backcrossed with inbred C57BL/6J mice for nine generations to reduce 129Sv background genes, the Macs mutation did not effect IP-MF length or hippocampal PKCepsilon expression and impaired spatial learning relative to wild-type controls, which now showed proficient spatial learning. Moreover, in a different strain (B6SJL(N1), the Macs mutation also produced a significant impairment in spatial learning that was reversed by transgenic expression of MARCKS. Collectively, these data indicate that the heterozygous Macs mutation modifies the expression of linked 129Sv gene(s), affecting hippocampal mossy fiber development and spatial learning performance, and that MARCKS plays a significant role in spatial learning processes.

Animals↗

PubMed1998

Role for neuronally derived fractalkine in mediating interactions between neurons and CX3CR1-expressing microglia.

A recently identified chemokine, fractalkine, is a member of the chemokine gene family, which consists principally of secreted, proinflammatory molecules. Fractalkine is distinguished structurally by the presence of a CX3C motif as well as transmembrane spanning and mucin-like domains and shows atypical constitutive expression in a number of nonhematopoietic tissues, including brain. We undertook an extensive characterization of this chemokine and its receptor CX3CR1 in the brain to gain insights into use of chemokine-dependent systems in the central nervous system. Expression of fractalkine in rat brain was found to be widespread and localized principally to neurons. Recombinant rat CX3CR1, as expressed in Chinese hamster ovary cells, specifically bound fractalkine and signaled in the presence of either membrane-anchored or soluble forms of fractalkine protein. Fractalkine stimulated chemotaxis and elevated intracellular calcium levels of microglia; these responses were blocked by anti-CX3CR1 antibodies. After facial motor nerve axotomy, dramatic changes in the levels of CX3CR1 and fractalkine in the facial nucleus were evident. These included increases in the number and perineuronal location of CX3CR1-expressing microglia, decreased levels of motor neuron-expressed fractalkine mRNA, and an alteration in the forms of fractalkine protein expressed. These data describe mechanisms of cellular communication between neurons and microglia, involving fractalkine and CX3CR1, which occur in both normal and pathological states of the central nervous system.

Amino Acid Sequence↗

PubMed1998

Distribution of the protein kinase C substrates MARCKS and MRP in the postnatal developing rat brain.

The myristoylated alanine-rich C kinase substrate (MARCKS) and MARCKS-related protein (MRP) are both membrane-associated phosphoproteins that interact with calmodulin and filamentous actin in a protein kinase C phosphorylation-dependent manner. In the present study, we examined MARCKS and MRP gene expression in the postnatal (P) rat brain (1, 7, 14, 21, and 90 days after birth) by using quantitative in situ hybridization. At P1, MRP expression was high in neocortex, striatum, thalamus, cerebellar cortex, and hippocampus (CA1-CA3, hilus, and granule cell layer) but low in brainstem and, between P7 and P14, exhibited a dramatic decline in each of these regions except hippocampal CA1 and granule cell layers. Between P14 and P21, MRP expression increased in white matter regions including the corpus callosum, fimbria/fornix, and cerebellar deep white matter. At P90 (adult), MRP remained strongly expressed in the olfactory bulb, medial habenula, hippocampal CA1, and the inner two-thirds of granule cell layer, temporal, and entorhinal cortices, the corpus callosum and fimbria/fornix, and cerebellar white matter. At P1, MARCKS was strongly expressed in the majority of brain regions except the brainstem, which subsequently declined gradually to approximate adult levels by P14. Between P14 and P21, MARCKS expression declined gradually in the hilus, remained elevated in hippocampal CA1, CA3, and granule cell layers, and increased dramatically in the corpus callosum and fimbria/fornix. At P90, MARCKS expression declined in hippocampal CA3 and hilus and remained strongly expressed in hippocampal CA1 and granule cell layers, regions of the olfactory bulb, the medial habenula, temporal cortex, and cerebellar granule and Purkinje cells. Expression of both MARCKS and MRP in regions undergoing neuronal proliferation, migration, and neurite outgrowth suggest a common role in these developmental events, whereas differences in expression during development and in the adult brain provide evidence of differential regulation.

Aging↗

PubMed1998

Neurobiology of lithium: an update.

Lithium remains a first-line approach for the treatment of acute mania and the prophylactic management of manic-depressive illness, yet the underlying neurobiological mechanisms remain as yet undefined. In this paper we critically examine the accumulated preclinical and clinical evidence for the action of lithium in the brain and suggest areas that may be most productive for future investigation, i.e., membrane transport systems, neurotransmitter receptor regulation, second messenger generating systems, protein kinase C (PKC) regulation, and gene expression. In their experimental design, preclinical investigations have often jeopardized the physiologic relevance of their studies by a relative lack of attention to issues such as therapeutic concentrations, acute versus chronic exposure, and a lack of adequate cation and/or psychotropic controls. Future studies should account for the established prophylactic efficacy of lithium, the higher risk for relapse into mania after abrupt discontinuation, the ability of lithium to stabilize recurrent depression associated with unipolar disorder, and the efficacy of lithium in the treatment of refractory major depressive disorder in the presence of an antidepressant. Studies of the action of lithium in receptor mediated phosphoinositide signaling in the brain over the past several years have opened up heuristic lines of investigation that stem from lithium's uncompetitive inhibition of the enzyme inositol monophosphatase. Subsequent studies involving regulation of inositol transport, PKC isozymes and activity, and the expression of the major PKC substrate MARCKS (myristoylated alanine-rich C-kinase substrate) have offered potential avenues for understanding the complexity of the action of long-term lithium in the brain. These studies will offer us a better understanding of the neuroanatomical sites of action of lithium and together with ongoing clinical investigations using brain imaging in patients with manic-depressive illness a more complete understanding of the pathophysiology of this disease.

Bipolar Disorder↗

PubMed1997

Comparative distribution of myristoylated alanine-rich C kinase substrate (MARCKS) and F1/GAP-43 gene expression in the adult rat brain.

Myristoylated alanine-rich C-kinase substrate (MARCKS) and F1/GAP-43 (B-50/neuromodulin) are both major specific substrates for protein kinase C (PKC) and appear to play an important role in the regulation of neuroplastic events during development and in the adult brain. Since PKC isozymes are differentially expressed in brain and the expression of F1/GAP-43 and MARCKS are differentially regulated by PKC through posttranslational mechanisms, the present study examined the relative distribution of both mRNAs in the adult brain by using in situ hybridization histochemistry. MARCKS hybridization was most pronounced in the olfactory bulb, piriform cortex (layer II), medial habenular nucleus, subregions of the amygdala, specific hypothalamic nuclei, hippocampal granule cells, neocortex, and cerebellar cortex, intermediate in the superior colliculus, hippocampal CA1, and certain brainstem nuclei including the locus coeruleus, and low-absent in regions of the caudate-putamen, geniculate, thalamic nuclei, lateral habenular nucleus, and hippocampal CA3 pyramidal and hilar neurons. Consistent with previous reports, prominent F1/GAP-43 hybridization was observed in neocortex, medial geniculate, piriform cortex (layer II), substantia nigra pars compacta, hippocampal CA3 pyramidal cells, thalamic and hypothalamic nuclei, lateral habenular nucleus, locus coeruleus, raphe nuclei, and cerebellar granule cells, intermediate in regions of the thalamus, hypothalamus, and amygdala, and low-absent in regions of the olfactory bulb, caudate-putamen, medial habenular nucleus, hippocampal granule cells, and superior colliculus. Overall, F1/GAP-43 was highly expressed in a greater number of regions compared to MARCKS and, in a number of regions, including the hippocampus, habenular complex, ventral tegmentum, geniculate, and certain brain stem nuclei, a striking inverse pattern of expression was observed. These results indicate that MARCKS gene expression, like that of F1/GAP-43, remains elevated in select regions of the adult rat brain which are associated with a high degree of retained plasticity. The potential role of PKC in the regulation of MARCKS and F1/GAP-43 gene expression in brain is assessed.

Animals↗

PubMed1997

Tolerance develops to the spatial learning deficit produced by diazepam in rats.

The present experiment sought to determine in rats if 1) tolerance develops to the amnesic effect of diazepam after chronic treatment, 2) the sedative and amnesic effects of diazepam can be dissociated via differential rates of tolerance development, and 3) withdrawal from long-term diazepam treatment affects mnemonic processes. Rats were given diazepam (3 mg/kg) acutely or chronically for 5, 15, or 30 d prior to behavioral testing. Sedation was assessed as exploratory activity in an open field and amnesia was assessed as spatial learning in the Morris water maze. Tolerance to the sedative effect of diazepam was exhibited after 5 d pretreatment whereas tolerance to the amnesic effect of diazepam was exhibited only after 30 d pretreatment. Withdrawal from diazepam produced a transitory and mild disruption of spatial learning. The data demonstrate 1) tolerance can develop to the amnesic effect of diazepam with extended treatment, 2) the sedative and amnesic effects of diazepam are largely independent, and 3) withdrawal from chronic diazepam treatment can retard optimal learning.

Amnesia↗

PubMed1996

Distinctions between hippocampus of mouse and rat: protein F1/GAP-43 gene expression, promoter activity, and spatial memory.

We began these experiments as an attempt to replicate in the mouse the induction by kainate (KA) of F1/GAP-43 mRNA we observed in adult rat hippocampal granule cells [Mol. Brain Res., 33 (1995) 22-28]. However, even though KA induced behavioral seizures in the mouse similar to those in the rat, neither induction of F1/GAP-43 mRNA nor subsequent mossy fiber sprouting observed in the rat was detected in three different mouse strains. It was also surprising that the distribution of constitutive levels of F1/GAP-43 mRNA in mouse and rat hippocampus was qualitatively different. Indeed, F1/GAP-43 expression in CA3 pyramidal cells was significantly greater in rat than mouse, while F1/GAP-43 expression in CA1 cells of rat and mouse was equivalent using densitometric analysis. Thus, F1/GAP-43 expression in rat is quantitatively higher in CA3 and CA1 pyramidal cells. In mouse, expression was equivalent in these two subfields. In a transgenic mouse bearing a rat F1/GAP-43 promoter-reporter (lacZ) construct (line 252), in-vivo promoter activity of F1/GAP-43 was studied in hippocampal cells. Transgene expression in hippocampal pyramidal subfields, high in CA3, low in CA1 pyramidal cells, paralleled the distribution of rat F1/GAP-43 mRNA levels, not mouse. Differences in the constitutive F1/GAP-43 expression pattern in hippocampus between rat and mouse may therefore be determined by different recognition elements present on the F1/GAP-43 promoter. KA injected into the line 252 transgenic mouse did not activate the rat F1/GAP-43 promoter in mouse hippocampal granule cells. The absence of both F1/GAP-43 mRNA expression induction and promoter activation in mouse granule cells after KA is likely related to genera differences in transcriptional regulatory mechanisms, though post-transcriptional mechanisms cannot be excluded. Since the different hippocampal chemistry of F1/GAP-43 in rat and mouse likely extends to other molecular species, behaviors in rat and mouse that depend on hippocampal function might be different as well. We therefore evaluated spatial memory ability in a delayed matching-to-sample task. In contrast to rat, we were surprised to find no evidence of the ability to learn this task in three different mouse strains. Since interest in mouse genetics in relation to behavior and memory functions of hippocampus is growing, generalizations concerning hippocampal function from studies carried out on the mouse need to be made with caution considering the specific behavioral, pharmacological, and general molecular differences observed here. One can also be opportunistic and exploit the natural variations between these two genera to gain insight into the molecular mechanisms underlying information storage.

Animals↗

PubMed1996

Baclofen, a selective GABAB receptor agonist, dose-dependently impairs spatial learning in rats.

The present investigation assessed the effects of the selective GABAB receptor agonist baclofen (1, 3, and 6 mg/kg) on spatial learning in the Morris water maze, an aversively motivated spatial learning task. Potential anxiolytic and sedative effects of baclofen were also assessed in an open field. Baclofen dose-dependently reduced locomotion in the open field but had little effect on thigmotaxia (anxiety). In the water maze, baclofen dose-dependently impaired spatial learning and reduced swim speed. During the probe trial given after training, only rats treated with the highest dose of baclofen (6 mg/kg) failed to show a bias for the correct quadrant. Following four additional retraining trials, a second drug-reversal probe trial was given and it was found that rats switched from saline to the highest dose of baclofen (6 mg/kg) showed a bias for the correct quadrant, as did rats switched from the two lowest doses of baclofen (1 and 3 mg/kg) to saline. Rats switched from the highest dose of baclofen (6 mg/kg) to saline failed to show a quadrant bias. Performance on a visible platform task was not impaired by baclofen at any dose. Together these results suggest that baclofen resembles GABAA agonists/positive modulators in that it impairs spatial learning, but not performance of a previously acquired escape response; but differs in that it does not reduce thigmotaxia (anxiety). Potential mechanisms by which baclofen impairs mnemonic processes are discussed.

Animals↗

PubMed1996

Prolonged alteration in E-box binding after a single systemic kainate injection: potential relation to F1/GAP-43 gene expression.

The presence in hippocampus of a basic helix-loop-helix (bHLH) family of transcription factors (TFs) specifically binding in an electrophoretic mobility shift assay (EMSA) to the E-box recognition element was established by selective blockade of binding both by cold competition and by an antibody to MyoD1, an E-box TF. Protein source was from a micro-dissected preparation enriched in hippocampal granule cells. Specific E-box binding of hippocampal transcription factors was significantly reduced in kainate acid (KA) treated animals. This was observed at 24 and 72 h, but not before (3, 6 h) or after (96 h). This is the first report to our knowledge to study functional regulation of E-box binding protein in adult hippocampus. To determine the generality of this E-box regulatory event, we studied four other situations, in addition to kainate treatment, where axonal growth is known or has been suggested to increase: NGF treatment of PC12 cells, unilateral hilar lesions, long-term potentiation after 1 h, and postnatal rat hippocampal development. In all four cases, decreased E-box binding was observed. The recent link of F1/GAP-43 mRNA induction in hippocampal granule cells by KA to growth of their axons, the mossy fibers in the adult rat, suggests a potential role for the F1/GAP-43 5' flanking promoter region in regulating neurite outgrowth. Since in all cases decreased E-box binding preceded increased F1/GAP-43 mRNA expression, it is suggested that E-box binding to the F1/GAP-43 promoter in hippocampal granule cells could negatively regulate F1/GAP-43 gene expression. Indeed, analysis of recognition elements on the F1/GAP-43 gene revealed an arrangement, previously described in other genes, of multiple adjacent E-box elements. E-box binding of bHLH transcription factors is likely to occur on several different genes in addition to F1/GAP-43. It is, therefore, attractive to think that E-box binding is regulated by in vivo activation of the adult brain and that this gene regulatory event participates in the orchestration of molecular and cellular responses underlying axonal growth.

Amino Acid Sequence↗

PubMed1996

Effect of aging on the spatial learning deficit produced by diazepam in rats.

1. After pretraining in an undrugged state, young (6 months) and aged (18-24 months) rats were trained on a spatial learning-set task after receiving one of four doses of diazepam (1, 2, 3 or 5 mg/kg) or the drug vehicle. The effects of 5 mg/kg of diazepam were also assessed on the spatial learning-set task one full hour after injection (delay condition) as well as on the visible platform task. 2. During pretraining (undrugged), aged rats demonstrated a transient impairment on the visible platform task but subsequently did not differ significantly from young rats on the submerged platform task. On the spatial learning-set task, aged rats performed as well as young rats under control conditions and diazepam produced a comparable dose-dependent impairment of spatial learning. However, when the 1 hr delay was interposed between diazepam administration and maze testing, only aged rats exhibited a spatial learning impairment. Diazepam did not impair performance on the visible platform task in either young or aged rats. 3. These results indicate that although the amnesic effect of diazepam is not initially greater in aged rats, it persists for longer periods.

Aging↗