Biomedical subjects

Richard H Dyck

Publications and source records attributed to Richard H Dyck.

15 recordsLinked to original sources

PubMed2006

Slow progressive degeneration of nigral dopaminergic neurons in postnatal Engrailed mutant mice.

The homeobox transcription factors Engrailed-1 and Engrailed-2 are required for the survival of mesencephalic dopaminergic neurons in a cell-autonomous and gene-dose-dependent manner. Because of this requirement, the cells die by apoptosis when all four alleles of the Engrailed genes are genetically ablated (En1-/-;En2-/-). In the present study, we show that viable and fertile mice, heterozygous null for Engrailed-1 and homozygous null for Engrailed-2 (En1+/-;En2-/-), have an adult phenotype that resembles key pathological features of Parkinson's disease. Specifically, postnatal mutant mice exhibit a progressive degeneration of dopaminergic neurons in the substantia nigra during the first 3 mo of their lives, leading to diminished storage and release of dopamine in the caudate putamen, motor deficits similar to akinesia and bradykinesia, and a lower body weight. This genetic model may provide access to the molecular etiology for Parkinson's disease and could assist in the development of novel treatments for this neurodegenerative disorder.

Animals↗

PubMed2005

Retrograde tracing of the subset of afferent connections in mouse barrel cortex provided by zincergic neurons.

The barrel cortex of rodents is densely innervated by a prominent subclass of glutamatergic neurons that sequester and release zinc from their synaptic boutons. These neurons may play an important role in barrel cortex function and plasticity, as zinc has been shown to modulate synaptic function by regulating neurotransmitter release, excitatory and inhibitory amino acid receptors, and second messenger signaling cascades. Here, we utilized intracortical infusions of sodium selenite to identify the source of the zincergic innervation to the mouse barrel cortex. Our results demonstrate that the majority of zincergic projections to the barrel cortex arose from ipsilateral and callosal neurons, situated in cortical layers 2/3 and 6. Regionally, these labeled neurons were most abundant within the barrel cortex itself, posterior parietal association cortex, secondary somatosensory cortex, and motor cortex. Labeled neurons were also found in other somatosensory regions corresponding to the trunk, fore- and hindlimb, as well as more distant regions such as the visual, rhinal, dorsal peduncular and insular cortices, the claustrum, and lateral and basolateral amygdaloid nuclei. Further, some mice were injected with the retrograde tracer cholera toxin subunit B to compare retrograde labeling of zincergic neurons with that of the general population of neurons innervating the barrel cortex. Our data indicate that all cortical regions providing inputs to the barrel cortex possess a zincergic component, whereas those from thalamic or brainstem structures do not. These findings demonstrate that zincergic pathways comprise a chemospecific associational network that reciprocally interconnects the barrel cortex with other cortical and limbic structures.

Animals↗

PubMed2005

Disrupted tonotopy of the auditory cortex in mice lacking M1 muscarinic acetylcholine receptor.

Sensory cortices have multiple and distinct functional maps that systematically represent environmental information. Development of these maps is precisely controlled by a number of intrinsic and extrinsic factors. Cortical cholinergic regulation is a crucial factor for normal cortical morphogenesis. In this study, we test the role of the M1 muscarinic acetylcholine receptor, the main muscarinic receptor subtype in the neocortex in the development of tonotopic maps in the auditory cortex. Mice lacking M1 receptors have normal hearing sensitivity but exhibit disrupted tonotopic organization and frequency tuning in the auditory cortex. In contrast, tonotopic organization and frequency tuning remain normal in the auditory midbrain. In addition, cortical layer IV neurons of M1 mutants exhibit significantly shorter or sparser dendrites compared to neurons of wildtype mice. In summary, our data suggest that the M1 receptor appears to be critical for the refinement or normal maturation of cortical tonotopy that is guided by thalamocortical inputs during early development.

Acoustic Stimulation↗

PubMed2004

Distribution of zincergic neurons in the mouse forebrain.

Synaptically released zinc is thought to play an important role in neuronal signaling by modulating excitatory and inhibitory receptors and intracellular signaling proteins. Consequently, neurons that release zinc have been implicated in synaptic plasticity underlying learning and memory as well as neuropathological processes such as epilepsy, stroke, and Alzheimer's disease. To characterize the distribution of these neurons, investigators have relied on a technique that involves the retrograde transport of zinc-selenium crystals from axonal boutons to the cell bodies of origin. However, one major problem with this method is that labeling of cell bodies is obscured by high levels of staining in synaptic boutons, particularly within forebrain structures where this staining is most intense. Here, we used a modification of the retrograde labeling method that eliminates terminal staining for zinc, thereby enabling a clear and comprehensive description of these neurons. Zincergic neurons were found in all cerebral cortical regions and were arranged in a distinct laminar pattern, restricted to layers 2/3, 5, and 6 with no labeling in layer 4. In the hippocampus, labeling was present in CA1, CA3, and the dentate gyrus but not in CA2. Labeled cell bodies were also observed in most amygdaloid nuclei, anterior olfactory nuclei, claustrum, tenia tecta, endopiriform region, lateral ventricle, lateral septum, zona incerta, superior colliculus, and periaqueductal gray. Moreover, retrograde labeling was also noted in the dorsomedial and lateral hypothalamus, regions that previously were thought to be devoid of neurons with a zincergic phenotype. Collectively these data show that zincergic neurons comprise a large population of neurons in the murine forebrain and will provide an anatomical framework for understanding the functional importance of these neurons in the mammalian brain.

Animals↗

PubMed2004

MAO(A) knockout mice are more susceptible to seizures but show reduced epileptogenesis.

The role of elevated neuroactive amine exposure during embryonic and early postnatal development on seizure threshold and epileptogenesis was examined using both electrical and pentylenetetrazol (PTZ) kindling in monoamine oxidase A knockout (MAO(A) KO) mice and their wildtype, parental strain (C3H). In the first experiment permanent bilateral electrodes were implanted in the amygdala of both C3H and MAO(A) KO mice. The mice had their afterdischarge threshold determined and then seizures were kindled daily for a total of 20 days. We observed that the MAO(A) KO mice had lower afterdischarge thresholds and less severe seizures compared to the C3H mice. In the second experiment, seizures were elicited in experimentally naive mice using 50mg/kg of PTZ once daily for 7 days. We observed that the MAO(A) KO mice had shorter latencies to the onset of the first seizure, shorter total duration of seizures and fewer seizures per day. Overall the results of both experiments suggest that MAO(A) KO mice have an increased susceptibility to seizures, but are more resistant to epileptogenesis. We conclude that the high levels of neuroactive amines in the MAO(A) KO mice reorganize the brain to make the mice more susceptible to seizures but the remaining high levels of serotonin and norepinephrine likely inhibit epileptogenesis.

Animals↗

PubMed2004

The neuregulin receptor, ErbB4, is not required for normal development and adult maintenance of the substantia nigra pars compacta.

Degeneration of dopaminergic neurons in the substantia nigra is associated with one of the most prominent human neurological disorders, Parkinson's disease. It is therefore of high interest to identify molecules with trophic effects on this neuronal population. We show here that the neuregulin receptor ErbB4 is differentially expressed in mesencephalic dopaminergic neurons, found in the substantia nigra and in a subregion of the ventral tegmentum but not in the retrorubral field. Early developmental onset and continued expression of ErbB4 into the adult and the presence of two high affinity ligands, neuregulin-1 and betacellulin, in the basal ganglia, suggested that these molecules might participate in the differentiation and/or maintenance of the nigrostriatal system. In order to address this hypothesis, we used a loxP flanked ErbB4 allele in combination with a nestin-Cre transgene and generated brain-specific ErbB4 null mice. These mutant animals survived into adulthood. The distribution of dopaminergic cell bodies in the midbrain, the expression of numerous genes specific to mesencephalic dopaminergic neurons, and the axonal projection to the basal ganglia all appeared normal. Finally, an assessment of their motor function revealed no behavioral deficits. The apparent lack of any mutant phenotype suggests the presence of a strong compensatory mechanism.

Aging↗

PubMed2003

An improved method for visualizing the cell bodies of zincergic neurons.

Physiological studies have shown that synaptically released zinc plays an important role in neural signaling by modulating a number of excitatory and inhibitory neurotransmitter receptors and intracellular signaling proteins. In order to localize neurons having a zincergic phenotype, Slomianka et al. [Neuroscience 38 (1990) 843] developed a labeling technique, based on the systemic administration of sodium selenite, that results in the retrograde transport of zinc-selenide crystals from axonal boutons to the cell bodies of origin. A major problem associated with this method is that the zincergic neurons are obscured by high levels of staining within synaptic boutons. In the present study, we describe a modification of the procedure for retrograde labeling of zincergic neurons, that uses a preincubation step with H2O2, which eliminates labeling of axon terminals while leaving the staining of cell bodies intact. Using this method we reveal that zincergic neurons comprise a large proportion of neurons in the murine forebrain, underscoring their contribution to network properties therein.

Animals↗

PubMed2003

Developmental distribution of calretinin in mouse barrel cortex.

We describe the postnatal development of calretinin expression in the mouse barrel cortex by immunohistochemistry. A densely staining neuropil and numerous cell bodies appeared throughout layer V, but only within barrel septa of layer IV, at postnatal day 4. This staining pattern became most robust at postnatal day 8. Thereafter, calretinin expression became reduced until the third postnatal week when it attained its mature levels, and the barrel-specific staining was no longer apparent.

Animals↗

PubMed2003

Altered zincergic innervation of the developing primary somatosensory cortex in monoamine oxidase-A knockout mice.

Genetic inactivation of monoamine oxidase-A (MAO-A) significantly elevates levels of serotonin (5-HT) during early development and causes a disruption in the compartmented organization of thalamocortical axon terminals in layer 4 of the somatosensory cortex. In order to determine whether corticocortical innervation of the primary somatosensory cortex is also affected by this mutation, we examined the distribution of zinc-containing axon terminals (terminals known to originate from within the cortex) in the developing somatosensory cortex of MAO-A knockout mice, at postnatal days (PD) 3, 5, 6, 8, 10, 12, 15, 28, and 60. In layer 4 of wild-type mice, histochemical staining for zinc respected barrel-specific compartments at all ages beyond PD 5. By contrast, zinc staining in MAO-A knockout mice did not exhibit signs of barrel compartmentation at any age. Across cortical layers, substantial developmental changes in the distribution of zinc-containing terminals were observed in wild-type mice up until PD 12, at which time the mature lamina-specific pattern of zinc staining was achieved. Similar changes were observed in the somatosensory cortex of MAO-A knockout mice, except that its developmental time course was significantly compressed, with zincergic innervation achieving a mature appearance by PD 8. These results provide evidence that an excess of monoamines, most likely 5-HT, dramatically perturbs the columnar organization of intracortical zincergic afferents in layer 4 and significantly accelerates the appearance of a mature laminar pattern of zinc-containing corticocortical terminals.

Animals↗

PubMed2003

Experience-dependent regulation of the zincergic innervation of visual cortex in adult monkeys.

Zinc is packaged in, and released from, a subset of glutamatergic synapses in the mammalian telencephalon where it has been shown to act as a potent neuromodulator. In order to establish the functional role for zincergic neurons in visual cortical function and plasticity we have compared the topographic distribution of zincergic terminals in the primary visual cortex (V1) of normal adult vervet monkeys (Cercopithicus aethiops) to that in monkeys monocularly deprived of visual input for short (24 h) or long (3 months) survival times. In normal animals, staining levels for zinc were highest in layers 1-3, 4b, 5 and 6 and lowest in layers 4a and 4c. The laminar and tangential patterns of zinc staining were complementary to staining patterns demonstrated using cytochrome oxidase (CO) histochemistry. Following 3 months of monocular deprivation by enucleation, levels of zinc staining in layers 3, 4calpha and 6a were heterogeneously reduced, clearly revealing the ocular dominance pattern in V1. When compared with the pattern of CO staining, levels of both CO and zinc were reduced in cortical territory innervated by the enucleated eye. Zinc histochemistry also revealed the ocular dominance pattern after only 24 h of monocular impulse blockade induced by enucleation or intravitreal tetrodotoxin infusion. However, by either means of deprivation for 24 h, levels of zinc were increased in deprived-eye stripes relative to nondeprived-eye stripes. These results indicate that zincergic terminals demarcate distinct compartments in the primate visual cortex. Furthermore, levels of synaptic zinc are rapidly and dynamically regulated, suggesting that zinc and/or zincergic neurons participate in mediating activity-dependent changes in the organization of the adult neocortex.

Animals↗

PubMed2003

Cloning and cortical expression of rat Emx2 and adenovirus-mediated overexpression to assess its regulation of area-specific targeting of thalamocortical axons.

A goal of this study was to use recombinant adenovirus (AdV) to ectopically express Emx2 in the embryonic neocortex as a gain-of-function approach to study its role in the area-specific targeting of thalamocortical axons (TCAs), using the rat as a model. First, we cloned the cDNA for the full-length coding region of rat Emx2, a homologue of Drosophila empty spiracles. We also used this sequence to define the full-length coding region of mouse Emx2 from genomic DNA. Our analysis of Emx2 expression shows that in rat, as reported in mouse, Emx2 is expressed in high caudal to low rostral, and high medial to low lateral, gradients across the cortex throughout cortical neurogenesis, and expression is primarily restricted to progenitors in the neuroepithelium. We also carried out an analysis of the distribution of cells infected with a replication defective recombinant type 5 adenovirus (AdV) containing a CAG/LacZ expression construct, following an injection into the lateral ventricle of the cerebral hemisphere at different stages of embryonic cortical neurogenesis. AdV-infected cells are broadly distributed tangentially, but their laminar distribution is differentially restricted and reflects the temporal sequence of generation of cortical neurons. This finding indicates that the AdV predominantly infects progenitors in the ventricular zone, which leads to a preferential labeling of their immediate progeny, and infects cells that have recently become postmitotic and have yet to move far from the ventricular surface. We then show that AdV-mediated ectopic Emx2 expression results in aberrant intracortical pathfinding and areal targeting of TCAs from the dorsal lateral geniculate nucleus. These findings indicate that EMX2 imparts positional information normally associated with caudal cortical areas, such as the primary visual area, that influences the area-specific targeting of TCAs. These results are consistent with a role for EMX2 in areal specification of the neocortex as suggested by recent analyses of Emx2 null mutants.

Adenoviridae↗

PubMed2002

Enhanced epileptogenesis in S100B knockout mice.

S100B is a small calcium- and zinc-binding protein expressed by astrocytes in the central nervous system. Here, we examined the role of S100B in epileptogenesis using an amygdala kindling paradigm comparing S100B knockout mice with their wild-type counterparts. Astrocyte activation following kindling, assessed by glial fibrillary acidic protein expression in the hippocampus and amygdala, was similar in wild-type and knockout mice. In addition, wild-type and knockout mice did not have substantially different afterdischarge thresholds. However, knockout mice kindled more rapidly and exhibited more severe seizures. These results implicate normal levels of S100B in the attenuation of epileptogenesis.

Amygdala↗

PubMed2002

Rapid, experience-dependent changes in levels of synaptic zinc in primary somatosensory cortex of the adult mouse.

Electrophysiological studies have established that the adult cerebral cortex undergoes immediate functional reorganizations after perturbations of the sensory periphery. These activity-dependent modifications are thought to be mediated via the rapid regulation of the synaptic strength of existing connections. Recent studies have implicated synaptic zinc as contributing to activity-dependent mechanisms of cortical plasticity, such as long-term potentiation and long-term depression, by virtue of its potent ability to modulate glutamatergic neurotransmission. To investigate the role of synaptic zinc in cortical plasticity, we examined changes in the barrel-specific distribution of zinc in axon terminals innervating the primary somatosensory cortex of adult mice at different time points after whisker plucking. In layer IV of normal adult mice, zinc staining in the barrel field was characterized by intense staining in inter-barrel septae and low levels of staining in barrel hollows. Within 3 hr, and up to 1 week after the removal of a row of whiskers, zinc staining increased significantly in barrel hollows corresponding to the plucked whiskers. With longer survival times, levels of zinc staining gradually declined in deprived barrel hollows, returning to normal levels by 2-3 weeks after whisker removal. Increased levels of zinc staining in deprived barrel hollows were highly, negatively correlated with the length of whiskers as they regrew. These results indicate that levels of synaptic zinc in the neocortex are rapidly regulated by changes in sensory experience and suggest that zinc may participate in the plastic changes that normally occur in the cortex on a moment-to-moment basis.

Animals↗

PubMed2002

Relationship between membrane potential oscillations and rhythmic discharges in identified hippocampal theta-related cells.

Intracellular recordings of cells, classified according to the criteria of Colom and Bland as phasic theta-ON or phasic theta-OFF cells, were carried out in the dorsal region of the hippocampal formation in urethan-anesthetized rats. Cells were studied during two spontaneously occurring hippocampal field conditions, asynchrony, termed large-amplitude irregular activity, and synchrony, termed theta. During the spontaneous cycling between these two field states, the effect of four levels of intracellular depolarizing and hyperpolarizing constant current injections on the amplitude and phase of membrane potential oscillations (MPOs) and the rate and pattern of cell discharges was assessed. Labeled CA1 pyramidal cells and bistratified cells met the criteria for classification as phasic theta-ON cells and labeled CA1 pyramidal layer basket cells, mossy hilar cells, and granule cells met the criteria for classification as phasic theta-OFF cells. MPOs were recorded in CA1 pyramidal cells, CA1 layer basket cells, mossy interneurons, and granule cells only during theta field activity, their onset in theta-ON cells signaled by a depolarizing shift of 5-10 mV and in theta-OFF cells by a hyperpolarizing shift of 5-10 mV, in membrane potential. The effect of current injections in phasic theta-ON and theta-OFF cells during the theta field condition revealed that MPO amplitude was voltage dependent and frequency was voltage independent. There were no phase changes observed in phasic theta-ON cells during current injections; however, amplitude analysis revealed an inverted U-shaped curve asymmetrically distributed around the average value of the membrane potential occurring during the spontaneous theta (no current) control condition. The occurrence and rate of rhythmical cell discharges in CA1 pyramidal phasic theta-ON cells during the theta condition was precisely controlled within a critical range of membrane potential values from approximately -57 to -68 mV, corresponding to a range of MPO amplitudes of approximately 4-7 mV. Outside the critical range, rhythmic cell discharges were abolished. Membrane potential oscillations in CA1 pyramidal layer basket cells underwent an approximate 180 degrees phase reversal when the membrane potential was depolarized above -65 mV. The occurrence and rate of rhythmic cell discharges in CA1 pyramidal layer basket cell phasic theta-OFF cells during the theta condition was precisely controlled within a critical range of membrane potential values from approximately -62 to -60 mV, corresponding to a range of MPO amplitudes of approximately 7-7.5 mV. Outside the critical range, cell discharges were absent or occurred singly.

Animals↗

PubMedDate not supplied

Induction of reproducible focal ischemic lesions in neonatal mice by photothrombosis.

Focal stroke during the perinatal and neonatal period is a significant cause of cognitive and behavioral deficits. Currently, the number of models available to study neonatal brain injury is limited and many are technically difficult to induce in neonatal rodents. We demonstrate a reproducible method to induce a focal ischemic injury in the cerebral cortex of neonatal mice that utilizes the principle of photothrombosis. Postnatal day 7 pups were anesthetized and systemically administered rose bengal (50 mg/kg). Permanent focal ischemia was induced in the medial frontal cortex and somatosensory cortex by irradiating surface blood vessels with a laser (532 nm). By placing a mask having an aperture of defined shape and size on the skull surface, we were able to reliably and reproducibly induce infarcts in discretely defined cortical regions. Further, we demonstrate explicit control of infarct volume by modifying the duration of laser exposure. This tool will provide a means for researchers to safely, easily and noninvasively induce reproducible ischemic lesions in specified regions of the neonatal cortex.

Animals↗