Biomedical subjects

P Szot

Publications and source records attributed to P Szot.

At least 19 recordsLinked to original sources

PubMed2004

Chronic cortisol suppresses pituitary and hypothalamic peptide message expression in pigtailed macaques.

The effects of chronic elevations in circulating glucocorticoids on the expression of peptides and peptide receptors of the hypothalamic-pituitary-adrenal (HPA) axis have been studied extensively in rodents, but they have not been examined in primates. To determine the responses of the HPA axis in primates to elevated cortisol, hypothalamic and pituitary tissue from normal older pigtailed macaques (Macaca nemestrina) that had received daily oral administration of cortisol or placebo for 1 year were studied. Pro-opiomelanocortin in the anterior pituitary and corticotropin-releasing factor (CRF) mRNA expression in the hypothalamic paraventricular nucleus (PVN) were significantly reduced in cortisol-treated monkeys in comparison with controls. CRF receptor 1 (CRF-R1) expression in the anterior pituitary and arginine vasopressin mRNA expression in the PVN were unchanged by chronic cortisol administration. Sustained elevation of circulating glucocorticoids results in suppression of HPA peptide and peptide receptor expression in the PVN and anterior pituitary similar to those found in rodents. Chronic therapeutic administration of glucocorticoids in humans may have unintended consequences for hypothalamic and pituitary function.

Animals↗

PubMed2004

The anticonvulsant and proconvulsant effects of alpha2-adrenoreceptor agonists are mediated by distinct populations of alpha2A-adrenoreceptors.

The alpha2-adrenoreceptor (AR) is the most investigated noradrenergic receptor with regard to modulation of seizure activity. However, because of the complexity of multiple alpha2-AR subtypes and their distribution, the exact role of this receptor in modulating seizure activity is not clear. alpha2A- and alpha2C-ARs function as both autoreceptors (presynaptic) on noradrenergic neurons, where they regulate norepinephrine (NE) release, and as postsynaptic receptors on neurons that receive noradrenergic innervation, where they regulate the release of other neurotransmitters (heteroreceptor). The nonselective alpha2-AR agonist clonidine produced a proconvulsant effect on seizure susceptibility, while the selective alpha2A-AR agonist guanfacine was anticonvulsant. The effects of both alpha2-AR agonists were absent in alpha2a knockout mice, suggesting that the alpha2A-AR mediates the proconvulsant and anticonvulsant effect of alpha2-AR agonists on seizure susceptibility. To determine whether the alpha2-AR agonists were acting on inhibitory presynaptic autoreceptors to decrease NE release or on postsynaptic receptors on NE target neurons, the effects of clonidine and guanfacine were determined in dopamine beta-hydroxylase knockout (Dbh -/-) mice that lack NE. The anticonvulsant effect of guanfacine persisted in Dbh -/- mice, suggesting that guanfacine may act preferentially on alpha2A-postsynaptic receptors that regulate the action of NE on target neurons. In contrast, the proconvulsant effect of clonidine was lost in Dbh -/- mice, suggesting that clonidine may act on presynaptic autoreceptors to decrease NE release. We hypothesize that the alpha2A-presynaptic autoreceptor is responsible for the proconvulsant effect of alpha2-AR agonists, while the alpha2A-postsynaptic receptor is responsible for the anticonvulsant effect of alpha2-AR agonists. These data help to clarify the inconsistent effects of alpha2-AR agonists on seizure activity.

Adrenergic alpha-Agonists↗

PubMed2001

Genetic comparison of seizure control by norepinephrine and neuropeptide Y.

Epilepsy is a disease of neuronal hyperexcitability, and pharmacological and genetic studies have identified norepinephrine (NE) and neuropeptide Y (NPY) as important endogenous regulators of neuronal excitability. Both transmitters signal through G-protein-coupled receptors, are expressed either together or separately, and are abundant in brain regions implicated in seizure generation. NPY knock-out (NPY KO) and dopamine beta-hydroxylase knock-out (DBH KO) mice that lack NE are susceptible to seizures, and agonists of NE and NPY receptors protect against seizures. To examine the relative contributions of NE and NPY to neuronal excitability, we tested Dbh;Npy double knock-out (DKO) mice for seizure sensitivity. In general, DBH KO mice were much more seizure-sensitive than NPY KO mice and had normal NPY expression, demonstrating that an NPY deficiency did not contribute to the DBH KO seizure phenotype. DKO mice were only slightly more sensitive than DBH KO mice to seizures induced by kainic acid, pentylenetetrazole, or flurothyl, although DKO mice were uniquely prone to handling-induced seizures. NPY contributed to the seizure phenotype of DKO mice at high doses of convulsant agents and advanced stages of seizures. These data suggest that NE is a more potent endogenous anticonvulsant than NPY, and that NPY has the greatest contribution under conditions of extreme neuronal excitability.

Animals↗

PubMed2001

Norepinephrine is required for the anticonvulsant effect of the ketogenic diet.

Ketogenic diet (KD) is a high fat, low carbohydrate diet used to treat children with epilepsy that are refractory to conventional antiepileptic drugs (AEDs). The anticonvulsant mechanism of the KD is unknown. To determine if the noradrenergic system has a role in mediating the anticonvulsant action of the KD, dopamine beta-hydroxylase knockout (Dbh -/-) mice that lack norepinephrine (NE) and Dbh +/- littermates that have normal NE content were fed either a standard rodent chow or the KD. When exposed to the convulsant flurothyl, Dbh +/- mice fed the KD had significantly longer latencies to myoclonic jerk (MJ) and generalized clonic-tonic (CT) seizures than Dbh +/- mice fed normal chow. In contrast, Dbh -/- mice fed the KD had seizure latencies to both MJ and CT comparable to Dbh -/- mice fed normal chow. These results suggest that an intact, functional noradrenergic nervous system is required for the KD to exert an anticonvulsant effect.

Animals↗

PubMed2001

Behavioral and metabolic features of repetitive seizures in immature and mature rats.

Seizure incidence varies significantly with age, with seizure susceptibility particularly high during the first few years of life. Of significant concern is what effects do brief, repetitive seizures have on the developing brain. We approached this issue by examining the change in seizure threshold, and related markers of neuronal activity and metabolic activity (c-fos mRNA and 2-deoxyglucose [2DG]), as a function of repetitive seizure episodes in immature and mature rats. Starting on postnatal day 15 (P15) (immature) or P60 (adult) rats were given two flurothyl seizures a day for 5 days (nine or ten seizures). The seizure latency profile, our measure of threshold, in immature versus adult rats across the 5-day testing period was different. In immature rats, threshold for the second seizure on each day was significantly lower than for the first seizure, suggesting that there was little refractoriness after the first seizure of the day. In contrast, the mature animal had a significantly longer threshold latency to the second seizure for the first 3 days of testing. The immature animal was also more likely than the adult to exhibit tonic extension as a feature of the first seizure of the day. Following repetitive seizures, more regions of the CNS showed c-fos mRNA expression in the immature animal than adults, suggesting that repetitive seizures in the immature animal activated a greater percentage of the brain. Compared with the effects of a single seizure, repetitive seizures resulted in less 2DG labeling in most regions of the brain (except the hippocampus); in the immature brain this difference was more distinct than in adults. The consequences of repetitive seizures in the immature animal results in distinctly different seizure behavior and neuronal activity pattern (c-fos expression) than that observed in the mature animal.

Aging↗

PubMed2001

Alpha(1) and beta(2) adrenoreceptor agonists inhibit pentylenetetrazole-induced seizures in mice lacking norepinephrine.

It has been known for many years that norepinephrine (NE) is a potent endogenous anticonvulsant, yet there is confusion as to which receptor(s) mediate this effect. This is probably due to multiple factors, including the importance of distinct signaling pathways for different seizure paradigms, a lack of comprehensive pharmacological studies, and difficulty in interpreting existing pharmacological results due to the presence of endogenous NE. We sought to circumvent these problems by testing the anticonvulsant activity of selective agonists for most known adrenoreceptors (ARs) in dopamine beta-hydroxylase knockout (Dbh -/-) mice that lack endogenous NE. Dbh -/- mice are hypersensitive to pentylenetetrazole (PTZ)-induced seizures, demonstrating that endogenous NE inhibits PTZ-induced seizures in the wild type. Pretreatment of Dbh -/- mice with an alpha(1)AR or beta(2)AR, but not an alpha(2)AR or beta(1)AR agonist significantly protected against PTZ-induced seizures. In contrast, only the beta(2)AR agonist showed anticonvulsant activity in heterozygous controls. Furthermore, an alpha(1)AR antagonist exacerbated PTZ-induced seizures in control mice, whereas a beta(2)AR antagonist had no effect. We conclude that activation of the alpha(1)AR is primarily responsible for the anticonvulsant activity of endogenous NE in the murine PTZ model of epilepsy. Endogenous NE probably does not activate the beta(2)AR under these conditions, but exogenous activation of the beta(2)AR produces an anticonvulsant effect.

Adrenergic alpha-1 Receptor Agonists↗

PubMed2000

Tyrosine hydroxylase and norepinephrine transporter mRNA expression in the locus coeruleus in Alzheimer's disease.

Despite the loss of locus coeruleus (LC) noradrenergic neurons in Alzheimer's disease (AD), cerebrospinal fluid norepinephrine (NE) levels are normal or increased in AD. This paradox suggests compensatory upregulation of NE synthetic capacity or downregulation of the NE transporter (NET) in the remaining LC neurons. LC tyrosine hydroxylase (TH) mRNA expression in the LC was measured in AD subjects (n=5) and in age and gender comparable non-demented subjects (n=6). When AD subjects were divided into those still ambulatory prior to death (CDR 3/4) and those in a prolonged 'vegetative' state prior to death (CDR 5), differences among groups became apparent at specific levels of the LC. In CDR 3/4 AD subjects there was increased TH mRNA expression per neuron compared to non-demented subjects in the caudal half of the LC. However, expression of NET mRNA in the same subjects was not significantly different at any level of the LC. These preliminary results suggest an upregulation of NE biosynthetic capacity in at least some LC neurons in AD prior to the very late stage of the disease.

Aged↗

PubMed2000

Changes in 5-HT(7) serotonin receptor mRNA expression with aging in rat brain.

We examined 5-HT(7) receptor mRNA expression with in situ hybridization histochemistry in the brains of young (3 months), middle-aged (12 months) and old rats (24 months). In the ventral CA3 area of the hippocampus 5-HT(7) mRNA expression is reduced by approximately 30% between young and middle age without further decline between middle and old age. In other brain areas 5-HT(7) mRNA expression is unaffected by age.

Aging↗

PubMed2000

Morphological plasticity in an infant monkey model of temporal lobe epilepsy.

PURPOSE/METHODS: Seizures in early life are thought to contribute to the development of human temporal lobe epilepsy. To examine the consequences of early seizures, we elicited status epilepticus in immature, 5.5- to 7.0-month-old pigtailed macaques by unilateral microinfusion of bicuculline methiodide into the entorhinal cortex. RESULTS: This report focuses on neuropathological changes in the hippocampus. Bicuculline infusion consistently elicited limbic-like seizures with prolonged, relatively localized electrographic activity. Magnetic resonance imaging revealed enhanced signal intensity in the ipsilateral hippocampus after seizures; in some cases, there was also progressive hippocampal atrophy. Histological changes were variable; in two of five monkeys, there was significant hippocampal neuron loss, gliosis, granule cell dispersion, and mossy fiber reorganization. CONCLUSIONS: The histopathological findings and associated magnetic resonance imaging abnormalities after bicuculline-induced status epilepticus in infant monkeys mimic common aspects of human temporal lobe epilepsy.

Animals↗

PubMed1999

Norepinephrine-deficient mice have increased susceptibility to seizure-inducing stimuli.

Several lines of evidence suggest that norepinephrine (NE) can modulate seizure activity. However, the experimental methods used in the past cannot exclude the possible role of other neurotransmitters coreleased with NE from noradrenergic terminals. We have assessed the seizure susceptibility of genetically engineered mice that lack NE. Seizure susceptibility was determined in the dopamine beta-hydroxylase null mutant (Dbh -/-) mouse using four different convulsant stimuli: 2,2,2-trifluroethyl ether (flurothyl), pentylenetetrazol (PTZ), kainic acid, and high-decibel sound. Dbh -/- mice demonstrated enhanced susceptibility (i.e., lower threshold) compared with littermate heterozygous (Dbh +/-) controls to flurothyl, PTZ, kainic acid, and audiogenic seizures and enhanced sensitivity (i.e., seizure severity and mortality) to flurothyl, PTZ, and kainic acid. c-Fos mRNA expression in the cortex, hippocampus (CA1 and CA3), and amygdala was increased in Dbh -/- mice in association with flurothyl-induced seizures. Enhanced seizure susceptibility to flurothyl and increased seizure-induced c-fos mRNA expression were reversed by pretreatment with L-threo-3, 4-dihydroxyphenylserine, which partially restores the NE content in Dbh -/- mice. These genetically engineered mice confirm unambiguously the potent effects of the noradrenergic system in modulating epileptogenicity and illustrate the unique opportunity offered by Dbh -/- mice for elucidating the pathways through which NE can regulate seizure activity.

Acoustic Stimulation↗

PubMed1999

Tyrosine hydroxylase mRNA is increased in old age and norepinephrine uptake transporter mRNA is decreased in middle age in locus coeruleus of Brown-Norway rats.

In normal aging, cell loss occurs in the locus coeruleus (LC), the major noradrenergic nucleus in the brain. This study examined changes in the LC of aged rats by measuring mRNA expression for tyrosine hydroxylase (TH) and the norepinephrine uptake transporter (NET). TH and NET mRNA expression were measured by in situ hybridization in young, middle-aged and aged rats. It appears that in middle age, the transporter system responds initially to LC cell loss by decreasing NET mRNA expression. Then, with further aging and cell loss, TH mRNA expression increases which may potentially increase NE synthesis in the remaining neurons. These findings suggest that multiple regulatory components are used to maintain stable noradrenergic synaptic levels despite neuronal loss. Published by Elsevier Science B.V.

Aging↗

PubMed1999

Neurotransmitter transporters: target for endocrine regulation.

Aminergic signaling in the CNS is terminated by clearance from the synapse via high-affinity transporter molecules in the presynaptic membrane. Relatively recent sequence identification of these molecules has now permitted the initiation of studies of regulation of transporter function at the cellular and systems levels. In vitro studies provide evidence that the transporters for dopamine, serotonin, and gamma-aminobutyric acid are substrates for regulation by protein kinase C signaling. In vivo studies provide evidence that insulin and adrenal and gonadal steroid hormones may regulate the synthesis and activity of the transporters. Future directions should permit evaluation of the role of endocrine regulation in neurotransmitter clearance, and thus in the maintenance of normal CNS aminergic signaling.

Animals↗

PubMed1999

Developmental seizure susceptibility of kv1.1 potassium channel knockout mice.

Potassium channels play a critical role in limiting neuronal excitability. Mutations in certain voltage-gated potassium channels have been associated with hyperexcitable phenotypes in both humans and animals. However, only recently have mutations in potassium channel genes (i.e. KCNQ2 and KCNQ3) been discovered in a human epilepsy, benign familial neonatal convulsions. Recently, it has been reported that mice lacking the voltage-gated Shaker-like potassium channel Kv1.1 alpha-subunit develop recurrent spontaneous seizures early in postnatal development. The clinical relevance of the Kv1.1 knockout mouse has been underscored by a recent report of epilepsy occurring in a family affected by mutations in the KCNA1 locus (the human homologue of Kv1.1) which typically cause episodic ataxia and myokymia. Here we summarize preliminary studies characterizing the developmental changes in seizure susceptibility and neuronal activation in the three genotypes of Kv1.1 mice (-/-, +/-, +/+). Using behavioral and immediate-early gene indicators of regional brain excitability, we have found that a seizure-sensitive predisposition exists in Kv1.1 -/- animals at a very young age (P10), before either spontaneous seizure activity or changes in c-fos mRNA expression can be demonstrated. Kv1.1 +/- mice, although behaviorally indistinguishable from wild types, also have an increased susceptibility to seizures at a similar early age. The Kv1. 1 knockout mouse possesses many features desirable in a developmental animal epilepsy model and represents a clinically relevant model of early-onset epilepsies.

Animals↗

PubMed1999

Development of a model of status epilepticus in pigtailed macaque infant monkeys.

Seizures, particularly multiple episodes and/or status epilepticus (SE) are prevalent in pediatric patients. Pediatric SE is associated with brain changes that have been hypothesized to contribute to the onset of temporal lobe epilepsy (TLE). In order to gain insight into the effects of seizures on the immature brain and the risk for later TLE, we have developed a model of limbic SE in the pigtailed macaque monkey. In separate studies, bicuculline methiodide or a bicuculline 'cocktail' was infused into three regions of the brain (area tempestas, hippocampus, entorhinal cortex) to induce seizures. Measures included MRI, electrophysiology, behavior and morphology. Our results suggest that monkey models of SE may provide useful tools for understanding the effects of prolonged seizures during infancy and the origins of TLE in humans.

Animals↗

PubMed1999

Reduced gene expression for dopamine biosynthesis and transport in midbrain neurons of adult male rats exposed prenatally to ethanol.

BACKGROUND: Prenatal ethanol exposure affects brain dopaminergic neuronal systems, and many of these alterations are permanent. METHODS: The primary objective of this study was to determine the effects of prenatal ethanol exposure on adult mRNA expression for two key regulatory proteins in the mesolimbic and nigrostriatal dopaminergic cell groups which mediate behavioral responses to alcohol and other drugs of abuse: tyrosine hydroxylase (TH) and dopamine transporter (DAT) in the substantia nigra pars compacta (SNpc) and ventral tegmental area (VTA). To also address the effects on noradrenergic regulation, we quantitated mRNA expression for TH and norepinephrine transporter (NET) in the noradrenergic loci of the locus coeruleus (LC). RESULTS: Daily dietary ethanol consumption by female Sprague-Dawley rats for 3 weeks before, and continuing throughout, pregnancy decreased both DAT (approximately 68%,p < 0.002) and TH (approximately 45%,p < 0.002) mRNA expression in the VTA of adult male offspring. This prenatal exposure also suppressed DAT mRNA expression in the SNpc (approximately 81 %;p < 0.03), although TH mRNA expression in this region was not significantly altered. Prenatal ethanol exposure did not alter significantly either TH or NET mRNA expression in the LC of adult male offspring, which suggests that this brain catecholaminergic response may be limited to DA neurons. CONCLUSION: These results demonstrated that prenatal maternal ethanol consumption suppresses mRNA expression for important regulatory proteins in the mesolimbic and nigrostriatal dopaminergic systems of adult male rat offspring. These persistent prenatal ethanol-induced changes in mRNA expression may thus contribute to the persistent effects of fetal ethanol exposure on the diverse behavioral and/or metabolic responses mediated by the mesolimbic and nigrostriatal dopaminergic systems in the adult.

Animals↗

PubMed1998

Function and distribution of three rat 5-hydroxytryptamine7 (5-HT7) receptor isoforms produced by alternative splicing.

Serotonin (5-HT7) receptor pre-mRNA is alternatively spliced in rat tissue to produce three isoforms, 5-HT(7a), 5-HT(7b) and 5-HT(7c), which differ in the amino acid sequences of their carboxyl terminal tails. Substantial species differences in structure and expression patterns exist for 5-HT7 isoforms. We have now compared some of the functional characteristics and level of expression for the three rat 5-HT7 receptor isoforms. Recombinant receptor isoforms were expressed in COS-7 cells for examination of [3H]5-HT binding characteristics and in JEG-3 cells to ascertain their ability to stimulate cAMP production. These studies showed that all three isoforms are functionally active and have similar agonist binding characteristics. Distribution of expression of the three rat receptor isoforms were examined in several brain regions and peripheral tissues using RT-PCR and in situ hybridization. The relative proportions of total 5-HT7 receptor message lent by each isoform varied little between these areas. In contrast to what has been observed in human tissue, the 5-HT(7a) isoform predominated in all regions examined, while the 5-HT(7c) isoform revealed a low level of expression (3% of total transcript). In situ hybridization was used to determine if the overall low level of expression of the 5-HT(7c) isoform by RT-PCR could be attributed to a small localized subpopulation of cells expressing high levels 5-HT(7c) message. In situ hybridization results indicate a generalized low level of expression of the 5-HT(7c) isoform throughout the CNS. These data suggest that while all three known 5-HT7 receptor isoforms in the rat are functionally competent, any functionally important differences between the three isoforms are not likely to involve differences in ligand binding or gross differences in adenylate cyclase coupling. However, differences in receptor phosphorylation, regulation or coupling to other effectors or cell trafficking could still exist.

Alternative Splicing↗

PubMed1998

Bupropion and desipramine increase dopamine transporter mRNA expression in the ventral tegmental area/substantia nigra of rat brain.

1. Regulation of dopamine transporter (DAT) mRNA was studied in rats treated with the DAT blocker bupropion (BUP; 15 or 30 mg/kg tid x 2d), the norepinephrine transporter blocker desipramine (DMI; 10 mg/kg/d x 2d), or saline. 2. mRNA expression was assessed via in situ hybridization histochemistry. 3. BUP and DMI both increased DAT mRNA expression in the ventral tegmental area/substantia nigra. 4. These findings suggest that DAT mRNA expression in the brain may be regulated by both noradrenergic and dopaminergic mechanisms.

Animals↗

PubMed1998

Dopamine transporter mRNA is increased in the CNS of Zucker fatty (fa/fa) rats.

The obese Zucker fa/fa rat is characterized by hyperinsulinemia, obesity, and altered monoamine metabolism in the central nervous system (CNS). It has been proposed that the changes in monoamine metabolism may contribute to the metabolic pathophysiology of these animals. Because it has been reported that insulin may regulate the catecholamine reuptake transporters, which terminate monoaminergic synaptic signaling, in the present study we tested whether messenger ribonucleic acid (mRNA) levels for the noradrenergic (NE) or dopaminergic (DA) transporters were altered in obese fa/fa vs. lean Fa/Fa Zucker rats. We found significantly elevated DA transporter levels in both the ventral tegmental area/substantia nigra pars compacta (VTA/SNc) and zona incerta (ZI) of obese Zucker fa/fa rats (164 +/- 24% of control levels, p = .024; and 316 +/- 61% of control levels, p = .019, respectively). Measurement of mRNA for tyrosine hydroxylase (TH), the rate-limiting enzyme for NE and DA synthesis revealed no effect of the fa gene in either NE or DA neurons. These findings suggest that increased DA clearance, and perhaps decreased DA signaling, may occur in the obese Zucker fa/fa rat.

Animals↗