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Biomedical subjects

M Palkovits

Publications and source records attributed to M Palkovits.

At least 73 records · Page 4Linked to original sources
PubMed1998

Localization and dynamic regulation of biogenic amine transporters in the mammalian central nervous system.

The monoamines, serotonin, dopamine, norepinephrine, epinephrine and histamine, play a critical role in the function of the hypothalamic-pituitary-adrenal axis and in the integration of information in sensory, limbic, and motor systems. The primary mechanism for termination of monoaminergic neurotransmission is through reuptake of released neurotransmitter by Na+, CI-dependent plasma membrane transporters. A second family of transporters packages monoamines into synaptic and secretory vesicles by exchange of protons. Identification of those cells which express these two families of neurotransmitter transporters is an initial step in understanding what adaptive strategies cells expressing monoamine transporters use to establish the appropriate level of transport activity and thus attain the appropriate efficiency of monoamine storage and clearance. The most recent advances in this field have yielded several surprises about their function, cellular and subcellular localization, and regulation, suggesting that these molecules are not static and most likely are the most important determinants of extracellular levels of monoamines. Here, information on the localization of mRNAs for these transporters in rodent and human brain is summarized along with immunohistochemical information at the light and electron microscopic levels. Regulation of transporters at the mRNA level by manipulation in rodents and differences in transporter site densities by tomographic techniques as an index of regulation in human disease and addictive states are also reviewed. These studies have highlighted the presence of monoamine neurotransmitter transporters in neurons but not in glia in situ. The norepinephrine transporter is present in all cells which are both tyrosine hydroxylase (TH)- and dopamine beta-hydroxylase-positive but not in those cells which are TH- and phenyl-N-methyltransferase-positive, suggesting that epinephrine cells may have their own, unique transporter. In most dopaminergic cells, dopamine transporter mRNA completely overlaps with TH mRNA-positive neurons. However, there are areas in which there is a lack of one to one correspondence. The serotonin transporter (5-HTT) mRNA is found in all raphe nuclei and in the hypothalamic dorsomedial nucleus where the 5-HTT mRNA is dramatically reduced following immobilization stress. The vesicular monoamine transporter 2 (VMAT2) is present in all monoaminergic neurons including epinephrine- and histamine-synthesizing cells. Immunohistochemistry demonstrates that the plasma membrane transporters are present along axons, soma, and dendrites. Subcellular localization of DAT by electron microscopy suggests that these transporters are not at the synaptic density but are confined to perisynaptic areas, implying that dopamine diffuses away from the synapse and that contribution of diffusion to dopamine signalling may vary between brain regions. Interestingly, the presence of VMAT2 in vesicles underlying dendrites, axons, and soma suggests that monoamines may be released at these cellular domains. An understanding of the regulation of transporter function may have important therapeutic consequences for neuroendocrine function in stress and psychiatric disorders.

Amino Acid Sequence↗
PubMed1998

Dopamine biosynthesis is selectively abolished in substantia nigra/ventral tegmental area but not in hypothalamic neurons in mice with targeted disruption of the Nurr1 gene.

To ascertain the function of an orphan nuclear receptor Nurr1, a transcription factor belonging to a large gene family that includes receptors for steroids, retinoids, and thyroid hormone, we generated Nurr1-null mice by homologous recombination. Mice, heterozygous for a single mutated Nurr1 allele, appear normal, whereas mice homozygous for the null allele die within 24 h after birth. Dopamine (DA) was absent in the substantia nigra (SN) and ventral tegmental area (VTA) of Nurr1-null mice, consistent with absent tyrosine hydroxylase (TH), L-aromatic amino acid decarboxylase, and other DA neuron markers. TH immunoreactivity and mRNA expression in hypothalamic, olfactory, and lower brain stem regions were unaffected. L-Dihydroxyphenylalanine treatments, whether given to the pregnant dams or to the newborns, failed to rescue the Nurr1-null mice. We were unable to discern differences between null and wild-type mice in the cellularity, presence of neurons, or axonal projections to the SN and VTA. These findings provide evidence for a new mechanism of DA depletion in vivo and suggest a unique role for Nurr1 in fetal development and/or postnatal survival.

Animals↗
PubMed1998

Effects of glutamate-induced excitotoxicity on calretinin-expressing neuron populations in the area postrema of the rat.

We mapped the distribution of calretinin-immunoreactive neuron populations in a circumventricular organ of the rat, the area postrema, and investigated their sensitivity to excitotoxic stimuli mediated by subcutaneously administered monosodium glutamate. We were specifically interested to ascertain whether the presence of calretinin can, per se, confer an in vivo intrinsic resistance for area postrema neurons to glutamate excitotoxicity. We found that dense populations of calretinin-positive neurons displayed a subregional compartmentation in coronal sections of the area postrema along its rostrocaudal axis. We demonstrated that calretinin-positive neurons differ in their sensitivities to monosodium glutamate depending on their position within the area postrema. Neurons in the caudal area postrema were the most sensitive ones, while those in the rostral area postrema were spared of degeneration. We conclude that calretinin-positive neurons in the area postrema are not uniformly protected against glutamate excitotoxicity. It is possible that differences in the local concentrations of monosodium glutamate due to regional heterogeneities in density and permeability of the capillary bed rather than neuronal expression of calretinin account for the observed effects.

Animals↗
PubMed1998

Analysis of purine and pyrimidine bases, nucleosides and deoxynucleosides in brain microsamples (microdialysates and micropunches) and cerebrospinal fluid.

A new chromatographic method is reported for the synchronous analysis of endogenous purine and pyrimidine bases, ribonucleosides, and deoxyribonucleosides in brain samples. An optimized gradient chromatography system with a cooled reversed-phase column allows the detection of these compounds in very low concentrations in microsamples (microdialysates and micropunches). Chromatographic peaks were identified via the retention times of known standards, with detection at two wavelengths, and also by electrospray tandem mass spectrometry, which permits the identification of certain compounds at extremely low concentrations. The method was tested on in vivo brain microdialysis samples, micropunch tissue sample and cerebrospinal fluid of rats. Extracellular concentrations of pyrimidine metabolites in brain samples and of various purine metabolites in thalamic samples are reported here first. A comparison of the results on microdialysis and cerebrospinal fluid samples suggests that the analysis of cerebrospinal fluid provides limited information on the local extracellular concentrations of these compounds. Basic dialysis experiments revealed temporarily stable baseline levels one hour after implantation of the microdialysis probes. An elevated potassium concentration in the perfusion solution caused increases in the extracellular levels of adenosine and its metabolites, and of guanosine and the pyrimidine nucleoside uridine.

Animals↗
PubMed1998

Distribution of angiotensin type-1 receptor messenger RNA expression in the adult rat brain.

Angiotensin II and angiotensin III in the brain exert their various effects by acting on two pharmacologically well-defined receptors, the type-1 (AT1) and the type-2 (AT2) receptors. Receptor binding autoradiography has revealed the dominant presence of AT1 in brain nuclei involved in cardiovascular, body fluid and neuroendocrine control. The cloning of the AT1 complementary DNA has revealed the existence of two receptor subtypes in rodents, AT1A and AT1B. Using specific riboprobes for in situ hybridization, we have previously shown that the AT1A messenger RNA is predominantly expressed in the rat forebrain; in contrast the AT1B subtype predominates in the anterior pituitary. Using a similar technical approach, the aim of the present study was to establish the precise anatomical localization of cells synthetising the AT1A receptor in the adult rat brain. High AT1A messenger RNA expression was found in the vascular organ of the lamina terminalis, the median preoptic nucleus, the subfornical organ, the hypothalamic periventricular nucleus, the parvocellular parts of the paraventricular nucleus, the nucleus of the solitary tract and the area postrema, in agreement with previous autoradiographic studies, describing a high density of AT1 binding sites in these nuclei. In addition, AT1A messenger RNA expression was detected in several brain areas, where no AT1 binding was reported previously. Thus, we identify strong expression of AT1A messenger RNA expression in scattered cells of the lateral parts of the preoptic region, the lateral hypothalamus and several brainstem nuclei. In none of these structures was the AT1B messenger RNA detectable at the microscopic level. In conclusion, it is suggested that angiotensins may exert their central effects on body fluid and cardiovascular homeostasis mainly via the AT1A receptor subtype.

Angiotensin II↗
PubMed1998

Binding of girisopam (a 2,3-benzodiazepine derivative) to the substantia nigra is prevented by lesioning of the striatonigral pathway.

The binding sites of girisopam, a homophthalazine (2,3-benzodiazepine)-derivate have a specific distribution pattern restricted to the striato-pallido-nigral system of the rat brain. Following kainic acid lesions in the caudate-putamen or the ventral striatum (nucleus accumbens, olfactory tubercle), as well as after surgical transection of the striatonigral pathway, [3H]girisopam binding sites were reduced or completely eliminated from the substantia nigra and the entopeduncular nucleus. Kainic acid lesions of the globus pallidus failed to act on girisopam binding sites in the substantia nigra. Surgical transections or 6-hydroxydopamine lesions of the striatonigral pathway, as well as intranigral kainic acid injections did not influence binding sites in the striatum or the pallidum. These findings indicate that girisopam in the striatum to be postsynaptic on striatonigral projecting neurons. Girisopam in the striatum seems is present in striatonigral projecting neurons. The binding sites are transported from the striatum (mainly from the caudate-putamen, partly from the ventral striatum) to the substantia nigra and the entopeduncular nucleus. The exact identity of these striatonigral fibres bearing homopthalazines is uncertain.

Animals↗
PubMed1998

Alterations in corticotropin-releasing hormone gene expression of central amygdaloid neurons following long-term paraventricular lesions and adrenalectomy.

Corticotropin-releasing hormone messenger RNA expression in the amygdala of rats after adrenalectomy and bilateral lesions of the hypothalamic paraventricular nucleus was examined by in situ hybridization histochemistry. Corticotropin-releasing hormone messenger RNA-containing cells are abundant in the intermediate subdivision of the central amygdaloid nucleus. Some corticotropin-releasing hormone-labeled cells are scattered in other subdivisions of the central nucleus and throughout the anterior amygdaloid area. Five days after bilateral adrenalectomy, the number of corticotropin-releasing hormone messenger RNA-containing cells was reduced both in the central nucleus and the anterior area of the amygdala. This reduction was prevented by corticosterone replacement and contrasts sharply with the known rise of corticotropin-releasing hormone messenger RNA in the paraventricular nucleus after adrenalectomy. Corticotropin-releasing hormone messenger RNA expression in the amygdala was up-regulated in rats with six-week bilateral lesions of the paraventricular nucleus. This elevation in corticotropin-releasing hormone messenger RNA was not influenced by adrenalectomy or corticosterone, and it did not correlate with plasma levels of adrenocorticotrophic hormone or corticosterone. The possible direct innervation of the amygdala by the paraventricular nucleus is supported by the demonstration of labeled axons from the paraventricular nucleus to the amygdala after injection of an anterograde tracer, Phaseolus vulgaris leucoagglutinin, into the paraventricular nucleus. Labeled fibers take two courses: through the lateral hypothalamus ventral amygdalofugal path and through the stria terminalis. Data presented here suggest that the paraventricular nucleus-amygdala connection is likely to be inhibitory to corticotropin-releasing hormone neurons in the central amygdala. These neurons may participate in behavioral responses to stress effected through brainstem autonomic centers rather than directly through the hypothalamo-pituitary adrenal axis.

Adrenalectomy↗
PubMed1998

Alteration of protease levels in different brain areas of suicide victims.

Numerous recent studies found that proteases play a major role in brain function. In addition to their role in protein turnover, they have modulatory functions and an important role in apoptosis, pathological changes, and other mechanisms. To explore possible differences in brain protein metabolism of suicide victims, we examined the activity of two proteases, cathepsin D and calpain (I and II combined), in eleven discrete areas of postmortem brain tissue of 21 victims of suicide and of 31 age- and sex-matched control subjects without a history of psychiatric or neurological disease. The levels of functionally important amino acids in five of these areas were also measured. Cathepsin D activity was found to be lower in two of eleven regions of brains of suicide victims, the parahippocampal cortex and the medial hypothalamus, by 26% and 27%, respectively. Calpain activity was lower in two different areas tested, 29% in the medulla oblongata and 26% in the lateral prefrontal cortex, and was 18% higher in the midbrain. There were no significant differences in the other areas (globus pallidus, hippocampus, amygdala, caudate nucleus, ventral tegmental area, and nucleus accumbens). Protease distribution was regionally heterogeneous--the levels in the globus pallidus were low, and in the hippocampus high, with about a two-fold difference. The length of the postmortem period for obtaining tissue, the storage time of the frozen tissue, and the age of the subject had no apparent influence on the results obtained. Although there was a tendency toward higher levels of aspartate and glycine in brain areas from suicide victims, the difference was not significant. The variations among individual brains were greater in amino acid levels than in protease levels. The findings indicate the possible role of protein metabolism in depressive or suicidal behavior.

Amino Acids↗
PubMed1998

Growth-associated protein (GAP-43), its mRNA, and protein kinase C (PKC) isoenzymes in brain regions of depressed suicides.

The aim of this study was to investigate whether the previously observed adaptive changes in the monoaminergic receptors in post-mortem brains of depressed suicide victims are associated with alteration in some functional proteins involved in serotonergic neuronal signalling, namely PKC and GAP-43. Selected regions from ten brains of antidepressant-free depressed suicide victims and ten matched controls were used to examine the levels of GAP-43 protein, GAP-43 mRNA and PKC isoenzymes by Western blotting with monoclonal antibodies specific for these proteins. A major finding of the study was a significant decrease in GAP-43 protein levels and its mRNA expression in prefrontal cortex (BA9) (by 24% and 34%, respectively) of suicide brains compared to controls. No significant changes were found in GAP-43 protein or its mRNA in frontopolar cortex (BA10), amygdala, substantia nigra or putamen. Levels of PKC isoenzymes had a heterogenous regional distribution but were not significantly altered in any of the regions examined. Given the role of GAP-43 in the establishment and reorganization of synaptic connections, the finding of selective reduction of this protein in prefrontal cortex suggests that a dysfunctional synaptic organization in this region may be associated with depression and suicidal behaviour. This study provides the first evidence of an alteration in a protein related to the neuronal plasticity in the brain of depressed suicide victims.

Adult↗
PubMed1998

Heterogeneous neurochemical responses to different stressors: a test of Selye's doctrine of nonspecificity.

Selye defined stress as the nonspecific response of the body to any demand. Stressors elicit both pituitary-adrenocortical and sympathoadrenomedullary responses. One can test Selye's concept by comparing magnitudes of responses at different stress intensities and assuming that the magnitudes vary with stress intensity, with the prediction that, at different stress intensities, ratios of increments neuroendocrine responses should be the same. We measured arterial plasma ACTH, norepinephrine, and epinephrine in conscious rats after hemorrhage, intravenous insulin, subctaneous formaldehyde solution, cold, or immobilization. Relative to ACTH increments, cold evoked large norepinephrine responses, insulin large epinephrine responses, and hemorrhage small norepinephrine and epinephrine responses, whereas immobilization elicited large increases in levels of all three compounds. The ACTH response to 25% hemorrhage exceeded five times that to 10%, and the epinephrine response to 25% hemorrhage was two times that to 10%. The ACTH response to 4% formaldehyde solution was two times that to 1%, and the epinephrine response to 4% formaldehyde solution exceeded four times that to 1%. These results are inconsistent with Selye's doctrine of nonspecificity and the existence of a unitary "stress syndrome," and they are more consistent with the concept that each stressor has its own central neurochemical and peripheral neuroendocrine "signature."

Adrenocorticotropic Hormone↗
PubMed1998

Uneven regional distribution of nucleotide metabolism in human brain.

Adenine and uridine nucleotides and adenosine are proposed to act as neuromodulators and other nucleotides and nucleosides are also suggested to be involved in brain function. A following major step towards the verification of the functional role of nucleotides and nucleosides in the brain would be the examination of regional distribution of purines, pyrimidines and the enzymes involved in their metabolism. Using our recently developed chromatography-based assay for nucleosides from tissue homogenates, we analysed nucleosides in microdissected samples derived from various regions of human brain. Marked differences in the levels of nucleosides were measured in the cerebral cortex, cerebellar cortex, thalamus and white matter. The greatest levels of most nucleosides were found in the cerebral cortex, followed by the cerebellar cortex and the white matter while the smallest concentrations were found in the thalamus, although adenosine and xanthine showed a different distribution pattern in these brain areas. Within the cerebral cortex, the measured substances showed little variations except certain high levels in the cingulate and low levels in the frontal cortex. Even distribution of nucleosides was found in the thalamic nuclei while relative high values were measured in the medial geniculate body. Since a dramatic change in nucleoside concentrations occurs after death, the measured nucleoside concentrations are an interplay of original nucleotide and nucleoside concentrations and enzyme reactions following death. Thus our results suggest regional differences in nucleotide and nucleoside composition and nucleotide metabolising enzyme activities between brain areas.

Adenosine↗
PubMed1998

Neuroprotective effect of GYKI 52466 on AMPA-induced neurotoxicity in rat striatum.

The neuroprotective effect of intraperitonally administered GYKI 52466 (2,3-benzodiazepine derivate) was investigated on AMPA (alpha-amino-3-hydroxy-5-methyl-4-isoxalon-propionic acid)-induced neuronal degeneration in the striatum of adult rats. The dose-dependent neurotoxic effect of AMPA was evaluated by the decrease in the activity of choline acetyltransferase (ChAT), due to degeneration of cholinergic neurons. An injection of 25 mg/kg GYKI 52466 30 min prior to the striatal application of 50 nmol AMPA, followed by repeated application of GYKI 52466 (10 times 5 mg/kg at 10 min intervals, reaching a final dose of 75 mg/kg) was able to prevent neuronal damage monitored by ChAT activity. Conversely, co-injection of GYKI 52466 (50 and 75 mg/kg) with AMPA (50 and 100 nmol) did not elicit any significant protection against the neuronal loss as measured by the ChAT enzyme activity. Therefore, one dose of agonist decreasing ChAT activity by about 40% (50 nmol) was tested on [3H]girisopam binding sites and on the immunoreactivity of glial fibrillary acid protein. The lesions were measured on methylene blue-stained serial sections with a computer assisted image analysis program (NIH Image 1.60). As a result of the AMPA treatment [3H]girisopam binding sites became depleted, and the immunoreactivity of glial fibrillary acid protein increased and on the site of the injection in the striatum a lesion developed. In the presence of AMPA (50 nmol) administered intrastriatally, GYKI 52466 (75 mg/kg i.p.) was able to make the radioactive signal of [3H]girisopam reappear. The volume of AMPA induced neuronal damage in the striatum and the extent of gliosis was reduced. These data provide evidence for the neuroprotective effect of GYKI 52466, and suggest a potential therapeutic value in some neurological disorders.

Animals↗
PubMed1997

Sample and probe: a novel approach for identifying development-specific cis-elements of the enkephalin gene.

We have developed a novel 'sample and probe' approach as a means to identifying specific DNA elements of the enkephalin gene that control differentiation of the enkephalinergic phenotype during neurodevelopment. The approach is a systematic spatiotemporal analysis of protein-DNA interactions; soluble nuclear proteins ('samples') prepared from microdissected regions of the developing brain are 'probed' with radiolabeled DNA fragments representing various regulatory regions of the enkephalin gene. The resulting spatiotemporal 'molecular maps', i.e. characteristic patterns of protein-DNA complexes showed DNA regions that harbor potential cis-elements regulating differentiation of the enkephalin phenotype at various stages of neurodevelopment. DNase I footprint analysis of such a DNA region identified a binding site (GACGGGAGATCGCTCGT) which is similar to the motif for a lymphoid-specific, developmentally regulated transcription factor, Ikaros, suggesting that the developing brain expresses Ikaros-like transcription factor(s) in a spatiotemporally defined manner. In summary, our approach offers a unique view into the chronology of coordinated protein-DNA interactions and will greatly facilitate identifying DNA elements and isolating development-specific transcription factors.

Animals↗
PubMed1997

Anxiolytic homophthalazines increase Fos-like immunoreactivity in selected brain areas of the rat.

Nerisopam, an anxiolytic and antipsychotic homophthalazine induces rapid, intense expression of Fos-like immunoreactivity in the rostral, dorsomedial and lateral parts of the striatum in the rat. Fos-positive cells also occurred in the globus pallidus, the olfactory tubercle and in the accumbens nucleus (in the cone and shell portions) but the substantia nigra, the entopeduncular and the subthalamic nuclei were virtually Fos-negative. 5 h after nerisopam application, however, cells in the reticular zone of the substantia nigra showed Fos-like immunopositivity. After a daily application of nerisopam for two weeks, relatively weak Fos-like immunoreactivity was observed in the striatum and the subthalamic nucleus but not in the globus pallidus. Unilateral surgical transection of the striato-nigral pathway, which depleted tyrosine hydroxylase immunostaining in the ipsilateral striatum did not influence nerisopam-induced Fos-like immunoreactivity in the striatal neurons, either ipsi- or contralateral to the knife cut. Our results suggest that the striatal neurons are the primary targets of this anxiolytic and antipsychotic drug in the central nervous system.

Animals↗
PubMed1997

Expression of angiotensin type-1 (AT1) and type-2 (AT2) receptor mRNAs in the adult rat brain: a functional neuroanatomical review.

The discovery that all components of the renin-angiotensin system (RAS) are present in the central nervous system led investigators to postulate the existence of a local brain RAS. Supporting this, angiotensin immunoreactive neurons have been visualized in the brain. Two major pathways were described: a forebrain pathway which connects circumventricular organs to the median preoptic nucleus, paraventricular nucleus, and supraoptic nucleus, and a second pathway connecting the hypothalamus to the medulla oblongata. Blood-brain barrier deficient circumventricular organs are rich in angiotensin II receptors. By activating these receptors, circulating angiotensin II may act on central cardiovascular centers via angiotensinergic neurons, providing a link between peripheral and central angiotensin II systems. Among the effector peptides of the brain RAS, angiotensin II and angiotensin III have the same affinity for the two pharmacologically well-defined receptors: type 1 (AT1) and type 2 (AT2). When injected in the brain, these peptides increase blood pressure, water intake, and anterior and posterior pituitary hormone release and may modify memory and learning. The cloning of AT1 and AT2 receptor cDNAs has revealed that these receptors belong to the seven transmembrane domain receptor family. In rodents, two AT1 receptor subtypes, AT1A and AT1B, have been isolated. Using specific riboprobes for in situ hybridization histochemistry, recent studies mapped the distribution of AT1A, AT1B, and AT2 receptor mRNAs in the adult rat and found a predominant expression of AT1A and AT2 mRNA in the brain and of AT1B in the pituitary. Very limited overlap was found between the brain expression of AT1A and AT2 mRNAs. In several functional entities of the brain, such as the preoptic region, the hypothalamus, the olivocerebellary system, and the brainstem baroreflex arc, the colocalization of receptor mRNA, binding sites, and angiotensin immunoreactive nerve terminals suggests local synthesis and expression of angiotensin II receptors. In other areas, such as the bed nucleus of the stria terminalis, the median eminence, or certain parts of the nucleus of the solitary tract, angiotensin II receptors are likely of extrinsic origin. The neuronal expression of AT1A and AT2 receptors was demonstrated in the subfornical organ, the hypothalamus, and the lateral septum. By using double label in situ hybridization, AT1A receptor expression was localized in corticotropin releasing hormone but not in vasopressin containing neurons in the hypothalamus. The information is discussed together with functional data concerning the role of brain angiotensins, in an attempt to provide a better understanding of the physiological and functional roles of each receptor subtype.

Angiotensin I↗