Role of p38 and inducible nitric oxide synthase in the in vivo dopaminergic cells' degeneration induced by inflammatory processes after lipopolysaccharide injection.

Accumulating evidences suggest that neuroinflammation is involved in the progressive death of dopaminergic neurons in Parkinson's disease. Several studies have shown that intranigral injection of lipopolysaccharide induces inflammation in the substantia nigra leading to death of tyrosine hydroxylase-positive cells. To better understand how the inflammatory response gives rise to neurotoxicity we induced inflammation in substantia nigra by injecting lipopolysaccharide. The damage of substantia nigra dopaminergic neurons was evaluated by immunohistochemistry, reverse transcription-PCR and Western blot analysis of tyrosine hydroxylase. In parallel, activation of microglial cells, a hallmark of inflammation in CNS, was revealed by immunohistochemistry. Similarly the expression of molecules involved in the inflammatory response and apoptotic pathway was also tested, such as cytokines (tumor necrosis factor-alpha, interleukin-1beta, interleukin-6), inducible nitric oxide synthase and caspase-11. Tyrosine hydroxylase expression (both mRNA and protein) started to decrease around 3 days post-injection. At the mRNA level, our results showed that the cytokines expression peaked shortly (3-6 h) after lipopolysaccharide injection, followed by the induction of inducible nitric oxide synthase and caspase-11 (14 h). However, inducible nitric oxide synthase protein peaked at 24 h and lasted for 14 days. The lipopolysaccharide-induced loss of substantia nigra dopaminergic neurons was partially inhibited by co-injection of lipopolysaccharide with S-methylisothiourea, an inducible nitric oxide synthase inhibitor. Co-injections of lipopolysaccharide with SB203580, a p38 MAP kinase inhibitor, reduced inducible nitric oxide synthase and caspase-11 mRNA expression, and also rescued dopaminergic neurons in substantia nigra. In summary, this is the first report to describe in vivo the temporal profile of the expression of these inflammatory mediators and proteins involved in dopaminergic neuronal death after intranigral injection of lipopolysaccharide. Moreover data strongly support that lipopolysaccharide-induced dopaminergic cellular death in substantia nigra could be mediated, at least in part, by the p38 signal pathway leading to activation of inducible nitric oxide synthase and caspase-11.

Potential role of endogenous brain-derived neurotrophic factor in long-term neuronal reorganization of the superior colliculus after bilateral visual deprivation.

The role of the brain-derived neurotrophic factor (BDNF), the BDNF receptor (TrkB), and the glutamic acid decarboxylase (GAD67) after neonatal, bilateral nerve deafferentiation during postnatal development was investigated in the rat superior colliculus (SC). BDNF and GAD67 mRNA expression were significantly increased in optic (Op) and intermediate gray (InG) layers at 5, 8, 15, and 21 days after birth, but not in adult animals. However, TrkB mRNA expression was not modified at any time tested. At 15 days, where changes in BDNF and GAD67 mRNAs were more evident, an upregulation of the NMDAR(1A) mRNA glutamate receptor in the Op and InG, a modification in the pattern of synaptic zinc in the superficial layers of SC, and an increased synaptophysin immunoreactivity in the Op was found. This indicates the existence of a synergic mechanism between BDNF and NMDA to determine refinement of connections after the loss of visual input in SC.

Aquaporins in the central nervous system.

In this review, we have tried to summarize most available data dealing with the aquaporin (AQP) family of water channels in the CNS. Two aquaporins have been identified so far in the CNS, AQP1 and AQP4. AQP1 is restricted to the choroid plexus of the lateral ventricles, which raises a role for this aquaporin in cerebrospinal fluid formation. AQP4 is the predominant water channel in the brain and it is more widely distributed than originally believed, with a marked prevalence over periventricular areas. In the first part of this review, we examine the complete distribution pattern of AQP4 in the CNS including its rostro-caudal localization to end with its subcellular location. After discussing scarce data dealing with regulation of aquaporins in the CNS, we focus in potential roles for aquaporins. Novel recent data highlights very important roles for this aquaporin in the normal and pathological brain including, among others, role in potassium buffering, body fluid homeostasis, central osmoreception and development and restoration of brain edema.

Decreased messenger RNA expression of key markers of the nigrostriatal dopaminergic system following vitamin E deficiency in the rat.

We have evaluated the effect of a vitamin E-deficient diet on the rat nigrostriatal dopaminergic system. After 15 days of deficient diet, the amount and activity of striatal and nigral tyrosine hydroxylase increased, which contrasted with a decreased messenger RNA expression for tyrosine hydroxylase and the dopamine transporter in the ventral mesencephalon. When we prolonged the deficiency of vitamin E for 30 days, dopamine levels did not differ in both areas. In contrast, messenger RNA levels for tyrosine hydroxylase and the dopamine transporter were markedly reduced in 30-day deficient rats. In addition, the number of oxidatively modified proteins significantly increased in the striatal and nigral areas studied. Overall, we propose that these changes suggest an important role of vitamin E in maintaining the normal equilibrium of the dopaminergic nigrostriatal system.

Histamine infusion induces a selective dopaminergic neuronal death along with an inflammatory reaction in rat substantia nigra.

We have evaluated the effects of a direct infusion of histamine, as mediator of inflammatory response, in substantia nigra, striatum, medial septum, and medial lemniscus. Injection of 100 and 250 nmol of histamine in substantia nigra produced a selective damage in dopaminergic neurons evidenced by the loss of tyrosine hydroxylase mRNA-expressing cells, tyrosine hydroxylase-immunolabeled-positive cell bodies, and dopamine and 3,4-dihydroxyphenylacetic acid levels. In parallel we found an acute inflammatory response manifested by a loss of glial fibrillary acidic protein-immunolabeled astrocytes and, at precisely the same area, an activation of microglia. In the striatum, only high doses (500 nmol) produced an evident terminal degeneration. The selective neurotoxicity of histamine for dopaminergic cells was demonstrated by the unaltered transcription of glutamic acid decarboxylase mRNA in substantia nigra. Moreover, intraseptal injection of 100 nmol of histamine failed to alter the pattern of choline acetyltransferase mRNA-expressing cells, and intraparenchymal injection of histamine in medial lemniscus failed to alter the pattern of serotonin-immunolabeled cells. We conclude that the substantia nigra is highly sensitive to histamine-derived neurotoxicity, where inflammatory processes mediated by histamine could be important in the pathological changes that lead to dopaminergic neuronal damage after histamine infusion.

Upregulation of BDNF mRNA and trkB mRNA in the nigrostriatal system and in the lesion site following unilateral transection of the medial forebrain bundle.

We have performed unilateral transection of the medial forebrain bundle (MFB) and studied BDNF mRNA and trkB mRNA levels at different postlesion times in the nigrostriatal system by means of in situ hybridization. BDNF mRNA levels were transiently induced in the substantia nigra pars compacta at 1 day postaxotomy. The disposition of BDNF mRNA expressing cells at this postlesion time in substantia nigra mimicked that of the dopaminergic neurons expressing the mRNA for the dopamine transporter. TrkB mRNA levels remained unaltered in the ventral mesencephalon at the different postlesion times examined-1 to 14 days. In contrast, trkB mRNA levels were significantly induced in the striatum at the longer postlesion time examined-14 days-when all neurodegenerative events are completed. It is becoming apparent that nigral BDNF mRNA levels are anterogradely transported to its target tissue in striatum. However, following axotomy, the lesion site represents a second potential target for BDNF action. Consequently, we also analyzed the pattern of mRNA expression for BDNF and trkB at the lesion site where dopaminergic axons are disconnected. There, we found notable inductions of both BDNF mRNA and trkB mRNA levels at 4 days postaxotomy. BDNF mRNA expressing cells were confined at the site of axotomy, which coincided precisely to that showing induction of trkB mRNA. Altogether, our results anticipate promising trophic roles of BNDF in the injured nigrostriatal system.

Detailed localization of aquaporin-4 messenger RNA in the CNS: preferential expression in periventricular organs.

We have performed a detailed in situ hybridization study of the distribution of aquaporin-4 messenger RNA in the CNS. Contrary to expectation, we demonstrate that aquaporin-4 is ubiquitously expressed in the CNS. Strong hybridization labeling was detected in multiple olfactory areas, cortical cells, medial habenular nucleus, bed nucleus of the stria terminalis, tenia tecta, pial surface, pontine nucleus, hippocampal formation and multiple thalamic and hypothalamic areas. A low but significant hybridization signal was found, among others, in the choroid plexus of the lateral ventricles, ependymal cells, dorsal raphe and cerebellum. Overall, a preferential distribution of aquaporin-4 messenger RNA-expressing cells was evident in numerous periventricular organs. From the distribution study, the presence of aquaporin-4 messenger RNA-expressing cells in neuronal layers was evident in neuronal layers including the CA1 -CA3 hippocampal pyramidal cells, granular dentate cells and cortical cells. Further evidence of neuronal expression comes from the semicircular arrangement of aquaporin-4 messenger RNA-expressing cells in the bed nucleus of the stria terminalis and medial habenular nucleus exhibiting Nissl-stained morphological features typical of neurons. Combined glial fibrillary acidic protein immunohistochemistry and aquaporin-4 messenger RNA in situ hybridization demonstrated that aquaporin-4 messenger RNA is expressed by glial fibrillary acidic protein-lacking cells. We conclude that aquaporin-4 messenger RNA is present in a collection of structures typically involved in the regulation of water and sodium intake and that aquaporin-4 water channels could be the osmosensor mechanism responsible for detecting changes in cell volume by these cells.

Differential upregulation of aquaporin-4 mRNA expression in reactive astrocytes after brain injury: potential role in brain edema.

Astrocytes and aquaporin-4 (AQP4) play a significant role in brain ion homeostasis. Consequently the regulation of AQP4 mRNA in the CNS after different neurological insults was of interest. A single intrastriatal injection of ringer or quinolinic acid strongly induced AQP4 mRNA in the striatum, specially at the core of the lesion. Colocalization studies demonstrated that AQP4 mRNA induction was restricted to hypertrophic astrocytes. The extent of striatal AQP4 mRNA induction did not correlate with neuronal degeneration, but it did with extravasation of Evans blue dye as a marker of BBB disruption. Distant lesions were additionally induced by either 6-OHDA or a knife cut in the medial forebrain bundle (MFB). The former, but not the latter, induced a high AQP4 mRNA expression in the lesioned substantia nigra. However, axotomy of the MFB induced a high AQP4 mRNA expression at the lesion site. We conclude that the induction of AQP4 mRNA expression is related to disruption of the blood-brain barrier and under brain edema conditions this water channel plays a key role in the reestablishment of the brain osmotic equilibrium.

The non-NMDA glutamate receptor antagonists 6-cyano-7-nitroquinoxaline-2,3-dione and 2,3-dihydroxy-6-nitro-7-sulfamoylbenzo(f)quinoxaline, but not NMDA antagonists, block the intrastriatal neurotoxic effect of MPP+.

Altered glutamatergic neurotransmission appears to be central to the pathophysiology of Parkinson's disease; consequently, considerable effort has been made to elucidate neuroprotective mechanisms against such toxicity. In the present study, the possible neuroprotective effect of glutamate receptor antagonists against MPP+ neurotoxicity on dopaminergic terminals of rat striatum was investigated. Different doses of glutamate receptor antagonists were coinfused with 1.5 microg of MPP+ into the striatum; kynurenic acid, a nonselective antagonist of glutamate receptors (30 and 60 nmol), partially protected dopaminergic terminal degeneration in terms of rescue of dopamine levels and tyrosine hydroxylase immunohistochemistry. Dizocilpine, a channel blocker of the NMDA receptor (1, 4, and 8 nmol), and 7-chlorokynurenic acid, a selective antagonist at the glycine site of the NMDA receptor (1 and 10 nmol), failed to protect dopaminergic terminals from MPP+ toxicity. However, 6-cyano-7-nitroquinoxaline-2,3-dione (0.5 and 1 nmol) and 2,3-dihydroxy-6-nitro-7-sulfamoylbenzo(f)quinoxaline (1 nmol), two AMPA-kainate receptor antagonists, protected against MPP toxicity. Our findings suggest that the toxic effects of MPP+ on dopaminergic terminals are not mediated through a direct interaction with the NMDA subtype of glutamate receptor, but with the AMPA-kainate subtype.

Localization of aquaporin-3 mRNA and protein along the gastrointestinal tract of Wistar rats.

Since specific proteins responsible for water transport (aquaporins, AQPs) have been identified in a great variety of tissues, we decided to study the presence of AQP3 in the gastrointestinal tract (GIT) of Wistar rats. Poly(A+) RNA was purified from the mucosa of the stomach, jejunum, ileum and colon, and gross detection of AQP3 mRNA was done by Northern blot analysis. In situ hybridization studies were carried out to precisely localize the distribution of this transcript. Sections of the different tissues were hybridized with @400-bp [35S]riboprobes. The results presented here demonstrate that AQP3 is expressed throughout the GIT, with its expression in the colon and ileum greater than that in the stomach. Immunohistochemistry experiments, using a polyclonal antibody against AQP3, revealed that AQP3 protein is present at the basolateral membrane of the epithelial cells lining the villus tip of the small intestine and colon. The finding of AQP3 in the intestinal epithelia strongly suggests that this protein functions as a pathway for water transport in this epithelium.

Increased activity and expression of tyrosine hydroxylase in the rat substantia nigra after chronic treatment with nomifensine.

We have studied the effect of chronic treatment with nomifensine on dopaminergic functioning in the nigrostriatal system. The striatal dopaminergic system was not altered by chronic nomifensine treatment. In contrast, there were overall decreases of different dopamine (DA) metabolites in the cell body region in the substantia nigra after nomifensine treatment, which clearly indicates a diminished DA turnover. These results suggest that long-lasting inhibition of the high affinity DA uptake system triggers long term regulatory, compensatory mechanisms in the cell body region to preserve normal dopaminergic function in the terminal field in striatum. We also tested whether transcriptional regulatory mechanisms were altered. We studied the cellular expression of tyrosine hydroxylase (TH) mRNA in substantia nigra by in situ hybridization, and the amount and activity of TH enzyme in the cell body and terminal field regions. Our results indicate that nomifensine treatment increased TH mRNA levels within individual nigral cells, which paralleled the changes in TH enzyme amount and activity in this brain area. Our data confirm the important role of the high affinity DA uptake system in regulating dopaminergic transmission in the nigrostriatal system.

Detailed mapping of the histamine H2 receptor and its gene transcripts in guinea-pig brain.

Autoradiographic studies of the distribution of the histamine H2 receptor and its messenger RNAs were performed on serial frontal and a few sagittal sections of guinea-pig brain using [(125)I]iodoaminopotentidine for radioligand binding and a 33P-labelled complementary RNA probe for in situ hybridization, respectively. Both probes were validated by assessing non-specific labelling using non-radioactive competing H2 receptor ligands and a sense probe for binding sites and gene transcripts, respectively. In some areas, e.g., cerebral cortex, hippocampal complex or cerebellum, such studies were completed by identification of neurons expressing the H2 receptor messenger RNAs on emulsion-dipped sections. Nissl-stained sections from comparable levels were used to localize brain structures. In many brain areas, the distribution of the H2 receptor and its messenger RNAs appeared to parallel that known for histaminergic axons. For instance. high levels of both H2 receptor markers were detected in striatal and limbic areas known to receive abundant histaminergic projections. In contrast, in septum, hypothalamic, pontine and several thalamic nuclei, a comparatively low density of both H2 receptor markers was detected, suggesting that histamine actions in these areas are mediated by H1 and/or H3 receptors. Generally, the distribution of H2 receptor messenger RNA correlates well with that of [(125)I]iodoaminopotentidine binding sites, although some differences were observed. In a few regions (e.g., substantia nigra, locus coeruleus) high or moderate densities of binding sites were accompanied by a much more restricted expression of H2 receptor transcripts. Conversely, the mammillary region and the pontine nucleus exhibited higher levels of hybridization than of binding sites. In hippocampus, cerebral and cerebellar cortex there was a selective localization of the H2 receptor messenger RNA in the granule cells of dentate gyrus, pyramidal cells of the Ammon's horn and cerebral cortex, and Purkinje cells of cerebellum, whereas [(125)I]iodoaminopotentidine binding sites were located in layers where the dendritic trees of these messenger RNA-expressing neurons extend. The same discrepancy between messenger RNAs and binding sites suggests that striatonigral endings are endowed with the H2 receptor. The histamine H1 and H2 receptors both appear to be present in several brain areas, in some cases in a way suggesting their potential co-expression by the same neuronal populations, e.g., in granule and pyramidal cells in the hippocampal formation. This co-expression accounts for synergic responses, e.g., on cAMP generation, previously observed upon co-stimulation of both receptor subtypes. The widespread distribution of the H2 receptor, namely in thalamic nuclei or in telencephalic areas such as most layers of the cerebral cortex, together with its excitatory role previously established in electrophysiological studies, support its alleged function in mediating the histamine-driven control of arousal mechanisms. In addition, the detection of H2 receptor expression in brainstem areas from which other monoaminergic pathways involved in the control of states of sleep and wakefulness emanate, e.g., several raphe nuclei, locus coeruleus or substantia innominata, suggests possible interrelationships between all of these systems with highly divergent projections to the thalamus and telencephalon. The present mapping of the H2 receptor and its gene transcripts should facilitate neurochemical, neurophysiological and behavioural studies aimed at clarifying the role of histaminergic systems in brain.

In vivo protection of striatal dopaminergic system against 1-methyl-4-phenylpyridinium neurotoxicity by phenobarbital.

We have studied the effect of a semichronic and acute treatment of phenobarbital on in vivo 1-methyl-4-phenylpyridinium ion- (MPP+)-induced neurotoxicity. A group of rats were intraperitoneally injected for 12 days with phenobarbital (80 mg/Kg of body weight, semichronic treatment) in order to induce cytochrome P450 levels in brain. At day 10 of treatment, rats received unilateral left striatal injections of 1 or 2 microg of MPP+. Two days after the injection of the toxin a dose-dependent loss of dopamine uptake along with a concomitant decrease of dopamine levels and its metabolites was produced in control rats. In phenobarbital treated animals striatal injection of 1 microg of MPP+ did not produce any effect on dopaminergic parameters but injection of 2 microg of MPP+ caused losses of dopamine levels and dopamine transporter although smaller than in control rats. TH immunohistochemistry in semichronic phenobarbital treated rats also demonstrated the protective effect of this drug against MPP+ toxicity. Dopamine uptake in synaptosomes from semichronic phenobarbital treated rats did not change with respect to the controls, thereby diminished MPP+ toxicity in phenobarbital treated rats is not due to an alterated uptake of the toxin. Neuroprotection found by intraperitoneal injection of phenobarbital 30 min before MPP+ intrastriatal injection (acute treatment) could discard the induction of cytochrome P450 as responsible for this suppressed neurotoxicity of MPP+. The neuroprotective effect of phenobarbital could be produced by its action as an excitatory amino acid antagonist or as a GABA agonist.

Deprenyl induces the tyrosine hydroxylase enzyme in the rat dopaminergic nigrostriatal system.

Chronic treatment of aged rats with deprenyl prevents age-induced protein oxidation in substantia nigra and protects tyrosine hydroxylase (TH) enzyme against inactivation [11]. With these precedents, we treated adult rats with deprenyl for 3 weeks in order to get further insight in the mechanism by which deprenyl exerts such actions. After completing the treatment, dopamine (DA) levels markedly increased in both striatum and substantia nigra while levels of the acid DA metabolites, 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA), decreased in the two brain areas, thus proving MAO-inhibiting properties of the treatment. We then studied the cellular expression of TH mRNA by in situ hybridization. Following treatment with deprenyl, levels of TH mRNA were significantly higher in individual dopaminergic nigral cell bodies than in those of control rats (+74%). Western blotting analysis of TH enzyme amount revealed a positive effect of the treatment in both the terminal field (+44%) and the cell body region (+31%). This correlation between TH mRNA and amount was also extended to TH enzyme activity in the two brain areas studied, which significantly increased in striatum (+57%) and substantia nigra (+35%) following deprenyl treatment. Taken together, our results clearly suggest a TH-inducing effect of deprenyl in the dopaminergic nigrostriatal system, which seems to be independent of its protective action against oxidative stress described previously. These results expand our knowledge about the beneficial effect of deprenyl in the therapy of Parkinson's disease.

Expression of 5-HT7 receptor mRNA in rat brain during postnatal development.

The present study is the first one to demonstrate the expression of 5-HT7 receptor mRNA by in situ hybridization during postnatal development. No quantitative developmental changes in the 5-HT7 gene expression was observed in neocortex, pyramidal layers of CA1 and CA2, dentate gyrus, most of thalamic nuclei, mammillary region, superior colliculus and central gray. However, in retrosplenial cortex, subiculum and medial habenula an increase of labeling is observed between postnatal days (PN) PN15 and PN21. Striatum showed a transient expression during the first stages of development to be undetectable in adults. CA3 pyramidal cell layer, intramediodorsal thalamic nucleus and lateral habenula displayed a high mRNA expression at PN5 and PN8 which decreased throughout development but it was still present in adults. A possible non-neurotransmitter trophic function of 5-HT mediated through 5-HT7 receptors could be suggested.

(-)-Deprenyl treatment restores serum insulin-like growth factor-I (IGF-I) levels in aged rats to young rat level.

We studied the effects of treatment with (-)-deprenyl, a monoamine oxidase B inhibitor, on plasma levels of insulin-like growth factor-I (IGF-I) (as indicator of growth hormone (GH) secretion), levels of monoamines and their metabolites, and the activity and content of tyrosine hydroxylase - the rate-limiting enzyme in the biosynthesis of catecholamines - in the hypothalamus and hypophysis of old male rats. Male Wistar rats (22 months old) were treated with 2 mg deprenyl/kg body weight s.c. three times a week for 2 months. At the end of the treatment period, blood was collected for measurement of plasma IGF-I levels by radioimmunoassay (RIA). The concentrations of dopamine, serotonin (5-HT) and their main metabolites were determined by high performance liquid chromatography (HPLC) with electrochemical detection, and the tyrosine hydroxylase content in hypothalamus and hypophysis was determined by enzyme-linked immunoabsorbent assay (ELISA). (-)-Deprenyl treatment produced a pronounced increase in dopamine and 5-HT in both the hypothalamus and hypophysis (P < 0.01). The main dopaminergic metabolite, 3,4-dihydroxyphenylacetic acid (DOPAC), decreased in hypothalamus but not in hypophysis, and treatment had no effect on the concentration of 5-hydroxyindole-3-acetic acid (5-HIAA). The tyrosine hydroxylase activity and tyrosine hydroxylase content increased in hypothalamus and hypophysis (P < 0.05). In the hypophysis the increase in tyrosine hydroxylase activity was consistent with the increase in tyrosine hydroxylase amount. Moreover, (-)-deprenyl treatment restored the IGF-I plasma levels in old rats to a concentration similar to those found in young animals. Postulated anti-aging effects of (-)-deprenyl could hence be due to restoration of hypothalamic hormones such as GH.

Developmental expression of 5-HT7 receptor mRNA in rat brain visual structures after neonatal enucleation.

Binocular enucleation is a useful experimental tool for studying mechanisms of neuronal plasticity. Serotonin (5-HT) is a neuromodulator that mediates a wide range of physiological functions by activating multiple receptors. We have performed an in situ hybridization study to analyse in detail the regional distribution of 5-HT7 receptor mRNA expression during postnatal development in different brain visual areas following neonatal binocular enucleation. We found that eye removal clearly induced 5-HT7 receptor mRNA expression in the stratum opticum of superior colliculus, this effect being especially evident at postnatal day 21 (P21). Similarly, there was a clear lesion-induced up-regulation of receptor mRNA expression in the primary visual cortex from P15 through P21. These results suggest a plastic role of 5-HT7 receptor during neurogenesis triggered by eye removal.

The guinea pig histamine H2 receptor: gene cloning, tissue expression and chromosomal localization of its human counterpart.

The guinea pig is the prototypic animal species for the histamine H2 receptor. Using a strategy based upon nucleotide sequence homology and starting from the sequence of the rat histamine H2 receptor (Ruat et al., Biochem. Biophys. Res. Commun. 1991, 179: 1470-78), we have cloned an intronless highly homologous DNA very likely encoding the guinea pig H2 receptor. The encoded 359 amino acid protein displays 83 to 86% identity with the rat-, human- or dog-H2 receptors. Northern blot analysis identified a single transcript of 4.6 kb in peripheral tissues and brain areas in which the presence of the H2 receptor had been revealed previously by either photoaffinity labeling or binding studies. In brain, the distribution of transcripts, established by either Northern blots or in situ hybridization studies, was consistent with the localization of the H2-receptor. In addition, using Southern analysis of a chromosome mapping panel constructed from human x hamster hybridomas, we assigned the H2 receptor gene to human chromosome 5.

Endogenous histamine induces c-fos expression within paraventricular and supraoptic nuclei.

Thioperamide, an H3-receptor antagonist that enhances endogenous histamine release, induced c-fos mRNA expression and Fos-like immunoreactivity in magnocellular neurones of rat supraoptic and paraventricular nuclei. This response was prevented as a result of blockade of the H1 receptor, indicating that endogenous histamine is able to activate these magnocellular neurones via stimulation of this receptor.

[125I]iodoproxyfan, a new antagonist to label and visualize cerebral histamine H3 receptors.

Iodoproxyfan, i.e., 3-(1H-imidazol-4-yl)propyl-(4-iodophenyl)-methyl ether, is a novel potent and selective histamine H3 receptor antagonist. [125I]Iodoproxyfan binding to membranes of the rat striatum was reversible and saturable. Specific binding defined with 1 microM (R)-alpha-methylhistamine corresponded to 65% of the total at 30 pM. Scatchard analysis indicated a Kd of 65 pM and maximal binding capacity of 78 fmol/mg of protein. The specificity of [125I]Iodoproxyfan binding to H3 receptors was demonstrated by its pharmacological profile. A series of H3 receptor agonists inhibited [125I]iodoproxyfan binding with a similar maximal effect and with the expected order of potency and stereoselectivity ratio. H3 receptor antagonists inhibited the specific binding with the expected Ki values. In the presence of guanylnucleotides, 40% of sites exhibited a approximately 40-fold lower affinity for histamine, indicating that the H3 receptor belongs to the superfamily of G protein-coupled receptors and revealing the existence of two populations of sites. Well contrasted autoradiographic pictures of total [125I]iodoproxyfan binding to sections of the rat brain were obtained in a short time and over a low nonspecific binding. The heterogenous distribution of H3 receptors with high labeling of anterior cerebral cortex, ventral striatum and other limbic areas was confirmed. In addition, a clearly distinguishable laminated pattern of labeling was evidenced in the cerebral cortex and hippocampal formation. Hence, this new probe should be useful for sensitive assay and localization of the H3 receptor.