Copy number elevation of 22q11.2 genes arrests the developmental maturation of working memory capacity and adult hippocampal neurogenesis.

Working memory capacity, a critical component of executive function, expands developmentally from childhood through adulthood. Anomalies in this developmental process are seen in individuals with autism spectrum disorder (ASD), schizophrenia and intellectual disabilities (ID), implicating this atypical process in the trajectory of developmental neuropsychiatric disorders. However, the cellular and neuronal substrates underlying this process are not understood. Duplication and triplication of copy number variants of 22q11.2 are consistently and robustly associated with cognitive deficits of ASD and ID in humans, and overexpression of small 22q11.2 segments recapitulates dimensional aspects of developmental neuropsychiatric disorders in mice. We capitalized on these two lines of evidence to delve into the cellular substrates for this atypical development of working memory. Using a region- and cell-type-selective gene expression approach, we demonstrated that copy number elevations of catechol-O-methyl-transferase (COMT) or Tbx1, two genes encoded in the two small 22q11.2 segments, in adult neural stem/progenitor cells in the hippocampus prevents the developmental maturation of working memory capacity in mice. Moreover, copy number elevations of COMT or Tbx1 reduced the proliferation of adult neural stem/progenitor cells in a cell-autonomous manner in vitro and migration of their progenies in the hippocampus granular layer in vivo. Our data provide evidence for the novel hypothesis that copy number elevations of these 22q11.2 genes alter the developmental trajectory of working memory capacity via suboptimal adult neurogenesis in the hippocampus.

Different interactions of prolyl oligopeptidase and neurotensin in dopaminergic function of the rat nigrostriatal and mesolimbic pathways.

Prolyl oligopeptidase (PREP) is an intracellular enzyme digesting small proline-containing peptides. Since PREP resides the same brain areas as neurotensin in the nigrostriatal and mesolimbic dopaminergic pathways, we were interested to study if there is an intracellular interaction between them. A colocalization of PREP with neurotensin and neurotensin receptor 1 (NTS1) in the rat striatum, nucleus accumbens (NAcc), substantia nigra (SN) and ventral tegmental area (VTA) was studied with immunofluorescence. From the same brain areas, the levels of dopamine and its metabolites were measured 1 h after the injection of saline, NTS1 ligands (JMV-449; 5 µg) or antagonist (SR142948; 5 µg) to the rat striatum or NAcc. We also studied whether an intraperitoneal injection of a PREP inhibitor (KYP-2047; 5 mg/kg) affects the levels of dopamine and its metabolites alone or modifies the effects of the NTS1 ligands. PREP was highly colocalized with neurotensin and NTS1 in the VTA, and with NTS1 in the SN. Colocalization was moderate or low in other brain areas. When injected to the striatum, JMV-449 had a tendency to increase dopamine (p = 0.052) and metabolite levels in the striatum and SN, whereas SR142948 did not. After the injection to the NAcc, JMV-449 but not SR142948, increased dopamine levels in the VTA and dopamine metabolite levels in the NAcc and VTA. KYP-2047 decreased the dopamine levels in the striatum, but increased dopamine metabolite levels in the NAcc and VTA. Our results suggest a novel role for PREP in the modulation of dopaminergic transmission, which may be different in nigrostriatal and mesolimbic pathways.

Epithelial transport and deamidation of gliadin peptides: a role for coeliac disease patient immunoglobulin A.

In coeliac disease, the intake of dietary gluten induces small-bowel mucosal damage and the production of immunoglobulin (Ig)A class autoantibodies against transglutaminase 2 (TG2). We examined the effect of coeliac patient IgA on the apical-to-basal passage of gluten-derived gliadin peptides p31-43 and p57-68 in intestinal epithelial cells. We demonstrate that coeliac IgA enhances the passage of gliadin peptides, which could be abolished by inhibition of TG2 enzymatic activity. Moreover, we also found that both the apical and the basal cell culture media containing the immunogenic gliadin peptides were able to induce the proliferation of deamidation-dependent coeliac patient-derived T cells even in the absence of exogenous TG2. Our results suggest that coeliac patient IgA could play a role in the transepithelial passage of gliadin peptides, a process during which they might be deamidated.

Degradation of coeliac disease-inducing rye secalin by germinating cereal enzymes: diminishing toxic effects in intestinal epithelial cells.

Currently the only treatment for coeliac disease is a lifelong gluten-free diet excluding food products containing wheat, rye and barley. There is, however, only scarce evidence as to harmful effects of rye in coeliac disease. To confirm the assumption that rye should be excluded from the coeliac patient's diet, we now sought to establish whether rye secalin activates toxic reactions in vitro in intestinal epithelial cell models as extensively as wheat gliadin. Further, we investigated the efficacy of germinating cereal enzymes from oat, wheat and barley to hydrolyse secalin into short fragments and whether secalin-induced harmful effects can be reduced by such pretreatment. In the current study, secalin elicited toxic reactions in intestinal Caco-2 epithelial cells similarly to gliadin: it induced epithelial cell layer permeability, tight junctional protein occludin and ZO-1 distortion and actin reorganization. In high-performance liquid chromatography and mass spectroscopy (HPLC-MS), germinating barley enzymes provided the most efficient degradation of secalin and gliadin peptides and was thus selected for further in vitro analysis. After germinating barley enzyme pretreatment, all toxic reactions induced by secalin were ameliorated. We conclude that germinating enzymes from barley are particularly efficient in the degradation of rye secalin. In future, these enzymes might be utilized as a novel medical treatment for coeliac disease or in food processing in order to develop high-quality coeliac-safe food products.

Expression and traffic of cellular prolyl oligopeptidase are regulated during cerebellar granule cell differentiation, maturation, and aging.

Prolyl oligopeptidase (POP) is an endopeptidase which cleaves short proline-containing neuropeptides, and it is involved in memory and learning. POP also has an intercellular function mediated through the inositol pathway, and has been involved in cell death. POP has been early considered as a housekeeping enzyme, but the recent research indicates that POP expression is regulated across tissues and intracellularly. In the brain, POP is exclusively expressed in neurons and most abundantly in pyramidal neurons of cerebral cortex, in the CA1 field neurons of hippocampus and in cerebellar Purkinje's cells. Intracellularly, POP is mainly present in the cytoplasm and some in intracellular membranes, like rough endoplasmic reticulum and Golgi apparatus. In this paper, we systematically studied the levels of expression of POP along the life of cerebellar granule cells (CGC) in culture and the distribution of POP within different intracellular compartments. We used the tight-binding inhibitor JTP-4819 covalently coupled with fluorescein (FJTP) as a tool to study the changes on expression and localization of POP protein. Our results indicate that POP activity levels are regulated during the life of the neurons. POP was found mainly in cytoplasm and neuronal projections, but at an early developmental phase significant amounts were found also in nuclei. Along the life of the neurons, POP activity fluctuated in 7-day cycles. In young neurons, the cytosolic POP activity was low but increased by maturation so that the activity peak coincided with full differentiation. Over aging, cytoplasmic POP was concentrated around nucleus, but the activity decreased with time. POP was also present in vesicles across the neuron. No major changes were seen in the nuclear or membrane bound POP over aging until activity disappeared upon neuronal death. This is the first time when POP was found in the nuclei of human neuronal cells.

Spatial association of prolyl oligopeptidase, inositol 1,4,5-triphosphate type 1 receptor, substance P and its neurokinin-1 receptor in the rat brain: an immunohistochemical colocalization study.

Prolyl oligopeptidase (POP) is a serine endopeptidase which hydrolyzes proline-containing peptides shorter than 30 amino acids. It has been suggested that POP is associated with cognitive functions, possibly via the cleavage of neuropeptides such as substance P (SP). Recently, several studies have also linked POP to the inositol 1,4,5-triphosphate (IP(3)) signaling. However, the neuroanatomical interactions between these substances are not known. We used double-labeled immunofluorescence to determine the POP colocalization with SP, SP receptor (neurokinin-1 receptor, NK-1R) and IP(3) type 1 receptor (IP(3)R1) in the rat brain. Furthermore, since striatal and cortical GABAergic neurons are involved in SP neurotransmission, we studied the coexpression of POP, SP and GABA by triple-labeled immunofluorescence. POP was moderately present in IP(3)R1-containing cells in cortex; the colocalization was particularly high in the thalamus, hippocampal CA1 field and cerebellar Purkinje cells. Colocalization of POP with SP and NK1-receptor was infrequent throughout the brain, though some POP and SP coexpression was observed in cerebellar Purkinje cells. We also found that POP partially colocalized with SP-containing GABAergic neurons in striatum and cortex. Our findings support the view that POP is at least spatially associated with the IP(3)-signaling in the thalamus, hippocampus and cerebellar Purkinje cells. This might point to a role for POP in the regulation of long-term potentiation and/or depression. Moreover, the low degree of colocalization of POP, SP and its NK-1R suggests that a transport system is needed either for POP or SP to make hydrolysis possible and that POP may act both intra- and extracellularly.

On the role of prolyl oligopeptidase in health and disease.

Prolyl oligopeptidase (POP) is a serine peptidase which digests small peptide-like hormones, neuroactive peptides, and various cellular factors. Therefore, this peptidase has been implicated in many physiological processes as well as in some psychiatric disorders, most probably through interference in inositol cycle. Intense research has been performed to elucidate, on the one hand, the basic structure, ligand binding, and kinetic properties of POP, and on the other, the pharmacology of its inhibitors. There is fairly strong evidence of in vivo importance of POP on substance P, arginine vasopressin, thyroliberin and gonadoliberin metabolism. However, information about the biological relevance of POP is not yet conclusive. Evidence regarding the physiological role of POP is lacking, which is surprising considering that peptidase inhibitors have been exploited for drug development, some of which are currently in clinical trials as memory enhancers for the aged and in a variety of neurological disorders. Here we review the recent progress on POP research and evaluate the relevance of the peptidase in the metabolism of various neuropeptides. The recognition of novel forms and relatives of POP may improve our understanding of how this family of proteins functions in normal and in neuropathological conditions.

Elimination of extracellular dopamine in the medial prefrontal cortex of conscious mice analysed using selective enzyme and uptake inhibitors.

We have shown in a previous study that in the medial prefrontal cortex (mPFC) of Comt knockout animals, uptake1 followed by oxidation accounts for approximately 50% and uptake2 followed by O-methylation for the remaining 50% of dopamine clearance. However, compensatory mechanisms in genetically modified animals may have affected the result. Therefore, in the present study, we gave a high dose (30 mg/kg) of tolcapone in combination with pargyline and reboxetine to C57BL/6J mice to see whether the earlier findings could be confirmed. The three drugs were also given together. We used intracerebral microdialysis to determine the levels of extracellular dopamine and its metabolites in the mPFC. In addition, we analyzed dopamine, 3,4-dihydroxyphenyl acetic acid (DOPAC) and homovanillic acid (HVA) contents in cortical and striatal synaptosomes to estimate the amount of releasable dopamine and dopamine turnover. In the prefrontal cortex of male C57BL/6J mice, the combination of two drugs (pargyline + tolcapone or reboxetine + tolcapone) generally elevated extracellular dopamine levels more than any single drug. Similar responses, although much weaker, were observed in female mice. Unexpectedly, triple treatment with pargyline, reboxetine and tolcapone did not increase dopamine outflow in the mPFC in either sex, and the treatment actually diminished dopamine outflow in the dorsal striatum. This seems to indicate that such an extensive treatment induces a fast and effective shut-down of dopamine release both in the mPFC and striatum to protect the brain from excess dopaminergic stimulation. The observed decrease in extracellular dopamine levels was not due to the depletion of releasable dopamine because abundant amounts of dopamine were present in synaptosomes. These results imply that the relative proportion of COMT-induced dopamine clearance may be somewhat lower than earlier estimated.

Generation of membrane-bound catechol-O-methyl transferase deficient mice with disctinct sex dependent behavioral phenotype.

Catechol-O-methyltransferase (COMT) has two isoforms: soluble (S-COMT), which resides in the cytoplasm, and membrane-bound (MB-MT), anchored to intracellular membranes. COMT is involved in the O-methylation of L-DOPA, dopamine and other catechols. The exact role of MB-COMT is still mostly unclear. We wanted to create a novel genetically modified mouse model that specifically lacks MB-COMT activity and to study their behavioral phenotype. MB-COMT knock-in mutant mice were generated by introducing two point mutations in exon 2 of the Comt gene (ATGCTG->GAGCTC disabling the function of the P2 promoter and allowing only the P1-regulated S-COMT transcription. The first mutation changes methionine to glutamic acid whereas the second one does not affect coding. The expression of the two COMT isoforms, total COMT activity in several areas of the brain and peripheral tissues and extracellular dopamine concentrations after L-DOPA (10 mg/kg) and carbidopa (30 mg/kg) subcutaneous administration were assessed. A battery of behavioral tests was performed to compare MB-COMT deficient mice and their wild type littermates of both sexes. MB-COMT deficient mice were seemingly normal, bred usually and had unaltered COMT activity in the brain and periphery despite a complete lack of the MB-COMT protein. MB-COMT deficient male mice showed higher extracellular dopamine levels than their wild-type littermates in the striatum, but not in the mPFC. In addition, the MB-COMT deficient male mice exhibited a distinct endophenotype characterized by schizophrenia-related behaviors like aggressive behavior and reduced prepulse inhibition. They also had prolonged immobility in the tail suspension test. Both sexes were sensitized to acute pain and had normal motor activity but disturbed short-term memory. Hence the behavioral phenotype was not limited to schizophrenia-related endophenotype and some behavioural findings were not sex-dependent. Our findings indicate that MB-COMT is critical for behavior, and its function in COMT-dependent brain areas cannot be entirely substituted by the remaining S-COMT.

Anesthetics and thyrotropin secretion in the rat.

The effects of seven anesthetics (thiopentone, 50 mg/kg ip; pentobarbitone, 50 mg/kg ip; chloral hydrate, 300 mg/kg ip; urethane, 1,5 g/kg, 1/2ip, 1/2sc; ether; methoxyflurane, 1,5%; halothane, 2%) on basal serum TSH concentrations and on the cold-induced as well as the TRH-induced TSH responses were studied in Sprague-Dawley rats. The basal TSH level in female rats were decreased by ether and halothane at 30 min and somewhat increased by pentobarbitone and chloral hydrate. The cold-induced (4C, 30-60 min) TSH response of the warm-adapted male rats (30 C, 7 days) was decreased by all of the anesthetics studied, but the effect of pentobarbitone was not significant. The TRH-induced (50 ng iv) TSH response in female rats was totally abolished only by deep ether anesthesia but augmented by bariturates and chloral hydrate. It is concluded that all of the anesthetics studied can modify the secretion of TSH by their central effects. Ether in high concentration seems to be effective also at the pituitary level. The use of anesthetics may be a source of error when studying the neurotransmitter control of TSH-TRH secretion in the rat.

Pharmacokinetics of nalidixinic acid and oxolinic acid in healthy women.

The pharmacokinetics of oral nalidixic acid (NA, 1 gm 4 times a day) and oxolinic acid (OA, 750 mg 2 times a day) administered for 7 days were studied in the same 10 healthy women on the first, third, and seventh days of the treatment. The peak concentrations of NA + OH-NA (hydroxynalidixinic acid) in serum at 2 to 3 hr were 34 mug/ml (total) and 23 mug/ml (unconjugated) on the first day and nearly two times higher on the third and seventh days; 82% to 85% of these amounts were NA. The protein-free fraction of NA + OH-NA was 8.8% to 18.3%. The total concentration of NA + OH-NA in urine was 1,220 to 2,700 mug/ml, the unconjugated concentration, 250 to 350 mug/ml, and the chemotherapeutically active concentration, 55 to 75 mug/ml. In steady state the 24-hr recovery of the total drug was 79% of the daily dose. The excretion rate in urine was 591 to 853 mg/6 hr. The OA concentration in serum was very low on the first day of the treatment, but increased to 4- to 5-fold on the third and seventh days: 6.2 to 6.4 mug/ml (total) and 3.3 to 3.6 mug/ml (unconjugated). The protein-free OA represented 19% to 23% of the total amount. The modest initial serum concentrations of OA were confirmed by the low urine concentrations on the first day. In steady state the OA concentration in urine was 570 mug/ml (total) and 35 mug/ml (unconjugated), and the 24-hr recovery, 49% and 3%, respectively. The microbiologic assay gave somewhat higher concentrations of the active drug than did the chemical assay. When taken with food, the excretion of OA in urine was retarded by 6 hr but the 48-hr recovery was not decreased.

Development of tolerance to the hormonal effects of morphine without changes in the aminergic functions in the brain of the rat.

The effect of morphine on cold-stimulated secretion of TSH and prolactin was studied in male rats, both in acute studies and after the chronic administration of morphine for 14 days (twice a day with increasing doses). The duration of the stimulatory effect of a single dose of morphine on secretion of prolactin was shorter (less than 2 hr) than its inhibitory effect on cold-stimulated secretion of TSH (over 2 hr). In the rats pretreated with morphine, a tolerance to the depressant effect of TSH of the challenge dose of morphine was seen at 2 hr but not at 1 hr after the injection. In contrast, a tolerance to the stimulatory effect of morphine on prolactin was seen at 1 hr after the acute dose of morphine. The minor alterations of the hypothalamic amine neurotransmitters and their metabolites did not correlate with the hormonal responses or to the development of tolerance.

Activation of 5-HT2A receptors impairs response control of rats in a five-choice serial reaction time task.

The present experiments investigated the effects of agents acting at serotonin (5-HT)-2 receptors on the performance of rats in a choice serial reaction time (5-CSRT) task in order to examine the role of 5-HT2 receptors in the modulation of attention and response control. The results indicate that DOI, [(+/-)-1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane hydrochloride; 0.05, 0.1 and 0.2 mg/kg, subcutaneously], a 5-HT(2A/2C) agonist, slightly impaired the choice accuracy of the well performing rats and markedly increased their premature responding. DOI (0.05 and 0.1 mg/kg) had no effect on the latency to collect earned food pellets or to respond correctly, indicating that these lower doses of DOI did not reduce motivation for the food reward in this task. The selective effect of a low dose of DOI (0.1 mg/kg) on premature responding was completely blocked by ketanserin (0.2 mg/kg), a 5-HT2A antagonist, and ritanserin (0.3 mg/kg), a 5-HT(2A/2C) antagonist, but only partially blocked by a high dose of SER082 (1.0 mg/kg), a 5-HT2C antagonist. In contrast to DOI, mCPP, [1-(3-phenyl)piperazine; 0.05 and 0.15 mg/kg], a 5-HT2C agonist, had no effect on choice accuracy or premature responding, but it reduced behavioral activity and/or arousal as indicated by the decreased number of trials completed and increased the probability of omissions. SER082 (1.0 mg/kg) blocked the effects of mCPP on performance. These data suggest that the overactivation of 5-HT2A receptors impairs response control in a 5-CSRT task, whereas the overactivation of 5-HT2C receptors can affect behavioral activity and/or arousal state of the animals for this food rewarded task.

Synthesis and in vitro pharmacology of a series of new chiral histamine H3-receptor ligands: 2-(R and S)-Amino-3-(1H-imidazol-4(5)-yl)propyl ether derivatives.

To investigate stereospecificity and the mechanism of activation of the histamine H3-receptor, a series of 2-(R and S)-amino-3-(1H-imidazol-4(5)-yl)propyl ether derivatives were synthesized. In these compounds, the structures of the well-known antagonist iodoproxyfan and the full agonists R- or S-(alpha)-methylhistamine were combined in one molecule. The obtained "hybrid" molecules were tested for H3-receptor affinity on rat cerebral cortex. Some selected compounds were further screened for H3-receptor functional activity with GTPgamma[35S] autoradiography studies using rat brain tissue sections. The affinity of all the synthesized compounds (-log Ki = 5.9-7.9) was lower than that found for iodoproxyfan or two of its analogues; however, the compounds showed stereospecificity. The S-configuration of the series of 2-amino-3-(1H-imidazol-4(5)-yl)propyl ether derivatives, which resembles the stereochemistry of R-(alpha)-methylhistamine, was more favorable. Incorporation of an amino group in the propyl chain of iodoproxyfan and analogues did not alter the antagonistic behavior for compounds with an aromatic side chain. However, when also the aromatic moiety was replaced by a cyclohexyl group, the compounds behaved as agonists. This indicates that an interaction between the side chain amino group and the H3-receptor protein is involved in H3-receptor activation. The 2-(S)-amino-3-(1H-imidazol-4(5)-yl)propyl cyclohexylmethyl ether (23) has H3-receptor agonistic properties with high affinity for the histamine H3-receptor (-log Ki = 7.9 +/- 0.2) and might serve as a useful tool for further studies concerning drug design and receptor-ligand interactions.

Synthesis of some novel potent and selective catechol O-methyltransferase inhibitors.

A series of disubstituted catechol derivatives was synthesized and tested as potential COMT inhibitors. The most active compounds were more than 1000 times more potent (IC50 = 3-6 nM) in vitro than the known COMT inhibitor, 3',4'-dihydroxy-2-methylpropiophenone (U 0521, IC50 = 6000 nM). The new compounds were also highly selective COMT inhibitors with no activity against other essential enzymes involved in the synthesis and metabolism of catecholamines.

Different in vivo properties of three new inhibitors of catechol O-methyltransferase in the rat.

1. We compared three new catechol O-methyltransferase (COMT) inhibitors (OR-611, Ro 40-7592 and CGP 28014; 10 and 30 mg kg-1, i.p.) in male rats given levodopa (L-DOPA, 50 mg kg-1, i.p.) and carbidopa ((-)-L-alpha-methyl dopa, 50 mg kg-1, i.p.). In some studies pretreatment with pargyline (80 mg kg-1, i.p.) was used to block the function of monoamine oxidase (MAO). 2. Decreases of hypothalamic and striatal 3-O-methyl-dopa (3-OMD) levels were used as measures of the inhibition of peripheral COMT. The inhibition of brain COMT activity was estimated by decreases of hypothalamic and striatal homovanillic acid (HVA) and 3-methoxytyramine (3-MT; after pargyline) levels. 3. The three COMT inhibitors studied had different individual characteristics. OR-611 was primarily a peripherally acting COMT inhibitor, decreasing 3-OMD levels in the striatum (to 31-52%) and in the hypothalamus (to 16-27%) both in the control and pargyline-treated animals at 1 and 3 h. It did not have any effect on brain HVA and 3-MT. 3. Ro 40-7592 was a broad spectrum COMT inhibitor decreasing striatal and hypothalamic 3-OMD (always to less than 30%), HVA (to less than 50%) and 3-MT levels (to less than 23%) significantly both at 1 and 3 h. It was more potent than OR-611. 4. CGP 28014 functioned as a weak COMT inhibitor in the periphery inhibiting 3-OMD formation only at 3 h. In contrast, it was fairly potent in decreasing the brain HVA and 3-MT levels at 1 h (to 37-22% and 42-35% in the striatum, and to 57-33% and 64-35% in the hypothalamus, respectively) but not at 3 h. Since CGP 28014, unlike OR-611 and Ro 40-7592, did not generally increase the brain DOPA, dopamine or DOPAC levels, it was not a typical COMT inhibitor.

Comparison of two new inhibitors of catechol O-methylation on striatal dopamine metabolism: a microdialysis study in rats.

1. Effects of two new inhibitors of catechol O-methylation (CGP 28014 and entacapone; 30 mg kg-1, i.p.) were compared by means of brain microdialysis in rats treated with L-3,4-dihydroxyphenylalanine (L-dopa)/carbidopa (50/50 mg kg-1, i.p., respectively) or saline. 2. In saline-treated rats, CGP 28014 maximally (max) increased striatal dopamine and 3,4-dihydroxyphenylacetic acid (DOPAC) effluxes by 41% and 49%, respectively, whereas homovanillic acid (HVA) levels were decreased by 71%. 3. In the presence of L-dopa/carbidopa, a peripherally active inhibitor of catechol O-methyltransferase (COMT) entacapone had a short-lasting increasing effect on L-dopa efflux. Compared to the effects of L-dopa/carbidopa alone 3-O-methyldopa (3-OMD) levels were effectively reduced (max 79%) by entacapone, but not by CGP 28014. 4. Entacapone, in contrast to CGP 28014, increased striatal dopamine efflux (max 492% of that after L-dopa/carbidopa alone). Also DOPAC levels were increased by entacapone (255% at 180 min), but not significantly by CGP 28014 (159% at 180 min). 5. Both compounds initially decreased HVA efflux. The effect of CGP 18014 was longer-lasting. By the end of the measurement, entacapone even increased HVA levels (max 259%). 6. Our results demonstrate that entacapone is a peripheral COMT inhibitor and support the view that CGP 18014 is mainly a centrally acting inhibitor of O-methylation.

Effect of modified brain histamine contents on prolactin and thyrotropin secretion in male rats.

Effects of modified brain histamine contents on thyrotropin and prolactin secretion were studied in male rats. Under basal conditions the histamine content in the hypothalamus was approximately 8-10-fold higher than that in the striatum and the rest of the brain. L-histidine (1000 mg/kg, ip), a histamine precursor, and metoprine (20 mg/kg, ip), an inhibitor of histamine methyltransferase, elevated histamine content in the brain by 65% and 167%, respectively. When the treatments were given together an additive effect (119-250% increase) on brain histamine was observed. Metoprine significantly decreased serum prolactin levels, while L-histidine had no effect. This effect of metoprine was not modified by treatment with L-histidine. Thus, metoprine has an inhibitory effect on prolactin secretion that is not related to elevated brain histamine contents. The increased brain histamine content after L-histidine treatment had no effect on prolactin secretion. Basal levels of serum thyrotropin were decreased by both L-histidine and metoprine, L-histidine being more potent. In rats treated with alpha-fluoromethylhistidine, an inhibitor of L-histidine decarboxylase, the cold-induced (rats kept for 60 min at +4 degrees C) thyrotropin secretion was increased while the stress-induced prolactin secretion was decreased. In these rats, metoprine did not affect thyrotropin release but blunted the prolactin response. In conclusion, endogenous histamine inhibits thyrotropin secretion but does not affect prolactin release. Owing to its other effects, metoprine is not suitable as a tool to elevate endogenous histamine contents in the brain, at least when the regulation of anterior pituitary hormone release is being studied.

Effects of cysteamine pretreatment and hypothalamic periventricular nucleus lesion on the cold-stimulated thyrotropin responses to intracerebroventricular 5-hydroxytryptamine in male rats.

Abstract The hypothalamic somatostatinergic system was devitalized in male rats by intracerebroventricular (icv) cysteamine (CSH) pretreatment (250 mug/rat/day into the third ventricle) on 4 consecutive days or by a limited lesion of the hypothalamic periventricular nucleus (PeVNx). The acute effect of icv serotonin (5-HT) on the cold-stimulated thyrotropin (TSH) and prolactin responses were studied in these animals. The experiments were performed 24 h after the last saline or CSH infusions and 7 days after the sham- or PeVN-lesions. CSH and PeVNx decreased the hypothalamic somatostatin content by 44% to 57% and 19% to 28%, respectively. PeVNx did not affect hypothalamic thyrotropin-releasing hormone content. 5-HT infusion (9 mug/rat icv) into the anterior third ventricle elevated, although not significantly, TSH levels in both saline- or CSH-pretreated rats. 5-HT infusion into the anterior third ventricle did not affect TSH in sham-operated rats. However, 5-HT augmented the cold-stimulated TSH levels after PeVNx compared to sham-lesion. Inversely, 5-HT infusion (9 mug/rat) into the posterior third ventricle inhibited TSH secretion irrespective of the pretreatment or lesion. The inhibitory action of 5-HT on TSH was significantly suppressed by CSH. 5-HT infusions elevated serum prolactin levels irrespective of the infusion site, pretreatment or lesion. 5-HT infusion into both the anterior and the posterior third ventricle decreased rectal temperature in saline-pretreated, sham- and PeVN-lesioned rats. The hypothermie effect of 5-HT was weakened by CSH. The hypothalamic levels of noradrenaline, dopamine and their metabolites were not significantly affected by CSH and PeVNx. 5-HT infusion into the anterior third ventricle decreased hypothalamic dopamine content in both saline- and CSH-pretreated rats. However, such an effect was not seen in sham- or PeVN-lesioned animals. Although CSH is an inhibitor of dopamine-beta-hydroxylase, this activity was not reflected in serum TSH or prolactin levels. The results support our hypothesis of the site-dependent action of icv 5-HT or TSH secretion. The elevation of TSH levels may arise from the inhibition of somatostatin release from rostral anterior hypothalamus. The inhibition of TSH secretion may result from the inhibition of thyrotropin-releasing hormone release from more caudal periventricular structures of the hypothalamus.

Ondansetron, an antagonist of 5-HT3 receptors, antagonizes the anti-exploratory effect of caerulein, an agonist of CCK receptors, in the elevated plus-maze.

Systemic treatment with caerulein (0.25-5 micrograms/kg SC), non-selective agonist of cholecystokinin (CCK) receptors, dose-dependently suppressed the exploratory behaviour of rats in an elevated plus-maze without producing remarkable changes in the locomotor activity of animals in an open field test. Ondansetron, a selective antagonist of 5-HT3 receptors, increased the number of open arm entries in the plus-maze test only at a dose 10 micrograms/kg. The other doses of ondansetron (0.1, 1 and 100 micrograms/kg IP) did not significantly change either the locomotor activity or the exploratory behaviour of rats. Pretreatment of rats with ondansetron (at 10 micrograms/kg, but not at 0.1, 1 or 100 micrograms/kg) completely reversed the anti-exploratory effect of caerulein (5 micrograms/kg). The concomitant treatment with caerulein and ondansetron did not cause any major change in the locomotor activity of animals in open field. Consequently, we propose that 5-HT-ergic mechanisms are involved not only in the regulation of CCK release in the cerebral cortex and nucleus accumbens, but also in the modulation of the anti-exploratory effect of caerulein, a CCK agonist, in the elevated plus-maze.