A simple, sensitive and reliable assay for serotonin and 5-HIAA in brain tissue using liquid chromatography with electrochemical detection

Influence of 5,7-dihydroxytryptamine lesions of the rat fornix-fimbria and cingulum bundles on spontaneous activity in an aversive maze

Exposure to aversive environmental stimuli stimulates the serotonergic neurones that project to the forebrain and inhibit spontaneous activity when studied in a simple maze. This study explored the putative role of the principal 5-hydroxytryptamine (5-HT) neurones that project to the hippocampus from the median raphe nucleus in this response to an aversive environment by lesioning the 5-HT fibres that project through the fornix/fimbria and cingulum bundles. The effects of the lesions were investigated in independent groups of animals tested in an enclosed four-arm maze and a more aversive elevated maze of the same dimensions composed entirely of four open arms. The rats were significantly less active in the open maze, the principal effect of maze design being observed during the first 5 min sub-trial of a 15 min trial. This response to the more aversive environment was totally abolished by the lesion. It is concluded that exposure to an explicitly aversive environment elicits a brief stimulation of the 5-HT neurones that project to the hippocampus from the median raphe nucleus and that this stimulation inhibits the initial burst of exploratory activity that is observed in animals placed in a less aversive novel environment.

In vitro effects of adrenomedullin and calcitonin gene related peptide on the release of serotonin and amino acids from rat dorsal spinal cord

Adrenomedullin (AM) and calcitonin gene-related peptide (CGRP) are structurally related, interact with each others receptors and show overlapping biological activities. Immunoreactivity (IR) and mRNAs along with binding sites for both CGRP and adrenomedullin have been shown in the rat spinal cord. CGRP mediates the transmission of nociceptive information at the spinal cord level and both peptides has shown to induces c-fos expression and accumulation of cAMP in spinal cells. In this study, HPLC methods were used to investigate the effects of AM and CGRP on the basal and K+-evoked release of serotonin, glutamate (Glu), aspartate (Asp), glycine (Gly) and gamma amino butyric acid (GABA) from the slices prepared from the rat spinal cord. Neither CGRP (10(-7) and 10(-6) M) nor AM (10(-7) and 10(-6) M) had significant effects on the basal release of serotonin and the amino acids tested in this study. However, CGRP produced statistically significant increases in the K+-evoked release of Asp and Glu, whereas AM failed to do so. Neither AM nor CGRP (10(-7) and 10(-6) M) showed any significant effects on the K+-evoked release of serotonin, GABA and Gly. Present data suggest that the stimulatory effects of CGRP on the release of Asp and Glu were exerted by distinct types of CGRP receptors.

Regulation of corticosteroid receptors in the rat brain: the role of serotonin and stress

It has been suggested that physiological resistance to repeated stress is associated with increased 5-hydroxytryptamine (5-HT) release in the dorsal hippocampus and that dysregulation of this neuroadaptation may be implicated in the psychopathology of depression. This study used 5,7-dihydroxytryptamine lesions to investigate the role of 5-HT projections to the hippocampus in physiological responses to repeated stress and putative changes in corticosteroid receptor immunoreactivity in the brain. Repeated exposure to elevated open platform stress (1 h/day) caused regionally selective changes in glucocorticoid and mineralocorticoid receptor immunoreactivity in the dorsal hippocampus that were not observed in ventral hippocampus, frontal cortex, hypothalamus or parietal cortex. Glucocorticoid receptor immunoreactivity in the dorsal hippocampus was decreased after 5 days but increased after 20 days of stress. Mineralocorticoid receptor immunoreactivity was increased after 5 or 10 days of stress. The increases in glucocorticoid and mineralocorticoid receptor immunoreactivity, evoked by repeated stress, were abolished by lesions of the principal 5-HT projections to the hippocampus. The lesions abolished the increased defecation observed in stressed animals, but had no effects on the plasma corticosterone response to the stressor or the habituation of this response observed following repeated stress. The experiments have revealed a dissociation in the regulation of corticosteroid receptor expression in the dorsal and ventral hippocampus by repeated stress and 5-HT. The data suggest that adaptation to inescapable stress is associated with regionally selective changes in corticosteroid receptor expression in dorsal hippocampus that are largely 5-HT-dependent, although these changes do not mediate habituation of the pituitary adrenocortical response to the stressor.

Evidence for a mutual interaction between noradrenergic and serotonergic agonists in stimulation of ACTH and corticosterone secretion in the rat

We investigated the mutual interactions between hypothalamic norepinephrine (NE) and serotonin (5-HT) in mediating the ACTH and corticosterone responses to direct stimulation of the paraventricular nucleus (PVN) with adrenergic and serotonergic agonists. The hormone responses to the intrahypothalamic injection of the alpha1-adrenergic agonist phenylephrine (20 nmol/2 microl) were significantly reduced by prior depletion of hypothalamic 5-HT with intra-PVN injection of the serotonergic neurotoxin 5,7-dihydroxytryptamine (5,7-DHT), but not after depletion of hypothalamic NE by intra-PVN injection of the noradrenergic neurotoxin 6-hydroxydopamine (6-OHDA). The ACTH and corticosterone responses to intrahypothalamic injection of the 5-HT(1A) receptor agonist 8-OH-DPAT (20 n mol/2 microl) were significantly reduced by depletion of hypothalamic NE with 6-OHDA, but not after depletion of hypothalamic 5-HT with 5,7-DHT. These mutual interactions between the NE and 5-HT neuronal systems, which innervate the PVN, may explain previous findings of equivalent reductions in the hypothalamic-pituitary-adrenal axis responses to neural stimulation after neurotoxic lesioning of either the NE or 5-HT systems.

Effects of adrenergic and serotonergic agonists in the amygdala on the hypothalamo-pituitary-adrenocortical axis

The effect of direct administration of adrenergic and serotonergic (5-HT) agonists into the central nucleus of the amygdala (AMG) on the hypothalamo-pituitary-adrenal (HPA) axis have been studied in intact male rats and in animals with 6-hydroxydopamine (6-OHDA) or 5, 7-dihydroxytryptamine (5,7-DHT) neurotoxic lesions in the paraventricular nucleus of the hypothalamus (PVN). In intact animals, the administration of phenylephrine, an alpha1 adrenergic agonist or 8-hydroxy-2-(di-n-propylamino)-tetralin (8-OH-DPAT) a 5-HT(1A) agonist caused depletion of median eminence corticotropin releasing hormone and a rise in serum adrenocorticotrophic hormone (ACTH) and corticosterone (CS) levels. Isoproterenol a beta agonist was more effective than phenylephrine and a 5-HT(1B) agonist CP-93, 129 was less effective than 8-OH-DPAT on the adrenocortical activity. The 6-OHDA or 5,7-DHT hypothalamic lesions prevented the stimulatory effects of phenylephrine and 8-OH-DPAT, respectively, which where injected into the AMG, on serum ACTH and CS levels. In view of our previous studies on the effects of the adrenergic and 5-HT antagonists in the AMG and the present data, it is suggested that norepinephrine and 5-HT play an important role in the stimulatory effect of the AMG on the HPA axis. These effects depend on the presence of these excitatory neurotransmitters in the PVN.

Monoamines, amino acids and acetylcholine in the preoptic area and anterior hypothalamus of rats: measurements of tissue extracts and in vivo microdialysates

A microbore column high-performance liquid chromatography (HPLC) system was used to measure neurotransmitters in tissue extracts and in vivo microdialysates obtained from the preoptic area (PO) and anterior hypothalamus (AH) of rats. The extracts contained norepinephrine, epinephrine, 3,4-dihydroxyphenylacetic acid (DOPAC), dopamine, 5-hydroxyindoleacetic acid (5-HIAA), homovanillic acid (HVA), 5-hydroxytryptamine (5-HT), aspartate, glutamate, GABA, acetylcholine (ACh) and choline. The microdialysates obtained from the PO and AH of freely moving rats contained all of these substances except for norepinephrine, epinephrine, dopamine, and 5-HT. During collection of microdialysate from the PO and AH, core body temperature and locomotor activity were simultaneously measured by means of telemetry. The locomotor activity and body temperature increased during the night. This was accompanied by increased levels of 5-HIAA. The results suggest that serotonergic neuronal mechanisms in the PO and AH may be involved in hypothalamic regulation of spontaneous behaviors and body temperature.

New isocratic high-performance liquid chromatographic procedure to assay the anti-sickling compound hydroxyurea in plasma with ultraviolet detection

A new procedure using high-performance liquid chromatography (HPLC) with ultraviolet detection to assay hydroxyurea (HU) levels in plasma has been developed. The drug was isolated from plasma by a direct deproteinization process with sulfosalicylic acid. Following neutralization of the acidic supernatant, an aliquot was loaded onto an Aminex HPX-72S column (300x7.8 mm). Chromatography was performed at 55 degrees C using a mobile phase consisting of acetonitrile-0.025 M ammonium sulfate buffer (pH 8.5) including 0.1% triethylamine, 0.01 M sodium sulfate, and 5 mM sodium heptane sulfonate. The UV absorbance of effluent was monitored at 214 nm. A flow-rate of 0.8 ml/min was used for analyzing HU in both human and mouse plasma. Under these conditions, the drug eluted at 12.6 min. The assay possessed linearity up to 425 microg/ml, with a lower limit of quantitation of 3.32+/-0.0004 microg/ml (mean+/-S.D., n=10). Intra-day and inter-day coefficients of variation were less than 8.5% and 8.7% respectively. Absolute differences were less than 7.4%. The method has been employed in clinical studies and the sensitivity of the assay was shown to be adequate for characterizing the plasma pharmacokinetics of HU in mice. In conclusion, the procedure described herein could be ideally suited for therapeutic monitoring of hydroxyurea.

The excitatory effects of the amygdala on hypothalamo-pituitary-adrenocortical responses are mediated by hypothalamic norepinephrine, serotonin, and CRF-41

The hypothalamic neural mechanisms that are involved in the facilitatory effects of the amygdala (AMG) on the hypothalamo-pituitary-adrenocortical (HPA) axis have been investigated in rats. Stimulation of the central AMG nucleus caused a depletion of hypothalamic CRF-41, presumably due to its release into the portal circulation, and a subsequent rise in plasma ACTH and corticosterone (CS) levels. These effects were inhibited in rats in which hypothalamic norepinephrine (NE) or serotonin (5-HT) was depleted by catecholamine or serotonin neurotoxins, respectively. Furthermore, the administration of prazosin, an alpha1, but not of atenolol, which is a beta-blocker, as well as administration of the 5-HT2 blocker ketanserin inhibited the ACTH and CS responses to AMG stimulation. These results indicate that the facilitatory effects of the AMG on the HPA axis are mediated by hypothalamic NE via alpha1 receptors and by 5-HT via 5-HT2 receptors, as well as by CRF-41 in the paraventricular nucleus.

Hypothalamic mechanisms mediating glutamate effects on the hypothalamo-pituitary-adrenocortical axis

The effect of local administration of glutamate into the hypothalamic paraventricular nucleus (PVN) on the hypothalamo-pituitary adrenocortical (HPA) axis was studied in male rats. Glutamate caused CRH-41 depletion from the median eminence (ME) and a consequent rise in ACTH and corticosterone (CS) serum levels. In rats pretreated with systemic dexamethasone (dex) these effects were completely inhibited. The administration of the glucocorticoid receptor antagonist RU-38486 abolished the inhibitory effect of dex on the adrenocortical discharge. In addition, the depletion of hypothalamic norepinephrine (NE) and serotonin (5-HT) by specific neurotoxins administered into the ventral noradrenergic blundle or into the raphe nuclei respectively, inhibited the response of serum ACTH and CS following PVN glutamate administration. These data indicate that glutamate stimulated the HPA axis via the release of ME CRH-41 into the portal circulation. This response is steroid sensitive involving type II glucocorticoid receptors. Hypothalamic NE and 5-HT participate in the glutamate induced HPA axis activation.

Serotonin promotes the differentiation of glutamate neurons in organotypic slice cultures of the developing cerebral cortex

The monoamines serotonin (5-HT), noradrenaline (NA), and dopamine (DA), which are present in the developing brain apparently before they assume their neurotransmitter functions, are regarded as strong candidates for a role in the maturation of the cerebral cortex. Here we sought to investigate their effects on the generation and differentiation of cortical cell types. Slice cultures, prepared from the cortices of embryonic day (E) 14, E16, and E19 rat fetuses, were kept in defined medium or in defined medium plus 5-HT for 7 d. E16 cortices were also exposed to NA or DA for the same period. At the end of this period, the proportions of the neuronal [glutamate (Glu)-, GABA-, calbindin-, calretinin-labeled], glial (GFAP), and neuroepithelial (nestin) cell types were estimated for all conditions. We found that in E16 cultures, application of 5-HT, but not of NA or DA, significantly increased the proportion of Glu-containing neurons without affecting the overall neuronal population or the proportions of any other cell types. A similar effect was observed in co-cultures of E16 cortex with slices through the midbrain raphe nuclei of E19 rats. The total amount of cortical Glu, as measured with HPLC, was also increased in these co-cultures. To investigate whether the effect of 5-HT was the result of changes in cell proliferation, we exposed slices to bromodeoxyuridine (BrdU) and found that the proportion of BrdU-labeled cells was similar in the 5-HT-treated and control slices. These results indicate that 5-HT promotes the differentiation of cortical Glu-containing neurons without affecting neuroepithelial cell proliferation.

Diet-induced changes in serum cholesterol concentrations do not alter tryptophan hydroxylation rate or serotonin concentrations in gerbil brain

The relationship between serum cholesterol concentrations and serotonin synthesis rate in brain was examined in Mongolian gerbils chronically fed diets containing 20% fat (safflower oil, beef tallow or butterfat) with or without added cholesterol (0.5%, dry weight). After 22 days on these diets, circulating cholesterol concentrations ranged between approximately 1.5 and approximately 20 mumol/ml. Despite this enormous range, in vivo tryptophan hydroxylation rate, and serotonin and 5-hydroxyindoleacetic acid concentrations in cerebral cortex, hypothalamus and brainstem did not differ significantly among the diet groups. Tryptophan concentrations in serum and brain were also unaffected. These results do not support the hypothesis that the link between depression, suicide and violent deaths and below-normal or reduced serum cholesterol concentrations in humans involves an alteration in serotonin synthesis and/or release by brain neurons.

Posterior hypothalamic deafferentation or 5,7-dihydroxytryptamine inhibit corticotropin-releasing hormone, ACTH and corticosterone responses following photic stimulation

The effect of posterior hypothalamic deafferentation (PHD) or hypothalamic serotonin (5-HT) depletion by 5,7-dihydroxytryptamine on corticotropin-releasing hormone (CRH), ACTH and corticosterone (CS) responses, following photic stimulation, was investigated in male rats. In intact animals, photic stimulation caused median eminence (ME) CRH depletion and a rise in serum ACTH and CS levels. In rats with PHD, in which previous studies have demonstrated 5-HT depletion, or with neurotoxin induced hypothalamic 5-HT reduction, these responses were markedly inhibited. This indicates that the blockage in the release of ME CRH into the portal circulation in rats with hypothalamic 5-HT depletion is responsible for the inhibition of the pituitary-adrenocortical responses following photic stimulation.

Simultaneous determination of histamine and serotonin in mast cells by high-performance liquid chromatography

A sensitive and rapid high-performance liquid chromatographic method for the simultaneous determination of histamine and 5-hydroxytryptamine (serotonin) in supernatants and cellular extracts from mouse bone marrow-derived mast cells was developed. The described method is based on a precolumn derivatization of histamine and serotonin with o-phthaldialdehyde (OPA) and subsequent separation of the amine-OPA adducts with an analytical reversed-phase C18 column combined with fluorometric detection (excitation wavelength 360 nm, emission at 455 nm). The mobile phase was 0.02 M sodiumacetate buffer (pH 8) including 5 mM 1-octanesulfonic acid and 50% methanol. The detection limits for histamine and serotonin were 3.3 pmol and 6.9 pmol, respectively (signal-to-noise ratio 2:1). The variations of peak areas of repeatedly injected low or high amounts of amine standards were 23.3% or 6.9% (for 0.5 ng or 12.5 ng histamine) and 26.4% or 4.0% (for 5.0 ng or 250 ng serotonin) during an experimental period of 4 weeks. The variation of retention times over 2 days was 1.1% for histamine and 1.7% for serotonin. A perfect linear relationship of amine concentrations and peak areas was documented by correlation coefficients of r > 0.999 for both histamine (0.1-125 ng) and serotonin (0.5-250 ng).

Brain cholecystokinin octopeptide (CCK-8) concentrations: effect of tryptophan and other serotonergic agents

The effects of 1-week drug treatment on the brain contents of neuropeptides were investigated. The cholecystokinin (CCK) concentrations in the hypothalamus were significantly decreased by tryptophan treatment but not by imipramine and cyproheptadine, which changed the serotonergic function. Proglumide, the CCK antagonist, induced in the hypothalamic and hippocampal-striatal areas an increase in CCK concentration, which was not reversed in the presence of tryptophan. Dynorphin and substance P(SP) concentrations were also modified by proglumide treatment.

Serotonin involvement in the antitumour and host effects of flavone-8-acetic acid and 5,6-dimethylxanthenone-4-acetic acid

The relationship of serotonin (5-HT) receptors to the action of the experimental antitumour drugs flavone-8-acetic acid (FAA) and 5,6-dimethylxanthenone-4-acetic acid (5,6-MeXAA) was studied. Both FAA and 5,6-MeXAA are known to induce the synthesis of tumour necrosis factor-alpha (TNF) and to stimulate nitric oxide synthesis in vivo, as measured by elevation of plasma nitrate. Serotonin potentiated the effect of a subtherapeutic dose of 5,6-MeXAA (20 mg/kg) as measured both by plasma nitrate increase and by growth delay of s.c. implanted colon 38 tumours. On the other hand, administration of the serotonin 5-hydroxytryptamine-2 (5-HT2) antagonist cyproheptadine (20 mg/kg) inhibited both the plasma nitrate response and, to a lesser extent, the induction of tumour haemorrhagic necrosis by 5,6-MeXAA, FAA and TNF. Reduction of circulating plasma serotonin by pre-treatment with p-chlorophenylalanine and reserpine reduced the plasma nitrate response, but not the tumour necrosis response, to 5,6-MeXAA (30 mg/kg). It is suggested that serotonin is necessary for the induction of nitric oxide synthases and acts, either directly or indirectly, in concert with TNF. Serotonin agonists may have utility in increasing nitric oxide synthesis in response to TNF or to agents that induce TNF as part of their antitumour action.

Effect of 6-hydroxydopamine and 5,7-dihydroxytryptamine on tissue uptake and cell nuclear retention of corticosterone in the rat hypothalamus

Previous studies have shown that norepinephrine and serotonin can modulate the glucocorticoid (GC) binding capacity in the hippocampus. The aim of the present study was to evaluate the role of these neurotransmitters in regulating GC receptors in the hypothalamus. Injection of the neurotoxin 6-hydroxydopamine (6-OHDA) into the ventral noradrenergic bundle (VNAB) and 5,7-dihydroxytryptamine (5,7-DHT) into the raphe nuclei caused a marked depletion in norepinephrine and serotonin, respectively, in the paraventricular nucleus (PVN) and mediobasal hypothalamus (MBH). The injection of these neurotoxins did not change the basal levels of ACTH and corticosterone. Injection of 6-OHDA into the VNAB caused a significant reduction in the cell nuclear binding of corticosterone in the PVN but not in the MBH. Conversely, injection of 5,7-DHT into the raphe nuclei caused a significant reduction in cell nuclear binding of corticosterone in the MBH but did not affect binding in the PVN. These results demonstrate that at least part of the nuclear corticosteroid receptors in the PVN and MBH are differentially regulated by the noradrenergic and serotonergic systems.

Effect of tryptophan on extracellular concentrations of tryptophan and 5-hydroxyindoleacetic acid in the striatum and cerebellum

The effects of L-tryptophan (50 mg/kg i.p.) on extracellular concentrations of tryptophan and the 5-hydroxytryptamine (5-HT) metabolite 5-hydroxyindoleacetic acid (5-HIAA) were determined in the rat striatum and cerebellum, regions with rich and poor 5-HT innervation, respectively. Determinations were on perfusates from dialysis probes in the brains of conscious, freely moving rats. The pharmacokinetic profiles of dialysate tryptophan after tryptophan load (peak concentration, time to peak concentration, area under curve, and half-life) in the two regions did not differ significantly. The dialysate 5-HIAA concentration in the striatum rose two- to threefold after the administration of tryptophan. Therefore, as 5-HIAA was undetectable in the cerebellum either before or after the administration of tryptophan, the increase of 5-HIAA in the striatum is unlikely to depend appreciably on its production within the cerebral vasculature or outside the brain or on its entering the striatum through a blood-brain barrier damaged by placement of the dialysis probe. Overall, the findings strengthen previous evidence that extracellular 5-HIAA concentrations determined by cerebral dialysis are a valid measure of the metabolism of 5-HT of brain neuronal origin.

Effect of hypothalamic norepinephrine depletion on median eminence CRF-41 content and serum ACTH in control and adrenalectomized rats

In this study we examined the role of the noradrenergic innervation of the hypothalamus on the adrenalectomy-induced changes in median eminence (ME) CRF-41 and serum ACTH. 6-Hydroxydopamine (6-OHDA), the catecholaminergic neurotoxin, or vehicle was injected into the ventral noradrenergic bundle of male rats. One week later animals underwent adrenalectomy or sham operation and were sacrificed 18 or 120 h later. In sham-operated rats 6-OHDA did not affect ME CRF-41 content or serum ACTH. In vehicle-injected adrenalectomized rats ACTH was increased approximately 3-fold at 18 h and almost 6-fold at 120 h. At 18 h CRF-41 content was markedly depleted (reduced approximately 20-fold) but by 120 h CRF-41 content had partially recovered and was about 70% of control animals. In adrenalectomized animals, 6-OHDA lesions caused a complete inhibition of the increase in serum ACTH both at 18 h and at 120 h. Pretreatment with 6-OHDA partially attenuated the drastic reduction in ME CRF-41 content following adrenalectomy at 18 h. However, at 120 h, the neurotoxin prevented the recovery of CRF-41 following adrenalectomy. These results suggest that intact norepinephrine innervation to the hypothalamus is necessary for the increased production of ACTH following adrenalectomy and that its interruption interferes with both the adrenalectomy-induced ME CRF-41 reduction and subsequent recovery.

Depletion of hypothalamic norepinephrine and serotonin enhances the dexamethasone negative feedback effect on adrenocortical secretion

The role of norepinephrine (NE) and serotonin (5-HT) in the negative feedback effect of dexamethasone (DEX) on the adrenocortical response to ether stress was investigated. Injection of the catecholamine neurotoxin, 6-hydroxydopamine, into the ventral noradrenergic bundle or the paraventricular nucleus of the hypothalamus (PVN) which produced a very significant depletion in hypothalamic NE content enhanced the negative feedback effect of DEX. Injection of the 5-HT neurotoxin, 5,7-dihydroxytryptamine, into the raphé nuclei or PVN, which caused a depletion of hypothalamic 5-HT, produced a similar effect on the adrenocortical response to DEX. The degree of negative feedback may be viewed as a balance of neural stimulatory and glucocorticoid influences of the hypothalamus. Thus the removal of the stimulatory effects of NE and 5-HT on adrenocortical secretion, by the neurotoxic lesions, enhanced the inhibitory influence of DEX.

Adrenal responses and neurotransmitters in posterior hypothalamic deafferentation

The effects of a small posterior hypothalamic deafferentation (PHD) on adrenocortical responses to peripheral neural stimuli were investigated in rats. PHD inhibited the rise in plasma corticosterone (CS) following photic and acoustic stimulation, but did not affect the adrenocortical response following sciatic nerve stimulation. PHD did not change the content of norepinephrine in the paraventricular nucleus of the hypothalamus, however, it reduced the serotonin content by about 30%. The possible role of serotonin or of another tonic caudal input into the hypothalamus for the activation of the pituitary-adrenocortical axis, following certain neural stimuli, is discussed.

Serotonin and 5-hydroxyindoleacetic acid are increased in the sigmoid colon in severe idiopathic constipation

The distribution of serotonin and dopamine beta-hydroxylase was examined in sigmoid colon specimens from patients with severe idiopathic constipation and control patients with carcinoma of the rectum or colon. Specimens were divided into three regions: (a) the mucosa; (b) the myenteric and submucosal plexuses with the longitudinal and circular smooth muscles; and (c) the circular smooth muscle, for biochemical analysis of serotonin and 5-hydroxyindoleacetic acid (total indoles) and noradrenaline. In both groups of patients, serotonin- and dopamine beta-hydroxylase-like immunoreactivity was localized in nerves in the myenteric and submucosal plexuses, and a sparse innervation was observed in the circular muscle. In addition, intense serotonin-like fluorescence was present in a large number of enterochromaffin cells in the mucosa. Total indole levels were significantly increased in the mucosa (p less than 0.02) and circular muscle (p less than 0.05) of the constipated patients. In contrast, no changes in noradrenaline levels were observed in any of the regions studied. Altered levels of total indoles may thus contribute to severe idiopathic constipation. Analysis of biopsy specimens could be a useful tool in clinical diagnosis and future investigations of diseases of the gut.

Effect of an oral tryptophan/carbohydrate load on tryptophan, large neutral amino acid, and serotonin and 5-hydroxyindoleacetic acid levels in monkey brain

Plasma and brain levels of tryptophan and other large neutral amino acids, and brain levels of serotonin and 5-hydroxyindoleacetic acid (5 HIAA) were measured in groups of adult cynomolgus monkeys 1 hr after they ingested one of four doses of a tryptophan-carbohydrate mixture. The doses had been administered once daily for 13 weeks. Dose-related increments occurred in plasma tryptophan, the plasma ratio of tryptophan to the sum of other large neutral amino acids, and in brain tryptophan levels. In contrast, the plasma ratios and brain levels of the other neutral amino acids each declined. Serotonin and 5 HIAA levels increased significantly, and in a dose-related manner in the brainstem and striatum, but not in cortex or hypothalamus. The results suggest that while tryptophan administration can stimulate serotonin production in primate brain, the effect may be restricted to certain brain regions. They also suggest that the transport of the large neutral amino acids into brain occurs via a competitive mechanism similar to that for other mammals.

Effect of 8-hydroxy-2-(di-n-propylamino)-tetralin on the tryptophan-induced increase in 5-hydroxytryptophan accumulation in rat brain

The injection of 8-hydroxy-2-(di-n-propylamino)-tetralin [8-OH-DPAT]reduced 5-hydroxytryptophan accumulation in vivo in rat cerebral cortex, hypothalamus and brainstem. Brain tryptophan levels were unaffected. Dose-related increases in 5-hydroxytryptophan accumulation produced by single injections of L-tryptophan (0, 25, 75 mg/kg ip) were substantially diminished by pretreatment with 8-OH-DPAT. The drug did not affect the tryptophan-induced increments in brain tryptophan level. Since 8-OH-DPAT is known to reduce the activity of serotonin neurons in vivo, these results suggest that when serotonin neurons are relatively inactive, the ability of an injection of tryptophan to stimulate serotonin synthesis is greatly attenuated.

Smoking-associated changes in the serotonergic systems of discrete regions of human brain

This paper describes the results of a postmortem study of the effects of tobacco smoking on the concentrations of 5-hydroxytryptamine (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) as well as the binding of [3H]-8-hydroxy-(di-n-propylamino)-tetralin ([3H]-8-OH-DPAT) and [3H]-ketanserin in six discrete regions of human brain. Smoking was associated with significant decreases in the concentrations of 5-HIAA in the hippocampal neocortex (P less than 0.001), hippocampal formation (P less than 0.05) and the median raphe nuclei (P less than 0.05). The 5-HT level of the hippocampal formation was also significantly reduced in smokers (P less than 0.05). These changes were accompanied by significant increases in the binding of [3H]-8-OH-DPAT in the hippocampal neocortex (P less than 0.01) and hippocampal formation (P less than 0.05). [3H]-Ketanserin binding in the brain regions studied was unaffected by smoking. It is concluded that smoking is associated with a regionally selective decrease in the activity of the serotonergic system of the human hippocampus.

A comparison of the distribution of neurotransmitters in brain regions of the rat and guinea-pig using a chemiluminescent method and HPLC with electrochemical detection

Six brain areas of rats and guinea-pigs, killed by microwave irradiation, were used for the concomitant measurement of the levels and regional distribution of cholinergic, biogenic amine, and amino acid neurotransmitters and metabolites. Acetylcholine (ACh) and choline (Ch) were quantified by chemiluminescence; noradrenaline (NA), dopamine (DA), 5-hydroxytryptamine (5-HT), and their metabolites by HPLC with electrochemical detection (HPLC-EC); and six putative amino acid neurotransmitters by HPLC-EC following derivatisation. The levels and regional distribution of these transmitters and their metabolites in the rat were similar to those reported in previous studies, except that biogenic amine transmitter levels were higher and metabolite concentrations were lower. The guinea-pig showed a similar regional distribution, but the absolute levels of ACh were lower in striatum and higher in hippocampus, midbrain-hypothalamus, and medulla-pons. In all areas, the levels of Ch were higher and those of NA, 5-HT, and taurine were lower than in the rat. The most marked differences between the rat and guinea-pig were in the relative proportion of DA metabolites and 5-HT turnover, as estimated by metabolite/transmitter ratios. This study can be used as a basis for a comprehensive understanding of the central effects of drugs on the major neurotransmitter systems.

In vivo tyrosine hydroxylation rate in retina: effects of phenylalanine and tyrosine administration in rats pretreated with p-chlorophenylalanine

p-Chlorophenylalanine was administered to rats to inhibit hepatic phenylalanine hydroxylase activity. Two days later, phenylalanine injection was noted to produce substantial increases in serum phenylalanine levels, and relatively modest increments in serum tyrosine levels. Rats injected with p-chlorophenylalanine 2 days earlier showed a normal light-induced activation of retinal tyrosine hydroxylase activity in vivo, measured as dihydroxyphenylalanine accumulation following pharmacologic inhibition in vivo of aromatic L-amino acid decarboxylase activity. In addition, tyrosine injection into p-chlorophenylalanine-treated rats in the light produced anticipated increments in retinal tyrosine hydroxylation rate, showing the enzyme to be functionally normal. The acute administration of phenylalanine (62.5-500 mg/kg i.p.) to p-chlorophenylalanine-treated rats produced dose-related increments in retinal phenylalanine. In vivo tyrosine hydroxylation rate in retina was normal at all doses below 300 mg/kg. However, at the highest dose (500 mg/kg), when retinal phenylalanine levels were almost 5-times normal tyrosine hydroxylation rate consistently fell (to about half-normal values). These results demonstrate that very large elevations in tissue phenylalanine levels do not stimulate tyrosine hydroxylation in vivo, and that at extremely high levels phenylalanine inhibits tyrosine hydroxylation rate.

Alterations in serotonin and neuropeptide Y content of cerebrovascular sympathetic nerves following experimental subarachnoid hemorrhage

The effect of an experimental subarachnoid hemorrhage (SAH) upon neurotransmitter content in sympathetic nerves supplying the major cerebral arteries of the rat has been examined by immunohistochemical analysis and high performance liquid chromatography with electrochemical detection (HPLC-ECD). In particular, changes that occur in sympathetic nerve content of the vasoconstrictor agents serotonin (5-HT) and neuropeptide Y (NPY), which are colocalized with noradrenaline, were assessed. Subarachnoid hemorrhage was induced by a single injection of autologous arterial blood into the cerebrospinal fluid (CSF) space of the cisterna magna. The density of 5-HT-containing and NPY-containing perivascular nerve fibers per unit area of vessels was measured at defined intervals from 15 min to 5 days post-SAH. In addition, an HPLC study was performed to quantify the actual amounts of 5-HT and noradrenaline present in circle of Willis vessels at 3 h post-SAH. Comparison was made with sham-operated animals and animals that received a cisternal injection of buffered saline in place of blood. Our results reveal a major increase in cerebrovascular sympathetic nerve content of serotonin, arising by uptake, presumably from subarachnoid blood clot, within the first 3 h post-SAH. Neuropeptide Y content, however, decreased from 3 up to 48 h posthemorrhage. By 3 days post-SAH, when the majority of subarachnoid clot had resorbed, the sympathetic nerve content of both NPY and 5-HT was restored to normal. This pattern of change was not observed in either sham-operated or saline-injected controls.

Serotonin turnover in rat brain during semistarvation with high-protein and high-carbohydrate diets

Serotonin (5-HT) and 5-hydroxyindolacetic acid (5-HIAA) were determined in seven brain regions of semistarved and control male rats. After semistarvation on a high carbohydrate diet serotonin turnover, as indicated by 5-HIAA/5-HT ratio, was increased in the total brain and several regions both three and 24 hours after the last meal. In contrast, after semistarvation on a high-protein diet serotonin turnover was decreased three hours after ingestion of the final meal, but increased 24 hours thereafter. Compulsary running wheel activity for one hour did not influence diet induce changes in serotonin turnover. Alterations in plasma corticosterone during semistarvation were not related to changes in central serotonin turnover. Data suggest that the interaction of caloric restriction and diet composition determines serotonin turnover during semi-starvation.

Thyrotropin induces the acidification of the secretory granules of parafollicular cells by increasing the chloride conductance of the granular membrane

Secretory granules of sheep thyroid parafollicular cells contain serotonin, a serotonin-binding protein, and calcitonin. Parafollicular cells, isolated by affinity chromatography, were found to secrete serotonin when activated by thyrotropin (TSH) or elevated [Ca2+]e. TSH also induced a rise in [Ca2+]i. We studied the effect of these secretogogues on the pH difference (delta pH) across the membranes of the secretory granules of isolated parafollicular cells. The trapping of the weak bases, acridine orange or 3-(2,4 dinitro anilino)-3'-amino-N-methyl dipropylamine (DAMP), within the granules was used to evaluate delta pH. In contrast to lysosomes, which served as an internal control, the secretory granules of resting parafollicular cells displayed a limited and variable ability to trap either acridine orange or 3-(2,4 dinitro anilino)-3'-amino-N-methyl dipropylamine; however, when parafollicular cells were stimulated with TSH or elevated [Ca2+]e, the granules acidified. Weak base trapping was also used to evaluate the ATP-driven H+ translocation into isolated parafollicular granules. The isolated parafollicular granules did not acidify in response to addition of ATP unless their transmembrane potential was collapsed by the K+ ionophore, valinomycin. Secretory granules isolated from TSH-treated parafollicular cells had a high chloride conductance than did granules isolated similarly from untreated cells. Furthermore, ATP-driven H+ translocation into parafollicular granules isolated from TSH-stimulated parafollicular cells occurred even in the absence of valinomycin. These results demonstrate that secretogogues can regulate the internal pH of the serotonin-storing secretory granules of parafollicular cells by opening a chloride channel associated with the granule membrane. This is the first demonstration that the pH of secretory vesicles may be modified by altering the conductance of a counterion for the H+ translocating ATPase.

Progressive changes in adrenergic, serotonergic, and peptidergic nerves in proximal colon of streptozotocin-diabetic rats

The effect of progression of diabetes on adrenergic, serotonergic, and peptidergic innervation of the proximal colon of the rat at 8, 16, and 25 wk after induction of diabetes with streptozotocin was investigated using immunohistochemical, biochemical, and immunochemical methods. Two different responses to diabetes emerged from the present study. The first response, which involves noradrenaline and vasoactive intestinal peptide, was characterized by a sign of degeneration, where there was an initial increase in tissue level and immunoreactivity of the transmitters followed by a decrease in tissue level and density of nerve fibers at 16 and 25 wk after induction of diabetes. The second response, which involves 5-hydroxytryptamine, substance P, and calcitonin gene-related peptide, was characterized by changes in tissue level and immunoreactivity of the transmitters with no evidence of degeneration. The third feature was one of resistance to change due to diabetes, which was demonstrated by neuropeptide Y-containing nerves, where there was neither a change in tissue level of neuropeptide Y nor a change in immunoreactivity. It seems likely that the overall changes described will have profound implications in the function of the gut in the streptozotocin-diabetic rat model that may have some parallels in diabetic humans.

Interaction of thyrotropin-releasing hormone (TRH) and serotonin in cardiovascular control

Intravenous injection of the synthetic TRH analog, MK-771, to anesthetised cats raised the blood pressure by a central mechanism, i.e. by activating the outflow of sympathetic stimuli from the CNS to the periphery and raising the plasma concentration of adrenaline and noradrenaline. In contrast, noradrenaline in the CSF was lowered by intravenously injected MK-771. The concentration of 5-HT in the CSF was increased and the pressor action of the peptide was correspondingly enhanced by 5-HT antagonists. These findings suggest that the release of 5-HT into the CSF lowers blood pressure and thus reduces the hypertensive effect of MK-771. Methysergide acts synergistically with MK-771 to combat the sudden fall in pressure induced by acute hemorrhage in the anesthetised cat. Combination of the two drugs enhanced and accelerated recovery from this hypotensive state.

Serotonin is localized in endothelial cells of coronary arteries and released during hypoxia: a possible new mechanism for hypoxia-induced vasodilatation of the rat heart

In this report we demonstrate the immunocytochemical localization of serotonin in endothelial cells of rat coronary vessels and a significant increase in the release of serotonin into the perfusate of Langendorff rat heart preparations during hypoxia. It is suggested that serotonin, localized in endothelial cells, is released during hypoxia and could provide part of a pathophysiological mechanism for vasodilatation to protect the heart from damage due to hypoxia.

Activation of mesencephalic dopamine neurons by chemical stimulation of the nucleus tegmenti pedunculopontinus pars compacta

Unilateral stereotaxic microinjection of a small amount of kainic acid (KA) into the nucleus tegmenti pedunculopontinus pars compacta (TPC) of male Wistar rats produced constant ipsiversive circling behavior. The rate of the TPC-derived circling was significantly attenuated by blocking agents of dopamine systems, including haloperidol and alpha-methyl-tyrosine (both injected intraperitoneally) and also 6-hydroxydopamine (injected into the bilateral medial forebrain bundles). Administration of norepinephrine antagonists (phenoxybenzamine hydrochloride and DL-propranolol) had no effect on the rate of the TPC-derived circling. Bilateral preinjections of atropine sulfate into the ventral midbrain tegmentum, including the ventral tegmental area and the pars compacta of the substantia nigra, significantly attenuated the rate of the circling. The unilateral KA injection into the TPC dramatically increased the ratio of HVA + DOPAC/dopamine, an indicator of dopamine turnover, in the nucleus accumbens as well as in the striatum bilaterally. The increase of the ratio in the nucleus accumbens was selectively suppressed by pretreatment with atropine sulfate administered into the bilateral ventral midbrain tegmentum. These facts indicate: (1) the TPC-derived circling behavior is mediated by the dopamine system, (2) the chemical stimulation of TPC by KA might produce an activation of midbrain dopamine neurons by excitatory TPC efferents to the dopamine neurons and enhance the dopamine turnover in the nucleus accumbens as well as in the striatum, (3) the excitatory TPC efferents may be muscarinic cholinergic in accordance with previous reports.

Decrease in tetrahydrobiopterin content and neurotransmitter amine biosynthesis in rat brain by an inhibitor of guanosine triphosphate cyclohydrolase

To investigate the regulatory role of tetrahydrobiopterin in neurotransmitter amine biosynthesis, 2,4-diamino-6-hydroxypyrimidine, a potent inhibitor of guanosine triphosphate cyclohydrolase which is a rate-limiting enzyme of tetrahydrobiopterin biosynthesis, was administered intraperitoneally to weanling rats. Four h after 4 injections at 4-h intervals, the biopterin contents in plasma and liver were reduced to the level of 9 and 3.5%, respectively, of those in the control group injected with saline; while the contents in the whole brain, neocortex + striatum, diencephalon, and brainstem were 34, 50, 33 and 28%, respectively, of the control level. When in vivo tyrosine and tryptophan hydroxylase activities were measured over a 30-min period after the inhibition of aromatic amino acid decarboxylase, the accumulation of dihydroxyphenylalanine was reduced to 74, 77, 67 and 69% of the control in the whole brain, neocortex + striatum, diencephalon, and brainstem, respectively; and the accumulation of 5-hydroxytryptophan, to 71, 74, 66 and 65% of the control, respectively. On the other hand, 5-hydroxytryptamine and 5-hydroxyindole acetic acid contents were not altered in any brain regions, although norepinephrine and dopamine contents were reduced to approximately 70% of the control in the brainstem and the contents of dopamine metabolites were significantly decreased in the diencephalon and brainstem. Plasma phenylalanine level was significantly elevated, while the plasma tyrosine level was reduced, compared with the control level of these amino acids. These results indicate that the drug-treated rats could be an animal model for tetrahydrobiopterin-deficient disease involving neurological disorder.

N-0437: a selective D-2 dopamine receptor agonist in in vitro and in vivo models

The selectivity of the potent dopamine D-2 agonist 2-(N-propyl-N-2-thienylethylamino)-5-hydroxytetralin (N-0437) was examined in a series of in vivo and in vitro pharmacological models. In radioligand binding assays, N-0437 showed high potency (Ki = 0.69 nM) and selectivity for D-2 receptors as compared to its potency and selectivity at various other neuronal receptors (Ki in nM): D-1 (678) dopamine, alpha 1-(534) and alpha 2-(195) adrenoceptor, S1-(6940) and S2-(5900) serotonin and muscarine (2660). Very low activity (Ki greater than 10(-5) M) was seen at the beta-adrenoceptor, A1-adenosine, GABAA and benzodiazepine receptors. Furthermore, N-0437 inhibited the calcium-dependent release of [3H]dopamine (IC50: 4 nM) and [3H]acetylcholine (IC50: 6.3 nM) from rabbit striatal slices in the nanomolar range. These effects of N-0437 were mediated through activation of D-2 dopamine autoreceptors and D-2 dopamine heteroreceptors, respectively. Presynaptic dopaminergic activity in vivo was measurable as an inhibition of the locomotor activity of mice, and in this model N-0437 was more effective than apomorphine. Moreover, the effect of N-0437 could be antagonized by sulpiride but not by yohimbine. N-0437 was equipotent with apomorphine in inducing circling behaviour in 6-OHDA-lesioned rats. N-0437 had almost no serotonergic activity in vivo. The results show that N-0437 is a selective dopamine D-2 agonist, and thus, that it is a new ligand of choice for studies on the D-2 receptor.

Neurochemical findings in neuroacanthocytosis

We performed a neurochemical study of the brain of two unrelated patients, living in different continents, with neuroacanthocytosis. The levels of monoamines and their metabolites, gamma-aminobutyric acid and substance P, were measured in several brain areas and the monoamine metabolites in cerebrospinal fluid. The binding of 3H-spiperone to striatal membranes and to lymphocytes was also measured. Both patients had a progressive neurological disorder with onset in the third decade of life and characterized by a complex movement disorder, epilepsy, muscular wasting, and changes in behavior. The movement disorder initially manifested with oromandibular dystonia and limb chorea, but at the time of death was characterized by a severe dystonic syndrome. The chemical changes were similar in the two patients. The most important neurochemical findings were a depletion of dopamine and its metabolites in most brain areas, most notably in the striatum, and elevation of norepinephrine levels in the putamen and globus pallidus. Substance P was markedly reduced in the striatum and substantia nigra. Our findings may provide clues to the neurochemical mechanisms underlying dystonia.

Lack of release of vasoactive intestinal polypeptide and calcitonin gene-related peptide during electrical stimulation of enteric nerves in streptozotocin-diabetic rats

The simultaneous release of endogenous acetylcholine, serotonin, vasoactive intestinal polypeptide, substance P, and calcitonin gene-related peptide was measured during electrical field stimulation of isolated preparations of rat ileum from control and 8-wk streptozotocin-treated diabetic rats. Electrical field stimulation of the control rat ileum caused a significant increase in the release of all the above substances from the enteric nerves. The electrically evoked, but not the basal, release of these substances was inhibited by tetrodotoxin. In the diabetic rat ileum, however, there was no increase in the release of vasoactive intestinal polypeptide and calcitonin gene-related peptide during electrical stimulation, whereas endogenous release of acetylcholine, serotonin, and substance P was unaffected by the diabetic state. This was surprising in view of the increased fluorescence intensity and tissue content of vasoactive intestinal polypeptide-like immunoreactivity in the same tissue reported previously. The lack of increase in evoked release of vasoactive intestinal polypeptide in the diabetic preparations might be due to an impaired mechanism of release at the terminal site or to defective axonal transport of the peptide, whereas in the case of calcitonin gene-related peptide, it might be the result of the low level of the peptide present in the enteric nerve fibers of the diabetic rat ileum. The differential effect of diabetes on enteric nerves is discussed.

Use of a novel type of rotating disc electrode and a flow cell with laminar flow pattern for the electrochemical detection of biogenic monoamines and their metabolites after Sephadex gel chromatographic purification and high-performance liquid chromatographic isolation from rat brain

A novel type of rotating disc electrode and a flow cell with laminar flow pattern were developed and applied to the electrochemical detection of dopamine, 3,4-dihydroxyphenylacetic acid, homovanillic acid, 3-methoxytyramine (3-MT), noradrenaline, 3-methoxy-4-hydroxyphenylethyleneglycol (MOPEG), 5-hydroxytryptamine (5-HT), and 5-hydroxyindoleacetic acid after HPLC of these compounds. The active surface of the rotating disc working electrode was made from solid paraffin (40% wt/wt) and graphite powder (60% wt/wt). The sensitivity of the detector was proportional to the square root of the angular velocity and was practically independent of the flow rate of the mobile phase. The surface of the working electrode was very large (radius = 12 mm), and so the percentage of oxidation was 24-67% (flow rate = 1.0 ml/min), depending on the compound. Electrical noise between 20 and 40 pA and background current of 20-60 nA were observed. In practice, the sensitivity for the detection of the compounds examined here was 8-16 nA/ng, and so a detection limit of 5 pg/injection could be achieved, when the detector was combined with reversed-phase HPLC. Supernatants obtained from the extracts of the tissue samples (nine brain parts of rat brain were studied) were purified by using Sephadex G-10 gel chromatography. Before this procedure, the proteins of the tissue extracts were precipitated by 0.2 M HClO4, and the excess of HClO4 was precipitated by KOH/HCOOH buffer. Simultaneously, the pH of the extracts was set to 2.4 by the above buffer.(ABSTRACT TRUNCATED AT 250 WORDS)

The role of hippocampal 5-HT in the effects of nicotine on habituation to an X-maze

Neither the chronic administration (40 daily subcutaneous injections) of nicotine (0.4 mg/kg) nor its withdrawal (3 days) influenced avoidance of the more aversive open runways of an elevated X-maze in rats which had been habituated to the apparatus. Lesions of the serotonergic fibres innervating the hippocampus increased total activity (P less than 0.05). However, analysis of covariance indicated that reduced 5-hydroxytryptamine secretion in the hippocampus was probably not the mechanism by which nicotine stimulated total activity in these rats.

The effects of diazepam on brain 5-HT and 5-HIAA in stressed and unstressed rats

Diazepam, administered to rats at a high dose (25 mg/kg PO) has been shown to have no effect on the plasma corticosterone response to the stress of an elevated open platform. It did however, reduce the plasma corticosterone in rats repeatedly exposed to the apparatus. Diazepam-withdrawal from stress-habituated rats increased plasma corticosterone (p less than 0.01) whereas withdrawal of diazepam from unstressed rats had no effect on plasma corticosterone. It is concluded that this effect of diazepam-withdrawal may reflect the development of dependence upon the drug. Significant effects were not observed following the administration of a lower non-selective dose (5 mg/kg PO) of diazepam and, therefore, it is not clear whether dependence to its sedative, rather than the anxiolytic properties have been measured. Acute diazepam (25 mg/kg) increased (p less than 0.05) hippocampal 5-hydroxyindoleacetic acid; its withdrawal from unstressed rats after 40 days reduced (p less than 0.01) hypothalamic 5-hydroxytryptamine. There was no evidence that the effects of diazepam or its withdrawal on plasma corticosterone in stressed rats were associated directly with changes in brain 5-hydroxyindoles.

Pharmacological profile of a new potent and specific alpha 2-adrenoceptor antagonist, L-657,743

L-657,743,(2S,12bS)1',3'-dimethylspiro(1,3,4,5',6,6',7,12 b-octahydro-2H- benzo[b]furo[2,3-a]quinolizine)-2,4'-pyrimidin-2'-one, was tested in several in vitro and in vivo models for alpha 2-adrenoceptor antagonism. L-657,743 exhibited a high affinity (less than or equal to 1 nM) for alpha 2-adrenoceptors labelled by [3H] rauwolscine or [3H]clonidine with a 240-fold selectivity versus alpha 1-adrenoceptors labelled by [3H]prazosin. L-657,743 was a potent, selective, and competitive alpha 2-adrenoceptor antagonist in the rat isolated vas deferens (pA2 = 9.3 vs. clonidine; pA2 = 7.1 vs methoxamine). In vivo, L-657,743 potently blocked clonidine-induced mydriasis in the rat and stimulated cerebrocortical norepinephrine synthesis, two indices of central alpha 2-adrenoceptor antagonism. L-657,743 exhibited a comparatively low affinity for several monoamine receptor subtypes (D1, D2, 5-HT1, 5-HT2) in radioligand binding assays in vitro and a comparatively low potency to alter the synthesis of brain DA and 5-HT in vivo indicating a marked alpha 2-specificity versus other monoamine receptor mechanisms. Compared to yohimbine, L-657,743 had considerably higher alpha 2-antagonist potency and alpha 2/alpha 1 selectivity and was significantly more alpha 2-specific (i.e., vs. DA, 5-HT receptors).

Spontaneous activity and brain 5-hydroxyindole levels measured in rats tested in two designs of elevated X-maze

The spontaneous activity of rats tested both acutely and chronically (15 minutes per day for 25 days) in an elevated X-maze composed entirely of open runways was found to be significantly less (P less than 0.01) than that measured for rats tested in a maze of similar dimensions composed entirely of enclosed runways. Acute exposure to both mazes caused significant increases (P less than 0.01) in plasma corticosterone when compared with unstressed control rats. Chronic exposure to the open, but not the enclosed maze caused a significant (P less than 0.01) attenuation of this response. Chronic exposure to the open maze caused significant increases (P less than 0.01) in the concentrations of 5-hydroxytryptamine (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) in hippocampus, hypothalamus and cerebral cortex when compared with unstressed control rats. When compared with the data for the rats tested repeatedly in the enclosed maze, chronic exposure to the open maze increased the 5-HT concentrations in hypothalamus (P less than 0.05) and cerebral cortex (P less than 0.01) and the 5-HIAA concentrations in hypothalamus (P less than 0.01) and hippocampus (P less than 0.01). The spontaneous locomotor activity of the rats tested in the open maze, correlated significantly (P less than 0.01) with plasma corticosterone and the 5-HIAA concentrations in hippocampus (P less than 0.01), hypothalamus (P less than 0.05) and cerebral cortex (P less than 0.01). In the rats tested in the enclosed maze, spontaneous activity only correlated significantly (P less than 0.01) with hippocampal 5-HIAA. It is concluded that the study has revealed clear differences in the behavioral, plasma corticosterone and brain 5-hydroxyindole responses to the two mazes but that the results do not provide unequivocal evidence that these differences occurred because the open maze was more aversive than the enclosed. It is also concluded that the study provides further support for the hypothesis that 5-HT turnover in the hippocampus may be directly related to the level of spontaneous locomotor activity.

A simultaneous analytical method for catecholamines, indoleamines, and related compounds in 11 rat brain regions

A simple high-performance liquid chromatographic method that allows the determination of 10 biogenic amines and related compounds for crude brain extracts has been developed. The compounds that can be quantified comprise norepinephrine, epinephrine, 3,4-dihydroxyphenylacetic acid, 3-methoxy-4-hydroxyphenylglycol, dopamine, 5-hydroxyindole-3-acetic acid, homovanillic acid, 3-methoxytyramine, 5-hydroxytryptamine and tryptophan. The detection system involves a three electrode-coulometric determination followed by fluorometric determination. This method is highly selective and sensitive, and in the present study, the usefulness of this methodology was confirmed by applying it to the determination of the levels of these various substances in 11 rat brain regions.

Dietary fat source influences neuronal mitochondrial monoamine oxidase activity and macronutrient selection in rats

We previously reported that qualitative changes in dietary fat influence certain monoaminergic mediated behaviours such as pain sensitivity and thermoregulation in a cold environment after an amphetamine challenge. The purpose of this study was to further explore the behavioural consequences of alterations in dietary fat intake by examining another behaviour known to be mediated by the monoamines--food intake regulation--and to begin investigating a biochemical link between dietary fat composition and behaviour. Rats were stabilized to 20% (w/w) soybean oil (SBO) or lard diets for 10 days and then allowed to select for protein (PRO) and carbohydrate (CHO) intake. While total food intake was unchanged, rats fed the SBO diet selected lower PRO (3.1 +/- 0.6 vs. 4.9 +/- 0.6 g/day, SBO vs. lard, respectively) and higher CHO (9.6 +/- 0.7 vs. 7.8 +/- 1.2) intakes than those consuming the lard based diet. Comparable differences were seen in a second trial. Current evidence suggests that the regulation of PRO and CHO intake is under serotonergic control. Therefore to determine whether dietary fat is mediating its effect on macronutrient selection via alterations in serotonin (5HT) metabolism, brain stem concentrations of 5HT and its metabolite 5-hydroxyindole acetic acid (5HIAA) and whole brain (minus brain stem) mitochondrial monoamine oxidase (MAO) activity were measured in a separate set of animals fed the SBO or lard diets for 28 days. Vmax of MAO was decreased in rats fed the SBO diets (20.2 +/- 7.4 vs. 27.9 +/- 8.9 nmol/mg prot/20') compared to those fed the lard diets. Km was unaltered by dietary fat fed. The change in activity of MAO was insufficient to alter steady-state levels of 5HT or 5HIAA. We propose that changes in neuronal functioning, induced by altered dietary fat, contributed to the differences seen in PRO and CHO selection.

Regional distribution of substance P- and thyrotrophin-releasing hormone-like immunoreactivity and indoleamines in the rabbit spinal cord

The distribution of thyrotrophin-releasing hormone (TRH), substance P, and the indoleamines [5-hydroxytryptamine (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA)] has been examined in selected regions of the thoracic and lumbar spinal cord of the rabbit using sensitive radioimmunoassays for the first two and HPLC with electrochemical detection for the indoleamines. The levels of TRH- and substance P-like immunoreactivity (TRH-I and SP-I, respectively) were greatest in the ventral and dorsal grey matter, respectively. The level of TRH-I in most thoracic regions was greater than that in equivalent lumbar regions, but the only segmental difference in SP-I was in the ventral grey matter, where the lumbar segment contained more immunoreactivity. 5-HT and 5-HIAA were more evenly distributed than either peptide and showed no segmental variation in levels in equivalent regions, but the ventral grey matter contained significantly higher levels of 5-HT and had a greater 5-HT/5-HIAA ratio than all other regions. The absolute levels and the overall distribution of SP-I, TRH-I, and indoleamines in the thoracolumbar cord of the rabbit was very similar to that previously reported in both rats and humans, and the possible functional role of the peptides and indoleamines in spinal neurones is discussed.

Prenatal development of serotonin binding protein in relation to other transmitter-related characteristics of central serotonergic neurons

Serotonin binding protein (SBP) is a neuron-specific protein that binds serotonin (5-HT) with high affinity and is concentrated in synaptic vesicles. 5-HT has been shown to be stored in situ in a macromolecular complex with SBP. We have now investigated the ontogeny of SBP in the rat CNS. The time course of the appearance of SBP was related to the appearance of tryptophan hydroxylase, endogenous 5-HT and monoamine oxidase (MAO; types A and B). Binding of [3H]5-HT by SBP was assayed using molecular sieve chromatography. SBP had appeared by day E16; its activity then rose rapidly and reached adult levels (150 nmol [3H]5-HT/g protein) at days E18-E19. Tryptophan hydroxylase activity was measured by following the accumulation in vivo (30 min) of 5-hydroxytryptophan (5-HTP) in the brains of rat embryos whose mothers were treated with the aromatic L-amino acid decarboxylase inhibitor, NSD-1015, (100 mg/kg; i.p.). Tryptophan hydroxylase activity was first detectable at E15, remained present but at a low level through day E20 and then rapidly increased to reach 75% of the adult level at birth (747 pmol/g brain wet wt.). The development of stores of endogenous 5-HT paralleled the time course of development of tryptophan hydroxylase rather than that of SBP. 5-HT was first detected at E15, remained low until the end of intrauterine life and at birth was 50% of the adult level (2640 pmol/g brain wet wt.). MAO activity was determined in crude mitochondrial fractions by measuring 5-hydroxyindoleacetic acid produced from 5-HT as substrate. This activity was already present prior to day E15 (the activity of type B MAO was higher than that of type A) and reached adult levels at day E20 (55 pmol/mg protein/min; A, B). It is concluded that the potential of neurons to store 5-HT, as measured by the activity of SBP, develops more rapidly than their ability to produce 5-HT. Moreover, although the ratio of its two forms changes, MAO activity appears very early in development.

Paraventricular nucleus serotonin mediates neurally stimulated adrenocortical secretion

The purpose of this study was to further elucidate the role of serotonin (5-HT) in adrenocortical regulation. The effects of stimulating the frontal cortex and extrahypothalamic limbic structures, on plasma corticosterone (CS) responses, were studied in rats with vehicle or 5,7-dihydroxytryptamine (5,7-DHT) injection into the midbrain raphe nuclei. In another group of rats the neurotoxin was injected locally into the paraventricular nucleus (PVN) in view of its importance in adrenocortical regulation, and the effects of photic and dorsal hippocampal stimulation on plasma CS were studied. 5,7-DHT caused a significant depletion of hypothalamic 5-HT and blocked the rise in plasma CS following the stimulation of the above neural modalities. These studies suggest that the PVN 5-HT mediates the adrenocortical responses following afferent neural stimuli.