5-HT1A receptor agonist effects of BMY-14802 on serotonin release in dorsal raphe and hippocampus.

BMY-14802 (BMS-181100; alpha-(4-fluorophenyl)-4-(5-fluoro-2-pyrimidinyl)-1-piperazine butanol monohydrochloride) is a sigma receptor antagonist with potential antipsychotic activity. BMY-14802 also binds to 5-HT1A receptors and is able to inhibit the firing of dorsal raphe serotonergic neurons, suggesting that this compound has 5-HT1A receptor agonist properties in vivo. In the present study, we used in vivo microdialysis to study the effects of BMY-14802 on extracellular serotonin (5-hydroxytryptamine), 5-hydroxyindole-3-acetic acid (5-HIAA) and homovanillic acid (HVA) in the dorsal raphe and ventral hippocampus in the awake rat. Systemic injections of 5-20 mg/kg BMY-14802 induced a simultaneous dose-dependent decrease in 5-HT and markedly increased the dopamine metabolite, HVA concentrations in dialysates from dorsal raphe and hippocampus. Extracellular concentrations of the 5-HT metabolite, 5-HIAA decreased only after 20 mg/kg BMY-14802. The 5-HT decreases in dorsal raphe and hippocampus produced by BMY-14802 were completely antagonized by pretreatment with 1.0 mg/kg of the specific 5-HT1A antagonist, WAY-100635 (N-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-N-(2-pyridinyl) cyclohexanecarboxamide trihydrochloride). These data indicate that BMY-14802 decreases dorsal raphe and hippocampal release of 5-HT by interaction with somatodendritic 5-HT1A receptors in the raphe nuclei and suggest that this compound is a potential anxiolytic.

Effects of neuropeptide Y (NPY) and [D-Trp32]NPY on monoamine and metabolite levels in dialysates from rat hypothalamus during feeding behavior.

Administration of neuropeptide Y (NPY) into hypothalamic areas or into the cerebral ventricles induces marked increases in food consumption in satiated rats. Since monoamines have been suggested to be involved in NPY-induced feeding, we investigated the effects of NPY and [D-Trp32]NPY, a putative NPY antagonist, on extracellular levels of norepinephrine (NE), dopamine (DA), serotonin (5-HT), 3,4-dihydroxyphenyl acetic acid (DOPAC), homovanillic acid (HVA) and 5-hydroxyindole-3-acetic acid (5-HIAA) in the hypothalamus, including the paraventricular hypothalamic nuclei (PVN), during feeding behavior. Intracerebroventricular (i.c.v.) injections of NPY (20 microg) significantly increased extracellular NE (1.5-fold), DA (2.5-fold), DOPAC (2-fold) and HVA (3-fold), and did not change 5-HT or 5-HIAA levels. This dose of NPY significantly increased food intake over a 2 h period. The putative NPY antagonist [D-Trp32]NPY (40 microg, i.c.v.) produced similar neurochemical changes to NPY: it increased dialysate levels of NE (1.7-fold), DA (2.5-fold), DOPAC (1.6-fold) and HVA (2.2-fold) and did not change 5-HT or 5-HIAA levels. [D-Trp32]NPY also produced a significant increase in food intake. I.c.v. administration of [D-Trp32]NPY 5 min before NPY did not significantly change the increase in NE, DA, HVA and DOPAC induced by NPY. In these animals, food consumption was also significantly increased. These data indicate that NPY-induced feeding is associated with activation of the hypothalamic monoaminergic system and that [D-Trp32]NPY, at the dose given, acts as an agonist and not as an antagonist at NPY receptors in vivo.

Serotonin (5-HT) release in the dorsal raphé and ventral hippocampus: raphé control of somatodendritic and terminal 5-HT release.

Somatodendritic and terminal release of serotonin (5-HT) was investigated by simultaneously measuring extracellular concentrations of 5-HT, 5-hydroxyindole-3-acetic acid (5-HIAA) and homovanillic acid (HVA) in the dorsal raphé and ventral hippocampus in freely moving rats. Perfusion of tetrodotoxin (TTX, 1 microM and 10 microM) into the dorsal raphé simultaneously decreased dorsal raphé and hippocampal 5-HT release. However, following TTX perfusion into the hippocampus (10 microM), hippocampal 5-HT release was profoundly reduced but dorsal raphé 5-HT remained unchanged. Systemic injections with 5-HT1A agonist, buspirone (1.0-5.0 mg/kg, i.p.) decreased 5-HT and 5-HIAA and increased HVA concentrations in the dorsal raphé and in the hippocampus. The decreases in the raphé and hippocampal 5-HT induced by systemic buspirone were antagonized in rats pretreated with 1.0 mM (-) pindolol, locally perfused into the dorsal raphé. Local dorsal raphé perfusion of (-) pindolol alone (0.01-1.0 mM) increased dorsal raphé 5-HT and concomitantly induced a small increase in hippocampal 5-HT. Buspirone perfusion into the dorsal raphé did not change (10 nM, 100 nM), or produced a small increase (1.0 mM) in raphé 5-HT, without changing hippocampal 5-HT. These data provide evidence that 5-HT release in the dorsal raphé is dependent on the opening of fast activated sodium channels and that dorsal raphé 5-HT1A receptors control somatodendritic and hippocampal 5-HT release

Relationship between analgesia and extracellular morphine in brain and spinal cord in awake rats.

Extracellular concentrations of morphine from the dorsal spinal cord, the periaqueductal gray (PAG) including the dorsal raphé, and the lateral hypothalamus were measured by microdialysis in awake rats after intraperitoneal (i.p.) administration of 2.5, 5.0 and 10 mg/kg morphine. Morphine concentrations in all areas showed similar time courses: morphine was detected in the first dialysate sample (13-15 min) and maximal concentrations were reached at 45 min after injection. When in vivo recoveries of morphine from the spinal cord and brain areas were taken into account, no significant differences between morphine concentrations in the various areas were found. The relationship between extracellular morphine concentrations and morphine-induced analgesic behavior was investigated by simultaneously measuring morphine in the dialysate and its analgesic effect in the paw-withdrawal and tail-flick tests. In all areas sampled, the extracellular concentrations of morphine at different times after i.p. injection, significantly correlated with the magnitude of behavioral analgesia assessed by either test. The highest correlation was obtained between extracellular concentrations of morphine in the spinal cord and PAG and behavioral analgesia assessed in the paw-withdrawal test. Our data indicate that, after systemic injection, morphine is evenly distributed throughout the spinal cord and brain including potential anatomical sites of morphine's analgesic action. We estimate that the minimal extracellular morphine concentration in spinal cord that is required to produced a significant increase in nociceptive threshold is approximately 100 pg/25 microl, which corresponds to a tissue concentration of about 100 mg/g of morphine.

Simultaneous measurement of extracellular morphine and serotonin in brain tissue and CSF by microdialysis in awake rats.

In this report, we describe an HPLC with electrochemical detection assay for the simultaneous measurement of levels of morphine, serotonin, 5-hydroxyindole-3-acetic acid, and homovanillic acid in dialysates of various brain areas and CSF in the awake rat. Morphine could be detected in the dialysates after a single intraperitoneal injection, with doses as low as 1.0 mg/kg. The time course of extracellular morphine content in the lateral hypothalamus, striatum, cerebellum, periaqueductal gray, and dorsal horn of the spinal cord and in CSF, from the ventricles and cisterna magna, was similar. We detected morphine in the first 15-min sample, and levels peaked 45-60 min after injection. Maximal dialysate levels, however, varied with the type of dialysis probe used and the area sampled. The most efficient in vivo recovery was in CSF dialysates from the cisterna magna, presumably because of minimal tissue interference with the dialysis probe. For this reason, the cisterna is an ideal region for sampling CSF. Morphine had no significant effect on the extracellular concentrations of serotonin in any of the areas studied and did not modify or only slightly increased levels of tissue metabolites; however, morphine markedly increased the CSF levels of 5-hydroxyindole-3-acetic acid and homovanillic acid. Because microdialysis in freely moving animals permits assessment of the behavioral effects of morphine while continuously monitoring the drug levels in discrete brain regions, this approach will greatly facilitate future studies of the neurochemical basis of morphine's effects in the brain.

Characterization of monoamine release in the lateral hypothalamus of awake, freely moving rats using in vivo microdialysis.

Extracellular levels of serotonin (5-HT), dopamine (DA) and their major metabolites 5-hydroxyindoleacetic acid (5-HIAA), 3,4-dihydroxyphenylacetic acid (DOPAC), and homovanillic acid (HVA), were measured in the lateral hypothalamus of awake, freely moving rats using microdialysis combined with HPLC and electrochemical detection. To characterize the factors which control 5-HT release, the effects of various drugs were assessed. TTX had a reversible inhibitory effect on the basal levels of 5-HT, 5-HIAA, DOPAC and HVA. Infusion of K+ concomitantly increased 5-HT and DA and decreased 5-HIAA and HVA. Imipramine increased extracellular levels of 5-HT and DA and decreased 5-HIAA levels; this effect was TTX-sensitive. Systemic pargyline increased extracellular 5-HT and markedly decreased the metabolic levels. Pargyline pretreatment in the presence of imipramine, infused through the dialysis probe, slowly increased 5-HT levels above that produced by the reuptake blocker alone. Infusion with AMPH produced a dramatic, TTX-insensitive, increase in 5-HT and DA and a decrease in the metabolic levels. These results provide evidence that (1) basal release of 5-HT in the lateral hypothalamus results from neuronal activity, (2) the metabolites in the extracellular fluid derive primarily from intracellular monoamine oxidase (MAO) activity, (3) 5-HT is mainly removed from the extracellular space by a reuptake mechanism, with minimal contribution of an extracellular MAO, and (4) the AMPH-evoked release of 5-HT and DA is a Na+ channel-independent process.

Comparison of the effects of intracerebrally administered MPP+ (1-methyl-4-phenylpyridinium) in three species: microdialysis of dopamine and metabolites in mouse, rat and monkey striatum.

Intracerebral microdialysis in 3 awake species allowed the measurement of the basal output of dopamine (DA), dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA) and 5-hydroxyindole-acetic acid (5-HIAA) from rat and mouse striatum and monkey caudate in vivo. The DOPAC/HVA ratios in dialysates from mouse and rat striatum were about 1 and 2 respectively, but only 0.09 in monkey caudate dialysates. The extracellular levels of the metabolites correlated well with reported tissue levels, while extracellular DA levels were 3 orders of magnitude lower than tissue concentrations. The effects of the intracerebrally administered dopaminergic neurotoxin 1-methyl-4-phenylpyridinium (MPP+) were essentially similar in the 3 species. In all cases an immediate, massive release of DA was accompanied by a pronounced decrease in the output of the metabolites. Basal DA release was no longer detectable 5-12 h after MPP+ administration and a second MPP+ perfusion failed to increase the release of DA.

Opioid agonist and antagonist effects of configurational stereoisomers of 3-(dimethylamino)-2,2-dimethyl-7-hydroxy-1-tetralol.

The opioid agonist and antagonist effects of two configurational aminotetralin stereoisomers, namely, the cis-(MRSAL) and trans-(RMG) diastereo isomers of 3-(dimethylamino)-2,2-dimethyl-7-hydroxy-1-tetralol were studied using the guinea pig ileum longitudinal muscle preparation. MRSAL demonstrated opioid antagonist activity but failed to show agonist effects. In contrast, RMG showed agonist activity which was partially reversed by NX and MRSAL. RMG also exhibited weak antagonist activity towards DHM, NM and DADLE. These results showed that MRSAL was an opioid antagonist while RMG possessed weak mixed opioid agonist-antagonist activities.

Opioid receptor effects of two 3-amino-2,2-dimethyltetralin analogs in guinea pig ileum longitudinal muscle.

Two substituted analogs of 3-amino-2,2-dimethyltetralin, namely 3-dimethylamino-2,2-dimethyl-7-hydroxy-1-tetralone HBr (J) and 3-dimethylamino-2,2-dimethyl-7-hydroxy-1-tetralol (MRSAL), were evaluated for opioid agonist and antagonist activity using the electrically driven guinea pig ileum longitudinal muscle preparation (GPI). Compound J appeared to be an opioid agonist with a preference for mu receptors while MRSAL was an opioid antagonist with little selectivity for mu or kappa receptors.