C. Jacquot

Ontogeny of brain monoamines in lean and obese female Zucker rats

Differences in monoamine and metabolite levels were previously observed between lean and obese 16 week-old female Zucker rats. In order to test whether these variations exist initially in young animals, catecholamines (CA), serotonin (5-HT) and some of their metabolites were assayed in brain areas of Zucker rats between 5 and 16 weeks of age. The levels of most compounds in all areas studied increased with age in both groups. At 5 weeks of age, there was no difference between lean and obese rats. At 8 weeks, a reduction of dopamine (DA) metabolites appeared in the striatum and cortex of obese rats and persisted up to 16 weeks. A reduction of the 5-HT metabolite, 5-hydroxyindolacetic acid (5-HIAA), occurred at 8 weeks only. At 16 weeks, increases of DA and 5-HT in the hypothalamus and decreases of norepinephrine (NE), 5-HT and 5-HIAA in the hippocampus appeared. These data suggest that the development of obesity occurs before any monoamine alterations.

Fenfluramine and brain transmitters in the obese zucker rat

Genetically obese Zucker rats and their lean litter mates were treated for 5 days with fenfluramine. Levels of noradrenaline (NA), dopamine (DA), 5-hydroxytryptamine (5-HT) and gamma-aminobutyric acid (GABA) and their metabolism were assayed in the hypothalamus, striatum, medulla-oblongata pons and remainder of the brain. Fenfluramine induced a slight increase in the level of NE in the hypothalamus in lean rats and a marked decrease in obese rats. No change in the synthesis of NE was found. Fenfluramine had no effect on the level and metabolism of DA. The levels of 5-HT were decreased by fenfluramine in obese and lean rats, and the metabolism was increased. The levels of GABA were not changed by fenfluramine. Synthesis of GABA was increased in the remainder of the brain of obese and lean rats. These data suggest that fenfluramine acts on 5-HT systems in both obese and lean rats and are consistent with reports of the pharmacological effects of fenfluramine.

Effects of dexfenfluramine and opioid peptides, alone or in combination, on food intake and brain serotonin turnover in rats.

Dexfenfluramine (d-FF) and opiate agonists both act on food intake but in opposite ways. Serotonin is known to be involved in the pharmacological action of both d-FF and opiates, but not necessarily in the feeding effect of the latter. In order to test this hypothesis, the effects of three opioid agonists, beta-endorphin, dynorphin and D-Ser2-Leu-Enk-Thr6 (DSLET) and of an antagonist, naltrexone, were investigated individually and in combination with d-FF on food intake and brain serotonin turnover. The opioid agonist-d-FF combinations generally produced a similar anorectic effect to that of d-FF alone, with the exception of DSLET which showed a reciprocal antagonism. The serotonergic effects varied according to the opioid tested, alone or in combination with d-FF. This does not allow to highlight a general pattern of serotonin involvement in the feeding effects of these peptides. However, all the treatments which decreased feeding (d-FF, naltrexone and the combinations dynorphin-d-FF and beta-endorphin-d-FF) displayed similar trends in hypothalamic serotonergic variations. This study evidences a role of serotonin in the feeding effect of opiates, although not similar for all of them. The use of d-FF provides a tool for assessing this involvement.

Changes in brain neuropeptide Y induced by cholecystokinin peptides

Cholecystokinin (CCK) and neuropeptide Y (NPY) are two peptides with opposite effects on the regulation of feeding behaviour. The possible interaction between these two systems has always been controversial. In this study, rat brain NPY levels were assayed after treatment with CCK 8 S and with a potent CCK agonist (Boc-(Nle 28-Nle 31)-CCK 26-33). CCK 8 S and its agonist analogue (50 micrograms/kg i.p.) both decreased hypothalamic and hippocampal NPY levels. This result suggests a negative relationship between NPY and CCK-peptides which is not surprising given their opposite role in the control of feeding. The hypothalamus and secondarily the hippocampus appear to be the site of this interaction; no change in NPY levels was observed in other brain areas (striatum and cortex). The same pattern of variation was found in the plasma, suggesting a direct release from the brain via a mechanism which remains to be investigated. The effect appeared later with the CCK analogue than with CCK 8 S itself; this is not surprising with regard to other behavioural and biochemical effects of the analogue and provides further characterization of its action.

Effects of a new cholecystokinin analogue (JMV 236) on food intake and brain monoamines in the rat

JMV 236, a new cholecystokinin-octapeptide-sulfate (CCK 8 S) derivative (Boc-Tyr (SO3)-Nle-Gly-Trp-Nle-Asp-Phe-NH2) has been synthesized in the Centre de Pharmacologie-Endocrinologie (Montpellier). This peptide has been shown to present the same activity as CCK 8 S on pancreatic amylase secretion and has the advantage of a better chemical stability. With a view to further characterization, the effect of JMV 236 on food intake and brain monoamine and metabolite variations was assayed in the rat after intraperitoneal (i.p.) and intracerebroventricular (i.c.v.) administrations. JMV 236 decreased food intake 2 and 3 hours after i.p. administration of 12.5 and 50 micrograms/kg but was inactive after i.c.v. injection. Its global action was similar to that of CCK 8 S, but was less marked with delayed onset of response. As in our previous work with CCK 8 S, JMV 236 was more potent in inducing monoaminergic variations after i.p. than after i.c.v. administration. The main effects were decreases in striatal dopamine metabolite levels and increases in hypothalamic and striatal serotonin metabolite (5-HIAA) levels. These effects are classically observed with CCK 8 S and are described in our previous reports. The interesting peptide will require further characterization and may serve as a possible reference compound for studies on CCK derivatives.

Effects of food intake and body weight on a serotonergic turnover index in rat hypothalamus.

Absolute levels and ratio of serotonergic compounds in food-related hypothalamic nuclei were determined with a chromatographic method comparing for control (C) versus lean (L) versus obese (O) rats. In all three groups, a second parameter, i.e., fasting (F) versus satiation (S) was superimposed on the body weight factor. Indoleamine levels failed to show statistical differences depending on the body weight and/or the nutritional status. A significant negative correlation between an index of the serotonin turnover, the 5-HIAA/5-HT ratio, and body weight was found for the paraventricular (PVN) nucleus in the C and L groups as well as for the lateral (LH) nucleus for the C and O groups. A positive correlation was found for the ventromedian (VMH) nucleus in the O group. These data suggest that the body weight factor is implicated in the central serotonergic regulation more than the feeding parameter.

A comparison of the kinetics of d- and l-amphetamine in the brain of isolated and aggregated rats.

The kinetics of d- and l-amphetamine were investigated in isolated and aggregated male rats. The i.p. injection of 15 mg/kg of d- or l-14C-amphetamine was followed by the determination of drug concentrations in the cerebral cortex, hypothalamus, medulla oblongata-pons, cerebellum, striatum, hippocampus, and the whole brain after solvent extraction.In isolated rats, the disappearance curves of the labelled amphetamines were monoexponential. The half-lives of d- and l-amphetamine in whole brain were 1.2±0.1 and 1.3±0.1 h, respectively. In whole brains of aggregated rats the disappearance curves were biexponential (half-lives: d-amphetamine, 0.9±0.1 and 2.3±0.2 h; l-amphetamine, 0.7±0.1 and 2.3±0.1 h).For the brain areas of isolated rats, the elimination curves of amphetamines were monoexponential and the half-lives of d- and l-amphetamine were almost identical. In aggregated rats certain differences were observed. d-Amphetamine was eliminated from the striatum and hippocampus as a biexponential function, and l-amphetamine elimination was biphasic only in the striatum. In other brain regions both d- and l-amphetamine were eliminated as a monoexponential function. The half-lives of d-amphetamine in different brain areas were, however, shorter than those of the l-isomer.The observed differences between d- and l-amphetamine kinetics in brain areas of isolated and aggregated rats may explain certain aspects of the pharmacological activities of these drugs.

Effects of amphetamine on brain biogenic amines in isolated and aggregated rats.

d- and 1-amphetamine were injected (15 mg/kg i.p.) into isolated or aggregated rats. Both d- and 1-forms decreased the noradrenaline levels of brain areas in isolated and in aggregated rats. d-Amphetamine decreased 5-hydroxytryptamine (5-HT) and 5-hydroxyindolacetic acid (5-hiaa) levels in aggregated rats only. 1-Amphetamine induced no change in 5-HT and 5-HIAA levels. The greater sensitivity of aggregated rats to d-amphetamine can be ascribed to a change in 5-HT metabolism rather than to a modification of noradrenaline levels.

Fasting affects more markedly neuropeptide Y than monoamines in the rat brain

Monoamine turnover and neuropeptide Y (NPY) levels were evaluated in the CNS of 48- and 72-h-fasting adult, male rats in four brain areas: the hypothalamus, cortex, hippocampus, and striatum. In 48-h-fasted rats, NPY levels increased in the cortex and decreased in the striatum. The dopaminergic turnover increased in the hippocampus. The serotonergic turnover decreased in the hippocampus, striatum, and cortex and was still decreased after 72 h of fasting. In 72-h-fasted rats, an overall significant increase of NPY levels was observed except in the striatum, where it decreased significantly. No relationship appeared between NPY and monoamine levels, suggesting that NPY can act independently in feeding behavior and play, in different brain areas, an important role in its regulation.

Opposite dopaminergic activity in lateral and median hypothalamic nuclei in relation to the feeding effect ofd-Ser2-Leu-Enk-Thr6 (DSLET)

The Leu-enkephalin analogue D-Ser2-Leu-Enk-Thr6 (DSLET) had been shown to enhance feeding in rats, increase dopaminergic activity in the striatum like other opiate agonists, and particularly to decrease dopaminergic activity in the hypothalamus. In this study, the latter effect was found to be localized in the hypothalamic nuclei involved in the regulation of feeding such as the paraventricular (PVN), ventromedian (VMH), dorsomedian (DMH) nuclei and the lateral hypothalamus (LH). DSLET produced the same decrease in dopaminergic activity in the LH as in the whole hypothalamus. In the median nuclei (PVN and VMH and to a lesser extent in the DMH), an opposite effect was observed, resembling that in the striatum. The relevance of these opposite variations with regard to the feeding effect of DSLET is discussed. The decreased dopaminergic activity in the LH would appear to be the most specifically related to the behavioural effect given the known role of dopamine in this region. These data reconcile apparently contradictory aspects of the role of dopamine and the functional opposition between the lateral and median hypothalamus in food intake control.