Pharmacological characterization of perifornical hypothalamic dopamine receptors mediating feeding inhibition in the rat

Food and water intake responses of the domestic fowl to norepinephrine infusion at circumscribed neural sites

The effect on food and water intake of injection of norepinephrine into circumscribed brain sites of the domestic fowl was investigated. Injection of norepinephrine into sites throughout the preoptic area caused reliable increases in food intake. Food intake was also increased by injection of norepinephrine in the ventromedial nucleus, paraventricular nucleus, and medial septal sites. Food intake was decreased by injections near the lateral septal organ and the anterior portion of both the nucleus reticularis superior, pars dorsalis, and the tractus occipitomesencephalicus. Within the preoptic area, water intake was increased at basolateral sites but was inconsistently affected at more medial sites. No consistent trends were noted at sites examined outside the preoptic-hypothalamic area.

The pharmaco-ontogeny of the perifornical lateral hypothalamic beta 2-adrenergic and dopaminergic receptor systems mediating epinephrine- and dopamine-induced suppression of feeding in the rat

The functional ontogeny of beta 2-adrenergic and dopaminergic receptors in the perifornical lateral hypothalamus (PLH) that mediate adrenergic and dopaminergic suppression of feeding in rats was investigated. Rat pups, ranging in age from 2 to 15 days, were removed from their mothers and implanted with a brain cannula directed unilaterally at the PLH or a more rostral site lateral to the anterior nucleus of the hypothalamus. On the next day, following a 22-h period of food and water deprivation, each pup was implanted with an intra-oral cannula for oral infusion of milk that could be swallowed or rejected. Subsequently, each pup received an intracerebral injection of saline, or a single dose of epinephrine (EPI, 0.1-30.0 nmol), the beta 2-adrenergic receptor agonist salbutamol (1.0-30.0 nmol) or the dopaminergic receptor agonist apomorphine (1.0-30.0 nmol). Milk intake was then assessed following a 1-h period of infusion. The results showed significant dose-dependent suppression of milk intake in pups as young as 2 days of age in response to PLH injection of EPI, salbutamol and apomorphine. In contrast to its effectiveness in the PLH at 2 days of age, EPI failed to suppress milk intake at this age following injection into a more rostral site lateral to the anterior nucleus of the hypothalamus. Together, these findings suggest that both beta 2-adrenergic and dopaminergic receptors, mediating adrenergic and dopaminergic suppression of feeding, are functionally mature very early in the postnatal development of the rat. Moreover, consistent with evidence in adult rats, these catecholaminergic receptors in young pups appear to be located in the region of the PLH.

Spontaneous feeding-related monoaminergic changes in the rostromedial hypothalamus revealed by microdialysis

The activity of hypothalamic monoamines in response spontaneous feeding was investigated using the in vivo technique of brain microdialysis together with the instrumental recording of feeding pattern. The simultaneous variations of dopamine (DA), serotonin (5-HT), and their respective metabolites, DOPAC and 5-HIAA, were measured in the rostromedian hypothalamus, where the probe was located between the PVN and VMH. Throughout the experiment, the changes in DOPAC followed a mirror image of those in DA: DA regularly increased, reaching its zenith within the 15-min sample collected during the meal before returning to the same level as just before the meal. Following a premeal plateau, both 5-HT and 5-HIAA increased as soon as the beginning of feeding; 5-HT reached its zenith during the meal while 5-HIAA showed a more delayed and prolonged increase. When a new meal was initiated, 60 to 70 min later, a similar monoaminergic pattern was observed again. These data suggest that building up hunger is announced by an ascending slope of DA and setting up of satiation is concomitant with a descending slope of DA. Concerning serotonergic changes, the sharp 5-HT release during the meal would be a signal of satiation (transient preabsorptive fullness) while the longer-lasting increase in 5-HIAA, reflecting 5-HT synthesis, would be associated with satiety (more persistent postabsorptive state substituting satiation). These data partially confirm and extend previous pharmacological studies as well as the findings on deprivation-induced, imposed meals. They suggest a possible causal relation between monoaminergic changes and behavioral initiatives.

Anorectic activity of fluoxetine and norfluoxetine in rats: relationship between brain concentrations and in-vitro potencies on monoaminergic mechanisms

The present study was aimed at establishing the importance of brain monoamine uptake and release mechanisms in the anorectic activity of fluoxetine, relating them to the actual brain concentrations of the parent drug and its metabolite norfluoxetine after anorectic doses in rats. Both compounds showed anorectic activity when administered intraperitoneally, norfluoxetine being slightly more active (ED50 = 22.9 mumol kg-1) than fluoxetine (ED50 = 35.0 mumol kg-1) despite the fact that the metabolite is about ten times less potent than the parent drug in inhibiting 5-hydroxytryptamine (5-HT) uptake. Comparing the brain concentrations of norfluoxetine, in terms of maximum concentrations (Cmax) and area under the curve (AUC), after the ED50 of fluoxetine or synthetic norfluoxetine, it also appeared that the metabolite plays a major role in the anorectic effect of the parent drug in rats. Brain Cmax of fluoxetine (48.7 microM) and norfluoxetine (21.7 and 27.3 microM after metabolite and drug, respectively) were several times those blocking 5-HT uptake in-vitro (0.5 microM), making it unlikely that fluoxetine (directly or through its metabolite) reduces food intake by specifically blocking 5-HT neuronal uptake. Brain Cmax of fluoxetine but particularly norfluoxetine were more compatible with those capable in-vitro of affecting catecholaminergic mechanisms, such as inhibition of dopamine and noradrenaline uptake and enhancement of dopamine release. These results together with recent in-vitro findings that the parent compound and its active metabolite induce tritium release from hippocampal synaptosomes previously loaded with [3H]5-HT suggest that mechanisms other than inhibition of 5-HT uptake are involved in the anorectic action of these compounds in rats.

Sensitivity of dopamine receptors in the lateral hypothalamus is altered in 6-hydroxydopamine treated rats

Amine accumulation is observed in the lateral hypothalamus (LH) after nigrostriatal neurons degenerate. It has been proposed that this accumulation is a source of amines which are released into the hypothalamus thereby affecting the function of adjacent aminergic receptors. To approximate this condition of continuous exposure of LH receptors to endogenous amines, dopamine (DA) was injected into the LH of rats once daily for 5 consecutive days. A control group received 4 daily injections of tartaric acid vehicle and then DA on day 5. Rats pretreated with DA showed severe impairment of open field performance and motor reflex control on day 5 when they were compared to control animals which received vehicle pretreatment. In a second study, the DA receptor antagonist haloperidol was injected into the area of amine accumulation in the LH to determine whether this might block amine release from areas of accumulation thereby to attenuate lesion-induced rotation. Haloperidol administered once daily for 4 out of 7 days, once daily for 7 days or via a continuous infusion for 7 days, all reduced d,l-amphetamine-induced turning to control levels. These results suggest that prolonged exposure of hypothalamic DA receptors alters their sensitivity to subsequent doses of DA and that amine released from areas of accumulation may be blocked by haloperidol to enhance behavioral recovery from DA depleting lesions. Moreover, these findings indicate that the hypothalamus participates in the behavioral effects induced by DA depleting lesions and highlight the importance of hypothalamic pathology in Parkinson's disease.

Serotonin may play a role in the anorexia induced by amphetamine injections into the lateral hypothalamus

Amphetamine (AMPH) injections into the lateral hypothalamus (LH) are known to inhibit feeding and this effect has been shown to be mediated by the release and the reuptake blockade of catecholamines. LH serotonin (5-HT) has been suggested to be involved in feeding inhibition and a recent study showed that LH amphetamine infusion increases extracellular dopamine (DA), norepinephrine (NE) and 5-HT, which suggests that 5-HT might also be involved in amphetamine anorexia. The present study investigated this possibility. A correlational study was performed between the anorectic effect of LH unilateral microinjections of each monoamine and the anorectic effect of AMPH. Six groups of male rats were used. The rats in each group were submitted to 2 series of 6 experimental sessions. Each session consisted of one microinjection in 24 h food-deprived rats, followed by the measurement of food intake 30 min later. The first series was similar for all groups and explored the AMPH effect (difference between the mean food intake after 3 AMPH injections (40 micrograms/0.5 microliter) and the mean food intake after 3 saline injections (0.5 microliter)). The second series explored the effects of DA (40 micrograms), NE (25 micrograms), EPI (25 micrograms), 5-HT (25 micrograms) or AMPH again, in a similar way as described for AMPH in the first series. Linear regression analysis on the first series AMPH effect and the amine effect of the 2nd series showed a positive correlation between both series of AMPH, AMPH and DA, and AMPH and 5-HT. This last correlation was replicated in a different group. No correlation was found between AMPH and NE or AMPH and epinephrine (EPI).(ABSTRACT TRUNCATED AT 250 WORDS)

Ventromedial hypothalamus vs. lateral hypothalamic D2 satiety receptors in the body weight increase induced by systemic sulpiride

Two experiments were conducted in order to see if dopamine satiety receptors in the lateral hypothalamus or satiety mechanisms in the ventromedial hypothalamus were involved in the hyperphagia and body weight increase induced by systemic sulpiride. In the first experiment, it was shown that systemic sulpiride (20 mg/kg) does not block the anorexia caused by intraperifornical injections of amphetamine. In the second experiment, sulpiride (20 mg/kg during 18 days) did not produce an additional increase in body weight in previously VMH-lesioned female rats. This last fact cannot be explained by a ceiling effect since insulin (5 U/day during 7 days) increased body weight in the same VMH rats in which sulpiride was not effective. These results do not support the hypothesis that systemic sulpiride reaches the perifornical dopamine D2 receptors to disinhibit feeding, but suggest instead an involvement of the ventromedial hypothalamus. This last suggestion is more in agreement with the hypothesis that sulpiride alters feeding and body weight gain through the induction of a functional gonadectomy.

Hypothalamic sites affecting masticatory neurons in rats

The effects of hypothalamic electrical stimulation and dl-sulpiride injections on the unit activity of masticatory trigeminal neurons were assessed in rats. Unilateral electrodes or bilateral cannulas were implanted in the perifornical hypothalamus. The animals which exhibited eating to electrical stimulation or to sulpiride injections were selected. Then, under urethane anesthesia, electrical stimuli or sulpiride injections were applied at sites which elicited eating while a passive jaw movement-related neuron was recorded. Electrical stimulation or sulpiride injections affected the basal firing rate of 15 out of 32 (53%), and 13 out of 17 (76%) jaw movement-related neurons, respectively. The basal firing rate of 3 out of 18 (16.6%) was affected by electrical stimulation of noneliciting feeding nearby places. Facilitation was observed in 7 out of those 13 jaw movement-related trigeminal neurons after intrahypothalamic sulpiride injections. When dopamine was injected in the hypothalamus 3 minutes before sulpiride, this drug could only affect the basal firing rate of 1 out of 12 (8%) jaw movement-related neurons. The electrical stimulation and sulpiride injections into the hypothalamus had the same inhibitory or excitatory effect on a given trigeminal neuron as the passive jaw movement did. A similar phenomenon was observed with the sulpiride-induced facilitation. These results suggest that hypothalamic D2 satiety receptors modulate brain stem feeding reflexes.

Effects of insulin on brain monoamine metabolism in the Zucker rat: influence of genotype and age

Disturbances of insulin or brain monoamine metabolism may play a role in the impaired regulation of food intake and body weight in the obese Zucker rat. We investigated a possible insulin-monoamine interaction by measuring monoamine levels in the hypothalamus and striatum of obese (fa-fa) and lean (Fa-Fa and Fa-fa) Zucker rats after peripheral insulin administration. The classically reported effects of insulin, i.e., increases in tryptophan, 5-hydroxy-indolacetic acid (5-HIAA) and dihydroxyphenylacetic acid (DOPAC) levels, were observed in the hypothalamus of Fa-Fa and Fa-fa rats, but not in obese fa-fa rats. Given the mechanism of action of insulin, this lack of effect in the obese rats may be related to the peripheral insulin resistance they exhibit. Furthermore, given the role of these monoaminergic systems, this reduced effect may be related to the impaired regulation of food intake and body weight. At 8 wk of age, however, insulin restored the decreased basal 5-HIAA levels observed in the obese rats. Increase in 5-HIAA levels following insulin administration appeared in the striatum of Fa-Fa rats only, suggesting that, as for brain insulin content, other central insulin-related disturbances may be related to the presence of the "fa" gene. In addition, certain effects of insulin on striatal dopamine release were observed in only the Fa-Fa and fa-fa rats, suggesting a particular disturbance related to the heterozygous character. This latter point calls for further investigations on the central dopaminergic effects of insulin.

Dopamine in the lateral hypothalamus may be involved in the inhibition of locomotion related to food and water seeking

Experiments were conducted in male rats to assess the motor effects of bilateral intraperifornical microinjections of sulpiride, dopamine (DA) and other drugs. Sulpiride increased locomotion of the animals in all the experiments reported here. DA (10 micrograms) administered 5 minutes before sulpiride (8 micrograms) reduced the motor stimulant effect of the neuroleptic from 1601.3 +/- 337.6 to 742.5 +/- 180.4 counts/30 min. SCH 23390 (15 micrograms), haloperidol (2.5 micrograms) and atropine (18 micrograms) did not modify the locomotion level of animals acclimated to the actimeters. After carbachol (5 micrograms) the animals attained a level of hyperactivity (1459.5 +/- 146.5 counts/30 min) similar to that induced by sulpiride (1595.7 +/- 365.7 counts/30 min) in the same experiment. In other experiments DA (10 micrograms) administered 30 min before sulpiride again blocked the effect of 8 micrograms of sulpiride, and reduced the initial hyperactivity of food- and water-deprived animals previously familiarized with the actimeters (922.4 +/- 49.38 counts/15 min under saline, vs. 544 +/- 29 counts/15 min under DA). The same DA dose did not modify the initial spontaneous activity of nonfamiliarized nonfood-deprived rats (508.9 +/- 96.1 after saline vs. 520.9 +/- 47.1 after DA). These results suggest the presence of cells in the lateral hypothalamus involved in the control of locomotion. These experiments also suggest that locomotion triggered by the LH may be exploratory behavior essential to the search for water and food. As a corollary, DA in the LH appears to be involved not only in the inhibition of feeding and drinking but also in the inhibition of exploratory and food- and water-directed locomotion.

Opposite dopaminergic activity in lateral and median hypothalamic nuclei in relation to the feeding effect of D-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.

The effects of the enantiomers of the dopamine agonist N-0437 on food consumption and yawning behaviour in rats

The enantiomers of the potent and selective dopamine (DA) D-2 receptor agonist 2-(N-propyl-N-thienylethyl-amino)-5-hydroxytetralin, N-0437, were tested for their effects on palatable food consumption and yawning behaviour in rats. (-)-N-0437 (1.0 and 5.0 mumols/kg). This confirms the agonistic action of (-)-N-0437 on postsynaptic receptors as food consumption is considered to be related to stimulation of postsynaptic DA receptors. Yawning behaviour was stimulated by (-)-N-0437 (0.5 mumol/kg) and could be antagonized by the autoreceptor-selective antagonist (+)-UH 232 (25 mumols/kg), which suggests an agonistic action on DA autorecptors. (+)-N-0437 (5.0 and 10.0 mumols/kg) also reduced food consumption and the effect could be antagonized by YM 09151-2 (0.03 mumol/kg). The weaker effect of (+)-N-0437 on food intake in comparison to that induced by (-)-N-0437 can be explained if it assumed that (+)-N-0437 is a partial agonist. (+)-N-0437 did not induce yawning behaviour in rats, suggesting that autoreceptors mediating the release of DA may be involved in stimulating yawning by DA agonists.

The selective dopamine D1 receptor agonist SK&F 38393: its effects on palatability- and deprivation-induced feeding, and operant responding for food

A series of experiments investigated the involvement of the dopamine D1 receptor subtype in relation to feeding responses. The selective D1 agonists, SK&F 38393 (1.0-20 mg/kg) and SK&F 75760 (5 mg/kg), significantly reduced palatable food consumption in nondeprived rats. The anorectic effect of SK&F 38393 (10 mg/kg) was additive with that of the selective D2 receptor agonist, N-0437 (0.3 mg/kg). In nondeprived mice, SK&F 38393 had a stereoselective effect to reduce palatable food intake. At a peripherally-selective dose (3.0 mg/kg), the peripheral dopamine D1 receptor agonist, fenoldopam, had no effect on food intake. At 10 mg/kg, however, it exhibited anorectic properties, although this may have been due to some penetration of the blood-brain barrier. In rats adapted to a food-deprivation schedule, SK&F 38393 (3.0-30 mg/kg) produced significant dose-dependent reductions in consumption of powdered chow and in lever-pressing for food pellets on a FR8 schedule of reinforcement. In rats adapted to a water-deprivation schedule, SK&F 38393 (3.0-30 mg/kg) was substantially less effective in reducing water intake. The results are discussed in terms of a possible selective effect of D1 agonist activity on feeding behaviour.

Microstructural analysis of the anorectic effect of N-0437, a highly selective dopamine D2 agonist

Drug actions, mediated by dopamine D2 receptors, have been shown to reduce food consumption in rodents. The present study used a microstructural approach to feeding responses to determine the behavioural changes which underlie the anorectic effect of a selective D2 agonist, N-0437. Non-deprived male rats were trained to consume a palatable, sweetened mash in a 30 min test under familiar test conditions. N-0437 (1.0 and 3.0 mg/kg) significantly reduced food intake, but had no effect on the duration of feeding, the duration and frequency of feeding bouts, or on the time course of feeding. Its anorectic effect depended upon a selective reduction in the rate of eating. Microstructural analysis of other behavioural changes which followed treatments with N-0437 indicated that, at 0.3 mg/kg, the drug may have selective dopamine autoreceptor activity, but at 1.0 and 3.0 mg/kg it acts postsynaptically at D2 receptors. The results show that the anorectic effects of N-0437 can be clearly distinguished from the effects of psychomotor stimulants like D-amphetamine or cocaine, but they overlap in part with the effect of the mixed D1/D2 agonist, apomorphine. The results are discussed in relation to a proposed D2 receptor-mediation of one component of the behavioural changes that underlie feeding satiation.

Mechanism of the body weight increase induced by systemic sulpiride

Long-term intraperitoneal administration of sulpiride induced body weight increase in female but not in male rats. The hypothesis that systemic sulpiride causes an endocrine unbalance which in turn causes body weight gain and hyperphagia was tested in four experiments. First, it was shown that even when they are on a high-fat diet male rats do not show body weight gain induced by systemic sulpiride. Second, sulpiride suppressed the estrous cycle. Third, gonadectomy prevented the body weight gain induced by systemic sulpiride in female rats. Fourth, estradiol simultaneously administered with sulpiride prevented the expected sulpiride-induced body weight gain. These results are discussed in terms of an hypothetical functional castration produced by systemic sulpiride. The well known hyperprolactinemia, induced by the pituitary D2 dopamine receptor blockade, might bring about an impairment of the steroidogenesis with subsequent decrease in estrogens level, which in turn might be responsible for the hyperphagia and body weight increase induced by systemic injections of sulpiride.

Stimulation and inhibition of food intake by the selective dopamine D2 agonist, N-0437: a meal pattern analysis

Feeding and drinking responses were recorded in home-caged rats over 24-hour periods, and the data were analysed in terms of meal patterns. The highly selective dopamine D2 receptor agonist, N-0437, was injected IP at the start of the night phase. At the smallest dose (0.3 mg/kg), N-0437 increased food intake as a result of increases in meal size and duration. The rate of feeding during meals was not increased. This effect lasted 1-2 hours in the night phase. At higher doses (1.0 and 3.0 mg/kg), N-0437 inhibited food intake for 3-6 hours. The inhibition was due to a substantial reduction in meal size, with no change in meal frequency. Rate of feeding during meals tended to be reduced. A biphasic dose-effect relationship was not apparent in the drinking data, and there was not a significant effect of N-0437 on drinking responses. The meal pattern analysis results indicate the stimulation of D2 receptors produces increases and decreases in food intake and meal size. These results are discussed in terms of dose-dependent stimulation of presynaptic (autoreceptor) and postsynaptic D2 receptors, and the relationship to satiety within meals.

Sucrose sham-feeding in the rat after administration of the selective dopamine D2 receptor agonist N-0437, d-amphetamine or cocaine

Drugs which act as agonists at dopamine receptors, or which increase dopamine release (e.g., d-amphetamine, cocaine) are known to reduce food intake. The present experiments investigated, for the first time, the effects of a highly selective dopamine D2 receptor agonist, N-0437 (0.3-3.0 mg/kg, IP), on 5% sucrose sham-feeding in gastric fistulated rats, and compared these results with those of d-amphetamine (0.1-3.0 mg/kg, IP) and cocaine (3.0-10.0 mg/kg, IP). The results showed that sucrose sham-feeding was resistant to the effects of N-0437, even though the D2 agonist dose-relatedly reduced sucrose real-feeding in intact animals. The two psychomotor stimulants, d-amphetamine and cocaine, produced some reductions in sham-feeding, although in the case of the highest dose of d-amphetamine, the pronounced reduction in the consumption of sucrose was probably secondary to induced behavioral stereotypy. The results suggest that D2 receptor stimulation may interact with satiety cues to reduce ingestion of sucrose, but that in the absence of potent satiety stimuli D2 receptor stimulation is ineffective. Furthermore, N-0437 appeared not to be equivalent to either d-amphetamine or cocaine in their effects to reduce sucrose sham-feeding.

Effects of dopamine receptor antagonists on sucrose consumption and preference

Effects of the dopamine D2 receptor antagonist sulpiride and the D1 antagonist SCH-23390 were examined, in rats, in two-bottle preference tests (sucrose versus water) and in single-bottle tests, at different sucrose concentrations. Both drugs decreased sucrose intake in single bottle tests, at low sucrose concentrations, but had no effect at high concentrations; reducing drive level had exactly the opposite pattern of effects. In two-bottle tests, both drugs reduced preference for the weakest sucrose concentration (0.7%) but increased preference for the strongest concentration (34%). The effects of antagonizing either subtype of DA receptor appear to be similar to those of reducing the concentration of sucrose.

An improved circular tilt-cage shows that intrahypothalamic injections of sulpiride increase locomotion

A circular tilt-cage was designed and constructed to measure locomotor activity in rats. Some improvements in relation to previously described circular tilt-cages, as the easy calibration and the automation of the data collection, were introduced. The detection system was built interfacing the actimeters through a circuit board to a Casio FP-200 computer. The interface, the computer and the software can be used to count lever presses or other kind of switch closures. This apparatus was used in the present report to quantitate the locomotor activity induced by sulpiride injected in the perifornical region of the lateral hypothalamus. Bilateral injections of sulpiride (8 micrograms/0.5 microliters) increased locomotion immediately after the injections and for the next 75 min. Bilateral amphetamine (20 micrograms/0.5 microliters) did not change activity. Several doses of sulpiride (2, 4, 8, and 16 micrograms/0.5 microliters) increased activity in a dose-dependent fashion. These results are discussed in terms of the existence of postsynaptic D2 receptors in the lateral hypothalamus involved in inhibition of locomotion.

Sulpiride injections in the lateral hypothalamus induce feeding and drinking in rats

Amphetamine injections into the lateral hypothalamus inhibit feeding. This effect is blocked by local administration of neuroleptics, suggesting a role for dopamine in feeding inhibition. However, the type of dopamine receptor involved in satiety is not known. Therefore, we tested the effect of intrahypothalamic injections of sulpiride, a specific D2 receptor blocker, on amphetamine anorexia in food-deprived rats, and on spontaneous feeding and drinking in satiated rats. Sulpiride attenuated by 36% the anorexia produced by intrahypothalamic injections of amphetamine. In satiated rats, sulpiride (8 micrograms/0.5 microliter) elicited feeding (mean food intake after sulpiride: 5.4 g, and after vehicle 1.6 g, p less than 0.001), and drinking (mean water intake after sulpiride: 12.3 ml, and after vehicle: 0.9 ml, p less than 0.001). A dose response relationship was found between sulpiride dose and feeding or drinking. Sulpiride-induced drinking was observed in the absence of food, showing that it is not a postprandial phenomenon. These results suggest that hypothalamic D2 receptors might be involved in feeding and drinking regulation.

Alpha 2-adrenoceptor blockade attenuates feeding behavior induced by neuropeptide Y and epinephrine

Neuropeptide Y (NPY, 0.47 nmol) and epinephrine (28.9 nmol) evoked robust, and quantitatively similar, increments in food intake and local eating rate following administration into the third cerebral ventricle (IIIV). Whereas IIIV pretreatment with phentolamine (71 nmol), a nonselective alpha-adrenoceptor antagonist, or prazosin (9.5 nmol), a selective alpha 1-adrenoceptor antagonist, was without effect on NPY-induced feeding behavior, pretreatment with the alpha 2-adrenoceptor antagonist yohimbine (15 nmol) dramatically attenuated the stimulatory effects of NPY or epinephrine on both food intake (by over 50%) and local eating rate. Additionally, yohimbine administered alone was associated with a stimulatory effect on food intake for the periods of 80-110, and 110-140 minutes posttreatment. These data demonstrate that feeding behavior induced by IIIV administration of NPY or epinephrine is attenuated by prior blockade of alpha 2-adrenoceptors and suggest that, as in other systems innervated by neurons displaying NPY and adrenergic transmitter colocalization, the effects of NPY on feeding behavior may, at least in part, be mediated via alpha 2-adrenoceptors.

Profile of the selective dopamine D-2 receptor agonist N-0437: its effects on palatability- and deprivation-induced feeding, and operant responding for food

N-0437 is a potent and highly selective dopamine D-2 receptor agonist, which has been used in the present series of experiments to investigate its potential anorectic properties. In doses of 0.3-3.0 mg/kg (IP), N-0437 significantly reduced consumption of a sweetened palatable mash in nondeprived mice (minimal effective dose, 0.3 mg/kg) and rats (minimal effective dose, 0.56 mg/kg). Reduction in food intake were also produced in rats by the less potent, but selective, D-2 agonist RU 24213 (effective at 10.0 mg/kg), and by d-amphetamine (1.0 and 3.0 mg/kg). The anorectic effect of N-0437 (1.0 mg/kg) was completely antagonized by the selective D-2 antagonist, YM-09151-2 (0.01 mg/kg). Over a series of 10 injections, N-0437 (1.0 mg/kg) maintained its effect to reduce palatable food intake. In food-deprived rats, N-0437 (0.3-3.0 mg/kg, IP) also reduced consumption of standard laboratory food, and dose-dependently reduced operant responding for food under a FR8 schedule of reinforcement. The results of the experiments are discussed in terms of a possible direct effect to reduce feeding responses resulting from stimulation of postsynaptic dopamine D-2 receptors.

The function of lateral hypothalamic catecholamine and endorphin systems in the control of motor performance

Morphine (1 or 10 micrograms in 1 microliter) or beta-endorphin (1 microgram in 1 microliter) were injected bilaterally into the posterior lateral hypothalamus of Sprague-Dawley rats to determine what effect they may have on motor performance. Severe reductions in open field performance and motor reflex control were observed after the injection of 1 microgram of beta-endorphin or morphine into this area. The injection of 10 micrograms of morphine into the same area was less effective in causing motor impairment. The central (32.7 micrograms in 1 microliter) and peripheral (2 mg/kg) injection of naloxone did not prevent the motor impairment observed after the injection of beta-endorphin or morphine. Pretreatment with 6-hydroxydopamine into the lateral hypothalamus in a multistage regime did not prevent the motor impairment observed after beta-endorphin or morphine injection. These results indicate that lateral hypothalamic participation in the control of motor function may not involve the ascending nigrostriatal and mesocortical dopamine systems and that endogenous opiate systems may function independently to influence motor performance.

Amphetamine: effects on meal patterns and macronutrient selection

Catecholaminergic systems, specifically in the region of the lateral perifornical hypothalamus (PFH), have been linked to the inhibition of feeding behavior. The present studies examined the effects of d-amphetamine (AMPH), which is believed to act through the release of endogenous catecholamines (CAs), on spontaneous feeding and appetite regulation in rats. Injection of AMPH directly into the PFH caused a marked suppression of food intake; changes in computer-monitored meal patterns were characterized by an increase in the latency to meal onset and a consequent reduction in meal size and duration. This suggests that hypothalamic AMPH administration may influence primarily the initiation, rather than the termination, of feeding. In other experiments, chronic infusion of AMPH directly into the PFH was shown to suppress 24 hr food intake and body weight gain, indicating the effectiveness of lateral hypothalamic CA stimulation in overriding normal long-term patterns of feeding. The effect of hypothalamic CA stimulation on macronutrient selection was also investigated in groups of rats injected either centrally or peripherally with AMPH, or centrally with the CA agonists, dopamine and epinephrine. Each of these manipulations caused a strong inhibition of protein intake with no effect on carbohydrate, and only a mild suppression of fat ingestion after peripheral AMPH. These selective effects of AMPH on feeding patterns and diet choice, provide support for a role of CA innervation to the lateral hypothalamus in the modulation of natural feeding behavior and macronutrient selection.

The role of glucose, insulin and glucagon in the regulation of food intake and body weight

Glucose and related pancreatic hormones play a major role in the metabolism of monogastric mammals yet their influence on hunger and/or satiety is, as yet, poorly understood. Glucose, insulin and glucagon rise during a meal and gradually decline to baseline levels shortly after a meal. A sudden drop in plasma glucose as well as insulin have been reported just prior to the onset of a meal but the functional significance of this is not yet clear. Systemic injections of glucose have no acute satiety effects but intraduodenal and intrahepatic infusions reduce food intake and free-feeding and deprived animals respectively. Treatments which decrease cellular glucose utilization directly (2-DG) or indirectly (insulin) increase food intake while exogenous glucagon (which produces hyperglycemia) decreases it. There is considerable evidence that some or all of these effects may be due to a direct central action of glucose, 2-DG, insulin, and glucagon on brain mechanisms concerned with the regulation of hunger and satiety although influences on peripheral "glucoreceptors" have been demonstrated as well. The functional significance of glucoprivic feeding is, however, questioned. The feeding response to 2-DG and related compounds is capricious, and its temporal course does not parallel the hyperglycemic reaction which presumably reflects cellular glucopenia. Moreover, numerous brain lesions which increase, decrease, or have no effect on ad lib intake and often have no effect on the response to deprivation have been shown to severely impair or abolish feeding responses to systemic injections of 2-DG that produce severe central as well as peripheral glucopenia. Feeding responses to insulin are intact after most of these lesions, suggesting that this hormone may influence food intake in a fundamentally different fashion. The mechanism of insulin action is not understood--the classic feeding response is obtained only with doses that are pharmacological when compared to normal plasma levels and there is increasing evidence that lower doses may have opposite, inhibitory effects on food intake and body weight. Relatively small doses of glucagon decrease food intake (although opposite facilitatory effects have been reported after even smaller doses) but the effect does not appear to be due to hepatic mobilization of glucose as initially assumed. Decreases in food intake after intracranial injections of very small doses suggest a direct central action.

Evidence for the presence of D2 but not D1 dopamine receptors in rat hypothalamic perifornical area

Behavioural studies have shown that the perifornical hypothalamus (PFH) plays a fundamental role in mediating dopamine-induced anorexia. In the present report, we provide biochemical evidence for the occurrence of dopamine receptors in the PFH, but not in the paraventricular nucleus of the hypothalamus. Dopamine as well as bromocriptine, a D2 dopamine receptor agonist, strongly reduced the adenylate cyclase activity in the PFH. This inhibitory effect was reversed by haloperidol and by (-)-sulpiride, but not by (+)-sulpiride. On the contrary, the selective D1 dopamine agonist SKF 82526 was completely inactive in affecting adenylate cyclase activity. Our conclusion asserts the existence of dopamine D2 but not D1 receptors in the PFH, which therefore can be conceived as the only region in the brain where a single class of dopamine receptors is present.

Diurnal rhythm of alpha 2-noradrenergic receptors in the paraventricular nucleus and other brain areas: relation to circulating corticosterone and feeding behavior

The paraventricular nucleus alpha 2-noradrenergic system and the glucocorticoid hormone, corticosterone, are known to modulate feeding behavior and exhibit a circadian pattern which may be related to the natural periodicity of feeding in the rat. The results of the present study indicate that the binding of [3H]p-aminoclonidine to alpha 2-noradrenergic receptors specifically in the paraventricular nucleus varies concomitantly with plasma corticosterone levels, as well as spontaneous feeding. A monophasic peak of paraventricular noradrenergic receptor binding is detected at the onset of the dark period, when corticosterone levels are highest and feeding is initiated. On the other hand, the supraoptic nucleus exhibits the reverse diurnal pattern, i.e., a significant decline of [3H]p-aminoclonidine binding at the onset of the dark period. Other hypothalamic and extra-hypothalamic areas fail to show significant changes in alpha 2-noradrenergic receptors as a function of the diurnal cycle. This study supports other evidence indicating a close interaction between circulating corticosterone and alpha 2-noradrenergic receptors in specific hypothalamic areas. It also reveals a potential importance for this interaction in control of the natural feeding rhythm.

Brain serotonin and eating behavior

Studies indicate that hypothalamic monoamine systems involved in the control of food intake have specific effects on temporal feeding patterns and on appetite for specific macronutrients. Based on the evidence obtained in rats, it is proposed that serotonin acts, in part, through a satiety mechanism of the medial hypothalamus, to reduce ingestion of carbohydrate while sparing protein intake. In controlling the ratio of carbohydrate to protein intake, this serotonergic system, which is responsive to the anorectic agent fenfluramine, is believed to function in direct opposition to the alpha 2-noradrenergic system of the paraventricular nucleus, which inhibits satiety for carbohydrate and thereby potentiates the size of carbohydrate meals. This serotonergic system may also indirectly oppose the catecholaminergic systems of the lateral hypothalamus, which mediate amphetamine anorexia and which inhibit a hunger-stimulating system for protein intake, thereby delaying the initiation of protein meals. Examination of the rats' normal eating patterns, in conjunction with particular biochemical analyses, has indicated specific points in the circadian eating cycle where these hypothalamic monoamine systems, in association with changes in circulating hormones and nutrients, may be physiologically activated.

Analysis of dopamine D1 and D2 receptor involvement in d- and l-amphetamine-induced anorexia in rats

The concept of dopamine receptor subtypes and the recent development of selective dopamine receptor agonists and antagonists raises the possibility of specific subtype involvement in amphetamine-induced anorexia, and, furthermore, provides the means to evaluate the possibility. Using a test of palatable food consumption by nondeprived male rats, our data confirmed a more potent suppressant effect of d-amphetamine on food intake, compared to l-amphetamine (potency ratio 5.32:1). The test proved sensitive, with ED50s of 0.28 mg/kg and 1.49 mg/kg for d- and l-amphetamine, respectively. The modest anorectic effect of 0.3 mg/kg d-amphetamine was completely reversed by the selective dopamine D1 receptor antagonist, SCH 23390, but was not affected by the selective D2 receptor antagonist, sulpiride. A matched feeding-suppressant effect of 1.0 mg/kg l-amphetamine was reversed at one dose of SCH 23390, but was unaffected by sulpiride. Stronger anorectic effects produced by 1.0 mg/kg d-amphetamine and 3.0 mg/kg l-amphetamine were not antagonized either by SCH 23390 or sulpiride. The selective D1 receptor agonist, SKF 38393, produced a dose-dependent reduction in food consumption, without producing behavioural stereotypy. Unlike amphetamine, SKF 38393 is not self-administered, and therefore may provide an example of a novel pharmacological dissociation between anorectic and reinforcing effects of drug treatments mediated by dopamine receptors. Our data implicate dopamine D1 receptors in the control of feeding responses, and suggest that these receptors may mediate the anorectic effect of small-dose amphetamine treatments.

Postsynaptic alpha 2-noradrenergic receptors mediate feeding induced by paraventricular nucleus injection of norepinephrine and clonidine

This study examines the feeding response induced by hypothalamic noradrenergic stimulation, in terms of the type and synaptic position of its mediating receptor. Tests with norepinephrine or the alpha 2 receptor agonist clonidine, injected into the area of the paraventricular nucleus (PVN), revealed a potent feeding response in satiated animals. This response by either agonist was blocked, in a dose-dependent fashion, by local injection of the alpha 2-noradrenergic antagonists, rauwolscine and yohimbine. It was also blocked by the general antagonist, phentolamine. In contrast, it was unaffected by hypothalamic injection of the alpha 1-noradrenergic antagonists, prazosin and corynanthine. These results indicate that feeding elicited by noradrenergic stimulation in the region of the PVN is mediated through alpha 2-type receptors. These alpha 2 receptors appear to be located postsynaptically, since the effectiveness of clonidine in eliciting eating was undisturbed by prior injection of the catecholamine synthesis inhibitor, alpha-methyl-p-tyrosine.

Amine accumulation in behavioural pathology

When nigro-striatal and meso-cortical neurons degenerate there is a loss of dopamine in the terminal fields and an accumulation of amines in the axons of these systems as they traverse the hypothalamus through the medial forebrain bundle. Traditional lines of thought have attributed the occurrence of motor and consummatory deficits which occur after dopamine neuron degeneration to the loss of functional dopamine neurotransmitter in the terminal fields. However, we have hypothesized that hypothalamic amine accumulation represents an area of brain tissue where processes such as neurotransmitter release, ephaptic transmission or local axon swelling may be affecting adjacent neurons and may thereby participate in the production of behavioural deficits. There is a considerable amount of evidence from studies on both peripheral and central catecholamine-containing neurons indicating that when their axons degenerate a release of functional neurotransmitter can occur. Information from neuropharmacological studies indicates that several drugs which facilitate behavioural recovery from dopamine-depleting lesions may do so by affecting amine release or receptor sensitivity near areas of accumulation rather than depleted terminal fields. We conclude that amine accumulation is a component of dopamine neuron degeneration which should be considered when assessing the role of the central catecholamine systems in the control of various behavioural and physiological processes.

Food intake control in birds

The regulation of food intake has been a topic of intense investigation for several decades. Most investigators have used the rat in such studies while considerably fewer studies have been conducted using birds. Research concerned with the control of food intake in birds is discussed herein. In most instances, birds and mammals have similar control mechanisms. The alimentary tract and the liver are peripheral structures which function in the control of feeding in birds but much remains to be studied as to their role. Many brain loci, including the lateral hypothalamus, ventromedial hypothalamus, striatum and olfactory bulbs are also involved in controlling food intake. Studies with birds have revealed marked breed and line differences in the response to factors modulating food intake. The bird appears to provide an excellent model for studies designed to investigate how selection for growth can alter the mechanisms involved in food intake control.

Administration of small doses of apomorphine attenuates feeding in non-deprived pigeons

The dopamine agonist apomorphine was administered peripherally at small doses of 25, 50 or 100 micrograms to non-deprived pigeons, either in the morning or in the afternoon. The food and water consumption of the birds was then measured at 4 times (30, 60, 90 and 120 min) after the injection. In the control condition (injection of saline), the pigeons ate less in the morning than in the afternoon, whereas a reverse situation was observed for drinking. Administration of apomorphine attenuated the food consumption in a dose-related fashion, at both times of the day, and for no longer than 90 min post-injection; the reduction of feeding was relatively larger when the drug was given in the morning than in the afternoon, and it was not accompanied by consistent changes of the water consumption. These results show that in pigeons, the feeding-like responses to apomorphine treatment (pecking, swallowing, mandibulating) which have been described previously are not associated with an actual enhancement of the food intake. Possible mechanisms and loci of action of dopamine agonists on these 2 types of behaviors are discussed.

A role for amine accumulation in the syndrome of ingestive deficits following lateral hypothalamic lesions

Lesions of the lateral hypothalamus produce ascending catecholamine neuron degeneration which results in terminal depletion and proximal accumulation above the lesions. The occurrence of deficits in ingestive behaviour has been attributed traditionally to the loss of functional dopamine neurotransmitter in the terminal fields. However, release of functional amines may occur in the lateral hypothalamus at areas of accumulation, to produce at least some of the behavioural symptoms characterizing the lateral hypothalamic syndrome. Recovery from behavioural deficits as a result of various pharmacological treatments, after dopamine-depleting lesions, may be mediated by changes in amine release or modified sensitivity of receptors affected by released amines. We conclude that amine accumulation should be considered when interpreting experiments implicating central catecholamine systems in the control of consumatory behaviour and the regulation of body weight.

Feeding behavior after hypothalamic 6-hydroxydopamine injections

6-Hydroxydopamine (6-OHDA) injection into the rat hypothalamus produces profound changes in eating behavior and body weight gain. Willis and Smith have demonstrated an anorexic effect of lateral hypothalamic (LH) 6-OHDA, which they correlate with local catecholamine release from degenerating axons just behind the lesion. Work from our own laboratory has recently demonstrated that 6-OHDA injection into the medial paraventricular nucleus (PVN) has an initial effect of stimulating daily food intake and body weight gain. It is suggested that this phenomenon, consistent with reports of enhanced eating with PVN injection of norepinephrine (NE), is due to 6-OHDA-induced release of endogenous NE. Subsequently, PVN 6-OHDA causes hypophagia and reduced body weight. Although histochemical and biochemical analyses reveal a 60-90% decrease in PVN norepinephrine and dopamine after 6-OHDA treatment, a close association between the precise degree of catecholamine loss and magnitude of behavioral response could not be detected.

Deficits in locomotor behaviour and thermoregulation produced by intrahypothalamic dopamine injections

When nigrostriatal dopamine neurones degenerate, a loss of functional dopamine in the striatum occurs and is accompanied by increased dopamine in the degenerating axons which traverse the hypothalamus. While the behavioural deficits which occur after nigrostriatal degeneration have been attributed to the loss of functional dopamine neurotransmission, evidence produced by us suggests that the increased levels of amines in the degenerating axons may be neuroactive and participate in the production of these behavioural deficits. To test this hypothesis further, albino rats were injected bilaterally with 200 nmol of dopamine in a location just rostral to the diencephalon/mesencephalon border, where amine accumulation is commonly observed following lateral hypothalamic damage. The effect of these injections upon open field performance, thermoregulation and motor reflex control was determined 40 min after dopamine injection. In a second study, pargyline (15 mg/kg. i.p.) was administered 30 min before intracerebral dopamine to determine whether this treatment would increase the severity of motor and thermoregulatory deficits which occurred after dopamine injections alone. Deficits in locomotion, rearing and the ability to regulate body temperature were seen after the dopamine injections while motor reflex control in these animals was similar to that seen in vehicle-injected controls. The behavioural deficits displayed by pargyline pretreated, dopamine injected animals were slightly but not significantly more severe than those displayed by animals receiving dopamine injections alone. Fluorescent histochemical assessment of injection sites revealed that dopamine injection produced an increase in fluorescence or "amine accumulation" at the site of injection but this was considerably less than that seen after catecholamine degeneration.(ABSTRACT TRUNCATED AT 250 WORDS)

Psychopharmacological activity of anaphylatoxin C3a in rat hypothalamus

C3a anaphylatoxin injected into the perifornical hypothalamic region of sated rats increased the eating response to norepinephrine and the drinking response to carbamyl choline but had no effect on food or water intake in sated, saline control animals. This potentiation of drug-stimulated intakes was reversible by intrahypothalamic injection of catecholamine receptor antagonists haloperidol and phentolamine. We propose that C3a acts as a catecholamine agonist in the central nervous system. The results suggest that C3a may play a role in mediating the neuropsychiatric manifestations associated with immune complex formation or deposition in the central nervous system.

Feeding, drinking and body temperature of Leghorn chicks: effects of ICV injections of biogenic amines

The effects of dopamine (DA), norepinephrine (NE), epinephrine (E) and 5-hydroxytryptamine (5-HT) on food intake, water consumption and colonic body temperature (Tc) were investigated using Leghorn-type chicks. Food intake was not significantly affected by the intracerebroventricular injections of DA, NE or E. In contrast, 5-HT significantly decreased food intake in both sated and fasted chicks. Tc was significantly decreased by NE and E whereas DA and 5-HT prevented the decline seen in controls. Water consumption was not significantly affected by DA, NE or E; however, 5-HT increased water consumption of sated chicks and decreased water consumption in fasted ones. The feeding response of Leghorn chicks following ICV injection of these biogenic amines differs from that previously observed in the broiler-type chicks. This disparate response is discussed in relation to the different growth rates of the two types of birds.

The behavioural effects of intrahypothalamic multistage versus single injections of 6-hydroxydopamine

16 micrograms of 6-hydroxydopamine were injected bilaterally into the lateral hypothalamus of male Sprague-Dawley rats in either a single injection or in a series of multistage injections over a period of 75 days. While the single injection produced behavioural deficits typical of those seen following catecholamine depletion of the forebrain, the behaviour of animals injected incrementally with the same dose was indistinguishable from that of controls. Fluorescent histochemical assessment revealed that the animals in the multistage injection group, the behaviourally unimpaired, suffered more severe depletion of forebrain catecholamines than those in the single-stage injection group. Accumulation of amines proximal to the site of drug injection was extensive only in those animals displaying behavioural deficits, that is, the group with the lesser amount of forebrain catecholamine depletion. It is suggested that the severity of deficits in consummatory and motor behaviour occurring after hypothalamic trauma is determined by a lesion's effectiveness in producing amine accumulation rather than catecholamine depletion.

Endorphinergic and alpha-noradrenergic systems in the paraventricular nucleus: effects on eating behavior

Brain cannulated rats were injected with the opioid peptide beta-endorphin (beta-EP) directly into the hypothalamic paraventricular nucleus (PVN) where norepinephrine (NE) is most effective in stimulating eating behavior. Beta-Endorphin (1.0 nmole) reliably increased food intake in satiated animals, and this response was blocked by local administration of the selective opiate antagonist naloxone. The eating induced by beta-EP was positively correlated in magnitude with the NE response and, like NE, was antagonized by PVN injection of the alpha-noradrenergic blocker phentolamine. Naloxone had no effect on NE-induced eating, and the dopaminergic blocker fluphenazine failed to alter either beta-EP or NE eating. When injected simultaneously, at maximally effective doses, beta-EP and NE produced an eating response which was significantly larger than either of the responses elicited separately by beta-EP or NE and was essentially equal to the sum of these two responses. The evidence obtained in this study suggests that beta-EP and NE stimulate food ingestion through their action on PVN opiate and alpha-noradrenergic receptors, respectively, and that beta-EP's action is closely related to, and in part may be dependent upon, the PVN alpha-noradrenergic system for feeding control.

Enkephalin-immunoreactive neurons in the guinea-pig hypothalamus

An ultrastructural study of enkephalin-immunoreactive perikarya forming a hypothalamic nucleus, the magnocellular dorsal nucleus (MDN), was carried out in colchicine-treated guinea pigs. These large cells usually contain a well-developed rough endoplasmic reticulum, a prominent Golgi complex and neurosecretory granules approximately 100 nm in diameter. These granules are not numerous and sometimes appear preferentially located in the periphery of the cytoplasm. Using the PAP method on ultrathin sections, the immunostaining obtained with anti-enkephalin antisera is essentially confined to the granules but also to some ribosomes linked to membranes of the rough endoplasmic reticulum. These images suggest that the cells of the MDN synthetize the enkephalin-related peptide. Around the perikarya many nerve terminals are observed and many of them make axosomatic synaptic contacts. The exact nature of these nerve endings as well as the projection of these enkephalin-containing cells remain to be established.

Histochemical and pharmacological analysis of catecholaminergic projections to the perifornical hypothalamus in relation to feeding inhibition

Three techniques, namely, midbrain lesions, fluorescence histochemistry and brain cannulation, were used in combination to analyze catecholamine (CA) projections to the perifornical hypothalamus and their function in suppressing feeding behavior. The convergence of evidence indicates that the ventral adrenergic component of the central tegmental tract and dopaminergic projections from midbrain A8 and possibly A9 cell groups contain the crucial fibers which innervate the perifornical hypothalamus and mediate CA suppression of feeding behavior. The primary evidence for this conclusion is that ventral tegmental electrolytic or 6-OHDA lesions which damaged specifically these fibers invariably caused: (1) a marked reduction of CA varicosities in the perifornical area; (2) a strong reduction or loss of the anorectic response produced by perifornical injection of the presynaptically acting drugs amphetamine and mazindol; and (3) a potentiation of the anorectic response produced by perifornical injection of the CA receptor agonists dopamine and epinephrine. Lesions in the dorsal midbrain tegmentum, which left intact the ventral adrenergic and dopaminergic fibers but damaged the compact dorsal tegmental bundle, the dorsal fibers of the central tegmental tract and the medial and lateral tegmental CA radiations, had no apparent effect on the responsiveness of the perifornical hypothalamus to CA drug stimulation, as well as on the CA fluorescence in that region. Lesions in the area of the dopaminergic A10 cells and the midline tegmental CA radiations actually potentiated the effectiveness of the anorexigenic drugs in the perifornical hypothalamus.

Mapping study of brain dopamine- and epinephrine-sensitive sites which cause feeding suppression in the rat

Central injections of dopamine (DA) or epinephrine (EPI) have been found to suppress feeding behavior in hungry rats. In the present study, 24 different brain areas, in 299 animals, were examined to localize the precise region of catecholamine (CA) sensitivity. Essentially all sites outside the hypothalamus, as well as in the medial portion of the hypothalamus, were relatively or totally unresponsive to DA or EPI. The area of greatest sensitivity for both agonists (where they yielded a 50--70% suppression of feeding) was found to be the perifornical region of the lateral hypothalamus, extending from the caudal aspect of the paraventricular nucleus to the caudal aspect of the ventromedial nucleus. Dorsal, lateral, or ventrolateral movement of the injection site away from the fornix and into the zona incerta or the lateral hypothalamic medial forebrain bundle area caused a dramatic reduction in the effectiveness of the CA. These findings are consistent with histochemical studies, which have shown the fornix to be surrounded by CA varicosities, and pharmacological studies, which have shown the perifornical region to be most sensitive to the anorexic effect of centrally injected amphetamine, which releases endogenous CA. It is suggested that the perifornical hypothalamus plays a role in the process of inhibiting food consumption in response to increased dopaminergic and adrenergic activity.

L-Dopa feeding suppression: effect on catecholamine neurons of the perifornical lateral hypothalamus

Injection of L-Dopa (0.8--200 nmoles) into the perifornical hypothalamus produced a dose-dependent suppression of feeding in hungry rats. This effect was positively correlated in magnitude with the same effect produced by the catecholamine agonists dopamine and epinephrine, and by the catecholamine-releasing drug amphetamine. L-Dopa's action was partially antagonized by separate injections of the dopaminergic blocker haloperidol (58% blockade) and the beta-adrenergic blocker propranolol (38% blockade). Combined injections of these two antagonists produced a 90% blockade of L-Dopa's effect. Perifornical administration of the dopa decarboxylase inhibitors Ro 4-4602 and MK-486 was also shown to reverse L-Dopas feeding suppression, at doses that enhanced the effect of injected dopamine and epinephrine. On the basis of these findings, L-Dopa appears to suppress food consumption in part through increased catecholamine synthesis, specifically within dopaminergic and adrenergic neurons of the perifornical hypothalamic region.

Analysis of feeding suppression produced by perifornical hypothalamic injection of catecholamines, amphetamines and mazindol

The effects on feeding of perifornical hypothalamic injection of catecholamines, amphetamines and mazindol were examined in hungry rats. In pargyline-pretreated subjects, both dopamine and epinephrine significantly suppressed food intake, at doses as low as 31 ng for dopamine and 150 ng for epinephrine (the latter injected with an alpha-adrenoceptor blocker). This effect was reliably strengthened by inhibiting catecholamine deamination or presynaptic catecholamine uptake. Perifornical injections of amphetamine, mazindol, methamphetamine, and phenmetrazine also suppressed feeding. The magnitude of this effect in individual animals was positively correlated with the effect produced by catecholamine agonists. Moreover, this effect of mazindol was partially antagonized by perifornical injection of dopaminergic and beta-adrenoceptor blockers. The effects of amphetamine and epinephrine were abolished by these drugs, while dopamine's effect was selectively inhibited by the dopaminergic antagonist. Serotonergic antagonists produced no change. These findings lend support to the hypothesis that perifornical hypothalamic catecholamine neurons, through dopaminergic receptors and beta-adrenoceptors, are involved in inhibiting feeding behavior, as well as in mediating the anorexic action of the amphetamines and mazindol.