Disturbance of meal patterning following nucleus accumbens lesions in the rat

Medial versus lateral parabrachial nucleus lesions in the rat: effects on mercaptoacetate-induced feeding and conditioned taste aversion

The two experiments of the present study examined the influence of bilateral electrophysiologically-guided ibotenic acid lesions of the medial (gustatory) and lateral (viscerosensory) subdivisions of the parabrachial nucleus (PBN) on lipoprivic feeding and on the acquisition of a conditioned taste aversion. In Experiment 1, mercaptoacetate (0, 400, 600, or 800 micromol/kg) failed to enhance food intake in normal rats maintained and tested on standard laboratory chow. In the same procedure, rats with lesions of the medial or lateral PBN consumed less food during baseline but nonetheless were sensitive to the orexigenic action of mercaptoacetate. In Experiment 2, both types of PBN lesions prevented acquisition of a conditioned taste aversion induced by the oral self administration of lithium chloride. The results suggest that PBN neurons essential for conditioned taste aversion are not involved in the mercaptoacetate-induced feeding of rats maintained and tested on standard laboratory chow.

Meal patterns of free feeding rats treated with clozapine, olanzapine, or haloperidol

Selective dopamine D(2) antogonists increase meal size and decrease the rate of feeding within a meal. Three experiments investigated the extent to which the atypical antipsychotics, clozapine and olanzapine, and the prototypical antipsychotic, haloperidol, affected meal size and feeding rate. Microstructural analyses of meal patterning were made over a range of drug doses administered to free feeding male Lister hooded rats. Haloperidol and clozapine produced a short-term increase in food intake. Haloperidol (0.05-0.2 mg/kg) enhanced meal size (maximal at 0.1 mg/kg) and reduced feeding rate (monotonic decrease with increasing dose). Neither clozapine (1-10 mg/kg) nor olanzapine (0.3-3 mg/kg) enhanced meal size, although both drugs produced similar reductions in feeding rate to haloperidol. These data suggest that enhancement of meal size may be correlated with a high level of extrapyramidal side effects in an antipsychotic drug. The absence of an increase in meal size by two atypical compounds suggests that the increase in body weight associated with clinical treatment with these drugs cannot be modelled by acute stimulation of meal size in the rat.

Changes in the microstructure of feeding after administration of enterostatin into the paraventricular nucleus and the amygdala

The effects of enterostatin (ENT) injected into the paraventricular nucleus (PVN) and the amygdala (AMYG) on the microstructure of feeding was studied by using an automated feeding apparatus. In rats adapted to a 6-h meal feeding regime, ENT reduced the size and duration of the first meal after injection in both the PVN and the AMYG. Similar effects were observed when ENT was given at the beginning of the dark cycle in rats fed ad libitum although the onset of feeding was also delayed in this situation. The number of meals and the size of subsequent meals was unaffected by ENT but the eating rate within the first meal was reduced after ENT injection into the AMYG of meal-fed rats. Enterostatin injected into the AMYG at a dose that suppressed feeding did not produce a conditioned taste aversion. ENT given centrally therefore appears to reduce food intake by delaying the initiation of feeding and/or advancing meal termination suggesting that it affects both appetite and satiation mechanisms.