Interaction of brain stimulation and conditioned taste aversion: Osmotically induced drinking

Role of dopaminergic system(s) in mediation of the behavioural effects of bombesin

To test the effects of dopamine receptor blockade on bombesin (BN)-induced behavioural changes, adult male Sprague-Dawley rats were administered fluphenazine (0.01, 0.025, 0.1, 0.25 mg/kg, IP) followed 30 min later by BN (1 micrograms in 5 microliter) or saline (5 microliter) intracerebroventricularly (ICV). Subsequent behavioural effects were monitored in chambers equipped with strategically located infrared beam grids, controlled by a microprocessor. The following behaviours were monitored: locomotor activity (distance traversed), floor activity (horizontal or lateral displacement) and rearing activity (frequency of vertical displacement extending 17.8 cm above the floor). At all but the highest dose (0.25 mg/kg, which suppressed floor activity), fluphenazine failed to significantly alter any of the behavioural parameters monitored. Whereas at doses of 0.025 or lower, fluphenazine failed to alter BN-induced behavioural output, at doses of 0.1 mg/kg or greater, it significantly blocked the behavioural effects BN. In the next experiment, dopamine neurons of adult male Sprague-Dawley rats were lesioned using 6-hydroxydopamine (6-OHDA) (250 micrograms/10 microliter, ICV). The 6-OHDA and sham-lesioned (control) rats were administered BN (0.001, 0.01, 0.1 or 1.0 microgram, ICV) and their behaviour monitored. In the control animals, BN stimulated locomotor, floor and rearing activity in a dose-dependent manner. However, these behavioural effects of BN were markedly attenuated or absent in the 6-OHDA-lesioned animals. These data further support our contention that centrally administered BN may mediate its behavioural effects, through the dopaminergic system(s).

Ceruletide acts in the abdomen, not in the brain, to produce satiety

Ceruletide (caerulein), a decapeptide extracted from the skin of the frog, Hyla caerulea, is very similar in structure to the C-terminal octapeptide of cholecystokinin (CCK-8). Although ceruletide and CCK-8 act through similar or identical receptors to produce the same visceral effects, previous studies in the rat suggested that peripherally administered ceruletide acted directly on the ventromedial hypothalamic (VMH) area to decrease food intake, but peripherally administered CCK-8 acted at a vagally innervated abdominal site to decrease food intake. Since it is unprecedented for these two peptides to produce the same effect by acting at different sites, we investigated the site of action of ceruletide's satiety effect in the rat and compared it to the site of action of CCK-8. The major results were: (1) intraperitoneal administration of ceruletide and CCK-8 inhibited food intake, but intraventricular administration did not; (2) the satiety effect of ceruletide and CCK-8 was not changed by bilateral lesions of the VMH; and (3) the satiety effect of ceruletide and CCK-8 was abolished or markedly reduced by bilateral abdominal vagotomy. We conclude that ceruletide acts at the same vagally innervated abdominal site to produce satiety as CCK-8 does and that neither peptide acts directly on the VMH area.

Behavioral effects of bombesin administration in rats

Bombesin (BBS, 0.1-4.0 micrograms) administered to the lateral cerebral ventricle (IVT) of rats decreased food intake and feeding behavior. Grooming behavior increased and resting behavior decreased as doses greater than or equal to 0.01 microgram. IVT BBS (4.0 micrograms) caused greater suppression of food-deprivation-induced food intake and feeding behavior than the same dose and volume administered intraperitoneally (IP). After IVT BBS, rats displayed more grooming and less resting than normal, but after IP BBS, rats displayed a normal frequency of grooming and more resting. IVT BBS (greater than or equal to 0.01 microgram) also decreased drinking behavior, and drinking-associated feeding, and suppressed (greater than or equal to 0.1 microgram) water-deprivation-induced water intake. When neither food nor water was present, non-deprived rats displayed increased grooming and decreased resting after IVT BBS (1.0 microgram). The results show that IVT BBS inhibits feeding markedly, but the inhibition of feeding by IVT BBS does not resemble normal satiety or the effect of IP BBS because the central inhibition of feeding is always accompanied by excessive grooming and little resting. Furthermore, since IVT BBS decreases drinking at a dose lower than that required to reduce food intake, and IP BBS does not, the specific satiety effect of IP BBS on feeding cannot be mediated solely by increasing bombesin in the cerebrospinal fluid.