Showing papers by "Harvey J. Grill published in 1997"

Effect of oral versus gastric delivery on gastric emptying of corn oil emulsions

Abstract: Several studies have shown that fluids delivered to the stomach tend to empty more rapidly than when ingested by mouth. To better characterize the “delivery route effect” for corn oil, rats receive...

Contribution of caudal brainstem to d-fenfluramine anorexia

Abstract: Of the central 5-HT substrates that may mediate the anorexic actions of systemically administered d-fenfluramine (d-FEN), those in the forebrain have received the most attention. As a counterpoint to this forebrain focus, we evaluated the contribution of caudal brainstem substrates to the anorexic action of d-FEN. Two experimental protocols were employed. In one we compared the feeding response (intra-oral intake of 12.5% glucose) of intact and chronic supracollicular decerebrate (CD) rats to systemic administration of d-FEN. In the other, d-FEN was administered via fourth intracerebroventricular (ICV) injection to determine whether a dose-related suppression of intra-oral intake could be obtained. A dose-dependent suppression of intra-oral intake was obtained in the CD rat treated with d-FEN (0–8 mg/kg, delivered IP 20 min before testing). The threshold dose was two to three times higher in CD rats than in their intact controls, but the dynamic range of the dose-response curves of the two groups were overlapping with similar slopes of decline and with comparable maximal intake suppression. Fourth ICV administration of d-FEN in the intact rat yielded a dose-related suppression of intra-oral intake. Intake was also suppressed by fourth ICV d-FEN (30 mg) when rats drank 12.5% glucose solution from a spout. The reduced intra-oral intake following fourth ICV d-FEN treatment was partially attenuated by the systemic administration of the serotonin antagonist metergoline (0.4 mg/kg; IP). The CD results demonstrate the sufficiency of caudal brainstem receptors in mediating intake suppressive responses to systemic d-FEN. The fourth ICV results suggest further that 5-HT receptors in the caudal brainstem play a significant role in normal meal size control in the neurologically intact rat.

Intake suppression after hepatic portal glucose infusion: all-or-none effect and its temporal threshold.

Abstract: The effects of hepatic portal infusions of isotonic glucose on glucose intake (3.2%) were evaluated with use of the intraoral intake test, which, unlike traditional tests, permits delivery of portal infusions in explicit temporal relationship to intake onset in nondeprived rats. Continuous or discontinuous portal infusions (0.1 ml/min) of isotonic glucose or saline were initiated 0, 30, 60, or 120 min before meal onset. Jugular infusions of isotonic saline or glucose and portal infusions of isotonic saline were without effect. For all effective portal glucose infusions, intake was suppressed by approximately 30% of baseline values. Because the duration (and quantity) of effective portal glucose infusions varied by a factor of 10, we conclude that intraoral intake suppression under these conditions is all or none in nature. Whether an intake suppression was obtained depended more on when the infusion was delivered than on how much was infused. Thus 1.5 ml of isotonic glucose infused between 60 and 45 min before the intake test was effective, whereas 3.0 ml infused for the 30 min before intake was without effect. These results suggest that the liver participates in the control of future intake but not in the termination of an ongoing meal. The temporal requirement for intake suppression should be considered in analyses of the metabolic, hormonal, and/or neural mechanisms that underlie the liver's contribution to intake control.

Reward comparison in chronic decerebrate rats

Abstract: The simultaneous contrast paradigm was used to evaluate responsiveness to a low (0.05 M) and a high (0.5 M) concentration of sucrose under two conditions in intact and chronic decerebrate rats. In one condition the low concentration was presented on one day and the high concentration on another. In the other condition presentation of the two concentration was alternated within the same daily session. In each case there was a total of 40 trials/day during which the stimulus was delivered intraorally for 2 s at a rate of 1.5 ml/min with a 30-s intertrial interval. The results showed that the intact rats always licked more for the high than for the low concentration of sucrose but that the magnitude of the effect was larger when given the opportunity to compare the two concentrations within the same daily session. The decerebrate rats produced a similar pattern, but the concentration effect was evident only when the stimuli were alternated within the same daily session. These data stand as the first evidence that the isolated caudal brain stem is adequate for the expression of a behavior that depends on comparison processes involving short-term memory.

Gastric branch vagotomy and gastric emptying during and after intragastric infusion of glucose

Abstract: The effect of gastric branch vagotomy (GVX) on the gastric emptying of glucose was evaluated during two phases of emptying control: as the stomach fills and in the postload period. GVX and control ...