Role of instrumental learning in tolerance to cathinone hypophagia.

Abstract

The effects of dl-cathinone on milk intake and motor activity were investigated in bottle- and cannula-fed rats. Acute injections of cathinone produced dose-dependent increases in activity in both groups but only produced decreased intake in bottle-fed rats. With chronic injections, tolerance to the suppression of intake developed in the bottle-fed group, accompanied by decreased activity. After the tolerance phase, switching from bottle to cannula feeding produced further increases in intake, whereas switching from cannula to bottle feeding produced decreased intakes. These results suggest that (a) cathinone suppresses intake by inducing locomotion and stereotypy, which interfere with the appetitive phase of feeding, and (b) tolerance to drug-induced hypophagia involves learning to suppress such movements, as proposed by the instrumental learning model.

Blood–Cerebrospinal Fluid Barrier

“…Stereotypy is not incompatible Behavioral Tolerance B 215 B with milk drinking that only requires swallowing milk that is delivered intraorally. One approach for testing the learning hypothesis of behavioral tolerance is to compare the effects of an anorectic stimulant drug on milk swallowing versus milk drinking, e.g., Wolgin and Munoz (2006). You would hypothesize that stereotypy induced by a stimulant would disrupt milk drinking, but not milk swallowing such that tolerance would only be observed in the rats that must learn to approach and lick the fluid spout in the presence of drug-induced stereotypy.…”

Expression of c-fos mRNA in the basal ganglia associated with contingent tolerance to amphetamine-induced hypophagia

“…Such “contingent tolerance” is mediated by the learned suppression of stereotyped head movements, which interfere with feeding. When behavioral interference from stereotypy is bypassed by delivering milk directly into the mouth through intraoral cannulas, rats show little hypophagia to psychostimulants [61,64,66]. This demonstrates that food remains reinforcing and, therefore, can serve as an incentive for learning to suppress stereotypy.…”