Intra-Accumbens Baclofen, But Not Muscimol, Increases Second Order Instrumental Responding for Food Reward in Rats

Abstract

Stimulation of either GABAA or GABAB receptors within the nucleus accumbens shell strongly enhances food intake in rats. However the effects of subtype-selective stimulation of GABA receptors on instrumental responses for food reward are less well characterized. Here we contrast the effects of the GABAA receptor agonist muscimol and GABAB receptor agonist baclofen on instrumental responding for food using a second order reinforcement schedule. Bilateral intra-accumbens administration of baclofen (220–440 pmol) stimulated responding but a higher dose (660 pmol) induced stereotyped oral behaviour that interfered with responding. Baclofen (220–660 pmol) also stimulated intake of freely available chow. Muscimol (220–660 pmol) was without effect on responding for food on this schedule but did stimulate intake of freely available chow. Unilateral administration of either baclofen or muscimol (220 pmol) induced similar patterns of c-fos immunoreactivity in several hypothalamic sites but differed in its induction in the central nucleus of the amygdala. We conclude that stimulation of GABAA or GABAB receptors in the nucleus accumbens shell of rats produces clearly distinguishable effects on operant responding for food.

Medial Nucleus Accumbens Projections to the Ventral Tegmental Area Control Food Consumption

“…It has been proposed that the NAc restricts intake via control over the motor behaviors that comprise a feeding response (Kelley et al, 2005). We find that the mNAc!VTA circuitry bidirectionally regulates instrumental actions, not solely food consumption actions, consistent with previous reports that pharmacological inhibition of the NAc increases operant responding for food (Pulman et al, 2012;Stratford and Wirtshafter, 2012b). However, we did not find a statistically significant effect on locomotion or activity alone.…”

Neural circuits of eating behaviour: Opportunities for therapeutic development

“…Obese humans chronically treated with the opioid antagonist GSK1521498 show a reduction in the responsiveness of the pallidum, probably including the VP, to images of high-calorie palatable foods as well as a reduction in a novel measure of motivational responding (Cambridge et al, 2013). Infusion of both GABA-A and GABA-B receptor agonists into the NAc shell leads to a profound activation of feeding behaviour (Stratford and Kelley, 1997), although only GABA-A receptor stimulation leads to enhanced instrumental responding for food (Pulman et al, 2012). One mechanism through which NAc (shell) stimulation of GABA receptors may affect feeding behaviour is by stimulating the population of orexin-expressing cells in the LH (Baldo et al, 2004).…”