Effects of hippocampal damage on reward threshold and response rate during self-stimulation of the ventral tegmental area in the rat

Abstract

Kelley, Stephen P. and Mittleman, Guy (1999) AbstractThe main purpose of this study was to explore the role of the hippocampus in motivated behavior. Rats with bilateral excitotoxic lesions of the hippocampus and controls were trained to lever press for electrical stimulation of the ventral tegmental area. Rate-intensity functions were generated from an ascending and descending series of current intensities. Lesion-induced changes in sensitivity to reward were distinguished from enhancements in motor output by calculating reward thresholds and maximal response rates from the rate-intensity functions. Rats with hippocampal damage showed lower reward thresholds and higher maximal response rates than controls. These results provide further evidence of hippocampal modulation of the nucleus accumbens, suggesting that lesions of this structure enhance sensitivity to reward and increase motor output.

Motivational Responses to Natural and Drug Rewards in Rats with Neonatal Ventral Hippocampal Lesions An Animal Model of Dual Diagnosis Schizophrenia

“…However, adult rats subjected to bilateral ventral hippocampal lesions show resistance to extinction from food-reinforced behaviors (Clark et al 1992), an effect that differs from neonatal hippocampal lesions in the present study. Adult hippocampal lesions also decrease food neophobia, and increase the reinforcing effects of sucrose and brain stimulation reward (Burns et al 1996;Kelley and Mittleman 1999;Schmelzeis and Mittleman 1996), consistent with the effects of neonatal lesions on sucrose and cocaine reinforcement in the present study. In contrast, disruption of hippocampal theta waves of adult rats promotes extinction from brain stimulation reward (Holt and Gray 1983), suggesting that hippocampal activity is involved in bi-directional regulation of motivated behavior under reinforcement and extinction conditions.…”

“…Spatial learning may be more dependent on dorsal rather than ventral hippocampal regions (Moser and Moser 1998;Vann et al 2000), whereas instrumental learning involves stimulus-response associations that probably are more dependent on basal ganglia structures (Hollerman et al 2000). One possibility is that reward-related learning involving ventral striatal mechanisms may be "disinhibited" by hippocampal lesions, as suggested previously (Burns et al 1996;Chambers et al 2001;Kelley and Mittleman 1999;Schmelzeis and Mittleman 1996). Another consideration is that stimulus-response contingencies learned during acquisition may utilize different neural substrates than those involved in extinction of these learned contingencies, as suggested for acquisition and extinction of Pavlovian associations (Lattal and Abel 2001).…”

Movements of exploration intact in rats with hippocampal lesions

“…Such behavioral persistence is symptomatic of hippocampal rats in many test situations [31, Table A14]. For example, hippocampal rats display faster running speeds in maze tests [5], show higher peaks of activity in tests of circadian activity [19,51], are more responsive in tests of amphetamine induced locomotion [52,53], schedule induced behavior [4,38,39], adjunctive behavior [26], and to administration of electrical brain stimulation [24].…”

Rewarding effects of ethanol and cocaine in µ opioid receptor-deficient mice

“…This hypothesis was underlined by lesion experiments. Morphine rewarding properties were modulated by frontal cortical and hippocampal lesions (Glick and Cox 1978;Kelley and Mittleman 1999).…”