Catecholaminergic and cholinergic agents and duration regulation of ICSS in the rat

Abstract

ICSS in the diencephalon and midbrain was measured in a preferred duration situation as a function of pulse frequency and various pharmacological agents. Response measures were ON Time, the mean time ICSS was maintained; OFF Time, the mean time between the offset of a train and the initiation of the next; the log-log slopes of these two measures as a function of frequency; and Percentage Time ON. In both a shuttlebox (N = 13) and in an operant chamber (N = 10), Haloperidol (0.050 and 0.075 mg/kg) consistently decreased Percentage Time ON by elevating OFF times without consistent effects were greater at lower frequencies in the shuttlebox. Phentolamine (5 and 10 mg/kg), tested with 9 sites in the shuttlebox and 10 sites in the operant chamber, also differentially increased OFF Times with consistently greater effects at low frequencies. Evidence was not found for regional selectivity in the action of phentolamine or haloperidol among middle levels of the median forebrain bundle (MFB), the dorsal hypothalamus, the posterior MFB and the substantia nigra. Scopolamine (0.25, 0.50, and 1.00 mg/kg, six sites) and propranolol (10 and 15 mg/kg, seven sites) produced no consistent effects. FLA-63 (10 and 25 mg/kg, eight sites) produced some disruptions of performance at low frequencies but was without consistent effects. The results are consistent with a model of ICSS which includes a reward maintenance process, insensitive to catecholaminergic agents, and an approach-facilitation process which involves α-noradrenergic and dopaminergic systems.