Differential modulatory effects of cocaine on marmoset monkey recognition memory.

Acute and repeated exposure to cocaine alters the cognitive performance of humans and animals. How each administration schedule affects the same memory task has yet to be properly established in nonhuman primates. Therefore, we assessed the performance of marmoset monkeys in a spontaneous object-location (SOL) recognition memory task after acute and repeated exposure to cocaine (COC; 5mg/kg, ip). Two identical neutral stimuli were explored on the 10-min sample trial, after which preferential exploration of the displaced vs the stationary object was analyzed on the 10-min test trial. For the acute treatment, cocaine was given immediately after the sample presentation, and spatial recognition was then tested after a 24-h interval. For the repeated exposure schedule, daily cocaine injections were given on 7 consecutive days. After a 7-day drug-free period, the SOL task was carried out with a 10-min intertrial interval. When given acutely postsample, COC improved the marmosets' recognition memory, whereas it had a detrimental effect after the repeated exposure. Thus, depending on the administration schedule, COC exerted opposing effects on the marmosets' ability to recognize spatial changes. This agrees with recent studies in rodents and the recognition impairment seen in human addicts. Further studies related to the effects of cocaine's acute×prior drug history on the same cognitive domain are warranted.

Temporal and dose-dependent differences in simultaneously-induced cocaine hypervigilance and conditioned-place-preference in marmoset monkeys.

BACKGROUND: Although repeated exposure to cocaine can induce hypervigilance and conditioned-place-preference (CPP) in nonhuman primates (NHPs), more detailed analyses are warranted since the outcome can be influenced by different factors. METHODS: We evaluated in marmoset monkeys (Callithrix penicillata): (1) the onset time-course and dose-dependent (3 or 7mg/kg; i.p.) profile of their hypervigilance and CPP response to repeated cocaine exposure; (2) whether these behavioral measures are still detectable after a 15-day no-drug period; (3) the relationship between their hypervigilance and CPP responses; and (4) if these behavioral changes correlate with pre- and post-drug behaviors (i.e., vigilance, locomotion, exploration), and/or first response to cocaine. RESULTS: Hypervigilance had a slow-onset, was only effective with the 7mg/kg dose of cocaine, lacked long-term conditioned effects and was not related to the initial cocaine response or pre-drug behaviors, regardless of the dose tested. CPP was promptly induced with the 3 and 7mg/kg doses, and had a dose-dependent long-term effect and negative correlation with pre-drug locomotion and exploration. Hypervigilance and CPP were not significantly correlated. CONCLUSIONS: Although hypervigilance and CPP were induced, they had distinct temporal and dose-dependent profiles, and were not equally co-expressed in the same marmoset. Also, in NHPs, pre-drug locomotion and exploration were predictive of the low-dose CPP response.