TYROSINE AMELIORATES A COLD-INDUCED DELAYED MATCHING-TO-SAMPLE PERFORMANCE DECREMENT IN RATS

Exposure to cold stress has been shown to impair short-term, or workin g, memory which may be related to a reduction in brain catecholamines. Administration of the catecholamine precursor tyrosine may alleviate a cold-stress-induced memory impairment by preventing a deficit in bra in catecholamine levels. To test this hypothesis, eight rats performed a delayed matching-to-sample (DMTS) task at an ambient temperature of either 2-degrees-C (cold) or 22-degrees-C, following intraperitoneal administration of saline or tyrosine (50, 100 or 200 mg/kg). Rats admi nistered saline prior to 22-degrees-C exposure demonstrated a characte ristic delay gradient in which accuracy decreased as the delay interva l between sample and comparison stimuli increased from 1 to 16 s. Cons istent with previous research, and relative to 22-degrees-C exposure s essions, matching accuracy during 2-degrees-C exposure sessions was re duced, which is attributed to the effect of cold on short-term, or wor king, memory. In particular, during cold exposure sessions matching ac curacy was significantly reduced at the longer delay intervals, relati ve to matching accuracy at 22-degrees-C. Additional analysis of cumula tive matching errors within sessions showed that during exposure to co ld, errors occurred at a constant rate throughout the session, indicat ing rats' performance was equally debilitated by the stressor over the entire session. During cold exposure sessions, the higher doses of 10 0 and 200 mg/kg tyrosine significantly improved overall matching accur acy relative to saline, but did not completely reverse the effect of c old exposure, as overall matching accuracy did not increase entirely t o levels obtained at 22-degrees-C. A linear slope analysis of cumulati ve errors within cold sessions indicated that, relative to saline, the higher doses of tyrosine also significantly reduced errors, but did n ot reduce these errors to levels obtained during exposure to 22-degree s-C. It appears that supplemental tyrosine was effective in partially ameliorating the effects of cold stress on DMTS performance, possibly by preventing a cold-stress-induced reduction in brain catecholamine l evels.