Thyrotropin-releasing hormone(TRH) and its receptors are widely distributed throughout the hippocampus. It plays some role in neurotransmission and neuromodulation and may affect on learning and memory functions. In the present study the effects of intrahippocampal microinjections of TRH(1,3 and 10?g/?l) on the trace classical conditioning of the rabbit,s eyeblink were examined. Five minutes before starting any training sessions, 1 ?l of TRH solution was injected through an implanted cannula into the CA1 area of hippocampus. The results indicate that TRH, dose dependently, increased the percentage of conditioned responses and shortened the latency of responses, compared with those in the control group. Therefore, it seems that TRH facilitates eyeblink trace conditioning and it may have an improving action on learning and memory retention
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