The TRH analogue MK-771, increases acetylcholine release in hippocampus but not striatum of the conscious rat.

Hippocampal and striatal extracellular acetylcholine levels were monitored in conscious rats using the technique of intracerebral dialysis. Scopolamine (1 mg/kg, i.p.) resulted in a marked increase of acetylcholine release in both regions whereas the thyrotropin-releasing hormone (TRH) analogue MK-771 (2.5, 5 and 10 mg/kg, i.p.) only increased acetylcholine release in the hippocampus. The relevance of the present findings in relation to the known cognitive enhancing effects of TRH analogues is discussed.