Analeptic activity produced by TRH microinjection into basal forebrain area of the rat

Earlier, Kalivas and Horita demonstrated that the analeptic effect of TRH was mediated in part by cholinergic neurons in the medial septum-diagonal band of Broca (MS-DBB). Since the MS-DBB constitutes part of the cholinergic basal forebrain system, the present study investigated whether the area designated as the n. basalis of Meynert (NBM) was also sensitive to TRH in producing an antipentobarbital effect. Saline or TRH (0.5 ..mu..l) was microinjected via bilateral stainless steel cannulae implanted stereotaxically into the NBM using the coordinates of Wenk et al. Accuracy of cannula placement was confirmed by histological examination. Rats treated with PB (40 mg/kg, i.p.) lost their righting reflex for 130 +/- 28 min. Intrabasalis injection of TRH (but not saline) in doses of 0.1-1.0 ..mu..g exerted analeptic activity as follows: 0.1 ..mu..g = 81 +/- 21 min; 0.5 ..mu..g = 65 +/- 19 min; 1.0 ..mu..g = 45 +/- 10 min. All of these doses exerted significant shortening of narcosis duration of pentobarbitalized rats. The analeptic effect of TRH was blocked by atropine pretreatment, indicating that it was mediated via cholinergic mechanisms. High affinity, sodium-dependent /sup 3/H-choline uptake by cortical synaptosomes prepared from these animals was also increased by TRH. These resultsmore » suggest that the cholinergic neurons of NBM are highly sensitive to TRH and contributes to the analeptic effect of TRH.« less