Muscarinic mediation of the urethro genital reflex in spinal cord-transected rats

The effects of muscarinic receptor stimulation were tested on the urethro g enital reflex (UGR) in anesthetized and spinal cord-transected rats. Drugs were applied directly to the spinal cord. The elechomyographic activity (EM G) of the bulbospongiosus (BS) muscle was used for recording UGR. In six an imals BS as well as soleus, posterior biceps or peroneus tertius muscle EMG was recorded simultaneously. Muscarine (5, 10, 20, 50 and 100 mug) was app lied in 22 animals after cutting L6-S1 dorsal roots. Some observations were made on another six animals, to which an extensive bilateral dorsal rhizot omy (L3-S2) was performed. Rhythmic bursts of similar frequency and size to those seen during UGR were found in BS muscle a few minutes after muscarin e application. No rhythmic bursting was found on the hindlimb muscles, but exclusively on BS muscles. The effects of homatropine (25, 50, 100 and 200 mug), an acetylcholine muscarinic receptor antagonist, were tested in 21 ra ts after UGR was elicited three times at low stimulation intensity (7 mm Hg ). Homatropine produced two effects: (i) A significant increase in the late ncy of UGR. (ii) A facilitation of UGR inhibition. In view of these results it can be speculated that muscarinic receptor stimulation is involved in t he elicitation of UGR. (C) 2000 Elsevier Science Inc. All rights reserved.