DIFFERENCES IN THE CONNECTIVITY OF RAT PUDENDAL MOTOR NUCLEI AS REVEALED BY RETROGRADE TRANSNEURONAL TRANSPORT OF WHEAT-GERM-AGGLUTININ

Bilateral coordinated activation of pudendal motoneurons is an essenti al component of penile reflexes in male rats. However, little is known about the intraspinal organization of these reflexes. In the present study, retrograde transneuronal transport of wheat germ agglutinin (WG A) was used to examine the organization of spinal motoneurons and puta tive interneurons mediating penile reflexes in adult male rats. Inject ion of WGA into the ventral bulbospongiosus muscle resulted in direct retrograde labeling of motoneurons in the ipsilateral dorsomedial (DM) nucleus and transneuronal labeling of ipsilateral and contralateral D M motoneurons. Motoneurons in the ipsilateral and contralateral dorsol ateral (DL) nuclei were not labeled. WGA-labeled putative interneurons were observed bilaterally, primarily in the ventromedial spinal gray matter extending dorsally to the central canal and the dorsal gray com missure. The number of transneuronally labeled putative interneurons i ncreased with longer survival times. Injection of WGA into the ischioc avernosus muscle resulted in direct retrograde labeling of motoneurons in the medial subdivision of the ipsilateral DL nucleus. However, no WGA labeling was detected in motoneurons in the lateral subdivision of the ipsilateral DL nucleus, the contralateral DL nucleus, or the DM n uclei at any of the survival times studied (1-7 days). Only a small nu mber of transneuronally labeled putative interneurons was observed in the ventrolateral gray matter at longer survival times (3-7 days). Thu s, marked differences were observed between the DM and DL nuclei with respect to the transneuronal transport of WGA. These results are discu ssed with respect to the organization of the spinal circuits that medi ate pudendal motor reflexes. (C) 1995 Wiley-Liss, Inc.