ONTOGENY OF ANDROGEN RECEPTOR IMMUNOREACTIVITY IN LUMBAR MOTONEURONS AND IN THE SEXUALLY DIMORPHIC LEVATOR ANI MUSCLE OF MALE-RATS

We documented the ontogeny of androgen receptor (AR) immunoreactivity for rat lumbar motoneurons of the sexually dimorphic motor pools, the spinal nucleus of the bulbocavernosus (SNB) and the dorsolateral nucle us (DLN), and for the sexually monomorphic retrodorsolateral nucleus ( RDLN). We also assessed the ontogeny of AR immunoreactivity in the rat sexually dimorphic levator ani (LA), which is a target muscle for SNB motoneurons. Lumbar spinal cords and LA muscles from gonadally intact males at ages postnatal days (P)7, P10, and P14 and as adults were in cubated with the rabbit antiserum PG-21. Half of the prc?pubertal male s (P7-P14) received 200 mu g of testosterone propionate (TP) 2 hours p rior to death to enhance immunodetection of ARs. We found that SNB mot oneurons developed AR immunoreactivity first and achieved adult levels by P10. In contrast, the number of RDLN motoneurons with An-immunopos itive nuclei during development remained well below the adult number. Development of AR immunoreactivity in tile DLN shared characteristics with both the SNB and the RDLN. AR immunoreactivity developed in some DLN motoneurons by P10, although the percentage of labelled motoneuron s remained below that in adulthood. Acute TP treatment significantly i ncreased the number of SNB motoneurons with AR-positive nuclei at P7. The LA showed a robust pattern of AR immunostaining from P7 to adultho od. Immunostaining was present only in nuclei and constituted only a s ubpopulation of the nuclei present in muscle. The present results conf irm and extend previous results based on steroid autoradiography and s teroid binding assays regarding regional and developmental differences in the expression of ARs. (C) 1997 Wiley-Liss, Inc.