Additive effects of ciliary neurotrophic factor and testosterone on motoneuron survival; differential effects on motoneuron size and muscle morphology.

Testosterone and ciliary neurotrophic factor (CNTF) each enhance motoneuron survival in the spinal nucleus of the bulbocavernosus (SNB) of newborn rats. Here we directly compared the effects of CNTF and testosterone, alone and in combination, on SNB motoneuron number, SNB cell size, and morphology of the levator ani (LA) target muscle. Female rat pups were treated daily from postnatal day 1 through 6 (P1-P6) with recombinant human CNTF (hCNTF), testosterone propionate (TP), both hCNTF and TP, or neither. Effects of treatment were assessed on P7. TP and hCNTF each increased the number of SNB motoneurons and did so to a similar degree. Females treated with both hCNTF and TP had significantly more SNB cells than those receiving either hCNTF or TP alone. TP administered from P1 to P6 also increased SNB motoneuron size on P7. In contrast, hCNTF alone did not significantly affect SNB cell size, and hCNTF in combination with TP antagonized the effect of TP on motoneuron size. TP also increased LA muscle fiber number and LA fiber size, whereas hCNTF did not significantly influence LA muscle morphology in this study. Immunohistochemistry established that virtually all SNB motoneurons of both males and females express the CNTF alpha receptor (CNTFRalpha) between embryonic day 20 and postnatal day 6. Thus, effects of TP and hCNTF on SNB motoneuron survival were additive, and increases in motoneuron survival were dissociated from changes in target muscle morphology in hCNTF-treated animals. SNB motoneurons express CNTFRalpha perinatally and are therefore potential direct sites of hCNTF action.