Journal of Neuroscience, Vol 11, 3025-3033, Copyright © 1991 by Society for Neuroscience
Target-dependent hormonal control of neuron size in the rat spinal nucleus of the bulbocavernosus
I Araki, Y Harada and M Kuno
Department of Physiology, Kyoto University Faculty of Medicine, Japan.
The spinal nucleus of the bulbocavernosus (SNB) in the rat is a cluster of
sexually dimorphic motoneurons that innervate perineal muscles. In adult
male rats, the size of SNB neurons is reduced following castration, and
this effect is reversed by treatment with testosterone. However, androgen
receptors are present in the perineal muscles as well as in SNB neurons.
Therefore, it is not clear whether the neuronal size is regulated by direct
action of the hormone on SNB neurons or by a target-derived factor that may
be controlled via hormonal action on the innervated muscle. To address this
question, the peripheral (pudendal) nerve of SNB neurons on one side was
cut and united to the grafted soleus muscle, which lacks androgen
sensitivity. On the control side, the pudendal nerve was similarly cut but
was allowed to reinnervate the perineal muscles. The size of SNB neurons
was measured on both sides after a postoperative period of 10 weeks, during
which the animal had been castrated or treated with testosterone after
castration. The size of SNB neurons that had reinnervated perineal muscles
was reduced following castration and enlarged by testosterone treatment. In
contrast, the size of SNB neurons that had innervated the soleus muscle
remained unaltered in response to testosterone manipulation. It is
concluded that hormonal regulation of the size of SNB neurons in adult rats
is mediated by their target muscles.