Journal of Neuroscience, Vol 8, 4168-4176, Copyright © 1988 by Society for Neuroscience
Androgen regulates synaptic input to motoneurons of the adult rat spinal cord
A Matsumoto, PE Micevych and AP Arnold
Department of Anatomy, University of California, Los Angeles 90024.
Adult male rats (Sprague-Dawley) were castrated and implanted
subcutaneously with Silastic capsules containing testosterone or nothing.
Sham-castrated males served as controls. Four weeks following castration,
cholera toxin-horseradish peroxidase (CT-HRP) was injected bilaterally into
the bulbocavernosus muscles and animals were sacrificed 2 d later. The
spinal cords containing the spinal nucleus of the bulbocavernosus (SNB)
were dissected, processed with a modified tetramethylbenzidine (TMB) method
for visualization of retrogradely transported CT-HRP, and examined at the
ultrastructural level. Neuronal structures apposing the membranes of 150
TMB-labeled SNB neurons were analyzed by measuring the percentage of
somatic and proximal dendritic membranes covered by synaptic contacts,
synaptoid contacts, and neuron- neuron contacts. Most of the neuronal
structures in the control and experimental SNB motoneurons consisted of
synaptic contacts. The mean percentage of somatic and proximal dendritic
membranes covered by synapses 4 weeks after castration was reduced to
approximately 30% of those in control animals. However, treatment with
testosterone for 4 weeks after castration prevented this decline.
Castration and testosterone treatment also influenced the size and number
of synaptic contacts per unit length of somatic and proximal dendritic
membranes, and the incidence of neuron-neuron contacts and double synapses
onto SNB motoneurons. These results indicate that androgen is critical for
maintaining the organization of synaptic inputs to these spinal motoneurons
in adult male rats.
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