Neuroplasticity in Spinal Circuits Mediated by Sexual Experience and Cerebellar Lobules

We aimed to determine whether sexual experience modulates the soleus H-reflex in male rats and to assess the specific contribution of vermis lobules 6a and 7 to cerebellar-dependent spinal plasticity.

Thirty-six male Wistar rats were divided into sexually inexperienced (SI) and sexually experienced (SE) groups and assigned to one of three cerebellar conditions: intact control, lobule 6a lesion, or lobule 7 lesion. SE rats underwent repeated mating sessions until they achieved efficient copulatory performance. Subsequently, targeted electrolytic lesions were made, and electromyographic recordings of the soleus H-reflex were obtained under urethane anesthesia to quantify H-wave amplitude and temporal parameters.

The global linear mixed model yielded no significant main effects of sexual experience, cerebellar condition, or their interaction on H-wave amplitude. Planned contrasts revealed a near-significant trend toward higher H-wave amplitude in sexually experienced intact animals compared with inexperienced controls (p = 0.061, Cohen's d = 0.592, 95% CI [-1.44, 0.04] V), and significant amplitude reductions following lobule 6a (p = 0.029, d = 1.450, 95% CI [0.13, 2.33] V) and lobule 7 (p = 0.002, d = 2.256, 95% CI [0.74, 3.08] V) lesions specifically in sexually experienced animals. Neither sexual experience nor lesions significantly affected H-wave latency or duration, suggesting that modulation primarily targets synaptic excitability rather than axonal conduction. M-wave latency showed a significant effect of sexual experience (p = 0.026, d = 1.405, 95% CI [0.03, 0.45] ms).

Sexual experience appears to be associated with cerebellar-dependent modulation of soleus H-reflex excitability; lobules 6a and 7 of the cerebellar vermis contribute to this effect specifically in experienced animals. Shorter M-wave latency in experienced animals suggests parallel peripheral motor reorganization. Adequately powered confirmatory studies are needed to characterize the mechanisms underlying this association.