The effect of castration on dopamine receptor sensitivity in male young rats: behavioral and neurophysiological studies.

The effect of castration on the sensitivity of dopamine (DA) receptor to low doses of apomorphine was investigated using drug discrimination task and neurophysiological recording of the firing rate of DAergic neuron in the substantia nigra pars compacta in male young Wistar rats. In the behavioral study, castration did not change the dose-response curve for apomorphine (ip) discrimination (the ED50 values in sham-operated and castrated animals were 45.2 and 47.1 micrograms/kg, respectively). In the neurophysiological study, the inhibitory effect of apomorphine (iv) on the firing rate of DAergic neuron in the substantia nigra pars compacta was significantly enhanced by castration (the ED50 values in sham-operated and castrated animals were 6.15 and 2.96 micrograms/kg, respectively). These results suggest that castration does not change post-synaptic DA receptor sensitivity, whereas it potentiates the sensitivity of pre-synaptic DA receptor to low doses of apomorphine in the substantia nigra.