Decreased response of interneurons in the medial prefrontal cortex to 5-HT^sub 1A^ receptor activation in the rat 6-hydroxydopamine Parkinson model

This study examined the response of interneurons in the medial prefrontal cortex (mPFC) to 5-HT^sub 1A^ receptor agonist 8-OH-DPAT and change in expression of 5-HT^sub 1A^ receptor on glutamate decarboxylase 67 (GAD67)-positive neurons in rats with 6-hydroxydopamine (6-OHDA) lesions of the substantia nigra pars compacta (SNc). Systemic administration of 5-HT^sub 1A^ receptor agonist 8-OH-DPAT dose-dependently inhibited the firing rate of the interneurons at all doses tested in sham-operated rats. In 6-OHDA-lesioned rats, 8-OH-DPAT, at the same doses, also inhibited the firing rate of the interneurons, whereas the inhibition was significant only at a high cumulative dose. Furthermore, injection of 8-OH-DPAT into the mPFC inhibited the interneurons in sham-operated rats, while having no effect on firing rate of the interneurons in 6-OHDA-lesioned rats. In contrast to sham-operated rats, SNc lesion reduced the expression of 5-HT^sub 1A^ receptor on GAD67-positive neurons in the prelimbic cortex, a sub-region of the mPFC. Our results indicate that degeneration of the nigrostriatal pathway leads to decreased response of mPFC interneurons to 5-HT^sub 1A^ receptor activation, which attributes to the down-regulation of 5-HT^sub 1A^ receptor expression in these interneurons.[PUBLICATION ABSTRACT]