Ratio of excitatory and inhibitory synaptic processes in periaqueductal gray matter of the brain activated by the raphe magnus nucleus in a model of Parkinson's disease with hydrocortisone protection.

Background: The involvement of antinociceptive centers in neurodegeneration within the brain, particularly in Parkinson's disease (PD), which is accompanied by chronic pain, is not yet well understood. Methods: Electrophysiological recordings were conducted on 15 king albino rats across three experimental conditions: intact, a rotenone-induced PD model, and a PD model treated with hydrocortisone. Extracellular spike activity was recorded from 241 single neurons in the periaqueductal gray (PAG) in response to stimulation of the raphe magnus nucleus (RMG). Results: The PD model exhibited significant excitotoxicity in the recorded neurons, indicative of substantial neurodegeneration, which appeared to precede both depressor (tetanic depression [TD], post-tetanic depression [PTD]) and excitatory (tetanic potentiation [TP], post-tetanic potentiation [PTP]) post-stimulus effects. A mathematical analysis of pre- and post-stimulus activation frequencies revealed the following: in the PD model with hydrocortisone protection, compared to the unprotected PD model, the pre-stimulus activation frequency of PAG neurons during high-frequency stimulation of the RMG was reduced, bringing the values closer to normal levels. The post-stimulus activation frequency of PAG neurons in the treatment group also decreased, both in depressor (TD, PTD) and excitatory (TP, PTP) responses, approaching normal levels. Conclusions: These findings, in conjunction with the previous research on the protective role of hydrocortisone in depressive reactions, suggest that hydrocortisone effectively mitigates excitotoxicity and provides significant neuroprotection in the context of PD.