Modulation by GABA transmission in the substantia nigra compacta and reticulata of locomotor activity in rats exposed to high pressure.

Helium pressure of > 20 bar causes neuroexcitatory changes referred to as the high pressure neurological syndrome. In rodents, symptoms include locomotor and motor activity (LMA), myoclonia and, at greater pressure, convulsions. We studied the effects of the GABA reuptake inhibitor nipecotic acid, the GABA transaminase inhibitor gamma-vinyl-GABA (GVG), the GABAA receptor agonist muscimol, and the GABAB receptor agonist baclofen. Whatever the drug used, bilateral administration in the substantia nigra reticulata (SNR) or in the substantia nigra compacta (SNC) showed no significant effects on myoclonia. In contrast, administration in the SNR of nipecotic acid, GVG, and baclofen resulted in a significant decrease of LMA; administration of muscimol in the SNR increased LMA. No significant effect was seen when drugs were injected in the SNC. These results suggest that changes in GABA transmission in the SNR, but not in the SNC, play a crucial role in the control of motor activity and the regulation of movement.