MODULATION OF SENSORY AND EXCITATORY AMINO-ACID RESPONSES BY NITRIC-OXIDE DONORS AND GLUTATHIONE IN THE VENTROBASAL THALAMUS OF THE RAT

Nitric oxide has been identified as having a role in synaptic transmis sion in the central nervous system. In the ventrobasal complex of the thalamus (VB), the precursor of nitric oxide synthesis, L-arginine, ca uses enhancement of excitatory amino acid responses and somatosensory transmission. In this study, the nitric oxide donors sodium nitropruss ide, 3-morpholinosydnonimine and S-nitrosoglutathione were applied to VB relay neurons by iontophoresis and responses of single neurons were recorded extracellularly. Sodium nitroprusside caused selective inhib ition of responses to NMDA, probably mediated by a by-product, ferrocy anide, as described in previous studies. 3-Morpholinosydnonimine and S -nitrosoglutathione, however, caused potentiation of responses to sens ory stimuli and to excitatory amino acids. In contrast, glutathione in both its reduced and oxidized forms reduced such responses, and this suggests that the potentiating effect of S-nitrosoglutathione could be due to nitric oxide production. These results are consistent with the hypothesis that nitric oxide may have a local modulatory role in the thalamus. Data are presented which suggest that glutathione may have a negative modulatory influence on neurotransmission and excitatory ami no acid responses in the ventrobasal thalamus.