NITRIC-OXIDE MODULATES IN-VITRO INTRINSIC OPTICAL SIGNAL AND NEURAL ACTIVITY IN THE NUCLEUS-TRACTUS-SOLITARIUS OF THE RAT

Nitric oxide (NO) is a never neurotransmitter with important cardiores piratory functions. To determine the functional topography of NO in a brainstem preparation, extracellular and intrinsic optical signal reco rdings were simultaneously acquired from a 300 mu m coronal brainstem slice at the level of the obex. During control conditions, spontaneous spike activity in the nucleus tractus solitarius (NTS) was 6.2 +/- 1. 4 Hz. When the competitive NOS inhibitor, L-NAME, was applied to the b ath (1 mM), spike activity either ceased or was markedly reduced in fr equency (1.2 +/- 0.7 Hz; n = 7; P < 0.01). The decrease in activity wa s reversed when the NOS substrate L-arginine (L-Arg) was added to the bath (9.4 +/- 1.8 Hz; P < 0.04). Concurrent intrinsic optical signal i maging of the slice preparation consistently revealed coincident decre ases in activity within the NTS with L-NAME (Delta T/T: -2.4 +/- 0.9%; P < 0.02), and increases with L-Arg (+2.1 +/- 0.8%; P < 0.04). Such c hanges were absent in other regions such as the hypoglossal nuclei or area postrema. We conclude that in this brainstem region, NO modulatio n of neuronal activity is primarily circumscribed to the NTS. (C) 1997 Elsevier Science Ireland Ltd.