Mesencephalic trigeminal neurons are innervated by nitric oxide synthase-containing fibers and respond to nitric oxide

In the present study we found that mesencephalic trigeminal (Mes-V) neurons of the rat are innervated by nitrergic fibers and that nitric oxide (NO) modifies the electrophysiological properties of these cells. Mes-V neurons were surrounded by a network of fibers that contained neuronal nitric oxide synthase (nNOS); these fibers gave rise to terminal-, bouton-like structures which ended in Mes-V cells bodies. These cells, which did not display nNOS-like immunoreactivity were immunoreactive to a cGMP antibody. By performing intracellular recordings in the adult rat brain slice preparation. the effects of diethylenetriamine/NO adduct (DETA/NO) applications were examined, DETA/NO induced a depolarization that averaged 2.2 mV (range: 1-6 mV) in nine of 22 neurons. In 15 of 22 neurons (68% of the cells), there was a decrease in current threshold from 0.74 to 0.60 nA (19%; P<0.001). The excitatory effects of DETA/NO were abolished by ODQ, a block-er of soluble guanylate cyclase. Input resistance (R-10) decreased in 80% of the cells from a mean of 24.8 to 20.6 MOmega (17%; P<0.001) and the membrane time constant (tau(m)) decreased from 7.5 to 5.6 ms (25% P<0.05). The 'sag' seen in the membrane response of these cells to current pulses was augmented during DETA/NO application. These findings indicate that there is a nitrergic innervation of Mes-V neurons and that these sensor), cells are target for NO that may act on them as an excitatory neuromodulator promoting the synthesis of intracellular cGMP. (C) 2002 Elsevier Science B.V. All tights reserved.