NO VOLTAMMETRIC DETECTION IN THE RAT-BRAI N - VARIATIONS OF THE SIGNAL THROUGHOUT THE SLEEP-WAKING CYCLE

Nitric oxide (NO) is synthesized in the neurons by constitutive NO syn thase (NOS). Within given neuronal sets, this enzyme is colocalized wi th different other neurotransmitters such as, Sor example, GABA, aceth ylcholine or serotonin. Our attention has been focused on the fact tha t serotoninergic neurons, well known for their involvement in sleep tr iggering and maintenance, synthesize also NO. In order to evaluate the modalities of release of this compound throughout the rat sleep-wakin g cycle, we prepared a sensor allowing its specific detection in freel y moving animals. The active part of this sensor is a carbon fiber (ph i = 30 mu m) successively coated with porphyrin nickel and nafion. In vitro, together with differential normal pulse voltammetric measuremen ts, it allows the detection of a 650 mV signal varying linearly in NO solutions ranging from 5.10(-7) to 10(-4) M. At physiological concentr ations, L-arginine, L-citrulline, nitrites and nitrates do not yield a signal at 650 mV. Similarly, the compound administered to the animals , hydroxylamine, L-arginine p-nitroanilide (L-ANA and L-N omega-nitro arginine methyl ester (L-NAME) are not electroactive at 650 mV. L-ANA and L-NAME, also appear to be trapping agents for NO while leaving ele ctrochemical properties of the sensor untouched In vivo, in the fronta l cortex of the anesthetized rat, a signal is measured at 650 mV. The administration of hydroxylamine (40 mg/kg, ip.) induces a 100% increas e in its height. The administration of L-ANA (100 mg/kg, i.p.) produce s its complete disappearance within 50 min. Finally, the administratio n of L-NAME (100 mg/kg, i.p.) is without effect. This last aspect migh t be dependent upon the inability of L-NAME to cross the blood brain b arrier On the contrary the increase in the signal height obtained with hydroxylamine and its disappearance with L-ANA support that it NO. In vivo, and in animals also equipped with polygraphic electrodes, the s ignal measured in the same area of the cortex exhibits the highest hei ght during the waking state and decreases during either slow-wave slee p (-6%) or paradoxical sleep (-9%). These mild variations might repres ent the mean of several NO sources (cortical GABAergic interneurons, c holinergic and serotoninergic axonal nerve endings), each of them vary ing differently throughout the sleep-waking cycle.