Axotomy dependent purinergic and nitrergic co-expression.

Different lines of evidence indicate that ATP and nitric oxide (NO) play key roles in mediating neuronal responses after cell damage. Purinergic and nitrergic interactions have been proposed in non neural tissues physiological functions and, in different experimental models of brain injury, both purinergic and nitrergic activations have been reported. The present study was planned to ascertain possible relations of these two systems after brain damage. Variations in the expression of the nitric oxide synthase neuronal isoform (nNOS) enzyme, and of two subunits of purinergic ionotrophic receptors (P2X) namely P2X(1) and P2X(2) in precerebellar stations after cerebellar lesion in rats were analyzed and compared. After the lesion nNOS positive cells presented a clear increment followed by a decrement. Conversely, nNOS negative cells presented a rapid decrement in the first postlesional weeks that continued less pronounced afterward. Postlesional nNOS activation was related with time course of P2X(1) and P2X(2) activations. The capacity of the same cells to express both nNOS and P2X markers was investigated immunocytochemically. Confocal microscopy of double immunofluorescence showed a high percentage of co-localization among P2X(1)/nNOS, P2X(2)/nNOS and P2X(1)/P2X(2) in olivary and pontine neurons. In addition, NeuN/P2X(1) and NeuN/P2X(2) double immunofluorescence showed P2X(1) expressed only in neurons while P2X(2) expressed by both neurons and glia. Present data demonstrate that after cerebellar lesion nitrergic and purinergic systems are activated with similar time courses in precerebellar stations. Further, time differences in the relation between nNOS expression and cell survival suggest a multifarious role of NO in mediating cell reaction to axotomy. The tight cellular co-localization and temporal co-activation of purinergic and nitrergic markers indicate possible interactions between these two systems also in the CNS.