C-FOS AND N-NOS REACTIVE NEURONS IN RESPONSE TO CIRCULATING Phoneutria nigriventer SPIDER VENOM

RAPÔSO C. (1), ZAGO G.M. (1,2), MELO L.L. (3), CRUZ-HÖFLING M.A. (1)

(1) Dept Histology Embryology, IB, (2) Dept Pharmacology, FCM, UNICAMP, Campinas, SP, (3) Lab Neuropsychopharmacology, São Francisco Univ, Bragança Paulista, SP, Brazil

Drugs and neurotoxins activate specific neural circuits by increase or decrease neurotransmitters release (e.g. nitric oxide, NO), and by induction of immediate early genes (e.g. FOS). P. nigriventer venom (PNV) was shown to impair the microtubule-dependent transcellular barrier of blood-brain interface, but no visible alterations were seen in central neuronal cells. For clearing the central action of PNV we assess the distribution of highly activated neurons in the subcortical and cortical areas of the CNS 2h after intravenous injection of PNV, using FOS immunolabeling and the production of NO by immunodetection of neuronal nitric oxide synthase (nNOS). Male Wistar 7–10-week-old rats were divided into: a) rats received 0.5 ml 850g/Kg PNV in the tail vein; b) rats were given 0.5ml 0.9 % saline solution; c) non-envenomed rats were kept intact until sacrifice (n=5/group). Acoustic, visual, and olfactory stimuli in the room were kept to a minimum, since FOS is a sensible marker. The PNV sublethal dose produced in the rats excitatory signs of salivation, lachrymation, tremors, flaccidity followed by spastic paralysis of the hindlimbs and convulsion. After anesthesy and perfusion fixation, the brain was removed and freezed. 30m cryostat sections were serially collected at a 600m distance for free-floating immunohistochemical reaction. FOS positive neurons predominate at motor-related areas: dorsolateral and ventral periaqueductal gray matter, frontal and parietal motor cortex, periventricular thalamic nucleus, and acute-stress-related ones: periventricular thalamic nucleus and lateral septal nuclei. nNOS positive neurons predominate at the periventricular thalamic nuclei, followed by dorso lateral periaqueductal gray matter and parietal cortex motor area. We conclude that those motor- and acute stress-related areas may represent a key-neuronal pathway in PNV envenoming mechanism. The coincident localization of nNOS and FOS in same anatomic regions suggests a modulatory role of NO in the toxicant stimulus.

KEYWORDS: brain, toxin, convulsion

CORRESPONDENCE TO: hofling@unicamp.br

FINANCIAL SUPPORT: FAPESP, CNPq, FAEPEX-UNICAMP