Avaliação dos efeitos neurotóxicos da injeção intrahipocampal de três toxinas isoladas do veneno do escorpião Tityus bahiensis

Abstract

In Brazil, the scorpions of the genus Tityus belonging to the Buthidae family are the main responsible for serious accidents. Among them there are Tityus serrulatus and Tityus bahiensis; due to the high number of accidents they cause, they are considered of greater clinical importance. However, there are few studies on the action of the venom of T. bahiensis mainly in the central nervous system, even this venom presenting an important neurotoxic action. The neurotoxins are considered the main toxic elements of the venom, and among those already described, ion channels (sodium, potassium, calcium and chloride) are considered their main targets of action. The action of some of these toxins produces behavioral, electrographic and histopathological changes due to the alteration in the brain concentration of neurotransmitters. Therefore, the aim of our study was to evaluate the possible neurotoxic effects of three toxins from the venom of the scorpion on the hippocampus of rats, by evaluating the behavioral and electroencephaographic activity, and to evaluate possible changes on the levels of neurotransmitters and integrity of hippocampal neurons after intrahippocampal injection of the toxins. Thus, T. bahiensis scorpion venom was fractionated by gel filtration (Sephadex G25) into 5 fractions. The fraction that showed a higher activity on the tested model was chromatographed on HPLC generating 3 peaks (toxins Tb II-I, Tb II-II and Tb II-III), which had tested their activities on experimental models. Male Wistar rats used as experimental subjects were submitted to a stereotactic surgery for the implantation of cannulae and / or electrodes in the hippocampus. The animals were evaluated for behavioral activity, brain and neuronal integrity (histological sections of hippocampal tissue examined by an optical microscope for quantification of cells in the CA1, CA3 and CA4 areas) after injection of toxins. Microdialysis samples were collected for measurement of neurotransmitters that were performed on HPLC. The results show that the toxins induced behavioral (prostration, respiratory difficult, limited mobility, increased secretion, myoclonus and wet dog shake) electroencephalographic spikes and discharges) and histological alterations (cell death in the hippocampal CA1, CA3 and CA4 regions). More specifically in relation to Tb II-II, it was able to alter the levels of the neurotransmitters glutamate and GABA. Administration of glutamatergic antagonists AP-5 and MK-801 prior of injection of Tb II-II showed that this toxin acts on glutamate receptors, more effectively on non-NMDA type receptors, since the action of MK-801 in relation Tb II-II was more effective at blocking the onset of some behavioral, electroencephalographic and histopathological changes in comparison to the AP-5. With these results we can conclude that the three toxins were able to make changes on behavioral, electroencephalographic and histopathological parameters, and the action of Tb II-II is primarily a result of increased release of glutamate that generally seems to be more strongly linked to its action on glutamatergic non-NMDA -type receptors.