Study of corpus striatum and ventral mesencephalon endocanabinoid influence on neostriato-nigro-tectal GABAergic pathways during panic reactions of rodents threatened by venomous snakes

Abstract

The study of the neuropsychopharmacological bases of the fear- and panic-related behaviour has been the focus of several scientific researches. The mesencephalic tectum (MT) has been considered as responsible for the control of defensive responses evoked during threatening situations. The deep layers of the superior colliculus (dlSC) and the dorsal columns of the periaqueductal grey matter (dPAG) have been considered important structures for the elaboration of innate fear and defensive behaviour. The substantia nigra, pars reticulata (SNpr), is known to receive GABAergic inputs from cautatum-putamen (CPu) and send outputs to the mesencephalic tectum that can work as a sensory channel to dorsal midbrain neurons responsible for the elaboration of defensive responses in more ventral regions of this neural substrate. The dorsal mesencephalon, however, is connected to both compacta and reticulata divisions of the substantia nigra, through inputs rich in endogenous opioid peptides. In addition, both CPu and SNpr are rich in CB1 cannabinoid receptors, with putative involvement in this neural system that is known for these interactive properties with the opioid system, and has been the focus of interest of scientific community. The purpose of the present work is to investigate the role of CB1-cannabinoid receptors of CPu and of opioid and cannabinoide neurotransmnission in SNpr, structures rich in GABAergic neurons, in the modulation of defensive behaviour related to instinctive fear and panic reactions. Thus, it will be studied the effect of microinjections of CB1-cannabinoid receptors selective agonists and antagonists into the CPu or opioid and cannabinoid drugs in SNpr on the defensive behaviour elaborated by dorsal mesencephalon neurons, disinhibited by a GABAA receptor selective blockade in the dlSC/dPAG of Wistar rats confronted with Bothrops alternatus in a polygonal arena for snakes with an artificial burrow. (AU)