Involvement of GABAergic mechanisms of the dorsal periaqueductal gray and inferior colliculus on unconditioned fear

AUTOR(ES)

Reimer, Adriano Edgar, Oliveira, Amanda Ribeiro de, Brandão, Marcus Lira

FONTE

Psychology & Neuroscience

DATA DE PUBLICAÇÃO

2009-06

RESUMO

The fact that the dorsal periaqueductal gray (dPAG) and inferior colliculus (IC), together with superior colliculus, medial hypothalamus and amygdala, constitute the brain aversion system has been well-established. Stepwise increases in the intensity of electrical stimulation of dPAG or IC cause freezing and escape responses, which are followed by a freezing behavior that lasts after the interruption of the stimulation. Freezing and escape are unconditioned defensive behaviors derived from the stimulation of the output centers for the defense reaction, whereas the post-stimulation freezing is the behavioral counterpart of the processing of aversive information. Although GABA-A mechanisms of the midbrain tectum exert a tonic inhibitory influence on the neural substrates of unconditioned fear, their influence on the processing of aversive information is not completely understood. Thus, the present study examines the effects of injections of the GABA-A receptor agonist muscimol (1 and 2 nmol/0.2 µL) or the glutamic acid decarboxylase blocker semicarbazide (5 and 7.5 µg/0.2 µL) into dPAG or IC of Wistar rats on freezing and escape thresholds determined by electrical stimulation of these same structures and on post-stimulation freezing. Intra-dPAG injections of muscimol increased and semicarbazide decreased the freezing and escape thresholds of electrical stimulation of the dPAG. Only semicarbazide enhanced the dPAG post-stimulation freezing. Intra-IC injections of muscimol significantly increased aversive thresholds, while having no effect on IC post-stimulation freezing. Intra-IC injections of semicarbazide had no significant effects. These findings suggest that GABAergic mechanisms are important regulators of the expression of unconditioned fear in dPAG and IC, whereas only in dPAG GABA appears to play a role on the sensory gating towards aversive information during post-stimulation freezing.

Documentos Relacionados

• Lesion of the Ventral Periaqueductal Gray Reduces Conditioned Fear but Does Not Change Freezing Induced by Stimulation of the Dorsal Periaqueductal Gray
• Envolvimento de receptores 5-HT2A da substância cinzenta periaquedutal dorsal no medo condicionado e incondicionado de ratos
• Envolvimento de mecanismos glutamatérgicos da substância cinzenta periaquedutal dorsal e do hipotálamo medial no medo condicionado à luz
• Effects of contextual fear conditioning and pentylenetetrazol on panic-like reactions induced by dorsal periaqueductal gray stimulation with N-methyl-D-aspartate
• Anatomical connections of the periaqueductal gray: specific neural substrates for different kinds of fear