GABA A receptor blockade in dorsomedial and ventromedial nuclei of the hypothalamus evokes panic-like elaborated defensive behaviour followed by innate fear-induced antinociception

• Published in: Brain research Vol. 1305; pp. 118 - 131
• Main Authors: Freitas, Renato Leonardo, Uribe-Mariño, Andrés, Castiblanco-Urbina, Maria Angélica, Elias-Filho, Daoud Hibraim, Coimbra, Norberto Cysne
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 11-12-2009
• Subjects: Analysis of Variance; Animals; Behavior, Animal - drug effects; Bicuculline - pharmacology; Catheters, Indwelling; Dorsomedial division of the ventromedial hypothalamus; Dorsomedial Hypothalamic Nucleus - drug effects; Dorsomedial hypothalamus; Elaborated defensive escape behaviour; Escape Reaction - drug effects; Exploratory Behavior - drug effects; GABA A receptors; GABA Antagonists - pharmacology; Innate fear-induced antinociception; Male; Motor Activity - drug effects; Pain Threshold - drug effects; Panic - drug effects; Panic-like behaviour; Rats; Receptors, GABA-A - metabolism; Ventromedial Hypothalamic Nucleus - drug effects; Innate fear-induced antinociception; Dorsomedial hypothalamus; Elaborated defensive escape behaviour; Panic-like behaviour; GABA A receptors; Dorsomedial division of the ventromedial hypothalamus
• ISSN: 0006-8993; 1872-6240
• DOI: 10.1016/j.brainres.2009.09.096

Dysfunction in the hypothalamic GABAergic system has been implicated in panic syndrome in humans. Furthermore, several studies have implicated the hypothalamus in the elaboration of pain modulation. Panic-prone states are able to be experimentally induced in laboratory animals to study this phenomenon. The aim of the present work was to investigate the involvement of medial hypothalamic nuclei in the organization of panic-like behaviour and the innate fear-induced oscillations of nociceptive thresholds. The blockade of GABA
A receptors in the neuronal substrates of the ventromedial or dorsomedial hypothalamus was followed by elaborated defensive panic-like reactions. Moreover, innate fear-induced antinociception was consistently elicited after the escape behaviour. The escape responses organized by the dorsomedial and ventromedial hypothalamic nuclei were characteristically more elaborated, and a remarkable exploratory behaviour was recorded during GABA
A receptor blockade in the medial hypothalamus. The motor characteristic of the elaborated defensive escape behaviour and the patterns of defensive alertness and defensive immobility induced by microinjection of the bicuculline either into the dorsomedial or into the ventromedial hypothalamus were very similar. This was followed by the same pattern of innate fear-induced antinociceptive response that lasted approximately 40 min after the elaborated defensive escape reaction in both cases. These findings suggest that dysfunction of the GABA-mediated neuronal system in the medial hypothalamus causes panic-like responses in laboratory animals, and that the elaborated escape behaviour organized in both dorsomedial and ventromedial hypothalamic nuclei are followed by significant innate-fear-induced antinociception. Our findings indicate that the GABA
A receptor of dorsomedial and ventromedial hypothalamic nuclei are critically involved in the modulation of panic-like behaviour.