GABAergic regulation of the cardioinhibitory response in the crab Neohelice granulata

MARGARITA YANG; MARTÍN CARBÓ TANO; RAMIRO FREUDENTHAL; GABRIELA HERMITTE

Huerta Grande

Congreso; XXVI Congreso Anual de la Sociedad Argentina de Investigación en Neurociencia; 2011

San

Upon the presentation of a visual danger stimulus (VDS) as well as a relatively harmless visual stimulus (OFF) to the crab Neohelice granulata, heart arrest or bradycardia were elicited. We further investigated the regulation of this cardioinhibitory response upon visual stimulation in the presence of GABA antagonists. The administration of the non-competitive antagonist of GABA-A receptors, Picrotoxin, partially reduced the heart arrest, while no effect was observed using OFF. However, the administration of the competitive antagonist Bicuculline showed no effect on the cardioinhibitory response. In order to investigate the neuroanatomical substrate of this response, histological and immunohistochemical methods were used to examine the localization of the cardiac ganglion and GABA-like immunoreactivity within the cardiac system. Haematoxylin-eosin and Masson trichrome stains facilitated the identification of a distinct region compatible with the cardiac ganglion. GABA-like immunoreactivity detected in this region is originated from a single pair of processes close to the ganglion, giving rise to varicose branches that surround the somas of large neurons. Taken together, these findings support the idea that GABA mediates the extrinsic inhibition in this cardiac response.