Efeitos cardiovasculares produzidos pelo bloqueio dos receptores gaba ou inibição da enzima glumato-descarboxilase no hipotálamo dorsomedial de ratos acordados: investigação de assimetria funcional

Abstract

Emotional stress requires that central nervous system (CNS) produce a series of behavioral, autonomic and endocrine responses for maintaining body homeostasis (Clark et al. 1997). According to the studies, they have shown that neurons in the dorsomedial hypothalamus (DMH) are involved in the generation of an integrated response to stress. The activation of neurons in the DMH, after the blockade of GABAA receptors, causes physiological changes that resemble the responses classically described as fight or flight (Shekhar, 1993, Stotz-Potter et al.1996, Fontes et al., 2001, DiMicco et al. , 2002). Previous studies from our laboratory demonstrated that in anesthetized rats, the DMH neuron activation evoked by nanoinjection GABA antagonist bicuculline methiodide (BMI) caused a greater tachycardia when injected on the right side (DMH-R) compared to the left side of DMH ( DMH-L) indicating that the DMH-R has a dominant control over the heart beat rate control (HR) (Xavier et al, Neuroscience 2009). The main findings of this study were: i) the nanoinjection acute L-AG 10 µg/100 nl of DMH in conscious rats can produce responses similar to those described as defensive behavioral, ii) the highest dose of L-AG evaluated (10 g/100nl) produced more pronounced tachycardia when injected in DMH-R; iii) the duration of the tachycardia produced by blockade of GABAA receptors using nanoinjection BMI of 10 pmol/100 nl in DMH-R was nearly twice that produced in the DMH-L, iv) blockade of GABAB receptors with Saclofen (10 pmol/100 nl) have no changes in blood pressure or heart rate when nanoinjected in DMH-R and DMH-L v) the dose of 1 µg/100nl of L-AG in DMH was able to induce in animals sensitivity of the peripheral infusion of sodium lactate in both groups. The cardiovascular responses were not different when comparing the groups that received the injection of L-AG in the DMH-R or DMH-L. In conclusion our results extend the results of earlier studies showing that DMH-R has a different control on cardiac chronotropy mainly through GABAA receptors. Our data points to a differential input GABAergic DMH in awake rats.