RESUMEN
Background: The ventral tegmental area [VTA] is well known for its role in cardiovascular control. It is demonstrated that about 20-30% of the VTA neurons are GABAergic though their role in cardiovascular control is not yet understood. This study is carried out to find the effects of GABA A and GABA B receptors on cardiovascular response of the VTA
Methods: Experiments were performed on urethane anesthetized male Wistar rats. Drugs were microinjected unilaterally into the VTA. The average changes in mean arterial pressure [MAP] and heart rate [HR] were compared between the case and the control groups using t test and with the pre-injection values using paired t test
Results: Microinjection of muscimol, a GABAA agonist [500, 1500 and 2500 pmol/100nl] into the VTA had no significant effect on MAP and HR compared with the saline group and preinjection values. Injection of bicuculline methiodide [BMI, 100 and 200 pmol/100 nl], a GABAA antagonist, caused a significant increase in the MAP [11.1 +/- 1.95mmHg, P<0.5] and a decrease in HR [-32.07 +/- 10.2, P<0.01]. Microinjection of baclofen a GABAB receptor agonist [500 or 1000 pmole/100 nl] and phaclofen a GABAB receptor antagonist [500 or 1000 pmole/100 nl] had no significant effects on MAP and HR
Conclusion: For the first time it was demonstrated that GABA system of the VTA inhibits the cardiovascular system through the activation of GABAA but not the GABAB receptors
RESUMEN
The areas of the bed nucleus of the stria terminalis [BST] with a high density of estrogen receptors are involved in cardiovascular regulation and send axonal projections to the rostroventrolateral medulla [RVLM]. We aimed to find the contribution of the RVLM to cardiovascular responses elicited by glutamate microinjection into the BST. Experiments were done in alpha-chloralose anesthetized ovariectomized [OVX] or OVX estrogen treated [OVX+E] female Wistar rats. Drugs were microinjected into the BST and RVLM. The average changes in mean arterial pressure [MAP] and heart rate [HR] were compared between the case and control groups using t test and with the pre-injection values using paired t test. Unilateral microinjection of glutamate [0.25 M/50 nl] into the BST decreased MAP and HR, in the OVX+E and OVX rats. These cardiovascular responses were reversibly attenuated 10 minutes after microinjection of synaptic blocker cobalt chloride [CoCl2, 5 mM/50 nl] into the ipsilateral RVLM. Re-stimulation of the BST 60 min after CoCl2 injection elicited cardiovascular responses that were not different from the control values. Ipsilateral microinjection of GABA[A] antagonist bicuculline [1.0 mM/50 nl] into the RVLM caused a 50% attenuation of glutamate induced depressor and bradycardic responses in both groups. Ipsilateral microinjection of GABA[B] antagonist, phaclophen [5.0 mM/50 nl], into the RVLM did not affect the depressor and bradycardic responses due to re-stimulation of the BST by glutamate. The RVLM sympathetic premotor neurons contain GABA[A] receptors that mediate in part the sympathoinhibitory responses to stimulation of the BST in the OVX animals