Oxidative stress in the rostral ventrolateral medulla modulates excitatory and inhibitory inputs in spontaneously hypertensive rats

J Hypertens. 2012 Jan;30(1):97-106.  

Nishihara M, Hirooka Y, Matsukawa R, Kishi T, Sunagawa K.

This study aims at answering 3 important questions.

1. Determine whether chronic oxidative stress in the RVLM alters synaptic transmission through glutamatergic inputs.

2. Determine whether chronic oxidative stress in the RVLM alters synaptic transmission through GABA-ergic inputs.

3.  Determine whether chronic oxidative stress in the RVLM alters synaptic transmission through excitatory inputs from the PVN.

Adenoviral vectors encoding MnSOD was transferred into the RVLM of male SHRs and WKYs. Microinjection studies using Kynurenic acid (Glutamate receptor antagonist) and Bicuculline (GABA receptor antagonist) showed that reactive oxygen species (ROS) in the RVLM enhanced the excitatory glutamatergic inputs and reduced the GABAergic inputs to the RVLM neurons in SHRs. In addition, activation of the PVN neurons enhanced the pressor and sympathoexcitation through ROS in the RVLM. These findings suggest that ROS in the RVLM increases glutamatergic excitatory inputs and decreases GABAergic inputs in SHRs.

Madhan

SELECTIVE CONTROL OF SYMPATHETIC PATHWAYS TO THE KIDNEY, SPLEEN AND INTESTINE BY THE VENTROLATERAL MEDULLA IN RATS

 

J Physiol. 1990 September; 428: 371–385. K Hayes and L C Weaver

In this study, whether RVLM neurons produce differential responses to postganglionic renal, splenic and mesentric nerves were determined. Earlier studies in cats by other suggested that tonic influences from the RVLM to different sympathetic nerves are not uniform in distribution. Glycine was microinjected unilaterally in the RVLM of  Urethane anaesthetized male rats. Blockade by glycine produced a greater reductions in the renal than splenic nerve activity with no consistent changes in mesentric nerve activity. Interestingly the preganglionic nerves were not blocked to the same extend as the postganglionic nerves. It is possible that loss of activity in a small number of preganglionic axons could cause a greater loss of activity in the postganglionic neurons since many preganglionic inputs must get together to produce an action potential in the ganglionic cell. The findings from this study suggest that the sympathetic pathways to the kidney are more dependent on the excitatory drive from the RVLM than spleen and intestine. Selective effects of different sympathetic nerves can occur because of topographical organization within the medulla.  Questions such as how the brain stem selectively control different sympathetic outflows are yet to be answered.

-Madhan

Cardiovascular Effects Produced By Activation of GABA Receptors In The Rostral Ventrolateral Medulla of Conscious Rats

The major inhibitory neurotransmitter is GABA .As we already know anesthesia can potentiate the effects of GABA. In this article they looked at the role of GABA on GABA _A and GABA _B receptors in conscious animals. They used Wistar rats. They only looked at blood pressure and heart rate. Their finding suggest that the GABA _A receptor is the most important for mediating the inhibitory response under conscious conditions however , GABA _B receptor were not important for the transduction of inhibitory signals. This suggests that anesthesia might alter the GABA B receptor or even potentiate the effects of GABA binding to GABA _B receptors in anesthetized animals.