Subcortical sites mediating sympathetic responses from insular cortex in rats

Area of Science:

• Neuroscience
• Autonomic Nervous System Regulation
• Cardiovascular Physiology

Background:

• The insular cortex plays a role in autonomic functions.
• Connections exist between the insular cortex and subcortical areas like the lateral hypothalamus, parabrachial nucleus, and nucleus of the solitary tract.
• These subcortical areas project to sympathetic preganglionic neurons.

Purpose of the Study:

• To identify the specific subcortical pathway mediating sympathetic responses originating from the insular cortex.
• To elucidate the role of the lateral hypothalamic area, parabrachial nucleus, and nucleus of the solitary tract in this pathway.

Main Methods:

• Renal nerve activity, blood pressure, and heart rate were monitored in anesthetized rats.
• Electrical stimulation of the insular cortex was performed.
• Synaptic blockade was achieved by injecting cobalt into specific subcortical regions.
• Changes in renal nerve activity were analyzed before and after cobalt injections.

Main Results:

• Stimulation of the insular cortex evoked early increases or decreases in renal nerve activity.
• Cobalt injections into the lateral hypothalamic area attenuated these nerve responses by 10-100%.
• Cobalt injections into the nucleus of the solitary tract enhanced the response from pressor sites.
• Injections into the parabrachial nucleus did not alter the nerve responses.

Conclusions:

• A mandatory synapse in the lateral hypothalamic area is crucial for the pathway from the insular cortex to the sympathetic nervous system.
• The nucleus of the solitary tract may modulate this pathway.
• The parabrachial nucleus does not appear to be a critical relay in this specific circuit.