Perifornical hypothalamic pathway to the adrenal gland: Role for glutamatergic transmission in the glucose counter-regulatory response.
Adrenaline is an important counter-regulatory hormone that helps restore glucose homeostasis during hypoglycaemia. However, the neurocircuitry that connects the brain glucose sensors and the adrenal sympathetic outflow to the chromaffin cells is poorly understood. We used electrical microstimulation of the perifornical hypothalamus (PeH) and the rostral ventrolateral medulla (RVLM) combined with adrenal sympathetic nerve activity (ASNA) recording to examine the relationship between the RVLM, the PeH and ASNA. In urethane-anaesthetised male Sprague-Dawley rats, intermittent single pulse electrical stimulation of the rostroventrolateral medulla (RVLM) elicited an evoked ASNA response that consisted of early (60±3ms) and late peaks (135±4ms) of preganglionic and postganglionic activity. In contrast, RVLM stimulation evoked responses in lumbar sympathetic nerve activity that were almost entirely postganglionic. PeH stimulation also produced an evoked excitatory response consisting of both preganglionic and postganglionic excitatory peaks in ASNA. Both peaks in ASNA following RVLM stimulation were reduced by intrathecal kynurenic acid (KYN) injection. In addition, the ASNA response to systemic neuroglucoprivation induced by 2-deoxy-d-glucose was abolished by bilateral microinjection of KYN into the RVLM. This suggests that a glutamatergic pathway from the perifornical hypothalamus (PeH) relays in the RVLM to activate the adrenal SPN and so modulate ASNA. The main findings of this study are that (i) adrenal premotor neurons in the RVLM may be, at least in part, glutamatergic and (ii) that the input to these neurons that is activated during neuroglucoprivation is also glutamatergic.
Florey Institute of Neuroscience and Mental Health, University of Melbourne, Parkville, Victoria, Australia.
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Sabetghadam
Florey Institute of Neuroscience and Mental Health, University of Melbourne, Parkville, Victoria, Australia.
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Korim
University of Melbourne, Clinical Pharmacology and Therapeutics Unit, Department of Medicine, Austin Health, Heidelberg, Victoria 3084, Australia. Electronic address: antonius@unimelb.edu.au.
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Verberne
D000311:Adrenal Glands / Q000187:drug effects / Q000294:innervation / Q000378:metabolism*; D018686:Anesthetics, Intravenous / Q000494:pharmacology; D000818:Animals; D017776:Autonomic Pathways / Q000187:drug effects / Q000378:metabolism*; D004558:Electric Stimulation; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D005947:Glucose / Q000378:metabolism*; D018698:Glutamic Acid / Q000378:metabolism*; D007031:Hypothalamus / Q000187:drug effects / Q000378:metabolism*; D007736:Kynurenic Acid / Q000008:administration & dosage / Q000378:metabolism; D008159:Lumbar Vertebrae; D017207:Rats, Sprague-Dawley; D017470:Receptors, Glutamate / Q000378:metabolism; D013564:Sympathetic Nervous System / Q000187:drug effects / Q000378:metabolism*; D009435:Synaptic Transmission / Q000187:drug effects / Q000502:physiology; D014520:Urethane / Q000494:pharmacology
D018686:Anesthetics, Intravenous; D018691:Excitatory Amino Acid Antagonists; D017470:Receptors, Glutamate; D014520:Urethane; D018698:Glutamic Acid; D007736:Kynurenic Acid; D005947:Glucose
2-Deoxyglucose; Adrenal; Perifornical hypothalamus; Rostroventrolateral medulla; Sympathetic