Effects of Recurrent Hypoglycaemia on the Activation of Insulin‐Responsive Medullary and Spinal Neurons Controlling Adrenaline Release

Abstract

Recurrent episodes of low glucose availability (hypoglycaemia) lead to diminished adrenaline responses to subsequent bouts of hypoglycaemia, a condition known as hypoglycaemia‐associated autonomic failure (HAAF). To determine if any alteration in the activation of insulin‐responsive adrenergic neurons of the medulla oblongata and/or sympathetic preganglionic neurons (SPN) and/or adrenergic chromaffin cells of the adrenal medulla contribute to HAAF, we gave three groups of rats intraperitoneal injections of insulin (10 IU/kg, HAAF) or saline (Control) on 3 consecutive days or saline for 2 consecutive days and insulin on day 3 (Acute). Rats were fasted overnight prior to the last injection. Tail vein blood glucose was measured before injection and at 30 min on all days, and at 120 min on days 1 and 2 and at 90 min on day 3 at which time the rats were perfused with 4% formaldehyde. Coronal sections of perfused medulla (1:4 series) from the spinomedullary junction to mid‐facial nucleus, longitudinal sections of the spinal cord (1:2 series) containing segments T5–T8, T9–T11 and T12‐L2 and sections of adrenal gland (1:4 series) were immunoperoxidase stained to show Fos‐immunoreactivity (IR) with a black reaction product plus phenylethanolamine N‐methyltransferase (PNMT) or choline acetyltransferase (ChAT)‐immunoreactivity with a brown reaction product. At 90 min on day 3, blood glucose was significantly lowered from 5.5 ± 0.2 mmol/L and 5.9 ± 0.1 mmol/L to 1.4 ± 0.1 mmol/L and 1.3 ± 0.1 mmol/L (mean ± SEM, n=6–12) in the acute and HAAF groups, respectively. In the adrenal gland, nearly all PNMT‐IR chromaffin cells had Fos‐IR nuclei in both acute and HAAF groups. In response to both single and recurrent hypoglycaemia, many of the ChAT‐IR SPN in the intermediolateral cell column (IML) of thoracic segment T9–T10 had Fos‐IR nuclei. In HAAF rats that had recurrent hypoglycaemia, an average of 52.8 ± 4 PNMT‐IR C1 neurons of the RVLM had Fos‐IR nuclei which was not statistically different from rats that had single hypoglycaemia, in which 55 ± 6.2 PNMT‐IR C1 neurons in the RVLM had Fos‐IR nuclei. The proportion of Fos‐IR C2, C3 and vagal motor neurons did not appear to be different between the rats that had single hypoglycaemia and rats that had recurrent hypoglycaemia. These findings indicate that the activation of the main components of the medullo‐adrenal circuitry that control adrenaline release, including brainstem adrenergic neurons, SPN and adrenergic chromaffin cells, is unaffected by two episodes of antecedent hypoglycaemia. Thus, the primary reason for the defective adrenaline response in our model most likely lies within the adrenal gland.Support or Funding InformationDiabetes Australia Research TrustThis abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.