Effects of hypoglycaemia on neurotransmitter and hormone receptor gene expression in laser-dissected arcuate neuropeptide Y/agouti-related peptide neurones.

Arcuate neuropeptide Y (NPY)/agouti-related pepide (AgRP) neurones regulate energy homeostasis, and express the putative glucosensor, glucokinase (GCK). The present study performed multi-transcriptional profiling of these neurones to characterise NPY, AgRP and GCK gene expression during intermediate insulin-induced hypoglycaemia, and to determine whether these transcriptional responses acclimate to repeated insulin dosing. We also examined whether these neurones express insulin, glucocorticoid and oestrogen receptor gene transcripts, and whether the levels of these receptor mRNAs are modified by insulin-induced hypoglycaemia. Individual NPY-immunoreactive neurones were laser-microdissected from the caudal arcuate nucleus after single or serial dosing with neutral protamine Hagedorn insulin (NPH), and evaluated by quantitative real-time reverse transcriptase-polymerase chain reaction for the assessment of neurotransmitter and receptor gene expression. Mean NPY and AgRP mRNA in harvested NPY neurones was unchanged or augmented, respectively, by one NPH dose, although repeated NPH administration up-regulated NPY, whereas AgRP gene transcripts were down-regulated. NPH elicited divergent modifications in the ERalpha and ERbeta mRNA content of sampled neurones. ERalpha transcripts were amplified by both acute and chronic NPH-induced hypoglycaemia, whereas ERbeta gene expression was unaltered during a single bout, but suppressed during recurring hypoglycaemia. Glucocorticoid receptor (GR) mRNA levels were increased by a single insulin dose, but unaffected by serial NPH dosing. Insulin receptor-beta chain (InsRb) gene transcripts were insensitive to acute NPH-induced hypoglycaemia, but repeated NPH inhibited this gene transcript. Neither acute nor recurring hypoglycaemia modified GCK mRNA levels in caudal hypothalamic arcuate nucleus (ARH) NPY/AgRP neurones, but baseline GCK transcription was suppressed by the latter. This evidence for the habituation of hypoglycaemic patterns of InsRb, GR and ERbeta gene transcription to serial NPH dosing implies that such treatment may alter reactivity of caudal ARH NPY/AgRP neurones to receptor ligands, and supports the need to determine whether adaptive changes in neuronal sensitivity to insulin, corticosterone and/or oestrogen cause up- versus down-regulation of NPY and AgRP neurotransmission, respectively, by this caudal ARH subpopulation during chronic hypoglycaemia.