Effects of orchidectomy on adaptation of arcuate neuropeptide Y, proopiomelanocortin, and cocaine- and amphetamine-related transcript gene profiles to recurring insulin-induced hypoglycemia in the male rat

Our studies show that recurring insulin-induced hypoglycemia (RIIH) diminishes neuronal activation in several key components of the central metabolic regulatory circuitry, including the hypothalamic arcuate nucleus (ARH), and that orchidectomy (ORDX) modifies this impact of RIIH on Fos protein expression in this and other select neural structures. The testicular hormone, testosterone, regulates the expression of ARH neuropeptide genes of characterized metabolic relevance, including neuropeptide Y (NPY) and proopiomelanocortin (POMC). We investigated the hypothesis that acute hypoglycemia-associated patterns of ARH NPY, POMC, and cocaine and amphetamine-related transcript (CART) gene transcription, and potential RIIH-associated adaptive modifications in these expression profiles are regulated by testes-dependent mechanisms. ARH tissue was micropunched from serial frozen brains sections obtained from sham-operated (SHAM) or bilaterally ORDX male rats after sc injection of one or four doses of neutral protamine Hagedorn insulin, over as many days, or vehicle alone, and analyzed by quantitative real-time RT-PCR. In SHAM rats, acute hypoglycemia increased ARH NPY mRNA; precedent hypoglycemia elevated baseline gene expression in this group, but suppressed transcription during RIIH. In ORDX rats, ARH NPY mRNA was decreased during acute hypoglycemia and after multiple exposures; however, gene expression was not further suppressed by RIIH. ARH POMC gene transcription was not modified by acute or recurring hypoglycemia in the SHAM group. ORDX caused a reduction in both basal and acute hypoglycemic patterns of POMC transcription, relative to the SHAM controls, but enhanced baseline and RIIH-associated patterns of gene expression. ARH CART transcripts were not altered by acute or recurring hypoglycemia in SHAM rats, whereas ORDX animals exhibited elevated CART gene expression during RIIH. These data show that acute and recurring hypoglycemia exert opposite effects on ARH NPY gene expression in testes-intact male rats, and that these transcriptional responses are abolished by ORDX. Hypoglycemia had no impact on POMC nor CART mRNA profiles in the SHAM group, but both genes were upregulated during RIIH in ORDX rats. Collectively, these results demonstrate that in the male rat, testes-dependent mechanisms underlie patterns of acclimated or unvarying reactivity to RIIH of the specific ARH metabolic neuropeptide genes evaluated here.