| Abstract: |
Mu opioids significantly increase food intake following hypothalamic (HYP) and extra-hypothalamic injections. Yet the distribution of mu receptor (MOR-1 or MOP1) like immunoreactivity (LI) is quite sparse in the HYP. MOR-1 splice variants, contain the same first three exons as MOR-1 (i.e. 1, 2 and 3), but a series of different exons in place of exon 4. Their binding properties are similar to MOR-1, but their desensitization properties and regional distributions differ. Immunoreactivity of one, MOR-1C, is quite dense in HYP nuclei, suggesting that it may be responsible for some of the mu-mediated ingestive effects. The present study examined the central adaptive changes and opioid receptor plasticity in MOR-1 and MOR-1C in ad-libitum fed, acutely food-deprived and chronically food-restricted rats. The pronounced MOR-1-LI found in the nucleus tractus solitarius, parabrachial region, arcuate nucleus/median eminence (AN/ME) and nucleus accumbens was not significantly affected by either food deprivation or food restriction. MOR-1C-LI had pronounced labeling in the HYP paraventricular (PVN), periventricular and AN/ME nuclei and bed nucleus of the stria terminalis (BNST). Food restriction significantly and selectively increased MOR-1C-LI in the PVN, whereas both restricted and deprived animals displayed reductions in MOR-1C-LI in the BNST. These data suggest a role for these nuclei and MOR-1C in the opioid-mediated adaptive ingestive and weight-related changes in response to regulatory challenges. |
