Regulation of body weight and food intake by AGRP neurons during opioid dependence and abstinence in mice

Abstract

Dysregulation of body weight maintenance and opioid dependence are often treated as independent disorders. Here, we assessed the effects of both acute and long-term administration of morphine with and without chemogenetic activation of agouti-related peptide (AGRP)-expressing neurons in the arcuate nucleus (ARCAGRP neurons) to elucidate whether morphine and neuronal activation affect feeding behavior and body weight. First, we characterized interactions of opioids and energy deficit in wild-type mice. We observed that opioid administration attenuated both fasting-induced refeeding and ghrelin-stimulated feeding. Moreover, antagonism of opioid receptors blocked fasting-induced refeeding behavior. Next, we interfaced chemogenetics with opioid dependence. For chemogenetic experiments of ARCAGRP neurons, we conducted a priori behavioral qualification and post-mortem FOS immunostaining verification of arcuate activation following ARCAGRP chemogenetic activation. We administered clozapine during short-term and long-term morphine administration paradigms to determine the effects of dependence on food intake and body weight. We found that morphine occluded feeding behavior characteristic of chemogenetic activation of ARCAGRP neurons. Notably, activation of ARCAGRP neurons attenuated opioid-induced weight loss but did not evoke weight gain during opioid dependence. Consistent with these findings, we observed that morphine administration did not block fasting-induced activation of the ARC. Together, these results highlight the strength of opioidergic effects on body weight maintenance and demonstrate the utility of ARCAGRP neuron manipulations as a lever to influence energy balance throughout the development of opioid dependence.

Opioidergic signaling contributes to food-mediated suppression of AgRP neurons

“…Consistent with earlier AgRP neuron suppression studies, i.p. DAMGO injection at dark onset caused a small but significant decrease in food intake over the next 4 h. Remarkably, inline with a recent report, 31 administration of morphine, another MOR agonist with better brain access, caused much more robust appetite suppression ( Figures 4I and 4J ).…”

“…Consistent with a recent report, 31 we also found suppression of dark-onset feeding by both DAMGO and morphine. Interestingly, morphine suppressed feeding much more robustly, and unlike DAMGO, this effect persisted even in AgRP-MKO mice.…”

Anterior hypothalamic parvalbumin neurons are glutamatergic and promote escape behavior

“…Fast-spiking characteristics are correlated with the expression of specific ion channels such as the delayed rectifier voltage-gated potassium channel KCNC1 (Kv3.1) (Du et al, 1996; Rosato-Siri et al, 2015) and the potassium/sodium hyperpolarization-activated cyclic nucleotide-gated ion channel 2 (HCN2) (Aponte et al, 2006). Thus, to determine whether these molecular markers are expressed in AHA PV neurons, we performed fluorescent in situ hybridization on brain slices containing the AHA ( n = 4 mice; Figure 2B ) and analyzed these data using Autocount, a custom ImageJ macro tool (Laing, 2022). We observed that AHA PV neurons express both Kcnc1 and Hcn2 mRNA (360.3 ± 49.49 neurons of 445 ± 77.04 total Pvalb + neurons; Figure 2C ).…”

“…Cell counts were performed on every sixth brain slice, and AHA neurons were assessed for co-expression of Pvalb with Hcn2 and Kcnc1 using a custom ImageJ macro series called Autocount (Laing, 2022; Schindelin et al, 2012). This macro series identifies all DAPI-positive areas as individual regions of interest and measures fluorescence intensity across each channel.…”