Sex differences in subcellular distribution of delta opioid receptors in the rat hippocampus in response to acute and chronic stress

Abstract

Drug addiction requires associative learning processes that critically involve hippocampal circuits, including the opioid system. We recently found that acute and chronic stress, important regulators of addictive processes, affect hippocampal opioid levels and mu opioid receptor trafficking in a sexually dimorphic manner. Here, we examined whether acute and chronic stress similarly alters the levels and trafficking of hippocampal delta opioid receptors (DORs). Immediately after acute immobilization stress (AIS) or one-day after chronic immobilization stress (CIS), the brains of adult female and male rats were perfusion-fixed with aldehydes. The CA3b region and the dentate hilus of the dorsal hippocampus were quantitatively analyzed by light microscopy using DOR immunoperoxidase or dual label electron microscopy for DOR using silver intensified immunogold particles (SIG) and GABA using immunoperoxidase. At baseline, females compared to males had more DORs near the plasmalemma of pyramidal cell dendrites and about 3 times more DOR-labeled CA3 dendritic spines contacted by mossy fibers. In AIS females, near-plasmalemmal DOR-SIGs decreased in GABAergic hilar dendrites. However, in AIS males, near-plasmalemmal DOR-SIGs increased in CA3 pyramidal cell and hilar GABAergic dendrites and the percentage of CA3 dendritic spines contacted by mossy fibers increased to about half that seen in unstressed females. Conversely, after CIS, near-plasmalemmal DOR-SIGs increased in hilar GABA-labeled dendrites of females whereas in males plasmalemmal DOR-SIGs decreased in CA3 pyramidal cell dendrites and near-plasmalemmal DOR-SIGs decreased hilar GABA-labeled dendrites. As CIS in females, but not males, redistributed DOR-SIGs near the plasmalemmal of hilar GABAergic dendrites, a subsequent experiment examined the acute affect of oxycodone on the redistribution of DOR-SIGs in a separate cohort of CIS females. Plasmalemmal DOR-SIGs were significantly elevated on hilar interneuron dendrites one-hour after oxycodone (3 mg/kg, I.P.) administration compared to saline administration in CIS females. These data indicate that DORs redistribute within CA3 pyramidal cells and dentate hilar GABAergic interneurons in a sexually dimorphic manner that would promote activation and drug related learning in males after AIS and in females after CIS.

Chronic immobilization stress primes the hippocampal opioid system for oxycodone‐associated learning in female but not male rats

“…Summary of sex differences in the opioid system following CIS and oxycodone CPP in the rat hippocampus. Our previous light and electron microscopic studies have revealed notable sex differences in mossy fiber LEnk levels and in the redistributions of DORs and MORs in pyramidal cells and GABAergic interneurons following CIS and oxycodone CPP (Mazid et al, ; McEwen & Milner, ; Ryan et al, ). *Females in diestrus; ^Females in estrus…”

“…In males, but not females, CIS downregulates expression of opioid, stress and other signaling molecules in the hippocampus that are important for mediating synaptic plasticity (Randesi et al, ). In mossy fiber‐CA3 synapses, both mossy fiber LEnk levels and DOR density in CA3 dendritic spines remain elevated in females regardless of estrogen state following CIS (Mazid et al, ; Pierce, Kelter, McEwen, Waters, & Milner, ). The increase in DORs in CA3 spines following CIS in females resembles that seen previously in females at high‐estrogen states (Harte‐Hargrove et al, ).…”

“…In contrast, LEnk levels and DOR density in mossy fiber‐CA3 synapses are markedly reduced in CIS males (Pierce et al, ). Moreover, plasmalemmal‐associated DORs remain increased in CA3 pyramidal cell dendrites in CIS females but are decreased in CIS males (Mazid et al, ). The increased levels of DORs in mossy fiber spine synapses, together with the elevated levels of LEnks, which have a high affinity for DORs (Corbett, Paterson, & Kosterlitz, ) suggest the likelihood for excitation and opioid‐dependent LTP at mossy fiber‐CA3 synapses in CIS females (Harte‐Hargrove et al, ; Moore, Madamba, Schweitzer, & Siggins, ).…”

“…As PARV interneurons synapse on the somata of granule cells (Drake, Chavkin, & Milner, ), this rearrangement of the MORs in γ‐amino butyric acid (GABA)‐ergic interneurons would promote a greater disinhibition, and thus, a relative activation of granule cells in response to an opioid ligand (Drake & Milner, ). Moreover, CIS in females mobilizes DORs near the plasmalemma of GABAergic neuropeptide Y/somatostatin (NPY/SOM) interneuron dendrites (Mazid et al, ) to granule cell dendrites where they converge with entorhinal afferents (Milner & Bacon, ; Milner & Veznedaroglu, ). DORs inhibit NPY release; thus opioid ligand activation of DORs on NPY‐containing interneurons would promote lateral perforant pathway LTP (Sperk, Hamilton, & Colmers, ).…”

Effects of Acute and Chronic Restraint Stress on Reinstatement of Extinguished Methamphetamine-Induced Conditioned Place Preference in Rats

“…Several lines of evidence also have suggested that the reinstatement of drug seeking behaviors is mediated by dopamine receptors (Dai, Kang, Wang, & Ma, 2006;Gilbert et al, 2005). As well, Mazid et al, in 2016 suggest that desperate stress could affect opioid-related learning (Mazid et al, 2016). As well, it confirmed that desperate food deprivation facilitate reinstatement of morphine CPP in rats .…”