Regional, developmental, and cell cycle-dependent differences in ?, ?, and ?-opioid receptor expression among cultured mouse astrocytes

Abstract

The diversity of opioid receptor expression was examined in astrocytes in low-density and nondividing (confluent) cultures from the cerebral cortex, hippocampus, cerebellum, and striatum of 1-day-old mice. μ, δ, and κ Opioid receptor expression was assessed in individual cells immunocytochemically, by using flow cytometry, and functionally by examining agonist-induced changes in intracellular calcium ([Ca 2+ ] i ). Significant spatial and temporal differences were evident in the pattern of expression of μ, δ, and κ receptors among astrocytes. In low-density cultures, greater proportions of astrocytes expressed μ-opioid receptor immunoreactivity in the cerebral cortex and hippocampus (26-34%) than in the cerebellum or striatum (7-12%). At confluence, a greater percentage of astrocytes in cerebellar (26%) and striatal (30%) cultures expressed μ-immunoreactivity. Fewer astrocytes possessed δ-immunoreactivity in low-density striatal cultures (8%) compared to other regions (16-22%). The proportion of δ receptorexpressing astrocytes declined in the cerebellum but increased in the hippocampus. κ-Opioid receptors were uniformly expressed by 27-34% of astrocytes from all regions, except in cortical cultures where the proportion of κ expressing cells was 38% at low-density and decreased to 22% at confluence. Selective μ (PLO 17; H-Tyr-Pro-Phe (N-Me) -D-Pro-NH 2 , δ ([D-Pen 2 , D-Pen 5 ] enkephalin) or κ (U50,488H; trans-(±) cyclohexyl] benzeneacetamide methanesulfonate) opioid receptor agonists increased [Ca 2+ ] i in subpopulations of astrocytes indicating the presence of functional receptors. Lastly, opioid receptor immunofluorescence varied during the cell division cycle. A greater proportion of astrocytes in the G 2 /M phase of the cell cycle were μ or δ receptor immunofluorescence than at G 0 /G 1 . When astrocytes were reversibly arrested in G 1 , significantly fewer cells expressed δ receptor immunofluorescence; however, upon reentry into the cell cycle immunofluorescent cells reappeared. In conclusion, opioid phenotype varies considerably among individual cultured astrocytes, and this diversity was determined by regional and developmental (age and cell cycle

Astrocytes are a neural target of morphine action via glucocorticoid receptor‐dependent signaling

“…It has been shown that acute morphine stimulation can induce calcium signaling El-Hage et al, 2005) and ERK phosphorylation (Belcheva et al, 2003), while prolonged exposure affected proliferation (Stiene-Martin et al, 2001) and proteomic profile (Suder et al, 2009) in primary astrocytes. The absence of direct transcriptional effects of morphine in astrocytes in the current study may be explained by the low level of l opioid receptors in our cultures, which is consistent with previous reports (Ruzicka et al, 1995;Stiene-Martin et al, 1998). Similarly, earlier studies have shown that a very low fraction of astrocytes in the striatum of adult mice express lopioid receptors (Stiene-Martin et al, 2001).…”

Direct Evidence of Astrocytic Modulation in the Development of Rewarding Effects Induced by Drugs of Abuse

“…In this study, we demonstrated that cortical purified astrocytes were markedly activated by METH. Opioid receptors are widely expressed by astrocytes, and the activation of m-opioid receptors can modulate programmed cell death (Stiene-Martin et al, 1998;Khurdayan et al, 2004). Unlike METH, however, MRP failed to induce the morphological change in cortical purified astrocytes (Narita et al, 2005a).…”

The opioid antagonist, β-funaltrexamine, inhibits chemokine expression in human astroglial cells

“…For instance, depending on the receptor type, β-FNA can exhibit agonist or antagonist activity (Holtzman, 1997;Sayre et al, 1984). Astroglia express all three opioid receptor types (, δ and κ) and these receptors are differentially expressed among brain regions (Ruzicka et al, 1995;Stiene-Martin et al, 1998). Also, age-related and cell-cycle-dependent variations in opioid phenotype can be observed at the cellular level (Stiene-Martin et al, 1998).…”

“…Astroglia express all three opioid receptor types (, δ and κ) and these receptors are differentially expressed among brain regions (Ruzicka et al, 1995;Stiene-Martin et al, 1998). Also, age-related and cell-cycle-dependent variations in opioid phenotype can be observed at the cellular level (Stiene-Martin et al, 1998). However, morphine functions predominantly through MOR (Baumhaker et al, 1993;Stefano et al, 1996).…”