Opioid receptor‐mediated changes in the NMDA receptor in developing rat and chicken

Abstract

The use of opioids during pregnancy has been associated with neurodevelopmental toxicity in exposed children, leading to cognitive and behavioural deficits later in life. The N‐methyl‐D‐aspartate receptor (NMDAR) subunit GluN2B plays critical roles in cerebellar development, and methadone has been shown to possess NMDAR antagonist effect. Consequently, we wanted to explore if prenatal opioid exposure affected GluN2B subunit expression and NMDAR function in rat and chicken cerebellum. Pregnant rats were exposed to methadone (10 mg/kg/day) or buprenorphine (1 mg/kg/day) for the whole period of gestation, using an osmotic minipump. To further examine potential effects of prenatal opioid exposure in a limited time window, chicken embryos were exposed to a 20 mg/kg dose of methadone or morphine on embryonic days 13 and 14. Western blot analysis of cerebella isolated from 14 days old rat pups exposed to buprenorphine showed significantly lower level of the GluN2B subunit, while the opioid exposed chicken embryo cerebellar GluN2B expression remained unaffected at embryonic day 17. However, we observed increased NMDA/glycine‐induced calcium influx in cerebellar granule neurone cultures from opioid exposed chicken embryos. We conclude that prenatal opioid exposure leads to opioid receptor‐dependent reduction in the postnatal expression of GluN2B in rat cerebella, and increase in NMDA‐induced calcium influx in chicken embryo cerebella.

Prenatal exposure to methadone or buprenorphine alters µ‐opioid receptor binding and downstream signaling in the rat brain

“…As no methadone or buprenorphine was detected in the prepared homogenates, it is unlikely that the reduced Neither methadone nor buprenorphine affected the cerebral NMDAR binding in the offspring. Recently, we reported similar findings in the cerebellum from chicken embryos exposed to methadone on embryonic days 13 and 14 (Fjelldal et al, 2019). However, we also found that continuous gestational exposure to buprenorphine, but not methadone, reduced the cerebellar expression of the NMDAR subunit GluN2B in 14-day-old rat offspring (Fjelldal et al, 2019).…”

“…Recently, we reported similar findings in the cerebellum from chicken embryos exposed to methadone on embryonic days 13 and 14 (Fjelldal et al, 2019). However, we also found that continuous gestational exposure to buprenorphine, but not methadone, reduced the cerebellar expression of the NMDAR subunit GluN2B in 14-day-old rat offspring (Fjelldal et al, 2019). This was surprising as buprenorphine does not bind to the NMDAR, while methadone acts as an NMDAR antagonist (Garrido & Troconiz, 1999;Robinson, 2002a).…”

“…The receptor binding studies were performed as previously described (Fjelldal et al, 2019;Kvello et al, 2019). In brief, cerebrum and hippocampus homogenates were diluted to 10 mg tissue/ml in ice-cold incubation buffer containing 50 mM Tris-HCl, 120 mM NaCl, 5 mM KCl, 2 mM CaCl 2 , and 0.5 mM MgCl 2 .…”

Cerebellum and Prematurity: A Complex Interplay Between Disruptive and Dysmaturational Events

“…In particular, it showed how rat cerebella continuously exposed to opioids during the prenatal age may present an opioid-induced reduction of the NMDAR subunit GluN2B (the subunit primarily expressed prenatally in rodents) during the first 3 weeks after birth. This finding supports the idea that NMDAR might be an important target of opioids, especially during neurodevelopment, being potentially involved in their neurotoxic effects and long-term detrimental consequences ( Fjelldal et al, 2019 ).…”

Chronic Exposure to Methadone Induces Activated Microglia and Astrocyte and Cell Death in the Cerebellum of Adult Male Rats

“…GluN2B expression peaks around PND14 in the rat cerebellum, before GluN2C and GluN2A change into adulthood [21]. Therefore, the expression of various NMDAR subunits, particularly GluN2B, is critical for the plasticity growth of the cerebellum [22]. The short-and long-term complications of methadone have been studied in pregnant rats and its effect on neurodevelopmental dysfunction and growth retardation in the brain of the fetus rats have been reported [22].…”