Morphine pharmacokinetics and opioid transporter expression at the blood-retina barrier of male and female mice

Endogenous opiates and behavior: 2023

This paper is the forty-sixth consecutive installment of the annual anthological review of research concerning the endogenous opioid system, summarizing articles published during 2023 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides and receptors as well as effects of opioid/opiate agonists and antagonists. The review is subdivided into the following specific topics: molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors (1), the roles of these opioid peptides and receptors in pain and analgesia in animals (2) and humans (3), opioid-sensitive and opioid-insensitive effects of nonopioid analgesics (4), opioid peptide and receptor involvement in tolerance and dependence (5), stress and social status (6), learning and memory (7), eating and drinking (8), drug and alcohol abuse (9), sexual activity and hormones, pregnancy, development and endocrinology (10), mental illness and mood (11), seizures and neurologic disorders (12), electrical-related activity and neurophysiology (13), general activity and locomotion (14), gastrointestinal, renal and hepatic functions (15), cardiovascular responses (16), respiration and thermoregulation (17), and immunological responses (18).

ABCB1 genetic polymorphisms affect opioid requirement by altering function of the intestinal P-glycoprotein

The association between polymorphisms of the human ATP binding cassette subfamily B member 1 (ABCB1) gene and opioid response has attracted intense attention recently. As the ABCB1 gene encodes for the transporter P-glycoprotein in the brain and intestine involved in the pharmacokinetics of opioids, we investigated the effects of ABCB1 genetic polymorphisms on doses of opioids for pain relief and determined which pharmacokinetic process was affected in cancer pain patients. Sixty-eight cancer pain patients admitted for intrathecal therapy (ITT) were included. The association between ABCB1 genetic polymorphisms (C3435T, C1236T, G2677T/A and A61G) and systemic doses of opioids before ITT were investigated. Concentrations of oxycodone in plasma and cerebrospinal fluid (CSF) were determined by HPLC-MS/MS in 17 patients treated with oral oxycodone before ITT, and the influences of ABCB1 genetic polymorphisms on plasma-concentration to oral-dose ratios and CSF-concentration to plasma-concentration ratios of oral oxycodone were further analyzed. ABCB1 C3435T and G2677T/A polymorphisms were significantly associated with systemic doses of opioids before ITT, which coincided with the influences of ABCB1 C3435T and G2677T/A polymorphisms on the ratios of plasma-concentration to oral-dose. However, no significant difference was found in ratios of CSF-concentration to plasma-concentration among ABCB1 SNP genotypes. The present study provided the first evidence that ABCB1 C3435T and G2677T/A polymorphisms affect opioid requirement in cancer pain patients via altering transportation function of P-glycoprotein in the intestine, which will further expand our knowledge about pharmacokinetics of opioids and could contribute to the individualization of opioids use.

Dopamine enhances GABAA receptor-mediated current amplitude in a subset of intrinsically photosensitive retinal ganglion cells

Neuromodulation in the retina is crucial for effective processing of retinal signal at different levels of illuminance. Intrinsically photosensitive retinal ganglion cells (ipRGCs), the neurons that drive non-image forming visual functions, express a variety of neuromodulatory receptors that tune intrinsic excitability as well as synaptic inputs. Past research has examined actions of neuromodulators on light responsiveness of ipRGCs, but less is known about how neuromodulation affects synaptic currents in ipRGCs. To better understand how neuromodulators affect synaptic processing in ipRGC, we examine actions of opioid and dopamine agonists have on inhibitory synaptic currents in ipRGCs. Although μ-opioid receptor (MOR) activation had no effect on γ-aminobutyric acid (GABA) currents, dopamine (via the D1R) amplified GABAergic currents in a subset of ipRGCs. Furthermore, this D1R-mediated facilitation of the GABA conductance in ipRGCs was mediated by a cAMP/PKA-dependent mechanism. Taken together, these findings reinforce the idea that dopamine's modulatory role in retinal adaptation affects both non-image forming as well as image forming visual functions.