Toluene and TCE decrease binding to mu-opioid receptors, but not to benzodiazepine and NMDA receptors in mouse brain

Area of Science:

• Neuroscience
• Toxicology
• Pharmacology

Background:

• Abused organic solvents impact neurotransmitter systems like GABAergic, glutamatergic, and opioidergic.
• Understanding solvent neurotoxicity is crucial for public health and clinical management.

Purpose of the Study:

• To investigate the effects of acute toluene and 1,1,1-trichloroethane (TCE) exposure on neurotransmitter receptor binding in mice.
• To evaluate the impact of toluene exposure on morphine's antinociceptive effects using the hot-plate test.

Main Methods:

• Mice were exposed to 4,000 ppm toluene or 12,000 ppm TCE for 30 minutes.
• Brain receptor binding levels (mu-opioid, NMDA, benzodiazepine) were assessed via autoradiography 24 hours post-exposure.
• Nociceptive responses were measured using the hot-plate test after toluene exposure and morphine co-administration.

Main Results:

• Toluene inhalation decreased mu-opioid receptor binding in multiple brain regions (cingulate cortex, piriform cortex, caudate putamen, thalamus, amygdala, periaqueductal gray).
• TCE inhalation decreased mu-opioid receptor binding in the thalamus and periaqueductal gray.
• Both solvents reduced benzodiazepine receptor binding but did not affect NMDA receptor binding.
• Toluene exposure immediately followed by morphine blocked analgesia; delayed co-administration also blocked morphine's analgesic effects.

Conclusions:

• Mu-opioid receptors are key molecular targets for organic solvent neurotoxicity.
• Inhalation of toluene and TCE can interfere with the analgesic efficacy of opioids.
• These findings highlight potential risks associated with solvent abuse and concurrent opioid use.