An increase in the activity of brain stem locus coeruleus noradrenergic
neurons has been hypothesised to be a major factor accounting for opiate
withdrawal symptoms. These neurons are under GABAergic inhibition.
Their GABA_A receptors have unique pharmacological properties, most
likely due to the enriched expression of GABA_A receptor subtypes
containing novel epsilon and straight theta subunits. Using in situ
hybridisation of cryostat sections, we now report a significant increase
in the epsilon subunit mRNA expression after precipitation of opioid
withdrawal by naloxone. Similar changes were detected in tyrosine
hydroxylase mRNA expression. The results suggest increased formation of
unique GABA_A receptor subtype(s) in the locus coeruleus neurons during
increased neuronal activity.