Identification and immunohistochemical mapping of GABAA receptor subtypes containing the delta-subunit in rat brain

Synaptic inhibition in brain is mainly mediated via GABAA receptors which display a striking structural heterogeneity. A novel type of GABAA receptor subunit, the delta-subunit, has recently been described based on molecular cloning of its cDNA. To identify the prevalence and distribution of GABAA receptors which contain the delta-subunit protein in situ, polyclonal site-directed antisera were developed against three synthetic peptides derived form the rat delta-subunit cDNA-sequence. All antisera specifically recognized a 54 kDa protein in GABAA receptor preparations. Nearly 30% of the GABAA receptors contained the delta-subunit immunoreactivity and displayed high affinity GABA and high affinity benzodiazepine binding sites as shown by immunoprecipitation. Receptors which contain the delta-subunit were immunohistochemically shown to be restricted to a few brain areas such as the cerebellum, thalamus and dentate gyrus of the hippocampal formation. Thus, those neurons which express GABAA receptors with a delta-subunit have now been visualized and made accessible for a functional analysis of this GABAA receptor subtype in situ.