Opioid modulation of GABA release in the rat inferior colliculus
1 Neuro-Behavioural Biology Centre, Mahidol University Salaya Nakorn Pathom 73170 Thailand
2 Department of Vision and Ophthalmology, King's College London, St. Thomas' Hospital, London, UK
3 Department of Anatomy, Faculty of MedicineSrinakarinwirot University Bangkok 10110 Thailand
4 UCL Centre for Auditory Research, University College London, 330 Grays Inn Road London WCIX 8EE UK
5 Center for Neuroscience and Department of Pharmacology, Faculty of Science, Bangkok, Thailand
BMC Neuroscience 2004, 5:31 doi:10.1186/1471-2202-5-31Published: 7 September 2004
The inferior colliculus, which receives almost all ascending and descending auditory signals, plays a crucial role in the processing of auditory information. While the majority of the recorded activities in the inferior colliculus are attributed to GABAergic and glutamatergic signalling, other neurotransmitter systems are expressed in this brain area including opiate peptides and their receptors which may play a modulatory role in neuronal communication.
Using a perfusion protocol we demonstrate that morphine can inhibit KCl-induced release of [3H]GABA from rat inferior colliculus slices. DAMGO ([D-Ala(2), N-Me-Phe(4), Gly(5)-ol]-enkephalin) but not DADLE ([D-Ala2, D-Leu5]-enkephalin or U69593 has the same effect as morphine indicating that μ rather than δ or κ opioid receptors mediate this action. [3H]GABA release was diminished by 16%, and this was not altered by the protein kinase C inhibitor bisindolylmaleimide I. Immunostaining of inferior colliculus cryosections shows extensive staining for glutamic acid decarboxylase, more limited staining for μ opiate receptors and relatively few neurons co-stained for both proteins.
The results suggest that μ-opioid receptor ligands can modify neurotransmitter release in a sub population of GABAergic neurons of the inferior colliculus. This could have important physiological implications in the processing of hearing information and/or other functions attributed to the inferior colliculus such as audiogenic seizures and aversive behaviour.