Opioid modulation of GABA release in the rat inferior colliculus.
BACKGROUND
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.


RESULTS
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 micro rather than delta or kappa 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 micro opiate receptors and relatively few neurons co-stained for both proteins.


CONCLUSIONS
The results suggest that micro-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.
Tongjaroenbungam
Walaiporn
W
Neuro-Behavioural Biology Centre, Mahidol University Salaya Nakom Pathom 73170 Thailand. tongjaroen@yahoo.com
Jongkamonwiwat
Nopporn
N
Cunningham
Joanna
J
Phansuwan-Pujito
Pansiri
P
Dodson
Hilary C
HC
Forge
Andrew
A
Govitrapong
Piyarat
P
Casalotti
Stefano O
SO
D000818:Animals; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; D016308:Enkephalin, Leucine-2-Alanine / Q000378:metabolism; D007245:Inferior Colliculi / Q000737:chemistry* / Q000378:metabolism*; D009020:Morphine / Q000378:metabolism*; D009474:Neurons / Q000378:metabolism; D011189:Potassium Chloride / Q000378:metabolism; D051381:Rats; D017465:Receptors, Opioid, delta / Q000378:metabolism; D017473:Receptors, Opioid, kappa / Q000378:metabolism; D017450:Receptors, Opioid, mu / Q000378:metabolism; D005680:gamma-Aminobutyric Acid / Q000378:metabolism*
D017465:Receptors, Opioid, delta; D017473:Receptors, Opioid, kappa; D017450:Receptors, Opioid, mu; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; D005680:gamma-Aminobutyric Acid; D016308:Enkephalin, Leucine-2-Alanine; D011189:Potassium Chloride; D009020:Morphine