Abstract
It is known that μ opioid receptor (MOR) is located on the dendrite of striosomal medium-spiny (MS) projection neurons, and glutamatergic and non-glutamatergic presynaptic terminals innervating the MS neurons. The objective of this study was to investigate the MOR-mediated effects on the excitatory and inhibitory synaptic transmission in the striatal striosome/matrix compartment. To identify the striosomes, we used a transgenic mouse strain (TH-GFP mouse) harbouring an eGFP reporter construct under the promoter of tyrosine hydroxylase, the rate-limiting enzyme for cathecolamine synthesis. Because dopaminergic neurons densely innervate the striosomal cells in early postnatal stage, a striosome is identified as a bright area under fluorescence microscope. Using corticostriatal slices obtained from TH-GFP mice (P14-P28), we made whole-cell recordings from MS neurons. DAMGO, an agonist of MOR, significantly suppressed GABAergic IPSCs in the striosomes (-18.4%±3.6%), whereas DAMGO had no effects in the matrix (+3.1%±5.5%). On the contrary, the effect of DAMGO on EPSCs in the striosomes was identical to that in the matrix. The suppression of IPSCs was also observed in cholinergic interneurons located near the striosomes, therefore MOR-mediated suppression of IPSCs might affect the release of endogenous acetylcholine. The MOR-mediated effects on synaptic transmission may control the activity of local neural circuits in striosome/matrix compartment. [J Physiol Sci. 2007;57 Suppl:S8]
