Abstract
Many motor effects of opiates acting at μ-opioid receptors are thought to reflect functional interactions with dopaminergic inputs to the caudate- putamen nucleus. We examined the cellular and subcellular bases for this interaction in the rat caudate-putamen nucleus by dual immunocytochemical labelling for μ-opioid receptors and tyrosine hydroxylase, a marker mainly for dopamine in this region. μ-Opioid receptor-like immunoreactivity showed a patchy distribution by light microscopy. Within the patches, electron microscopy revealed that immunogold labelling for μ-opioid receptors was mainly distributed along extrasynaptic plasma membranes of medium spiny neurons. In contrast, immunoperoxidase labelling for tyrosine hydroxylase was exclusively located in axons and axon terminals without detectable μ-opioid receptor-like immunoreactivity. Forty-six percent of the total μ-opioid receptor-labelled neuronal profiles (n=1441) were in contact with tyrosine hydroxylase-immunoreactive axons and terminals. These contacts were characterized by closely apposed parallel plasma membrane segments, without well-defined synaptic junctions, or with punctate symmetric specializations. From 639 noted appositions, over 90% were between μ-opioid receptor-labelled dendrites and/or dendritic spines and tyrosine hydroxylase-containing terminals. The dendritic spines containing μ-opioid receptor-like immunoreactivity often received asymmetric synapses characteristic of excitatory inputs from unlabelled terminals. Axon terminals containing μ- opioid receptor-like immunoreactivity formed asymmetric synapses with dendritic spines, or apposed tyrosine hydroxylase-labelled terminals. Our results suggest that, in striatal patch compartments, μ-agonists and dopamine dually modulate the activity of single spiny neurons mainly through changes in their postsynaptic responses to excitatory inputs. In addition, our findings implicate μ-opioid receptors and dopamine in the presynaptic regulation of excitatory neurotransmitter release within the striatal patch compartments.
Original language | English (US) |
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Pages (from-to) | 757-771 |
Number of pages | 15 |
Journal | Neuroscience |
Volume | 81 |
Issue number | 3 |
DOIs | |
State | Published - Sep 26 1997 |
Keywords
- Extrasynaptic site
- Morphine
- Nigrostriatal afferent
- Stereotyped behaviour
- Tyrosine hydroxylase
- Ultrastructural localization
ASJC Scopus subject areas
- General Neuroscience