Mu opioid receptor: expression and vagotomy-induced depletion of the mRNA in medullary preganglionic neurons

Comparative distribution of GABAergic and peptide-containing neurons in the lateral lemniscal nuclei of the rat

By immunostaining, neurons expressing peptides (dynorphin and corticotropin-releasing factor, CRF) and glutamate decarboxylase (GAD), a GABA-synthesizing enzyme, were precisely mapped in the rat lateral lemniscal nuclei. While GAD neurons were numerous and preferably localized in the dorsal (DLL) and ventral (VLL) nuclei, neurons expressing these peptides were less numerous and localized primarily in the intermediate (ILL) nucleus of the lateral lemniscus. The ILL nucleus was shown to project to the inferior colliculus and to express Fos rapidly in response to peripheral acoustic stimulation, suggesting that the ILL nucleus may take part in non-GABAergic relay of acoustic information in the lateral lemniscus.

Distribution of neurons expressing alpha 1G subunit mRNA of T-type voltage-dependent calcium channel in adult rat central nervous system

T-type voltage-dependent calcium channel has central roles in neuronal burst firing. The alpha1G subunit of T-type channel has been recently cloned and we here reported a cellular distribution of the alpha1G by in situ hybridization in adult rat brain and spinal cord. The cells expressing alpha1G were widely distributed in the central nervous system. The distribution seemed to be restricted to neurons, and exhibited a specific pattern in the cerebellum, thalamus, hippocampus and cerebral cortex.

RhoN, a novel small GTP-binding protein expressed predominantly in neurons and hepatic stellate cells

A cDNA encoding a novel member of the small molecular weight GTP-binding protein (small G-protein) superfamily was cloned from rat spinal cord. The deduced amino acid sequence was highly homologous with those of so-far-known Rho proteins. Rho proteins were reported to alter many important cellular functions including formation of both actin stress fibers and focal adhesions. RNA blot hybridization and in situ hybridization analyses indicated that the novel small G-protein is expressed specifically in neurons in the brain and spinal cord and also in hepatic stellate cells. Based on the sequence similarity and neuron-specific expression in the brain, this protein was named RhoN. Unlike classical Rho proteins, RhoN was not susceptible to the ADP-ribosylation reaction by C3 botulinum toxin. Accordingly, RhoN seemed to be specifically involved in neuronal and hepatic functions as a C3 toxin-insensitive member of the Rho subfamily. Then, a mouse genomic DNA segment containing the RhoN gene was cloned. The locus was mapped on the mouse chromosome 11C-D. The sequence data showed that the protein-coding sequence for RhoN is divided by 4 introns, and that the defined 5 exons may encode intramolecular domains serving for different functions.

Co-localization of mu-opioid receptor-like immunoreactivity with substance P-LI, calcitonin gene-related peptide-LI and nitric oxide synthase-LI in vagal and glossopharyngeal afferent neurons of the rat

Co-localization of mu-opioid receptor (MOR)-like immunoreactivity (-LI) with substance P (SP)-LI, calcitonin gene-related peptide (CGRP)-LI and nitric oxide synthase (NOS)-LI in the nodose, petrosal and jugular ganglia was examined in the rat by a double immunofluorescence histochemical method. About 0.6%, 41% and 95% of neurons with MOR-LI, respectively, in the nodose, petrosal and jugular ganglia showed SP-LI; about 2%, 51% and 66% of MOR-like immunoreactive neurons displayed CGRP-LI in the nodose, petrosal and jugular ganglia, respectively. In addition, about 59% of MOR-like immunoreactive neurons in the nodose ganglia displayed NOS-LI, whereas no NOS-LI was detected in the petrosal or jugular ganglion. These data provide evidence for co-localization of MOR-LI with SP-LI, CGRP-LI and NOS-LI in the vagal and glossopharyngeal afferent neurons, and suggest that MOR may regulate the release of SP, CGRP and nitric oxide from the visceral primary afferent terminals in the nucleus of the solitary tract of the rat.

Effects of peripheral nerve ligation on expression of mu-opioid receptor in sensory ganglion neurons: an immunohistochemical study in dorsal root and nodose ganglion neurons of the rat

The present study was attempted to examine if mu-opioid receptor (MOR) might be transported by axonal flow peripherally through peripheral axons of somatic sensory ganglion neurons. After unilateral ligation of the sciatic nerve or the vagus nerve distal to the dorsal root ganglion (DRG) or nodose ganglion (NG), MOR-like immunoreactivity (MOR-LI) of neuronal cell bodies in the DRG of the fourth and fifth lumbar nerves, NG, ambiguus nucleus (Amb) and dorsal motor nucleus of the vagus nerve (DMV) on the side of the ligation was apparently reduced within 1 week after the nerve ligation. However, within 24 h after the nerve ligation, a transient enhancement of MOR-LI was observed in cell bodies of DRG neurons, sciatic nerve stump proximal to the ligature, and cell bodies of NG neurons on the side of the ligation; such a transient enhancement of MOR-LI was not detected in the Amb and DMV. The results suggest that MOR undergoes centrifugal axonal flow in peripheral axons of somatic and visceral sensory ganglion neurons, and that MOR synthesis in sensory ganglion neurons is vulnerable to damage of the peripheral axons.

Localization of mu-opioid receptor-like immunoreactivity in the central components of the vagus nerve: a light and electron microscope study in the rat

mu-Opioid receptor, the opioid receptor that shows the highest affinity for morphine, appears to induce a variety of side-effects, at least partly, directly through the mu-opioid receptor on neurons constituting the autonomic part of the vagus nerve. Thus, in the present study, location of mu-opioid receptor-like immunoreactivity in the central components of the autonomic part of the vagus nerve was examined in the rat. The intense immunoreactivity was observed light microscopically in the neuropil of the commissural subnucleus and the dorsal part of the medial subnucleus of the nucleus of the solitary tract, and in the neuropil of the rostral half of the ambiguus nucleus. The immunoreactivity was moderate in the neuropil of the rostral and lateral subnuclei and ventral part of the medial subnucleus of the nucleus of the solitary tract, and weak in the neuropil of the dorsal motor nucleus of the vagus nerve. In the nodose ganglion, many neurons of various sizes (17-48 microns in soma diameter) showed moderate immunoreactivity. After unilateral vagotomy at a level proximal to the nodose ganglion, the immunoreactivity in the ipsilateral ambiguus nucleus was apparently reduced within 48 h of the operation, and completely disappeared by the seventh day after the operation. In the nucleus of the solitary tract and dorsal motor nucleus of the vagus nerve, the reduction of immunoreactivity after the ganglionectomy was detectable on the fourth day after the operation, and became readily apparent by the seventh day after the operation; the immunoreactivity, none the less, still remained on the 10th day after the operation. Electron microscopically, the immunoreactivity in the ambiguus nucleus was seen mainly on dendritic profiles and additionally on somatic ones; no immunoreactivity was detected in axonal profiles. The immunoreactivity in the dorsal motor nucleus of the vagus nerve was observed only on dendritic profiles. The immunoreactivity in the nucleus of the solitary tract was seen on axonal and dendritic profiles, but not on somatic profiles. The immunoreactive axon terminals in the nucleus of the solitary tract were filled with spherical synaptic vesicles and made asymmetric synapses with dendritic profiles. The results indicate that the mu-opioid receptor in the central components of the autonomic part of the vagus nerve is located on dendrites and cell bodies of efferent neurons in the ambiguus, on dendrites of efferent neurons in the dorsal motor nucleus, and on axons which arise from nodose ganglion neurons and terminate in the nucleus of the solitary tract. The receptors on these structures may constitute the targets of enkephalin-containing and beta-endorphin-containing afferent axons arising from brainstem neurons. The receptors on the axon terminals of nodose ganglion neurons may be involved in regulation of the release of neurotransmitters and/or neuromodulators.

Molecular biology of the opioid receptors: structures, functions and distributions

Opiates like morphine and endogenous opioid peptides exert their pharmacological and physiological effects through binding to their endogenous receptors, opioid receptors. The opioid receptors are classified into at least three types, mu-, delta- and kappa-types. Recently, cDNAs of the opioid receptors have been cloned and have greatly advanced our understanding of their structure, function and expression. This review focuses on the recent advances in the studies on opioid receptors using the cloned cDNAs. We describe the molecular cloning of the opioid receptor gene family and studies of the structure-function relationships, modes of coupling to second messenger systems, pharmacological effects of antisense oligonucleotide and anatomical distributions of opioid receptors.