A. Mansour et al., IMMUNOHISTOCHEMICAL LOCALIZATION OF THE CLONED MU-OPIOID RECEPTOR IN THE RAT CNS, Journal of chemical neuroanatomy, 8(4), 1995, pp. 283-305
Three opioid receptor types have recently been cloned that correspond
to the pharmacologically defined mu, delta and K-1 receptors. In situ
hybridization studies suggest that the opioid receptor mRNAs that enco
de these receptors have distinct distributions in the central nervous
system that correlate well with their known functions. In the present
study polyclonal antibodies were generated to the C terminal 63 amino
acids of the cloned mu receptor (335-398) to examine the distribution
of the mu receptor-like protein with immunohistochemical techniques. m
u receptor-like immunoreactivity is widely distributed in the rat cent
ral nervous system with immunoreactive fibers and/or perikarya in such
regions as the neocortex, the striatal patches and subcallosal streak
, nucleus accumbens, lateral and medial septum, endopiriform nucleus,
globus pallidus and ventral pallidum, amygdala, hippocampus, presubicu
lum, thalamic and hypothalamic nuclei, superior and inferior colliculi
, central grey, substantia nigra, ventral tegmental area, interpeduncu
lar nucleus, medial terminal nucleus of the accessory optic tract, rap
he nuclei, nucleus of the solitary tract, spinal trigeminal nucleus, d
orsal motor nucleus of vagus, the spinal cord and dorsal root ganglia.
In addition, two major neuronal pathways, the fasciculus retroflexus
and the stria terminalis, exhibit densely stained axonal fibers. While
this distribution is in excellent agreement with the known mu recepto
r binding localization, a few regions, such as neocortex and cingulate
cortex, basolateral amygdala, medial geniculate nucleus and the media
l preoptic area fail to show a good correspondence. Several explanatio
ns are provided to interpret these results, and the anatomical and fun
ctional implications of these findings are discussed.