Distribution of CCK mRNA in particular regions (hippocampus, periaqueductal grey and thalamus) of the rat by in situ hybridization.

Cholecystokinin (CCK) mRNA was detected by in situ hybridization at high magnification in some rat brain regions where CCK octapeptide (CCK-8) is thought to produce its pharmacological effects. The labeling of the dentate gyrus and the sparse but intensively stained cells found in the CA1 layer, stratum radiatum and hilus could correspond to interneurons involved in hippocampal neural activity, in agreement with excitatory responses induced by local injection of CCK-8. The intense labeling of the Edinger-Westphal nucleus and more generally the presence of CCK mRNA in the periaqueductal gray and thalamus ventrobasal nuclei could account for the various effects of CCK in pain transmission.

Immunocytochemical distribution of neurons containing a peptide derived from thyrotropin-releasing hormone precursor in the rat brain.

Using an antiserum to a 22-amino acid synthetic peptide corresponding to sequence 178-199 of the precursor of thyrotropin-releasing hormone (pro-TRH), we have studied by immunocytochemistry the distribution of immunoreactive pro-TRH in the rat brain. Immunostaining found in several regions of the brain had a distribution similar to that previously reported for TRH. Reaction product was found in both neuronal cell bodies and processes. These results indicate that peptide(s) derived from pro-TRH are transported along the axons with TRH itself. Moreover, the presence of immunoreactive nerve endings in different areas including the median eminence suggests that this material might have a neuromodulator/neurotransmitter role in the central nervous system and could also be released into the pituitary portal plexus.

Galanin-like immunoreactivity within amygdaloid and hypothalamic neurons that project to the midbrain central grey in rat.

The possibility that galanin-immunoreactive cells within the central nucleus of the amygdala (Ce) and the lateral part of the bed nucleus of the stria terminalis (BSTL) project to the midbrain central grey in the rat was investigated using the combined immunofluorescence-retrograde tracing technique. Injections of Fluoro-Gold tracer were made into the ventrolateral midbrain central grey and the brain tissue was processed for galanin-like immunoreactivity using the avidin-biotin Texas red immunofluorescence technique. Cells containing both galanin-like immunoreactivity and fluorescent retrograde tracer were identified within the medial Ce and in the ventral part of the BSTL. Retrogradely labeled galanin-like immunoreactive cells were also observed within the medial preoptic area and to a lesser extent within the dorsomedial and paraventricular hypothalamic nuclei. The results of this study demonstrate the presence of long descending pathways containing galanin-like immunoreactivity that originate from discrete regions of the amygdala and hypothalamus and terminate within the midbrain central grey.

Central beta-endorphin release and recovery after exposure to nitrous oxide in rats.

To explore the hypothesis that nitrous oxide stimulates the beta-endorphin system in vivo, rats were exposed to nitrous oxide/oxygen at variable concentrations for one hour. beta-Endorphin concentration at sites along the neuraxis functionally involved with analgesia was elevated in nitrous oxide-exposed animals. The increase in beta-endorphin concentration was statistically significant at nitrous oxide concentrations of 60 and 80%. This elevation of beta-endorphin levels depended on the concentration of nitrous oxide delivered rather than on the duration of exposure. With cessation of nitrous oxide anesthesia, beta-endorphin concentration returned to control levels within 30 minutes.

Visualization of mu1 opiate receptors in rat brain by using a computerized autoradiographic subtraction technique.

We have developed a quantitative computerized subtraction technique to demonstrate in rat brain the regional distribution of mu1 sites, a common very-high-affinity binding site for both morphine and the enkephalins. Low concentrations of [D-Ala2, D-Leu5]enkephalin selectively inhibit the mu1 binding of [3H]dihydromorphine, leaving mu2 sites, while low morphine concentrations eliminate the mu1 binding of [3H][D-Ala2, D-Leu5]enkephalin, leaving delta sites. Thus, quantitative differences between images of sections incubated in the presence and absence of these low concentrations of unlabeled opioid represent mu1 binding sites. The regional distributions of mu1 sites labeled with [3H]dihydromorphine were quite similar to those determined by using [3H][D-Ala2, D-Leu5]enkephalin. High levels of mu1 binding were observed in the periaqueductal gray, medial thalamus, and median raphe, consistent with the previously described role of mu1 sites in analgesia. Other regions with high levels of mu1 binding include the nucleus accumbens, the clusters and subcallosal streak of the striatum, hypothalamus, medial habenula, and the medial septum/diagonal band region. The proportion of total specific binding corresponding to mu1 sites varied among the regions, ranging from 14% to 75% for [3H][D-Ala2, D-Leu5]enkephalin and 20% to 52% for [3H]dihydromorphine.