A. E. Bennett Award paper. Expression of the dopamine D2 receptor gene in brain

The cloning of the dopamine (DA) D2 receptor now permits the characterization and regulation of D2 messenger RNA (mRNA) in the brain. In this article, the authors describe their studies delineating the distribution of D2 receptor mRNA in the rodent and primate brain, and compare the distribution of message to D2 receptor binding sites. The effects of chronic DA agonist and antagonist treatment on D2 receptor mRNA are also presented, and provide insights into receptor regulation. Finally, the autoreceptor role of D2 receptors located in the midbrain is examined with a combination of 6-hydroxydopamine lesions and anatomic colocalization studies with tyrosine hydroxylase. These preclinical results provide a framework for subsequent investigation into the nature of D2 receptor gene expression in postmortem brains from patients with disorders putatively associated with dopaminergic dysfunction, especially schizophrenia. They also lay the groundwork for a more profound understanding of DA neurocircuitry by combining molecular biological and traditional anatomical techniques.

Minimal access surgery for gastroesophageal reflux: laparoscopic placement of the Angelchik prosthesis in pigs

Conventional surgery for gastroesophageal reflux is effective but requires laparotomy. Minimal access surgery for gastroesophageal reflux could provide a decrease in morbidity. The Angelchik antireflux prosthesis is an alternative to fundoplication for the treatment of this ailment. We evaluated the results of laparoscopic placement of the Angelchik prosthesis in 10 pigs. The duration of the procedure averaged 44 min. The mean lower esophageal sphincter pressure increased from 12.2 +/- 2.8 mmHg at baseline to 45.2 +/- 7.8 (P less than 0.05), 32.1 +/- 3.9 (P less than 0.05), and 25.1 +/- 6.5 mmHg (P greater than 0.05) as measured immediately postoperatively, at 1 week, and at 3 weeks, respectively, following placement of the prosthesis. There was no instance of prosthetic migration or esophageal perforation. One postoperative death due to distention and perforation of the colon occurred. Two animals developed distal esophageal impaction of food. We conclude that the antireflux prosthesis can be safely and effectively placed using laparoscopic methods in a porcine model. Further development of this technique is warranted.

Improved technique for establishing pneumoperitoneum for laparoscopy

The establishment of a pneumoperitoneum is essential for laparoscopy. Anatomical features of the umbilicus can be used to reduce associated complications and improve the ease of creating a pneumoperitoneum.

Distribution of D2 dopamine receptor mRNA in the primate brain

1. The distribution of the messenger RNA (mRNA) encoding the D2 dopamine receptor has been mapped in the monkey brain by in situ hybridization. 2. Using [35S]-labelled riboprobes corresponding to the region of the D2 dopamine receptor spanning the third cytosolic loop and the sixth and seventh transmembrane domains, specific hybridization was observed in a number of neural structures. 3. High levels of mRNA expression were observed in the caudate, putamen, and claustrum. Significant amounts were also identified in the hippocampus, lateral geniculate nucleus, much of the cortex, amygdala, pons, and thalamus. High levels of this mRNA were also visualized in the substantia nigra, likely reflecting autoreceptor synthesis. 4. While the distribution of D2 dopamine receptor mRNA was similar between the monkey and previously published maps in the rat, several differences were noted. 5. These results demonstrate the feasibility of visualizing this mRNA in the primate brain, and suggest that a similar analysis of human postmortem brain material may be possible.

A comparison of D1 receptor binding and mRNA in rat brain using receptor autoradiographic and in situ hybridization techniques

D1, a subtype of the dopamine receptors, is widely distributed in the nervous system and has been shown to be positively coupled to adenylate cyclase. Using a combination of in vitro receptor autoradiographic and in situ hybridization techniques, the present study examines the co-distribution of D1 receptor binding sites and D1 receptor messenger RNA in adjacent rat brain sections. D1 receptor binding sites were labeled using the selective antagonist [3H]SCH23390 (4.6 nM) in the presence of 1 microM ketanserin, while the D1 receptor messenger RNA was visualized with a 35S-labeled riboprobe corresponding to a region between transmembrane domains III and VI of the rat D1 receptor (bp 383-843). Analysis of serial sections suggested a good agreement between D1 receptor binding and messenger RNA in several brain regions, including the paleocortex, caudate-putamen, nucleus accumbens, amygdala and suprachiasmatic nucleus. Marked discrepancies between D1 receptor binding and messenger RNA were observed in other brain regions including the entopeduncular and subthalamic nuclei, substantia nigra (pars reticulata), hippocampus and cerebellum. While technical considerations may contribute to these results, much of the discordance between the distributions is likely due to the differential localization D1 receptor messenger RNA in cell bodies and receptor binding sites on fibers and may provide insights into receptor synthesis, transport and membrane insertion. In the basal ganglia, for instance, D1 receptors are synthesized in the striatum and are either transported to efferent projections in areas such as the substantia nigra, or remain localized in striatal cells bodies. Ibotenic acid lesions in the striatum are consistent with these conclusions and demonstrate a coordinate loss of D1 receptor binding and messenger RNA in the caudate-putamen that is accompanied by a degeneration of fibers projecting to substantia nigra and a loss of D1 binding in the pars reticulata. Neurons in the dentate gyrus and in the granular layer of the cerebellum, on the other hand, synthesize D1 receptors and transport them entirely to either their dendritic or axonal fields, respectively, in the molecular layer. This analysis provides a better understanding of dopaminergic receptor systems in the CNS and their anatomical organization.

Localization of dopamine D2 receptor mRNA and D1 and D2 receptor binding in the rat brain and pituitary: an in situ hybridization-receptor autoradiographic analysis

Several lines of evidence suggest the existence of multiple dopamine receptor subtypes, referred to as D1 and D2. The present study examines the distribution of these dopamine binding sites in the rat brain and pituitary in relation to the distribution of D2 receptor mRNA using a combination of in vitro receptor autoradiographic and in situ hybridization techniques. 3H-Raclopride and 3H-SCH23390 (in the presence of 1 microM ketanserin) were used to label D2 and D1 receptor binding sites, respectively, while a 495 bp cRNA probe synthesized from the Sac I-Bgl II fragment of a rat D2 receptor cDNA was used to visualize the D2 receptor mRNA. Analysis of adjacent tissue sections in which receptor autoradiography and in situ hybridization had been performed revealed several brain regions where the D2 binding site and corresponding mRNA appear to be similarly distributed, including the caudate-putamen, nucleus accumbens, olfactory tubercle, globus pallidus, substantia nigra, and ventral tegmental area. In the pituitary gland, D2 binding sites and mRNA appear to be codistributed with very dense levels in the intermediate lobe and individually labeled cells in the anterior lobe. Brain regions demonstrating a lack of correspondence between the distribution of the D2 binding site and D2 receptor mRNA include the olfactory bulb, neocortex, paleocortex, hippocampus, and zona incerta. Several hypotheses are discussed to explain the lack of correspondence in certain brain regions; these include the localization of receptor binding sites on both fibers and cell bodies and receptor transport. These studies provide a better understanding of the anatomical distribution of the D2 receptor and serve as a framework for future regulatory and anatomical mapping studies. By focusing on specific brain regions, such as the nigrostriatal system, hippocampus, and olfactory bulb, they provide insights into D2 receptor synthesis, transport, and insertion into cell membranes.

Distribution of D2 dopamine receptor mRNA in rat brain

The distribution of mRNA coding for the D2 dopamine receptor was studied in the rat brain by in situ hybridization. A cDNA probe corresponding to the putative third cytosolic loop and sixth and seventh transmembrane domains of the rat D2 receptor was used to generate an 35S-labeled riboprobe to hybridize to D2 receptor mRNA. D2 mRNA was found both in dopamine projection fields and in regions associated with dopamine-containing cell bodies, suggesting both postsynaptic and presynaptic autoreceptor localization. Highest concentrations of D2 mRNA were found in neostriatum, olfactory tubercle, substantia nigra, ventral tegmental area, and the nucleus accumbens. This distribution is consistent with those reported with D2 receptor autoradiography.

Familial Mediterranean fever in six Australian children

Six Australian children fulfilled the diagnostic criteria for familial Mediterranean fever. None had a family history of the disease, but five children came from ethnic groups that typically were associated with the disease. The symptoms commenced before five years of age in all the children, and three children underwent unnecessary operations because of the symptoms of recurrent fever and abdominal pain. All six children benefited from colchicine prophylaxis by mouth. More cases can be expected to be recognized in Australia because of the large number of Australian children with a Mediterranean heritage.

[Prevention of infections in gynecologic surgery]

Antibiotic prophylaxis is in vogue. It seems effective but is not a panacea. A strict technique and a thorough postoperative monitoring are undoubtedly non negligible means of preventing postoperative infections in gynaecological surgery.

Role of steric interactions in the delta opioid receptor selectivity of [D-Pen2, D-Pen5]enkephalin

In order to assess the individual effects of each of the 3-methyl groups in residue 2 of [D-Pen2, D-Pen5]enkephalin on binding affinity to mu and delta opioid receptors, (2S,3S)methylcysteine ((3S)Me-D-Cys) and (2S,3R)methylcysteine ((3R)Me-D-Cys) were synthesized and incorporated into the analogs, [(3S)Me-D-Cys2, D-Pen5] enkephalin and [(3R)Me-D-Cys2, D-Pen5]enkephalin. Of these analogs, [(3S)Me-D-Cys2, D-Pen5]enkephalin appears from 1H n.m.r. spectra to assume a conformation similar to those of [D-Pen2, D-Pen5]enkephalin and the less delta receptor-selective, but more potent, [D-Cys2, D-Pen5]enkephalin. Assessment of binding affinity to mu and delta receptors revealed that [(3S)Me-D-Cys2, D-Pen5]enkephalin exhibits delta receptor affinity intermediate between [D-Pen2, D-Pen5]enkephalin and [D-Cys2, D-Pen5]enkephalin while its mu receptor affinity is similar to that of [D-Cys2, D-Pen5]enkephalin. These results suggest that, for [D-Pen2, D-Pen5]enkephalin, adverse steric interactions between the D-Pen2 pro-R methyl group and the mu receptor binding site lead to the low mu receptor binding affinity observed for this analog. By contrast, both the pro-R and pro-S D-Pen2 methyl groups lead to minor steric interactions which contribute to the somewhat lower delta receptor affinity of this compound.

Autoradiographic differentiation of mu, delta, and kappa opioid receptors in the rat forebrain and midbrain

While there is an abundance of pharmacological and biochemical evidence to suggest the existence of multiple opioid receptors, their precise localization within the brain is unclear. To help clarify this issue, the present study examined the distributions of the mu, delta, and kappa opioid receptor subtypes in the rat forebrain and midbrain using in vitro autoradiography. Mu and delta receptors were labeled with the selective ligands 3H-DAGO (Tyr- D-Ala-Gly-MePhe-Gly-ol), and 3H-DPDPE (D-Pen2, D-Pen5-enkephalin), respectively, while the kappa receptors were labeled with 3H-(-)bremazocine in the presence of unlabeled DAGO and DPDPE. Based on previous findings in our laboratory, the labeling conditions were such that each ligand selectively occupied approximately 75% of each of the opioid sites. The results demonstrated that all 3 opioid receptor subtypes were differentially distributed in the rat brain. Mu binding was dense in anterior cingulate cortex, neocortex, amygdala, hippocampus, ventral dentate gyrus, presubiculum, nucleus accumbens, caudate putamen, thalamus, habenula, interpeduncular nucleus, pars compacta of the substantia nigra, superior and inferior colliculi, and raphe nuclei. In contrast, delta binding was restricted to only a few brain areas, including anterior cingulate cortex, neocortex, amygdala, olfactory tubercle, nucleus accumbens, and caudate putamen. Kappa binding, while not as widespread as observed with mu binding, was densely distributed in the amygdala, olfactory tubercle, nucleus accumbens, caudate putamen, medial preoptic area, hypothalamus, median eminence, periventricular thalamus, and interpeduncular nucleus. While all 3 opioid receptor subtypes could sometimes be localized within the same brain area, their precise distribution within the region often varied widely. For example, in the caudate putamen, mu binding had a patchy distribution, while delta and kappa sites were diffusely distributed, with delta sites being particularly dense ventrolaterally and kappa sites being concentrated ventromedially. These results support the existence of at least 3 distinct opioid receptors with possibly separate functional roles.

Pharmacological and anatomical evidence of selective mu, delta, and kappa opioid receptor binding in rat brain

While the distribution of opioid receptors can be differentiated in the rat central nervous system, their precise localization has remained controversial, due, in part, to the previous lack of selective ligands and insensitive assaying conditions. The present study analyzed this issue further by examining the receptor selectivity of [3H]DAGO (Tyr-D-Ala-Gly-MePhe-Gly-ol), [3H]DPDPE (2-D-penicillamine-5-D-penicillamine-enkephalin), [3H]DSLET (Tyr-D-Ser-Gly-Phe-Leu-Thr) and [3H](-)bremazocine, and their suitability in autoradiographically labelling selective subpopulations of opioid receptors in rat brain. The results from saturation, competition, and autoradiographic experiments indicated that the three opioid receptor subtypes can be differentiated in the rat brain and that [3H]DAGO and [3H]DPDPE selectively labelled mu and delta binding sites, respectively. In contrast, [3H]DSLET was found to be relatively non-selective, and labelled both mu and delta sites. [3H]Bremazocine was similarly non-selective in the absence of mu and delta ligands and labelled all three opioid receptor subtypes. However, in the presence of 100 nM DAGO and DPDPE, concentrations sufficient to saturate the mu and delta sites, [3H]bremazocine did label kappa sites selectively. The high affinity [3H]bremazocine binding sites showed a unique distribution with relatively dense kappa labelling in the hypothalamus and median eminence, areas with extremely low mu and delta binding. These results point to the selectivity, under appropriate conditions, of [3H]DAGO, [3H]DPDPE and [3H]bremazocine and provide evidence for the differential distribution of mu, delta, and kappa opioid receptors in rat brain.