Cortical regulation of dopaminergic neurons: role of the midbrain superior colliculus.

Dopaminergic (DA) neurons respond to stimuli in a wide range of modalities, although the origin of the afferent sensory signals has only recently begun to emerge. In the case of vision, an important source of short-latency sensory information seems to be the midbrain superior colliculus (SC). However, longer-latency responses have been identified that are less compatible with the primitive perceptual capacities of the colliculus. Rather, they seem more in keeping with the processing capabilities of the cortex. Given that there are robust projections from the cortex to the SC, we examined whether cortical information could reach DA neurons via a relay in the colliculus. The somatosensory barrel cortex was stimulated electrically in the anesthetized rat with either single pulses or pulse trains. Although single pulses produced small phasic activations in the colliculus, they did not elicit responses in the majority of DA neurons. However, after disinhibitory intracollicular injections of the GABAA antagonist bicuculline, collicular responses were substantially enhanced and previously unresponsive DA neurons now exhibited phasic excitations or inhibitions. Pulse trains applied to the cortex led to phasic changes (excitations to inhibitions) in the activity of DA neurons at baseline. These were blocked or attenuated by intracollicular administration of the GABAA agonist muscimol. Taken together, the results indicate that the cortex can communicate with DA neurons via a relay in the SC. As a consequence, DA neuronal activity reflecting the unexpected occurrence of salient events and that signaling more complex stimulus properties may have a common origin.

Ethanol exposure selectively alters beta-endorphin content but not [3H]-DAMGO binding in discrete regions of the rat brain.

The dopaminergic mesocorticolimbic system plays an important role in the reinforcing effects of ethanol. Opioid peptides modulate the activity of this system and have been suggested to mediate, at least in part, the reinforcing properties of ethanol. Thus, beta-endorphin (beta-END) could participate in the development of ethanol reinforcement and addiction. The aim of this work was to investigate the acute and chronic ethanol effects on beta-END content in regions of the mesolimbic system and to examine if chronic ethanol treatment alters ligand binding to mu opioid receptor (muOR). Male Wistar rats received a single acute ethanol dose of 2.5 g/kg or water by intra-gastric administration. For chronic ethanol treatment experiments, one group of rats was given ethanol (10% v/v solution) to drink, two groups were given equivalent volumes of sucrose (14.14% isocaloric solution) or water, respectively, and a fourth group had ad libitum access to food and water. Treatment was followed for 4 weeks. Beta-endorphin content in brain regions was quantified by radioimmunoassay and ligand binding studies to muOR were performed by quantitative autoradiography using 8 nM [(3)H]-DAMGO as radioligand. Acute ethanol decreased beta-END content in the hypothalamus (26%) 1h after administration. No ethanol effects were observed in the midbrain, ventral tegmental area, substantia nigra, nucleus accumbens, nucleus accumbens-septum and prefrontal cortex. Chronic ethanol treatment neither changed beta-END levels nor [(3)H]-DAMGO binding to mu opioid receptors in any of the regions studied. However, beta-END levels in the sucrose group were significantly increased in the nucleus accumbens and substantia nigra, in comparison to all other groups. These findings suggest that different neural mechanisms and specific brain regions may be involved in the reinforcing effects of ethanol and sucrose.

Acute ethanol induces Fos in GABAergic and non-GABAergic forebrain neurons: a double-labeling study in the medial prefrontal cortex and extended amygdala.

The purpose of this study was to further address the hypothesis that ethanol activates GABAergic neurons in specific brain neurocircuits that mediate motivated behavior and control of action, such as the central extended amygdala and medial prefrontal cortex. Male Sprague-Dawley rats received habituation to 7 days of daily intragastric administration of water (5 ml/kg) followed by a single acute intragastric dose of ethanol (2.5 g/kg) or water then, 2 h later, by paraformaldehyde perfusion. Rats left undisturbed in the animal room throughout the experiment were also perfused (naive group). Brain sections were processed for single Fos immunohistochemistry or dual Fos immunohistochemistry/glutamic acid decarboxylase (GAD) mRNA in situ hybridization. Intragastric water administration increased the number of Fos-immunoreactive cells in the infralimbic cortex and lateral part of the central nucleus of the amygdala compared with the naive group. Ethanol administration increased the number of Fos-immunoreactive cells in the infralimbic (+57.5%) and prelimbic (+105.3%) cortices, nucleus accumbens shell region (+88.2%), medial part of the central nucleus of the amygdala (+160%), and lateral part of the bed nucleus of the stria terminalis (+198.8%) compared with the water-treated group. In the nucleus accumbens shell region, central nucleus of the amygdala, and bed nucleus of the stria terminalis, more than 80% of Fos-immunoreactive neurons were GABAergic after ethanol administration. In contrast, in the prelimbic cortex, 75% of Fos-immunoreactive neurons were not GABAergic. These results constitute new evidence for region-specific functional interactions between ethanol and GABAergic neurons.

Acute ethanol administration differentially modulates mu opioid receptors in the rat meso-accumbens and mesocortical pathways.

Biochemical and pharmacological evidence suggest that the dopaminergic mesolimbic system plays a key role in mediating the reinforcing properties of alcohol and other drugs of abuse. Alcohol reinforcement and high alcohol drinking behavior have been postulated to be partially mediated by a neurobiological mechanism involving the alcohol-induced activation of the endogenous opioid system. The aim of this work was to study the effect of the in vivo acute administration of ethanol on mu (mu) opioid receptors in the rat dopaminergic meso-accumbens and mesocortical pathways by quantitative receptor autoradiography. [(3)H]DAMGO binding was significantly decreased in the ventral tegmental area (VTA) 30 min after ethanol administration. A small ethanol-induced reduction was observed in the shell region of the nucleus accumbens 1 h after exposure. In contrast, 2 h after ethanol administration, [(3)H]DAMGO binding was significantly increased in the frontal and prefrontal cortices. The observed changes correlated well with high ethanol plasma levels. Our results suggest that the reinforcing properties of ethanol may be partially mediated by mechanisms involving the ethanol-induced down- and up-regulation of mu receptors in the dopaminergic mesolimbic system. Mu receptors in the VTA and the frontal and prefrontal cortices may be involved in the in vivo acute responses to ethanol and could play a key role in modulating the dopaminergic activity of the mesocortical pathway in response to the drug. In contrast, the contribution of both mu and delta receptors in the nucleus accumbens might be relevant in these processes.

Multidisciplinary implant dentistry for improved aesthetics and function.

Functional and aesthetic restorations that involve implant-supported prostheses rely on the efforts of a multidisciplinary team composed of surgeon, prosthodontist, and laboratory technician. The team must examine the anticipated restorative site to determine the suitability of existing hard and soft tissues for implant placement. When the site requires osseous or gingival augmentation, the team must select the appropriate means of restoration from the armamentarium. This article describes chronologically the various parameters that must be considered by each member of the team as the treatment proceeds.

Asymptomatic carriers of Babesia canis in an enzootic area. / Etude du portage asymptomatique de Babesia canis en zone d'enzootie.

Dogs latently infected with Babesia canis were systematically detected amongst a population kept in an enzootic area over a year. Detection of parasite was carried out on 43 healthy dogs and identified by two blood cultures in an interval of a few months. A serological study was performed using indirect immunofluorescence and Western blot. This study distinguished two distinct groups: asymptomatic carrier dogs (latently infected or premunised-33%) and non-carrier dogs with sterilising immunity. There is no difference between carrier and non-carrier dogs concerning age, breed or history of babesial infection and 36 out of the 43 dogs studied are seropositive. The antibody titer did not completely correlate with the detection of parasitaemia. All carrier dogs are seropositive to Babesia canis, but half of the seropositive dogs are not carriers. This study confirms that serological detection is not a good indicator of latent babesial infection. This study did not detect any difference between antibody responses (quantitative response (IIF) or qualitative response (WB)), related to latent parasitaemia.

Immunolocalization and characterization of the low molecular weight antigen (4-5 kDa) of Toxoplasma gondii that elicits an early IgM response upon primary infection.

A striking feature of toxoplasmic seroconversion is the prominent and early IgM response to a low molecular weight antigen of 4-5 kDa. Two different monoclonal antibodies directed against the 4-5 kDa antigen have been generated and used to characterize this molecule. Using these monoclonal antibodies, we could demonstrate the surface localization of the low M(r) antigen by immunofluorescence and immuno-electron microscopy assays. By immunoblotting, we observed that one of the monoclonal antibodies was unable to recognize the 4-5 kDa antigen in tachyzoites propagated in cell culture, indicating an epitope variability between Toxoplasma gondii tachyzoites grown in vivo and in vitro. We discuss the implications of this latter finding in the design of diagnostic reagents.

Differential targeting of dense granule proteins in the parasitophorous vacuole of Toxoplasma gondii.

The biosynthesis and fate of 4 different dense granule proteins of Toxoplasma gondii were studied with 3 monoclonal antibodies raised against tachyzoites and 1 polyclonal antibody raised against a recombinant protein. These proteins have the following molecular weights: 27 kDa (GRA 1), 28 kDa (GRA 2), 30 kDa (GRA 3) and 40 kDa (GRA 4). All four proteins were found in dense granules by immunoelectron microscopy; in T. gondii-infected cells, they were found in the vacuolar network but, in addition, GRA 3 was also detected on the parasitophorous vacuole membrane. Therefore, dense granule contents undergo differential targeting when exocytosed in the parasitophorous vacuole. Metabolic labelling and immunoprecipitation showed that GRA 2 and GRA 3 were processed from lower molecular weight precursors, and that GRA 2 and GRA 4 incorporated [3H] glucosamine and are thus likely to be glycosylated.

Characterization of the lipid content of Toxoplasma gondii rhoptries.

Quantitative and qualitative analysis of lipids has been performed on a rhoptry fraction purified from Toxoplasma gondii tachyzoites. The lipid to protein ratio was estimated to be 0.26. The cholesterol to phospholipid ratio was unusually high at 1.48. Phosphatidylcholine was the major phospholipid; phosphatidylserine, phosphatidylinositol and sphingomyelin were absent whereas significant amounts of phosphatidic acid and lysophospholipids were found. This pelicular composition could be related to functional involvement of the organelle in host-cell invasion.

Characterization of the protein contents of rhoptries and dense granules of Toxoplasma gondii tachyzoites by subcellular fractionation and monoclonal antibodies.

A subcellular fractionation procedure has been established to isolate the rhoptries of Toxoplasma gondii tachyzoites on a self-generating Percoll gradient. The rhoptry fraction also contains dense granules. Monoclonal antibodies have been raised against the fraction and used to identify major proteins in the organelles by immunoelectron microscopy and Western blotting. Six major rhoptry proteins (60.5 kDa, Pi 5.8; 55, 57, 59, 60 kDa, all of Pi over 8; 42 kDa, Pi 4.8) and 3 dense granule proteins (30 kDa; 28kDa, Pi 7.5; 27 kDa, Pi 4.5) together with 5 other proteins of 57, 90, 120, 168, 220 kDa that have been located in the rhoptry area by indirect immunofluorescence have been identified.

Exocytosis of Toxoplasma gondii dense granules into the parasitophorous vacuole after host cell invasion.

Tachyzoites of Toxoplasma gondii have been shown to exocytose the contents of dense granules into the parasitophorous vacuole after host cell invasion. A monoclonal antibody specific for a 27-kDa protein was used to locate the dense granules by immunoelectron microscopy. The same antibody also reacted with the tubular network found in the parasitophorous vacuole, which confirmed that the dense granules were exocytosed by tachyzoites.

Changes in the rectal mucosa induced by hypertonic enemas.

The aspect of the rectal mucosa after administration of hypertonic enemas is occasionally confused with the macroscopic appearance of quiescent ulcerative colitis. Criteria for a diagnosis of enema reaction were derived from a retrospective series and tested prospectively on 11 healthy volunteers. Photographs and biopsies were obtained before and after administration of a sodium phosphate hypertonic enema. Three observers evaluated blindly the "before" and "after" macroscopic and microscopic pictures, graded the features, and made an overall diagnosis. In random studies, two observers mistakenly classified a macroscopic picture, but all correct histologic diagnoses of "before" and "after" biopsies. In decreasing order of discriminating power, the following features of an enema reaction were found to be useful: separation and mucous depletion of the glands (no observer variation), increase in mucosal fragility in 91 per cent of cases (82--100 per cent), edema of the lamina propria in 88 per cent (73--100 per cent), straightening of the basal membrane in 82 per cent (73--91 per cent) and an increase in extruded mucus in 70 per cent (18--100 per cent). In 39 per cent of cases (36--45 per cent), erythrocytes appeared focally in the lamina propria. The effects of hypertonic enemas can be recognized on biopsy.