Synaptic input and output of parvalbumin-immunoreactive neurons in the neostriatum of the rat

Previous studies have demonstrated that the calcium-binding protein parvalbumin, is located within a population of GABAergic interneurons in the neostriatum of the rat. Anatomical studies have revealed that these cells receive asymmetrical synaptic input from terminals that are similar to identified cortical terminals and that they innervate neurons with the ultrastructural features of medium spiny cells. Furthermore, electrophysiological studies suggest that some GABAergic interneurons in the neostriatum receive direct excitatory input from the cortex and inhibit medium spiny cells following cortical stimulation. The main objectives of the present study were (i) to determine whether parvalbumin-immunoreactive neurons in the rat receive direct synaptic input from the cortex, (ii) to determine whether parvalbumin-immunopositive axon terminals innervate identified striatal projection neurons and (iii) to chemically characterize this anatomical circuit at the fine structural level. Rats received stereotaxic injections of biocytin in the frontal cortex or injections of neurobiotin in the substantia nigra. Following an appropriate survival time, the animals were perfused and the brains were sectioned and treated to reveal the transported tracers. Sections containing the neostriatum were treated for simultaneous localization of the transported tracer and parvalbumin immunoreactivity. Tracer deposits in the cortex gave rise to massive terminal and fibre labelling in the neostriatum. Parvalbumin-immunoreactive elements located within fields of anterogradely labelled terminals were examined in the electron microscope and corticostriatal terminals were found to form asymmetrical synaptic specializations with all parts of parvalbumin-immunoreactive neurons that were examined. Tracer deposits in the substantia nigra produced retrograde labelling of a subpopulation of striatonigral neurons. Areas of the neostriatum and nucleus accumbens containing retrogradely labelled neurons and parvalbumin-immunoreactive structures were selected for electron microscopy. Parvalbumin-immunopositive axon terminals formed symmetrical synaptic specializations with the perikarya of retrogradely labelled medium spiny projection neurons. Postembedding immunocytochemistry for GABA revealed that parvalbumin-immunoreactive boutons in synaptic contact with medium spiny neurons were GABA-positive. These data demonstrate directly a neural circuit whereby cortical information may be passed to medium spiny cells, via GABAergic interneurons, in the form of inhibition and provide an anatomical substrate for the feed-forward inhibition that has been detected in spiny neurons in electrophysiological experiments.     

The role of antibiotics in the management of elective and post-traumatic hand surgery

Stunting syndrome (SS) is a viral enteric disease of turkey poults. The etiologic agent (stunting syndrome agent [SSA]) of this disease has been reported recently. The objective of this study was to develop a method for in vitro propagation of SSA. Primary cells, various continuous cell lines, and embryonated eggs were evaluated. Turkey embryos that were inoculated via the amniotic cavity at 24-25 days of incubation were susceptible to SSA infection. The jejunal maltase activity of SSA-inoculated turkey embryos was significantly (P < or = 0.001) lower than that of control embryos. D-xylose absorption was also altered in SSA-infected turkey embryos. The extent of reduction of D-xylose absorption and maltase activity in the infected embryos was nearly identical to that observed when day-old poults were infected with SSA. The intestines from the infected turkey embryos were pale, thin walled, and distended with fluid. Electron microscopic examination of the intestinal fluid and epithelial cell lysate of infected embryos revealed pleomorphic membraned SSA viral particles. SSA that had been serially passaged in turkey embryos retained its ability to induce SS in day-old poults. All the primary and continuous cells that were evaluated did not support the replication of SSA on the basis of cytopathic effects, electron microscopy, and turkey embryo inoculation. Inoculation of chicken embryos by various routes failed to support SSA. All routes of inoculation, other than the amniotic route at 24-25 days, failed to support SSA in turkey embryos. The results of the this study indicate that the SSA was successfully propagated in turkey embryos that exhibited alterations in embryo intestinal absorption and digestive enzyme activity similar to poults with SS. Successful propagation of SSA in turkey embryos should prove beneficial for future studies including characterization of SSA, prevention and control strategies, and enteric disease modeling.     

Patterns of connections between zona incerta and brainstem in rats

To understand better the organisation of zona incerta of the thalamus, this study has examined the patterns of connections that this nucleus has with various nuclei of the brainstem. Injections of biotinylated dextran or cholera toxin subunit B were made into the dorsal raphe, midbrain reticular nucleus, pedunculopontine tegmental nucleus, periaqueductal grey matter, pontine reticular nucleus, substantia nigra, superior colliculus, and ventral tegmental area of Sprague-Dawley rats, and their brains were processed by using standard tracer-detection methods. In general, our results show that zona incerta forms the major zone in the thalamus where these ascending brainstem axons terminate and from which descending axons that travel back to these same brainstem centres originate. These incertal inputs and outputs are limited largely to a distinct sector of zona incerta, the dorsal sector. An exception to this pattern is evident in the incertal projection to the deep layers of the superior colliculus; this projection, unlike all of the others, arises from cells in the ventral sector of zona incerta. Our results also show little evidence for a well-defined topography of projection between the brainstem and the zona incerta. For instance, small injections into each brainstem nucleus result in labelled terminals and in cells spread throughout much of the dorsal sector of zona incerta, with no local zone of concentration within the sector. Again, an exception to this pattern is seen in the incertal projection to the superior colliculus. This projection, unlike the others, shows a clear topographical organisation: A medial-lateral shift in the injection site in the colliculus results in a lateral-medial shift in the position of labelled cells in zona incerta. Curiously, even though the incertal projection to the colliculus appears to be mapped, the collicular projection back to zona incerta is not mapped. In conclusion, then, a number of brainstem nuclei (except for the deep collicular layers) have strong and overlapping connections within the same sector of zona incerta. This convergence of many functionally diverse brainstem afferents within zona incerta places this nucleus in a strategic position to sample the general activity of the brainstem and, perhaps, acts as a relay of this information to higher centres, such as the dorsal thalamic relay nuclei and the cerebral hemispheres.     

Alanine and glutamine kinetics at rest and during exercise in humans

PURPOSE: The purpose of this study was to quantify both alanine and glutamine kinetics during exercise of moderate intensity to determine the sum total of alanine and glutamine flux. METHODS: Tracer methods were used to quantify alanine and glutamine rates of appearance (Ra) in plasma at rest and during 180 min of approximately 45% VO2max treadmill exercise in six normal volunteers (25 +/- 2 yr, 68 +/- 2.5 kg, VO2max 43 +/- 2.4 mL.min-1.kg-1; means +/- SE). Bolus injections (N = 3) or primed-constant infusions (N = 3) of 2H5-glutamine and 3-13C-alanine were given at rest on 1 d and 10-15 min after the onset of exercise on a separate day less than 2 wk later. Plasma enrichment decay curves and plateau enrichments were used to estimate alanine and glutamine kinetics. RESULTS: Whereas alanine Ra increased significantly from rest to exercise (5.72 +/- 0.31 vs 13.5 +/- 1.9 mumol.min-1.kg-1, respectively; P < 0.01), glutamine Ra was not significantly altered by exercise (6.11 +/- 0.44 and 6.40 +/- 0.69 mumol.min-1.kg-1 at rest and during exercise, respectively). The total of alanine and glutamine flux increased from 17.93 +/- 0.88 to 25.98 +/- 3.04 (P < 0.05). CONCLUSIONS: Since most muscle amino-N is released as alanine and glutamine, these findings provide strong evidence that amino-N delivery from muscle to the liver is increased during exercise. In addition, it appears that alanine, rather than glutamine, is the predominant N carrier involved in the transfer of N from muscle to the liver during moderate intensity exercise.     

Renal resistive index in experimental partial and complete ureteral obstruction

RATIONALE AND OBJECTIVES: Recent clinical work suggests that the Doppler resistive index (RI) may be useful in distinguishing obstructive from nonobstructive hydronephrosis. We evaluated the usefulness of the RI in a rabbit model of hydronephrosis. METHODS: Unilateral partial ureteral obstruction was produced in nine rabbits and complete obstruction in another nine. Three sham operations were performed, and these animals served as control subjects. The RI was measured in all kidneys before and 6 hr after surgery and on days 1, 4, and 7 postoperatively. The RI and the difference in RI (delta RI) between the obstructed and normal kidney were evaluated over time using a two-way analysis of variance. The intravenous urography and Whitaker tests served as gold standards. RESULTS: Hydronephrosis was observed on sonograms in all obstructed kidneys. Comparing groups, there was no significant difference in mean RI or delta RI between the three groups at any time point. Looking at individual groups over time, there was no significant change in mean delta RI, whereas the change in mean RI was significantly elevated above baseline only in the complete obstruction group at 6 hr (p = .002) and on days 4 (p = .008) and 7 (p = .006). In evaluating varying thresholds of RI and delta RI, we could not consistently discriminate between normal and obstructed kidneys. CONCLUSION: Although complete obstruction caused a significant increase in RI, partial obstruction failed to do so. RI and delta RI values proved to be insensitive predictors of obstruction in this rabbit model.     

Adrenoceptor-mediated elevation of ambient GABA levels activates presynaptic GABA(B) receptors in rat sensorimotor cortex

At inhibitory synapses in the mature neocortex and hippocampus in vitro, spontaneous action-potential-dependent and -independent release of gamma-aminobutyric acid (GABA) activates postsynaptic GABA(A) receptors but not pre- or postsynaptic GABA(B) receptors. Elevation of synaptic GABA levels with pharmacological agents or electrical stimulation can cause activation of GABA(B) receptors, but the physiological conditions under which such activation occurs need further elucidation. In rodent sensorimotor cortex, epinephrine produced a depression in the amplitude of evoked monosynaptic inhibitory postsynaptic currents (IPSCs) and a concomitant, adrenoceptor-mediated increase in the frequency of spontaneous IPSCs. Blockade of GABA(B) receptors prevented the depression of evoked IPSC amplitude by epinephrine but did not affect the increase in spontaneous IPSC frequency. These data show that adrenoceptor-mediated increases in spontaneous IPSCs can cause activation of presynaptic GABA(B) receptors and indirectly modulate impulse-related GABA release, presumably through elevation of synaptic GABA levels.     

A genetic system to identify DNA polymerase beta mutator mutants

Hemagglutinins were determined in six species of mosquitoes that are susceptible and refractory to Brugia malayi (Filarioidea: Nematoda). High titers of hemagglutinins were found in the salivary gland extract and in the body fluid of a completely refractory species, Aedes taeniorhynchus, and in partially refractory species, Anopheles quadrimculatus but low levels of hemagglutinins were also present in the body fluid of Aedes aegypti (Black-eye, Liverpool strain), a susceptible species. Hemagglutinating activity was not found in the other three completely refractory species of mosquitoes, Culex quinquefasciatus, Culex nigripalpus, and Aedes albopictus in which blood coagulated rapidly after ingestion. High titers of hemagglutinins in the salivary glands of Ae. taeniorhynchus and An. quadrimaculatus facilitated rapid movement of sheathed microfilariae from the midgut to the hemocoel. It is suggested that high titers of hemagglutinins present in the hemocoel bound to the glycoconjugates with exposed carbohydrate moieties present on the microfilarial sheaths and developing abnormal larvae (L1) in the thoracic muscle cells. These hemagglutinin-bound glycoconjugates formed capsules that subsequently stimulated the immune response and resulted in melanization of microfilarial sheaths and sheathed microfilariae in the hemocoel and intracellularly developing abnormal L1 in the thoracic muscles. Only minimal encapsulation and melanization of B. malayi microfilariae was observed in the hemocoel of the other four species of mosquitoes that lacked hemagglutinins in the salivary glands. The results suggest that tissue specific hemagglutinins are one of several factors of vector susceptibility/refractoriness through immune reactions (encapsulation, activation of prophenoloxidases).