Neuroscience
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In the present study, we examined whether exposing rats to a high-dose regimen of manganese chloride (Mn) during the postnatal period would depress presynaptic dopamine functioning and alter nonassociative and associative behaviors. To this end, rats were given oral supplements of Mn (750 microg/day) on postnatal days (PD) 1-21. On PD 90, dopamine transporter (DAT) immunoreactivity and [3H]dopamine uptake were assayed in the striatum and nucleus accumbens, while in vivo microdialysis was used to measure dopamine efflux in the same brain regions. ⋯ Interestingly, acquisition of a fixed ratio task was impaired in Mn-exposed rats, suggesting a deficit in procedural learning. In sum, these results indicate that postnatal Mn exposure causes persistent declines in various indices of presynaptic dopaminergic functioning. Mn-induced alterations in striatal functioning may have long-term impact on associative and nonassociative behavior.
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It has previously been reported that dopaminergic grafts derived from early donor age, embryonic age 12-day-old (E12) rat embryos produced a fivefold greater yield of dopamine neurons than those derived from conventional E14 donors. The present study addresses whether E12 grafts are able to ameliorate lesion-induced behavioral deficits to the same extent as E14 grafts. In a unilateral rat model of Parkinson's disease, animals received grafts derived from either E12 or E14 donor embryos, dispersed at four sites in the lesioned striatum. ⋯ However, E12 grafts resulted in cell yields greater than previously reported for untreated primary tissue, with mean TH-positive cell counts in excess of 25,000 neurons, compared with E14 TH cell counts of 4000-5000 cells, representing survival rates of 75% and 12.5%, respectively, based on the expected adult complement. The equivalence of graft induced behavioral recovery between the two graft groups is attributed to a threshold number of cells, above which no further improvement is seen. Such high dopamine cell survival rates should mean that multiple, functioning grafts can be derived from a single embryonic donor, and if similar yields could be obtained from human tissues then the goal of one embryo per patient would be achieved.
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Regulation of adult hippocampal neurogenesis in mice responds to behavioral stimuli, including physical activity (RUN) and the exposure to enriched environments (ENR). If studied after days or weeks, these stimuli and the pathological stimulus of kainic acid-induced seizures (KA) show differential effects on different developmental stages of adult neurogenesis. The question thus arose, whether such differential effects would also be apparent under very acute conditions. ⋯ Twenty-four hours after the stimulus adult neurogenesis showed a very similar response to the three paradigms, in that cell proliferation increased. Detailed analysis, however, revealed the following new results: (1) KA, but not RUN and ENR stimulated the division of radial glia-like type-1 cells, (2) KA led to the disappearance of proliferative undetermined progenitor cells (type-2a), (3) only RUN increased proliferation of type-2a cells, (4) ENR and KA, in contrast, acted on lineage-determined progenitor cells (type-2b and type-3) even under acute conditions, and (5) only in the case of KA the short-term stimulus resulted in measurably increased survival of newborn neurons 4 weeks later. These results confirm and specify the idea that in the course of neuronal development in the adult hippocampus, precursor cells acutely sense and distinguish various forms of "activity" differentially and translate these stimuli into defined responses based on their stage of development.
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There is no adequate animal model of restless legs syndrome (RLS) and periodic leg movements disorder (PLMD), disorders affecting 10% of the population. Similarly, there is no model of rapid eye movement (REM) sleep behavior disorder (RBD) that explains its symptoms and its link to Parkinsonism. We previously reported that the motor inhibitory system in the brainstem extends from the medulla to the ventral mesopontine junction (VMPJ). ⋯ Beyond these common symptoms, an increase in phasic motor activity in REM sleep, resembling that seen in human RBD, was found in the caudal VMPJ-lesioned animals. In contrast, the increase in motor activity in SWS in rostral VMPJ-lesioned animals is similar to that seen in human RLS/PLMD patients. The proximity of the VMPJ region to the substantia nigra suggests that the link between RLS/PLMD and Parkinsonism, as well as the progression from RBD to Parkinsonism may be mediated by the spread of damage from the regions identified here into the substantia nigra.
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Inflammation following ischemic stroke is known to contribute to injury. NADPH oxidase (NOX) is a major enzyme system originally studied in immune cells that leads to superoxide (O.*) generation. Apocynin is a NOX inhibitor that has been studied as a potential treatment in experimental stroke. ⋯ Using hydroethine fluorescence to delineate O.* in the brain, neurons and some microglia/macrophages, but not vascular endothelial cells were found to contain O.*. Apocynin at protective doses markedly prevented ischemia-induced increases in O.*. Our data suggested that apocynin can protect against experimental stroke, but with a narrow therapeutic window.