Neuroscience
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Comparative Study
Serotonergic serotonin (1A) mixed agonists/antagonists elicit large-magnitude phase shifts in hamster circadian wheel-running rhythms.
The biological clock that generates circadian rhythms in mammals is located within the suprachiasmatic nuclei at the base of the hypothalamus. The circadian clock is entrained to the daily light/dark cycle by photic information from the retina. The retinal input to the clock is inhibited by exogenously applied serotonin agonists, perhaps mimicking an endogenous inhibitory serotonergic input to the clock arriving from the midbrain raphe. ⋯ These results suggest that pharmacologically blocking raphe input to the suprachiasmatic circadian clock results in substantially larger photically induced phase advances in wheel-running rhythms. This is further evidence that raphe input to the circadian clock is probably acting to dampen the clock's response to light under certain conditions. The large-magnitude phase shifts, and temporal-activity profile seen with BMY 7378 and S 15535, suggest that compounds with this unique pharmacological profile may be beneficial in the treatment of circadian phase delays recently reported to be a complication resulting from Alzheimer's disease.
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Comparative Study
Acetoacetate protects hippocampal neurons against glutamate-mediated neuronal damage during glycolysis inhibition.
Glucose is the main substrate that fulfills energy brain demands. However, in some circumstances, such as diabetes, starvation, during the suckling period and the ketogenic diet, brain uses the ketone bodies, acetoacetate and beta-hydroxybutyrate, as energy sources. Ketone body utilization in brain depends directly on its blood concentration, which is normally very low, but increases substantially during the conditions mentioned above. ⋯ We have previously demonstrated that accumulation of extracellular glutamate after inhibition of its transporters, induces neuronal death in vivo during energy impairment induced by glycolysis inhibition. In the present study we have assessed the protective potentiality of the ketone body, acetoacetate, against glutamate-mediated neuronal damage in the hippocampus of rats chronically treated with the glycolysis inhibitor, iodoacetate, and in hippocampal cultured neurons exposed to a toxic concentration of iodoacetate. Results show that acetoacetate efficiently protects against glutamate neurotoxicity both in vivo and in vitro probably by a mechanism involving its role as an energy substrate.
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Comparative Study
Intrinsic collaterals of layer 6 Meynert cells and functional columns in primate V1.
Meynert cells are a distinct type of large neuron which project to area MT/V5 and to subcortical targets, including the superior colliculus. They have recently been shown to have extensive intrinsic collaterals spreading up to 8.0 mm within layer 6 of area V1 [J Comp Neurol 441 (2001) 134]. Using intrinsic signal imaging combined with tracer injections, this study investigates how Meynert cell collaterals are mapped in relation to the functional architecture of area V1 in macaque monkeys. ⋯ This contrasts with the same-eye bias previously reported for intrinsic collaterals of pyramidal neurons in layer 3. The suggestion is that the system of Meynert intrinsic collaterals is involved with binocular interactions over wide sectors of the visual field. This might be related to processes such as optic flow or, especially given the wide-field spread, even contour completion or interpolation.
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Comparative Study
A comparative magnetoencephalographic study of cortical activations evoked by noxious and innocuous somatosensory stimulations.
We recorded somatosensory-evoked magnetic fields and potentials produced by painful intra-epidermal stimulation (ES) and non-painful transcutaneous electrical stimulation (TS) applied to the left hand in 12 healthy volunteers to compare cortical responses to noxious and innocuous somatosensory stimulations. Our results revealed that cortical processing following noxious and innocuous stimulations was strikingly similar except that the former was delayed approximately 60 ms relative to the latter, which was well explained by a difference in peripheral conduction velocity mediating noxious (Adelta fiber) and innocuous (Abeta fiber) inputs. The first cortical activity evoked by both ES and TS was in the primary somatosensory cortex (SI) in the hemisphere contralateral to the stimulated side. ⋯ The time course of the vertex potential corresponded to that of the activity of the medial temporal area. Our results suggested that cortical processing was similar between noxious and innocuous stimulation in SI and SII, but different in insular cortex. Our data also implied that activities in the amygdala/hippocampal formation represented common effects of noxious and tactile stimulations.
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Comparative Study
Long-term effects of maternal separation on ethanol intake and brain opioid and dopamine receptors in male Wistar rats.
Accumulating evidence indicates that an animal's response to a drug can be profoundly affected by early environmental influences. The brain opioid and dopamine systems may play a critical role in these effects, since various types of stress and drugs of abuse promote alterations in these brain systems. To study this further, we investigated long-term behavioural and neurochemical effects of repeated maternal separation in male Wistar rats. ⋯ Ethanol-induced changes were observed in D(2)-like receptor density in the ventral tegmental area in MS360, and in the ventral tegmental area and frontal-parietal cortex in animal facility-reared rats. These findings show that early experiences can induce long-lasting changes in especially brain dopamine receptor density and that ethanol consumption induces alterations in opioid and dopamine receptor density in distinct brain areas. It is also suggested that changes induced by repeated MS15 may provide protection against high voluntary ethanol intake.