Neuroscience
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Comparative Study
A change in the pattern of activity affects the developmental regression of the Purkinje cell polyinnervation by climbing fibers in the rat cerebellum.
Pattern of activity during development is important for the refinement of the final architecture of the brain. In the cerebellar cortex, the regression from multiple to single climbing fiber innervation of the Purkinje cell occurs during development between postnatal days (P) 5 and 15. However, the regression is hampered by altering in various ways the morpho-functional integrity of the parallel fiber input. ⋯ Thus, a change in the pattern of activity during a narrow developmental period may affect climbing fiber-Purkinje cell synapse competition resulting in occurrence of multiple innervation at least up to 3 months of age. Our results extend the current view on the role of the pattern of activity in the refinement of neuronal connections during development. They suggest that many similar results obtained by different gene or receptor manipulations might be simply the consequence of disrupting the pattern of activity.
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Previous research in this laboratory has shown that a diet of intermittent excessive sugar consumption produces a state with neurochemical and behavioral similarities to drug dependency. The present study examined whether female rats on various regimens of sugar access would show behavioral cross-sensitization to a low dose of amphetamine. After a 30-min baseline measure of locomotor activity (day 0), animals were maintained on a cyclic diet of 12-h deprivation followed by 12-h access to 10% sucrose solution and chow pellets (12 h access starting 4 h after onset of the dark period) for 21 days. ⋯ Nine days later locomotor activity was measured in response to a single low dose of amphetamine (0.5 mg/kg). The animals that had experienced cyclic sucrose and chow were hyperactive in response to amphetamine compared with four control groups (ad libitum 10% sucrose and chow followed by amphetamine injection, cyclic chow followed by amphetamine injection, ad libitum chow with amphetamine, or cyclic 10% sucrose and chow with a saline injection). These results suggest that a diet comprised of alternating deprivation and access to a sugar solution and chow produces bingeing on sugar that leads to a long lasting state of increased sensitivity to amphetamine, possibly due to a lasting alteration in the dopamine system.
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Sleep deprivation exerts antidepressant effects after only one night of deprivation, demonstrating that a rapid antidepressant response is possible. In this report we tested the hypothesis that total sleep deprivation induces an increase in extracellular serotonin (5-HT) levels in the hippocampus, a structure that has been proposed repeatedly to play a role in the pathophysiology of depression. Sleep deprivation was performed using the disk-over-water method. ⋯ During an additional sleep recovery day, 5-HT remained elevated even though rats displayed normal amounts of sleep. Stimulus control rats, which had been allowed to sleep, did not experience a significant increased in 5-HT levels, though they were exposed to a stressful situation similar to slee-deprived rats. These results are consistent with a role of 5-HT in the antidepressant effects of sleep deprivation.
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Comparative Study
Synaptic loss following depletion of noradrenaline and/or serotonin in the rat visual cortex: a quantitative electron microscopic study.
Biogenic amines have a trophic-like role for the formation and the maintenance of synapses in the CNS. We examined the changes in the number of synaptic profiles in the developing and adult rat visual cortex following selective depletion of noradrenaline and/or serotonin. By the drug-induced decreases in levels of noradrenaline or serotonin between 1 and 2 weeks after birth, the number of synaptic profiles was decreased by 29-55% compared with that of control animals. ⋯ The number of axodendritic synapses was the highest between 2 and 7 weeks after birth, and decreased to 50% at 11 weeks after birth. These data demonstrate that synapses in the rat visual cortex are overproduced during the early developmental period. We suggest that both serotonin and noradrenaline are necessary for synapse formation during the early stages of development of the rat visual cortex.
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Comparative Study
Sex differences in the hippocampal dentate gyrus of the guinea-pig before puberty.
The aim of the present research was to ascertain the presence of sex differences in the hippocampal dentate gyrus of the guinea-pig, a long-gestation rodent which gives birth to mature young and whose brain is at a more advanced stage of maturation at birth than that of the rat and mouse. The brains of neonatal (15-16 days old) and prepubescent (45-46 days old) male and female guinea pigs were Golgi-Cox stained. Granule cells were sampled from the upper (suprapyramidal) and lower (infrapyramidal) blade of the septal dentate gyrus and their dendritic tree and soma were measured. ⋯ In the lower blade the granule cells showed very few sex differences in both neonatal and prepubescent animals. This study shows wide dynamically changing sex differences in the granule cells located in the upper blade of the septal dentate gyrus, but almost no differences in the lower blade. These results demonstrate that sex differences are not ubiquitous in the dentate gyrus and suggest that the lower blade, unlike the upper blade, might be involved in non-sexually dimorphic behaviors.