By K. Ernesto. The Catholic University of America.
Brain slices were prepared to estimate the extent of connections between layers II/III and V using photostimulation of caged glutamate near cells in layers II/III amitriptyline 25 mg low price. The normal cortex showed a strong preference for layer II/III cells above two or three separate septal zones to converge upon single layer V neurons beneath a septum. However this feature of intracortical circuitry was degraded by global SD, so that each layer V neuron received dimin- ishing convergent inputs from layer II/III cells in direct proportion to lateral dis- tance, independent of whether they were under barrels or septa. Anatomical Changes Produced by Global Sensory Deprivation The physiological changes after SD predict that anatomical connections also will be altered by the global SD. An important background note to anatomical changes caused by SD is that many intrinsic connections in barrel cortex develop in the second and third postnatal weeks by increasing the length of horizontal connections through the progressive elongation of more extensive axon arbors (Miller, et al. The maximum impact of low activity rearing has been produced by peripheral nerve damage through cutting the infraorbital nerve on PND 7 and analyzing the spread of cortical connections on PND 42. This nerve damage proce- dure produces a drastic reduction in the horizontal spread of axon terminals in all layers of the barrel cortex. Micheva and Beaulieu118,119 ﬁrst reported a reduction in GABAergic cells and GABA-immunoreactive axon terminals (puncta) in the row B, C, and D barrel columns contralateral to plucking almost all whiskers (B, C, D rows). They also observed an increase in GABA-positive elements in layer IV of the ipsilateral barrel cortex, a ﬁnding that contributes further evidence that the nondeprived cortex is also affected by unilateral deprivation. The plucking started just after birth and continued for 60 d, with no recovery period before analysis. It is not clear whether the ipsilateral changes represent some form of indirect compensation related to altered function in the deprived cortex, or perhaps an effect related to the greater use of the intact whiskers giving rise to greater activity in the cortex contralateral to the intact whiskers during unilateral SD. Whatever the correct interpretation turns out to be, the quantitative demonstration that both hemispheres were affected by a unilateral manipulation is important. A later paper from the same laboratory showed that while the density of dendritic spines was not changed in cortex following the SD, the total numbers were increased by 67% in ipsilateral barrels due to the greater thickness of layer IV. The authors interpret these changes as a product of activity- dependent plasticity driven by thalamocortical inputs from the intact whiskers, with little if any contribution from the events occurring in the contralateral barrel cortex. However, given the recent results described below following restricted SD, the possibility remains open that interhemispheric changes could contribute to bilateral effects.
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