http://nova.newcastle.edu.au/vital/access/services/Feed ${session.getAttribute("locale")} 5 http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:7566 Circumscribed retinal lesions in adult cats result in a reorganization of circuitry in area 17 such that neurons in the lesion projection zone (LPZ) can now be activated, not from their original receptive fields (RFs) but from regions of normal retina adjacent to the lesion ('ectopic' RFs). We have studied this phenomenon further by making circumscribed monocular retinal lesions in 8-week-old kittens and recording responses to visual stimuli of neurons in the LPZ of area 17 when these cats reached adulthood. These responses have been compared with those in adult-lesioned cats either of relatively short postlesion survival (2–24 weeks) or long postlesion survival (3.5–4.5 years). In both kitten-lesioned and adult-lesioned animals most LPZ neurons recorded from the supragranular layers (II and III) not only exhibited new ectopic RFs when stimuli were presented via the lesioned eye but the RF properties (e.g. the sizes of excitatory RFs, orientation and direction selectivities, velocity preferences and upper cut-off velocities) were often indistinguishable from those seen when stimuli were presented via the nonlesioned eye. Similarly, in both kitten-lesioned and adult-lesioned animals, most LPZ neurons recorded from the granular and infragranular layers (IV, V, VI), like those recorded from the supragranular layers, were binocular. However, in adult-lesioned but not in kitten-lesioned animals, the responses and the upper cut-off velocities of LPZ cells recorded from the granular and infragranular layers to stimuli presented via ectopic RFs tended to be, respectively, substantially weaker and lower than those for stimuli presented via the nonlesioned eye. The age-related laminar differences in reorganizational plasticity of cat striate cortex correlate with the lamino-temporal pattern of distribution of N-methyl-d-aspartate glutamate receptors in striate cortex. 2011-04-12T06:00:01.960Z ]]> http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:7564 We have previously reported to the Society that in cats in which monocular retinal lesions were made in adulthood or adolescence cells in the lesion projection zone (LPZ) of area 17 recovered sensitivity to photic stimuli but the receptive fields (RFs) were now ectopic, i.e. outside the lesion (Burke et al. 2000). When the lesions were made in adult cats (AL), stimuli presented via the lesioned eye gave lower peak discharge rates and lower cut-off velocities than those presented via the non-lesioned eye. By contrast, in kitten-lesioned cats (KL) the cut-off velocities and the peak discharge rates were similar for stimuli presented via the lesioned and the non-lesioned eye. There was, however, a difference in the time from lesion to experiment between the AL and KL groups, 2-24 weeks vs. 28-68 weeks. It was, therefore, important to see if this factor could be responsible for the neural effects. Ectopic RFs are believed to be mediated via axon collaterals of pyramidal cells interconnecting mainly in laminae 2 and 3. We, therefore, also investigated the location of the LPZ neurones (supragranular (SG) - laminae 1-3: granular/ infragranular (G/I) - laminae 4-6). In addition to the two groups already described (AL 4 cats; KL 5 cats) we prepared a third group in which the lesion was made in the adult cat but the cat then survived 3.5-4.5 years (AL/L 3 cats). Retinal lesions 8-12 deg in diameter were made in cats anaesthetized with xylazine (3 mg kg-1) and ketamine (30 mg kg-1). Single neurones in area 17 were studied in cats anaesthetized with 0.5-0.7 % halothane in 67/33 N2O/O2, given gallamine triethiodide 7.5 mg kg-1 h-1 I.V. and artificially respired. EEG, ECG, end-tidal CO2, lung pressure and deep body temperature were monitored and kept within normal limits. Animals were humanely killed at the end of the experiments. In the G/I laminae we found no difference between AL and AL/L cats but a significant difference between AL/L and KL cats and between AL and KL cats with regard to peak discharge rates and cut-off velocities (Wilcoxon, P < 0.05). Thus it seems that the interval between lesion and experiment is not a critical factor. By contrast, in the SG laminae there was no difference between AL and KL cats with respect to peak discharge rates and cut-off velocities. Thus following monocular retinal lesions there appears to be a critical period for the LPZ cells recorded from the G/I layers of area 17, after which the presumed cortical mechanisms underlying establishment of ectopic RFs are not capable of good compensation for the loss of the retinal input. 2011-04-12T05:50:03.507Z ]]>