Structural and functional consequences of neonatal deafferentation in the superficial layers of the hamster's superior colliculus

Abstract

Intracellular recording and horseradish peroxidase (HRP) injection techniques were used to evaluate the effects of neonatal enucleation upon the structural and functional properties of cells in the superficial retinorecipient laminae of the hamster's superior colliculus (SC). The physiological recordings confirmed previous results that normally visual superficial layer neurons develop somatosensory receptive fields in the enucleated animals. This study further showed that all of the physiological subclasses of somatosensory neurons normally encountered in the deep layers were present in the superficial laminae. With the exception of marginal cells, all of the morphological classes of neurons in the superficial SC laminae of sighted hamsters (narrowfield vertical cells, widefield vertical cells, stellate cells, horizontal cells, and giant stellate cells) were recovered from the blinded animals. Quantitative comparison of neurons within a given morphological class demonstrated only slight differences between cells from blind and sighted hamsters. However, there was a significant reduction in the percentage of neurons with dorsally directed dendrites in the neonatally enucleated animals. Additional experiments with the Golgi technique also demonstrated that neonatal enucleation altered the distribution of morphological cell types in the superficial SC laminae. These results suggest that enucleation in the hamster may result in relative reductions in specific cell types in the superficial SC laminae rather than dendritic changes in all of the cell classes present in these layers.

Synapse maturation is enhanced in the binocular region of the retinocollicular map prior to eye opening

“…7). The dendritic shape of roughly half of the reconstructed neurons could be classified into one of the previously described classes of dendritic morphologies in the upper layers of the SC (Langer and Lund 1974;May 2006;Mooney et al 1992), whereas the remaining neurons had no clearly recognizable structure (Table 3). This is the first direct evidence, to our knowledge, that a diverse population of neuron types in the SGS receives functional retinal input as early as P3.…”

Functional Topography of Converging Visual and Auditory Inputs to Neurons in the Rat Superior Colliculus

“…It is highly likely that the strong projection from the nBIC to the dSC that we observed at least in part underlies the auditory sensitivity of rat SC neurons (Gaese and Johnen 2000). The contribution of sSC inputs to the visual responses of rat dSC neurons is not known, although studies in other rodents have shown that those responses are derived from the sSC (Mooney et al 1992). Our results therefore suggest that, at around the time of eye opening and the onset of hearing (Friauf 1992), there exists a welldeveloped circuitry that could support multisensory interactions.…”

The neural basis of cognitive development: A constructivist manifesto

“…The basic idea behind this, then, is that every portion of a dendrite will have a limited temporal window in which activity-dependent processes can effect its structure. Although there are instances in which dendrites that have already undergone development can be altered (e.g., Mooney et al 1992), the signal that initiates this large-scale modification is itself a large-scale event, such as deafferentation, that requires a change at that scale.…”