Synapses of the Inner Plexiform Layer of Kitten Retina During Postnatal Development: A Quantitative Study

Crooks, Jill (1990) Synapses of the Inner Plexiform Layer of Kitten Retina During Postnatal Development: A Quantitative Study. PhD thesis, University of Glasgow.

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The development of the synapses of the inner plexiform layer (IPL) was studied in a reproducible area of cat retina which was chosen to be the area centralis. The number of bipolar cell ribbons and conventional synapses during development has been counted from large montages of electron micrographs in 17 kittens of ages ranging from newborn to 200 days and also in three adult cats. Measurements of synaptic profile size and their orientation and distribution within the IPL were also taken, in case there was a systematic change with age which would affect the frequency of occurrence of the profiles. A very considerable degree of bipolar cell synaptogenesis was shown to occur in the postnatal period, indicated by the increase in frequency of bipolar cell synaptic ribbons and floating ribbons. This synaptogenesis followed an exponential growth pattern, levelling off at about 100 days of age. This change was not dependent upon any age related shift in ribbon size or orientation; therefore it was inferred that retinal ganglion cells must receive a considerable increase in excitatory input during the postnatal period. In addition, the profiles of the bipolar cell ribbon synapses were then also subdivided into monads and dyads. While there was a considerable increase of dyad frequency, monad frequency was found to remain constant. This was interpreted to add support to the sequence of dyad formation requiring the initial formation of a floating ribbon then intermediate formation of a monad. Bipolar cell ribbons were uniformly distributed throughout the 5 strata of the IPL in the neonatal retina whilst a peak was present in strata 3 and 4 in the mature retina. Possible reasons for this finding are discussed. In marked contrast to the ribbon synapses of bipolar cells, conventional synapses remained invariant in number during postnatal development. In addition, the length of the synapse and the number of vesicles per synapse remained constant. Furthermore, the range of orientations and distribution through the depth of the IPL was mature at birth, as was the number of serial conventional synapses. The considerable increase in bipolar cell ribbon frequency and the constancy of conventional synapse frequency during postnatal development are discussed with relation to the conflicting electrophysiological evidence during development.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Keywords: Physiology, Developmental biology, Ophthalmology
Date of Award: 1990
Depositing User: Enlighten Team
Unique ID: glathesis:1990-78028
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 30 Jan 2020 15:43
Last Modified: 30 Jan 2020 15:43

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