Amblyopia decreases activation of the corticogeniculate pathway and visual thalamic reticularis in attentive rats: a `focal attention' hypothesis
Section snippets
Monocular deprivation
The right eye of male and female Long–Evans rat pups (raised in the animal quarters of the Waisman Center) was lid-sutured under ether anaesthesia at 14 days-postnatal, just prior to the time of eye opening. MD was maintained until 45 days-postnatal, when the right eyelid was opened under Ketamine-Xylazine anaesthesia. Ophthalmoscopy at this time revealed a normal cornea, ocular media and fundus. The rats were maintained in a 12 h light/dark cycle with lights-off at 12 noon.
Exploration test
Five MD rats (Table 1
Activation patterns in the left and right visual segments of the thalamic reticular nucleus
In the monocular amblyopic rats processed after exploration of the novel-complex environment there was Fos-detected activation of the caudodorsal visual segment of TRN. However, in all these animals there was a reduction in the number of Fos-IR neurons in the left TRNv, contralateral to the deprived eye, in comparison to the right TRNv, contralateral to the normal eye. This is shown qualitatively in microphotographs (Fig. 1) of left and right TRNv at caudal levels (A, B) and at more rostral
Discussion
The results showed: (1) Amblyopia by visual deprivation in the right eye induced, in rats exploring a novel-complex environment, a gradient of diminished activation in the analysed cortical and subcortical visual structures contralateral to the deprived eye in comparison to those contralateral to the normal eye. The activation asymmetry was strongest in the TRNv, less strong in layer 6 of the monocular segment of the visual cortex, and weakest in layer 4 of the monocular visual cortex, while
Acknowledgements
I thank Carol Gabel for excellent technical assistance on the immunocytochemistry and in all phases of this study. Supported by grants MH57558 and S97-19 from the Whitehall Foundation to V.M.M., and HD03552 to the Waisman Center.
Note added in proof—A recent study [Pinault M. and Deschênes M. (1998) Eur. J. Neurosci. 10, 3462–3469] provided anatomical evidence for a role of TRN in generating surround inhibition in dorsal thalamic nuclei, consistent with the hypothesis presented above, at least
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