Optic nerve innervation of so-called interneurons of the rat lateral geniculate body

c-fos induction in sensory pathways of rats exploring a novel complex environment: shifts of active thalamic reticular sectors by predominant sensory cues

In normal rats exploring a novel, complex environment, in comparison to control nonexploring rats, there is induction of the FOS protein, a marker of neuronal activity, in all layers of the striate visual cortex (particularly in the granular and supragranular layers), in the stratum griseum superficiale of the superior colliculus, and in the dorsal lateral geniculate nucleus, as well as in all layers of the whiskers barrel field in the somatosensory cortex. A surprising finding was a selective activation of the visual sector of the thalamic reticular nucleus, in dorsocaudal parts of the nucleus. To the contrary, in visually deprived rats exploring a novel environment which would depend critically on whiskers tactile clues for exploration there was instead a selective activation of the somatic sector in central parts of the thalamic reticular nucleus, in conjunction with activation of cortical whiskers barrel field. From these results it is concluded: (1) Different sensory sectors of the rat thalamic reticular nucleus are activated depending on prevalent sensory channels used in recognition of the environment, suggesting a role of thalamic reticular nucleus in optimizing thalamocortical transmission of essential external cues to guide adequate behaviour. (2) In the awake state, the granular and supragranular layers of the visual and somatosensory cortices are more active when attention is paid to sensory stimuli that are essential for recognition of the environment. (3) The selective induction of c-fos in the visual and somatosensory cortices, and in the stratum griseum superficiale of superior colliculus of rats exploring a novel, complex environment might be related to plastic changes that have been demonstrated in these centres in rats raised in complex environments. These plastic changes are likely to be the result of target late-response genes activated by c-fos.

Morphology of identified relay cells and interneurons in the dorsal lateral geniculate nucleus of the rat

The morphology of neurons in the lateral geniculate nucleus of the rat has been examined in both Golgi impregnated and in horseradish peroxidase (HRP) filled material. Two major classes of neurons are seen in Golgi material which encompass the variety of cells described in previous reports. Cells of one group (class A) are routinely labelled by injections of HRP into the visual cortex or optic radiations. This group also displays some morphological variation which may be related to the presence of parallel information channels in the retino-fugal pathway, but clear subgroups cannot be identified on the basis of morphological criteria alone. Cells of the other group (class B) are not labelled by HRP injections into visual cortex or the optic radiations, and are probably local circuit interneurons.