Distribution of synapses in the lateral geniculate nucleus of the cat: Differences between laminae A and A1 and between relay cells and interneurons

Abstract

Laminae A and A1 of the lateral geniculate nucleus in the cat are generally considered to be a structurally and functionally matched pair of inputs from two eyes, although there are subtle light microscopic and physiological differences. The present study aims to display ultrastructural differences between these two laminae based on electron microscopic observances on the connectivity patterns of their afferents onto two main cell types: relay cells, and interneurons present in this nucleus. In a design of population measurement from randomized sample areas in laminae A and A1 from six brains, all synaptic contacts made by three terminal types of the geniculate nucleus were identified, and a number of relative distribution properties were analyzed. When the A-laminae were considered as a homogeneous structure, the distribution of the three terminal types on geniculate cells was similar to previously reported results, confirming the validity of the sampling strategies used; RLP (retinal) terminals provided one-fifth of all synapses, whereas RD (from cortex and brainstem) and F (inhibitory) types constituted one-half and one-third, respectively. The relay cells alone received a similar composition of afferents. However, interneurons alone received approximately equal amounts of synapses from the three sources. Similar analyses comparing the distributions in lamina A and A1 revealed that RD and F terminals, but not RLP terminals, innervate these two laminae differently; more RD and fewer F terminals were found in lamina A1. This difference was also present in the distribution of terminals on relay cells alone, but not on interneurons. These results suggest that (1) retinal terminals form a significantly larger fraction of the input to interneurons than to relay cells; correspondingly, cortex and brainstem provide a smaller fraction of all inputs to interneurons than to relay cells; and (2) laminae A and A1 are not strictly equivalent projection sites of the two retinae. The results are discussed in relation to the Y-cell subpopulation in lamina A1 that is involved in corticotectal, as well as corticogeniculate circuits, as opposed to Y-cells of lamina A that are involved in only the latter.

Comparison of the ultrastructure of cortical and retinal terminals in the rat dorsal lateral geniculate and lateral posterior nuclei

“…In comparison to RL corticothalamic terminals, which contacted very few interneurons (2%), we found that interneurons comprised 26% of the postsynaptic targets of retinal terminals. This distribution is similar to the contacts of retinogeniculate terminals in the cat (31.2%; Erisir et al, 1998). Thus, in both the rat and cat a substantial fraction of the synaptic targets of retinogeniculate terminals are interneurons.…”

Morphology and connectivity of parabrachial and cortical inputs to gustatory thalamus in rats

“…7). Although in visual, auditory, and somatosensory thalamic nuclei, principal sensory relay cells also receive their primary input at large-caliber, presumably proximal, dendrite segments (Liu et al, 1995;Erisir et al, 1998;Bartlett et al, 2000;Guillery and Sherman, 2002), highly exclusive and invasive targeting of initial dendrite segments of gustatory thalamic cells is unique to the gustatory system.…”

Do the quantitative relationships of synaptic junctions and terminals in the thalamus of genetic absence epilepsy rats from Strasbourg (GAERS) differ from those in normal control Wistar rats

“…In the cat, the GABA immunoreactive F terminals represent inhibitory inputs from local interneurons and neurons of the thalamic reticular nucleus (TRN) [15,[40][41][42][43][44][45][46][47]. However, in the rat, the thalamic nuclei other than the LGN lack interneurons [43,44].…”