GABAergic pathways in the rat subcortical visual system: a comparative study in vivo and in vitro

Abstract

Inhibitory pathways project from the pretectal nuclear complex to the ipsilateral superior colliculus (SC) and dorsal lateral geniculate nucleus (dLGN). Both pathways arise from GABAergic neurones that are located in the dorsal pretectal nuclear complex. In the present experiments, we compared the anatomy and physiology of these two pathways with the objective of determining whether they have similar functions. First, we injected retrograde axonal tracers that fluoresce at different wavelengths in the dLGN and SC of single animals to determine if individual GABAergic neurones in the pretectum project to both structures. The results showed that the dLGN and SC receive input from different cell groups. Next, morphological reconstructions of cells labelled after in-vitro whole-cell patch-clamp recordings demonstrated that the pretectal-recipient cells in the dLGN are GABAergic interneurones, whereas those in the SC are projection cells. Finally, with in-vitro whole-cell patch-clamp recordings we showed that inhibitory currents generated by both pathways are mediated by GABA(A) receptors. Taken together, these results suggest that these inhibitory projections may function to facilitate the relay of information from the dLGN to the visual cortex by suppressing the activity of dLGN interneurones, and to reduce the level of activity leaving the SC by inhibiting the projection neurones. These hypotheses will be discussed in the context of the known functions of the pretectal complex.

Not a one-trick pony: Diverse connectivity and functions of the rodent lateral geniculate complex

“…Inhibitory neurons in the ipsilateral pretectum also project to dLGN (Born & Schmidt, 2007), however evidence suggests that these projections innervate dLGN interneurons not TC relay cells (Wang et al, 2002; Born & Schmidt, 2007), adding further complexity to dLGN circuitry.…”

“…Finally, the last significant source of nonretinal inputs to dLGN are inhibitory GABAergic inputs that arise from both local inhibitory neurons and projection neurons in the TRN, a region that forms a lateral shell around dorsal thalamus in nocturnal rodents (Hale et al, 1982; Guillery & Harting, 2003; Pinault, 2004). Inhibitory neurons in the ipsilateral pretectum also project to dLGN (Born & Schmidt, 2007), however evidence suggests that these projections innervate dLGN interneurons not TC relay cells (Wang et al, 2002; Born & Schmidt, 2007), adding further complexity to dLGN circuitry.…”

GABAergic cell types in the superficial layers of the mouse superior colliculus

“…A number of different GABAergic SC cell types have been described. The SC contains GABAergic projection cells that innervate the pretectum (PT), lateral geniculate nucleus (LGN), and parabigeminal nucleus (PBG; Born & Schmidt, , ; Gale & Murphy, , ). In addition, a number of different intrinsic GABAergic cell types have been described based on axon projections, orientation of dendritic arbors, grouping of synaptic vesicles within dendritic appendages or shafts, and/or the colocalization of a variety of immunocytochemical markers (Appell & Behan, ; Behan, Steinhacker, Jeffrey‐Borger, & Meredith, ; Boka et al, ; Gale & Murphy, , ; Lane, Allan, Bennett‐Clarke, Howell, & Rhoades, ; Mize, Spencer, & Sterling, ; Olivier, Corvisier, Pauluis, & Hardy, ; Villalobos, Qiong Wu, Lee, & Basso, ; Zingg et al, ).…”