Figure 2.
Summary diagram of the type I bottlebrush tectothalamic neuron pathway in mammals (A, based on work in ground squirrels) and birds (B, based on work in pigeons and chickens) from Major et al.64 The schematic shows the high similarity in neuronal morphology of these neuron types in mammals and birds. Additionally, the circuitry of this neuron type shows many similarities between birds and mammals, including (1) the inputs from W-type retinal ganglion cells (RGCs) and from cholinergic neurons of the parabigeminal nucleus in mammals and nucleus isthmi parvocellularis (Ipc) in birds; (2) an output to a thalamic cell group projecting to a visual processing region of the temporal telencephalic pallium (caudal/inferior pulvinar in mammals and nucleus rotundus in birds); and (3) an output to a GABAergic pretectal cell group(s) projecting to the thalamic target of the type bottlebrush neurons. Abbreviations: Ach, acetylcholine; GABA, gamma aminobutyric acid; Glut, glutamate; IPS, interstitio-pretecto-subpretectalis; NPA, anterior pretectal nucleus; NPP, posterior pretectal nucleus; NPT, nucleus pretectalis; PBG, parabigeminal nucleus; SP, nucleus subpretectalis; W RGCs, W-type retinal ganglion cells. Used with the kind permission of John Wiley and Sons.