Displaced amacrine cells in the ganglion cell layer of the ground squirrel retina

In some mammals a large portion of the retinal neurons of the ganglion cell layer are not ganglion cells. These neurons, lacking axons which pass to the brain via the optic nerve, are termed displaced amacrine cells. The present study assessed the number of displaced amacrine cells in the thirteen-lined ground squirrel (Spermophilus tridecemlineatus). We compared the number of labeled cells in the ganglion cell layer after HRP injection of optic tracts and target nuclei with the total number of neurons in the ganglion cell layer. We conclude that approximately one half of the neurons in the ganglion cell layer are displaced amacrine cells, the other one half are ganglion cells. The displaced amacrine cells are on the average smaller than the ganglion cells. Our results provide a rationale for renewed study of relation of ganglion cell morphology and physiological functional type in this species

Morphology and distribution of dopaminergic neurons in the ground squirrel retina

Tyrosine hydroxylase (TH), the rate limiting enzyme in the conversion of tyrosine to DOPA, is a reliable marker for catecholaminergic (dopaminergic) neurons. To investigate the distribution of dopamine in the retina of the thirteen-lined ground squirrel (Spermophilus tridecemlineatus), retinal sections and wholemounts were incubated with an antiserum directed against TH and then processed using the avidin-biotin immunohistochemical method. TH-like immunoreactivity was exhibited by amacrine and interplexiform-like cells in the innermost portion of the inner nuclear layer (INL) and by cells we presume to be displaced amacrines in the ganglion cell layer (GCL). Their somata were 12 to 20 microns in diameter, with the majority measuring approximately 18 microns. In transverse sections the processes of the three types of neurons were seen to extend into lamina 1 of the inner plexiform layer (IPL). In horizontal sections 2-3 primary dendrites were seen to ramify and the branches extended for considerable distances, with overlap between the dendritic fields of neighboring TH cells. A distance to the nearest neighbor analysis suggests the TH-neurons in the INL are distributed in a non-random fashion

Connections of the parabigeminal nucleus in ground squirrel: a horseradish peroxidase study

Las conecciones anatómicas del núcleo parabigémino (Pb) de la ardilla terrestre fueron determinadas por medio del método de peroxidasa de rábano (HRP). Luego de hacer inyecciones de HRP en las láminas superiores del colículo superior (SC). Se encontraron neuromas marcadas con HRP en los Pb ipsilateral y contralateral; solo se observaron terminales de axón marcados en el Pb ipsilateral. Estas conecciones mostraron alguna organización topológica. Las células marcadas en Pb eran multipolares o fusiformes. Mientras que un número mayor de células aparecieron marcada en el Pb ipsilateral, las células marcadas del Pb contralateral eran mayores en tamaño. Luego de hacer inyecciones de HTP en el núcleo parabigémino, se observaron células marcadas en las capas superficiales del SC ipsilateral. Las neuronas marcadas con HRP en SC eran células fusiformes y piriformes de tamaño mediano y neuronas multipolares pequeñas. Las conecciones anatómicas del núcleo parabigémino con las láminas superficiales del tecto sugieren un rol en el procesamiento de información visual