Earl Kicliter

Organization of the Amphibian Telencephalon

Living amphibians comprise three different groups or orders: Anura (frogs and toads, approximately 2600 species), Urodela (salamanders, approximately 300 species), and Apoda (caecilians, approximately 150 species). Each group is clearly separated from the others by extensive structural variation, and each is characterized by a distinct life style. These three orders are easily distinguished from their earliest appearance in the fossil record, but they also share a number of unique characters which suggest common ancestry. These characters include teeth with a weak, uncalcified segment between the base and crown (pedicellate teeth) and similarities in the middle ear bones and vertebral-skull articulation. Parsons and Williams (1963) concluded from these characters that modern amphibians represent a monophyletic group, the Lissamphibia. Most workers employ this tenable model of amphibian affinities; however, additional data are needed to accept this hypothesis (Thomson, 1968; Estes and Reig, 1973), particularly for the apodans.

Superior colliculus efferents to five subcortical visual system structures in the ground squirrel

We compared the laminar location and morphology of superior colliculus cells projecting to the dorsal and ventral lateral geniculate nuclei (LGd, LGv), the pretectum (PT), the parabigeminal nucleus (Pb), and nucleus lateralis posterior (LP) in the ground squirrel Spermophilus tridecemlineatus. Horseradish peroxidase was iontophoretically injected into LGd, LGv, PT, Pb and each of the 3 subdivisions of the LP. After survival periods of 24-72 h the animals were perfused intracardially and brain sections processed histochemically. A Zeiss ZIDAS image analysis system was used to determine the soma size of labeled neurons and to prepare histograms showing the relation between cell size and frequency. After injections in the LGd, LGv, Pb and PT, labeled neurons were present throughout the stratum griseum superficiale and the upper portion of the stratum opticum. They were mainly fusiform neurons whose long axes ranged from 12 to 44 microns. There were also some multipolar cells 9-22 microns in diameter with the highest frequencies found in the 12-14 and 16-17 microns ranges. Differences were found in the exact location and/or soma size of the neurons projecting to the 4 nuclei. After injections in rostrolateral and caudal LP the labeled cells were always large multipolar neurons specifically located in the lower half of the stratum griseum superficiale. Their somata measured 9-22 microns in diameter but the highest frequencies were found in the 16-17 and 19-20 microns ranges. Our findings suggest that there are different populations of superior colliculus cells projecting to different visual system structures.

Morphology of ganglion cells which project to the dorsal lateral geniculate and superior colliculus in the ground squirrel

We wished to determine whether retinal ganglion cells that have axons terminating in the dorsal lateral geniculate and/or the superior colliculus have specific sizes of somata, comprising only part of the entire size range of ganglion cell somata. If so, then perhaps the specific functional types described by Michael might be associated with morphological types based on soma size. HRP was injected into either the superior colliculus (SC) or dorsal lateral geniculate nucleus (LGd) of thirteen-lined ground squirrels. Soma diameter of labeled ganglion cells was measured and the relation between cell size and frequency determined. After SC injections HRP-filled cells were mostly small and medium-sized. They ranged in diameter from 3 to 14 microns and the mean diameter of labeled neurons was 7.35 microns. Cells labeled after SC injections were often distributed as doublets or triplets in the retina. After LGD injections the majority of labeled cells were medium and large-sized. They ranged from 4 to 18 microns in diameter with a mean of 9.1 microns and were more regularly spaced within the retinal region of labeled cells. Thus, the present results provide reason to believe that functional classes of ganglion cells in ground squirrels may be correlated with particular morphological types.

Spectral opponency of on-type ganglion cells and the blue preference of Rana pipiens.

Spectrally opponent processes of ON-type retinal ganglion cells and the blue preference behavior were identified by parallel physiological and behavioral experiments in Rana pipiens. Spectral opponency of retinal ON-units was measured by recording from optic nerve terminals in the anterior thalamus, while the retina was stimulated by combinations of monochromatic stimuli. Spectral opponency of the blue preference was determined in a Y-maze, using similar combinations of monochromatic stimuli. The opponent processes of the ON-units and blue preference are similar in the spectral ranges of excitatory and inhibitory effects. In both cases the spectral opponency can be described as short wavelength excitation and long wavelength inhibition. The data suggest that the short wavelength excitation is based, at least in part, on the green rod (P432) channel, while the long wavelength inhibition is caused, at least in part, by stimulation of the principal and/or single cone (P580) channel. A model is presented to show how receptor interactions may encode this spectrally opponent process. The results support the hypothesis that the blue preference is dependent on information supplied to the anterior thalamus by ON-type retinal ganglion cells.