Some telencephalic connections in the frog, Rana pipiens.

Some afferent, efferent and intrinsic connections of the telencephalon of Rana pipiens were studied using a horseradish peroxidase method. Afferents to the telencephalon from thalamic and brain stem cell groups were demonstrated. These findings, taken together with the results of previous studies, indicate that separate thalamic cell groups project visual, auditory and somatosensory information onto the striatum. A separate thalamic cell group projects to the medial telencephalic wall and probably conveys visual and somatosensory information. These telencephalic afferent systems do not appear to be directly comparable to those of birds and reptiles. Additionally, some telencephalic afferents demonstrated in previous studies using anterograde degeneration techniques were confirmed, and some intratelencephalic connections were identified.

Ascending afferents to the telencephalon of ranid frogs: an anterograde degeneration study.

Sources of telencephalic afferents were examined in two species of frogs, Rana catesbeiana and Rana pipiens, by study of anterograde degeneration resulting from hemisection of the brain at the isthmus or at the caudal border of the thalamus and from electrolytic lesions in various portions of the diencephalon. The results indicate that some telencephalic afferents arise from levels caudal to the isthmus, that some striatal afferents arise from a level between the isthmus and the caudal border of the thalamus, and that a projection to the ipsilateral striatum arises from the anterior and/or middle portions of the dorsal thalamus. Diencephalic projections to pallial portions of the hemisphere were also observed. These results demonstrate substantial non-olfactory afferent projections to the telencephalon in ranid frogs.

Morphology and location of tectal projection neurons in frogs: a study with HRP and cobalt-filling.

Tectal projection neurons were labeled by retrograde transport of horseradish peroxidase (HRP) or cobaltic-lysine. The tracer substances were delivered iontophoretically or by pressure injection or diffusion into various regions of the brain or spinal cord. Histochemical procedures allowed identification of labeled cells projecting to the injected regions. Many neurons were filled with cobaltic-lysine, resulting in a Golgi-like staining. After cobalt injections in the diencephalon most of the labeled cells, identified as small piriform neurons, were located in layer 8 of the tectum. Two types of small piriform neurons were distinguished. Type 1 neurons have flat dendritic arborizations confined to lamina D, while the dendrites of type 2 cells may span all of the superficial tectal strata. In smaller numbers large piriform, pyramidal, and ganglionic cells of the periventricular tectal layers were labeled after diencephalic injections. Rhombencephalic cobalt and HRP injections labeled cells whose axons form the tectobulbospinal tract. The neurons most frequently labeled were large ganglionic cells. Ipsilaterally, the majority of their somata were located in layer 7, and their dendrites arborized mainly in lamina F. Contralaterally, labeled ganglionic cell somata occupied the top of layer 6, and most of their dendritic end-branches entered lamina B. The possible functional significance of this anatomical arrangement is discussed. After tectal cobalt injections the topography of the tectoisthmic projection and the terminals of tectal efferent fibers in the diencephalon and brainstem were observed. It is concluded that the organization of frog tectofugal pathways is very similar to that of mammals.

Connections of the tectum of the rattlesnake Crotalus viridis: an HRP study.

We have studied the connections of the tectum of the rattlesnake by tectal application of horseradish peroxidase. The tectum receives bilateral input from nucleus lentiformis mesencephali, posterolateral tegmental nuclei, anterior tegmental nuclei and periventricular nuclei; ipsilateral input from nucleus geniculatus pretectalis, and lateral geniculate nucleus pars dorsalis; and contralateral input from dorso-lateral posterior tegmental nucleus and the previously undescribed nucleus reticularis caloris (RC). RC is located on the ventro-lateral surface of the medulla and consists of large cells 25--45 micrometer in diameter. Efferent projections from the tectum can be traced to the ipsilateral nucleus lentiformis mesencephali, the ipsilateral lateral geniculate region, anterior tegmental region and a wide bilateral area of the neuropil of the ventral tegmentum and ventral medualla. We have not found any direct tectal projections from the sensory trigeminal nuclei including the nucleus of the lateral descending trigeminal tract (LTTD). We suggest that in the rattlesnake, RC is the intermediate link connecting LTTD to the tectum.

Do retinal ganglion cells project bilaterally in ground squirrels?

Bilaterally projecting retinal ganglion cells have recently been reported in the Japanese monkey Macaca fuscata and albino rat. In the present experiments, we sought to determine whether ganglion cells project bilaterally in the 13-lined ground squirrel Spermophilus tridecemlineatus. We injected rhodamine-conjugated latex microspheres (red beads) into the right optic tract, superior colliculus and the dorsal lateral geniculate nucleus and FITC-conjugated latex microspheres (green beads) into these structures on the left side. In retinal wholemounts of all subjects, we found cells filled with red beads throughout the left retina and cells with green beads throughout the right retina. Ipsilaterally projecting ganglion cells were confined to the temporal retina where they were mixed with cells projecting contralaterally. In no case did we observe a doubly labeled cell. We interpret these observations as indicating that ganglion cells in this species do not project bilaterally.

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.

Effects of posterior neocortical lesions on wavelength, light/dark and stripe orientation discrimination in ground squirrels.

Thirteen-lined ground squirrels (Citellus tridecemlineatus) were trained on three two-choice visual discrimination problems: light/dark, color and stripe orientation. After posterior neocortical lesions in one or two stages, they were tested on all three discriminations. The results demonstrate that animals with large posterior neocortical lesions which produced retrograde changes throughout the dorsal lateral geniculate (LGNd) were capable of light/dark and wavelength discrimination. These animals were not able to discriminate stripe orientation. It is proposed that wavelength discrimination depends on extrageniculostriate mechanisms in posterior neodecorticates of this species.

Soybean agglutinin binding by primary olfactory and primary accessory olfactory projections in different frogs.

Comparing eight species of frogs adapted to habitats ranging from aquatic to arboreal, we observed differences in the affinity of primary olfactory projections to the lectin 'soybean agglutinin'. Particularly pronounced differences exist between Pipa, a frog that rarely leaves the water, and Eleutherodactylus, an arboreal species that does not even utilize aquatic environments for reproduction. We interpret these differences as reflecting specializations to the perception of air-borne vs. water-borne odors.

Differential labelling of primary olfactory system subcomponents by SBA (lectin) and NADPH-d histochemistry in the frog Pipa.

SBA and NADPH-d histochemistries allow identification of functionally distinct components of the amphibian primary olfactory system. In Pipa, a secondarily aquatic frog, combination of both methodologies, using alternate sets of histological sections, reveals that, apart from Jacobson's organ, this species has a "water-nose" and an "air-nose". The epithelia occupy separate chambers of the olfactory organ and give rise to olfactory nerve fiber bundles that are identified by the dual staining procedure.

Two groups of TH-like immunoreactive neurons in the frog (Rana pipiens) retina.

The morphology and distribution of TH-like immunoreactive (TH-IR) cells in the retina of Rana pipiens were studied in retinal whole mounts and in radial and horizontal sections. A large majority (96%) of the immunoreactive cells were found in the inner nuclear layer while a few cells were found in the ganglion cell layer. All TH-IR cells had round to oval somata with average diameter of 10 microm. The 2-4 primary processes of these cells distributed extensively to sublamina 1 of the inner plexiform layer (IPL) and sparsely to sublamina 5. Two groups of TH-IR cells were distinguished: one, designated thin cells, had only thin (<2 microm diameter) primary processes; the second, designated thick cells, had one or more primary processes with diameter(s) exceeding 2 microm for a distance of 5 microm or more from the soma. The thin cells did not significantly differ from the thick cells in soma diameter, number of primary processes, horizontal spread of processes or vertical lamination of processes. Nearest neighbor analyses of the two types revealed that the population of TH-IR cells (thick and thin together) have an orderly distribution while the thick cells alone are more randomly distributed, indicating that the thick cells do not comprise a functional population. The total number of TH-IR cells varied between retinas; the variability was due principally to variation of thin cell density. It is hypothesized that the thick cells are a subpopulation of the TH-IR cells which are in a particular physiological state at the time of fixation.

A comparison of spectral response functions of positive and negative phototaxis in two anuran amphibians, Rana pipiens and Leptodactylus pentadactylus.

Anuran (tailless) amphibians exhibit preferences for light; some species (photopositive) are attracted to light while others (photonegative) are repelled. The photopositive anuran Rana pipiens and the photonegative anuran Leptodactylus pentadactylus were tested in a Y-maze on a light versus dark task where the 'light' stimuli were monochromatic and equated for energy. During each trial the window in one of the choice alleys of the Y-maze was illuminated while the window in the other was dark. Photopositive behavior was defined as greater than 50% choice of the alley with the illuminated stimulus, while photonegative behavior was defined as less than 50% choice. Based on previously reported spectral response functions, it was expected that the photonegative species (L. pentadactylus) would exhibit a maximum photonegativity in the 490-570 nm range while the photopositive species (R. pipiens) would be most strongly attracted by short wavelengths. However, our results indicate that both species are affected most strongly by short wavelength light; only the sign of the response (repulsion versus attraction) is inverted for L. pentadactylus, the photonegative species. This suggests that the retinal circuitry for wavelength discrimination may be equivalent in photopositive and photonegative anurans.

Bulbar representation of the 'water-nose' during Xenopus ontogeny.

Olfactory epithelium that is specialized for the detection of water-borne odors is located in different cranial cavities in larval and postmetamorphic Xenopus. Soybean agglutinin histochemistry reveals that both "water-noses' innervate only the ventral olfactory bulb (OB). This is evidence for a parcellation of the OB into a ventral portion mediating information on water-soluble odorants and a dorsal part that processes information on volatile substances.

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.

Thalamic connections of the ground squirrel superior colliculus and their topographic relations.

The connections of the superior colliculus (SC) of the ground squirrel Spermophilus tridecemlineatus were studied with the horseradish peroxidase (HRP) method. Multiple pressure injections of HRP served to define the total pattern of SC projections while iontophoretic injections allowed differentiation of connections of the deep and superficial layers and determination of topographic relations of SC with its associated nuclei. The deep laminae were mainly connected with auditory, somatosensory and reticular regions of the brain, including the inferior colliculus, zona incerta, substantia nigra, mesencephalic central grey, pontine nuclei, spinal trigeminal nucleus, nucleus of the posterior commissure, thalamic reticular nucleus, raphe nuclei, lateral vestibular nucleus, the lateral superficial reticular formation of the medulla, the mesencephalic reticular formation, nucleus gracilis and the cervical spinal cord. The superficial laminae were connected with visual system structures. They were reciprocally connected with the dorsal and ventral lateral geniculate nuclei, the pretectum, nucleus lateralis posterior (LP), the parabigeminal nucleus and the contralateral SC. Connections between the SC and the dorsal lateral geniculate were topologic. LP was found to consist of three divisions: rostrolateral, rostromedial and caudal. SC was interconnected with the rostrolateral and caudal divisions. The connections between the SC and the rostrolateral division were topologic; those with the caudal division were not. The connections of the deep collicular layers in ground squirrels were similar to those which have been reported for cats and monkeys. The connections of the superficial laminae were more extensive than has been reported in other species. These elaborate interconnections indicate extensive interaction between primary retinal projection nuclei in the processing of visual information.