Connections of the corpus cerebelli in the green sunfish and the common goldfish

Examination of the connections of the corpus cerebelli in one perciform (Lepomis cyanellus) and one cypriniform teleost (Carassius auratus) reveal that ipsilateral afferent connections in both species arise from an anterior group of nuclei in the diencephalon and mesencephalon, and a posterior group of nuclei in the rhombencephalon. Some nuclei of the anterior group and all those of the posterior group have in addition a weaker, and the medial octavolateralis nucleus a stronger, contralateral component. The inferior olivary nucleus in both species projects solely contralaterally. Nucleus paracommissuralis, the ventral accessory optic nucleus and nucleus isthmi are minute in Carassius compared to Lepomis. The latter species has in addition a bilateral corpopetal projection (ipsilaterally stronger) from the lateral cuneate nucleus. Efferent fibers in both species reach the contralateral nucleus ruber, oculomotor nucleus, nucleus of the medial longitudinal fasciculus, torus semicircularis, ventromedial and ventrolateral thalamic nuclei, optic tectum and superior and inferior reticular formation. An additional weaker ipsilateral terminal field could be observed in all nuclei except in the ventrolateral and ventromedial thalamic nuclei, the dorsal periventricular pretectal nucleus and the optic tectum. Lepomis in addition has a bilateral terminal field in the ventral accessory optic nucleus (contralaterally stronger). In both species, stronger ipsilateral and weaker contralateral terminal fields were present in the torus Iongitudinalis and the valvula cerebelli. The two patterns of corpopetal connections in Lepomis and Carassius were used as models for perciforms and cypriniforms in the analysis of the existing information in the literature on teleosts. While most discrepancies in the literature on percomorphs and ostariophysines could be interpreted consistently, the available information on mormyrids revealed a very different pattern of corpopetal organization: presence of additional connections (from a division of the nucleus preglomerulosus) and absence of otherwise well-established corpopetal connections in teleosts. In a second step, a phyletic analysis of teleostean corpopetal organization revealed that while teleosts share with all other vertebrates a group of corpopetal connections from the rhombencephalon, they evolved many new, more anteriorly located afferent inputs to the corpus cerebelli. Furthermore, electroreceptive mormyrids in addition evolved newly at least one corpopetal connection and lost many others

An immunohistochemical study of the telencephalon of the african lungfish, Protopterus annectens

The telencephalon of the African lungflsh, Protopterus annectens , was studied by immunohistochemical techniques in order to identify the major subdivisions of the telencephalon and determine the possible homologues of these subdivisions, if any, in other vertebrates. The distributions of four different neuropeptides (substance P, leucine-enkephalin, avian pancreatic polypeptide, and LANT6), a neurotransmitter (serotonin), and a neurotransmitter-related enzyme that is involved in catecholamine synthesis (tyrosine hydroxylase) were examined. The resultant labeling patterns indicated that the telencephalon of lungfish consists of three major subdivisions–a rostrally and dorsally situated olfactory bulb, a dorsally situated pallial region located caudal to the olfactory bulbs, and a ventrally situated subpallial regions. The dorsal and lateral pallial regions, which both receive secondary olfactory input, are somewhat, distinct from one another cytoarchitectonically, but their immunohistochemical, labeling characteristics did not differ. Thus, the lateral pallium and the dorsal pallium together appear to constitute an olfactory pallium in lungfishes. The medial pallium was found to consist of three immunohisthochemically distinct subdivisions–a dorsal cell group, an intermediate cell group, and a ventral cell group. These medial pallial fields extend throughout the entire rostrocaudal extent of the medial wall of the telencephalon. Although one or more of these medial pallial cell groups may be homologous to specific portions of the medial pallium in land vertebrates, no specific similarities were observed to support any proposed one-to-one correspondences. The possibility that one or more of the medial pallial cell groups of lungfishes correspond to cell groups located in the dorsal pallium of land vertebrates could not be excluded. The subpallium is divided into lateral, medial, and caudal subdivisions. The lateral subdivision appears to be homologous to the basal ganglia of land vertebrates since it contains neuropeptide/neurotransmitter-specific neuronal populations that are characterstic of the striatal and pallidal portions of the basal ganglia of amniotes. The medial subdivision of the subpallium shows the topographic and immunohistochemical characteristics of the septal region and the nucleus accumbens region of the amniote telencephalon. The caudal subpallium does not show any distinctive immunohistochemical labeling characteristics and its possible homologue in land vertebrates is unclear. The present results indicate that the evolution of the telencephalon during the transition from fish to amphibians must have been characterized by a striking conservatism in the case of the subpallium. A basal ganglia and a septal region having many of the characteristics of those of land vertebrates appear to be present in the telencephalon of lungfishes, thereby suggesting that these cell groups were already present in the brains of the earliest lobe-finned fishes. Although the present results suggest that a lateral pallium, or olfactory cortex, was present in the telencephalon of ancestral lobe-finned fish, they do not provide evidence to support the existence in lobe-finned fish of a forerunner of the dorsal pallium of land vertebrates. Further, it is unclear whether the medial pallial cell groups in lungfishes are homologous to cell groups in the medial telencephalic walls of land vertebrates.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/50032/1/902560313_ftp.pd

A Reinterpretation of the Cytoarchitectonics of the Telencephalon of the Comoran Coelacanth

The cytoarchitecture of the telencephalon of the Comoran coelacanth, Latimeria chalumnae, was analyzed in the context of recent advances in our understanding of telencephalic organization in lungfishes and amphibians, which constitute the sister group to coelacanths. In coelacanths, the telencephalon is divided into pedunculated olfactory bulbs, paired hemispheres, and an unevaginated telencephalon impar. The hemispheres consist of a ventrally located subpallium and, dorsally, a greatly expanded pallium. Traditionally, the subpallium in coelacanths has been divided into a medial septal area and a lateral striatum. Re-examination of the lateral subpallial wall, however, suggests that the striatum is more restricted than previously believed, and it is replaced dorsally by a more scattered plate of cells, which appears to represent the ventral pallium. The putative ventral pallium is continuous with a ventromedial pallial formation, which appears to receive input from the lateral olfactory tract and should be considered a possible homolog of the lateral pallium in tetrapods. The putative lateral pallium is replaced by a more dorsomedial pallial formation, which may represent the dorsal pallium. This formation is replaced, in turn by an extensive lateral pallial formation, which appears to be homologous to the medial pallium of tetrapods. An expanded medial pallium in coelacanths, lepidosirenid lungfishes, and amphibians may be related to well developed spatial learning. Traditionally, the telencephalon impar of coelacanths, has been interpreted as an enlarged preoptic area, but reanalysis indicates that the so-called superior preoptic nucleus actually consists of the medial amygdalar nucleus

Central projections of the lateral line nerves in the shovelnose sturgeon

Primary projections of the anterior (ALLN) and posterior (PLLN) lateral line nerves were traced in the shovelnose sturgeon by means of horseradish peroxidase (HRP) histochemistry and silver degeneration. The trunk of the ALLN divides into dorsal and ventral roots as it enters the medulla. Fibers of the dorsal root form ascending and descending branches that terminate within the ipsilateral dorsal octavolateralis nucleus and the dorsal granular component of the lateral eminentia granularis. Fibers of the ventral root of the ALLN, as well as fibers of the PLLN, enter the medulla ventral to the dorsal root of the ALLN where some of the fibers terminate among the dendrites of the magnocellular octaval nucleus. The bulk of the fibers form ascending and descending branches that terminate within the ipsilateral medial octavolateralis nucleus. A portion of the ascending fibers continue more rostrally land terminate in the ipsilateral eminentia granularis and bilaterally in the cerebellar corpus. Some fibers of the descending rami of both the ALLN and PLLN extend beyond the caudal limit of the medial octavolateralis nucleus to terminate in the caudal octavolateralis nucleus. The HRP cases also revealed retrogradely filled large neurons whose axons course peripherally in the lateral line nerve and are likely efferent to the lateral line organs.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/50022/1/902250114_ftp.pd

Evolution of reptilian visual systems: Retinal projections in a nocturnal lizard, Gekko gecko (linnaeus)

On the basis of the development of the dorsal ventricular ridge of the telencephalon, lizards can be divided into a type I group, to which Gekko and the majority of lizard families belong, and a type II group with more derived features, of which Iguana is representative. Most studies of retinal projections have utilized lizards of the type II group, which are adapted to a diurnal niche. Gekko gecko is differently adapted in that it is nocturnal. Study of the retinal projections was undertaken in Gekko gecko in order to insure that conclusions regarding the pattern of retinal pathways in saurians would be based on a sample which was more representative of the total range of variation. Unilateral removal of the retina by suction cannula was carried out on 12 adult specimens of Gekko gecko . After survival times of 10 to 74 days, brains were processed with various silver methods. The retina projects contralaterally to the pars dorsalis and pars ventralis of the lateral geniculate nucleus and the pars ventralis of the ventrolateral nucleus in the thalamus, nuclei geniculatus pretectalis, lentiformis mesencephali, and posterodorsalis in the pretectum, layers 8–14 of the optic tectum and nucleus opticus tegmenti. Additionally, the retina projects ipsilaterally to the dorsal and ventral lateral geniculate nuclei and to the pretectal nuclei, as well as to the optic tectum, particularly layers 8 and 9. The finding of ipsilateral retinothalamic projections in Gekko supports the idea that this pathway is generalized among saurians. However, presence of ipsilateral retinothalamic projections and the degree of binocular overlap cannot be correlated when lizards, snakes, crocodiles, and turtles are compared. The functional significance of this pathway therefore remains obscure. Ipsilateral retinotectal projections have not been previously described in land vertebrates other than mammals. Whether their presence is correlated with nocturnal visual habits or is generalized among type I lizards remains to be determined. The pattern of retinal projections has been studied in too few representatives of non-mammalian land vertebrates to presently permit conclusions regarding the origin of non-decussating pathways.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/49995/1/901570407_ftp.pd

Retinofugal pathways in fetal and adult spiny dogfish, Squalus acanthias

Retinofugal pathways in fetal and adult spiny dogfish were determined by intraocular injection of [3H]proline for autoradiography. Distribution and termination of the primary retinal efferents were identical in pups and adults. The retinal fibers decussate completely, except for a sparse ipsilateral projection to the caudal preoptic area. The decussating optic fibers terminate ventrally in the preoptic area and in two rostral thalamic areas, a lateral neuropil area of the dorsal thalamus and more ventrally in the lateral half of the ventral thalamus. At this same rostral thalamic level, a second optic pathway, the medial optic tract, splits from the lateral marginal optic tract and courses dorsomedially to terminate in the rostral tectum and the central and periventricular pretectal nuclei. The marginal optic tract continues caudally to terminate in a superficial pretectal nucleus and also innervates the superficial zone of the optic tectum. A basal optic tract arises from the ventral edge of the marginal optic tract and courses medially into the central pretectal nucleus, as well as continuing more caudally to terminate in a dorsal neuropil adjacent to nucleus interstitialis and in a more ventrally and medially located basal optic nucleus.Comparison of the retinofugal projections of Squalus with those of other sharks reveals two grades of neural organization with respect to primary vusula projections. Squalomorph sharks possess a rostral dorsal thalamic nucleus whose visual input is primarily, if not solely, axodendritic, and an optic tectum in which the majority of the cell bodies are located deep to the visual terminal zone. In contrast, galeomorph sharks are characterized by an enlarged and migrated rostrodorsal thalamic visual nucleus, and an optic tectum in which the majority of the cell bodies are located within the visual terminal zone. These data suggest that evolution of primary visual pathways in sharks occurs by migration and an increase in neuronal number, rather than by the occurence of new visual pathways.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/23625/1/0000588.pd

Localization of neurons afferent to the telencephalon in a primitive bony fish, Polypterus palmas

Telencephalic horseradish peroxidase injections in bichirs reveal projections from the dorsal thalamus, posterior tuberculum, nucleus of the torus lateralis, superior raphe and locus coeruleus. Comparison of these data with those from tetrapods reveals a number of diencephalic homologies.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/24423/1/0000694.pd

Retinal projections in the australian lungfish

Autoradiographic analysis of the primary retinofugal projections in the Australian lungfish reveals contralateral retinal projections to a ventral portion of the periventricular preoptic nucleus, throughout its rostrocaudal extent, and to 4 distinct terminal fields in the thalamus. Only one of these thalamic fields (t4) likely receives dendrites soley from dorsal thalamic neurons. Thalamic terminal field 1 probably receives dendrites from both dorsal and ventral thalamic neurons, and fields 2 and 3 from only ventral thalamic neurons. Contralateral retinofugal fibers terminate in the pretectum and in the superficial and central tectal zones. The central tectal terminal field is restricted to the medial one-third of the tectum. At pretectal levels a contralateral basal optic tract arises from the marginal optic tract and terminates along the lateral edge of the tegmentum, as a series of glomerular puffs, and in the rostral pole of a superficial isthmal nucleus. The Australian lungfish, unlike the African and South American lungfish, possesses ipsilateral retinal projections to all of the nuclei that receive contralateral retinal input.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/23294/1/0000231.pd

Experimental determination of the primary trigeminal projections in lampreys

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/23607/1/0000569.pd