Afferent and efferent fiber connections of the lobus inferior (LI) were studied in a percomorph teleost, Thamnaconus (Navodon) modestus. The LI of Thamnaconus is composed of the nucleus diffusus lobi inferioris (NDLI), the nucleus recessus lateralis pars lateralis et medialis (NRLl and NRLm), and the nucleus centralis lobi inferioris pars anterior et posterior (NCa and NCp). The NDLI receives projections from the secondary gustatory nucleus, preglomerular tertiary gustatory nucleus, corpus glomerulosum, dorsal region of the area dorsalis telencephali pars medialis (dDm), and area dorsalis telencephali pars lateralis. Different subdivisions of the dorsal telencephalon project to discrete regions of the NDLI. The NDLI projects to the corpus mamillare, NRLl, NCa, and NCp. Thus the NDLI could be regarded as an intrahypothalamic relay nucleus. The NCa receives projections from the NDLI and projects to the preglomerular tertiary gustatory nucleus, secondary gustatory nucleus, nucleus lateralis valvulae, and NRLl. The NCa appears to be primarily an extrahypothalamic projection nucleus. The NCp receives projections from the NDLI. Efferent connections of the NCp remain to be studied. The NRLl receives projections from the NDLI, and projects to the nucleus ruber (NR) of Goldstein [1905] and the preglomerular tertiary gustatory nucleus. Dense projections of the NR to the stratum opticum and stratum fibrosum et griseum superficiale of the optic tectum are demonstrated. The NRLm receives projections from the medial part of the dDm. Efferent connections of the NRLm remain unclear. The LI as a whole receives projections from the locus coeruleus and nucleus raphe superior. These results suggest that the LI receives gustatory and/or general visceral information from the secondary and tertiary gustatory nuclei, visual and somatosensory inputs from the corpus glomerulosum. Inputs from the dorsal telencephalic subdivisions could be of various modalities (e.g. visual, acousticolateral, gustatory and/or general visceral). The present study also suggests that information processed in the LI is transmitted to the optic tectum via the NR, to the corpus mamillare, to the secondary and tertiary gustatory nuclei, and to the cerebellum via the nucleus lateralis valvulae.

Central fiber connections of the gustatory system were examined in a percomorph fish Oreochromis (Tilapia) niloticus by means of the horseradish peroxidase (HRP), biocytin, and carbocyanine dye tracing methods. The primary gustatory areas in tilapia are the facial, glossopharyngeal, and vagal lobes of the medulla. The secondary gustatory nucleus (SGN) is a dumb-bell-shaped structure located in the isthmic region. In the SGN, there are two or three layers of neurons lining the ventromedial periphery of the nucleus and a molecular layer constituting of the major part of the nucleus. The SGN receives bilateral projections from the facial lobes and ipsilateral projections from the glossopharyngeal and vagal lobes. Ascending fibers originating from the SGN form the ipsilateral tertiary gustatory tract. A major part of the tract courses rostrally and terminates ipsilaterally in several diencephalic nuclei: the preglomerular tertiary gustatory nucleus (pTGN), the posterior thalamic nucleus, the nucleus diffusus lobi inferioris, the nucleus centralis of inferior lobe, and the nucleus recessus lateralis. The remaining small fiber bundle enters the medial and lateral forebrain bundles and terminates directly in two telencephalic regions; the area ventralis pars intermedia (Vi) and the area dorsalis pars posterior (Dp). Ascending fibers from the pTGN pass through the lateral forebrain bundle and terminate ipsilaterally in the dorsal region of area dorsalis pars medialis (dDm) of the telencephalon. Following biocytin injections into the dDm, small, round cells were labeled in the pTGN. After biocytin injections into the Vi and Dp of the telencephalon, retrogradely labeled cells were found in the ipsilateral SGN. The results show that the ascending fiber connections of the central gustatory system in the percomorph teleost tilapia are essentially similar to those of mammals. That is, the pathway from the primary gustatory areas (facial, glossopharyngeal, and vagal lobes) through the SGN and pTGN to the dDm in tilapia corresponds with the mammalian gustatory pathway from the solitary nucleus through the pontine taste areas (nucleus parabrachialis) and the thalamic relay nucleus (ventral posteromedial nucleus) to gustatory neocortices. In addition, the pathway from the primary gustatory areas through the SGN to the Vi and Dp in tilapia corresponds with the pathway from the solitary nucleus through the pontine taste areas to the amygdala in mammals.

Central fiber connections of the gustatory system were examined in a percomorph fish Oreochromis (Tilapia) niloticus by means of the horseradish peroxidase (HRP), biocytin, and carbocyanine dye tracing methods. The primary gustatory areas in tilapia are the facial, glossopharyngeal, and vagal lobes of the medulla. The secondary gustatory nucleus (SGN) is a dumb-bell-shaped structure located in the isthmic region. In the SGN, there are two or three layers of neurons lining the ventromedial periphery of the nucleus and a molecular layer constituting of the major part of the nucleus. The SGN receives bilateral projections from the facial lobes and ipsilateral projections from the glossopharyngeal and vagal lobes. Ascending fibers originating from the SGN form the ipsilateral tertiary gustatory tract. A major part of the tract courses rostrally and terminates ipsilaterally in several diencephalic nuclei: the preglomerular tertiary gustatory nucleus (pTGN), the posterior thalamic nucleus, the nucleus diffusus lobi inferioris, the nucleus centralis of inferior lobe, and the nucleus recessus lateralis. The remaining small fiber bundle enters the medial and lateral forebrain bundles and terminates directly in two telencephalic regions; the area ventralis pars intermedia (Vi) and the area dorsalis pars posterior (Dp). Ascending fibers from the pTGN pass through the lateral forebrain bundle and terminate ipsilaterally in the dorsal region of area dorsalis pars medialis (dDm) of the telencephalon. Following biocytin injections into the dDm, small, round cells were labeled in the pTGN. After biocytin injections into the Vi and Dp of the telencephalon, retrogradely labeled cells were found in the ipsilateral SGN. The results show that the ascending fiber connections of the central gustatory system in the percomorph teleost tilapia are essentially similar to those of mammals. That is, the pathway from the primary gustatory areas (facial, glossopharyngeal, and vagal lobes) through the SGN and pTGN to the dDm in tilapia corresponds with the mammalian gustatory pathway from the solitary nucleus through the pontine taste areas (nucleus parabrachialis) and the thalamic relay nucleus (ventral posteromedial nucleus) to gustatory neocortices. In addition, the pathway from the primary gustatory areas through the SGN to the Vi and Dp in tilapia corresponds with the pathway from the solitary nucleus through the pontine taste areas to the amygdala in mammals.

A case of cerebellar medulloblastoma with clusters of mature ganglion cells and glial cells is described. The patient, a 15 ‐year ‐old girl, underwent three operations followed each time by radiation and chemotherapy during the four‐year clinical course. Histologically, the ganglion cells were clearly identifiable by their abundant eosino‐philic cytoplasm, round nuclei with prominent nucleoli, tigroid granules, and argyrophilic fibrils and axons. Im‐munohistochemically, the cells were NSE‐ and NF positive, and ultrastructurally they contained abundant tubules and filaments, neurosecretory granules and well developed rough endoplasmic reticulum. There were many cells transitional in appearance between primitive cells and mature ganglion cells. The tumor also had many mature yet atypical astrocytes and oligodendrocytes. The exact mechanism of the extensive neuronal and glial maturation of medulloblastoma cells is unclear, but the repetitive surgical interventions, radiation and chemotherapy might have had certain cytostatic effects on rapidly dividing medulloblastoma cells, giving them a chance to mature into postmitotic cells with potential for neuronal and glial differentiation. Acta Pathol Jpn 40: 50–56, 1990.

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