Neuronal organization of the optic tectum in the river lamprey, Lampetra japonica: a Golgi study.

The neuronal and laminar organization of the optic tectum (OT) in the river lamprey was studied using the rapid Golgi method. Based primarily on the distribution pattern of the dendrites, the OT neurons were divided into vertical, horizontal and stellate neurons. The river lamprey OT shows a laminar structure consisting of eight concentric strata. The stratum ependymale consists of several rows of ependymal cells. The stratum cellulare periventriculare contains one to two rows of vertical neurons. The stratum fibrosum periventriculare is thin and contains a few vertical neurons. The stratum cellulare et fibrosum internum consists of several alternating cellular and fibrous layers: a large variety of vertical and horizontal neurons are distributed in this stratum. The stratum fibrosum centrale consists of compact horizontal fiber bundles, among which a few horizontal neurons are disseminated. In the stratum cellulare et fibrosum externum, numerous fibers run horizontally in a loosely organized plexus; various types of vertical, horizontal and stellate neurons are distributed among these fibers. The stratum opticum is the main terminal area of the optic nerve, and contains stellate and horizontal neurons. The stratum marginale is a thin layer and consists of sparse populations of vertical and horizontal neurons. Besides the above outer to inner laminar structure, the OT is divided into medial (m-OT) and lateral parts (1-OT), based primarily on the distribution pattern of the dendrites. The dendrites of neurons in the m-OT are distributed almost exclusively within the OT. On the other hand, the dendrites of some neurons in the 1-OT extended into the confines of the torus semicircularis (TS), and conversely, the dendrites of some neurons in the TS are distributed in the 1-OT. These findings are discussed in relation to the neuronal and laminar organization of the OT in other lamprey species and to recent hodological studies.

Neuronal organization of the spinal cord in the red stingray (Dasyatis akajei: chondrichthyes).

The neuronal organization of the spinal cord in red stingray was studied using the rapid Golgi method. The gray matter of the spinal cord was divided into seven laminae: RS-I, RS-II, RS-III, RS-IV, RS-V, RS-VI and RS-VII. RS-I is cell dense lamina which occupies the major part of the dorsal horn and corresponds to laminae I and II of the spinal cord of mammals, birds and reptiles. The neurons of the lamina I are interspersed with those of lamina II, without forming a discrete lamina. RS-II is located at the base of the dorsal horn and is considered to correspond to the nucleus proprius. RS-III and IV form the intermediate zone and are highly reticulated. A few neurons of various shapes and sizes are distributed among the numerous fibers. The nuclei such as the intermediolateral, intermediomedial or Clarke's nucleus cannot be identified in the intermediate zone. RS-V and VI constitute the ventral horn. RS-V occupies the major part of the ventral horn and contains motoneurons which are distributed diffusely, without forming any distinct cell groups. RS-VI is located in the ventromedial part of the ventral horn, contains commissural neurons and correspond to lamina VIII. RS-VII is a small area surrounding the central canal and corresponds to lamina X. Thus, while the major features of the spinal cord of the red stingray can be correlated with those of the spinal cord of mammals, birds and reptiles, the neuronal organization of the spinal cord of the red stingray remains in an undifferentiated state.

Distribution of the parathyroid hormone-related peptide and its receptor in the saccus vasculosus and choroid plexus in the red stingray (Dasyatis akajei: Elasmobranch).

1. The exact role of the parathyroid hormone-related peptide (PTHrP) is not fully understood. We used immunohistochemistry to localize the PTHrP and its receptor in the brain of the red stingray, particularly in the saccus vasculosus (SV) and choroid plexus. 2. Immunoreactive PTHrP and its receptor were detected in the epithelial cells of the SV and the choroid plexus. In addition, the neuronal perikarya in the nucleus of the SV located in the hypothalamus is positive for the PTHrP. 3. No PTHrP-containing neurons were detected in the choroid plexus. Extracts of SV and choroid plexus showed positive reactions against the PTHrP and its receptor antibody in Western blot analysis. 4. High levels of immunoreactive PTHrP were detected in the plasma equivalent to those present in human humoral malignant hypercalcemia. In contrast, the immunoreactive PTHrP concentration in the cerebrospinal fluid was below detectable levels. 5. Our results suggest that the regulation of the PTHrP in the SV differs from that in the choroid plexus in the red stingray.

Neuronal organization of the olfactory bulb in the hagfish, Eptatretus burgeri: a Golgi study.

The neuronal organization of the olfactory bulb (OB) in the hagfish (Eptatretus burgeri) was studied using the rapid Golgi method. Cytologically, two groups of cells, the mitral and stellate cells, were discernible in the OB. Cytoarchitecturally, the OB showed a distinct laminar structure. From the periphery inward, the following four strata were distinguished: the stratum nervosum, stratum glomerulosum, stratum mitrale and stratum stellatum. Olfactory fibers from the olfactory epithelium reach the rostral aspect of the OB and form the stratum nervosum. The olfactory fibers run deeply in the OB, enter the stratum glomerulosum and terminate in the olfactory glomeruli which are arranged in three to four rows. Numerous mitral and a few stellate cells are distributed in periglomerular areas. The dendrites of the mitral cells terminate in one to two glomeruli in tufted terminals, while those of the stellate cells are distributed in periglomerular areas. The stratum mitrale also consists of mitral and stellate cells. The mitral cells in this stratum extend long dendrites to 4-5 widely separated glomeruli and generate axons traveling caudally. The dendrites of the stellate cells are long and are distributed in the stratum glomerulosum and stratum stellatum, as well as within the stratum mitrale. The stratum stellatum occupies a narrow caudal area and consists mainly of stellate cells extending long dendrites to the stratum stellatum and stratum mitrale.