In xanthophores, microtubules were observed to radiate out from the microtubule organization center which was also the center of a central pigment mass. A similar pattern of microtubules was identified in both cells with dispersed or aggregated pigments. Brief vinblastine incubation, which depolymerized the microtubules of pigment-aggregated cells, failed to disrupt the central pigment mass. Subsequent removal of the vinblastine and the addition of ACTH dispersed pigment granules before the reassembly of microtubules. These results suggest that a radiating microtubular system is not essential to the maintenance or the dispersion of the aggregated pigment mass. Prolonged incubation with vinblastine eventually dispersed the aggregated pigment mass even in an ACTH-free medium, suggesting that certain components responsible for pigment association were finally destroyed by vinblastine. Moreover, these dispersed pigments could be induced to reaggregate into small clusters in the absence of microtubules, and finally into a large, tight aggregate when the microtubule system was fully reconstituted. We thus conclude that microtubules may serve to guide the centripedal movement of small pigment clusters toward the cell center, and they may not be essential to pigment dispersion and the maintenance of the central pigment mass.

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The arrangement of the enteric nerve plexuses, and the distributions and projections of chemically specified neurons in the proximal colon of the guinea-pig were studied. The neural plexuses were examined using immunoreactivity to neuron specific enolase, and individual subpopulations were studied using antibodies raised against vasoactive intestinal peptide (VIP), substance P (SP), enkephalin, neuropeptide Y (NPY), gastrin releasing peptide (GRP), galanin, somatostatin, calbindin and calretinin. Nitric oxide producing neurons were studied using NADPH diaphorase histochemistry. The myenteric and submucous plexuses were not uniform around the entire circumference; at the mesenteric aspect of the colon there was almost no longitudinal muscle and the circular muscle was unusually thick and cord-like. In this region there was no tertiary plexus of fibres, and the ganglia of the myenteric and submucous plexuses were elongated in the direction of the circular muscle. Neuronal pathways within the antimesenteric aspect of the colon were investigated using nerve lesioning procedures. VIP, GRP, galanin, calbindin and NADPH diaphorase containing neurons lay in anally projecting pathways within the myenteric plexus, while enkephalin and somatostatin appeared in orally projecting nerve pathways. Few NPY immunoreactive nerve cells were found in the myenteric plexus of the proximal colon. The longitudinal muscle was innervated with VIP, SP, enkephalin and NADPH diaphorase containing fibres. The circular muscle was innervated by axons containing all substances investigated except NPY. Galanin, NPY, somatostatin and VIP fibres, all particularly dense in the mucosa, largely arose from nerve cell bodies in the submucous plexus. The results of the present study indicate that chemically specified neuronal populations in the proximal colon of the guinea-pig are more similar to the distal colon than the ileum, but that neurochemical and anatomical differences exist between the proximal and distal colon.

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The present study describes the development and differentiation of microglial cells in the spinal cord of postnatal rats ranging from 1 day to 3 weeks of age. Using the monoclonal antibody OX-42, three different morphological forms of immunoreactive cells (SP, TLP, and AP) were identified based on their staining intensities, cell shapes and configurations of their cytoplasmic processes. Round or oval cells with short thick processes (SP) and cells with thick or thin long processes (TLP) were common in younger rats (1 day-1 week), while cells with attenuated processes (AP) preponderated in older animals (2-3 weeks). The immunoreactivity of microglial cells was gradually reduced as the cells differentiated progressively from the SP through the TLP type into the AP form. Similar results were obtained using the monoclonal antibody OX-18 and the isolectin Griffonia simplicifolia. None of the cells were stained with the antiboby OX-6. A quantitative study showed a rapid increase in the cell density of OX-42 positive cells in both the gray and white matter from 1 day to 2 weeks of age, but this appeared to decrease thereafter. The increase in the cell density was attributed to the active proliferation of the cells as shown by the detection of many bromodeoxyuridine-labelled cells in the same region. Its reduction in 3-week-old rats was most probably due to the apparent expansion of the spinal cord as a result of the growth of its fibre size and other structural elements.

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The postnatal development of the pineal organ of the ferret (Putorius furo) was investigated electron-microscopically with special interest given to the cerebrospinal fluid (CSF)-contacting pinealocytes and their large, vesiculated cilia.
In the pineal of the newborn ferrets, there is a lumen —a pineal ventricle—which is a diverticle of the third ventricle of the diencephalon. The luminal surface of the pineal is bordered by ependymal cells and CSF-contacting pinealocytes. A sensory, 9×2+0 type cilium arises from the free surface of the pinealocytes and thickens in the first week. There are mitotic figures in the wall of the pineal ventricle, being reduced to a pineal recess during the second and third postnatal week.
In two week-old animals, vesicles appear in the cilia of the pinealocytes. The vesicles may form rows and fill the enlarged cilium at the third week. Near the basal bodies, a proximal connecting piece remains narrow and free of vesicles. In older animals, there are multivesicular and dense bodies in the pineal cilia. The reduction of the pineal ventricle closes the CSF-contacting cilia in the intercellular spaces.
Axon-like processes of pinealocytes form synaptic ribbon-containing terminals on secondary pineal neurons. Axons of pineal neurons enter the fiber bundles of the pineal tract running to the habenular nuclei. All these structures do not differ from the light conducting pathway of the submammalian pineals. The ultrastructure of the cilia investigated resembles that of the developing outer segments of the retina and represents a preserved light perceiving structure of the mammalian pinealocytes. Further studies are necessary to elucidate whether the early differentiation of the cilia and synapses indicates a timing of the circadian light rhythmicity in young ferrets by direct pineal photosensitivity.

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Light-microscopic immunocytochemistry for various bioactive peptides including some gastroenteropancreatic hormones and a neuronal enzyme, neuron-specific enolase (NSE), was applied to taste buds in the circumvallate papillae of rats, mice and guinea pigs. In all the species positive immunoreactivities were demonstrated for Met-enkephalin-Arg⁶-Gly⁷-Leu⁸ (Met-Enk-8). The Met-Enk-8-like immunoreactivity was confined to parts of the spindle-shaped bud cells. These cells in rats and guinea pigs displayed a concomitant immunoreactivity for NSE. In the mouse taste buds, however, there appeared no such correlation between the immunoreactivities.
Considering our previous data, the present finding supports a possibility that opioid peptide (s) derived from preproenkephalin A might be the transmitter (s) of the gustatory cell.

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Light microscopy of tissue sections stained with cationic iron colloid (pH 1.0-1.5) showed that the adult rat spinal cord contains some neurons which are provided with strongly negative-charged surface coats. These neurons are distributed preferentially in the posterior and intermediomedial columns of the grey matter. The present study thus supplements our previous study of the rat brain (MURAKAMI et al., 1993b), and proves that the neurons with strongly negative-charged surface coats occur widely in the central nervous system of the adult rat.

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The distribution, pathways and origins of peptide-containing nerve fibers in the anterior two thirds of the dog tongue were investigated using immunohistochemistry combined with retrograde axonal tracing and denervation experiments. Within the epithelium of the fungiform papillae, varicose nerve fibers immunoreactive to substance P (SP) and calcitonin generelated peptide (CGRP) were present. These disappeared completely after severance of the lingual nerve (LN) alone. Dense CGRP-immunoreactive varicose fibers surrounded cell bodies in the intralingual ganglia (ILG), which consisted of neurons immunoreactive to vasoactive intestinal polypeptide (VIP), neuropeptide Y (NPY) and SP. These CGRP-immunoreactive fibers disappeared following severance of the chorda tympani (CT) alone. SP-, CGRP-, VIP-, NPY- and tyrosine hydroxylase (TH)-immunoreactive nerve fibers were distributed around the walls of blood vessels, especially arteriovenous anastomoses (AVAs). None of these immunoreactive fibers completely disappeared after severance of the LN or CT alone, but SP- and CGRP-immunoreactive fibers disappeared following severance of both the LN and CT. TH-immunoreactive fibers disappeared after ganglionectomy of the superior cervical ganglion (SCG) or severance of the hypoglossal nerve (HGN). VIP- and NPY-immunoreactive fibers invariably remained after various denervation experiments. In tracing experiments, CGRP-immunoreactive as well as SP and CGRP-immunoreactive cells in the trigeminal ganglion were labelled from the LN, and those in the geniculate ganglion and jugular ganglion were labelled from the CT. A large number of neurons in the SCG were labelled from the HGN, with some of these being SP and CGRP-immunoreactive. These results demonstrate that SP- and CGRP-immunoreactive fibers from the trigeminal ganglion are distributed to the lingual epithelium; vascular walls receive SP- and CGRP-immunoreactive sensory fibers from the LN as well as CT, some SP and CGRP-immunoreactive fibers from the SCG in addition to catecholaminergic sympathetic fibers, and VIP- and NPY-immunoreactive parasympathetic fibers from the ILG. The ILG is also considered to be innervated by CGRP-immunoreactive sensory fibers from the CT.

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Morphometric studies were conducted on rat developing submandibular gland. Terminal tubule cells from 5 and 15-day-old, and acinar cells from 15 and 30-day-old animals, were respectively studied. Radii of approximately spherical terminal tubule cell nuclei were measured in 0.5μm thick sections; the nuclear volumes were estimated using BACH's method. The volume of nuclei from non-spherical acinar cell was obtained indirectly. The fractions of cellular volume occupied by the nucleus and cytoplasm in both secretory cells were also evaluated and the cytoplasmic volumes thus obtained. Volume density, surface density and surface-to-volume ratio of the rough endoplasmic reticulum, Golgi complex, secretory granules and mitochondria, and derived stereological parameters, were determined. The secretory cells of older rats exhibited a greater cytoplasmic volume and higher total volume and surface area of organelles than cells from younger animals. The net daily accumulation of rough endoplasmic reticulum membrane surface area in terminal tubule and acinar cells was 157.7μm² and 330.4μm², respectively. These values represent a gain of rough endoplasmic reticulum membrane surface of 10.0% and 6.7%, respectively, along the intervals studied.

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The immunocytochemical localization of a major lysosomal membrane sialoglycoprotein with a molecular mass of 107kDa, which was designated as LGP107, was investigated in osteoblast lineage cells involved in osteoclastic bone resorption using specific polyclonal antibody against LGP107. Osteoclastic bone resorption was induced by transplantation of parathyroid glands. In control experiments, no immunoreaction product for LGP107 was recognized in osteoblasts and osteocytes. Strong immunoreaction products for LGP107 occurred on the plasma membranes in the osteoblasts and osteocytes prior to the appearance of osteoclasts one day after transplantation of the parathyroid glands. Furthermore, two days after induction, strong diaminobenzidine reactions were also observed on the plasma membranes in the osteoblastic cells adjacent to the active osteoclasts.
These data suggest that LGP107 in osteoblastic cells and osteocytes may play an important role in cellrecognition and/or cell-adhesion, and that LGP107 may be involved in osteoblastic degradation of the osteoid as well as exposure of the bone surface.

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Canine taste buds were observed by transmission electron microscopy with special reference to the gustatory cell function. The cells forming the taste bud were divided into five types: four of these corresponded to the previously reported Types I, II, III and IV (basal cell); another type, a slender, immature-looking cell located at the outermost layer, was identified as the peripheral cell known in the rat.
The Type I cell was supportive in nature, located between other cell types and enveloping nerve fibers. This cell apically secretes dense mucous substances.
The Type II cell was in broad contact with nerve fibers and constantly contained a subsurface cistern beneath them. In the dog, this cell was characterized by a large supranuclear Golgi apparatus.
The Type III cell was, as in other animals, regarded as the gustatory cell since it made synaptic contacts with nerves and contained synaptic vesicles. Numerous large cored vesicles were intermingled with some small clear vesicles. In addition to accumulating to the synaptic areas, the vesicles often filled the base of the cell, which was irregularly thickened, showing a more or less extensive contact with the basement membrane. In this area, numerous large cored vesicles approached the cell base. Blood capillaries close to the base of the taste bud were fenestrated in the endothelium. These findings supported a hypothesis that the transmitters may be released from the base of the gustatory cell and possibly exert paracrine and endocrine (hemocrine) effects. The salivary gland of Ebner was suggested as one such target. The nerve terminals on the Type III cell also contained synaptic vesicles, suggesting a reciprocal nature of the synapses.
The Type IV cell was the immature basal cell which has been established in other species; mitosis could be seen in this cell.

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