The arrangement of the enteric nerve plexuses in the colon of the guinea-pig and the distributions and projections of chemically specified neurons in this organ have been studied. Immunoreactivity for neuron specific enolase was used to examine the total population of neurons and individual subpopulations were studied using antibodies raised against calbindin, calcitonin gene-related peptide (CGRP), leu-enkephalin, gastrin releasing peptide (GRP), galanin, gamma aminobutyric acid, neurokinin A, neuropeptide Y (NPY), somatostatin, substance P, tyrosine hydroxylase and vasoactive intestinal peptide (VIP). Neuronal pathways within the colon were lesioned using myotomy and myectomy operations and extrinsic pathways running between the inferior mesenteric ganglia and the colon were also severed. Each of the antibodies revealed nerve cells and nerve fibres or only nerve fibres within the wall of the colon. VIP, galanin and GRP were in anally projecting pathways in the myenteric plexus, as they are in other species. In contrast, there are differences in the projection directions of enkephalin, substance P, NPY and somatostatin nerve fibres between regions and species. Surprisingly, somatostatin and NPY fibres have opposite projections in the small intestine and colon of the guinea-pig. The majority of nerve fibres that innervate the circular muscle, including fibres with immunoreactivity for VIP, enkephalin, substance P, NPY, galanin and GRP come from the myenteric ganglia. The mucosa is innervated by fibres from both the myenteric and submucous ganglia. The present results suggest that the guinea-pig distal colon is a suitable place in which to determine relations between structure, neurochemistry and functions of enteric neural circuits.

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The rat labial incisor alveolar bone facing the enamel and bearing the occlusal force was examined by electron microscopy after being compared with the lingual alveolar bone by histological and scanning electron microscopic (SEM) observations.
On the labial side, shallow resorptive lacunae were recognized all over the bone surface; these were mainly covered by osteoclasts and some mononuclear cells. The cement line was absent from the bone matrix. On the lingual side, residues of Sharpey's fibers, the bone formation surface and deep resorptive lacunae were observed by SEM. Histologically, bone remodeling areas showing both osteoclasts and active bone-forming osteoblasts on the bone surface, as well as many cement lines in bone matrix, were recognized.
Furthermore, electron microscopic and cytochemical studies demonstrated that mononuclear cells located close to osteoclasts displayed osteoblastic characteristics such as alkaline phosphatase activity, a developed Golgi apparatus, and a rough endoplasmic reticulum.
These findings indicate that continuous bone resorption occurs on the labial bone surface, while active bone remodeling occurs on the lingual surface. Even on the labial surface, osteoblastic cells close to osteoclasts seem to play an important role in the differentiation and/or activation of osteoclasts.

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The labial side of rat incisor alveolar bone facing the enamel is continuously resorbed as the result of compressive force produced by the occlusion and eruption of incisors. In order to clarify the relationship between this mechanical compressive force and the bone cells involved in bone remodeling, we examined morphological changes occurring in the alveolar bone once the compressive force was eliminated by the removal of the proliferative odontogenic base (root resection according to BERKOVITZ and THOMAS, 1969).
After root resection, the incisor migrated halfway along the socket. On the crestal part where incisor still existed, active osteoclasts were prominent on the bone surface, and flattened mononuclear cells lay close upon active osteoclasts. Sinusoidal blood vessels or capillaries were observed at short distances from the bone surface. On the basal part where socket was vacant, osteoblasts lined up on the newly formed bone, and the osteogenic cell layer lay on the osteoblasts. Between the two parts, which correspond to the reversal phase proposed by BARON (1977), osteoblastic cells with developed cell organelles increased in number and the distance between blood vessels and bone surface increased. Osteoclasts reduced their activities, and osteoblastic cells often wedged themselves between the osteoclasts and bone surface.
These findings indicate that the elimination of compressive force mediated by incisors leads to the activation of osteoblastic cells and inactivation of osteoclasts, which results in a conversion from bone resorption to bone formation. Thus, osteoblastic cells may play an important role in controlling osteoclastic activity in conversion from bone resorption to bone formation, partly by a direct effect and partly by controlling the access of blood vessels to the bone surface.

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The three-dimensional architecture of filamentous components in the lamina densa of the Schwann cell basement membrane was studied in the mouse sciatic nerve by transmission and scanning electron microscopy after osmium-maceration treatment and also by conventional electron microscopy. In conventionally prepared specimens, the lamina densa of the basement membrane was the most electron-dense showing up as a felt-like layer 20-30nm thickness. The interstitial surface of this layer had a spongy appearance with numerous shallow pits. Maceration of the specimens with 0.1% O_SO₄ for 2-4 days effectively removed amorphous, non-filamentous components from the basement membrane, thus exposing fine filamentous structures embedded in the lamina densa; these were about 10-15nm in diameter and elaborately interwoven and/or connected with each other to form the framework of the lamina densa. Occasionally, some of them appeared to twine around adjoining collagen fibrils. The nature of these filamentous structures is discussed in terms of the chemical components of the basement membrane.

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This study examined the lymphocyte content of the subcapsular sinus of lymph nodes of diverse anatomical sites, from euthymic and athymic animals of various ages. One unusual feature which prevailed in young euthymic animals consisted of the accumulation of lymphocytes on the outer wall of the subcapsular sinus, following differential patterns with respect to diverse domains or areas of the subcapsular sinus of a node compartment. It is concluded that such an accumulation is due to the retention of lymphocytes on the sinus outer wall. Whether the retention reflects a step in unspecific defence mechanisms, in an immunological reaction pathway, or a transient state of the misfunctioning of lymph-carried cells, is considered. Some findings favor the latter possibility. In this case, retention would be due to a mild form of lymphocyte alteration caused by the emergence of an abnormal milieu in a drained tissue, and conceivably involving mast cell products. Whatever the case, the retention on the outer wall of the subcapsular sinus, instead of on its inner wall, would prevent any hindering of the usual activity of the latter wall.

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This paper reports on a form of atrophy of lymph node compartments occurring in mesenteric nodes of athymic nude rats whose perinodal tissue had become unusually rich in mast cells and fibrotic. The subcapsular sinus of an affected compartment was depleted of lymphocytes, while the medullary sinuses were loaded with macrophages. A progressive expansion of medullary sinuses into the medullary cords, the extrafollicular zone, the deep cortex unit and, finally, the folliculo-nodules of the compartment was accompanied by a gradual atrophy of the usual lymphoid cell populations of these nodal components. The occurrence of such a mode of atrophy of a compartment, associated with a lack of lymphocytes in the afferent lymph, agrees with our previous proposal that lymphocytes of the afferent lymph provide the stimuli for the development and maintenance of the structures of the node. The involvement of mast cells and fibrosis in the emergence of the present form of nodal atrophy, which further weakens the immune system of an immunodeficient animal, is considered.

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The ultrastructural co-localization of vasoactive intestinal polypeptide (VIP) and acetylcholine (ACh)-like cation was demonstrated in the rat endocrine pancreas. Immunoperoxidase cytochemical procedure for the detection of VIP was followed by ionic fixation of ACh by silicotungstic acid. All the VIP-immunoreactive nerve endings displayed punctiform precipitates revealing ACh-like cations in the small clear vesicles. Almost all the VIP-immunoreactive nerve terminals were in contact with endocrine A, B or D cells, but not in the close vicinity of blood vessels. Nerve endings devoid of VIP immunoreactivity but containing ACh-like cations were seen either in contact with endocrine cells or in close vicinity to blood vessels. These data suggest that VIP might modulate, concomitantly with ACh, the hormonal secretion of the endocrine pancreas, although the possibility of the neurosecretion of ACh and VIP into the blood vessels should not be excluded. ACh might also control some function of the endothelial cells of blood vessels.

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The innervation of the periodontal ligament in hamster incisors was investigated by means of immunohistochemistry for nervous-specific proteins and electron microscopy.
The lingual periodontal ligament was found to be exclusively innervated by Ruffini endings which appeared to be most developed in this species among rodents; the labial periodontal ligament lacked them. The Ruffini endings occupied the alveolar half of the periodontal ligament, being intertwined with transverse collagen fibers. In electron microscopy, the Ruffini endings displayed expanded axon terminals filled with large-sized mitochondria. Three-dimensional reconstructions of the Ruffini endings at the electron microscopic level revealed complicated shapes for the axon terminals and a characteristic relationship with the associated terminal Schwann cells. The axon terminals were plate- or knob-shaped, the former being predominant. Each axon terminal was covered by thick Schwann sheaths derived from more than two terminal Schwann cells whose cell bodies were located apart from the axon terminals and contained a developed Golgi apparatus and rough endoplasmic reticulum. On the other hand, each terminal Schwann cell simultaneously extended their cytoplasmic processes to several axon terminals just like astrocytes. The thick Schwann sheath, for the most part, was covered by a multiple layer of basal lamina.
These findings have aided us in understanding the entire structure of the periodontal Ruffini endings.

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Aberrant ganglion cell morphogenesis associated with the ophthalmic placode was observed within the epidermis of the chick embryo at stages 20 through 26. This process was studied using immunohistochemistry and scanning and transmission electron microscopy. Clusters of ganglion cells were covered by epidermis and seen as epidermal nodules distributed diffusely in the supraorbital region. The ganglion cell clusters found within these nodules were not delineated by basement membrane from the epidermis, and were provisionally termed ectopic ganglia. The cell bodies within the ganglia possessed neurites containing microtubules and neurofilament protein. The cell bodies were also immunoreactive to monoclonal antibodies, E/C8 and HNK-1, indicating neuronal phenotypes. The neurites were often associated with the ophthalmic nerve or its branches as well as being distributed in the ectoderm. The ectopic ganglia seemed to represent the delayed gangliogenesis of a part of the ophthalmic placode which failed to detach from the ectoderm during ophthalmic ganglion formation.

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Spot 35 protein is identical to rat brain calbindin, as based on the complete homology of their nucleotide sequence, and is named here as spot 35-calbindin. The immunoreactivity for this protein was first detected on embryonic Day 16 (E16) in the anterior pituitary anlages. As the development proceeded, spot 35-immunoreactive cells increased in number in the pars distalis, especially in its antero-ventral portion, and also pars tuberalis. No sex difference was noticed in the pupulation dentsity of the immunoreactive cells until postnatal Week 3. At postnatal Week 5 and thereafter through adulthood, spot 35-immunoreactive cells were much more numerous in the male anterior pituitary than in the female organ. All immunopositive cells for spot 35-calbindin contained secretory granules, and no folliculostellate cells were immunopositive. Any of the anterior pituitary hormones including ACTH, GH, LH, PRL and TSH could be simultanously expressed with spot 35-calbindin in the granulated cells. Based on the ultrastructure of the secretory granules, spot 35-immunoreactive cells were classified into four types: cells containing round granules, 350nm; those containing granules of irregular contour larger than 350nm; those containing small granules, up to 150nm; and those containing a mixture of the round large and small granules. Cells containing large round granules were dominant in males, while cells containing small granules were dominant in females. The functional significance of spot 35-calbindin in the anterior pituitary is briefly discussed.

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