Substance P positive (SP+) immunoperoxidase reaction product has been localized in light and electron microscopic preparations of rat lumbar spinal cord using an immunocytochemical method. SP+ reaction product was found to be highly concentrated in dorsal horn laminae I, II, portions of III, Lissauer's tract, s small nucleus in the dorsal part of the lateral funiculus, and in a longitudinal bundle of fibers just ventral to the central canal. Moderate accumulations of SP+ reaction product were observed in portions of laminae III-V, lamina X and in a narrow zone bordering fasciculus gracilis which expanded in its ventral aspect to include nucleus cornucommissuralis dorsalis and nucleus dorsalis. Remaining portions of the spinal gray matter exhibited extremely sparse staining. Light microscopic observations indicated that SP+ product was concentrated in fine axons and collaterals, which displayed densely-stained varicosities and terminal puncta. These varicosities and puncta were closely associated with neurons and blood vessels.



Dorsal rhizotomy produced a marked reduction in the number of SP+ fibers in Lissauer's tract, dorsal horn laminae I-III and the nucleus of the dorsolateral funiculus. However, dorsal root fibers were not the only source of SP+ structures in these regions since some SP+ fibers remained following dorsal root resections. In addition, this residual population of SP+ fibers did not appear to be altered by a combination of dorsal rhizotomy and ipsilateral transverse hemisection of the spinal cord. In conjunction with the results of other investigators, this finding suggests that the SP+ fibers which remain after dorsal rhizotomy are derived from local circuit interneurons of the spinal cord.



Electron microscopic observations revealed that certain axons and axon terminals contained concentrations of SP+ product which were associated with large, granular vesicles, while lesser amounts were in the terminal cytoplasm and associated with the exterior surfaces of small, agranular synaptic vesicles. SP+ terminals formed axodendritic, axosomatic and axoaxonal synapses, but the deposition of SP+ product often was not concentrated precisely at the “active sites” of these synaptic junctions. Some SP+ axons also made rudimentary contacts with astrocytic processes including those surrounding blood vessels. Since many of the SP+ terminals are similar in several respects to neuroendocrine terminals, it is possible that substance P may be released at several different types of non-synaptic sites as well as at conventional synaptic junctions. Thus our findings suggest that substance P could participate in a variety of neural functions ranging from those which are limited to synaptic junctions to those which are more generally distributed via an involvement of axonal plexuses as well as the glial, vascular and ventricular systems.

The origin, distribution and synaptic relationships of substance P axons in rat spinal cord.

KIF3A is a classical member of the kinesin superfamily proteins (KIFs), ubiquitously expressed although predominantly in neural tissues, and which forms a heterotrimeric KIF3 complex with KIF3B or KIF3C and an associated protein, KAP3. To elucidate the function of the kif3A gene in vivo, we made kif3A knockout mice. kif3A −/− embryos displayed severe developmental abnormalities characterized by neural tube degeneration and mesodermal and caudal dysgenesis and died during the midgestational period at ∼10.5 dpc (days post coitum), possibly resulting from cardiovascular insufficiency. Whole mount in situ hybridization of Pax6 revealed a normal pattern while staining by sonic hedgehog ( shh ) and Brachyury ( T ) exhibited abnormal patterns in the anterior-posterior (A-P) direction at both mesencephalic and thoracic levels. These results suggest that KIF3A might be involved in mesodermal patterning and in turn neurogenesis.

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Left-Right Asymmetry and Kinesin Superfamily Protein KIF3A: New Insights in Determination of Laterality and Mesoderm Induction by kif3A−/− Mice Analysis

Subnuclei in the rat hypothalamic paraventricular nucleus: a cytoarchitectural, horseradish peroxidase and immunocytochemical analysis.

Holosteans and Teleosts

The pineal organ of teleost fish is a directly photosensory organ that contains photoreceptor cells similar to those of the retina. It conveys photoperiod information to the brain via neural pathways and by release of indoleamines, primarily melatonin, into the circulation. The photoreceptor cells respond to changes in ambient illumination with a gradual modulation of neurotransmission to second-order neurons that innervate various brain centres, and by modulation of indoleamine synthesis. Melatonin is produced rhythmically, and melatonin synthesis may be regulated either directly by ambient photoperiod, or by an endogenous circadian oscillator that is entrained by the photoperiod. During natural conditions, melatonin is produced at highest levels during the night. Although the pineal organ undoubtedly influences a variety of physiological parameters, as assessed by experimental removal of the pineal organ and/or administration of exogenous indoleamines, its role in any physiological situation is not clear cut. The effects of any interference with pineal functions appear to vary with the time of year and experimental photothermal regimes. There are strong indications that the pineal organ is one component in a central neural system that constitutes the photoperiod-responding system of the animal, i.e. the system that is responsible for correct timing of daily and seasonal physiological rhythms. It is important to envisage the pineal organ as a part of this system; it interacts with other photosensory structures (the retina, possibly extraretinal non-pineal photoreceptors) and circadian rhythm generators

The pineal organ of teleost fishes

The cerebrospinal fluid (CSF) contacting neurons have a dendritic process which protrudes into the central canal, and is provided with one long kinocilium and many shorter stereocilia (about 80 in the turtle) as revealed by scanning electron microscopy. The shape, number and arrangement of the cilia are similar to those of known receptor endings.

Special dendritic and axonal endings formed by the cerebrospinal fluid contacting neurons of the spinal cord

The presence of rhodopsin was investigated by an indirect immunocytochemical method in the pineal complex of various vertebrates (Carassius auratus, Cyprinus carpio, Hypophthalamichthys molitrix, Lucioperca lucioperca, Triturus vulgaris, Bombina bombina, Rana esculenta, Pseudemys scripta elegans, Lacerta agilis et viridis, white leghorn chickens, rat), in the retina of Lebistes reticulatus, Lucioperca lucioperca, Rana esculenta, Lacerta agilis, Pseudemys scripta elegans, the chicken and the rat, and the cerebrospinal (CSF) contacting neurons of Triturus vulgaris. The outer segments of the photoreceptor terminals of the pineal organ, frontal organ, parapineal organ of lower vertebrates and of the retina of the species investigated, were intensely stained with the antirhodopsin reaction. There was no significant positivity in the pineal organ of the reptiles, the chicken and the rat, and the parietal eye of the lizards. We failed to demonstrate any immunoreactive staining in the CSF contacting neurons of various hypothalamic areas and of the spinal cord. The light microscopic immunocytochemical results seem to contradict a photoreceptive role of the CSF contacting neurons and strengthen the view that the receptory cells of the pineal complex of lower vertebrates are involved in light perception by means of the visual pigment rhodopsin.

Comparison of the pineal complex, retina and cerebrospinal fluid contacting neurons by immunocytochemical antirhodopsin reaction.

The presence of opsin was investigated with light microscopic immunocytochemistry in pinealocytes of reptiles and birds (Emys orbicularis, Pseudemys scripta elegans, Lacerta agilis et viridis, Gallus domesticus, Columba livia, Melopsittacus undulatus, Serinus canaria, Taeniopyga punctate). The outer segments of pinealocytes selectively bound antiopsin antibody as revealed by indirect immunocytochemical techniques, indicating the occurrence of a rhodopsin-like photopigment in these structures. The results were compared with those obtained in retinal photoreceptors of the same species as well as in the pineal organ of fishes and amphibians (Cyprinus carpio, Carassius auratus, Rana esculenta). Corresponding to immunoreactive structures seen in the light microscope, we found typical outer segments on a large number of pinealocytes in most of the reptiles and birds studied. The presence of opsin in the numerous well developed pineal outer segments of these reptilian and avian species contradicts the earlier hypothesis on the gradual regression of pineal sensitive structures in the avian line of evolution.

Immunoreactive opsin in the pineal organ of reptiles and birds.

The magnocellular preoptic nucleus of fishes (Anguilla anguilla, Amiurus nebulosus, Cyprinus carpio, Carassius auratus, Ctenopharyngodon idella, Cichlasoma nigrofasciatum) has been studied by light and electron microscopy.

B. Aros

Papers

Special dendritic and axonal endings formed by the cerebrospinal fluid contacting neurons of the spinal cord

Comparison of the pineal complex, retina and cerebrospinal fluid contacting neurons by immunocytochemical antirhodopsin reaction.

Immunoreactive opsin in the pineal organ of reptiles and birds.

Cerebrospinal fluid-contacting neurons, ciliated perikarya and “peptidergic” synapses in the magnocellular preoptic Nucleus of teleostean fishes

Fluorescence histochemical studies on the preoptic recess organ in various vertebrates.