Comparative ultrastructure of cerebrospinal fluid-contacting neurons and pinealocytes

Abstract

The pinealocytes of fishes, amphibians, reptiles, birds and mammals have been compared with cerebrospinal fluid (CSF) contacting neurons. We found that the intraventricular dendrite terminal of the latter resembles the pinealocytic inner segment and that the atypical cilium (9x2+0 tubules) of the CSF contacting neurons is analogous with the outer segment of the pinealocytes, even though the outer segment bears photoreceptor lamellae in lower vertebrates. Regular, but small-sized photoreceptor outer segments were also found on pinealocytes of the chicken. In mammals, too, primitive outer segments are present in the form of 9x2 to cilia similar to those of CSF contacting dendritic terminals. In the Golgi areas of the perikarya of both cell types there are granulated vesicles which may contain transmitter substances and/or neurohormones. The synaptic junctions of the pinealocytes differ from those in the CSF contacting neurons. Many synapses occur on the latter, but they appear only rarely on pinealocytes. The axons of the CSF contacting neurons form synaptic connections with other cells, or terminate as neurohormonal synaptic hemidesmosomes on the basal lamina of the brain surface. The pinealocyte axons give rise to terminals containing synaptic ribbons. Such ribbons do not occur in CSF contacting neurons. In Lacertilians, we found pinealocytic terminals without ribbons on dendrite-like profiles. On the basis of the ultrastructural comparisons, we consider the CSF contacting neurons and pinealocytes to be very similar, but not to represent precisely the same cell type.

Concept of Paraneurons

“…Recent studies on the liquor contacting neurons have revealed their characteristic apical structures and their synaptic connections (VIGH and VIGH-TEICHMANN, 1973;VIGH-TEICHMANN and VIGH, 1974). The morphology of these cells strongly supports the view that they are chemoreceptors of the cerebrospinal liquor, although this has not been evidenced by physiological experiments.…”

Two Components of the Pineal Organ in the Mink(Mustela vison): Their Structural Similarity to Submammalian Pineal Complexes and Calcification.

“…Contrary to the general view that the mammalian pinealocytes are simple glandular cells, they actually exhibit structures typical of a photosensory cell by their 9+0-type cilia and innersegment-like processes (WOLFS, 1965;CLABOUGH, 1971;ZIMMERMANN and Tso, 1975;MOLLER, 1986), by their synaptic ribbons found in about 30 mammalian species (MCNULTY and Fox, 1922) and by their axonal processes forming synapses on secondary pineal neurons in some species (VIGH and VIGH-TEICHMANN, 1975;VIGH et al, 1975VIGH et al, , 1986bVIGH-TEICHMANN, 1991), and further by the presence of substances known for their role in retinal phototransduction (KALSOW and WACKER;1977;VIGH-TEICHMANN et al, 1986;ABE and SHINOHARA, 1990;PALCZEWSKI et al, 1990;VIGH-TEICHMANN and VIGH, 1992;LOLLEY et al, 1992).…”

“…This neurosensory character may explain the ability to concentrate calcium ions (see below). It also raises the question of whether the pinealocytes of all mammalian species have indeed lost their direct photosensitivity (VIGH and VIGH-TEICHMANN, 1989a;VIGH-TEICHMANN and VIGH, 1992). Like insectivores, the mustelids are ancient carnivores, representing a phylogenetically old group of mammals.…”

“…x 18,600 and/or synaptic bars, spherules /c/, facing the basal lamina /d/). These terminals pierce the superficial/ perivascular limiting glial membrane of the pineal nervous tissue (VIGH et al, 1986a). In the mink, pinealocytes of both organs form neurohormonal endings on the surface of the pineal tissue.…”

Complicated central effects of endothelin on blood pressure in rats.

“…However, it is probable that ENT directly exerts an effect upon the neurons in the CNS, since it is suggested that ENT is an endogenous agonist of Ca channels (YANAGISAWA et al, 1988a, b), which play a significant role in neural conduction as well as in vascular smooth muscle contraction. On the other hand, since peptides can be rapidly distributed into the brain interstitial space of the circumventricular organs, i.e., about six small regions around the ventricles which lack a blood-brain barrier (WEINDL, 1973), and the cerebrospinal fluid (CSF) is capable of transmitting information from one area of the brain to another by virture of special nerve cells with processes straight into the CSF (VIGH and VIGH-TEICHMANN, 1973), it is probable that i.c.v. injected ENT is capable of influencing the neurons in the CNS.…”