Milena Kemali

Substance P-, met-enkephalin- and somatostatin-like immunoreactivity distribution in the frog spinal cord.

The distribution of substance P-, Met-enkephalin- and somatostatin-like immunoreactivity was studied in the thoracic spinal cord of the frog using immunohistochemical techniques. In fibres, probably nerve terminals, immunoreactivity was greatest in the grey matter (mainly dorsal horn), but it was also present in white matter regions. While substance P- and, perhaps, somatostatin-like immunoreactivity appeared to be contained in primary afferents, the presence of all 3 peptides in neuronal cells of the grey matter indicates the existence of a propriospinal peptidergic system.

Substance p and hydra: An immunohistochemical and physiological study

1. The distribution of substance P-like immunoreactivity was studied in Hydra attenuata using the peroxidase-antiperoxidase technique. 2. Positive immunoreactivity was observed in ectodermal nerve cells and fibers as well as in nematoblasts at various stages of differentiation. 3. Administration of synthetic substance P to regenerating hydra did not affect regeneration rates. Exogenous substance P administration stimulated tentacle contraction and nematocyst displacement within battery cells. 4. It is suggested that substance P acts on the contractile apparatus of Hydra tissues.

The dense core of vertebrate central nervous system synapses revealed by potassium permanganate fixation as formed by small membrane-bounded vesicles

Large dense core vesicles occur in small number in the company of clear synaptic vesicles in various parts of the central nervous system following osmium or aldehydes fixation. When fixed by potassium permanganate large vesicles occur that contain one or more membrane-bounded small spherical vesicles, as is demonstrated in the habenular nuclei of the frog Rana esculenta. On a morphological basis we suppose that the population of this kind of synapse consists of the same type of vesicles, the majority being free while some are enclosed within a larger vesicle. An hypothesis on the meaning of these composite vesicles is presented.

A modification of the rapid Golgi method.

An extremely rapid Golgi procedure for immersion impregnation of the whole brain of the frog Rana esculenta is described. It uses an isotonic 2% osmium tetroxide solution buffered with sodium barbital at pH 7.2 that has previously been used for electron microscopy. To 15 ml of this solution 85 ml 3% potassium dichromate is added just before use. Twelve-hour treatments (6 hr in the chrome-osmium solution plus 6 hr in 0.75% silver nitrate) are sufficient to obtain consistently excellent impregnations of external brain formations. Twenty-four-hour treatments (12 hr in the chrome-osmium solution and 12 hr in the silver solution) impregnate also the deeper regions of the brain. The results show neuronal details on a clear background.

Light- and electron-microscopic structure of cells protruding into the mesencephalic ventricle of Scyllium stellare (Elasmobranchii, Selachii).

SummaryIn the elasmobranch fish, Scyllium stellare, a complex group of cells protrudes into the cavity of the mesencephalic ventricle of the optic tectum. It consists of six to seven large spherical perikarya which resemble neurons of the mesencephalic nucleus of the Vth cranial nerve. The bundled processes of these cells form a stalk connecting the protrusion with the brain tissue. The protrusion is located in the region where the mesencephalic ventricle joins the cerebral aqueduct. This complex was not found in all specimens examined in the present study. The functional role of this peculiar group of cells, which contain dense core granules and are bathed in the cerebrospinal fluid, is open to discussion.

An ultrastructural analysis of myelin in the central nervous system of an amphibian

SummaryAn ultrastructural analysis of myelin in the ventral habenular and in the interpeduncular nuclei of the adult frog Rana esculenta has been carried out. In the ventral habenular nuclei, in addition to normally myelinated fibres, some myelin irregularities have been observed. They consist of myelin enwrapping the perikarya of some neurons and of isolated flaps of collapsed myelin. In the interpeduncular nucleus numerous myelinated fibres occur but few redundant myelin irregularities have been noticed.The morphological data suggest that myelination of fibres in these sites is due to the spiral wrapping mechanism from a glial cell process while the myelin irregularities described in the ventral habenular nuclei are probably due to membrane synthesis within the cytoplasm of the myelinated neurons and of the oligodendrocytes which are sometimes observed in contact with the ensheathed neurons. In the interpeduncular nucleus myelinated fibres indenting astrocytes and oligodendrocytes have been observed.

Drugs and the frog retina. Effect of dopaminergic agents on the pigment screening of light- and dark-adapted frogs.

This is a study, using the light and electron microscope, of the action of a dopamine agonist (apomorphine) and of a dopamine antagonist (haloperidol) on the retinal pigment screening (PS) of light- and dark-adapted frogs. Pigment screening is a phenomenon which consists of the migration of melanin granules into processes of the pigment epithelium that extend between photoreceptors, in response to changes in the conditions of illumination. In the light the pigment migrates vitreally , in the dark it aggregates sclerally . A single intravenous injection of apomorphine (0.15 mg/kg) and of haloperidol (1 mg/kg) did not induce substantial modifications in the pattern of pigment screening which was similar to that of controls both in light- and dark-adapted frogs. This suggests that dopamine is probably not directly involved in the phenomenon of pigment screening in the retina of the frog.

Non-ependymal cilia in the habenulae and the interpeduncular nucleus of the frog tadpole.

SummaryCilia of the 9+2 pattern are found electron microscopically in nonependymal cells of the habenulae and the interpeduncular nucleus of the tadpole of Rana esculenta at an early stage of development (8 mm length, head to tip of tail). A comparison is made between these and the ependymal and sensory cilia in the same specimens. The cilia project into the neuropil emerging from a perikaryon rich in free ribosomes and displaying a prominent Golgi apparatus. These perikarya contain dense core vesicles. Synapses with vesicles of the clear spherical type have been observed along the ciliary shaft. On a purely morphologic basis the authors hypothesize that these cilia, at least in this early ontogenetic stage, may extend considerably the conducting surface of the cell and represent a sensory structure which could be stimulated by terminal processes belonging to distantly located cells. In addition, they could also be involved in the trophic exchange of material with the adjacent structures.

The interpeduncular nucleus (ITP)

SummarySpecial types of cells of the interpeduncular nucleus (ITP) in the frog, Rana esculenta, are described after three types of fixation: osmium tetroxide, aldehydes and potassium permanganate. Large granules with a sub-unit structure occurring together with bundles of filaments and elongated mitochondria are illustrated in the processes of cells, the perikarya of which lie distant from the ependymal lining of the aqueduct of Sylvius. Such processes cross the ITP in a dorso-ventral direction perpendicular to the fibers which traverse the nucleus in a horizontal and frontal plane. They reach the subpial ventral surface of the nucleus ending in foot-like expansions where granules and mitochondria are assembled. The secretory nature of the granules is assumed. The release of possible peptide hormones into the interpeduncular cistern, where a pool of cerebrospinal fluid and large blood vessels occur, cannot be excluded.

The ultrastructure of the large granular vesicles of the frog's habenula

Two types of large granular vesicles in the habenular nuclei of the frog Rana esculenta following aldehyde fixation are described. One type is almost completely filled by a dense droplet. The other type contains a globular substructure. Both satisfy the morphological criteria for neurosecretory granules.