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Biomedical subjects

J De Juan

Publications and source records attributed to J De Juan.

13 recordsLinked to original sources
PubMed1996

Formation and dissolution of spinules and changes in nematosome size require optic nerve integrity in black bass (Micropterus salmoides) retina.

Teleost retinas adapted to light show numerous spinules invaginated in the cone pedicles and small nematosomes in the distal horizontal cells. Darkness induces the dissolution of spinules and the presence of large and numerous nematosomes. The aim of this work is to study the influence of optic nerve integrity on spinule formation/dissolution and changes in nematosome size during light or dark adaptation of black bass (Micropterus salmoides) retinas. Eyes from fish, dark- or light-adapted, were removed and the eyecups placed in oxygenated Ringer's solution and immediately exposed to light or dark, respectively, for 1 h. The number of spinules per pedicle and the nematosome diameter were measured on electron micrographs. Isolation of eyecups in the dark, impaired both spinule formation and nematosome size reduction when they were superfused in light. In the same way, isolation of eyecups in the light, impaired both spinule dissolution and nematosome size increase when they were superfused in dark. No significant differences in spinule number and nematosome size, following dopamine superfusion, were found in comparison to retinas superfused with Ringer's solution only. Our results suggest: (1) optic nerve integrity is necessary to yield spinule formation/disruption and changes in nematosome size during light or dark adaptation. (2) dopamine does not appear to be the primary agent responsible for spinule formation.

Adaptation, Ocular↗
PubMed1995

Substance P-immunoreactive neurons in the human retina.

Substance P (SP) is a neuropeptide that acts as a neurotransmitter or a neuromodulator in the retina. The aim of this study was to identify the type(s) and the distribution of the SP-immunoreactive (SP-IR) cells in the human retina. We have used an antiserum to SP to immunostain neurons in postmortem human retinae. Immunostained retinae were processed with the avidin-biotin complex (ABC) to visualize the cells either whole mounted in glycerol or embedded in plastic. Some retinae were also sectioned at 20 microns in order to obtain radial views of stained cells. SP-IR amacrine cells stain intensely and appear to be of a single type in the human retina. They are large-field cells with large cell bodies (16 microns diameter) lying in normal or displaced positions on either side of the inner plexiform layer (IPL). Their sturdy, spiny, and appendage-bearing dendrites stratify in stratum 3 (S3) of the IPL, where many overlapping, fine dendrites intermingle to form a plexus of stained processes. Either cell bodies or primary dendrites emit an "axon-like" process that, typically, divides into two long, fine processes, which run in opposite directions for hundreds of micrometers in S5 and S3 before disappearing as distinct entities in the stained plexus in S3. Long, fine dendrites also pass from the dendritic plexus to run in S5 and down to the nerve fiber layer to end as large varicosities at blood vessel walls. In addition, fine processes are emitted from the dendritic plexus that runs in S1, and some pass up to the outer plexiform layer (OPL) to run therein for short distances. The SP-IR amacrine cell has many similarities to the thorny, type 2 amacrine cells described from Golgi studies. In addition to the SP-IR amacrine cells, a presumed ganglion cell type is faintly immunoreactive. Its 20-22 microns cell body gives rise to a radiate, sparsely branched, wide-spreading dendritic tree running in S3. Its dendrites and cell body become enveloped by the more intensely SP-IR processes and boutons from the SP-IR amacrine cell type. The SP-IR ganglion cell type most resembles G21 from a Golgi study.

Cell Count↗
PubMed1995

Two types of mitochondria are evidenced by protein kinase C immunoreactivity in the Müller cells of the carp retina.

The localization of protein kinase C (PKC) was studied immunocytochemically in the Müller cells of the carp retina. Electron microscope immunocytochemistry (using a monoclonal antibody to the alpha and beta isoenzymes of PKC) showed PKC-immunoreactivity mainly inside some mitochondria, especially along the mitochondrial cristae whereas other mitochondria in the same Müller cells showed no staining. Despite a detailed analysis we did not find any significant morphological difference between labeled and unlabeled mitochondria. These results demonstrate, for the first time, the presence of PKC immunoreactivity inside mitochondria and suggest that individual mitochondria may differ in signal transduction pathway.

Adenosine Triphosphate↗
PubMed1993

Visual experience during postnatal development determines the size of optic nerve axons.

The size of any axon is generally related to an internal programme (probably common for all neurones) that determines the number and organization of its cytoskeletal components. Here we show that axons from visually deprived rats are smaller than controls, although the number of microtubules and neurofilaments remains unchanged. Moreover the distance between both microtubules and neurofilaments and the amounts of 200 kDa, 160 kDa and 68 kDa neurofilament proteins are also diminished in the deprived axons. We suggest that cytoskeletal organization and axonal calibre are not only determined by intrinsic (genomic) factors, but that environmental stimulation is important for normal growth of nerve cells.

Animals↗
PubMed1993

Dendrites of rod dominant ON-bipolar cells are coupled by gap junctions in carp retina.

Gap junctions are supposed to be the anatomical substrate for electrical coupling between neurons. In fish retina, bipolar cells are electrically coupled and their receptive field diameters are always larger than dendritic field size, however, gap junctions have not been described between dendrites of bipolar cells. In this paper, using immunostaining for protein kinase C, we show that every rod dominant ON-bipolar cell is connected with its neighboring dendrites by gap junctions forming a plexus in the outer plexiform layer. These dendritic processes provide the site of electrical coupling. We suggest that dendrites of bipolar cells could be involved in lateral pathways in retina.

Animals↗
PubMed1993

A compiled BASIC program for analysis of spatial point patterns: application to retinal studies.

The pattern of distribution of a population of cells is of considerable interest to biologists and neurobiologists. However, the labor involved in collecting and analyzing the data often requires a significant amount of time. This paper presents a compiled BASIC program written using the Microsoft QuickBasic compiler for Apple Macintosh to facilitate such studies. The program allows collection and analysis of data that can be introduced either with the aid of a digitizing tablet of directly imported as x,y coordinates from different sources as, for example, word processors or image analysis software. Subsequently the program provides a quick, easy and interactive way of access to statistical, mathematical and graphical techniques used in the analysis of spatial point patterns. These techniques include several measures of dispersion (quadrat count, nearest neighbor and a 2-dimensional point autocorrelogram analysis) and arrangement. Although the program has been tested on spatial organization of retinal cells, it can be used to study the distribution of other cells in the nervous system and for different projects, as for example the distribution of microtubules and neurofilaments inside the axons. This software is available from the authors.

Animals↗
PubMed1992

Axon types classified by morphometric and multivariate analysis in the rat optic nerve.

Calibers of the rat optic nerve axons distribute unimodally and it is difficult to distinguish groups among them. However, these fibers arose from 3 types of ganglion cells and showed 3 conduction velocities. Performing a cluster analysis over several ultrastructural parameters we found 3 main groups of fibers. These groups are present in a very similar proportion to the ganglion cells groups described in the rat retina.

Animals↗
PubMed1991

Nematosomes in external horizontal cells of white perch (Roccus americana) retina: changes during dark and light adaptation.

Cytoplasmic inclusions resembling nucleoli and termed nematosomes have been described in several areas of the nervous system but not in the retina. Here we report the presence of these structures in the external horizontal cells of white perch (Roccus americana). Nematosomes were larger and more numerous in dark-adapted retinas than in light-adapted ones. An inverse relation of horizontal cell spinules was found in these cells, suggesting that electron-dense material observed in spinules may originate from nematosomes.

Adaptation, Ocular↗
PubMed1991

A useful programme in BASIC for axonal morphometry with introduction of new cytoskeletal parameters.

Interest in the structure of axons and quantification of their components has been growing over the last years. However, the existing literature contains few reports of available computer programmes to facilitate such studies. This paper presents a fully comprehensive BASIC programme for the morphometric analysis of electron micrographs of cross-sectional nerve fibres. From drawings of fibre and axonal contours and dots of the microtubules and neurofilaments, the programme calculates the following parameters: area, diameter and form factor of the fibres and axons, number and density of microtubules and neurofilaments, proportion between microtubules and neurofilaments (R-proportion), myelin thickness and the diameter of the axon relative to its sheath (g-ratio). The programme also introduces three new parameters to analyse the degree of uniformity of microtubule and neurofilament distribution: distances between microtubules and between neurofilaments, equilateral index and cytoskeletal intermingling index. The programme is written in Microsoft BASIC Interpreter for Apple Macintosh (Microsoft Corporation) but can be used on other computers. Although the programme has been tested on adult rat optic nerve fibres, it can be used for different projects concerning axonal morphometry.

Animals↗
PubMed1990

Postnatal development of striatal connections in the rat: a transport study with wheat germ agglutinin-horseradish peroxidase.

This paper deals with the postnatal development of afferent and efferent connections of the rat striatum as revealed by the transport of horseradish peroxidase conjugated with wheat germ agglutinin (WGA-HRP). Tracer was injected weekly from birth to the end of the first postnatal month in the head of the caudate nucleus. To control for transport from cortical areas contaminated by the micropipette, injections in newborn rats were made by either vertical or lateral penetrations. In addition some newborn and 14-day-old animals were injected only in the cortex. The results showed that at birth there was retrograde transport to the thalamus, substantia nigra and raphe nuclei. Labelling in the cortex was seen at birth but was probably due to cortical contamination. Transport from the striatum was clearly established on day 7, when a few labelled neurons were observed on both the ipsi and contralateral sides. These neurons increased in number and were distributed through layers III to VI by day 14. At this time labelled cell bodies were observed in the claustrum and lateral amygdaloid nucleus as well as in the globus pallidus and entopeduncular nucleus. On day 21 the contralateral labelling of the lateral amygdaloid nucleus was apparent. The anterograde transport from the striatum to globus pallidus, entopeduncular nucleus and substantia nigra was already visible at birth although its intensity increased during the first postnatal month.

Aging↗
PubMed1990

Alterations in prolactin secretion during the 1st postnatal month following perinatal dopaminergic blockade with haloperidol.

This research was intended to study the effects of perinatal haloperidol administration on the postnatal secretion of prolactin (PRL) with the aim of investigating the existence of a 'critical period' during which the lack of dopamine influence could cause long-term alterations in the secretion of this hormone. A first group of animals, composed of pregnant rats, was injected daily with haloperidol (1 mg/kg) from day 16 of gestation to delivery. A second group of newborn rats received the same dose from days 2 to 6 after birth. Pituitary and serum PRL were measured weekly by radioimmunoassay during the 1st postnatal month in pups from the injected mothers, in postnatally injected rats, and in controls. The results showed a significant increase in the pituitary amounts of PRL that was more intense after the prenatal treatment, especially in the females. In serum, the prenatal treatment induced PRL levels higher than in the controls, whereas the postnatally injected group exhibited a V-shaped response which has been described as characteristic of neuroleptic withdrawal. These data confirm the existence of a 'critical period' during which perinatal administration of haloperidol alters the postnatal PRL production and secretion patterns. The persistence of high PRL contents in pituitary may reflect an alteration in the hormone synthesis and/or an increase in the rate of somatomammotrophes that differentiate into lactotrophes after suppression of dopamine influence. The high PRL levels in serum indicate a failure in the control of PRL release, perhaps after damaging the tuberoinfundibular neurons as a consequence of the high prolactinemia induced by the treatment.

Animals↗
PubMed1978

Number, diameter and distribution of the rat optic nerve fibers.

Light- and electron-microscopic methods for nerve fiber counting and diameter measuring are described. These methods were applied to the rat optic nerve. Differences between light- and electron-microscopic results are shown. Coincidences and divergences with the current literature data are discussed.

Animals↗