PubMed Health⌕ Search

Biomedical subjects

A Merchán-Pérez

Publications and source records attributed to A Merchán-Pérez.

8 recordsLinked to original sources
PubMed2002

Spaceflight induces changes in the synaptic circuitry of the postnatal developing neocortex.

The establishment of the adult pattern of neocortical circuitry depends on various intrinsic and extrinsic factors, whose modification during development can lead to alterations in cortical organization and function. We report the effect of 16 days of spaceflight [Neurolab mission; from postnatal day 14 (P14) to P30] on the neocortical representation of the hindlimb synaptic circuitry in rats. As a result, we show, for the first time, that development in microgravity leads to changes in the number and morphology of cortical synapses in a laminar-specific manner. In the layers II/III and Va, the synaptic cross-sectional lengths were significantly larger in flight animals than in ground control animals. Flight animals also showed significantly lower synaptic densities in layers II/III, IV and Va. The greatest difference was found in layer II/III, where there was a difference of 344 million synapses per mm(3) (15.6% decrease). Furthermore, after a 4 month period of re-adaptation to terrestrial gravity, some changes disappeared (i.e. the alterations were transient), while conversely, some new differences also appeared. For example, significant differences in synaptic density in layers II/III and Va after re-adaptation were no longer observed, whereas in layer IV the density of synapses increased notably in flight animals (a difference of 185 million synapses per mm(3) or 13.4%). In addition, all the changes observed only affected asymmetrical synapses, which are known to be excitatory. These results indicates that terrestrial gravity is a necessary environmental parameter for normal cortical synaptogenesis. These findings are fundamental in planning future long-term spaceflights.

Adaptation, Physiological↗
PubMed1999

Decalcification by ascorbic acid for immuno- and affinohistochemical techniques on the inner ear.

An ascorbic acid decalcifying solution was applied to immuno- and affinohistochemical studies on the inner ear. Rat inner ears fixed in 4% paraformaldehyde in PBS or in 2% acetic acid in ethanol solutions were adequately decalcified in an ascorbic acid solution, at a temperature of 4 degrees C. The decalcifying solution was prepared with 1% ascorbic acid and 0.84% sodium chloride in distilled water (pH 2.5-2.6). The decalcification time was in a direct relationship to the specimen calcification. In this study, two neuroactive substances (gamma-aminobutyric acid and calcitonin gene-related peptide), neurofilaments, and the galectine endogenous lectin were successfully detected immunohistochemically.

Animals↗
PubMed1993

Ontogeny of gamma-aminobutyric acid in efferent fibers to the rat cochlea.

Cochlear efferent innervation originates in two different groups of neurons located in the superior olivary complex. A first group of olivocochlear neurons (lateral efferent neurons) lies in the lateral superior olive. They send axons to the organ of Corti, where they synapse with radial afferent dendrites of primary auditory neurons, postsynaptic to the inner hair cells. The second group of neurons (medial efferent neurons) is found in medial subnuclei of the superior olivary complex and sends axons to synapse with outer hair cells. Subpopulations of both medial and lateral olivocochlear neurons probably use gamma-aminobutyric acid (GABA) as a neurotransmitter. We have used an immunoperoxidase technique to detect GABA-like immunoreactivity (GABA-LI) in postnatal maturing rat cochleas. The GABA-LI appeared in the inner hair cell region by P3 (P1 = birth) and reached a mature appearance by P15-P16. In the outer hair cell region, GABA-like immunoreactive fibers and terminals could not be identified until P9 and they were only found in the apical end of the cochlea. There was a dual gradient of maturation of GABA-LI in the cochlea. The GABA-LI appeared first at the cochlear base and then extended towards the apex. It also appeared earlier (about a week) in the inner hair cell region than in the outer hair cell region. This dual gradient of maturation is in close agreement with previous data concerning the maturation of the cochlea.

Animals↗
PubMed1989

A morphometrical method to estimate isoproterenol-induced infarct size in the rat.

A morphometrical method to quantify the geometrical distribution of ventricular necrosis induced in rat following the s.c. injection of isoproterenol was developed and tested. Each ventricle was divided into two portions, apical and basal, and then 10 microns thick sections of both portions were cut. Necrotic areas were detected with nitro blue tetrazolium. Total and necrotic areas were measured for each section. Thereafter, the total and necrotic volume were calculated assuming that the ventricles form a cone-like structure composed of successive frustum of a cone crowned by an apical cone. The study of volumes, necrotic and whole cardiac could be relevant for a more actual experimental comparison of the anti-ischemic drugs activity. Our results indicated that necrotic volume is unevenly distributed, especially at lower doses of isoproterenol treatment, being greater at the apical than at the basal portions of the ventricles. The importance of careful study of the ventricular apex is stressed. Potential sources of error in determining necrotic volume are discussed.

Animals↗
PubMedDate not supplied

Estimation of the number of synapses in the cerebral cortex: methodological considerations.

In the present work we discuss several sampling procedures commonly used for counting synapses in the cerebral cortex. We compare, within the same tissue, two frequently used sterereological methods for determining the numerical density of synapses per unit volume, using as an example the estimation of the number of types of synapses by layers in the neuropil of the adult human temporal neocortex. These two methods are a size-frequency method (formula N(A)/d) and the disector method (sigmaQ-/a x h). Since the size-frequency method is assumption-based and the disector method is considered to be an unbiased method, the latter is often recommended for the quantification of synapses and other objects. We obtained, however, similar estimates for the numerical density of the different types of synapses using both methods, although they presented different technical difficulties and statistical properties. In addition, we show that the size-frequency method is more efficient and easier to apply than the disector method. Nevertheless, there are other methods for quantification which may also be valid, depending on the aim of the research; but the data reported in many articles are often complicated, which makes it very difficult for the reader to follow all the steps of the calculation. If certain basic information were given, this would facilitate the interpretation and sharing of important information with other laboratories, regardless of the method used for quantification. Finally, based on our present results and previous literature, we propose a simple general protocol for estimating the numerical synaptic density by volume in the neuropil of the cerebral cortex.

Adult↗
PubMedDate not supplied

Expression of GAP-43 in growing efferent fibers during cochlear development.

The development of olivocochlear efferent fibers has been studied by means of the immunocytochemical detection of the growth-associated protein GAP-43. This study has been carried out in pre- and postnatal, developing, pigmented rats. Results indicate that olivocochlear efferents reach the developing auditory epithelium from embryonic day 18 on. GAP-43-like immunoreactivity persists in the organ of Corti until the beginning of the second postnatal month. The relationships between the expression of GAP-43 in olivocochlear efferent fibers and other plasticity-related phenomena are discussed.

Animals↗
PubMedDate not supplied

Synaptophysin immunoreactivity in the cochlear nuclei of mammals: a comparative study.

Synaptophysin is a Ca(2+)-binding glycoprotein located in the presynaptic membrane and synaptic vesicles. This glycoprotein has been also involved in the release of neurotransmitters. The presence of synaptophysin within the cochlear nuclear complex of several animal species was analyzed. Differences in size and neuronal density of the cochlear nuclei were observed between the animal species studied. In fact, cat and rat cochlear nuclei showed a very similar morphology and neuronal distribution, while mouse, hamster and guinea pig exhibited important differences. The morphology and arrangement of synaptic boutons, for each neuronal type considered, were similar among species.

Animals↗