Biomedical subjects

I Azcoitia

Publications and source records attributed to I Azcoitia.

30 records · Page 2Linked to original sources

PubMed1998

Viral superantigen-induced negative selection of TCR transgenic CD4+ CD8+ thymocytes depends on activation, but not proliferation.

T-cell negative selection, a process by which intrathymic immunological tolerance is induced, involves the apoptosis-mediated clonal deletion of potentially autoreactive T cells. Although different experimental approaches suggest that this process is triggered as the result of activation-mediated cell death, the signal transduction pathways underlying this process is not fully understood. In the present report we have used an in vitro system to analyze the cell activation and proliferation requirements for the deletion of viral superantigen (SAg)-reactive Vbeta8.1 T-cell receptor (TCR) transgenic (TG) thymocytes. Our results indicate that in vitro negative selection of viral SAg-reactive CD4+ CD8+ thymocytes is dependent on thymocyte activation but does not require the proliferation of the negatively signaled thymocytes.

Animals↗

PubMed1989

Evidence for apical secretion in the subcommissural organ of the chicken (Gallus gallus).

The apical surface and apical cytoplasm of the ependymal cells of the subcommissural organ (SCO) of the chicken, Gallus gallus were investigated by scanning and transmission electron microscopy. The presence of "secretory elements" formed by dilated and irregularly shaped RER cisternae in the proximity of the apical plasma membrane and located into ventricular protusions of apical cytoplasm, evidence an ependymal secretion towards the cerebrospinal fluid (CSF), which is responsible of the Reissner's fibre (RF) by means of an apocrine mechanism. The observed ependymal lysosomal population has been related with an endocytotic mechanism from the ventricular CSF which could also suggest an absorptive role for the SCO.

Animals↗

PubMed1989

Evidence for basal secretion in the subcommissural organ of the chicken (Gallus gallus).

The basal region of the subcommissural organ (SCO) was studied in the chicken Gallus gallus. The presence of concentric rough endoplasmic reticulum associated with lipid droplets in the basal processes of the ependymal cells, along with the increase of the lysosomal population, can be interpreted as evident signs of degeneration of the basal processes. The nearly absence of secretory processes ending on the meningeal blood vessels, suggests that the leptomeningeal route is missing. On the contrary, the presence of basal ependymal processes in contact with the hypendymal vessels could indicate that the ependymo-vascular pathway is well developed. In this sense, several structural features suggest a basal secretory mechanism from the SCO-cells: 1) Positive staining with paraldehyde-fuchsin of secretory material in the pericapillar region of hypendymal vessels and in the basal processes which reach the capillary wall; 2) presence of secretory material within the process endfeet in contact with hypendymal capillaries, and 3) existence of labyrinthis of the basal lamina of the capillaries.

Animals↗

PubMed1988

Ultrastructural peculiarities of the supraoptic nucleus of Mauremys caspica (turtle): its evolutionary interest in reptiles.

The hypothalamic Supraoptic Nucleus (SON) supposes an evolutionary achievement in the reptiles, zoological group in which this nucleus is first differentiated. Its scarce development in the chelonian, subject of the present study, is related to their primitive brain pattern. The peculiar location and the topographical configuration of the SON in the hypothalamus of the turtle Mauremys caspica allows to evidence morphologically the successive steps in the evolutionary process from lower to higher vertebrates. The marked neurosecretory character of the chelonian SON is the unequivocal proof of its philogenetic origin derived from the magnocellular preoptic nucleus of lower vertebrates.

Animals↗

PubMed1986

Annulate lamellae and whorl bodies in the diffuse supraoptic nucleus of the hamster.

The ultrastructure of neurons of the diffuse supraoptic nucleus of the hamster has been studied. These neurons show two specializations of the endoplasmic reticulum: annulate lamellae and whorl bodies. From one to three whorl bodies are found in the same neuron. The annulate lamellae and the whorl body cisterns are continuous with the cisterns of the rough endoplasmic reticulum. These neurons present an extraordinarily developed rough endoplasmic reticulum, small mitochondria, neurosecretory vesicles and a Golgi complex filled with electron-dense material. Astrocytic processes of different thickness surround the neurosecretory cells.

Animals↗

PubMed1986

Altered structures in the cytoplasm of the ependymal cells next to the periventricular nucleus of the turtle Mauremys caspica.

In the apical cytoplasm of some ependymal cells of the Hypothalamic Periventricular Nucleus of the turtle Mauremys caspica large amount of cell structures of difficult diagnose are found. Their morphology is variable seeming to correspond to cell organelles in a process of degeneration, characteristic feature of the high metabolic activity in the ventricular barrier. Their possible physiological significance is discussed in the present work.

Actin Cytoskeleton↗

PubMed1986

Ventricular labyrinths of the ependyma adjacent to the hypothalamic paraventricular nucleus in the turtle Mauremys caspica.

Labyrinthic recesses projecting to the subependymal tissue have been observed in the ependyma of the III ventricle in close relation to the neurons of the hypothalamic paraventricular nucleus in the turtle Mauremys caspica. There seems to be evidence of a direct contact between the paraventricular nucleus neurons and the cerebrospinal fluid whose physiological significance is discussed in the present work.

Animals↗

PubMed1985

Ciliated neurons in the paraventricular nuclei in old hamsters.

The ciliated neurons of the paraventricular nuclei in old hamsters have been studied by electron microscope. These neurons exhibit cilia of 9 + 0 pattern. The single cilia, emerging from typical basal bodies, project into the intercellular space in parallel to the plasmalemma. The basal bodies are connected to ciliary rootlets and close to the Golgi complex. Double or single centrioles in different locations, frequently related to rootlets, can be observed. From a morphological point of view we suggest that these cilia, in the aging process, may represent a sensory structure which could perceive stimuli from the intercellular space.

Aging↗

PubMed1985

Is the avian glycogen body a secretory organ?

In the present study we have observed with the electron microscope the glycogen body of the chick, Gallus domesticus, which constitutes a spinal cord circumventricular organ specific of birds. We have detected in young chickens and embryos the presence of considerable amounts of glycogen particles in the cerebrospinal and vascular compartments, coming from the glycogen body cells, which are able to discharge part of their glycogen into either the central canal or the capillary lumen, via ependymal and endothelial cells respectively. If this secretion is a physiological condition, we propose that the glycogen body would play a role in the maintenance of the hydric and glucose haemostasia in the central nervous system, as well as in the osmoregulation.

Animals↗

PubMedDate not supplied

Insulin-like growth factor-I receptors and estrogen receptors interact in the promotion of neuronal survival and neuroprotection.

Several in vitro and in vivo studies have shown that estrogen has neuroprotective properties. The neuroprotective effects of estrogen are probably exerted through several mechanisms. It is established that estrogen can provide neuroprotection by actions that are independent of estrogen receptor activation. In addition, in several experimental models, activation of estrogen receptors appears to be indispensable for neuroprotection. This review focuses on neuroprotection mediated by estrogen receptors. The interaction of estrogen with growth factor receptor signaling to induce neuroprotection is discussed. Evidence is presented that estrogen receptors and insulin-like growth factor-1 receptors interact in the promotion of neuronal survival and neuroprotection.

Animals↗

PubMedDate not supplied

Sex steroids and the brain: lessons from animal studies.

Gonadal steroid hormones have multiple effects throughout development on steroid responsive tissues in the brain. The belief that the cellular morphology of the adult brain cannot be modulated or that the synaptic connectivity is "hard-wired" is being rapidly refuted by abundant and growing evidence. Indeed, the brain is capable of undergoing many morphological changes throughout life and gonadal steroids play an important role in many of these processes. Gonadal steroids are implicated in the development of sexually dimorphic structures in the brain, in the control of physiological behaviors and functions and the brain's response to physiological or harmful substances. The effect of sex steroids on neuroprotection and neuroregeneration is an important and expanding area of investigation. Astroglia are targets for estrogen and testosterone and are apparently involved in the actions of sex steroids on the central nervous system. Sex hormones induce changes in the expression of glial fibrillary acidic protein, the growth of astrocytic processes and the extent to which neuronal membranes are covered by astroglial processes. These changes are linked to modifications in the number of synaptic inputs to neurons and suggest that astrocytes may participate in the genesis of gonadal steroid-induced sex differences in synaptic connectivity and synaptic plasticity in the adult brain. Astrocytes and tanycytes may also participate in the cellular effects of sex steroids by releasing neuroactive substances and by regulating the local accumulation of specific growth factors, such as insulin-like growth factor-I, that are involved in estrogen-induced synaptic plasticity and estrogen-mediated neuroendocrine control. Astroglia may also be involved in the regenerative and neuroprotective effects of sex steroids since astroglial activation after brain injury or after peripheral nerve axotomy is regulated by sex hormones.

Animals↗

PubMedDate not supplied

[The neuroprotective properties of sex steroids and neurosteroids].

INTRODUCTION: The nervous system is a target for steroid hormones as well as a steroidogenic tissue, and it produces steroids that have a paracrine or autocrine effect on neurons and glial cells. Steroids formed in nervous tissue are called neurosteroids in order to differentiate them, in terms of their origin, from the peripheral steroids, although they both share the same molecular structure. DEVELOPMENT: We analyse the capacity of neurons and glial cells to synthesise steroids and describe the role played in steroidogenesis by certain key molecules, such as steroidogenic acute regulatory protein, peripheral benzodiazepine receptor and aromatase enzyme, which acts as a catalyst in the conversion of testosterone into estradiol. We also provide a description of the different mechanisms of action of the hormonal steroids and neurosteroids in the nervous system. These include both the regulation of protein synthesis by neurons and glial cells, by acting on nuclear receptors, and rapid effects mediated by membrane receptors or the allosteric modulation of neurotransmitter receptors. We review the clinical and experimental evidence for the neuroprotective effects of sex steroids and neurosteroids, and the limitations of hormone replacement therapy following menopause. CONCLUSIONS: Given the restraints involved in the systemic use of hormones as neuroprotective therapy, alternative strategies that take advantage of the neuroprotective properties of steroids must be sought. These could involve locally increasing their synthesis inside the brain or developing molecules that activate the steroid receptors in the nervous system and not in the peripheral organs.

Animals↗