International journal of developmental neuroscience : the official journal of the International Society for Developmental Neuroscience
-
Int. J. Dev. Neurosci. · Oct 2000
Long-term microglial and astroglial activation in the hippocampus of trimethyltin-intoxicated rat: stimulation of NGF and TrkA immunoreactivities in astroglia but not in microglia.
In the present study we investigated the microglial and astroglial response after trimethyltin (TMT) exposure over a prolonged period of time. Male Wistar rats were given a single dose of TMT (8 mg/kg, i.p.) and survived 4, 7, 21, 60 and 180 days after the administration of the toxin. Histochemistry (Griffonia simplicifolia lectin staining) and immunocytochemistry for GFAP were applied to identify micro- and astroglial cells, respectively. ⋯ In addition, the biochemical evaluation of GFAP and NGF were carried out at chosen timepoints using immunoblotting technique and ELISA, respectively. The main findings of our study were as follows. (1) A protracted activation of microglia (at least up to 2 months posttreatment). (2) A long-lasting expression of GFAP immunoreactivity (at least up to 6 months posttreatment) and a steady increase in GFAP content (at least up to 2 months posttreatment). (3) The appearance of enormously enlarged, round-shape astrocytes exclusively localized to CA1 and observed 2 months posttreatment. (4) The stimulation of NGF and TrkA expression in reactive astrocytes. (5) The strongest activation of micro- and astroglia coincided with the most prominent neurodegeneration in the hippocampus, i.e., in CA4/CA3c and CA1. It is tempting to assume that the activation of glial cells in the hippocampal areas particularly vulnerable to TMT may affect neuronal fate after neurotoxic insult.
-
Int. J. Dev. Neurosci. · Jul 1997
Discharge properties of pigeon single auditory nerve fibers after recovery from severe acoustic trauma.
The time course of recovery of compound action potential (CAP) thresholds was observed in individual adult pigeons after severe acoustic trauma. Each bird had electrodes implanted on the round window of both ears. One ear was exposed to a tone of 0.7 kHz at 136-142 dB SPL for 1 hr under general anesthesia. ⋯ However, the onset of recovery is delayed and the time course is slower than after destruction of short (abneural) hair cells alone. Also, recovery is incomplete, both functionally and morphologically. There is residual permanent hearing loss, and regeneration of short (abneural) hair cells is incomplete.
-
Int. J. Dev. Neurosci. · Jul 1997
Time course of nerve-fiber regeneration in the noise-damaged mammalian cochlea.
The time course of events which are essential for nerve-fiber regeneration in the mammalian cochlea was determined using a group of chinchillas that had been exposed for 3.5 hr to an octave band of noise with a center frequency of 4 kHz and a sound pressure level of 108 dB. The animals recovered from 40 min (0 days) to 100 days at which times their inner ears were fixed and the organs of Corti prepared for phase-contrast and bright-field microscopy as plastic-embedded flat preparations. ⋯ Outer hair cells degenerated first followed by outer pillars, inner pillars, inner hair cells and other supporting cells; (2) Myelinated nerve fibers in the osseous spiral lamina became fragmented, starting at the distal ends of the fibers. This degeneration gradually extended back to Rosenthal's canal; (3) Fibrous processes, originating from Schwann-like cells in the osseous spiral lamina, extended laterally on the basilar membrane; (4) Schwann cells lined up medial to the habenulae perforata in the areas of severest damage, apparently ready to migrate through the habenulae onto the basilar membrane; (5) Schwann-cell nuclei appeared on the basilar membrane beneath the developing layer of squamous epithelium which was in the process of replacing the degenerated portion of the organ of Corti; (6) Regenerated nerve fibers with thin myelin sheaths or a simple investment of Schwann cell cytoplasm appeared in areas of total loss of the organ of Corti; and (7) The myelin sheaths on the regenerated nerve fibers gradually became thicker.
-
Int. J. Dev. Neurosci. · Nov 1996
Essential role of thyroid hormones in maturation of olfactory receptor neurons: an immunocytochemical study of number and cytoarchitecture of OMP-positive cells in developing rats.
Neurogenesis and proliferation of olfactory receptor neurons (ORNs) in the olfactory epithelium (OE) are reduced in postnatal hypothyroid rats and upregulated following restoration of thyroid function, leading to compensatory growth and restitution of these deficits [Paternostro M. A. and Meisami E. (1993). Dev. ⋯ Withdrawal of PTU resulted in marked restoration of these deficits so that, at 90 days, the total number of OMP(+) cells were only 20% less than 90-day-old controls. These results indicate that thyroid hormones are essential for maturation of single ORNs and accretion of new mature ORNs in the OE of suckling and post-weaning rat. Also, the process of maturation and the final number of mature ORNs show remarkable recovery from hypothyroid-induced growth retardation.
-
Int. J. Dev. Neurosci. · Nov 1996
Regulation of c-Fos mRNA and fos protein expression in olfactory bulbs from unilaterally odor-deprived adult mice.
Odorant deprivation, produced by unilateral naris closure, profoundly reduces tyrosine hydroxylase (TH) expression within intrinsic olfactory bulb dopamine neurons. The TH gene contains an AP-1 site, which interacts with the product of the immediate early gene, c-fos. c-Fos exhibits activity dependent regulation in the CNS. The hypothesis that odorant stimulation and deprivation might modify c-fos expression in TH neurons was tested in adult CD-1 mice, subjected to unilateral naris closure. ⋯ In olfactory bulbs ipsilateral to naris closure, odor stimulation also induced c-fos mRNA expression in the mitral and granule cell layers and sparsely within limited periglomerular regions. Odor induced expression in mitral and granule cell layers may represent increased centrifugal activity acting on as yet unknown genes. These results suggest a correlation between c-fos mRNA expression and increased neuronal activity in the olfactory bulb which, in turn, acts to regulate TH expression in periglomerular neurons.