GABA uptake and phenotypic characteristics of the subcommissural ependymocytes of the semi-desertic rodent, Meriones shawi: correlation with serotoninergic innervation

Abstract

Many studies have emphasized species differences in the serotoninergic innervation and phenotypic characteristics of the subcommissural organ in mammals. The post-natal distribution patterns of serotonin-containing fibers, the onset of gamma-aminobutyric acid uptake, and glial markers have been studied in the subcommissural organ of the semi-desertic rodent, Meriones shawi, by using immunohistochemical and autoradiographic techniques. Abundant serotoninergic fibers can be observed in the subcommissural organ of the newborn Meriones, some of them running among the ependymocytes and reaching the apical part of this organ. During the first 2 post-natal weeks of development, the subcommissural organ displays a progressive increase of serotonin fiber density throughout the organ, including the apical part. The existence of a dense serotonin-containing basal plexus concomitantly with a high apical innervation in this organ is a specific characteristic of Meriones. Ependymocytes of this organ have the ability to take up gamma-aminobutyric acid at birth. This uptake decreases and completely disappears from the 2nd week. The reappearance of gamma-aminobutyric acid accumulation in ependymocytes of the adult subcommissural organ after destruction of the serotonin innervation by a neurotoxin (5-7 dihydroxytryptamine) suggests an inhibitory effect of the serotonin innervation on this accumulation. Immunohistochemical studies of the phenotype of the ependymocytes with respect to glial markers during ontogeny show the transitory expression of glial fibrillary acidic protein, the presence of vimentin and the absence of S100 protein expression. No correlation has been found between the serotonin innervation and the expression of the glial markers.

Neural input and neural control of the subcommissural organ

“…Besides, inhibition of serotonin synthesis with parachlorophenylalanine increased the rate of 3 H-GABA accumulation (Didier-Bazes et al, 1989. Supporting these results, the neurotoxic destruction of serotonergic innervation with 5,7-DHT in Meriones shawi led to the reappearance of GABA accumulation into the SCO (Laalaouli et al, 1996). It has been described an absence of GABA accumulation in the adult rat SCO, lacking serotonergic innervation, after grafting the SCO into the fourth ventricle (Didier-Bazes et al, 1991, pages 461-467, this…”

“…In addition, there is an absence of GABA accumulation in the rat SCO after destruction of the serotonergic innervation with 5,7-DHT at birth (Didier-Bazes et al, 1991). Supporting these observations, it has been described that the SCO of the newborn semi-desert rodent Meriones shawi is capable of GABA uptake and is also innervated by serotonin at this age (Laalaouli et al, 1996). This GABA uptake decreased and disappeared from the second week of age on coinciding with an increase of the serotonergic innervation.…”

“…shawi led to the reappearance of GABA accumulation into the SCO (Laalaouli et al, 1996). It has been described an absence of GABA accumulation in the adult rat SCO, lacking serotonergic innervation, after grafting the SCO into the fourth ventricle (Didier-Bazes et al, 1991, pages 461-467, this issue).…”

The subcommissural organ of the frog Rana perezi is innervated by nerve fibres containing GABA

“…A coexistence of serotonin and GABA has also been reported for some neurons of the raphe nuclei of the rat (Harandi et al 1987), the origin of the serotoninergic fibres innervating the SCO in this species (Mikkelsen et al 1997). The functional significance of this phenomenon remains obscure but the accumulation of GABA seems to depend on the serotoninergic innervation (Chouaf et al 1989;Gamrani et al 1981;Didier-Bazes et al 1991;Laalaoui et al 1996). The functional significance of this phenomenon remains obscure but the accumulation of GABA seems to depend on the serotoninergic innervation (Chouaf et al 1989;Gamrani et al 1981;Didier-Bazes et al 1991;Laalaoui et al 1996).…”