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

Abstract

The innervation of the frog subcommissural organ was studied by light-microscopic and ultrastructural immunocytochemistry using antisera against serotonin, noradrenaline, dopamine, γ-aminobutyric acid (GABA), glutamic acid decarboxylase, different GABA receptor subunits and bovine Reissner's fibre material (AFRU). In the proximity of the organ, serotonin-and noradrenalinecontaining fibres were rare whereas dopamine-immunoreactive fibres were more numerous. Many GABA-and glutamic acid decarboxylase-containing nerve fibres were found at the basal portion of the ependymal cells of the subcommissural organ. Under the electron microscope, these GABA-immunolabelled nerve endings appeared to establish axoglandular synapses with secretory ependymal cells of the subcommissural organ. In addition, the secretory ependymal cells expressed high amounts of the β 2 -subunit of the GABA A receptor. Since GABA-immunoreactive neurons were present in the frog pineal organ proper and apparently contributed axons to the pineal tract, we suggest that at least part of the GABAergic fibres innervating the frog subcommissural organ could originate from the pineal organ.

Cloning of the GABAB Receptor Subunits B1 and B2 and their Expression in the Central Nervous System of the Adult Sea Lamprey

“…More studies in other groups of vertebrates are necessary to determine the evolution of this character due to the large evolution distance between mammals and lampreys. In addition, the cells of the subcommissural organ, a special type of ependymal cells, also lack the GABA B receptor both in lampreys, and in other vertebrates like teleosts, frogs and mammals (Jiménez et al, 2000; Saha et al, 2000; Nürnberger and Schöniger, 2001). Studies in these vertebrates have shown that the GABAergic responses in the subcommissural organ are also mediated by GABA A receptors.…”