Localisation of amino acid neurotransmitters during postnatal development of the rat retina

Abstract

We used postembedding immunocytochemistry to determine the localisation of the amino acid neurotransmitters glutamate, gamma-aminobutyrate (GABA), and glycine, potential neurotransmitter precursors (aspartate and glutamine), and taurine in the rat retina during postnatal development. All amino acids investigated were present at birth; however, only the inhibitory neurotransmitters GABA and glycine displayed neuronal localisation. GABA was localised in a sparse population of amacrine cells, and glycine immunoreactivity was found in cells within the ventricular zone that appeared to migrate through the neuroblastic layer. Glutamate labelling was diffuse across the retina until postnatal day (PND) 8. Localisation of glutamine was evident within Müller's cells by PND 6, in agreement with the known age of onset of glutamine synthetase activity. Based on the findings of uptake of radiolabelled glutamate and GABA by PND 8 and changes in immunoreactivity, we propose that Müller's cells evolve at PND 6-8 from their precursor cells, the radial glial cells. Evidence for differences in glutamate turnover in the infant retina was seen on examination of aspartate and glutamine immunoreactivity. Aspartate labelling was weak until PND 11, when ganglion cells and some amacrine cells were labelled. Unlike the mature retina, a large number of amacrine cells were glutamine immunoreactive in the PND 6 retina. One reason for the observed differences in precursor pooling may be a lack of neuronal neurotransmitter release and overall low metabolic activity. We also investigated the response of the developing retina to ischaemic insult to test the physiological hypoxia model of vascular development. Our findings are consistent with the hypothesis that the developing retina has increased tolerance to ischaemic insult. Our findings suggest that, although the retina is morphologically adult like by PND 8, there are differences in neurotransmitter turnover in the immature rat retina.

Localization of CD15 immunoreactivity in the rat retina

“…To identify whether CD15 and GABA immunoreactivities are expressed within the same amacrine cells, double-labeling experiments using antisera to CD15 and GABA were performed. Immunostaining using GABA antibodies is in good agreement with earlier reports on the rat retina (Agardh et al 1986;Mosinger et al 1986;Versaux-Botteri et al 1989;Lake 1994;Fletcher and Kalloniatis 1997), with numerous GABA-immunoreac-134 Fig. 3A, B Light micrographs taken from 40-µm-thick vertical vibratome sections processed for CD15 immunoreactivity.…”

Neurotransmitter contents in the retina of RCS rat

“…In the retina, taurine localizes in the photoreceptor, bipolar and Mueller's cells and its content increases with age [8,9]. Growing evidence suggests that taurine is important for osmoregulation within photoreceptors and protects rod outer segments from the effects of light and chemical exposure by interacting with ion permeability and water accumulation in membranes [18,20].…”

“…In the mammalian retina, both acetylcholine (ACh) and dopamine (DA) are contained in the amacrine cells and fulfill all the criteria for functional neurotransmitters. Furthermore, glutamate mediates neurotransmission in the retinal "through" pathway (photoreceptor-bipolar cells-ganglion cells), whereas γ-aminobutyric acid (GABA) and/or glycine mediate(s) neurotransmission in the "lateral" pathway (amacrine cells, horizontal cells) [8]. It is also evident that taurine is concentrated within the photoreceptor cell layer and reduction of retinal taurine levels occur secondary to the loss of photoreceptor cells [22].…”

Comparison of the ontogeny of the vesicular glutamate transporter 3 (VGLUT3) with VGLUT1 and VGLUT2 in the rat retina

“…Amacrine cells are the primary inhibitory interneurons that comprise the inner retina, and classically have been thought to release GABA or glycine [9,30,34,37]. It has been proposed by Johnson et al, [24] that VGLUT3 expressing amacrine cells release both inhibitory and excitatory neurotransmitters like starburst amacrine cells.…”