Roberta G. Pourcho

Dopaminergic amacrine cells in the cat retina

Autoradiographic studies of cat retina showed an accumulation of [3H]dopamine in a subpopulation of amacrine cells whose process ramify in the outermost stratum of the inner plexiform layer. Dendrites of these cells are characterized by numerous varicosities measuring up to 2 micron in diameter which are connected by fine intervaricose segments. The dopaminergic amacrine cells are presynaptic to other labeled cells and to unlabeled amacrine populations but not to bipolar or ganglion cells. [3H]Dopamine-labeled processes provide extensive synaptic input to the somata and lobular appendages of type AII amacrine cells. This relationship suggests that dopaminergic amacrine cells may play an important role in the regulation of rod pathways in the cat retina.

Uptake of [3H]glycine and [3H]GABA by amacrine cells in the cat retina

After intravitreal injection, [3H]glycine accumulates in 3 distinct subpopulations of amacrine cells in the cat retina whereas [3H]GABA accumulates in 4 different subpopulations. Each labeled cell type can be distinguished on the basis of size and cytologic features. The density of label associated with each subpopulation serves as an additional distinguishing characteristic. [3H]Glycine is concentrated within the outer two-thirds of the inner plexiform layer (IPL). [3H]GABA is localized in two narrow bands in the outer half of the IPL and in a wider band adjacent to the ganglion cell layer.

Distribution of GABA immunoreactivity in the cat retina: A light- and electron-microscopic study

The distribution of GABA-like immunoreactivity in the cat retina was studied through the use of preembedding immunocytochemistry for light microscopy and by postembedding immunogold techniques for electron microscopy. Staining was observed in both inner and outer plexiform layers. Approximately 30% of the somata in the amacrine portion of the inner nuclear layer were immunoreactive and included amacrine and interplexiform cells. Horizontal cells and a subpopulation of cone bipolar cells were also stained. In the ganglion cell layer, staining was observed in both small- and medium-sized neurons. GABA-labeled amacrine cells were presynaptic to somata of amacrine cells and to dendrites of amacrine, bipolar, and ganglion cells. Bipolar cells were a major target, receiving more than 60% of all labeled synapses in the inner plexiform layer. Many of these contacts were reciprocal synapses. These findings support a major role for GABA-labeled amacrines in providing feedback inhibition to bipolar cells in the inner retina.

Localization of AMPA-selective glutamate receptor subunits in the cat retina: A light- and electron-microscopic study

The distribution of AMPA-selective glutamate receptor subunits was studied in the cat retina using antisera against GluR1 and GluR2/3. Both antisera were localized in postsynaptic sites in the outer plexiform layer (OPL) as well as the inner plexiform layer (IPL). Immunoreactivity for GluR1 was seen in a subpopulation of OFF cone bipolar cells and a number of amacrine and ganglion cells. Within the IPL, processes staining for GluR1 received input from OFF and ON cone bipolar cells but not from rod bipolars. Labeling for GluR2/3 was seen in horizontal cells, an occasional cone bipolar cell, and numerous amacrine and ganglion cells. In the IPL, GluR2/3 staining was postsynaptic to cone bipolar cells in both sublaminae. AII amacrine cells which receive rod bipolar input were also labeled for GluR2/3. With both antisera, staining was limited to a single member of the bipolar dyad complex, providing morphological evidence for functional diversity in glutamatergic pathways.

GABA-immunoreactivity in ganglion cells of the rat retina☆

Ganglion cells in the rat retina were labeled with the fluorescent dye, Diamidino-yellow, by retrograde transport from the superior colliculus and subsequently reacted for GABA-like immunoreactivity with a rhodamine-conjugated antiserum. Examination of sectioned retinas by fluorescence microscopy showed double labeling in approximately 6% of the ganglion cells. The presence of GABA in these neurons suggests that they may be involved in providing direct inhibitory input to the rat tectum.

Neurotransmitters in the retina

Processing of visual information within the retina depends in large measure upon a complement of chemical neurotransmitters which are released at synaptic contacts between individual neurons. Numerous investigators have participated in the identification of many of these transmitters and their assignment to specific neuronal subpopulations. However, it is now clear that the action of each transmitter depends upon the receptor molecules to which it binds. Multidisciplinary studies are underway to characterize these receptors as well as to investigate transporter molecules which may serve not only to inactivate certain neurotransmitters but may also function in their release.

Immunocytochemical evidence for the involvement of glycine in sensory centers of the rat brain.

Glycine-like immunoreactivity was localized to a number of sites in the rat brain which are involved in processing sensory information. In the auditory and vestibular systems, glycine immunoreactivity was seen in dorsal and ventral cochlear nuclei, superior olive, trapezoid body, medial and lateral vestibular nuclei, and inferior colliculus. Staining in the visual system was seen in retina, dorsal lateral geniculate nucleus, and superior colliculus. The olfactory system exhibited staining in the olfactory bulb and accessory olfactory formation. Somatosensory centers with glycine immunoreactivity included the dorsal column nuclei, spinal trigeminal nucleus, principal sensory nucleus of V, reticular formation, and periaqueductal gray. Glycine-immunoreactive neurons were also seen in cerebellar cortex, deep cerebellar nuclei, hippocampus, cerebral cortex, and striatum. The distribution of staining indicates that glycine plays a major role in sensory centers with actions at both strychnine-sensitive and strychnine-insensitive receptors.

Immunocytochemical demonstration of glycine in retina

An antiserum against glycine (Gly) conjugated to bovine serum albumin was raised and used to localize Gly-containing neurons in the retina. Reactive cells were also seen in the brainstem. This provides the first direct confirmation of the Gly content of these cells.

Autoradiographic localization of [3H]muscimol in the cat retina

In the cat retina, [3H]muscimol is localized in 5 morphologically distinct subpopulations of neurons with cell bodies in the amacrine layer and in other neurons located in the ganglion cell layer. Müller cells are unlabeled. The labeled subpopulations in the amacrine layer correspond to the subpopulations which also exhibit preferential uptake of [3H]GABA. The [3H]muscimol-labeled cells include interplexiform cells and type-AI reciprocal amacrine cells.

Distribution of AMPA-selective glutamate receptor subunits in the cat retina

Immunocytochemical techniques were used to localize AMPA-selective glutamate receptor subunits in the cat retina. The antisera employed recognize GluR1, GluR2/3 or GluR4 subunits. Each antiserum produced a distinctive staining pattern which included horizontal cells, cone bipolar cells, and amacrine and ganglion cells. Some cells such as alpha ganglion cells expressed multiple subunits whereas amacrine cells were typically immunoreactive with only one of the antisera.