Presumptive GABAergic centrifugal input to the lamprey retina: a double-labeling study with axonal tracing and GABA immunocytochemistry.

The distribution of GABA-like immunoreactivity (GABA-LI) was performed in the lamprey retinopetal system which was previously identified by either anterograde or retrograde axonal tracing methods. This study was carried out at the ultrastructural level for the retina and under both the light and electron microscope for the mesencephalic retinopetal centers (M5 and RMA). The GABA-LI was distributed in about 40% of anterogradely HRP-labeled axon terminals in the inner retina. These made synaptic contacts upon either HRP-labeled ganglion cell dendrites or mostly on GABA-LI or on immunonegative amacrine cell dendrites and somata. The other immunonegative HRP-labeled axon terminals also established synaptic contacts on amacrine cell dendrites and somata. The mesencephalic retinopetal neurons, retrogradely labeled with HRP or [3H]proline, were GABA-LI in 65% of M5 somata and only in 15% of RMA neurons. M5 and RMA retinopetal neurons and dendrites, either GABA-LI or immunonegative, were contacted: (1) asymmetrically by HRP-labeled or unlabeled axon terminals containing rounded synaptic vesicles, always immunonegative and (2) symmetrically by HRP-unlabeled axon terminals containing pleiomorphic synaptic vesicles, which were either GABA-LI or immunonegative. The role of GABA as a putative neurotransmitter in the centrifugal visual system is discussed.

[Immunocytochemical research on mediators of centrifugal visual neurons in lampreys (Lampetra fluviatilis)]. / Recherche immunocytochimique sur les médiateurs des neurones visuels centrifuges de la lamproie (Lampetra fluviatilis).

The aim of this study has been to investigate different neuroactive substances in the lamprey centrifugal visual neurons (CVN) by combining axonal tracing methods and immunocytochemistry. The CVN somata are immunonegative to antibodies recognizing FMRF-amide, LH-RH, 5 HT and TH, but immunopositive to an anti-GABA antiserum (GABA+) in a proportion of 40%. In the retina, the GABA+ axon terminals mainly synapse upon GABA+ and GABA- amacrine cell bodies and dendrites, and on dendrites of GABA- ganglion cells.

Visual system degeneration in the glaucomatous albino quail.

The peripheral (eye, retina, optic nerve) and central (primary optic tracti and centers, centrifugal visual tractus and nucleus) visual system of an imperfect albino quail mutant with a sex linked recessive gene was examined in 32 specimens ages 1 week - 16 months-hatch using various histological techniques. During the first weeks the visual system was normal and comparable in its overall organization to that found in the pigmented quail. However, the ipsilateral retinal projections were observed to be weaker in the young mutant, then completely disappeared two months after birth. Initial signs of the bupthalmos, a form of spontaneous glaucoma, appeared between the 3rd and 5th months. This was characterized by a distention of the eye linked to an increase in intraocular pressure. The pathological process was progressive and at 16 months the eye was very prominent, the anterior chamber deep and a large and globular cornea was noted. The glaucoma progressively induced different histopathological changes in the visual system including: cupping of the optic disc, degeneration of optic axons and their parent ganglion and centrifugal cells and cavernous degeneration. All of these phenomena were identifiable at about the 10th post-natal month and progressed in a relatively constant and orderly manner. The retinal projections to the nucleus ectomamillaris, ventral and lateral optic tectum and ventral pretectum were the first to degenerate. The degeneration of optic fibers attaining the dorsal pretectum and dorsal thalamus occurred later. Furthermore the retrograde degeneration in the centrifugal isthmo-optic nucleus progressed from the external to the internal pole. The mechanisms involved in the selective degeneration of centrifugal and centripetal optic fibers is discussed.

Time course of degeneration of the visual system induced by spontaneous glaucoma in the albino quail (Coturnix coturnix japonica).

The retinal projection of an imperfect albino quail mutant with a sex-linked recessive gene was examined 2 weeks-16 months post-hatch using various histological methods. During the first weeks the visual system was normal. Initial signs of buphthalmos, a form of spontaneous glaucoma, appeared between the 3d and 5th months. Its development induced a degeneration of the retinal projections according to a relatively precise sequence progressing from the mesencephalic tegmentum to the optic tectum, then from the pretectum to the thalamus. The data suggest that the degeneration of the optic axons results from their mechanical compression due to the increased intraocular pressure.

The anatomical organization of retinal projections in the shark Scyliorhinus canicula with special reference to the evolution of the selachian primary visual system.

The retinal projections of the shark Scyliorhinus canicula were investigated using both the degeneration technique after eye removal and the radioautographic method following the intraocular injection of various tritiated tracers (proline, leucine, fucose, adenosine). The results showed contralateral projection via different optic tract components (TOM, AOT, TOm, TOl, ROVm, RODm) to various areas and nuclei of the hypothalamus (NSC), thalamus (NODLAT, NODMAT, NTTOM, NOVT, NODPT), pretectum (NOPC, NOCPd, NOCPv), tectum (SFGS, SGI) and mesencephalic tegmentum (AOTMd, NOTMv). Ipsilateral retinal projections were found to arborize within 7 distinct zones at the hypothalamic (NSC), thalamo-pretectal (NODLAT, NTTOM, NOVT, NOPC, NOCpd) and tectal (SFGS) levels. A comparison of the data with those previously obtained in different species of elasmobranchs and batoids indicate the existence of a common and consistent pattern of organization of the primary visual system in all selachians. Many of the discrepancies reported in studies on the organization of selachian retinal projection may be listed to methodological differences and/or interspecies variations in the cytoarchitecture of the different visual centers. Moreover, a comparison of the primary visual system of more primitive squalomorph sharks with that of the more advanced galeomorph sharks and batoids suggests that this system evolved through an increase in the neuronal density of the target structures and transformations in the dendritic configurations of the postsynaptic neurons rather than through an increase in the total number of projection zones.