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L R Britto

Publications and source records attributed to L R Britto.

At least 55 records · Page 3Linked to original sources
PubMed1991

Cholecystokinin-like immunoreactive retinal ganglion cells project to the ventral lateral geniculate nucleus in pigeons.

A subpopulation of retinal ganglion cells projecting to the pigeon ventral lateral geniculate nucleus was shown to contain cholecystokinin-like immunoreactivity. These ganglion cells were mainly distributed in the peripheral retina, and their somata sizes were medium to large (14-23 microns). Taken together with previous findings, these results indicate that the retinal input to the ventral geniculate is chemically heterogeneous.

Animals↗
PubMed1991

A subpopulation of displaced ganglion cells of the pigeon retina exhibits substance P-like immunoreactivity.

Immunohistochemical and retrograde tracing techniques were combined to demonstrate the occurrence of displaced ganglion cells (DGCs) exhibiting substance P-like immunoreactivity (SP-LI) in the pigeon retina. Following injections of rhodamine-labeled latex microspheres into the nucleus of the basal optic root (accessory optic system), about 5200 DGCs were observed to contain rhodamine fluorescence in the contralateral retina. Approximately 26% of the retrogradely labeled DGCs also contained SP-LI. The soma sizes of the doubly labeled DGCs ranged from 12 to 24 microns, and their distribution mirrored the overall distribution of DGCs projecting to the nucleus of the basal optic root. The density of doubly labeled DGCs ranged from 2 to 15 cells/mm2, with density peaks occurring in the superior-nasal and inferior-temporal retinal quadrants. Larger DGCs projecting to the nBOR (25-32 microns) were never seen to contain SP-LI. Together with previous results of enucleation experiments, these data indicate the existence of a subpopulation of SP-LI DGCs which are connected with the accessory optic system in the pigeon. The present results also contribute information on the heterogeneity of retinal ganglion cells transmitters and modulators.

Animals↗
PubMed1991

Endo-oligopeptidase A, a putative enkephalin-generating enzyme, in the vertebrate retina.

Endo-oligopeptidase A, EC 3.4.22.19, converts small enkephalin-containing peptides into the corresponding enkephalins in vitro. We investigated the presence of endooligopeptidase A in the retina and its possible colocalization with enkephalins in retinal neurons. The specific activity of endo-oligopeptidase. A found in pigeon retinae (30.3 +/- 7.3 mU/mg, mean +/- standard deviation) was four times higher than in rabbit retinae (7.0 +/- 1.1 mU/mg). The enzyme activity was not modified by EDTA, but it was enhanced by dithiothreitol and inhibited by zinc and 5,5'-dithiobis(2-nitrobenzoic acid). Immunohistochemical experiments with a purified antiserum against rabbit endo-oligopeptidase A revealed labeled neurons in both the inner nuclear layer and the ganglion cell layer of pigeon and rabbit retinae. Double-labeling immunofluorescence experiments demonstrated that about 90% of neurons containing endo-oligopeptidase A-like immunoreactivity also contained [Leu5]-enkephalin-like immunoreactivity. These colocalization results may represent an important step toward the demonstration of the possible involvement of endo-oligopeptidase A in enkephalin generation in vivo.

Amino Acid Sequence↗
PubMed1991

Extraretinal modulation of accessory optic units in the pigeon.

1. Electrophysiological methods were used to investigate the pretectal and telencephalic control of units within the nucleus of the basal optic root (nBOR) of the accessory optic system of pigeons. 2. Electrical stimulation of the pretectal lentiform nucleus mainly produced excitatory effects on nBOR units with temporal-to-nasal directional preference (among 109 cells, 51% were excited, 23% were inhibited and 23% were not affected) and inhibitory effects on units with nasal-to-temporal preferences (among 88 cells, 43% were inhibited, 38% were not affected, and 19% were excited). 3. Electrical stimulation of the visual Wulst (considered to be the equivalent of the visual cortex) produced mainly inhibitory effects on units with downward preferences (among 123 units, 47% were inhibited, 24% were excited and 29% were not affected), and mixed effects on units with upward preferences (among 70 cells, 30% were excited, 36% were inhibited and 34% were not affected). 4. Excitatory effects of LM stimulation had first-spike latencies ranging from 2-20 ms (mean +/- SEM, 5.5 +/- 0.7 ms), whereas latencies of W stimulation ranged from 6 to 30 ms (13.0 +/- 0.9 ms). 5. These results provide additional information about the neural substrates of the optokinetic nystagmus.

Animals↗
PubMed1990

Key pecking operant conditioning in detelencephalated pigeons (Columba livia).

The present paper analyzed the acquisition and maintenance of key pecking reinforced with food by pigeons with massive ablation of telencephalon structures (detelencephalated pigeon). The subjects were adult pigeons maintained at 80% of their free feeding weight. Expt. I analyzed the acquisition of key pecking by 3 previously detelencephalated pigeons and 3 normal controls. Expt. II investigated the effects of detelencephalation on the retention of learning through comparisons of pre- and postsurgery key peck rates in schedules of continuous reinforcement. In both experiments the duration of reinforcement was manipulated (20 s and 10 s). The results showed that detelencephalated pigeons are able to learn an operant response and to retain it after telencephalic ablation. Variability in key pecking rate was greater when the lesion preceded conditioning. The data suggest that the telencephalic systems participate in the organization of the key pecking behaviour patterns under this schedule of reinforcement but are not essential for this kind of learning. It is also suggested that subtelencephalic systems participate in the retention of learning.

Animals↗
PubMed1990

Thalamic origin of neuropeptide Y innervation of the accessory optic nucleus of the pigeon (Columba livia).

Immunohistochemical and tracing techniques were used in combination to reveal the source of a neuropeptide Y-like immunoreactive (NPY-LI) plexus in the nucleus of the basal optic root (nBOR) of the pigeon accessory optic system. Injections of rhodamine-labeled latex microspheres into nBOR produced retrograde labeling of a population of neurons interposed between the principal optic nucleus of the dorsolateral thalamus (equivalent to the mammalian dorsal lateral geniculate nucleus) and the ventral lateral geniculate nucleus. The retrogradely labeled neurons were distributed mainly in the immediate vicinity of the lateral, dorsal, and ventral aspects of the nucleus rotundus. Immunohistochemical methods revealed many NPY-containing somata within the same intergeniculate thalamic area. Double-labeling immunohistochemical and retrograde tracing experiments evidenced that many NPY-LI neurons in the intergeniculate area contained rhodamine microspheres that had been previously injected into the ipsilateral nBOR. The projection of that general thalamic area to the nBOR was then confirmed by means of anterograde transport of Phaseolus vulgaris leucoagglutinin. In these experiments, the intergeniculate region was demonstrated to project to all divisions of the nBOR and to every other retino-recipient structure, including the suprachiasmatic nucleus. Finally, electrolytic lesions of the intergeniculate area produced a dramatic reduction in the number of NPY-LI axons and terminals within the ipsilateral nBOR and also within other retino-recipient structures. These data indicate the existence of a thalamic NPY-LI projection to the pigeon nBOR of the accessory optic system. This chemically specific projection originates from the intergeniculate area, which was shown in this study to project to all other retino-recipient structures. Thus, NPY may have a role in the functional organization of the accessory optic system and also of the avian visual system as a whole.

Animals↗
PubMed1990

Visual telencephalon modulates directional selectivity of accessory optic neurons in pigeons.

The directional selectivity of units within the nucleus of the basal optic root (nBOR) of the accessory optic system (AOS) was studied before and after lesions of the visual telencephalon (visual Wulst) in urethane-anesthetized pigeons. In intact pigeons, most nBOR units preferred upward motion with a temporal component or downward motion with a nasal component. The ipsilateral and bilateral telencephalic lesions generated a dramatic reduction in the number of cells with optimal responses to upward motion. The overall distribution of preferred directions was still bimodal following ipsilateral or bilateral Wulst lesions, with most units showing best responses to a straight temporal or to downward-nasal directions. The contralateral Wulst lesions produced, instead, a marked reduction in downward preferences. The nBOR units which were studied in these cases showed mainly upward-temporal and upward-nasal responses. These data suggest an involvement of the visual Wulst in the determination of the directional selectivity of nBOR neurons in the pigeon. Specifically, the responses of nBOR units to upward motion appeared to depend on the integrity of the telencephalic descending systems which impinge, in both direct and indirect ways, upon that AOS nucleus. Taken together with data for the mammalian AOS, the present results indicate that nonretinal afferents to AOS nuclei have an important role in the functional organization of that subcortical visual pathway.

Animals↗
PubMed1990

Presumptive catecholaminergic ganglion cells in the pigeon retina.

An antiserum directed against tyrosine hydroxylase (TH), the rate-limiting enzyme in the synthesis of dopamine, was used to study the pigeon retina. Labeled cells were observed in both the inner nuclear layer (INL) and ganglion cell layer (GCL). Two populations of TH-immunoreactive neurons were observed in the INL. Some of these cells were 7-10 microns in diameter and gave rise to processes that arborized in three layers of the inner plexiform layer (IPL). These cells appeared similar to the dopaminergic amacrine cells described previously (Marc, 1988). Other labeled cells in the INL were 12-20 microns in diameter and were recognizable as a previously described subpopulation of TH-immunoreactive displaced ganglion cells (Britto et al., 1988). A population of labeled cells was observed in the GCL. Counts of these cells in two retinae revealed 5000 and 7000 cells, respectively. They ranged in size from 8-15 microns in diameter in the central retina and from 8-20 microns in diameter in the peripheral retina. The density of labeled cells was highest in the central retina and red field and lowest in the retinal periphery. The difference in cell size and cell density as a function of eccentricity is characteristic of the total population of ganglion cells in the avian retina (Ehrlich, 1981; Hayes, 1982). Some of the TH-positive cells in the GCL could be classified as ganglion cells for two reasons: (1) The axons of many of the TH-positive cells in the GCL were TH-immunoreactive as well and could be followed to the optic nerve head. (2) The injection of rhodamine-labeled microspheres into the nucleus geniculatus lateralis, pars ventralis (GLv), resulted in the retrograde labeling of many of the TH-positive cells in the contralateral retina.

Animals↗
PubMed1990

Accessory optic-pretectal interactions in the pigeon.

This electrophysiological study analyzes the influence of the nucleus of the basal optic root (nBOR) of the avian accessory optic system on units within the lentiform nucleus (LM), which is the avian equivalent of the pretectal nucleus of the optic tract. A prominent depression of the spontaneous firing rate of neurons within the LM occurred following electrical stimulation of the ipsilateral nBOR. A close correlation was also found between the directional selectivity of LM units and the apparent displacements generated by rotations of the head around the horizontal semicircular canal axis. This is consistent with a possible role of the LM in the coordinate transformation from visual inputs to a vestibular reference system.

Animals↗
PubMed1990

Efferent projections of the pigeon intergeniculate leaflet containing neuropeptide Y.

The present study was preformed to map efferent projections of the pigeon intergeniculate leaflet (IGL) to other visual structures, with emphasis on the pathways containing neuropeptide Y (NPY). After injections of an anterograde tracer (Phaseolus vulgaris leucoagglutinin) into the IGL, labeled axons and presumptive terminals were seen in several retinorecipient and visually-related nuclei. All such areas contained immunoreactive fibers to antibodies against NPY. Electrolytic lesion of the IGL provoked a marked reduction in the number of NPY-labeled fibers in these visual structures. The data suggest that the IGL is the source of NPY-labeled axons which occur in many visual nuclei of the pigeon brain.

Animals↗
PubMed1989

Neurotransmitters, receptors, and neuropeptides in the accessory optic system: an immunohistochemical survey in the pigeon (Columba livia).

Immunohistochemical techniques were used to survey the distribution of several conventional transmitters, receptors, and neuropeptides in the pigeon nucleus of the basal optic root (nBOR), a component of the accessory optic system. Amongst the conventional neurotransmitters/modulators, the most intense labeling of fibers/terminals within the nBOR was obtained with antisera directed against glutamic acid decarboxylase (GAD) and serotonin (5-HT). Moderately dense fiber plexuses were seen to label with antibodies directed against tyrosine hydroxylase (TH) and choline acetyltransferase (ChAT). GAD-like immunoreactivity (GAD-LI) was found in many small and medium-sized perikarya within the nBOR. Some of the medium-sized cells were occasionally positive for ChAT-LI. Cell body and dendritic staining was also commonly seen with the two tested antisera against receptors-anti-GABA-A receptor and anti-nicotinic acetylcholine receptor. The antisera directed against various neuropeptides produced only fiber labeling within the nBOR. The densest fiber plexus staining was observed with antiserum against neuropeptide Y (NPY-LI), while intermediate fiber densities were seen for substance P (SP-LI) and cholecystokinin (CCK-LI). A few varicose fibers were labeled with antisera against neurotensin (NT), leucine-enkephalin (L-ENK), and the vasoactive intestinal polypeptide (VIP). Unilateral enucleation produced an almost complete elimination of TH-LI in the contralateral nBOR. SP-LI and CCK-LI were also decreased after enucleation. No apparent changes were seen for all other substances. These results indicate that a wide variety of chemically-specific systems arborize within the nBOR. Three of the immunohistochemically defined fiber systems (TH-LI, SP-LI, and CCK-LI fibers) were reduced after removal of the retina, which may indicate the presence of these substances in retinal ganglion cells. In contrast, the fibers exhibiting ChAT-LI, GAD-LI, 5-HT-LI, NPY-LI, NT-LI, L-ENK-LI, and VIP-LI appear to be of nonretinal origin. Two different populations of nBOR neurons exhibited GAD-LI and ChAT-LI. However, these two populations together constituted only about 20% of the nBOR neurons.

Animals↗
PubMed1989

Chemically specific retinal ganglion cells collateralize to the pars ventralis of the lateral geniculate nucleus and optic tectum in the pigeon (Columba livia).

Immunohistochemical and retrograde tracing techniques were combined to study the retinal ganglion cells which project to the pars ventralis of the lateral geniculate nucleus (GLv) in the pigeon. Using two different fluorescent tracers, two histochemically-distinct populations of ganglion cells were found to project to both the GLv and the optic tectum. The first population of ganglion cells exhibited tyrosine hydroxylase-like immunoreactivity and represented about 20% of all ganglion cells which were retrogradely labeled from the GLv. The second population of ganglion cells showed substance P-like immunoreactivity and represented about 13% of all ganglion cells projecting to the GLv. These results confirm earlier suggestions that the retinal axons projecting to the GLv also project elsewhere and demonstrate that heterogeneity of retinal ganglion cells transmitters is evident even within a single retino-recipient nucleus such as the GLv.

Animals↗
PubMed1988

The rat accessory optic system: effects of cortical lesions on the directional selectivity of units within the medial terminal nucleus.

Single units within the medial terminal nucleus of the accessory optic system were recorded and examined for their responses to a moving pattern, in both intact and decorticated urethane-anesthetized rats. The preferred directions of motion in control rats were mainly upward with a temporal component and downward with a nasal component. The responses to upward motion were almost absent after cortical ablation, with most units now preferring temporal or downward-nasal directions. These data suggest that cortical structures modulate the directional selectivity of accessory optic neurons in the rat.

Action Potentials↗
PubMed1988

Catecholaminergic subpopulation of retinal displaced ganglion cells projects to the accessory optic nucleus in the pigeon (Columba livia).

In birds, displaced ganglion cells (DGCs) constitute the exclusive source of retinal input to the nucleus of the basal optic root (nBOR) of the accessory optic system. Tyrosine-hydroxylase (TH) immunoreactivity was examined in the pigeon retina after injections of rhodamine-labeled microspheres into the nBOR. A population of about 400 DGCs was observed in each case to exhibit both TH immunoreactivity and rhodamine bead fluorescence. This corresponded to about 10-15% of the total number of identified DGCs in each retina. Double-labeled cells were medium- to large-size (12 to 20 microns in the largest axis) and were always located at the border between the inner nuclear and the inner plexiform layers. Their dendrites could be followed horizontally in lamina 1 of the inner plexiform layer for up to 300 microns from the cell body. The distribution of double-labeled DGCs appeared to be mostly peripheral, matching the overall distribution of identified DGCs. Larger DGCs (21-28 microns) were never seen to contain TH immunoreactivity. Examination of brain sections revealed plexuses of thin varicose TH-positive axons in all subdivisions of the nBOR. Unilateral enucleation produced an almost complete elimination of TH immunoreactivity in the contralateral nucleus. Such results suggest the existence of a population of catecholaminergic DGCs projecting into the accessory optic system of the pigeon. They also support the emerging hypothesis concerning the neurotransmitter heterogeneity of ganglion cells in the vertebrate retina.

Animals↗
PubMed1988

Telencephalic and pretectal modulation of the directional selectivity of accessory optic neurons in the pigeon.

Direction-selective units within the accessory optic system of the pigeon were shown to respond more strongly to motion along two main directions, downward-nasal and upward-temporal. Following ipsilateral telencephalic or pretectal lesions, these directions were modified in a systematic way. In the former, the principal response directions were downward-nasal and temporal and in the latter, downward-temporal and upward-temporal. These data indicate that the non-retinal afferents play an important role in the functional organization of the accessory optic system.

Animals↗
PubMed1987

The pretectal nucleus of the optic tract modulates the direction selectivity of accessory optic neurons in rats.

Direction-selective single units within the medial terminal nucleus of the rat were shown to prefer motion in upward-temporal or downward-nasal directions. Lesions of the optic tract nucleus practically abolished responses to the nasal direction of motion and increased the directional bias toward the temporal direction. Such results suggest a significant role of that pretectal nucleus in the determination of direction selectivity of accessory optic neurons.

Action Potentials↗
PubMed1983

A pretectal projection upon the accessory optic nucleus in the pigeon: an anatomical and electrophysiological study.

Neurons of the nucleus lentiformis mesencephali, the avian homologue of the optic tract nucleus, were retrogradely filled with horseradish peroxidase after injections of the enzyme into the accessory optic nucleus in pigeons. The projection appeared exclusively ipsilaterally, and was confirmed by unitary and evoked potential recordings. Together with previous reports in both birds and mammals, the present study contributes information linking the accessory optic system to the pretectal nucleus of the optic tract and thence to horizontal optomotor mechanisms.

Afferent Pathways↗