Biomedical subjects

A E Hendrickson

Publications and source records attributed to A E Hendrickson.

At least 37 records · Page 2Linked to original sources

PubMed1993

Immunocytochemical localization of GABA and glycine in amacrine and displaced amacrine cells of macaque monkey retina.

Recent studies have varied widely in the percentages of GABA- and glycine-immunoreactive (GABA+, GLY+) amacrines reported for primate retina. We compared the distributions of GABA+ and GLY+ amacrines and displaced amacrines at seven locations along the horizontal meridian of macaque retina using postembedding immunogold labeling with silver intensification. The percentage of GABA+ amacrine profiles was higher in central retina (50-55%) than peripheral retina (30-40%), whereas the percentage of GLY+ amacrine profiles did not vary much with eccentricity (52-57%). GABA and glycine were colocalized in 5-20% of amacrines, depending on the eccentricity, whereas 5-30% of amacrines were not immunoreactive for either neurotransmitter. GABA+ amacrines were slightly larger than GLY+ amacrines or Müller cells. In the ganglion cell layer, 5-20% of neurons were labeled for either GABA or glycine and were identified as displaced amacrines. Of these, 53% were GABA+ only, 11% were GLY+ only, and 37% were double-labeled. A few large, very lightly labeled GABA+ cells were identified as ganglion cells. Other features that varied with eccentricity included the linear density of GABA+ and GLY+ amacrines, and the ratio of amacrines to Müller cells.

Animals↗

PubMed1992

VVA-labelled cells in monkey visual cortex are double-labelled by a polyclonal antibody to a cell surface epitope.

The staining patterns produced by the lectin Vicia villosa and by a commercially available polyclonal antibody generated to substance P were analysed and compared in monkey visual cortex at the light and electron microscopic levels. Vicia villosa lectin labels the cell surface of a subpopulation of cortical cells, producing a meshlike pattern over the soma and proximal dendrites. The polyclonal antibody labels three distinct elements in the cortex: a pericellular epitope present on a subpopulation of non-pyramidal cells, and putative intracellular sites in a type of small pyramidal cell located at the layer 5/6 border, and in a small number of non-pyramidal cells in the underlying white matter. Because of the similarity of the appearance of the Vicia villosa lectin labelling and the pericellular labelling produced by the polyclonal antibody, further experiments were conducted to determine the relationship between the cell surface sites recognized by these markers. Double-labelling experiments show that both sites are present on the same population of cells, and at the ultrastructural level both markers appear to outline the intersynaptic cell membrane, sometimes extending around presynaptic elements. However, preadsorption experiments indicate that the markers recognize different sites on the cell membrane. Preadsorption experiments also show that the pericellular epitope recognized by the polyclonal antibody is unlikely to be substance P, but it may be structurally similar to keyhole limpet haemocyanin. Comparison of cortical and subcortical staining patterns produced with the polyclonal antibody and with a commonly used monoclonal antibody to substance P reveal that one of the putative intracellular epitopes recognized by the polyclonal antibody is likely to be substance P.

Animals↗

PubMed1992

Development of synapses in macaque monkey striate cortex.

A quantitative electron-microscopic (EM) analysis of the development of synaptic density (number of synapses/100 microns2 neuropil) has been done in primary visual cortex (striate, area 17) of the Old World monkey Macaca nemestrina. A comparative EM morphological study of developing synaptic contacts also was done in the same tissue. We find that a few immature synaptic contacts are present at fetal (F) 75 days either in the marginal zone, which becomes layer 1, or in the deepest portion of the cortical plate, the future layer 6. At F90-140 days synaptic contacts are found throughout the cortical plate, but their density remains higher in lower cortical layers. By F140 days synaptic density averaged for all layers (10.9) is three times higher than at F90 days. Just before and after birth, synaptic density rises very rapidly to peak at postnatal (P) 12 weeks (63) and then declines slowly to reach adult values (37.7) between 2-6 years. This pattern was further tested by comparing synaptic density in layer 2 which contains the last cells generated in the striate cortex to that in layer 6 which contains the first cells generated in the striate cortex. Layer 6 contained the first synapses, and had a higher density up to F140 days (an "inside-to-outside" distribution). Synaptic density was equal in the two layers at F152 days and P2 days, but by P12 weeks synaptic density in layer 2 was 27% higher than that in layer 6 (an "outside-to-inside" distribution). After P12 weeks, the synaptic density declined 51% in layer 2 and 21% in layer 6 so that both layers achieved similar densities by P6 years. A light and EM comparison of neuropil and synaptic contact morphology finds that, at each age up to birth, synapses in layer 2 are generally less mature than those in layer 6, but these differences disappear shortly after birth. Between P6-24 weeks, synaptic contacts throughout the cortex acquire a mature morphology that clearly differentiates between asymmetric and symmetric types, although asymmetric contacts continue to acquire more postsynaptic density until adulthood. This complex developmental pattern suggests a sequence for synaptic developments which is more related to neuron birthdate than to the arrival of extrinsic pathways or developmental events occurring in specific laminae.

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PubMed1991

Development of the calcium-binding protein parvalbumin and calbindin in monkey striate cortex.

The development of immunoreactivity for the calcium-binding proteins parvalbumin (PV) and calbindin-D28K (Cal) was studied in Macaca nemestrina striate cortex from fetal (F) 60 days to postnatal (P) 5 + years. We correlated changes in PV and Cal staining patterns with the well-documented developmental sequence for primate striate cortex neuron generation and maturation, synaptogenesis, and thalamocortical axon interactions in an attempt to deduce a functional role for these proteins. Our major findings is that Cal and PV have diametrically opposed developmental patterns except in layer 1. At F60 days both are present only in neurons of layer 1 and the number of labeled cell bodies and processes increases up to F125 days. Almost all Cal+ and PV+ cells in layer 1 disappear by P12 weeks. Cal is present by F113 days in pyramidal and stellate neurons, particularly layers 4-6. The numbers and staining density of cells in layers 2-6 increases up to birth and then both decline by P9-12 weeks. Supragranular layers show a second increase in Cal labeling from P20-36 weeks, and then there is a slow decline to the adult pattern which is reached by P1-2 years. Cell bodies in layers 4A, 4C alpha, and deep 4C beta are heavily Cal+ during pre- and early post-natal periods, but upper 4C beta remains unlabeled. PV is not seen until F155-162 days in layers 2-6. Large stellate and a few pyramidal cells appear first in layers 5/6 and 4C alpha, but PV+ stellate neurons are found in all layers except 4C beta by P6 weeks. Layer 4C beta contains a few PV+ cell bodies at P3 weeks, and light neuropile staining at P6 weeks, but then PV labeling rapidly increases so that by P12 weeks the density of 4C beta exceeds that of 4C alpha. Striate cortex has an adult pattern of cell number and neuropile density by P20 weeks. These developmental patterns suggest that the highest density of Cal cell body staining does not correlate with synaptogenesis, or the postnatal critical period of visually driven, binocular interactions. Rather Cal appears when lateral geniculate axons arrive in cortex, persists over the entire span of thalamocortical interactions, and disappears during the decline of cortical plasticity. The appearance of PV is highly correlated with the onset of complex visually driven activity at birth, while both the number of PV+ cell bodies and the density of PV+ neuropile reach adult levels coincident with the completion of thalamocortical connections.

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PubMed1991

Distribution of the calcium-binding proteins parvalbumin and calbindin-D28k in the sensorimotor cortex of the rat.

This study examined and compared the immunocytochemical distribution of the two calcium-binding proteins parvalbumin and calbindin-D28k in the primary motor and somatosensory areas of the rat neocortex. Parvalbumin-immunoreactive cells were found in all layers of the cortex except layer 1 and reached their peak density in the middle layers. The two cortical areas differed markedly in the number, cell size and morphology of immunoreactive cells. Parvalbumin-positive cells were more than twice as numerous in the somatosensory cortex compared to the motor cortex. In addition, the average size of their cell bodies was 25-30% larger in the somatosensory area. Parvalbumin cells in the motor area represented several classes of nonpyramidal cells, while the somatosensory cortex contained in addition many large cells with thick vertically oriented primary dendrites. Some of these cells resembled regular or inverted pyramidal neurons. Punctate neuropil labeling was much heavier in the upper layers of the somatosensory than in the motor cortex and was especially heavy in layer 4. Dense parvalbumin-positive perisomatic puncta surrounded large, unstained pyramidal cells in layer 5B of the motor cortex. Calbindin-D28k neuronal staining in both areas was confined to two populations. The most prominent was darkly labeled, small nonpyramidal cells confined to two bands in layers 2/3 and 5/6. There was also a lighter stained population composed of many pyramidal cells distributed throughout layers 2 and 3. In addition, the motor area contained a band of lightly stained, large pyramidal cells in layer 5B. Calbindin-D28k neuropil labeling was heaviest in layers 1 to 3. In contrast to parvalbumin, we found only minor differences in distribution, size and morphology of calbindin-D28k cell body or neuropil staining in the two cortical areas. Double-labeling immunocytochemistry showed that the large majority of immunoreactive cells contained only calbindin-D28k or parvalbumin, but a distinct population of multipolar cells in the upper layers of the somatosensory cortex contained both. The clear parcellation of parvalbumin immunoreactivity in the rat neocortex suggests that parvalbumin is preferentially associated with specific neuronal populations and terminals in the somatosensory cortex. The more general and homogeneous labeling of the upper layers of the cortex indicates that calbindin-D28k could be related to the relatively high density of calcium channels or N-methyl-D-aspartate receptors in the superficial layers of the rat cortex.

Animals↗

PubMed1990

Development redistribution of photoreceptors across the Macaca nemestrina (pigtail macaque) retina.

Redistributions of monkey cones and rods during the first year after birth include a fivefold increase in peak foveal cone density from 43,000 to 210,000 cones/mm2, a decrease in the diameter of the rod-sparse area, and a two- to threefold decrease in peripheral photoreceptor density. Two weeks before birth, higher cone density is already apparent in the future fovea, as are the nasotemporal asymmetry in cone distribution, a higher density "cone streak" along the horizontal meridian, a large rod-sparse central fovea, and a ring of high rod density. Despite the early appearance of these basic patterns, photoreceptor distribution is not mature until 1 to 5 years postnatally. Total cones varied from 4 million at birth to 3.1 million in the average adult. The two oldest eyes had fewer cones, suggesting up to a 25% loss late in development. There were 60 to 70 million rods in the adult macaque retina and little evidence of postnatal changes in number. Neither of these small changes is sufficient to account for the reduction in peripheral photoreceptor density and both are in the wrong direction to explain increasing foveal density, ruling out a major role for either photoreceptor death or generation. Retinal area increased by a factor of 2.4 from 2 weeks before birth to adulthood. In contrast, the posterior pole of the retina was dimensionally stable throughout this period, with the distance between the fovea and optic disc varying nonsystematically from 3.37 to 4.05 mm. Retinal coverage of the globe was also stable at 48-60%. Thus postnatal growth can be ruled out as a factor in the density changes occurring in central retina. Adult retinas have a higher proportion of both cones and rods in midperiphery, whereas young retinas have a higher proportion of photoreceptors in far periphery. It appears that photoreceptors are radially redistributed from peripheral toward central retina during postnatal development, resulting in the marked increase in foveal cone density and the decrease in the eccentricity of the rod ring. Up to 13 weeks postnatally, midperipheral growth of the retina is substantial and increases with eccentricity. At later ages, expansion continues only in the very far periphery. Retinal growth appears sufficient to explain the decreases in peripheral rod and cone density with age. These and previous data strongly suggest that differentiated photoreceptors, with complex cytology and synaptic contacts, migrate toward the foveal center, explaining the increase in foveal photoreceptor density.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1990

Calcium-binding proteins as markers for subpopulations of GABAergic neurons in monkey striate cortex.

Recent studies have shown that the presence of immunoreactivity for parvalbumin (PV-IR) and calbindin-D 28k (Cal-IR) can be used as markers for certain types of gamma-aminobutyric acid (GABA) immunoreactive interneurons in monkey cerebral cortex. Little quantitative information is available regarding the features that distinguish these two subpopulations, however. Therefore, in this study we localized PV-IR and Cal-IR neurons in Macaca monkey striate cortex and analyzed quantitatively their laminar distribution, cell morphology, and co-localization with GABA by double-labeling immunocytochemistry. PV-IR was found in nonpyramidal cells in all layers of the cortex, although PV-IR cells in layer 1 were rare. In contrast, Cal-IR was found mainly in nonpyramidal cells in two bands corresponding to layers 2-3 and 5-6. We found very few double-labeled PV-IR/Cal-IR cells but confirmed that almost all PV-IR and Cal-IR cells are GABAergic. Overall, 74% of GABA neurons in striate cortex displayed PV-IR compared to only 12% that displayed Cal-IR and 14% that were GABA-IR only. Quantitative analysis indicated that the relative proportion of GABA cells that displayed PV-IR or Cal-IR showed conspicuous laminar differences, which were often complementary. Cell size measurements indicated that PV-IR/GABA cells in layers 2-3 and 5-6 were significantly larger than Cal-IR/GABA cells. Analysis of the size, shape, and orientation of stained cell bodies and proximal dendrites further demonstrated that each subpopulation contained several different types of smooth stellate cells, suggesting that Cal-IR and PV-IR are found in functionally and morphologically heterogeneous subpopulations of GABA neurons. There was a thick bundle of PV-IR axons in the white matter underlying the striate but not prestriate cortex. PV-IR punctate labeling matched the cytochrome oxidase staining pattern in layers 4A and 4C, suggesting that PV-IR is present in geniculocortical afferents as well as intrinsic neurons. Cal-IR neuropil staining was high in layers 1, 2, 4B, and 5, where cytochrome oxidase staining is relatively low. We did not find a preferential localization of either PV-IR or Cal-IR cell bodies in any cytochrome oxidase compartments in layers 2-3 of the cortex. These findings indicate that PV and Cal are distributed into different neuronal circuits.

Animals↗

PubMed1990

Human photoreceptor topography.

We have measured the spatial density of cones and rods in eight whole-mounted human retinas, obtained from seven individuals between 27 and 44 years of age, and constructed maps of photoreceptor density and between-individual variability. The average human retina contains 4.6 million cones (4.08-5.29 million). Peak foveal cone density averages 199,000 cones/mm2 and is highly variable between individuals (100,000-324,000 cones/mm2). The point of highest density may be found in an area as large as 0.032 deg2. Cone density falls steeply with increasing eccentricity and is an order of magnitude lower 1 mm away from the foveal center. Superimposed on this gradient is a streak of high cone density along the horizontal meridian. At equivalent eccentricities, cone density is 40-45% higher in nasal compared to temporal retina and slightly higher in midperipheral inferior compared to superior retina. Cone density also increases slightly in far nasal retina. The average human retina contains 92 million rods (77.9-107.3 million). In the fovea, the average horizontal diameter of the rod-free zone is 0.350 mm (1.25 degrees). Foveal rod density increases most rapidly superiorly and least rapidly nasally. The highest rod densities are located along an elliptical ring at the eccentricity of the optic disk and extending into nasal retina with the point of highest density typically in superior retina (5/6 eyes). Rod densities decrease by 15-25% where the ring crosses the horizontal meridian. Rod density declines slowly from the rod ring to the far periphery and is highest in nasal and superior retina. Individual variability in photoreceptor density differs with retinal region and is similar for both cones and rods. Variability is highest near the fovea, reaches a minimum in the midperiphery, and then increases with eccentricity to the ora serrata. The total number of foveal cones is similar for eyes with widely varying peak cone density, consistent with the idea that the variability reflects differences in the lateral migration of photoreceptors during development. Two fellow eyes had cone and rod numbers within 8% and similar but not identical photoreceptor topography.

Cell Count↗

PubMed1990

Distribution of GABA-immunoreactive amacrine cell synapses in the inner plexiform layer of macaque monkey retina.

The distribution patterns of GABA immunoreactive (+) and immunonegative (-) amacrine cell synapses and profiles in the inner plexiform layer (IPL) were analyzed in three macaque monkey retinas using postembedding electron-microscopic (EM) immunogold cytochemistry. Synapses and profiles were counted at 5% intervals throughout the IPL depth in three EM montages (total area = 6509 microns 2), with 0% depth at the inner nuclear layer/IPL border. Nearly 70% of all amacrine synapses were GABA+, and they contacted all major classes of neurons that arborize in the IPL: bipolars (45%), ganglion cells (25%), and GABA+ (20%) and GABA- (10%) amacrines. A major relationship was seen between GABA+ amacrine processes and bipolar terminals: 76% of all amacrine-to-bipolar synapses were GABA+, and 82% of bipolar output dyads contained at least one GABA+ amacrine. GABA+ amacrine profiles (N = 2455) were concentrated in three wide bands at IPL depths of 0-25%, 40-60%, and 75-100%, corresponding to the dense bands seen with light-microscopic immunocytochemistry. In contrast, GABA+ amacrine synapses (N = 1081) were distributed evenly throughout the IPL depth, rather than being confined to the three dense bands. GABA- amacrine synapses (N = 516) were concentrated at 40% and 60% depths. Each category of amacrine output synapses had a characteristic pattern of stratification in the IPL. GABA+ amacrine-to-bipolar synapses occurred throughout the IPL but were most frequent at 20% and 80% IPL depths, where the dendrites of midget cone bipolars arborize (Polyak, 1941). In contrast, GABA+ amacrine-to-ganglion cell synapses were concentrated at 30% and 70% IPL depths, near the dendritic arborizations of parasol ganglion cells (Watanabe & Rodieck, 1989). GABA+ synapses onto bipolars and amacrines were also concentrated at the level of rod bipolar terminals. GABA+ amacrines must play significant but different roles in ON and OFF midget and parasol pathways as well as the rod pathway.

Animals↗

PubMed1989

Photoreceptor topography of the retina in the adult pigtail macaque (Macaca nemestrina).

In spite of the crucial role retinal photoreceptors play in mapping optical images into a pattern of neural excitation, there are no complete studies of photoreceptor topography in any primate retina. We have measured the spatial density and inner segment areas of cones and rods across the whole mounted retinas of three adult pigtail macaques (Macaca nemestrina) and constructed maps of photoreceptor density and inner segment diameter. These retinas contain an average of 3.1 million cones (2.8-3.3 million), with an average peak foveal cone density of 210,000 cones/mm2 (190,000-260,000 cones/mm2). Cone density falls steeply with increasing eccentricity, to 100,000 cones/mm2 at 200 microns from the fovea, and to 50,000 cones/mm2 at 750 microns. Imposed on this gradient is a "streak" of higher cone density along the horizontal meridian. At equivalent eccentricities, cone density is higher in nasal and inferior retina. Cone inner segments increase in diameter from 2.3 microns at the foveal center to 11 microns in far temporal retina and 10 microns in far nasal retina. These retinas contain an average of 60.1 million rods (44.9-75.3 million). Rod density is zero within 20 microns of the foveal center, increases to the crest of a "rod ring" at the eccentricity of the optic disk, and then declines. Central rod topography is asymmetric, with higher densities in superior retina. Density along the crest of the rod ring peaks in superior retina at 177,000 rods/mm2, dips as low as 120,000 rods/mm2 along the horizontal meridian, and increases to about 150,000 rods/mm2 in inferior retina. Far peripheral rod topography is relatively symmetric around the fovea. Rod inner segment diameter ranged from 1.5 microns in the fovea to 4 microns at the temporal edge and 3.4 microns at the nasal edge of the retina. At eccentricities exceeding 6 mm, rod inner segment diameter was greater temporally than nasally. Cone inner segments cover 85-90% of the central fovea, with extrareceptor space accounting for the remainder. Cone coverage declines with increasing eccentricity to 20% at the temporal edge and 35% at the nasal edge of the retina. In contrast, rod coverage increases from zero at the foveal center to a maximum of 65% in temporal retina and 50% in nasal retina. The photoreceptor topography of the pigtail macaque is qualitatively similar to that of other macaques and to humans. Photoreceptor topography is formed by a complex interaction between regional changes in cone and rod density and inner segment diameter.

Animals↗

PubMed1989

Visual fields of monocularly deprived macaque monkeys.

The effects of postnatal monocular deprivation have been studied in macaque monkeys using behavioral perimetry field testing. The types of deprivation were: (1) early eyelid suture at 22-26 days after birth and then reverse suture at 10-13 months postnatally, (2) late eyelid suture beginning at 3 or 5 months postnatally and continued for 18 months, and (3) long-term occlusion by contact lenses. Response levels were normal for group 1 monkeys with some reduction in visual field extent. A reduced response level but no change in visual field extent was observed for the deprived eyes of group 2 monkeys. One monkey from group 3 that wore an occluder lens from birth to 19 months postnatally had no responses in any part of the visual field. Two other monkeys of group 3, whose occlusion started at 9 or 12 days of age and lasted for 2 years, had no responses to stimuli presented to the previously occluded eyes in their nasal visual fields and had reduced levels of response to stimuli presented in their temporal fields. The results indicate that the effects of monocular deprivation on macaque monkeys are affected by the start, length and type of deprivation. Some of these results are also consistent with a model of binocular competition in which the magnitude of the competition declines along a nasal-to-temporal gradient of visual field eccentricity. However, a mechanism that is independent of binocular competition is needed to account for the loss of responses to stimuli presented in the monocular visual segment.

Animals↗

PubMed1989

GABA-immunoreactive synaptic plexus in the nerve fiber layer of primate retina.

Synaptic contacts onto fibers and somata in the nerve fiber layer (NFL) and ganglion cell layer (GCL) of macaque and human retina were demonstrated at the electron microscopical (EM) level. Many presynaptic processes in monkey NFL are gamma aminobutyric acid (GABA) immunoreactive, using anti-GABA antiserum with an EM immunogold procedure. Immunocytochemistry at the light microscopic level revealed that many GABA-reactive cells in the GCL send branching processes into the NFL, forming a sparse synaptic plexus. The presence of long, unbranched GABA-reactive fibers running horizontally in the NFL and entering the optic nerve suggests that some ganglion cells may be GABAergic. GABA-reactive cells contributing to the plexus appear to be a new class of displaced amacrines that arborize in the NFL.

Animals↗

PubMed1989

The lectin Vicia villosa labels a distinct subset of GABAergic cells in macaque visual cortex.

The morphology and distribution of neurons labeled specifically by the lectin, Vicia villosa (VVA), were examined in striate cortex of adult macaque monkeys. Following incubation with VVA conjugated to histochemical markers, fine punctate reaction product appears to cover the surface of the soma and proximal dendrites of a population of cortical neurons. Although a small number of VVA-labeled cells are located in layers 2, 3A, 5, and 6, approximately 75% are located in a strip of cortex overlying layers 3B through 4Ca. Layers 1 and 4C beta are virtually devoid of labeled cells. The morphology of labeled cells varies throughout the layers. In the supragranular layers, the labeled cells generally display a round or multipolar soma with a small number of radially disposed dendrites. In deeper layers, labeled cells are multipolar or horizontal, and their proximal dendrites are often more densely labeled. There is no clear correlation between the distribution of labeled cells and the pattern of cytochrome oxidase staining in supragranular layers. Double labeling of single sections for VVA and for GABA (gamma-aminobutyric acid) immunoreactivity revealed that most VVA-labeled cells are also immunoreactive for GABA. The double-labeled cells comprise approximately 30% of all GABA immunoreactive cells. Soma size analysis of double-labeled cells shows that medium-to-large GABA cells in each layer are labeled by VVA. The soma size, laminar distribution, and morphology of the VVA-labeled GABA cells suggest that they include the large basket cells originally observed in Golgi preparations.

Animals↗

PubMed1989

Some mammalian retinae lack FMRF-amide-like immunoreactive efferents.

The retinae of a monkey, cat, rat and mouse were examined for FMRF-amide immunoreactivity, a marker for efferent fibers in the retinae of lower vertebrates. No FMRF-amide immunoreactive retinal fibers were found despite their presence in the rat CNS. Therefore, we conclude that efferent fibers, if present in mammalian retinae, are immunologically different from efferent fibers in lower vertebrates.

Animals↗

PubMed1988

Ultrastructural localization of immunoreactivity in the developing piriform cortex.

The purpose of this study was to determine the ultrastructural basis for the immunoreactivity patterns in synaptic structures during development in layers I and II of the piriform cortex (PC) of rats. Antisera to cholecystokinin (CCK) and glutamic acid decarboxylase (GAD) were used at several different postnatal days (PN) and in adults to describe the distribution, characteristics, and relative frequency of labeled profiles--especially axons and terminals--with emphasis on details of the synaptic contacts. GAD-positive terminals occur from PN 2 to adulthood but only form contacts in deeper sublayers (Ib and II) initially. Contacts increase in layer I after PN 6 and are reduced in layer II after PN 21 when the GAD-labeled terminals and synapses take on adult features with flattened vesicles and symmetric contacts. CCK-labeled terminals are present in deeper sublayers at PN 2 but are few and rarely form contacts. Both terminals and contacts increase between PN 2 and 9, taking on distinctive shapes and vesicle morphology by PN 13. At PN 21 and older, CCK terminals have mainly flattened vesicles and mostly form symmetric contacts onto dendrites and somata in deeper layers (Ib and II). Superficial sublayer Ia has very few CCK-labeled synapses and axons. Thus immunoreactivity occurs in terminals prior to synapse formation; labeling of the presynaptic specializations precedes subsequent maturation; synaptic vesicle morphology and membrane specializations are similar for the vast majority of both CCK and GAD terminals; inhibitory (GABA) synapses are established sooner than the possibly excitatory CCK synapses; a deep to superficial gradient of synaptogenesis is associated with GAD-positive terminals in the PC; and the labeling patterns may be related to critical developmental or synaptogenic periods.

Aging↗

PubMed1988

Ultrastructure of synaptic remodeling in piriform cortex of adult rats after neonatal olfactory bulb removal: an immunocytochemical study.

The purpose of this investigation was to study possible remodeling in synaptic structures of the piriform cortex (PC) of adult rats following neonatal deafferentation by removal of the olfactory bulb (OB) at birth. Emphasis was placed on possible qualitative changes in the ultrastructure and immunocytochemical localization of cholecystokinin (CCK, a possible excitatory neurotransmitter or modulator) and glutamic acid decarboxylase (GAD, precursor enzyme to the inhibitory transmitter GABA) in axons, terminals, and synaptic complexes. Light microscopic results in normal adult material show that GAD-positive terminals form a dense band subjacent to the lateral olfactory tract (LOT), become less dense in deeper Ib, and are rare in layer II. Following deafferentation, GAD-positive terminals appear denser and more homogeneously distributed throughout layer I and are also more prevalent in layer II. Ultrastructural results of normals and controls indicate GAD-positive terminals normally contain pleomorphic or flattened vesicles and form symmetric contacts onto dendritic shafts and branches throughout layer I. In deafferented layer I not only do there appear to be greater numbers of symmetric GAD-positive contacts, but in contrast to normals, asymmetric contacts mainly onto spines are now present. Light microscopic results from deafferented material also show an apparent proliferation with spread or sprouting of CCK-positive fibers or axonlike structures mainly into layer Ia, whereas these fibers are normally observed only in the LOT and are generally few in number. Also in normals the few CCK-positive terminals in the area subjacent to the LOT contain flattened or pleomorphic vesicles and form symmetric contacts. Deafferentation results in CCK-positive terminals throughout layer I with a greater frequency of synaptic contacts which now also include a few asymmetric contacts onto spines. The findings clearly show modifications in synaptic patterns of immunocytochemical-labeled terminals that might be compatible with the process of atypical reinnervation of deafferented postsynaptic sites and possible ingrowth of new axons.

Animals↗

PubMed1988

Localization of glycine-containing neurons in the Macaca monkey retina.

Autoradiography following 3H-glycine (Gly) uptake and immunocytochemistry with a Gly-specific antiserum were used to identify neurons in Macaca monkey retina that contain a high level of this neurotransmitter. High-affinity uptake of Gly was shown to be sodium dependent whereas release of both endogenous and accumulated Gly was calcium dependent. Neurons labeling for Gly included 40-46% of the amacrine cells and nearly 40% of the bipolars. Synaptic labeling was seen throughout the inner plexiform layer (IPL) but with a preferential distribution in the inner half. Bands of labeled puncta occurred in S2, S4, and S5. Both light and postembedding electron microscopic (EM) immunocytochemistry identified different types of amacrine and bipolar cell bodies and their synaptic terminals. The most heavily labeled Gly+ cell bodies typically were amacrine cells having a single, thick, basal dendrite extending deep into the IPL and, at the EM level, electron-dense cytoplasm and prominent nuclear infoldings. This cell type may be homologous with the Gly2 cell in human retina (Marc and Liu: J. Comp. Neurol. 232:241-260, '85) and the AII/Gly2 of cat retina (Famiglietti and Kolb: Brain Res. 84:293-300, '75; Pourcho and Goebel: J. Comp. Neurol. 233:473-480, '85a). Gly+ amacrines synapse most frequently onto Gly- amacrines and both Gly- and Gly+ bipolars. Gly+ bipolar cells appeared to be cone bipolars because their labeled dendrites could be traced only to cone pedicles. The pattern of these labeled dendritic trees indicated that both diffuse and midget types of biopolars were Gly+. The EM distribution of labeled synapses showed Gly+ amacrine synapses throughout the IPL, but these composed only 11-23% of the amacrine population. Most of the Gly+ bipolar terminals were in the inner IPL, where 70% of all bipolar terminals were labeled. These findings are consistent with previous data from cats and humans and suggest that both amacrine and bipolar cells contribute to glycine-mediated neurotransmission in the monkey retina.

Animals↗

PubMed1988

Serotonergic axons in the monkey's lateral geniculate nucleus.

Axons containing serotonin (5-hydroxytryptamine, 5-HT) in the lateral geniculate nucleus of Macaca monkeys were stained using light or electron microscopic (EM) immunocytochemical labeling techniques. 5-HT labeled axons were sparsely and homogeneously distributed throughout the entire nucleus. Small varicosities were located irregularly along each axon giving them a beaded appearance. Examination of these axons at the EM level revealed that the varicosities contained synaptic vesicles that were variable in size and shape. Nearly all of the varicosities lacked synaptic contacts; only two out of over two hundred labeled varicosities appeared to form a synaptic contact, and serial sections through ten varicosities showed no discernible pre- or postsynaptic membrane specializations. 5-HT labeled axon varicosities were not observed to be preferentially located in proximity to any specific neuronal structures at either the light or EM level. 5-HT varicosities were estimated to form about 1% of the profiles containing synaptic vesicles in the neuropil of the lateral geniculate nucleus. We conclude that axons containing serotonin in the lateral geniculate nucleus release this neurotransmitter to act in a neuromodulatory manner throughout the neuropil, probably to set a general level of neuronal excitability.

Animals↗