Quantitative light and electron microscopic analysis of cytochrome oxidase-rich zones in V II prestriate cortex of the squirrel monkey

Area 18 of V II of the prestriate cortex of the squirrel monkey was examined at both the light and electron microscopic (EM) levels for cytochrome oxidase (C.O.) activity. At the 17/18 border, the intense C.O. staining of lamina 4 abruptly ended and a new pattern continued for approximately 6 mm into the adjacent prestriate cortex. Here, periodic puffs of high C.O. activity appeared in laminae (lam.) 2 and 3, with the highest activity in lower 3 (3B) extending slightly into upper 4. There was a hint of a columnar pattern in that lam. 4 and especially 5 below the puffs were slightly more reactive than adjacent areas. A thin band of activity could also be seen in upper 5 (5A) and another one between 5 and 6. Tangential sections revealed that the puffs were arranged in alternating wide and narrow rows that radiated orthogonally from the 17/18 border. The puffs in the wider rows tended to be larger (700–1,100 μm in diameter) than those in the narrow rows (400–890 μm in diameter). The center-to-center spacing between the puffs was approximately 1,100 μm. Both C.O.-reactive and nonreactive stellate and pyramidal cells were found between lam. 2 and 6. Quantitative analysis of the supragranular layers indicated that the mean area of reactive neurons was significantly larger than that of nonreactive neurons in both the puffs and interpuff (nonpuff) regions. The relative density of reactive neurons was also significantly greater than that of nonreactive neurons, and was highest within the puffs. At the EM level, reactive neurons were medium to large pyramidal cells as well as medium-sized stellates with mild to severely indented nuclei and darker cytoplasm filled with reactive mitochondria. The majority of small stellates with scanty cytoplasm and few mitochondria were nonreactive Extensive quantitative analysis of mitochondrial number and level of reactivity in different neuronal profiles indicated that the number and area of darkly reactive mitochondria was significantly higher in the puffs than in the nonpuffs, and that the majority of them resided in dendritic profiles. Between a third to half of the mitochondria in axonal profiles were darkly reactive, the frequency being slightly higher in profiles with flattened vesicles making symmetrical synapses than those with round vesicles making asymmetrical synapses. Mitochondria in axonal trunks and myelinated axons contributed to only a small percentage of the total population. Glial cells, in general, were not very reactive. Quantitative analysis of synapses indicated that there were twice as many asymmetrical synapses as symmetrical synapses in the puffs, while the difference was much less in the nonpuffs. The majority of the synapses were axodendritic, about 1–3% were axosomatic, and less frequent ones were somatodendritic and serial synapses. The frequency of asymmetrical axosomatic synapses was much higher in the puffs than the nonpuffs. The results indicate that an organized array of metabolically active zones exists in the supragranular layers of the prestriate cortex, and that it is made up of a higher percentage of reactive neurons, reactive dendritic arborizations of local and/or deeper neurons, and axonal terminals of intrinsic and/or extrinsic sources. There is also a higher concentration of asymmetrical synapses suggestive of a greater degree of excitatory synaptic influence on both the pyramidal and nonpyramidal interneurons there. These findings may form the structural basis for some of the physiological properties recently discovered in the primate visual cortex.     

Differential glutamatergic innervation in cytochrome oxidase-rich and -poor regions of the macaque striate cortex: Quantitative EM analysis of neurons and neuropil

One of the hallmarks of the primate striate cortex is the presence of cytochrome oxidase (CO)-rich puffs and CO-poor interpuffs in its supragranular layers. However, the neurochemical basis for their differences in metabolic activity and physiological properties is not well understood. The goals of the present study were to determine whether CO levels in postsynaptic neuronal compartments were correlated with the proportion of excitatory glutamate-immunoreactive (Glu-IR) synapses they received and if Glu-IR terminals and synapses in puffs differed from those in interpuffs. By combining CO histochemistry and postembedding Glu immunocytochemistry on the same ultrathin sections, the simultaneous distribution of the two markers in individual neuronal profiles was quantitatively analyzed. As a comparison, adjacent sections were identically processed for the double labeling of CO and GABA, an inhibitory neurotransmitter. In both puffs and interpuffs, most axon terminals forming asymmetric synapses (84%)—but not symmetric ones, which were GABA-IR—were intensely immunoreactive for Glu. GABA-IR neurons received mainly Glu-IR synapses on their cell bodies, and they had three times as many mitochondria darkly reactive for CO than Glu-rich neurons, which received only GABA-IR axosomatic synapses. In puffs, GABA-IR neurons received a significantly higher ratio of Glu-IR to GABA-IR axosomatic synapses and contained about twice as many darkly CO-reactive mitochondria than those in interpuffs. There were significantly more Glu-IR synapses and a higher ratio of Glu- to GABA-IR synapses in the neuropil of puffs than of interpuffs. Moreover, Glu-IR axon terminals in puffs contained approximately three times more darkly CO-reactive mitochondria than those in interpuffs, suggesting that the former may be synaptically more active. Thus, the present results are consistent with our hypothesis that the levels of oxidative metabolism in postsynaptic neurons and neuropil are positively correlated with the proportion of excitatory synapses they receive. Our findings also suggest that excitatory synaptic activity may be more prominent in puffs than in interpuffs, and that the neurochemical and synaptic differences may constitute one of the bases for physiological and functional diversities between the two regions. © 1996 Wiley-Liss, Inc.     

Double labeling of GABA and cytochrome oxidase in the macaque visual cortex: Quantitative EM analysis

In the primate striate cortex, cytochrome oxidase (CO)-rich puffs differ from CO-poor interpuffs in their metabolic levels and physiological properties. The neurochemical basis for their metabolic and physiological differences is not well understood. The goal of the present study was to examine the relationship between the distribution of gamma aminobutyric acid (GABA)/non-GABA synapses and CO levels in postsynaptic neuronal profiles and to determine whether or not a difference existed between puffs and interpuffs. By combining CO histochemistry and postembedding GABA immunocytochemistry on the same ultrathin sections, the simultaneous distribution of the two markers in individual neuronal profiles was quantitatively analyzed. In both puffs and interpuffs, GABA-immunoreactive (GABA-IR) neurons were the only cell type that received both non-GABA-IR (presumed excitatory) and GABA-IR (presumed inhibitory) axosomatic synapses, and they had three times as many mitochondria darkly reactive for CO than non-GABA-IR neurons, which received only GABA-IR axosomatic synapses. GABA-IR neurons and terminals in puffs had a larger mean size, about twice as many darkly reactive mitochondria, and a higher ratio of non-GABA-IR to GABA-IR axosomatic synapses than those in interpuffs (2.3:1 vs. 1.6:1; P < 0.01). There were significantly more synapses of both non-GABA-IR and GABA-IR types in the neuropil of puffs than of interpuffs; however, the ratio of non-GABA-IR to GABA-IR synapses was significantly higher in puffs (2.86:1) than in interpuffs (2.08:1; P < 0.01). Our results are consistent with the hypothesis that the level of oxidative metabolism in postsynaptic neurons and neuronal processes is tightly governed by the strength and proportion of excitatory over inhibitory synapses. Thus, the present results suggest that (1) GABA-IR neurons in the macaque striate cortex have a higher level of oxidative metabolism than non-GABA ones because their somata receive direct excitatory synapses and their terminals are more tonically active; (2) the higher proportion of presumed excitatory synapses in puffs imposes a greater energy demand there than in interpuffs; and (3) excitatory synaptic activity may be more prominent in puffs than in interpuffs because puffs receive a greater proportion of excitatory synapses from multiple sources including the lateral geniculate nucleus, which is not known to project to the interpuffs. © 1995 Wiley-Liss, Inc.     

Laminar and sublaminar ultracytochemical localization of cytochrome oxidase in the optic tectum of normal goldfish

Distinct laminae and sublaminae in the goldfish optic tectum exhibit substantial differences in cytochrome oxidase (C.O.) reactivity. To determine whether these differences are associated with differential reactivity of different neuronal profiles, each tectal sublamina was examined at the ultrastructural level following C.O. treatment. The greatest abundance of darkly reactive mitochondria was found in the optically innervated layers within both pre- and postsynaptic profiles in correspondence with the most intense staining of these layers at the light microscopic level. Many reactive mitochondria were localized within terminals that were presumed to be optic on the basis of cytological criteria or were shown to be optic by filling optic fibers with HRP and processing so as to simultaneously demonstrate both mitochondrial C.O. reactivity and HRP labeling. These optic terminals tended to differ from each other in size and level of reactivity. The largest terminals were located within sublamina d of the stratum fibrosum et griseum superficials (SFGSd), and these were the most intensely reactive and contained the greatest number of darkly reactive mitochondria. Medium-sized terminals were found within sublaminae SFGSa, SFGSb, and a and c of the stratum album centrale (SACa,c). These were also darkly reactive but contained fewer mitochondria. Other medium-to-small optic terminals were found in stratum opticum a and b (60a,b), SFGSb, SFGSc, and stratum griseum centrale c (SGCc). These typically contained fewer mitochondria that also tended to be relatively less reactive, although darkly reactive mitochondria were also present. We suggest that the metalbolic differences within optic terminals of different size and sublaminar stratification arise from different ganglion cell classes and that the different optic layers of tectum are functionally substratified. As expected, darkly reactive mitochondria were most abundant in th intensely stained sublaminae, which included the optic lamina SFGS and nonoptic sublamina SGCa, and they were found not only within optic terminals but also within dendrites, presynaptic dendrites, and nonoptic terminals as well. Glial processes tended to contain less reactive mitochondria. The most prominent of the nonoptic terminals were the large-diameter P1 terminals, which contained pleomorphic vesicles and formed symmetric (presumed inhibitory) synapses. In stratum marginale most of the darkly reactive mitochondria were localized within dendrites. In the rest of the tectal layers most of the darkly reactive mitochondria were found in both presynaptic terminals and dendrites.(ABSTRACT TRUNCATED AT 400 WORDS)     

Differential effect of visual deprivation on cytochrome oxidase levels in major cell classes of the cat LGN

Cytochrome oxidase histochemistry was used to examine the effects of visual deprivation on the development of neurons in the lateral geniculate nucleus of the kitten. Early postnatal monocular suture results in a decrease in reactivity within the neuropil of visually deprived binocular laminae A, A1, magnocellular C, and medial interlaminar nucleus. Within these regions, monocular suture has a greater effect on the relative numbers of, and the growth of darkly reactive (normally large), presumed Y-cells than on other less reactive geniculate neuronal classes. The decreases in the reactivity of the neuropil may be attributed to the decreases in the number of mitochondria, the number of darkly reactive mitochondria, and/or the number of darkly reactive mitochondria localized within dendrites. Although all classes of dendrites appear to be adversely affected, the decrease in C.O. reactivity was most dramatic within the presumed proximal dendrites of class 1 Y-cells. These dendrites were identified by the type of synaptic contacts they formed with retinal terminals (Rapisardi and Miles, '84, J. Comp. Neurol. 223:515-534; Wilson et al., '84, Proc. R. Soc. Lond. [Biol.] 221:411-436). As with Y-cells, the effects of monocular suture on the large darkly reactive cells were not as dramatic at sites where binocular interactions were either absent or where they had been experimentally eliminated. Based on the present and previously reported findings from several laboratories, it is likely that the selective physiological and morphological effects of monocular suture on Y-cells are accompanied by metabolic deficits involving both dendrites and perikarya. These effects appear to be due more to binocular interactions than to visual deprivation per se.     

Laminar and cellular localization of cytochrome oxidase in the cat striate cortex

Cytochrome oxidase (C.O.) was histochemically localized in the cat striate cortex at the light and electron microscopic levels. The results indicate that the oxidative metabolic activity within the cat striate cortex may vary between (1) different laminae, (2) neurons and glia, (3) different neuron types, (4) dendrite and soma of the same cell, (5) different types of dendrites, (6) different segments of the same dendrite, and (7) different classes of symmetric and asymmetric axon terminals. Maximal laminar C.O. staining was localized within geniculoreceptive layer IV. Darkly reactive neurons include the large (presumed corticotectal) pyramids of layer V, and various classes of large and medium-sized presumed GABAergic nonpyramidal cells sparsely distributed throughout layers II-VI. The small and medium-sized pyramids of layers II, III, V, and VI, as well as many of the smaller presumed GABAergic neurons, were only lightly or moderately reactive. The darkly reactive neurons tended to be those that received convergent or proximally localized asymmetric axosomatic synapses, implying that they are strongly driven by excitatory synaptic input. The darkly reactive nonpyramids resembled those that form GAD+, symmetric axosomatic synapses with pyramidal cells. The dark reactivity of the symmetric synaptic terminals indicates that they mediate strong inhibition of neuronal discharge. The dark reactivity of a class of large asymmetric terminals in layer IV is likely to represent highly active geniculocortical terminals. The predominant distribution of elevated C.O. reactivity in dendrites is correlated with reported sites of (1) convergent excitatory synaptic input, (2) maximal field potentials, (3) highly active ion transport, and (4) Na+, K+-ATPase.     

The localization of cytochrome oxidase in the LGN and striate cortex of postnatal kittens

The distribution of cytochrome oxidase (C.O.) was examined in the lateral geniculate nucleus of the kitten during the first postnatal month and compared with the adult pattern. During the first week, most of the C.O. was localized within the perikarya of geniculate neurons. Perigeniculate neurons had darkly reactive dendrites as well as perikaya. A population of relatively large, darkly reactive neurons became distinguishable around the end of the first week, as the level of reactivity diminished to moderate-to-light within most medium and small neurons. On the basis of their relative size and pattern of distribution, most of the darkly reactive neurons are likely to represent ones that will later have class 1 morphology and develop Y receptive field properties. These cells normally undergo rapid growth earlier, and their growth is more adversely affected by early short-term monocular suture than other classes of less reactive geniculate neurons. Thus, in the LGN of developing kitten, C.O. histochemistry may be used as a functional marker for future class 1 Y-cells. The reactivity of the neuropil gradually increases as synapses with dendrites mature. At the electronmicroscopic level the increased reactivity of the neuropil is due mainly to an increase in the number of reactive mitochondria localized within the growing dendrites. In the developing striate cortex of postnatal kittens dark reactivity is localized in the outer part of layer II for the first 2 weeks and then disappears. Dark reactivity gradually increases in layer IV after the third week. The changes in C.O. reactivity accompany pathway-specific physiological and anatomical changes that occur during early postnatal development.     

An analysis of the cellular localization of cytochrome oxidase in the lateral geniculate nucleus of the adult cat

The distribution of cytochrome oxidase (C.O.) was examined in the normal adult cat lateral geniculate nucleus at the cellular and electron-microscopic levels. The darker reactivity of the X- and/or Y-receptive laminae (A, A1, magnocellular lamina C [Cm], and medial interlaminar nucleus [MIN]) compared with the lightly reactive W-receptive parvicellular lamina C (Cp) indicates that there are pathway-specific histochemical differences in the visual system of the cat. At the cellular level, darkly reactive large cells in the lateral geniculate nucleus (LGN) closely resemble class 1, Y-cells, in relative size and distribution, thus indicating that C.O. histochemistry may be used as a functional marker for these cells. Perigeniculate neurons are also darkly reactive. Neuronal classes 2, 4, and 3 (presumed X-cells, W-cells, and/or interneurons) have moderate to lightly reactive perikarya. The darkly reactive neuronal classes tend to receive relatively stronger proximal excitatory synaptic input than do the less reactive neuronal classes. Since all neuronal classes appeared to have darkly (or moderately) reactive dendrites, C.O. reactivity must differ between dendrite and soma of some neuronal classes. At the electron-microscopic level, distinct components of the neuropil tend to have specific levels of C.O. reactivity. The predominance of darkly reactive mitochondria in dendrites indicates that dendrites are metabolically very active. RLD and may F's, but few large axon terminals with round vesicles (RL) or small axon terminals with round vesicles (RS) profiles are darkly reactive, implying that specific classes of presynaptic structures are more active than others. Thus C.O. histochemistry may be useful for distinguishing not only functionally active neuronal classes such as Y-cells and perigeniculate (PG) neurons from less active neuronal classes, but also functionally more or less active parts of the same neuron including its dendrites, axons, and/or axon terminals.     

Dependence of cytochrome oxidase activity in the rat lateral geniculate nucleus on retinal innervation

Patterns of cytochrome oxidase (CO) activity were examined histochemically in the dorsal lateral geniculate nucleus (LGNd) and retina of pigmented rats. CO staining was not uniform and was distributed in a pattern similar to that of retinal afferents. Portions of the LGNd receiving an exclusively crossed projection were moderately reactive whereas regions receiving an uncrossed or overlapping crossed and uncrossed projection were darkly reactive. The dependence of oxidative metabolic activity in the LGNd on retinal innervation was verified in animals with unilateral enucleation. In adults, chronic monocular enucleation led to a decrease in CO staining in portions of the LGNd deprived of retinal input; in animals enucleated at birth, normal patterns of CO reactivity failed to develop and both LGNds had a more uniform pattern of moderate CO staining. Most neurons in the ganglion cell layer of the retina were moderately reactive for CO. However, there were approximately 3,000 darkly reactive cells, most of which appear to be ganglion cells. The darkly reactive cells were more numerous in the peripheral temporal retina. The laminar pattern of CO staining in the retina was similar to that described previously for carnivores and primates. The most reactive laminae were the inner and outer plexiform layers and the photoreceptor inner segments. Within the inner plexiform layer, sublamina a was more darkly stained than sublamina b. These results suggest that the physiological properties of crossed and uncrossed visual pathways in rats are functionally dissimilar at the level of both the retina and the LGNd.     

Metabolic and neurochemical plasticity of γ-aminobutyric acid-immunoreactive neurons in the adult macaque striate cortex following monocular impulse blockade: Quantitative electron microscopic analysis

The purpose of the present study was to examine the effects of retinal impulse blockade on γ-aminobutyric acid (GABA)-immunoreactive (GABA-IR) neurons in cytochrome oxidase (CO)-rich puffs of the adult monkey striate cortex. Specifically, we wished to know if changes occurred in their CO activity, GABA immunoreactivity, and synaptic organization. A double-labeling technique, which combined CO histochemistry and postembedding GABA immunocytochemistry on the same ultrathin sections, was used to reveal simultaneously the distribution of the two markers. We quantitatively compared changes in GABA-IR neurons of deprived puffs (DPs) with respect to non-deprived puffs (NPs) 2 weeks after monocular tetrodotoxin treatment. We found that the proportion of darkly CO reactive mitochondria in GABA-IR neurons of DPs drastically decreased to about half of those in NPs. There was a greater reduction of CO levels in GABA-IR axon terminals than in their cell bodies and dendrites. In contrast, most non-GABA-IR neurons displayed no significant change in their CO levels. Morphologically, GABA-IR neurons and axon terminals in DPs showed a significant shrinkage in their mean size. GABA immunoreactivity, as indicated by the density of immunogold particles in GABA-IR neurons, declined in DPs, and a greater decrease was also found in axon terminals than in cell bodies or dendrites. Moreover, the numerical density of GABA-IR axon terminals and synapses in DPs was significantly reduced without changes in that of asymmetric and symmetric synapses. Thus, the present results support the following conclusions: 1) Oxidative metabolism and neurotransmitter expression in GABA-IR neurons are tightly regulated by neuronal activity in adult monkey striate cortex; 2) GABA-IR neurons are much more vulnerable to functional deprivation than non-GABA-IR ones, suggesting that these inhibitory neurons have stringent requirement for sustained excitatory input to maintain their heightened oxidative capacity; and 3) intracortical inhibition mediated by GABA transmission following afferent deprivation may be decreased in deprived puffs, because the oxidative capacity and transmitter level in GABAergic neurons, especially in their axon terminals, are dramatically reduced. © 1996 Wiley-Liss, Inc.     

Ultrastructure of neurons in the nucleus basalis of Meynert in squirrel monkey

The nucleus basalis of Meynert in the squirrel monkey exhibits numerous labeled neurons following the retrograde transport of horseradish peroxidase from occipital cortical injection sites. The typically large, often clustered, labeled cells are seen most frequently in association with the fibrous bordering structures of the substantia innominata and in the internal and external laminae of the globus pallidus. Ultrastructurally the copious cytoplasm of nucleus basalis neurons abounds with organelles. Large, vacuolated lipofuscin granules proliferate as a function of age and are not evident in younger monkeys. Approximately 4% of the somal surface is occupied by symmetrical synapses with either flat or pleomorphic vesicles. The remainder is covered mostly by neuroglial processes. Somatic spines bearing synapses are occasionally observed. In the neuropil surrounding nucleus basalis somata, the synapses onto dendrites and spines are mostly asymmetrical with large, round vesicles. Labeled nucleus basalis cells in the substantia innominata immediately lateral to the optic tract are larger and rounder than cells in the internal and external pallidal laminae. However, no remarkable ultrastructural differences were observed between nucleus basalis somata in the substantia innominata and external pallidal lamina, or between horseradish peroxidase-labeled and unlabeled large cells.     

Histochemical localization of cytochrome oxidase in the retina and optic tectum of normal goldfish: a combined cytochrome oxidase-horseradish peroxidase study

Cytochrome oxidase (C.O.) was histochemically localized in the normal retina and optic tectum of goldfish in order to examine the laminar and cellular oxidative metabolic organization of these structures. In the optic tectum, C.O. exhibited a distinct laminar, regional, and cellular distribution. The laminae with highest C.O. levels were those that receive optic input, suggesting a dominant role for visual activity in tectal function. This was demonstrated by colocalizing C.O. and HRP-filled optic fibers in the same section. However, the distribution of C.O. within the optic laminae was not uniform. Within the main optic layers, the SFGS, four metabolically distinct sublaminae were distinguished and designated from superficial to deep as sublaminae a, b, c, and d. The most intense reactivity was localized within SFGSa and SFGSd, followed by SFGSb, then SFGSc. In SFGSd, intense reactivity was found to occur specifically within a class of large diameter axons and terminals that were apparently optic since these were also labeled with HRP and cobaltous lysine applied to the optic nerve. Regional C.O. differences across the tectum were also noted. Low levels were found in neurons and optic terminals along the growing immature medial, lateral, and posterior edges of tectum, but were higher at the more mature anterior pole and central regions of tectum. This suggests that the oxidative metabolic activity is initially low in newly formed tectal neurons and optic axons, but gradually increases with neuronal growth and functional axon terminal maturation. Most C.O. staining was localized within neuropil, whereas the perikarya of most tectal neurons were only lightly reactive. Only a few neuron classes, mostly the relatively larger projection neurons, had darkly reactive perikarya. In the retina, intense C.O. reactivity was localized within the inner segments of photoreceptors, the inner and outer plexiform layers, and within certain classes of bipolar and ganglion cells. The large ganglion cells in particular were intensely reactive. Like the large diameter optic terminals in SFGSd, the large ganglion cells were preferentially filled with HRP, suggesting that they may project to tectum and are the source of the darkly reactive large diameter axons and terminals in sublamina SFGSd. We propose a new scheme to describe tectal lamination that integrates laminar differences in C.O. reactivity with classical histological work.(ABSTRACT TRUNCATED AT 400 WORDS)     

Localization of cytochrome oxidase in the mammalian spinal cord and dorsal root ganglia, with quantitative analysis of ventral horn cells in monkeys

The spinal cord and dorsal root ganglia of mice, rats, cats, squirrel monkeys, and macaque monkeys were examined at both the light and electron microscopic levels for cytochrome oxidase activity. A similar histochemical pattern prevailed in all of the species examined. While the spinal gray exhibited a heterogeneous but consistent distribution of the enzyme, the white matter was only lightly stained. Highly reactive neurons were either singly scattered or aggregated into discrete clusters. The dorsal nucleus of Clarke, the lateral cervical nucleus (cat), the intermediolateral cell columns of the thoracic and upper lumbar levels, and selected groups of ventral horn neurons formed moderate to darkly reactive cell clusters, whereas fusiform and multipolar cells of Waldeyer in the marginal layer, small fusiform neurons in the ventral gray, funicular cells in the white matter, and ventral horn neurons of varying sizes tended to stand out against the neuropil as singly reactive neurons. At the electron microscopic level, reactive neurons were characterized by a greater packing density of darkly reactive mitochondria, while lightly reactive ones had fewer mitochondria, most of which showed very little reaction product. Reactive mitochondria were also found in the neuropil, mainly in dendritic profiles and some axon terminals. Glial cells, in general, were not very reactive. Ventral horn neurons from three macaque monkeys were measured for somatic areas and optical densities of cytochrome oxidase reaction product. A total of 1,770 neurons from representative sections of the cervical, thoracic, lumbar, and sacral cords of these animals were analyzed. The results indicated that the distribution of cell sizes as well as optical densities at every level of the cord fell on a continuum. Analysis of the regression coefficients revealed that the slopes were negative for all levels, indicating that there was a general inverse relationship between cell size and optical densities. However, there were representations of dark, moderate, and lightly reactive neurons in all three size categories (large, medium, and small). Thus, the level of oxidative metabolism of ventral horn neurons cannot be correlated strictly with size, but it is likely to reflect their total synaptic and spontaneous activities. Neurons of the dorsal root ganglia likewise exhibited heterogeneous distribution of cell sizes and levels of enzyme reactivity, while satellite cells, in general, were only lightly reactive. As in the case of the ventral horn, representatives of dark, moderate, and light levels of reactivity occurred in every size category of neurons.(ABSTRACT TRUNCATED AT 400 WORDS)     

Metabolic activity in SmI cortical barrels of adult rats is dependent on patterned sensory stimulation of the mystacial vibrissae

Cytochrome oxidase (CO) histochemistry was used to examine the effect of sensory deprivation on metabolic activity in the somatosensory cortex (SmI) of adult rats. Chronic trimming of one or several rows of mystacial vibrissae resulted in a decrease in CO reactivity in the corresponding barrels in layer IV. Reduced CO staining also was observed in cortical laminae superficial and deep to the affected layer IV barrels, suggesting that patterned deflections of the whiskers are important for maintaining the metabolic activity of neurons at least 3 and perhaps 4 synapses removed from the periphery.     

Changes in the visual system of monocularly sutured or enucleated cats demonstrable with cytochrome oxidase histochemistry

Endogenous cytochrome oxidase activity within the mitochondria of neurons and neuropil was demonstrated histochemically under normal and experimental conditions. Since enzymatic changes were noted with chronic neuronal inactivity in the auditory system (Wong-Riley et al), the present study sought to examine functionally induced enzymatic changes in the visual system of kittens. Eight kittens were used experimentally: 5 had monocular lid suture for varying periods of time; one had binocular lid suture followed by monocular suture followed by binocular opening; two had monocular enucleation. All initial procedures were performed before eye opening. Materials from other normal kittens and cats were also used as controls. At the end of the experiments, the animals were perfused with aldehyde solutions and frozen sections of the brains were incubated for cytochrome oxidase activity (a detailed protocol was outlined). The results indicated that the deprivation caused by monocular suture produced a decrease in the cytochrome oxidase staining of the binocular segment of the deprived geniculate laminae. Enucleation yielded a greater decrease in the cytochrome oxidase activity in the affected geniculate laminae. However, the staining in the 'normal' lamina extended across the interlaminar border to include a row of surviving large cells in the 'denervated' lamina. The staining of the monocular segment appeared not to be affected by lid suture, but was decreased by enucleation. At the cortical level, lamina IV in area 17 of normal cats was stained darkly as a continuous band. Following lid suture, this pattern was replaced in part by alternating columns of light and dark staining, suggestive of ocular dominance columns. Thus, a decrease in neuronal activity due to reduced visual stimulation or destruction of the primary afferent nerves led to a significant decrease in the level of oxidative enzyme activity one to several synapses away.     

Distribution of synapses on fast and slow pyramidal tract neurons in the cat. An electron microscopic study

Distributions of synapses on various portions of fast and slow pyramidal tract neurons (PTNs) in cat motor cortex were studied with electron microscopy. PTNs were identified by their antidromic invasion following stimulation of the medullary pyramid and were classified into fast and slow PTNs according to conduction velocities of their axons. Two fast and two slow PTNs were intracellularly labeled and, by systematic sampling, electron micrographs from various portions of these neurons were examined to compare the distributions of different types of synapses. It was found that most synapses formed on apical and basal dendrites of fast PTNs were with the dendritic shafts. In slow PTNs, while synapses on apical dendrites were mostly axospinous, about 70% of the sampled synapses on basal dendrites of slow PTNs were established with the dendritic shafts. Virtually all synapses on apical dendrites of slow PTNs belonged to asymmetrical type and most of the synapses sampled from basal dendrites of fast PTNs were also asymmetrical. On the other hand, about 29% of the synapses found on apical dendrites of fast PTNs were symmetrical and a trend was observed for this type of synapses to increase their number with increasing proximity to the cell body. Over 28% of the synapses on basal dendrites of slow PTNs were also symmetrical and seemed to be mainly distributed in layer VI. All synapses formed on the soma were symmetrical both for the fast and slow PTNs.     

Structure of the mitral cell in the olfactory bulb of the goldfish (Carassius auratus)

The mitral cell in the olfactory bulb of the goldfish was examined by means of light microscopy, high-voltage electron microscopy, and conventional electron microscopy. Mitral cells are located rather diffusely throughout the glomerular and plexiform layers. They do not make their own discrete layer. The cell bodies are rounded or triangular, and are about 10–25 μm in diameter. In Golgi-impregnated material, thick cylindrical dendrites can be seen arising from the cell bodies and branching in the glomerular layer. Dendritic branches of some cells make two or more rather compact tufts, while the dendrites of other cells intermingle loosely with one another. In semithin and thin sections, darkly stained nodules appear to be scattered diffusely in the glomerular layer without clustering into discrete spheres, which are characteristic of the mammalian glomerulus. Hence, instead of the glomerulus, the “glomerular area” is defined as an area consisting of darkly stained nodules with rather pale granular regions surrounding them. Branches of mitral cell dendrites in the glomerular area consist of cylindrical shafts and irregular appendages arising from them. The shafts appear in the pale granular region and the appendages are found in the darkly stained nodules. Synapses can be found on all parts of the mitral cell: the soma, axon hillock, axon initial segment, thick dendritic stems, and dendritic branches. The abundance of synapses seems to vary considerably from part to part, and is highest on the dendritic branches in the glomerular area. The mitral cell is postsynaptic to olfactory nerve terminals and granule cell dendrites, and presynaptic to granule cell dendrites and some processes of unknown origin. Olfactory nerve terminals make asymmetrical synapses specifically on the appendages of the dendritic branches. Of the synapses on the shafts of the mitral cell dendritic branches in the glomerular area, 90% are with granule cell dendrites. Of the synapses between two different kinds of processes 30% are mitral-to-granule asymmetrical synapses, 20% are granule-to-mitral symmetrical synapses, and 50% are reciprocal pairs. Gap junctions and mixed synapses are also seen on branches of mitral cell dendrites. Features of the goldfish mitral cell are compared with those of the mammal. The differences in neuronal organization between the olfactory bulbs of teleosts and mammals are discussed.     

Pyramidal cells of the rat basolateral amygdala: synaptology and innervation by parvalbumin-immunoreactive interneurons

The generation of emotional responses by the basolateral amygdala is determined largely by the balance of excitatory and inhibitory inputs to its principal neurons, the pyramidal cells. The activity of these neurons is tightly controlled by gamma-aminobutyric acid (GABA)-ergic interneurons, especially a parvalbumin-positive (PV(+)) subpopulation that constitutes almost half of all interneurons in the basolateral amygdala. In the present semiquantitative investigation, we studied the incidence of synaptic inputs of PV(+) axon terminals onto pyramidal neurons in the rat basolateral nucleus (BLa). Pyramidal cells were identified by using calcium/calmodulin-dependent protein kinase II (CaMK) immunoreactivity as a marker. To appreciate the relative abundance of PV(+) inputs compared with excitatory inputs and other non-PV(+) inhibitory inputs, we also analyzed the proportions of asymmetrical (presumed excitatory) synapses and symmetrical (presumed inhibitory) synapses formed by unlabeled axon terminals targeting pyramidal neurons. The results indicate that the perisomatic region of pyramidal cells is innervated almost entirely by symmetrical synapses, whereas the density of asymmetrical synapses increases as one proceeds from thicker proximal dendritic shafts to thinner distal dendritic shafts. The great majority of synapses with dendritic spines are asymmetrical. PV(+) axon terminals form mainly symmetrical synapses. These PV(+) synapses constitute slightly more than half of the symmetrical synapses formed with each postsynaptic compartment of BLa pyramidal cells. These data indicate that the synaptology of basolateral amygdalar pyramidal cells is remarkably similar to that of cortical pyramidal cells and that PV(+) interneurons provide a robust inhibition of both the perisomatic and the distal dendritic domains of these principal neurons.     

Reciprocal synaptic relationships between angiotensin II-containing neurons and enkephalinergic neurons in the rat area postrema

A preembedding double immunostaining technique was used to study synaptic relationships between angiotensin-II-like immunoreactive and enkephalin-like immunoreactive neurons in the rat area postrema. The angiotensin-II-like immunoreactive neurons were detected by silver-gold intensification of the DAB reaction results while the enkephalin-like immunoreactive neurons were detected by simple ABC-DAB reaction. The synaptic relationships were reciprocal between the two neurons. Most of the synapses found between these two neurons were the presynaptic enkephalin-like immunoreactive axon terminals that made synapses on the angiotensin-II-like immunoreactive perikarya and dendrites. Both the axo-somatic and axo-dendritic synapses were symmetrical. However, although angiotensin-II-like immunoreactive axon terminals also made synapses on enkephalin-like perikarya and dendrites, the axo-somatic synapses were symmetrical, while the axo-dendritic synapses were asymmetrical. The present results confirm the presence of angiotensin-II-like immunoreactive neurons in the area postrema and suggest that these angiotensinergic neurons in the area postrema may play a role in the regulation of blood pressure via coordinated synaptic interactions with enkephalinergic neurons.     

Substance P synaptic interactions with GABAergic and dopaminergic neurons in rat substantia nigra: An ultrastructural doublelabeling immunocytochemical study

The distribution of substance P (SP), tyrosine hydroxylase (TH), and glutamic acid decarboxylase (GAD) immunoreactivity in the substantia nigra of the rat was studied by means of an ultrastructural double-labeling immunocytochemical method. Direct synaptic contact between SP-immunoreactive terminals and GAD-positive nigral neurons was more often observed in the pars lateralis than the pars reticularis and was rarely observed in the pars compacta. Substance P-positive terminals also formed synapses with cell bodies and dendrites of TH-positive, dopaminergic neurons in the pars compacta and pars reticulata. Multiple SP-immunoreactive terminals were often observed with symmetrical and, less frequently, asymmetrical synapses on individual TH-containing dendrites. Evidence of SP-containing terminals contacting both GABAergic and dopaminergic neurons in the substantia nigra suggests a direct excitatory action upon nigral projection neurons.