Parvalbumin in the monkey striate cortex: a quantitative immunoelectron-microscopy study

Parvalbumin (PV) is present in a subpopulation of interneurons in the visual cortex, and also in thalamic afferents to the neocortex of primates. The object of this study is to confirm by immunoelectron-microscopy the presence of intrinsic and extrinsic connections containing parvalbumin in the monkey visual cortex, by the demonstration of parvalbumin-immunoreactivity in symmetric and asymmetric synapses. We analyzed the distribution of parvalbumin-immunoreactive profiles at the ultrastructural level in the primary visual cortex of old world monkeys (Macaca fascicularis). It has been shown by others that parvalbumin-immunoreactive cells resemble non-spiny stellate cells, double-bouquet cells, chandelier and basket cells. These neurons are known to be inhibitory and to form symmetric synapses. In fact, we observed that the vast majority of parvalbumin-immunoreactive synaptic contacts in the primary visual cortex of Macaca fascicularis are of the symmetric type (81.7%). Since parvalbumin-positive asymmetric contacts are also present (18.3%) and occur mostly in the thalamic recipient layers, 4C and 4A (9.9%), these afferents probably derive from parvalbumin-immunoreactive neurons located in the dorsal lateral geniculate nucleus of the thalamus.     

The termination of geniculocortical fibres in area 17 of the visual cortex in the macaque monkey

The termination of geniculocortical fibres within the different subdivisions of lamina IV in area 17 of the visual cortex of the monkey has been studied quantitatively with the electron microscope. In lamina IVCα the axon terminals of fibres coming from the magnocellular layers of the lateral geniculate nucleus (LGN) make significantly more synapses per bouton than those of fibres arising from the parvocellular layers and terminating in laminae IVA and IVCβ. In all parts of area 17 examined there was a clear difference in the relative proportions of multisynaptic geniculo-cortical boutons between the α and β divisions of lamina IVC. Calculations have shown that a single cell in the magnocellular laminae of the LGN may make about 6 times as many synaptic contacts within lamina IV of the visual cortex than one in the parvocellular laminae. It has also been estimated that there are at least 500 million geniculocortical boutons, or 1200 million synapses, in lamina IVCα and 1000 million boutons, 1200 million synapses, in lamina IVCβ for one hemisphere, giving an approximate total number of 1500 million boutons and 2400 million synapses.     

Effects of experimental strabismus on the architecture of macaque monkey striate cortex

Strabismus, a misalignment of the eyes, results in a loss of binocular visual function in humans. The effects are similar in monkeys, where a loss of binocular convergence onto single cortical neurons is always found. Changes in the anatomical organization of primary visual cortex (V1) may be associated with these physiological deficits, yet few have been reported. We examined the distributions of several anatomical markers in V1 of two experimentally strabismic Macaca nemestrina monkeys. Staining patterns in tangential sections were related to the ocular dominance (OD) column structure as deduced from cytochrome oxidase (CO) staining. CO staining appears roughly normal in the superficial layers, but in layer 4C, one eye's columns were pale. Thin, dark stripes falling near OD column borders are evident in Nissl-stained sections in all layers and in immunoreactivity for calbindin, especially in layers 3 and 4B. The monoclonal antibody SMI32, which labels a neurofilament protein found in pyramidal cells, is reduced in one eye's columns and absent at OD column borders. The pale SMI32 columns are those that are dark with CO in layer 4. Gallyas staining for myelin reveals thin stripes through layers 2-5; the dark stripes fall at OD column centers. All these changes appear to be related to the loss of binocularity in cortical neurons, which has its most profound effects near OD column borders.     

Bilateral corticospinal projections arise from each motor cortex in the macaque monkey: a quantitative study

The corticospinal projection is considered to influence fine motor function through nearly exclusively contralateral projections from the cortex in primates. However, unilateral lesions to this system in various species are frequently followed by significant functional improvement, raising the possibility that bilateral projections of this pathway may exist or emerge after injury. To examine the detailed anatomy and projections of the corticospinal motor neurons in rhesus monkeys (n = 4), we injected the high-resolution anterograde tracer biotinylated dextran amine (BDA) into 126 sites centered about the right lower extremity (LE) primary motor cortex. Projection and termination patterns were quantified at lumbar levels L1, L4, and L7 and mapped by using serial-section reconstructions. Notably, a mean of 10.1 +/- 0.6% (+/- SEM) of corticospinal tract (CST) axons descended in the lateral CST ipsilateral to the cortical BDA injection, and 87.9 +/- 1.0% of total CST axons projected in the contralateral lateral CST. The ipsilateral ventral CST contained only 1.0 +/- 0% of all projecting CST axons, whereas the contralateral ventral CST contained 0.3 +/- 0.2% of all axons. In addition, a minor dorsal column CST projection was identified. Measurement of BDA-labeled terminals in the spinal cord gray matter revealed that 11.2 +/- 2.2% of CST axons terminated ipsilateral to the side of cortical injection, and the remainder terminated contralaterally. As previously reported, most CST axons terminated in spinal cord laminae V-VIII, as well as the laterodorsal motoneuronal group of lamina IX (which innervates distal extremity muscles). Notably, many CST axons crossed the spinal cord midline (mean 19.9 +/- 4.9 axons per 40-microm-thick section). Detailed single-axon reconstructions revealed that most ipsilaterally projecting lateral CST axons terminated in ipsilateral gray matter. Notably, we found that the bouton-like swellings of many ipsilateral CST axons descending in the dorsolateral tract were located within Rexed's lamina IX, in close proximity to motoneuronal somata. Thus, bilateral projections of corticospinal axons originating from a single motor cortex could contribute to bilateral control of spinal motor neurons and to the highly evolved degree of fine motor control in primates. Furthermore, bilateral CST projections from a single motor cortex could represent a potential source of plasticity after injury, as well as a target of therapeutic effort in neural regeneration strategies.     

The mapping of visual space onto foveal striate cortex in the macaque monkey

Visuotopic maps of foveal striate cortex have been obtained by means of single cell recordings from four hemispheres in two awake, behaving macaque monkeys. The numbers of successful separate striate penetration sites in the four hemispheres were 42, 58, 81, and 61, for a total of 242. The resolution of the maps is 10 min of visual angle, nearly an order of magnitude finer than previous maps. No striate receptive field center was found more than 5 min into the ipsilateral visual field. The four maps were sufficiently compatible with one another that they could be combined into one. There are only minor magnification differences between the right and left hemispheres and between the upper and lower quadrants. There is a vertical/horizontal magnification anisotropy of about 1.5:1 in central foveal cortex (0 to 20 min). The composite map can be approximated by the complex logarithmic equation, w = 7.7 * ln (x + iy + 0.33), where w is expressed in millimeters and x and y are expressed in degrees.     

Ultrastructure of geniculocortical synaptic connections in the tree shrew striate cortex

To determine whether thalamocortical synaptic circuits differ across cortical areas, we examined the ultrastructure of geniculocortical terminals in the tree shrew striate cortex to compare directly the characteristics of these terminals with those of pulvinocortical terminals (examined previously in the temporal cortex of the same species; Chomsung et al. [ 2010 ] Cereb Cortex 20:997–1011). Tree shrews are considered to represent a prototype of early prosimian primates but are unique in that sublaminae of striate cortex layer IV respond preferentially to light onset (IVa) or offset (IVb). We examined geniculocortical inputs to these two sublayers labeled by tracer or virus injections or an antibody against the type 2 vesicular glutamate antibody (vGLUT2). We found that layer IV geniculocortical terminals, as well as their postsynaptic targets, were significantly larger than pulvinocortical terminals and their postsynaptic targets. In addition, we found that 9–10% of geniculocortical terminals in each sublamina contacted GABAergic interneurons, whereas pulvinocortical terminals were not found to contact any interneurons. Moreover, we found that the majority of geniculocortical terminals in both IVa and IVb contained dendritic protrusions, whereas pulvinocortical terminals do not contain these structures. Finally, we found that synaptopodin, a protein uniquely associated with the spine apparatus, and telencephalin (TLCN, or intercellular adhesion molecule type 5), a protein associated with maturation of dendritic spines, are largely excluded from geniculocortical recipient layers of the striate cortex. Together our results suggest major differences in the synaptic organization of thalamocortical pathways in striate and extrastriate areas. J. Comp. Neurol. 524:1292–1306, 2016. © 2015 Wiley Periodicals, Inc.     

Pale cytochrome oxidase stripes in V2 receive the richest projection from macaque striate cortex

Once the visual pathway reaches striate cortex, it fans out to a number of extrastriate areas. The projections to the second visual area (V2) are known to terminate in a patchy manner. V2 contains a system of repeating pale-thin-pale- thick stripes of cytochrome oxidase (CO) activity. We examined whether the patchy terminal fields arising from primary visual cortex (V1) projections are systematically related to the CO stripes in V2. Large injections of an anterograde tracer, [(3)H]proline, were made into V1 of both hemispheres in 5 macaques. The resulting V2 label appeared in layers 2-6, with the densest concentration in layer 4. In 21/29 injections, comparison of adjacent flatmount sections processed either for autoradiography or CO activity showed that the heaviest [(3)H]proline labeling was located in pale CO stripes. In 7/29 injections, there was no clear enrichment of labeling in the CO pale stripes. In 1 injection, the proline label correlated with dark CO stripes. On a fine scale, CO levels vary within V2 stripes, giving them an irregular, mottled appearance. In all stripe types, the density of proline label would often wax and wane in opposing contrast to these local fluctuations in CO density. Our data showed that V1 input is generally anti-correlated with the intensity of CO staining in V2, with strongest input to pale stripes. It is known that the pulvinar projects preferentially to dark stripes. Therefore, V2 receives interleaved projections from V1 and the pulvinar. Because these projections favor different stripe types, they may target separate populations of neurons.     

Chromatic mechanisms in striate cortex of macaque

We measured the responses of 305 neurons in striate cortex to moving sinusoidal gratings modulated in chromaticity and luminance about a fixed white point. Stimuli were represented in a 3-dimensional color space defined by 2 chromatic axes and a third along which luminance varied. With rare exceptions the chromatic properties of cortical neurons were well described by a linear model in which the response of a cell is proportional to the sum (for complex cells, the rectified sum) of the signals from the 3 classes of cones. For each cell there is a vector passing through the white point along which modulation gives rise to a maximal response. The elevation (theta m) and azimuth (phi m) of this vector fully describe the chromatic properties of the cell. The linear model also describes neurons in l.g.n. (Derrington et al., 1984), so most neurons in striate cortex have the same chromatic selectivity as do neurons in l.g.n. However, the distributions of preferred vectors differed in cortex and l.g.n.: Most cortical neurons preferred modulation along vectors lying close to the achromatic axis and those showing overt chromatic opponency did not fall into the clearly defined chromatic groups seen in l.g.n. The neurons most responsive to chromatic modulation (found mainly in layers IVA, IVC beta, and VI) had poor orientation selectivity, and responded to chromatic modulation of a spatially uniform field at least as well as they did to any grating. We encountered neurons with band-pass spatial selectivity for chromatically modulated stimuli in layers II/III and VI. Most had complex receptive fields. Neurons in layer II/III did not fall into distinct groups according to their chromatic sensitivities, and the chromatic properties of neurons known to lie within regions rich in cytochrome oxidase appeared no different from those of neurons in the interstices. Six neurons, all of which resembled simple cells, showed unusually sharp chromatic selectivity.     

NADPH diaphorase histochemistry in the macaque striate cortex

The distribution of the enzyme dihydronicotinamide adenine dinucleotide phosphate (NADPH) diaphorase was examined in the striate cortex of the rhesus monkey. The pattern of activity in the neuropil matched that of cytochrome oxidase in adjacent sections and the enzymes were similarly modulated by monocular deprivation. Scattered individual cells were also intensely positive for NADPH diaphorase. Labelled cells were most common in the white matter and layers 2 and 3; they were least common in layers 4 and 5. Diaphorase cells were morphologically diverse, but no pyramidal or spiny cells were labelled. Labelled cells often had multiple varicose processes, which extended laterally for over 1 mm. Although the function of this enzyme is unknown, the morphology and distribution of the diaphorase-positive cells resembles published reports of cortical cells containing somatostatin, avian pancreatic polypeptide, and neuropeptide Y-like immunoreactivity, and NADPH diaphorase is colocalized with these substances in the rodent striatum (S.R. Vincent, O. Johansson, T. H?kfelt, L. Skirboll, R.P. Elde, L. Terenius, J. Kimmel, and M. Goldstein, J. Comp. Neurol. 217:252-263, '83).     

Set size effects in the macaque striate cortex

Attentive processing is often described as a competition for resources among stimuli by mutual suppression. This is supported by findings that activity in extrastriate cortex is suppressed when several stimuli are presented simultaneously, compared to a single stimulus. In this study, we randomly varied the number of simultaneously presented figures (set size) in an attention-demanding change detection task, while we recorded multiunit activity in striate cortex (V1) in monkeys. After figure-background segregation, activity was suppressed as set size increased. This effect was stronger and started earlier among cells stimulated by the background than those stimulated by the figures themselves. As a consequence, contextual modulation, a correlate of figure-background segregation, increased with set size, approximately 100 msec after its initial generation. The results indicate that suppression of responses under increasing attentional demands differentially affects figure and background responses in area V1.     

GABA-like immunoreactivity in the macaque monkey retina: a light and electron microscopic study

The distribution of GABA-like immunoreactivity in the macaque monkey retina was studied by using postembedding techniques on semithin and ultrathin sections. At the light microscopic level, both inner and outer plexiform layers showed strong GABA-like immunoreactivity in the central retina. All the horizontal cells, some bipolar cells, 30-40% of amacrine cells, occasional interplexiform cells, and practically all displaced amacrine cells were labeled. In the peripheral retina (beyond 5 mm eccentricity), the outer plexiform layer and the horizontal cells were not labeled, but all other cell types showed the same labeling pattern as in the central retina. Synapses of the inner plexiform layer involving a pre- or postsynaptic GABA-labeled process were studied electron microscopically. Synapses involving a GABA-labeled presynaptic amacrine cell process made up 80% of the synapses observed. These GABA-labeled amacrine processes synapsed onto amacrine, bipolar, and ganglion cell processes as well as onto amacrine and ganglion cell bodies. Synapses involving a postsynaptic GABA-labeled process made up 20% of the synapses studied. The GABA-like immunoreactive processes were postsynaptic to bipolar cells at the dyads and to amacrine cells at conventional synapses.     

Pallido-thalamo-motor cortical connections: an electron microscopic study in the macaque monkey

We combined the retrograde transport of horseradish peroxidase conjugated to wheat germ agglutinin (WGA-HRP) technique and degenerating electron microscopic investigations to confirm the motor cortical area projection from the medial pallidal segment (GPm) via the thalamic nucleus ventralis lateralis pars oralis (VLo). We found first degenerated boutons arising from the GPm make synaptic contact with the somata and proximal dendrites of VLo neurons containing WGA-HRP reaction products transported retrogradely from motor area.     

Arborisation pattern and postsynaptic targets of physiologically identified thalamocortical afferents in striate cortex of the macaque monkey

The monosynaptic targets of different functional types of geniculocortical axons were compared in the primary visual cortex of monkeys. Single thalamocortical axons were recorded extracellularly in the white matter by using horseradish-peroxidase-filled pipettes. Their receptive fields were mapped and classified as corresponding to those of parvi- or magnocellular neurons in the lateral geniculate nucleus. The axons were then impaled and injected intraaxonally with horseradish peroxidase. Two magnocellular (MA) and two parvicellular (PA) axons were successfully recovered and reconstructed in three dimensions. The two MA axons arborised mainly in layer 4C alpha, as did the two PA axons in layer 4C beta. Few collaterals formed varicosities in layer 6. Both MA axons had two large, elongated clumps of bouton (approx. 300-500 x 600-1,200 microns each) and a small clump. One PA axon had two clumps (each with a core appr. 200 microns in diameter); the other had only one (appr. 150-200 microns in axon had 1,380; one MA axon had 3,200 boutons; and those of the more extensive MA axon were not counted. The distribution of postsynaptic targets as well as the number of synapses per bouton has been established for a sample of 150 PA boutons and 173 MA boutons from serial ultrathin sections. The MA axons made on average 2.1 synapses per bouton compared to 1.79 for one PA axon and 2.6 for the other. The sample of boutons taken from the two physiological types of axons contacted similar proportions of dendritic spines (52-68%), shafts (33-47%), and somata (0-3%). The postsynaptic elements were further characterized by immunostaining for GABA. All postsynaptic perikarya and some of the dendrites (4.5-9.5% of all targets) were positive for the amino acid. Near the thalamic synapse GABA-negative dendritic shafts frequently contained lamellar bodies, an organelle identical in structure to spine apparatus. Dendritic shafts and spines postsynaptic to the thalamocortical boutons frequently received an adjacent synapse from GABA-immunoreactive boutons. The similarity between the magno-and parvicellular axons in their targeting of postsynaptic elements, including the GABAergic neurons, suggests that the structural basis of the physiological differences between 4C alpha and 4C beta neurons should be sought in other aspects of the circuitry of layer 4C, such as local cortical circuits, or in the far greater horizontal extent of the thalamocortical and GABAergic axons in layer 4C alpha compared to those in the beta subdivision.     

The complete pattern of ocular dominance stripes in the striate cortex and visual field of the macaque monkey

Ocular dominance stripes in the striate cortex of a macaque monkey were labeled by autoradiography after injection of [3H]proline into one eye. The stripes were reconstructed on a representation of the flattened cortical surface by two independent techniques: one used computer graphics, and the other was the manual unfolding procedure of Van Essen and Maunsell (VanEssen, D. C., and J. H. R. Maunsell (1980) J. Comp. Neurol. 191: 255-281). The two reconstructions differed in many details of the pattern but were in agreement on its general features. As described in earlier studies, the stripes formed a system of parallel bands, with numerous branches and islands. They were roughly orthogonal to the V1/V2 border throughout the binocular segment of the cortex. In the lateral part of the operculum, where the fovea is represented, the stripes were less orderly than elsewhere. In the calcarine fissure the stripes ran directly across the striate cortex from its dorsal to its ventral margin. In the far periphery the stripes for the ipsilateral eye became progressively narrower, eventually fragmenting into small islands at the edge of the monocular segment. The overall periodicity (width of a left- plus right-eye pair of stripes) averaged 0.88 mm but decreased by a factor of about 2 from center to periphery. This decrease was not accounted for solely by shrinkage of the ipsilateral eye stripes. The flattened cortical reconstruction was transformed back into visual field coordinates, using information about visual field topography obtained from the detailed mapping study of Van Essen et al. (Van Essen, D.C., W.T. Newsome, and J.H.R. Maunsell (1984) Vision Res. 24: 429-448), as well as from more limited mapping done in the same monkey that was used for the reconstruction. In the transformed map, the stripes increased in width about 40-fold from the fovea to the far periphery. As deduced previously (LeVay, S., D. H. Hubel, and T. N. Wiesel (1975) J. Comp. Neurol. 159: 559-576; Hubel, D. H., and D. C., Freeman (1977) Brain Res. 122: 336-343), there were portions of the map in which the stripes followed curves approximating isoeccentricity lines, but this relationship was not very exact or consistent. The pattern of stripes appears to be more meaningfully related to the geometry of the cortical surface. This has significant implications for understanding the developmental mechanisms involved in stripe formation.     

Local circuit neurons of macaque monkey striate cortex: II. Neurons of laminae 5B and 6

This study investigates the intrinsic organization of axons and dendrites of aspinous, local circuit neurons of the macaque monkey visual striate cortex. These investigations use Golgi Rapid preparations of cortical tissue from monkey aged 3 weeks postnatal to adult. We have earlier (Lund, '87) described local circuit neurons found within laminae 5A and 4C; this present account is of neurons found in the infragranular laminae 5B and 6. Since the majority of such neurons are GABAergic and therefore believed to be inhibitory, their role in laminae 5B and 6, the principal sources of efferent projections to subcortical regions, is of considerable importance. We find laminae 5B and 6 to have in common at least one general class of local circuit neuron-the "basket" neuron. However, a major difference is seen in the axonal projections to the superficial layers made by these and other local circuit neurons in the two laminae; lamina 5B has local circuit neurons with principal rising axon projections to lamina 2/3A, areas whereas lamina 6 has local circuit neurons with principal rising axon projections to divisions of 4C, 4A, and 3B. These local circuit neuron axon projections mimic the different patterns of apical dendritic and recurrent axon projections of pyramidal neurons lying within laminae 5B and 6, which are linked together by both dendritic and axonal arbors of local circuit neurons in their neuropils extending between the two laminae. The border zone between 5B and 6 is a specialized region with its own variety of horizontally oriented local circuit neurons, and it also serves as a special focus for pericellular axon arrays from a particular variety of local circuit neuron lying within lamina 6. These pericellular axon "baskets" surround the somata and initial dendritic segments of the largest pyramidal neurons of layer 6, which are known to project both to cortical area MT (V5) and to the superior colliculus (Fries et al., '85). Many of the local circuit neurons of layer 5B send axon trunks into the white matter, and we therefore, suspect them of providing efferent projections. The axons of lamina 6 local circuit neurons have not been found to make such clear-cut contributions to the white matter.     

Topographic organization of cortical input to striate cortex in the Cebus monkey: a fluorescent tracer study

Cortical afferents to area V1 were studied in seven Cebus monkeys by means of retrograde fluorescent tracers. Injections were placed in V1, under electrophysiological guidance, in the regions of representation of both the upper and lower visual quadrants, at eccentricities that ranged from 0.5 to 64 degrees. In all cases retrogradely filled neurons were found in retinotopically corresponding portions of areas V2 and MT, as defined electrophysiologically (Rosa et al: J. Comp. Neurol. 275:326, 1988; Fiorani et al: J Comp Neurol 287:98, 1989). The results also revealed two other visual zones located anterior to V2 here named third and fourth visual areas. A topographical organization of the connections was observed in these areas, with upper quadrant located ventrally and lower quadrant located dorsally. A clear central-peripheral gradient, from the lateral to the medial cortical surface, was also observed in these areas. Lower field injections revealed crude topographic organization in area DZ and a diffuse projecting zone in the annectent gyrus. Peripheral injections in V1 revealed a clear upper and lower field segregation in areas PO and prostriata as well as a complex topography in MST. In addition, another region of labeling revealed the presence of an area, the temporal ventral posterior region, with an organized topographic representation of the upper field, with a central to peripheral gradient, from the lateral to the medial cortical surface. Three groups of cortical areas were distinguished according to the laminar distribution of neurons labeled from V1. In the first group, which is characterized by dense infra- and supragranular labeling, only V2 was included. The second group consists of areas V3, MT, and PO. These areas show dense labeling in the infragranular layers and occasionally sparse labeling in the supragranular layers. Finally, V4 and the other projecting areas, which are characterized by exclusive labeling of the infragranular layers were included in the third group.     

Extrageniculate projections to the visual cortex in the macaque monkey: an HRP study

Extrageniculate projections to the visual cortex were examined in the macaque monkeys by the horseradish peroxidase (HRP) method. Extrageniculate neurons sending fibers to the visual cortex were found in the lateral and inferior pulvinar nuclei, paracentral thalamic nucleus, claustrum, basal nucleus of Meynert, lateral part of the basal amygdaloid nucleus, lateral hypothalamus, locus coeruleus, and dorsomedial and midline regions of the pontine tegmentum.     

Ontogeny of somatostatin in cerebral cortex of macaque monkey: an immunohistochemical study

Distribution of somatostatin-immunoreactive cells in the cerebral cortex of macaque monkeys at embryonic day 120 (E120), E140, newborn, postnatal day 60 (P60) and adult stages were studied by the avidin-biotin-peroxidase immunohistochemical method. At all stages, there existed 3 types of cells in the gray matter: bipolar, multipolar and small-sized cells which stained only in perikaryon. Somatostatin-immunoreactive cells were observed from E120. The cell number increased between E120 and E140 and decreased until P60. At the newborn stage, a high density of cells was distributed in layer II of the prefrontal and parietal cortices (areas FD and PE). In layer I of the postcentral, parietal, temporal and preoccipital cortices (areas FA, PC, PE, TA, TE and OA), small numbers of horizontal cells were detected only at the embryonic and newborn stages. In adulthood, the number of somatostatin cells was much smaller than at the early stages (E140 and newborn). Compared to other cortical areas, in occipital cortex (area OC), there was little change in cell number during development. In occipito-temporal cortices, there were increases in cell number from posterior to anterior portion at all the stages. The large number of somatostatin cells in all layers of the cerebral cortex during the early stages indicates that somatostatin plays a role in the development of the monkey cerebral cortex.