Modified technique for cytochrome oxidase histochemistry: increased staining intensity and compatibility with 2-deoxyglucose autoradiography

Time course of dorsolateral geniculate nucleus plasticity in adult monkeys with laser-induced retinal lesions

We studied changes in the expression of growth-associated protein 43 (GAP43), glial fibrillary acidic protein (GFAP), and calcium-binding proteins (calbindin [Cb] and parvalbumin [Pv]) in the dorsal lateral geniculate nucleus (dLGN) of four capuchin monkeys with laser-induced retinal lesions. The lesions were generated with the aid of a neodymium-YAG dual-frequency laser with shots of different intensity and at different survival time in each animal. The expression of these proteins in the layers of the dLGN was evaluated by performing histodensitometry of coronal sections throughout the nucleus. High-power laser shots administered at the border of the optic disc (OD)-injured fibers resulted in large scotomas. These lesions produced a devastating effect on fibers in this passage, resulting in large deafferentation of the dLGN. The time course of plasticity expressed in this nucleus varied with the degree of the retinal lesion. Topographically, corresponding portions of the dLGN were inferred by the extent of the ocular dominance column revealed by cytochrome oxidase histochemistry in flattened preparations of V1. In the region representing the retinal lesion, the expression of GFAP, GAP43, Pv, and Cb increased and decreased in the corresponding dLGN layers shortly after lesion induction and returned to their original values with different time courses. Synaptogenesis (indicated by GAP43 expression) appeared to be increased in all layers, while "cleansing" of the glial-damaged region (indicated by GFAP expression) was markedly greater in the parvocellular layers, followed by the magnocellular layers. Schematic drawings of optic discs laser lesions and of series of coronal sections of the dLGN, in three monkeys, depicting the areas of the nucleus deafferented by the lesions.

Refinement of the Primate Corticospinal Pathway During Prenatal Development

Perturbation of the developmental refinement of the corticospinal (CS) pathway leads to motor disorders. While non-primate developmental refinement is well documented, in primates invasive investigations of the developing CS pathway have been confined to neonatal and postnatal stages when refinement is relatively modest. Here, we investigated the developmental changes in the distribution of CS projection neurons in cynomolgus monkey (Macaca fascicularis). Injections of retrograde tracer at cervical levels of the spinal cord at embryonic day (E) 95 and E105 show that: (i) areal distribution of back-labeled neurons is more extensive than in the neonate and dense labeling is found in prefrontal, limbic, temporal, and occipital cortex; (ii) distributions of contralateral and ipsilateral projecting CS neurons are comparable in terms of location and numbers of labeled neurons, in contrast to the adult where the contralateral projection is an order of magnitude higher than the ipsilateral projection. Findings from one largely restricted injection suggest a hitherto unsuspected early innervation of the gray matter. In the fetus there was in addition dense labeling in the central nucleus of the amygdala, the hypothalamus, the subthalamic nucleus, and the adjacent region of the zona incerta, subcortical structures with only minor projections in the adult control.

Neuronal response properties across cytochrome oxidase stripes in primate V2

Cytochrome oxidase histochemistry reveals large-scale cortical modules in area V2 of primates known as thick, thin, and interstripes. Anatomical, electrophysiological, and tracing studies suggest that V2 cytochrome oxidase stripes participate in functionally distinct streams of visual information processing. However, there is controversy whether the different V2 compartments indeed correlate with specialized neuronal response properties. We used multiple-electrode arrays (16 × 2, 8 × 4 and 4 × 4 matrices) to simultaneously record the spiking activity (N = 190 single units) across distinct V2 stripes in anesthetized and paralyzed capuchin monkeys (N = 3 animals, 6 hemispheres). Visual stimulation consisted of moving bars and full-field gratings with different contrasts, orientations, directions of motion, spatial frequencies, velocities, and color contrasts. Interstripe neurons exhibited the strongest orientation and direction selectivities compared to the thick and thin stripes, with relatively stronger coding for orientation. Additionally, they responded best to higher spatial frequencies and to lower stimulus velocities. Thin stripes showed the highest proportion (80%) of neurons selective to color contrast (compared to 47% and 21% for thick and interstripes, respectively). The great majority of the color selective cells (86%) were also orientation selective. Additionally, thin stripe neurons continued to increase their firing rate for stimulus contrasts above 50%, while thick and interstripe neurons already exhibited some degree of response saturation at this point. Thick stripes best coded for lower spatial frequencies and higher stimulus velocities. In conclusion, V2 CytOx stripes exhibit a mixed degree of segregation and integration of information processing, shedding light into the early mechanisms of vision.

Neuronal Distribution Across the Cerebral Cortex of the Marmoset Monkey (Callithrix jacchus)

Using stereological analysis of NeuN-stained sections, we investigated neuronal density and number of neurons per column throughout the marmoset cortex. Estimates of mean neuronal density encompassed a greater than 3-fold range, from >150 000 neurons/mm3 in the primary visual cortex to ~50 000 neurons/mm3 in the piriform complex. There was a trend for density to decrease from posterior to anterior cortex, but also local gradients, which resulted in a complex pattern; for example, in frontal, auditory, and somatosensory cortex neuronal density tended to increase towards anterior areas. Anterior cingulate, motor, premotor, insular, and ventral temporal areas were characterized by relatively low neuronal densities. Analysis across the depth of the cortex revealed greater laminar variation of neuronal density in occipital, parietal, and inferior temporal areas, in comparison with other regions. Moreover, differences between areas were more pronounced in the supragranular layers than in infragranular layers. Calculations of the number of neurons per unit column revealed a pattern that was distinct from that of neuronal density, including local peaks in the posterior parietal, superior temporal, precuneate, frontopolar, and temporopolar regions. These results suggest that neuronal distribution in adult cortex result from a complex interaction of developmental/ evolutionary determinants and functional requirements.

Time course of cytochrome oxidase blob plasticity in the primary visual cortex of adult monkeys after retinal laser lesions

We studied the time course of changes of cytochrome oxidase (CytOx) blob spatial density and blob cross-sectional area of deprived (D) and nondeprived (ND) portions of V1 in four capuchin monkeys after massive and restricted retinal laser lesions. Laser shots at the border of the optic disc produced massive retinal lesions, while low power laser shots in the retina produced restricted retinal lesions. These massive and restricted retinal lesions were intended to simulate glaucoma and diabetic retinopathy, respectively. We used a Neodymium-YAG dual frequency laser to make the lesions. We measured Layer III blobs in CytOx-reacted tangential sections of flat-mounted preparations of V1. The plasticity of the blob system and that of the ocular dominance columns (ODC) varied with the degree of retinal lesions. We found that changes in the blob system were different from that of the ODC. Blob sizes changed drastically in the region corresponding to the retinal lesion. Blobs were larger and subjectively darker above and below the non deprived ODC than in the deprived columns. With restricted lesions, blobs corresponding to the ND columns had sizes similar to those from non-lesioned areas. In contrast, blobs corresponding to the deprived columns were smaller than those from nonlesioned areas. With massive lesions, ND blobs were larger than the deprived blobs. Plastic changes in blobs described here occur much earlier than previously described.

Distribution of cytochrome oxidase-rich patches in human primary visual cortex

We studied the tangential distribution of cytochrome oxidase (CytOx)-rich patches (blobs) in the striate cortex (V1) of normally sighted Homo sapiens. We analyzed the spatial density and cross-sectional area of patches in CytOx-reacted tangential sections of flat-mounted preparations of V1 and surrounding areas. CytOx-rich patches were most clearly defined in the supragranular cortical layers of V1, particularly at middle levels of layer III. Variations in patch spatial density were subtle across different visual eccentricity representations. Within the binocular representation of V1, the average patch spatial density decreased slightly with increasing cortical eccentricity, from around 1.0 patch/mm² in the foveal representation to 0.6 patch/mm² at the representation of ∼60° eccentricity, but seemed to increase again at the representation of the monocular crescent. Across the entire sample, the cross-sectional area of patches (i.e., patch size) varied from approximately 0.2-0.8 mm² , with a mean value of 0.32 mm² . Notably, there was no significant variation in the mean patch size across eccentricity representations. Human patches are on average larger than those reported for nonhuman primate brains, and analysis of species with different brain sizes suggests an approximately linear relationship between V1 area and patch size. The relative constancy of patch metrics across eccentricities is in stark contrast with the exponential variation in V1 cortical magnification, suggesting a nearly invariant modular organization throughout human V1.

Robust Visual Responses and Normal Retinotopy in Primate Lateral Geniculate Nucleus following Long-term Lesions of Striate Cortex

Lesions of striate cortex (V1) trigger massive retrograde degeneration of neurons in the LGN. In primates, these lesions also lead to scotomas, within which conscious vision is abolished. Mediation of residual visual capacity within these regions (blindsight) has been traditionally attributed to an indirect visual pathway to the extrastriate cortex, which involves the superior colliculus and pulvinar complex. However, recent studies have suggested that preservation of the LGN is critical for behavioral evidence of blindsight, raising the question of what type of visual information is channeled by remaining neurons in this structure. A possible contribution of LGN neurons to blindsight is predicated on two conditions: that the neurons that survive degeneration remain visually responsive, and that their receptive fields continue to represent the region of the visual field inside the scotoma. We tested these conditions in male and female marmoset monkeys (Callithrix jacchus) with partial V1 lesions at three developmental stages (early postnatal life, young adulthood, old age), followed by long recovery periods. In all cases, recordings from the degenerated LGN revealed neurons with well-formed receptive fields throughout the scotoma. The responses were consistent and robust, and followed the expected eye dominance and retinotopy observed in the normal LGN. The responses had short latencies and preceded those of neurons recorded in the extrastriate middle temporal area. These findings suggest that the pathway that links LGN neurons to the extrastriate cortex is physiologically viable and can support residual vision in animals with V1 lesions incurred at various ages.SIGNIFICANCE STATEMENT Patients with a lesion of the primary visual cortex (V1) can retain certain visually mediated behaviors, particularly if the lesion occurs early in life. This phenomenon ("blindsight") not only sheds light on the nature of consciousness, but also has implications for studies of brain circuitry, development, and plasticity. However, the pathways that mediate blindsight have been the subject of debate. Recent studies suggest that projections from the LGN might be critical, but this finding is puzzling given that the lesions causes severe cell death in the LGN. Here we demonstrate in monkeys that the surviving LGN neurons retain a remarkable level of visual function and could therefore be the source of the visual information that supports blindsight.

Glycogen distribution in the microwave-fixed mouse brain reveals heterogeneous astrocytic patterns

In the brain, glycogen metabolism has been implied in synaptic plasticity and learning, yet the distribution of this molecule has not been fully described. We investigated cerebral glycogen of the mouse by immunohistochemistry (IHC) using two monoclonal antibodies that have different affinities depending on the glycogen size. The use of focused microwave irradiation yielded well-defined glycogen immunoreactive signals compared with the conventional periodic acid-Schiff method. The IHC signals displayed a punctate distribution localized predominantly in astrocytic processes. Glycogen immunoreactivity (IR) was high in the hippocampus, striatum, cortex, and cerebellar molecular layer, whereas it was low in the white matter and most of the subcortical structures. Additionally, glycogen distribution in the hippocampal CA3-CA1 and striatum had a 'patchy' appearance with glycogen-rich and glycogen-poor astrocytes appearing in alternation. The glycogen patches were more evident with large-molecule glycogen in young adult mice but they were hardly observable in aged mice (1-2 years old). Our results reveal brain region-dependent glycogen accumulation and possibly metabolic heterogeneity of astrocytes. GLIA 2016;64:1532-1545.

Feedforward and feedback connections and their relation to the cytox modules of V2 in Cebus monkeys

To study the circuitry related to the ventral stream of visual information processing and its relation to the cytochrome oxidase (CytOx) modules in visual area V2, we injected anterograde and retrograde cholera toxin subunit B (CTb) tracer into nine sites in area V4 in five Cebus apella monkeys. The injection site locations ranged from 2° to 10° eccentricity in the lower visual field representation of V4. Alternate cortical sections, cut tangentially to the pial surface or in the coronal plane, were stained for CTb immunocytochemistry or for CytOx histochemistry or for Nissl. Our results indicate that the V4-projecting cells and terminal-like labeling were located in interstripes and thin CytOx-rich stripes and avoided the CytOx-rich thick stripes in V2. The feedforward projecting cell bodies in V2 were primarily located in the supragranular layers and sparsely located in the infragranular layers, whereas the feedback projections (i.e., the terminal-like labels) were located in the supra- and infragranular layers. V4 injections of CTb resulted in labeling of the thin stripes and interstripes of V2 and provided an efficient method of distinguishing the V2 modules that were related to the ventral stream from the CytOx-rich thick stripes, related to the dorsal stream. In V2, there was a significant heterogeneity in the distribution of projections: feedforward projections were located in CytOx-rich thin stripes and in the CytOx-poor interstripes, whereas the feedback projections were more abundant in the thin stripes than in the interstripes. J. Comp. Neurol. 522:3091–3105, 2014.

Precise visuotopic organization of the blind spot representation in primate V1

The optic disk is a region of the retina consisting mainly of ganglion cell axons and blood vessels, which generates a visual scotoma known as the blind spot (BS). Information present in the surroundings of the BS can be used to complete the missing information. However, the neuronal mechanisms underlying these perceptual phenomena are poorly understood. We investigate the topography of the BS representation (BSR) in cortical area V1 of the capuchin monkey, using single and multiple electrodes. Receptive fields (RFs) of neurons inside the BSR were investigated using two distinct automatic bias-free mapping methods. The first method (local mapping) consisted of randomly flashing small white squares. For the second mapping method (global mapping), we used a single long bar that moved in one of eight directions. The latter stimulus was capable of eliciting neuronal activity inside the BSR, possibly attributable to long-range surround activity taking place outside the borders of the BSR. Importantly, we found that the neuronal activity inside the BSR is organized topographically in a manner similar to that found in other portions of V1. On average, the RFs inside the BS were larger than those outside. However, no differences in orientation or direction tuning were found between the two regions. We propose that area V1 exhibits a continuous functional topographic map, which is not interrupted in the BSR, as expected by the distribution of photoreceptors in the retina. Thus V1 topography is better described as “visuotopic” rather than as a discontinuous “retinotopic” map.

Quantification of early stages of cortical reorganization of the topographic map of V1 following retinal lesions in monkeys

We quantified the capacity for reorganization of the topographic representation of area V1 in adult monkeys. Bias-free automated mapping methods were used to delineate receptive fields (RFs) of an array of neuronal clusters prior to, and up to 6 h following retinal lesions. Monocular lesions caused a significant reorganization of the topographic map in this area, both inside and outside the cortical lesion projection zone (LPZ). Small flashed stimuli revealed responses up to 0.85 mm inside the boundaries of the LPZ, with RFs representing regions of undamaged retina immediately surrounding the lesion. In contrast, long moving bars that spanned the scotoma resulting from the lesion revealed responsive units up to 1.87 mm inside the LPZ, with RFs representing interpolated responses in this region. This reorganization is present immediately after monocular retinal lesioning. Both stimuli showed a similar and significant (5-fold) increase of the RF scatter in the LPZ, 0.56 mm (median), compared with the undamaged retina, 0.12 mm. Our results reveal an array of preexisting subthreshold functional connections of up to 2 mm in V1, which can be rapidly mobilized independently from the differential qualitative reorganization elicited by each stimulus.

Voltage-sensitive dye imaging reveals improved topographic activation of cortex in response to manipulation of thalamic microstimulation parameters

Voltage-sensitive dye imaging was used to quantify in vivo, network level spatiotemporal cortical activation in response to electrical microstimulation of the thalamus in the rat vibrissa pathway. Thalamic microstimulation evoked a distinctly different cortical response than natural sensory stimulation, with response to microstimulation spreading over a larger area of cortex and being topographically misaligned with the cortical column to which the stimulated thalamic region projects. Electrical stimulation with cathode-leading asymmetric waveforms reduced this topographic misalignment while simultaneously increasing the spatial specificity of the cortical activation. Systematically increasing the asymmetry of the microstimulation pulses revealed a continuum between symmetric and asymmetric stimulation that gradually reduced the topographic bias. These data strongly support the hypothesis that manipulation of the electrical stimulation waveform can be used to selectively activate specific neural elements. Specifically, our results are consistent with the prediction that cathode-leading asymmetric waveforms preferentially stimulate cell bodies over axons, while symmetric waveforms preferentially activate axons over cell bodies. The findings here provide some initial steps toward the design and optimization of microstimulation of neural circuitry, and open the door to more sophisticated engineering tools, such as nonlinear system identification techniques, to develop technologies for more effective control of activity in the nervous system.

The DYT1 carrier state increases energy demand in the olivocerebellar network

DYT1 dystonia is caused by a GAG deletion in TOR1A, the gene which encodes torsinA. Gene expression studies in rodents and functional imaging studies in humans suggest that DYT1 dystonia may be a network disorder of neurodevelopmental origin. To generate high resolution metabolic maps of DYT1 dystonia and pinpoint dysregulated network elements, we performed 2-deoxyglucose autoradiography and cytochrome oxidase (CO) histochemistry in transgenic mice expressing human mutant (hMT1) torsinA and wild-type littermates. In comparison with controls, hMT1 mice showed increased glucose utilization (GU) in the inferior olive (IO) medial nucleus (IOM), IO dorsal accessory nucleus and substantia nigra compacta, and decreased GU in the medial globus pallidus (MGP) and lateral globus pallidus. The hMT1 mice showed increased CO activity in the IOM and Purkinje cell layer of cerebellar cortex, and decreased CO activity in the caudal caudate-putamen, substantia nigra reticulata and MGP. These findings suggest that (1) the DYT1 carrier state increases energy demand in the olivocerebellar network and (2) the IO may be a pivotal node for abnormal basal ganglia-cerebellar interactions in dystonia.

Distribution of neurofilament proteins in the lateral geniculate nucleus, primary visual cortex, and area MT of adult Cebus monkeys

We investigated the distribution pattern of SMI-32-immunopositive cells in the lateral geniculate nucleus (LGN) and in the primary (V1) and middle temporal (MT) cortical visual areas of the adult New World monkey Cebus apella. In the LGN, the reaction for SMI-32 labeled cells in both the magnocellular (M) and parvocellular (P) layers. However, the cellular label was heavier in M layers, which also showed a more intense labeling in the neuropil. In V1, the reaction showed a lamination pattern, with the heaviest labeling occurring in layer 4B and upper layer 6 (layers that project to area MT). Area MT shows a dense band of labeled neuropil and large pyramidal neurons in layer 3, large darkly labeled but less densely packed neurons in layer 5, and a population of small, lightly labeled cells in layer 6. These results resemble those found in other New and Old World monkeys, which suggest that the preferential labeling of projection neurons associated with fast-conducting pathways to the extrastriate dorsal stream is a common characteristic of simian primates. In the superficial layers of V1 in Cebus monkeys, however, SMI-32-labeled neurons are found in both cytochrome oxidase blobs and interblob regions. In this aspect, our results in Cebus are similar to those found in the Old World monkey Macaca and different from those described for squirrel monkey, a smaller New World Monkey. In Cebus, as well as in Macaca, there is no correlation between SMI-32 distribution and the blob pattern.

Increased electrical and metabolic activity in the dorsal raphe nucleus of Parkinsonian rats

Serotonin (5-HT) containing neurons in the dorsal raphe nucleus (DRN) may play important roles in Parkinson's disease (PD). This study investigated neural and metabolic activity of the DRN in animal PD models based on dopamine depletion. The data show both increased firing rate of DRN 5-HT neurons and increased cytochrome oxidase activity in dopamine-depleted rats, as compared to controls. These data support the hypothesis that the DRN 5-HT system is hyperactive in the dopamine-depleted brain.

The HSV-2 protein ICP10PK prevents neuronal apoptosis and loss of function in an in vivo model of neurodegeneration associated with glutamate excitotoxicity

Excessive glutamate receptor activation results in neuronal death, a process known as excitotoxicity. Intrastriatal injection of N-methyl-d-aspartate (NMDA) is a model of excitotoxicity. We used this model to examine whether excitotoxic injury is inhibited by the anti-apoptotic herpes simplex virus type 2 (HSV-2) protein, ICP10PK, delivered by the replication incompetent HSV-2 vector, DeltaRR. Intrastriatal DeltaRR administration (2500 plaque forming units) was nontoxic and did not induce microglial activation 5 days after injection. Intrastriatal injection of DeltaRR with NMDA or 4 h after NMDA injection showed increased neuronal survival and decreased mitochondrial damage compared to injection of NMDA alone. Neuroprotection was due to the inhibition of NMDA-induced apoptosis through ERK activation. DeltaRR-treated mice did not develop NMDA-associated behavioral deficits. The data suggest that DeltaRR is a promising platform for treatment of acute neuronal injury.

Distribution of calbindin-28kD and parvalbumin in V1 in normal adult Cebus apella monkeys and in monkeys with retinal lesions

Several proteins have their normal patterns of distributions altered by monocular visual deprivation. We studied the distribution of the calcium-binding proteins calbindin-28kD (Cb) and parvalbumin (Pv) in V1 in normal adult Cebus apella monkeys and in monkeys with monocular retinal lesions. In normal monkeys, the interblobs regions in layers 2/3 and the layer 4B are intensely labeled for Cb, while Pv reaction showed a complementary labeling pattern with a stronger staining in layers 4A, 4C and in the blob regions in layers 2/3. In monkeys with monocular retinal lesion, the laminar distribution of these proteins was differentially affected, although both reactions resulted in stronger labeling in non-deprived ocular dominance columns. While Cb reaction resulted in stronger labeling in layers 1 through 5, Pv labeling was heavier in layers 2/3, 4A and 4C. There was a clear reduction in the intensity of neuropil staining for both Pv and Cb in deprived ocular dominance columns with little or no reduction in number of labeled cells. This reduction could thus be attributed to activity-dependent changes at synapses level.

Populations of hippocampal inhibitory neurons express different levels of cytochromec

Cytochrome c (CC) immunoreactivity was quantified in functionally distinct rat hippocampal inhibitory neuron populations using double immunocytochemistry and laser scanning confocal microscopy to measure the CC expression level as well as the amount of mitochondria within the cells, which is a sign of neuronal activity. The CC signal showed a similar distribution to cytochrome c oxidase histochemical staining. Strongly stained somata, dendrites and axon terminal clouds were dispersed over the low intensity neuropil staining. The staining was granular and electron microscopic investigation confirmed that the signal was localized in mitochondria. Intensively labeled neurons, showing the morphological features of inhibitory cells, were most frequently found in the principal cell layers, stratum oriens of the CA1-3 areas, stratum lucidum and hilus. These neurons contained not only a higher number of mitochondria than the principal cells but the intensity of the mitochondrial staining was evidently stronger. Among the examined interneuronal populations, parvalbumin-immunoreactive neurons were intensively labeled for CC. Calbindin D28k- (CB), somatostatin- and cholecystokinin-labeled cells showed heterogeneous CC levels, whereas calretinin-immunoreactive cells never showed a strong CC signal. CB cells in stratum oriens and alveus layers, lucidum and the hilus were strongly labeled for CC. CB cells in such regions are known to project to the medial septum and contain somatostatin. We have demonstrated that the CA1 interneurons that project to the medial septum (hippocampo-septal neurons) express a high level of CC. Thus, similar to the parvalbumin-containing basket and axo-axonic cells, the hippocampo-septal neurons potentially have a high average activity level.

Differential expression of Zif268 and c-Fos in the primary visual cortex and lateral geniculate nucleus of normal Cebus monkeys and after monocular lesions

The transcription factors c-Fos and Zif268 have been used as markers of neuronal activity, and they also have been implicated in neuronal plasticity. In this study, we investigated the expression of c-Fos and Zif268 proteins in the lateral geniculate nucleus (LGN) and in the cortical primary visual area (V1) of normal adult Cebus apella monkeys and in animals with monocular lesions. In the LGN, the reaction for c-Fos showed immunopositive cells in both magnocellular (M) and parvocellular (P) layers; however, the label was heavier in P layers. In animals that suffered monocular lesions, the immunocytochemistry for c-Fos showed more labeling in layers related to the normal eye compared with those of the lesioned eye. No specific label was observed after the reaction for Zif268 in the LGN. In V1, the reaction for both Zif268 and c-Fos showed a pattern of lamination in which heavier labeling was found in layers 2/3, 4A, 4C, and 6. After monocular lesions, we observed a clear pattern of ocular dominance columns in V1 for both c-Fos and Zif268, in which the columns related to the normal eye are more heavily labeled than those related to the lesioned eye. This pattern is more evident in layer 4C after c-Fos reaction, whereas, after Zif268, it is more clearly observed in layers 2/3. These results suggest that, in addition to be regulated by functional activity, these transcription factors are involved in different processes during cortical reorganization.

Projections from primary visual cortex to cytochrome oxidase thin stripes and interstripes of macaque visual area 2

It has been controversial whether the cytochrome oxidase (CO)-dense blobs in primate primary visual cortex (V1) and CO-dense thin stripes in visual area 2 (V2) are parts of a cortical color-processing stream that is segregated from other functional streams. One of the key pieces of evidence for the segregated color stream is the previous report of specific connections between blobs and thin stripes, which is parallel to the connections between interblobs and interstripes. To study the degree of the segregation between the proposed different streams, in the current study, anatomical tracers were injected into different V2 compartments with the functional guidance of optical imaging. The spatial relationship between each labeled cell and the CO blobs in V1 were analyzed quantitatively. After tracer injections in the color-preferring modules in CO thin stripes, equal amounts of labeled cells were found in the blobs and interblobs. However, the density of the labeled cells was more than twice as high in the blobs as that in the interblobs, and most of the clusters of labeled cells partially overlapped with the blobs. Tracer injections in the interstripes labeled cells predominantly in the interblobs. Our results suggest that both the blobs and interblobs project to the thin stripes and call into question the proposition that different CO compartments in V1 and V2 are connected in parallel to form highly segregated functional streams.

Projections from the cytochrome oxidase modules of visual area V2 to the ventral posterior area in the macaque

The ventral part of the third visual cortical complex, the ventral posterior area (VP) or V3v, is located between the ventral half of visual areas V2 and V4. Because of its location and the physiological properties of its neurons, VP has been considered to be involved in the ventral stream visual areas. The ventral stream visual areas such as V4 and TEO receive projections from the cytochrome oxidase (CO)-rich thin stripes and CO-poor interstripe regions of V2; however, which CO-modules project to VP remains unclear. Moreover, it is not clear whether V1 projects to VP. We injected retrograde tracers into VP and found that VP receives projections from V2 neurons not only in the CO-rich thin stripes and CO-poor interstripe regions but also in the CO-rich thick stripes. We also confirmed the virtual absence of inputs from V1 to VP. These results support the hypothesis that VP constitutes a distinct extrastriate visual area and also suggest that, in addition to color and shape information, VP may also process visual information related to space and disparity.

Three streams of visual information processing in V2 of Cebus monkey

Gattass and collaborators (Gattass R, Rosa MGP, Souza APB, Piñon MCG, Neuenschwander S [1990a] Braz J Med Biol Res 23:375-393) proposed that the dorsal stream of visual processing, as defined by Ungerleider and Mishkin (Ungerleider LG, Mishkin M [1982] In: Ingle DJ, Goodale MA, Mansfield RJW, editors. Analysis of visual behavior. Cambridge: Massachusetts Institute of Technology. p 549-586), can be subdivided into dorsolateral and dorsomedial streams, and suggested that they may be involved in different aspects of the processing of motion and spatial perception, respectively. The goal of the present study was to provide additional evidence for this hypothesis by using cytochrome oxidase immunohistochemistry combined with retrograde tracing techniques. In Old World monkeys, the locations of visual area 4 (V4; ventral stream) and middle temporal area (MT; dorsal stream) projecting neurons in V2 supports the hypothesis that the cytochrome oxidase (CytOx)-rich thin stripes and the CytOx-poor interstripes are associated with the ventral stream, and that the CytOx-rich thick stripes belong to the dorsal stream. In this study we describe, in the New World monkey Cebus, the distribution of retrogradely labeled cells in V2 relative to the CytOx compartments after fluorescent tracers were placed in areas V4, MT, and the parietooccipital area (PO). We found PO-projecting neurons in CytOx-rich thick stripes and CytOx-poor interstripes in V2, whereas MT-projecting neurons appeared almost exclusively in thick stripes. In contrast, V4-projecting neurons were located mostly in CytOx-poor interstripes and CytOx-rich thin stripes. In addition, V4- and MT-projecting neurons were located mainly in supragranular layers, whereas PO-projecting neurons were located in supragranular and infragranular layers. These results support the hypothesis for the existence of three distinct streams of visual processing: ventral (including V4), dorsolateral (including MT), and dorsomedial (including PO).

Cytochrome oxidase activity in the monkey globus pallidus and subthalamic nucleus after ablation of striatal interneurons expressing substance P receptors

To understand functional roles of striatal interneurons in primate basal ganglia circuitry, we ablated interneurons expressing substance P (SP) receptors (SPR) in the putamen with SP-saporin, a SPR selective neurotoxin. The effect of SP-saporin injection into the putamen was evaluated by examining the loss of cholinergic interneurons and NADPHd-positive (nicotinamide adenine dinucleotide phosphate diaphorase positive) interneurons. We then analyzed regional metabolic changes using cytochrome oxidase (CO) histochemistry. CO activity in some regions of the internal and external segments of the globus pallidus (GP) in the lesioned hemisphere was lower than that in the contralateral or surrounding GP regions. CO activity in the subthalamic nucleus, however, showed no significant change. The present findings suggest that striatopallidal projection neurons exert enhanced inhibitory influence on the GP without modulatory control by the striatal SPR-expressing interneurons.

Immunoreactivity for Taurine Characterizes Subsets of Glia, GABAergic and non-GABAergic Neurons in the Neo- and Archicortex of the Rat, Cat and Rhesus Monkey: Comparison with Immunoreactivity for Homocysteic Acid

The cerebral cortex is an area rich in taurine (2-aminoethanesulphonic acid), but only limited information exists regarding its cellular distribution. We therefore examined taurine-like immunoreactivity in the cerebral cortex of the rat, cat and macaque monkey using antiserum directed against glutaraldehyde-conjugated taurine. Immunostaining was assessed at the light and electron microscopic level, and patterns obtained in light microscopic studies were compared to those produced with antiserum to gamma-aminobutyric acid (GABA) and homocysteic acid (HCA). In all three species, strong taurine-like immunoreactive perivascular endothelial cells, pericytes and oligodendrocytes were found. These cells were located throughout the neuropil, which itself showed a low level of immunoreactivity. In rats and cats, a small number of weakly taurine-enriched neurons were observed, particularly in superficial layers. In all cortical areas of the macaque, however, glial staining was matched by strong, selective staining of subpopulations of cortical neurons which were distributed in a bilaminar pattern involving layers II/III and VI. In addition, in primary visual cortex, area 17, immunopositive neurons were also present in sublayer IVCbeta, while in the hippocampus strongly taurine-positive neurons were most conspicuous in the granule cell layer of the dentate gyrus. In all regions, strongly taurine-positive neurons constituted only a subpopulation of the neurons occupying a given layer. Examination of adjacent sections for GABA immunoreactivity showed that the most strongly taurine-positive neurons in layers II/III were immunoreactive for GABA. The cells located in layers IVCbeta and VI, and the granule cells of the dentate gyrus, however, were GABA-negative. The morphological features of these latter groups suggested that the antiserum to taurine identifies subsets of spiny stellate, small pyramidal and dentate granule cells. None of these neurons showed immunoreactivity with antiserum to HCA in the primate; HCA-positive glia were found along the pial and white matter boundaries of the cortex, and showed no overlap with strongly taurine-positive glial elements. Although a transmitter role for taurine may be unlikely, particularly in view of its enrichment in subpopulations of both inhibitory and excitatory cells, the capacity of taurine to influence membrane-associated functions in excitable tissues, and its selective distribution demonstrated here, provides the potential for a contribution to communication between cortical cells.

Subarachnoid hemorrhage induces dynamic changes in regional cerebral metabolism in rats

Following a subarachnoid hemorrhage (SAH), adult rats exhibit dynamic regional changes in cerebral glucose metabolism characterized by an increase in metabolic rates and a subsequent upregulation of cytochrome oxidase (CO). We evaluated both local cerebral metabolic rates for glucose (ICMRglc: (mol/100 g/min) and CO in 23 brain regions of interest (ROI). Sham animals underwent anesthesia and superficial surgery; saline-controls received an injection of 0.9% saline into the cisterna magna; and SAH rats received an injection of autologous blood into the cisterna magna. This blood, measured by albumin labeled with radioactive carbon 14, distributed throughout the brain but predominated ventrally. After experimental animals were sacrificed at day 0 (3 h), 1, 3, and 7 days postinjection, ROI were analyzed using [14C]2-deoxy-D-glucose autoradiography and CO histochemistry. ICMRglc in SAH rats increased in many regions (ranging from 0.7% to 32.2% above sham levels). Cytochrome oxidase also increased from 1% to 9% above sham levels, peaking on day 3. Conversely, saline-controls exhibited prolonged depression of ICMRglc (ranging from 11% to 35% below sham levels) and CO (ranging from 4% to 11% below sham levels) from day 0 through day 7. All saline-control ROI for all time points showed this metabolic depression, and between 91% and 95% of saline-control ROI presented lower CO levels as compared to sham. Overall, ICMRglc and CO levels were greater in SAH than in saline-control ROI. However, when considering the influence of subarachnoid blood on metabolic changes in SAH animals, both CO and 2DG levels did not correlate well with the amount of 14C-albumin binding. While previous studies have measured both metabolic rates of glucose and CO soon after SAH, this is the first to simultaneously conduct these measurements in the same SAH rat model.

Anatomical sparing in the superior colliculus of hemispherectomized monkeys

Using the monkey as a model for human hemispherectomy, the effects of early removal of a whole cerebral hemisphere on the cytoarchitecture and cytochrome oxidase histochemistry of the superior colliculus (SC) were evaluated. Results show that the SC ipsilateral to the cortical lesion suffers a 29.9% average volume reduction and a 32.7% total loss of neurons compared to the contralateral SC. Neuronal densities and metabolic activity are similar in normal and hemispherectomized monkeys. Furthermore, the ipsi- and contralesional SC receive retinal inputs as revealed with intraocular injections of tritiated proline. These data suggest that the superior colliculus retains functional capabilities following hemispherectomy in monkey.

Exercise increases metabolic capacity in the motor cortex and striatum, but not in the hippocampus

Acute bouts of exercise have been shown to produce transient increases in regional cerebral glucose utilization, oxygen uptake, and cerebral blood flow in motor cortex, striatum, and hippocampus. The purpose of this study was to determine whether or not chronic exercise will cause long-term metabolic plasticity in brain structures activated during physical activity. The activity of cytochrome oxidase (COX), is coupled to the production of ATP, and reflects long-term plasticity in metabolic capacity. The present study examined whether or not 6 months of voluntary exercise would increase COX activity in the striatum, sensorimotor cortex, and three hippocampal subfields. Five-month-old, female Long-Evans hooded rats were randomly assigned to a control or exercise condition. Exercising rats had running wheels attached to their home cages. After the training period, fresh brains were rapidly frozen and sectioned with a cryostat. COX activity was measured using COX histochemical methods and optical densitometry. Rats in the exercise condition had significantly higher optical density in the hindlimb and forelimb motor cortices (18%, P<0.01) and dorsolateral caudate putamen (17%, P<0.01), but not in the ventrolateral caudate putamen or any subfield of the hippocampus. Although exercise is believed to increase neuronal activity in the hippocampus, motor cortex and striatum, only limb representations in the motor cortex and striatum increase bioenergetic capacity after regular exercise.

Retinal projections to the pregeniculate nucleus in the hemispherectomized monkey

Intraocular injections of tritiated proline were used to test the hypothesis that unilateral removal of all visual cortical areas results in increased distribution of retinal terminals in the pregeniculate nucleus (PGN) of the thalamus in monkeys. Following hemispherectomy, retinal input to the ipsilateral PGN was reduced by an average of 18.5% when compared to its contralateral homologue, which corresponded to the reduction in nuclear volume (19.3%). Our results show that removal of cortical afferents to the external layer of the PGN does not induce invasion of retinal projections into this region of the nucleus.

Laminar distribution of neurons in extrastriate areas projecting to visual areas V1 and V4 correlates with the hierarchical rank and indicates the operation of a distance rule

The directionality of corticocortical projections is classified as feedforward (going from a lower to higher hierarchical levels), feedback (interconnecting descending levels), and lateral (interconnecting equivalent levels). Directionality is determined by the combined criteria of the laminar patterns of the axon terminals as well as the cells of origins and has been used to construct models of the visual system, which reveals a strict hierarchical organization (Felleman and Van Essen, 1991; Hilgetag et al., 1996a). However, these models are indeterminate partly because we have no indication of the distance separating adjacent levels. Here we have attempted to determine a graded parameter describing the anatomical relationship of interconnected areas. We have investigated whether the precise percentage of labeled supragranular layer neurons (SLN%) in each afferent area after injection in either visual areas V1 or V4 determines its hierarchical position in the model. This shows that pathway directionality in the Felleman and Van Essen model is characterized by a range of SLN% values. The one exception is the projection of the frontal eye field to area V4, which resembles a feedforward projection. Individual areal differences in SLN% values are highly significant, and the number of hierarchical steps separating a target area from a source area is found to be tightly correlated to SLN%. The present results show that the hierarchical rank of each afferent area is reliably indicated by SLN%, and therefore this constitutes a graded parameter that is related to hierarchical distance.

Organization of sensory cortex in the East African hedgehog (Atelerix albiventris)

We investigated the organization of neocortex in the East African hedgehog (Atelerix albiventris) with microelectrode recordings from sensory areas that were later correlated with cytochrome oxidase patterns in sections of flattened cortex. The location of corticospinal projecting neurons was also examined and related to sensory areas by making small injections of wheat germ agglutinin-horseradish peroxidase into the spinal cord. Our goals were to determine how hedgehog cortex is organized, how much sensory areas overlap, and to compare results with recent findings in other insectivores. Evidence was found for three separate topographically organized somatosensory areas, two visual areas, and a caudolateral auditory area. A medial somatosensory area corresponded to S1, the primary somatosensory area, whereas two lateral areas partially encircled auditory cortex and corresponded to the parietal ventral area (PV) and the secondary somatosensory area (S2). Primary visual cortex (V1) was delineated by a caudomedial cytochrome oxidase dark oval, and a more lateral visual area between V1 and somatosensory cortex corresponded to V2, or area 18. Two patches of corticospinal projecting cells were found primarily overlapping S1 and S2. Some bimodal auditory and somatosensory responses were found in parts of PV and S2, but for the most part, areas had relatively sharp histochemically apparent and physiologically defined borders. The present results indicate that the caudal neocortex of hedgehogs has only a few sensory areas, corresponding to those commonly found in several other small-brained mammals. Hedgehog cortical organization differs significantly in somatotopy, number, and position of fields from that of closely related shrews and moles. Thus, clear specializations occur, even within the order Insectivora.

Classical conditioning modifies cytochrome oxidase activity in the auditory system

The effects of excitatory classical conditioning on cytochrome oxidase activity in the central auditory system were investigated using quantitative histochemistry. Rats in the conditioned group were trained with consistent pairings of a compound conditional stimulus (a tone and a light) with a mild footshock, to elicit conditioned suppression of drinking. Rats in the pseudorandom group were exposed to pseudorandom presentations of the same tone, light and shock stimuli without consistent pairings. Untrained rats in a naive group did not receive presentations of the experimental stimuli. The findings demonstrated that auditory fear conditioning modifies the metabolic neuronal responses of the auditory system, supporting the hypothesis that sensory neurons are responsive to behavioural stimulus properties acquired by learning. There was a clear distinction between thalamocortical and lower divisions of the auditory system based on the differences in metabolic activity evoked by classical conditioning, which lead to an overt learned behavioural response versus pseudorandom stimulus presentations, which lead to behavioural habituation. Increases in cytochrome oxidase activity indicated that tone processing is enhanced during associative conditioning at upper auditory structures (medial geniculate nucleus and secondary auditory cortices). In contrast, metabolic activation of lower auditory structures (cochlear nuclei and inferior colliculus) in response to the pseudorandom presentation of the experimental stimuli suggest that these areas may be activated during habituation to tone stimuli. Together these findings show that mapping the metabolic activity of cytochrome oxidase with quantitative histochemistry can be successfully used to map regional long-lasting effects of learning on brain systems.

Cerebral metabolism following neonatal or adult hemineodecortication in cats: effect on oxidative capacity using cytochrome oxidase histochemistry

In order to determine the degree and extent of changes in cerebral oxidative capacity following cerebral hemineodecortication, adult cats which had undergone surgery early postnatally (mean age: 11.4 days) or during adulthood were studied using cytochrome oxidase histochemistry. A total of 18 animals were employed and 50 brain regions were quantified bilaterally using optical densitometry. Although many subcortical regions exhibiting extensive degenerative features revealed lower levels of cytochrome oxidase (C.O.) activity, this reduction was relatively unremarkable compared to intact controls. Nevertheless, it was interesting that this decrease (down to 66-89%) of normal was more pronounced in neonatal-lesioned cats, reaching significance in a number of ipsilateral thalamic nuclei, compared to adult-lesioned animals (91-100% of normal), suggesting a contribution of glial cells to the density of C.O. staining in the latter cats. Regions of the brain spared from degeneration exhibited a bilateral increase in C.O. activity which may reflect the demands for energy to support the anatomical reorganization which is prevalent in these animals. Surprisingly, such increases were more robust within spared regions of the adult-lesioned brain, reaching significance in four ipsilateral and nine contralateral areas with the density of the reaction attaining levels over 125% of control. This may indicate different demands for oxidative metabolism in the adult-lesioned cats. These results enhance our understanding of the mechanism(s) underlying the greater extent of functional sparing or recovery in cats sustaining injury to the cerebral cortex early vs. late in life. In addition, the findings complement our previous companion report on glucose metabolism supporting the concept of energy compartmentalization, which reflects the dynamic interaction between anatomical and functional changes in this age-at-lesion model of recovery.

Tangential distribution of cytochrome oxidase-rich blobs in the primary visual cortex of macaque monkeys

We studied the tangential distribution of cytochrome c oxidase (CytOx)-rich blobs in four striate cortices of three normal monkeys (Macaca mulatta). The spatial density and cross-sectional area of blobs were analyzed in CytOx-reacted tangential sections of flat-mounted preparations of the striate cortex (V1). Well-delimited CytOx-rich blobs were found in the middle portion of cortical layer III of the V1. Throughout the binocular field representation, the spatial density of blobs was nearly constant with a mean value of four to five blobs per mm2. In the monocular portions of V1, however, blob spatial density diminished. In all cases, the mean cross-sectional area of blobs was constant in the V1. The small variation of CytOx blob topography with visual field eccentricity contrasts with the variation described in previously published material.

Neurofilament architecture of superior and mesial premotor cortex in the human brain

Monoclonal antibody (SMI-32) to neurofilament protein was used in an immunochemical study of the premotor cortex of two human brains in comparison with other architectonic techniques such as Nissi, myelin, cytochrome-oxidase and acetylcholinesterase staining in order to distinguish cortical subdivisions. SMI-32 immunoreactivity technique provides 'neurofilament architecture' patterns specific to area 4, caudal area 6 (area 6c) and rostral area 6 (area 6r). Particularly, the distinction between the two subdivisions of area 6, which is difficult to appreciate with the usual cytochemical or enzyme architectonic techniques, appears very apparent with this technique. Hence, it was possible to localize the topographic boundaries of area 6a alpha and 6a beta of the Vogts on the dorso-lateral convexity and the supplementary motor area and the presupplementary motor area on the mexial wall of the hemisphere.

Effects of intrauterine position on the metabolic capacity of the hypothalamus of female gerbils

The intrauterine position that a rodent fetus occupies relative to members of the same or opposite gender affects both its reproductive physiology and behavior when adult. Cytochrome oxidase histochemistry was used to assess regional differences in the oxidative metabolic capacity of the hypothalamus of female Mongolian gerbils that developed in utero between 2 female fetuses (n = 15) or between 2 male fetuses (n = 14). Cytochrome oxidase reactivity was measured densitometrically by experimenters unaware of subject intrauterine position. Gray-to-white matter ratios of optical density in 11 brain regions were used as a normalized index of metabolic capacity. Significant group differences in the metabolic capacity of the medial and the posterior parts of the anterior hypothalamus were revealed. Females that developed in utero between 2 male fetuses showed significant increases (19-22%) in cytochrome oxidase reactivity in these brain regions compared to that in females that developed between 2 female fetuses. The medial part of the anterior hypothalamus contributes to copulatory behavior, whereas the posterior part of the anterior hypothalamus may be involved in the control of pituitary gonadotropin secretion. Both these functions are influenced by intrauterine position during fetal life. To our knowledge, this is the first demonstration of metabolic changes in hypothalamic areas of the adult related to the differences in intrauterine position.

Quantitative cytochemistry of cytochrome oxidase and cellular morphometry of the human inferior colliculus in control and Alzheimer's patients

Quantitative cytochemistry of cytochrome oxidase (C.O.) was implemented in human brains to measure C.O. activity in the 3 main divisions of the inferior colliculus (IC): central (ICC), dorsal (ICD), and external (ICE). Units of C.O. activity (micromol/min/g tissue wet weight) were quantified in cellular compartments (overall average, neuropil, perikaryon, and dendrites) at the light microscope level using microdensitometry calibrated with C.O. activity standards measured spectrophotometrically. In a non-AD (Alzheimer's disease) control group (mean age = 79.6 +/- 3.1 years, postmortem time = 6.9 +/- 1.6 h), the ICC and ICD demonstrated higher (p < 0.008) overall average activities (mean = 183.40 +/- 18.7 and 184.98 +/- 45.1 units, respectively) relative to the ICE (56.46 +/- 15.9 units). Comparison of cellular morphometry (soma and nucleus area, perimeter, and diameter) revealed that the ICC contained cells of significantly larger soma size than in both the ICD and ICE (p < 0.002). The distribution of soma diameters in the ICC of controls showed a clear bimodality, enabling the typing of the cells into larger and smaller than average soma diameter. Brains from patients with Alzheimer's disease (AD; mean age = 78.3 +/- 2.9 years, postmortem time = 6.5 +/- 1.3 h) were compared with the non-AD controls. Significant group differences were found only in the large cells of the ICC. The AD large cells showed a decrement in C.O. activity relative to the corresponding controls in overall average activity (p < 0.032) and in peak activity of neuropil near the soma (p < 0.012). These findings provide the first quantitative cytochemical data of C.O. activity in humans. They also suggest that cellular alterations in C.O. metabolism in AD affect predominantly specific groups of larger projection neurons while neighboring neurons are spared.

Role of directed growth and target selection in the formation of cortical pathways: prenatal development of the projection of area V2 to area V4 in the monkey

In experiments combining retrograde tracers and histochemistry, we have looked at the prenatal development of the cortical pathway linking areas V2 and V4. Transient expression of acetylcholinesterase in fetal area V2 reveals the separate compartments that project to V4 (temporal directed pathway) and V5 (parietal directed pathway). During early stages of pathway formation, V2 neurons projecting to area V4 are clustered in the appropriate compartments. During the phase of rapid axonal growth, there is a selective increase of connections originating from the appropriate compartments leading to a strongly clustered organization at the peak of connectivity. During this phase, injections involving the white matter also showed clustering, but this was somewhat reduced in comparison to that of gray matter injections. The growth phase is followed by an elimination phase during which there is a tendency for a preferential loss of intercluster connections, which may sharpen the early formed pattern. These results demonstrate the primary role of axonal guidance and target recognition mechanisms followed by a limited extent of selective elimination during the formation of functional cortical pathways in the primate isocortex. Compared to previous findings, these results suggest that the developmental restriction of callosal connections is not a universal model of cortical development. In the present report, the directed growth and early specification of feed-forward connections contrast with the prolonged remodelling of monkey feedback projections, suggesting two distinct developmental strategies of pathway formation in the monkey.

Quantitative aspects of synaptogenesis in the rat barrel field cortex with special reference to GABA circuitry

The postnatal establishment of cortical connectivity was studied by estimating the number (numerical density, synapse-to-neuron ratio, and total number) of the overall synaptic population and its distribution into gamma-aminobutyric acid (GABA)-immunopositive and GABA-immunonegative synaptic contacts in the developing rat somatosensory cortex. These numerical data were obtained using the unbiased disector method in combination with GABA postembedding immunocytochemistry. The numerical density of both synaptic populations was low in the early postnatal period (postnatal days 5 and 10, P5, P10) after which it abruptly increased between P10 and P15 to approach adult values. However, since cortical volume continues to increase after this age, the number of synapses per neuron and the total number of synapses reached adult values only by P30. There was no evidence of overproduction of either GABA or non-GABA synapses. Direct comparison between the two synaptic populations revealed a similar developmental pattern with the exception of the period around P20 when the production of GABA synapses slowed down. Thus, while the formation of non-GABA synapses proceeded in a continuous manner throughout the first month of life, GABA synapse production was accomplished in two consecutive waves. We suggest that the second delayed wave of GABA synapse formation is related to the great developmental plasticity of the cortical inhibitory system.

Laminar and columnar patterns of geniculocortical projections in the cat: relationship to cytochrome oxidase

We examined the laminar and columnar arrangement of projections from different layers of the lateral geniculate nucleus (LGN) to the visual cortex in the cat. In light of recent reports that cytochrome oxidase blobs (which in primates receive specific geniculate inputs) are also found in the visual cortex of cats, the relationship between cytochrome oxidase staining and geniculate inputs in this species was studied. Injections of wheat germ agglutinin-conjugated horseradish peroxidase were made into the anterior "genu" of the LGN, where isoelevation contours of the geniculate layers are distorted due to the curvature of the nucleus. Consequently, anterograde labeling from the various LGN layers was topographically separated across the surface of the cortex, and labeling in a particular isoelevation representation of the cortex could be associated with a specific layer of the LGN. Labeling from the A layers, which contain X and Y cells, was coextensive with layers 4 and 6 in both area 17 and area 18, as previously reported. Labeling from the C layers, which contain Y and W cells, occupied a zone extending from the 4a/4b border to part way into layer 3 in area 17. The labeling extended throughout layer 4 in area 18. There was also labeling in layer 5a and layer 1 in both area 17 and area 18. Except in layer 1, labeling from the C layers was patchy. In the tangential plane, adjacent sections stained for cytochrome oxidase showed that the patches of labeling from the C laminae aligned with the cytochrome oxidase blobs. The cytochrome blobs were visible in layers 3 and 4a, but not in layer 4b in both areas 17 and 18. These results suggest that W cells project specifically to the layer 3 portion of the blobs, while Y cells, at least those of the C layers, project specifically to the layer 4a portion of the blobs in area 17. The heavy synaptic drive of the Y cells is probably the cause of the elevated metabolism, and thus, higher cytochrome oxidase activity, of the blobs.

Synaptophysin immunoreactivity and distributions of calcium-binding proteins highlight the functional organization of the rat's dorsal column nuclei

The mammalian dorsal column nuclei (DCN) are principally composed of the cuneate (CN) and gracile (GN) nuclei. Data presented here support previously published anatomical and functional evidence that the longitudinal organization of the CN and GN reflect the complex role of the DCN in somatosensory processing. The CN is organized longitudinally into three parts. Within the middle portion of this nucleus, primary afferent projections and cuneothalamic cells are concentrated. Although traditional cytoarchitectonic analyses had failed to detect this tripartite organization in rats, we found evidence for it, with a functional middle region, extending approximately 0.2-0.9 mm caudal to the obex, characterized by precise somatotopy of primary afferent terminations and corresponding somatotopy of cytochrome oxidase (CO) blotches. Additional evidence is presented here consistent with a functionally distinct middle region within the rat's CN: (1) patches of dense synaptophysin (a synaptic-vesical-associated protein)-immunoreactivity (SYN-IR) are limited to the middle CN region, coincident with the dense CO blotches; (2) neurons immunoreactive for the calcium-binding proteins calbindin-D28 (CB), calretinin (CR) and parvalbumin (PV) are concentrated in the middle CN region. Furthermore, in adult rats subjected to perinatal forepaw removal, (1) the patterns of SYN-IR in the middle region of the CN are disrupted, as had previously been shown for the patterns of CO blotches; (2) in contrast, however, distributions of CN cells with PV-, CB- and CR-IR are unaffected. Evidence for a tripartite division in the GN is also presented, based on the distributions of cells with PV-, CB- and CR-IR.

An anatomical substrate for experience-dependent plasticity of the rat barrel field cortex

The objective of this study was to examine the influence of sensory experience on the synaptic circuitry of the cortex. For this purpose, the quantitative distribution of the overall and of the gamma-aminobutyric acid (GABA) population of synaptic contacts was investigated in each layer of the somatosensory barrel field cortex of rats which were sensory deprived from birth by continuously removing rows of whiskers. Whereas there were no statistically significant changes in the quantitative distribution of the overall synaptic population, the number and proportion of GABA-immunopositive synaptic contacts were profoundly altered in layer IV of the somatosensory cortex of sensory-deprived animals. These changes were attributable to a specific loss of as many as two-thirds of the GABA contacts targeting dendritic spines. Thus, synaptic contacts made by GABA terminals in cortical layer IV and, in particular, those targeting dendritic spines represent a structural substrate of experience-dependent plasticity. Furthermore, since in this model of cortical plasticity the neuronal receptive-field properties are known to be affected, we propose that the inhibitory control of dendritic spines is essential for the elaboration of these functional properties.

Regional brain effects of sodium azide treatment on cytochrome oxidase activity: a quantitative histochemical study

The objective of the present study was to determine if regional variation in brain cytochrome oxidase activity was observed following systemic administration of sodium azide. An image analysis system calibrated with internal standards of known cytochrome oxidase activity was used to quantify cytochrome oxidase in histochemically stained brain sections. Rats receiving chronic infusion of sodium azide (400 micrograms/hr), which were sacrificed after two weeks, showed a substantial decrease in brain cytochrome oxidase activity over those infused with saline. All of the 22 regions sampled from telencephalic, diencephalic, and mesencephalic levels, showed a significant activity reduction which ranged between 26% and 37%. The regions that appeared significantly more vulnerable to the sodium azide effects were the mesencephalic reticular formation and the central amygdala, which displayed the largest decrease in activity. In addition, interregional correlations of activity showed a deeply modified pattern of correlative metabolic activity between hippocampal, amygdaloid and cortical areas after azide treatment. The regional effects found were consistent with azide-induced learning and memory dysfunctions.

Time course of the neuroprotective effect of transplantation on quinolinic acid-induced lesions of the striatum

Injection of quinolinic acid in the rat striatum mimics neurochemical changes observed in Huntington's disease. We previously demonstrated that intrastriatal transplantation of fetal striatum or gelfoam protects against toxicity induced by a subsequent intrastriatal injection of quinolinic acid performed one week later. Herein, we examined whether fetal striatum or sham transplantation provides protection against quinolinic acid that lasts up to four weeks. Intrastriatal quinolinic acid injection produces neuronal loss and gliosis in Nissl staining, loss of cytochrome oxidase histochemical staining, decrease in autoradiographic binding of [3H]SCH 23390-labeled dopamine D1 and [3H]CGS 21680-labeled adenosine A2 receptors, and increase in autoradiographic binding of [3H]PK 11195-labeled peripheral benzodiazepine binding sites. None of these changes was observed in rats transplanted with fetal striatum one, two or four weeks before quinolinic acid injection. In animals transplanted with fetal striatal tissue, Nissl staining showed healthy grafts located in normal appearing striata. Although sham transplantation performed one week before quinolinic acid injection also protected against histological, histochemical and binding changes, sham transplantation performed two or four weeks before quinolinic acid injection was less effective in attenuating quinolinic acid-induced striatal toxicity. Thus, sham transplantation provides transient protection against quinolinic acid-induced striatal toxicity, whereas implantation of tissue such as fetal striatum seems to be required for long-lasting protection. Our study suggests that intracerebral transplantation may also act through other mechanisms than restoration of deficient neurotransmitters or damaged pathways, a finding which may have significant clinical implications in assessing the potential benefit of this approach for the treatment of neurodegenerative disorders such as Huntington's disease.

Neonatal sensory deprivation induces selective changes in the quantitative distribution of GABA-immunoreactive neurons in the rat barrel field cortex

Modified activity of the rat vibrissae from birth to adulthood induces profound alterations of the responsiveness and selectivity of neurons in the contralateral somatosensory barrel field cortex of adult rats. Because these functional properties are under the control of the intracortical inhibitory mechanisms, we investigated the effects of unilateral removal of face pad vibrissae on the quantitative distribution of intracortical gamma-aminobutyric acid (GABA)-immunoreactive neurons in the rat contralateral and ipsilateral barrel field cortices. This distribution was then compared to a population of control animals. For the entire cortical depth, no significant changes in the density (7,700/mm3 vs. 7,400/mm3), proportion (13.6% vs. 14.4%), or size (11.7 microns vs. 12.5 microns) of GABA-immunoreactive neurons were found in the left contralateral vs. the right ipsilateral barrel field cortex. However, in cortical layer IV, contralateral to the deprivation, the density and proportion of GABA-immunoreactive neurons were lower (6,300/mm3 vs. 13,900/mm3, 6.0% vs. 13.6%; P < 0.01), and these neurons were larger (mean projected height of 15.1 microns vs. 10.8 microns; P < 0.01) than in the ipsilateral barrel field cortex, suggesting a specific loss of GABA expression in a subpopulation of small intracortical neurons. In addition to changes in the contralateral layer IV, GABA-immunoreactive neurons located in the ipsilateral granular layer were also affected. Indeed, their numerical density (13,900/mm3) and proportion (13.6%) were higher (P < 0.01) than in both hemispheres of control animals (average of 10,050/mm3 and 9.4%). On the other hand, GABA-immunoreactive neurons in the ipsilateral layer V were less numerous (5,600/mm3, 15.0%) than in both sides of the controls (average of 10,300/mm3, 22.0%; P < 0.01). Thus, our results show that a unilateral sensory deprivation induces highly selective changes in the intracortical GABA inhibitory circuitry of both hemispheres. These changes are located directly at the input of thalamic afferents and at an output layer of corticofugal and commissural axons and could result in a profound reorganization of the excitatory and inhibitory drives of both sides of the sensory-deprived barrel field cortex.

Effect of vestibular nerve section on cytochrome oxidase activity in the vestibular ganglion cells of the squirrel monkey

Cytochrome oxidase (CO) activity of the vestibular ganglion cells of the squirrel monkey was demonstrated histochemically under normal and experimental conditions. Under general anesthesia, right vestibular nerve section was performed on adult squirrel monkeys between the vestibular ganglion and brain stem. The left side was left intact and was used as a within-animal normal control. One squirrel monkey that did not undergo vestibular nerve section was also included in the normal group. Following a survival period of seven months, neurons in the vestibular ganglion of both sides were examined. In the normal control sides, a significant negative correlation between the size of the neuron and its optical density for CO stain was observed. Many neurons in the vestibular ganglion survived after vestibular nerve section, but their cell sizes and optical densities of CO stain decreased compared with those of the control side.

Postnatal development of GABA neurons in the rat somatosensory barrel cortex: a quantitative study

As an estimate of the numerical importance of GABA-containing neurons during development, their quantitative distribution was analysed in the primary somatosensory cortex of rats between postnatal days (P) 5 and 60, using the dissector method and GABA postembedding immunocytochemistry. In relation to the overall number of neurons in the barrel field cortex, the proportion of GABA neurons showed an early significant decrease between P5 and P10 from 14 to 11%, most likely due to termination of transient expression of GABA by some cells. It then remained stable until P20, after which it started slowly but steadily to increase, reaching 14% of the total at P60. The absolute number of GABA neurons also increased by nearly 50% during that period, whereas the number of all neurons remained constant. These changes are seemingly due to a subpopulation of neurons, shown to be of small size, which express GABA late in development. Thus, anatomical adjustments of the cortical GABA system may be observed at least until the end of the second postnatal month, reflecting both delayed maturation and adaptation of this inhibitory circuitry. We suggest the existence of three subpopulations of cortical GABA neurons depending on the time of onset and the regulation of their GABA expression: (i) neurons which express GABA before completion of migration and thus provide for its neurotrophic influence, (ii) neurons which express GABA immediately after completion of migration and build up the cortical inhibitory circuitry, and (iii) neurons which express GABA later in development and represent a substrate of experience-dependent plasticity.