Enkephalin-like immunoreactivity in the cat superior colliculus: distribution, ultrastructure, and colocalization with GABA

The distribution of enkephalin (ENK) immunoreactivity has been examined in the cat superior colliculus (SC) by means of light and electron microscope immunocytochemistry. The antisera were directed against leucine enkephalin but also recognized methionine enkephalin. Colocalization of ENK with gamma aminobutyric acid (GABA) was studied with a two-chromagen double-labeling technique. Enkephalin antiserum labeling was highly specific. Dense neuropil labeling was found only in a thin band 75-100 microns wide within the upper superficial gray layer of SC. Negligible neuropil labeling was seen deeper, except for patches of label within the intermediate gray layer. Intensely labeled neurons also had a specific distribution. Forty-seven percent were located within the upper 200 microns of SC, 40% within the deep superficial gray layer, 11% in the optic layer, and only 2% below that layer. Almost all ENK-labeled cells were small (mean area of 117 microns2). Some of these had horizontal fusiform cell bodies and horizontally oriented dendrites. Others had small round somata and thin, obliquely oriented dendrites. In double-labeling experiments, 18% of anti-ENK-labeled cells were also immunoreactive for GABA. Four distinct types of ENK-labeled profile were identified with the electron microscope. Presynaptic dendrites (PSD) with loose accumulations of synaptic vesicles were densely labeled with the antiserum. Conventional dendrites were also labeled. Both types of labeled profile received input from unlabeled synaptic terminals, including those from the retina that contained pale mitochondria and round synaptic vesicles and formed asymmetric synaptic contacts. Retinal terminals were never labeled with the antisera. However, some axon terminals with round synaptic vesicles, dark mitochondria, and symmetric synaptic densities were labeled by the antisera, as were some thinly myelinated axons. These results show that there is a small population of enkephalinergic neurons in the cat SC, some of which also contain GABA. Because not all cells with identical morphologies were double labeled, it appears that neurons of like morphology are chemically heterogeneous.     

Ultrastructural organization of GABA in the rabbit superior colliculus revealed by quantitative postembedding immunocytochemistry

We have studied the organization of gamma-aminobutyric acid (GABA)ergic profiles in the superior colliculus of the rabbit to determine whether the synaptic types found in cat and monkey also exist in a mammalian species whose visual system has a different organization. Ultrastructure of GABAergic profiles was examined by use of a polyclonal antibody to GABA and quantitative postembedding immunocytochemistry. Three distinct types of vesicle-containing profiles were labeled by the GABA antibody in the rabbit superior colliculus. One type was a putative presynaptic dendrite (PSD profile) that received synaptic input from other profiles and contained pleomorphic synaptic vesicles scattered throughout the profile. These PSD profiles frequently received retinal input and formed dendrodendritic synapses. A second type of profile was a large caliber dendrite, often horizontal in orientation (H profile), that had one or more discrete clusters of pleomorphic synaptic vesicles at sites of synaptic contact with conventional dendrites. These H profiles received few synaptic contacts. A third profile type was a putative axon terminal (F profile) with smaller, more flattened synaptic vesicles that densely and uniformly filled the profile. Quantitative analysis of gold particle density revealed that F profiles had a significantly higher gold particle density (14.3/ μm²) than did PSD or H profiles (10.4 and 10.2/ μm²), suggesting that GABAergic profile types contain different concentrations of GABA. The vesicle density of these profile types also differed, but no obvious relationship between vesicle and particle distributions was observed. We conclude that the profiles labeled by GABA in rabbit superior colliculus are similar to those in cat and monkey and must represent a phylogenetically conserved organization common to many mammals, and that particle density analysis of postembedding immunocytochemistry can distinguish different GABAergic profile types.     

Two types of GABA-accumulating neurons in the superficial gray layer of the cat superior colliculus

Two types of neuron in the upper superficial gray layer of the cat superior colliculus accumulated exogenous ³H-gamma-aminobutyric acid intensely. The first type was a horizontal cell with a fusiform cell body, horizontal dendrites, a low synaptic density, but a high percentage of cortical synaptic contacts. This cell had presynaptic dendrites. The second type was a granule cell (type A) with a small round cell body, thin and obliquely oriented dendrites, a moderate synaptic density, and few cortical synaptic contacts. These two types differed in size, shape, dendritic morphology, and patterns of synaptic input. They likely participate in different inhibitory mechanisms. Four types of unlabeled neurons were also identified. Type B granule cells were found only within the upper subdivision of the superficial gray layer. They had moderate-sized cell bodies, a high synaptic density, and numerous somatic spines. A third type of granule cell (type C) was found only in the deep subdivision of the superficial gray. This type had a low synaptic density and spines that contained synaptic vesicles. Vertical fusiform and stellate forms were also found. We conclude that at least six types of neurons populate the upper superficial gray layer of the cat superior colliculus.     

Ultrastructural organization of transmitters in the cat lateralis medialis-suprageniculate nucleus of the thalamus: an immunohistochemical study

The lateralis medialis-suprageniculate nuclear (LM-Sg) complex of the cat's posterior thalamus receives a rather wide variety of inputs from diverse cortical and subcortical areas. Previous ultrastructural studies of this nucleus demonstrated the presence of four types of vesicle-containing profiles and characterized some of these as gamma-aminobutyric acid (GABA)-containing terminals (Norita and Katoh [1987] J. Comp. Neurol. 263:54-67; Norita and Katoh [1988] Prog. Brain Res. 75:109-118). The present study has extended these observations by examining the immunoreactivity (ir) of LM-Sg, with antibodies raised against aspartate (Asp), glutamate (Glu), GABA, the acetylcholine (ACh) marker, choline acetyltransferase (ChAT), and substance P (SP), by using light and electron microscopy. Neuronal somata immunopositive for the excitatory amino acids (EAAs) Asp and Glu, were of medium size. EAA-ir terminals also were of medium size and contained round synaptic vesicles; they made asymmetrical synaptic contacts with dendritic profiles. Neuronal somata immunopositive for GABA were small. GABA-positive terminals also were small and contained pleomorphic synaptic vesicles; they formed symmetrical synaptic contacts with dendritic profiles. No neurons immunolabeled for ChAT were found. Terminals immunopositive for ChAT were small and contained round synaptic vesicles; these made symmetrical synaptic contacts, asymmetrical synaptic contacts, or both, of the en passant type with dendritic profiles. SP-immunolabeled neuronal somata were not found. Immunolabeled terminals were small, contained round synaptic vesicles, and made asymmetrical synaptic contacts with dendritic profiles. ChAT-ir and SP-ir axon terminals were not expressed evenly within LM-Sg. This difference in distribution suggests that within the LM-Sg, there may be a difference in specific sensory processing functions which correlate with transmitter type.     

Postembedding immunocytochemistry demonstrates directly that both retinal and cortical terminals in the cat superior colliculus are glutamate immunoreactive

Although the excitatory neurotransmitter glutamate is known to be present in the cat superior colliculus (SC), the types of synapses that contain glutamate have not been examined. We, therefore, studied the ultrastructure of synaptic profiles labeled by a glutamate antibody by using electron microscopic postembedding immunocytochemistry. In addition, unilateral aspiration lesions of areas 17–18 were made at 5–28 days before death in order to determine whether degenerating terminals from visual cortex were glutamate immunoreactive (Glu-ir). Three types of axon terminal were glu-ir: 1) those containing large, round synaptic vesicles and pale mitochondria, characteristic of retinal terminals (RT profiles); 2) those containing small, round synaptic vesicles and dark mitochondria (RSD profiles); and 3) those containing large, round synaptic vesicles and dark mitochondria (RLD profiles). Measures of mean gold particle density revealed that RT, RSD, and RLD profiles had similar average grain densities (11.3–12.7 particles/unit area). Other labeled profile types included cell bodies, large-calibre dendrites, and myelinated axons. Axon terminals containing flattened synaptic vesicles and vesicle-containing presynaptic dendrites, both of which contain γ-aminobutyric acid (GABA), had many fewer gold particles (3.6 and 4.8 mean particles/unit area, respectively). Following unilateral removal of visual cortex, normal RSD terminals were observed infrequently in the SC ipsilateral to the lesion. Synaptic terminals in the initial stages of degeneration were heavily labeled by the glutamate antibody, as were axon terminals and myelinated axons undergoing hypertrophied or neurofilamentous degeneration. These results show that both major sensory afferents to the superficial layers of cat SC contain glutamate—RT terminals from the retina and RSD terminals from visual cortex. The origin of RLD terminals is unknown. © 1996 Wiley-Liss, Inc.     

Variations in the retinal synapses of the cat superior colliculus revealed using quantitative electron microscope autoradiography

This study has examined the retinal synapses of the cat superior colliculus using electron microscope autoradiography and morphometric techniques. The depth of each retinal synapse was measured using a computer-based EM plotter. The area, perimeter, and synapse contact density of selected synapses were calculated using a computer-based digitizer. Pale mitochondria were found to be an accurate cytological marker of retinal input to the colliculus. Fifty-eight percent of pale mitochondria terminals were labeled in the colliculus contralateral to eye injections. Ten percent of pale mitochondria terminals were labeled in the ipsilateral colliculus. A few labeled terminals contained dark mitochondria. The labeled retinal terminals in the contralateral colliculus were concentrated in a 60 μm wide dense band at the top of the superficial gray layer. They were also found within the deep superficial gray and upper optic layers. This distribution corresponded exactly to a larger population of pale mitochondria terminals. The cross-sectional area and synaptic contact density of selected pale mitochondria terminals varied with depth. Within the upper superficial gray, the terminals were small (mean area= 1.26 μ²) and high contact densities (mean= 0.25 per μm). These small terminals were also found deeper within the colliculus. Below the upper subdivision of the superficial gray, some labeled terminals were much larger and had lower contact densities. These results suggest there may be two subpopulations of retinal terminal in the cat superior colliculus: (1) small terminals with scalloped contours and complex synaptic relationships which may correspond to W-type input; and (2) larger terminals with simpler synaptic relationships which are distributed deeper and may correspond to Y-type input.     

Direct synaptic connections of axons from superior colliculus with identified thalamo-amygdaloid projection neurons in the rat: Possible substrates of a subcortical visual pathway to the amygdala

The aim of the present study was to identify synaptic contacts from axons originating in the superior colliculus with thalamic neurons projecting to the lateral nucleus of the amygdala. Axons from the superior colliculus were traced with the anterograde tracers Phaseolus vulgaris leucoagglutinin or the biotinylated and fluorescent dextran amine “Miniruby.” Thalamo-amygdaloid projection neurons were identified with the retrograde tracer Fluoro-Gold. Injections of Fluoro-Gold into the lateral nucleus of the amygdala labeled neurons in nuclei of the posterior thalamus which surround the medial geniculate body, viz. the suprageniculate nucleus, the medial division of the medial geniculate body, the posterior intralaminar nucleus, and the peripeduncular nucleus. Anterogradely labeled axons from the superior colliculus terminated in the same regions of the thalamus. Tecto-thalamic axons originating from superficial collicular layers were found predominantly in the suprageniculate nucleus, whereas axons from deep collicular layers were detected in equal density in all thalamic nuclei surrounding the medial geniculate body. Double-labeling experiments revealed an overlap of projection areas in the above-mentioned thalamic nuclei. Electron microscopy of areas of overlap confirmed synaptic contacts of anterogradely labeled presynaptic profiles originating in the superficial layers of the superior colliculus with retrogradely labeled postsynaptic profiles of thalamo-amygdaloid projection neurons. These connections may represent a subcortical pathway for visual information transfer to the amygdala. J. Comp. Neurol. 403:158–170, 1999. © 1999 Wiley-Liss, Inc.     

Light microscopic and ultrastructural analysis of GABA-immunoreactive profiles in the monkey spinal cord

It is hypothesized that terminals containing gamma-aminobutyric acid (GABA) participate in presynaptic inhibition of primary afferents. To date, few convincing GABA-immunoreactive (GABA-IR) axo-axonic synapses have been demonstrated in support of this theory. The goal of this study is to document the relationship between GABA-IR profiles and central terminals in glomerular complexes in lumbar cord of the monkey (Macaca fascicularis). In addition, the relationship between GABA-IR profiles and other neural elements are analyzed in order to better understand the processing of sensory input in the spinal cord. GABA-IR cell bodies were present in Lissauer's tract (LT) and in all laminae in the spinal gray matter except lamina IX. GABA-IR fibers and terminals were heavily concentrated in LT; laminae I, II, and III; and present in moderate concentration in the deeper laminae of the dorsal horn, ventral horn (especially in association with presumed motor neurons), and lamina X. Electron microscopic analysis confined to LT and laminae I, II, and III demonstrated GABA-IR cell bodies, dendrites, and myelinated and unmyelinated fibers. GABA-IR cell bodies received sparse synaptic input, some of which was immunoreactive for GABA. The majority of the synaptic input to GABA-IR neurons occurred at the dendritic level. Furthermore, the presence of numerous vesicle-containing GABA-IR dendrites making synaptic interactions indicated that GABA-IR dendrites also provided a major site of output. Two consistent arrangements were observed in laminae I-III concerning vesicle-containing GABA-IR dendrites: 1) they were often postsynaptic to central terminals and 2) they participated in reciprocal synapses. The majority of GABA-IR axon terminals observed contained round clear vesicles and varying numbers of dense core vesicles. Only on rare occasions were GABA-IR terminals with flattened vesicles observed. GABA-IR terminals were not observed as presynaptic elements in axo-axonic synapses; however, on some occasions, GABA-IR profiles presumed to be axon terminals were observed postsynaptic to large glomerular type terminals. Our findings suggest that a frequent synaptic arrangement exists in which primary afferent terminals relay sensory information into a GABAergic system for further processing. Furthermore, GABA-IR dendrites appear to be the major source of input and output for this inhibitory system. The implications of this GABAergic neurocircuitry are discussed in relation to the processing of sensory input in the superficial dorsal horn and in terms of mechanisms of primary afferent depolarization (PAD).     

Projections to the inferior colliculus from the anteroventral cochlear nucleus in the cat: possible substrates for binaural interaction

The projections to the inferior colliculus of the cat are shown in autoradiographs after injections of 3H-amino acids into the anteroventral cochlear nucleus and anterograde axonal transport. Labeled bands of axons are seen in the central nucleus of the inferior colliculus, parallel to the fibrodendritic laminae, and in layers 3 and 4 of the dorsal cortex. A bilateral projection to the lateral, low-frequency part of the inferior colliculus is observed. In contrast, the more ventromedial, mid- and high-frequency parts receive only a contralateral input. The projections from the cochlear nucleus to both the contralateral midbrain and bilaterally to the superior olivary complex appear to be tonotopically organized. After HRP injections in the inferior colliculus, small numbers of stellate neurons are labeled in the lateral and ventral low-frequency parts of the anteroventral cochlear nucleus on the ipsilateral side. EM autoradiographs show labeled axonal endings from both sides of the anteroventral cochlear nuclei are present in the same proportion in pars lateralis. Axonal endings from either cochlear nucleus have small, round synaptic vesicles and make asymmetric synaptic contacts on dendrites. Axons from the contralateral side also make axosomatic contacts on large disc-shaped or stellate cells. Neurons from the ipsilateral anteroventral cochlear nucleus apparently make more synaptic endings per cell as compared to neurons from the contralateral side. Together, bilateral inputs from the anteroventral cochlear nucleus can account for a third of the endings with round synaptic vesicles in pars lateralis of the central nucleus. Morphological similarities among the ascending inputs to the inferior colliculus are discussed. Both direct circuits from the cochlear nucleus to the inferior colliculus and indirect circuits via the superior olivary complex or lateral lemniscus may display banding patterns, nucleotopic organization, or differential synaptic organization. The direct inputs from the anteroventral cochlear nucleus to the colliculus may influence binaural interactions which occur in the superior olivary complex. In addition, direct inputs may create new binaural responses in the inferior colliculus that are independent of lower centers.     

The terminations of corticospinal tract axons in the macaque monkey

This study examined the corticospinal tract in monkey by utilizing the anterograde transport of wheat germ lectin conjugated to horseradish peroxidase (WGA HRP) at the light microscopic level and the axonal transport of 3H-proteins with both light and electron microscopic autoradiographic techniques. The animals survived 3-9 days after the injections of 3H-leucine or 3H-leucine/WGA HRP into either motor or sensory cortices. With the laminar schema of Rexed as a guide to the layers of the spinal gray matter, qualitative and quantitative analyses of labeled projections of the corticospinal tract (CST) were made. With the light microscope, axons from the sensory cortex labeled with WGA-HRP could be observed in the contralateral spinal gray from lamina I to the border of laminae VI/VII, the heaviest distribution being located in medial III-VI. There was a small ipsilateral projection to V and VI. With 3H label, laminae I and II revealed few overlying silver grains; many grains overlay laminae III-VI. Projections from the motor cortex labeled with either WGA-HRP or 3H extended from the contralateral laminae III/IV border into the motor nucleus (lamina IX) and were seen to be somewhat more dense in the lateral areas of the spinal gray. The motor cortex projected heavily to ipsilateral VIII, and in sparse amounts to ipsilateral V and VI. Electron microscopy of radioactive axons from the sensory cortex to dorsal horn revealed many radioactive myelinated fibers and some labeled non-myelinated axons. Labeled terminals contacted medium to small dendrites; there were a few labeled C-type profiles in glomeruli and occasional axo-axonal or dendro-axonal contacts, the labeled cortical axons being the postsynaptic structure. In ventral horn following motor cortex injections, the labeled axons were all myelinated. The synaptic contacts were found on small, medium, and large proximal dendrites as well as on cell bodies. Labeled terminals which formed the central element in glomeruli were also seen in this region. Most of the labeled corticospinal terminals in dorsal and ventral horn contained rounded vesicles, but a significant number revealed pleomorphic vesicles. The relationship of these morphological findings to physiological studies of the CST is presented.     

Immunocytochemical localization of GABA in the cochlear nucleus of the guinea pig

The immunocytochemical distribution of gamma-aminobutyric acid (GABA) was determined in the cochlear nucleus of the guinea pig using affinity-purified antibodies made against GABA conjugated to bovine serum albumin. Light microscopic immunocytochemistry shows immunoreactive puncta, which appear to be GABA-positive presynaptic terminals, distributed throughout the cochlear nucleus. In the ventral cochlear nucleus, these puncta are often found around unlabeled neuronal cell bodies. While occasional labeled small cells are found in the ventral cochlear nucleus, most GABA-immunoreactive cell bodies are present in the superficial layers of the dorsal cochlear nucleus. Based on size and shape, immunoreactive cells in the dorsal cochlear nucleus are divided into 3 classes: medium round cells with diameters averaging 16 microns, small round cells with average diameters of 9 microns and small flattened cells with major and minor diameters averaging 11 and 6 microns, respectively. Labeled fusiform and granule cells are not seen. A similar distribution of label was seen using antibodies against glutamic acid decarboxylase. Electron microscopic immunocytochemistry of the anteroventral cochlear nucleus shows GABA immunoreactive boutons containing oval/pleomorphic synaptic vesicles on cell bodies and dendrites. Other major classes of terminals, including those with small round, large round and flattened synaptic vesicles are unlabeled.     

Superior colliculus neurons which project to the cat lateral posterior nucleus have varying morphologies

We have studied the laminar position, morphology, and synaptic relationships of neurons in the cat superior colliculus which project to the interadjacent division of the lateral posterior nucleus (LPi), using the retrograde transport of horseradish peroxidase. The neurons which project to LPi are remarkably varied in depth, size, morphology, and synaptic density and appear to consist of at least four cell types. Labeled cells were found laminae. Forty-seven percent were found in the superficial gray layer (50-550 micrometer), all but a few within its deep subdivision. Forty-seven percent were located in the optic layer (550-1,200 micrometer), the majority of these being within the upper one-half of the layer Seven percent were found in the intermediate and deep gray layers (below 1,200 micrometer). Cell body area varied widely, ranging from 37 to 768 micrometer 2 (mean of 243 micrometer2). Based on cell size, shape, and dendritic field orientation, we identified four distinct cell morphologies which were labeled. Thirty-five percent were stellate, 32% were vertical fusiform 19% were granule, and 12% were horizontal cells. Electron microscope analysis confirmed that neurons projecting to the lateral posterior nucleus are a morphologically diverse group. A sample of 71 labeled cells varied significantly in density of synaptic input as well as in size, shape, depth, dendritic distribution, and cytology.     

Ultrastructural study of large efferent neurons in the superior colliculus of the cat after retrograde labeling with horseradish peroxidase

The ultrastructure of large neurons in the stratum griseum intermedium of the cat superior colliculus was examined following injections of horseradish peroxidase (HRP) into the dorsal tegmental decussation. Four HRP-labeled cells were selected, and the synaptology of their cell bodies and selected regions of proximal and distal dendrites was examined. The four neurons represent four morphologically distinct cell types: multipolar radiating, tufted, large vertical, and medium-sized trapezoid radiating. These four neurons correspond with cell types X1, X2, X3, and T1 respectively, according to the recent classification of neurons in the superior colliculus of the cat by Moschovakis and Karabelas (J. Comp Neurol. 239:276-308, '85). The three X type neurons are similar in having 83% of their somata and over 74% of their proximal dendrites contacted by synaptic profiles. Distal dendrites of the X type neurons, however, receive fewer synaptic contacts. In contrast, in the T1 cell, only 69% of the soma membrane is contacted by synaptic profiles, and the synaptic coverage on proximal and distal dendrites does not vary much from this. Of the eight types of synaptic terminals described in the stratum griseum intermedium of the cat superior colliculus by Norita (J. Comp. Neurol. 190:29-48, '80), only five are found in contact with the X and T type efferent neurons described here. There are some regional differences in terminal distribution, although each terminal is represented on each cell. Type III terminals (small, contain mostly pleomorphic vesicles, and make symmetrical contacts) are the most abundant on cell bodies and dendrites of all four cell types. Terminal types II (medium-sized, containing round and flattened vesicles, and making asymmetrical contacts), and IV (medium to large in size, containing flattened vesicles, and making symmetrical contacts) are well represented. In general, terminal types I (small, containing densely packed round vesicles, and making asymmetrical contacts) and VI (small and irregular in shape, containing flattened vesicles and making symmetrical contacts) are found infrequently. The identity of different types of synaptic terminal is discussed.     

Organization and synaptic connections of cholinergic fibers in the cat superior colliculus

The cat superior colliculus (SC) receives a dense cholinergic input from three brainstem nuclei, the pedunculopontine tegmental nucleus, the lateral dorsal tegmental nucleus, and the parabigeminal nucleus (PBG). The tegmental inputs project densely to the intermediate gray layer (IGL) and sparsely to the superficial layers. The PBG input probably projects only to the superficial layers. In the present study, the morphology of choline acetyltransferase (ChAT)-immunoreactive axons and synaptic endings in the superficial and deep layers of the SC was examined by light and electron microscopy to determine whether these cholinergic afferents form different types of synapses in the superifical and deep layers. Two types of fibers were found within the zonal (ZL) and upper superficial gray layers (SGL): small diameter fibers with few varicosities and larger diameter fibers with numerous varicosities. Quantitative analysis demonstrated a bimodal distribution of axon diameters, with one peak at approximately 0.3–0.5 μm and the other at 0.9–1.0 μm. On the other hand, ChAT-immunoreactive fibers in the IGL were almost all small and formed discrete patches within the IGL. Two types of ChAT-immunoreactive synaptic profiles were observed within the ZL and upper SGL using the electron microscope. The first type consisted of small terminals containing predominantly round synaptic vesicles and forming asymmetric synaptic contacts, mostly on dendrites. The second type was comprised of varicose profiles that also contained round synaptic vesicles. Their synaptic contacts were always symmetric in profile. ChAT-immunoreactive terminals in the IGL patches contained round or pleomorphic synaptic vescles, and the postsynaptic densities varied from symmetric to asymmetric, including intermediate forms. However, no large varicose profiles were observed. This study suggests that cholinergic fibers include at least two differnt synaptic morphologies: small terminals with asymmetric thickenings and large varicose profiles with symmetric terminals. The large varicose profile in the superficial layers is absent in the IGL. This result suggests that the cholinergic inputs that innervate the superficial layers and the patches in the IGL of the cat SC differ in their synaptic organization and possibly also in their physiological actions. © 1993 Wiley-Liss, Inc.     

Changes in synaptic populations in the spinal dorsal horn following a dorsal rhizotomy in the monkey

Studies in monkeys have shown substantial neuronal reorganization and behavioral recovery during the months following a cervical dorsal root lesion (DRL; Darian‐Smith [2004] J. Comp. Neurol. 470:134–150; Darian‐Smith and Ciferri [2005] J. Comp. Neurol. 491:27–45, [2006] J. Comp. Neurol. 498:552–565). The goal of the present study was to identify ultrastructural synaptic changes post‐DRL within the dorsal horn (DH). Two monkeys received a unilateral DRL, as described previously (Darian‐Smith and Brown [2000] Nat. Neurosci. 3:476–481), which removed cutaneous and proprioceptive input from the thumb, index finger, and middle finger. Six weeks before terminating the experiment at 4 post‐DRL months, hand representation was mapped electrophysiologically within the somatosensory cortex, and anterograde tracers were injected into reactivated cortex to label corticospinal terminals. Sections were collected through the spinal lesion zone. Corticospinal terminals and inhibitory profiles were visualized by using preembedding immunohistochemistry and postembedding γ‐aminobutyric acid (GABA) immunostaining, respectively. Synaptic elements were systematically counted through the superficial DH and included synaptic profiles with round vesicles (R), pleomorphic flattened vesicles (F; presumed inhibitory synapses), similar synapses immunolabeled for GABA (F‐GABA), primary afferent synapses (C‐type), synapses with dense‐cored vesicles (D, mostly primary afferents), and presynaptic dendrites of interneurons (PSD). Synapse types were compared bilaterally via ANOVAs. As expected, we found a significant drop in C‐type profiles on the lesioned side (∼16% of contralateral), and R profiles did not differ bilaterally. More surprising was a significant increase in the number of F profiles (∼170% of contralateral) and F‐GABA profiles (∼315% of contralateral) on the side of the lesion. Our results demonstrate a striking increase in the inhibitory circuitry within the deafferented DH. J. Comp. Neurol. 518:103–117, 2010. © 2009 Wiley‐Liss, Inc.     

Plasticity of GABA- and glutamate-containing terminals in the mouse thalamic ventrobasal complex deprived of vibrissal afferents: an immunogold-electron microscopic study

GABA and glutamate immunogold staining demonstrated that nerve cells of the thalamic ventrobasal complex (VB) of mice were positive exclusively for glutamate. None of the neuronal perikarya reacted the GABA antibody. By using alternate thin sections of the normal VB, it was also shown that large "specific" somatosensory and small corticothalamic terminals, both of which contained spherical synaptic vesicles, exhibited only glutamate-like immunoreactivity. A third axonal type, containing flat-ovoid synaptic vesicles, stained only for GABA. Seventy-five days after coagulation of the vibrissal follicles in newborn mice, a characteristic multiplication of GABA positive axon terminals was observed. In addition, it was demonstrated that, similarly to modified cortical endings (Hámori et al., J. Comp. Neurol. 254:166-183, '86), many GABA positive terminals appeared as specific afferent endings, replacing the missing "specific" vibrissal afferents. This finding shows a remarkable plasticity of inhibitory GABA axons during developmental synaptogenesis and provides further evidence that the size, location, and the type of attachment of presynaptic terminals are dependent on their postsynaptic target.     

Ultrastructural examination of diffuse and specific tectopulvinar projections in the tree shrew

Two pathways from the superior colliculus (SC) to the tree shrew pulvinar nucleus have been described, one in which the axons terminate in dense (or specific) patches and one in which the axon arbors are more diffusely organized (Luppino et al. [1988] J. Comp. Neurol. 273:67-86). As predicted by Lyon et al. ([2003] J. Comp. Neurol. 467:593-606), we found that anterograde labeling of the diffuse tectopulvinar pathway terminated in the acetylcholinesterase (AChE)-rich dorsal pulvinar (Pd), whereas the specific pathway terminated in the AChE-poor central pulvinar (Pc). Injections of retrograde tracers in Pd labeled non-gamma-aminobutyric acid (GABA)-ergic wide-field vertical cells located in the lower stratum griseum superficiale and stratum opticum of the medial SC, whereas injections in Pc labeled similar cells in more lateral regions. At the ultrastructural level, we found that tectopulvinar terminals in both Pd and Pc contact primarily non-GABAergic dendrites. When present, however, synaptic contacts on GABAergic profiles were observed more frequently in Pc (31% of all contacts) compared with Pd (16%). Terminals stained for the type 2 vesicular glutamate transporter, a potential marker of tectopulvinar terminals, also contacted more GABAergic profiles in Pc (19%) compared with Pd (4%). These results provide strong evidence for the division of the tree shrew pulvinar into two distinct tectorecipient zones. The potential functions of these pathways are discussed.     

Cholinergic innervation of the superior colliculus in the cat

The superficial and intermediate gray layers of the superior colliculus are heavily innervated by fibers that utilize the neurotransmitter acetylcholine. The distribution, ultrastructure, and sources of the cholinergic innervation of these layers have been examined in the cat by using a combination of immuno-cytochemical and axonal transport methods. Putative cholinergic fibers and cells were localized by means of a monoclonal antibody to choline acetyltransferase (ChAT). ChAT immunoreactive fibers are distributed throughout the depth of the superior colliculus, with particularly dense zones of innervation in the upper part of the superficial grey layer and in the intermediate grey layer. Within the superficial grey layer, the fibers form a continuous, dense band, whereas within the intermediate grey layer the fibers are arranged in clusters or patches. Although the patches are present throughout the rostrocaudal extent of the superior colliculus, they are most prominent in middle to caudal sections. The structure of the ChAT immunoreactive terminals was examined electron microscopically. The appearance of the terminals is similar in the superficial and intermediate grey layers. They contain closely packed, mostly round vesicles, and form contacts with medium-sized dendrites that exhibit small, but prominent postsynaptic densities; a few of the terminals contact vesicle-containing profiles. To identify the sources of the cholinergic input to the superior colliculus, injections of wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP) were made in the superior colliculus and the sections were processed to demonstrate both the retrograde transport of WGA-HRP and ChAT immunoreactivity. Neurons containing both labels were found in the parabigeminal nucleus, and in the lateral dorsal and pedunculopontine tegmental nuclei of the pontomesencephalic reticular formation. Almost every cell in these nuclei that contained retrograde label was also immunoreactive for ChAT. The similarities between the laminar distributions of the ChAT terminals and the terminations of the pathway from the parabigeminal nucleus (Graybiel: Brain Res. 145:365-374, '78) support the view that the latter nucleus is a source of the cholinergic fibers in the superficial grey layer. The possibility that the pedunculopontine tegmental nucleus is a source of cholinergic fibers in the deep layers was tested by examining the distribution of labeled fibers following injections of WGA-HRP into this region of the tegmentum. Patches of labeled terminals were found in the intermediate grey layer that resemble in distribution the patches of ChAT immunoreactive fibers in this layer.(ABSTRACT TRUNCATED AT 400 WORDS)     

CalbindinD28k- and parvalbumin-immunoreactive neurons form complementary sublaminae in the rat superior colliculus

By using light microscopic immunocytochemistry and computer analysis, we have mapped the distributions of two calcium-binding proteins (CaBPs), calbindin_D28k (CB) and parvalbumin (PV), in the rat superior colliculus (SC). The patterns of CaBP expression were complementary. A band of heavily labeled, medium-sized CB-immunoreactive cells (CB-cells) was centered in the optic layer (OL), whereas PV-immunoreactive cells (PV-cells) were found predominantly in the intermediate gray layer (IGL), where they were clustered within patches of PV-labeled fibers. The superficial gray layer (SGL) could be divided into two sublaminae. CB-cells were found mostly in the dorsal half of the SGL, whereas PV-cells were scattered throughout the ventral SGL and the dorsal OL. Most of the CaBP-immunoreactive cells in the SGL were small bipolar cells with vertically oriented dendrites; however, there were also some PV-cells with horizontally oriented dendrites. Quantitative analysis of the CaBP distributions reinforced our observations that these cells are distributed in complementary tiers that are not restricted to the traditional laminae. The size and shape of some of these tiers were determined from a three-dimensional reconstruction of serial sections. The complementarity of the CaBP-immunoreactive tiers was also confirmed by fluorescence microscopy of double-labeled sections, in which few if any double-labeled neurons were observed. Complementary tiers of CB-cells and PV-cells have been observed previously in the SC of the cat. The present results demonstrate them in another species and further suggest that there are functional sublaminae in the SC that can be distinguished by CaBP content. J. Comp. Neurol. 394:205–217, 1998. © 1998 Wiley-Liss, Inc.     

High resolution radioautographic investigation of [H]GABA accumulating neurons in cat sensorimotor cortical areas

After the injection of [³H]GABA in the cat sensorimotor cortex, radioautographic analysis of thick and thin sections showed an intense labeling of numerous nerve fibers and of some neuronal cell bodies. Labeled boutons displayed either only clear vesicles or clear and large granular vesicles. They could constitute symmetrical synaptic differentiations upon dendrites or dendritic spines. Radioactive perikarya of stellate neurons could be labeled either by direct uptake or by retrograde axonal flow.