Experimental hypertrophy of myenteric neurones in the pig: a morphometric study

Muscular hypertrophy in the ileum of two pigs aged 6 weeks was induced using two different surgical techniques, narrowing of the gut circumference (mechanical stenosis) and segmental reversal of an ileal loop which results in a persistent antiperistalsis of that segment (functional stenosis). These pigs were sacrificed 5-6 weeks postoperatively. Cross sections through the gut wall at various distances from the operation sites revealed marked muscular hypertrophy in the pre-stenotic regions and in the reversed segment. Whole mounts from pre- and post-stenotic, as well as reversed ileal regions, were silver- impregnated. The corresponding ileal region of a third, nonoperated pig served as control. Using a computer-aided morphometric device, somal areas of five morphological neurone types were measured at various distances orally and anally from the operation sites and along the control ileum. Values between hypertrophic and nonhypertrophic zones as well as between two corresponding zones of nonoperated ileum were compared statistically. Along the control ileum, values revealed no differences in soma sizes. Within the experimentally altered material, somal areas of type VI neurones showed marked hypertrophy related to the sites of muscular hypertrophy whereas the other types remained constant throughout (II, IV in segmental reversal) or showed slightly larger somal areas within the post-stenotic, nonhypertrophied zones (I, V, IV in stenosis). Additionally, within the reversed segment, neuronal perikarya of type I, II, IV and V neurones were larger as compared to the neighbouring regions. However, this enlargement of perikarya within the reversed segment may not be correlated with muscular hypertrophy but rather with the transections of intramural axons before reversing this segment. The results suggest that morphologically distinct neurone types may play different roles within the mechanically stressed small intestine and possibly also in the coordination of normal muscular function.     

Morphological study of the rostral interstitial nucleus of the medial longitudinal fasciculus in the monkey,Macaca mulatta by Nissl,Golgi, and computer reconstruction and rotation methods

We have studied the morphology of silver-impregnated neurons (rapid Golgi technique) in the rostral interstitial nucleus of the medial longitudinal fasciculus (riMLF), a center involved in the control of vertical and torsional saccadic eye movements. This morphological study of riMLF neurons in the rhesus monkey was undertaken to further our understanding of the functional circuitry of the oculomotor system. Our study employed Nissl, Golgi, and computer- assisted methods. The cytoarchitectonic boundaries of the riMLF and its relationships to neighboring structures were determined in both Nissl and Golgi preparations. Five (I–V) distinct morphological types of riMLF neurons were distinguished in the Golgi impregnations on the basis of soma size, dendritic size, numbers of primary dendrites, number of dendritic branch points, as well as form, number, and distribution of dendritic appendages. Type I neurons impregnated most frequently and had the most extensive and highly branched dendritic tree. Type II neurons displayed thick dendrites with complex dendritic appendages, but the dendritic tree was much more compact than that of type I cells. Type III and type V cells had fusiform somas and relatively unbranched dendritic trees but differed greatly in size as well as dendritic morphology. The type IV cell was the smallest neuron and had many characteristics of the local interneurons found in other thalamic, subthalamic, hypothalamic, and midbrain centers. The type V was the largest neuron, least frequently impregnated, and found only at rostral riMLF levels. Digitized reconstructions of each type of neuron were rotated by the computer, which revealed that the dendritic trees of types I, III, and V occupy a disk-like compartment in the riMLF neuropil. In contrast, the trees of types II and IV occupy a roughly spherical compartment. We suggest that three of the cell types are well suited for specific purposes: type II cells for receiving, topographically organized inputs that contain spatial information, type I cells for short-lead burst neuron output to the motor neurons or other premotor centers, and type IV cells for inhibitory inputs to type I cells. © 1994 Wiley-Liss, Inc.     

The influence of ileitis on the neurochemistry of the caudal mesenteric ganglion in the pig

Background Some literature data suggest that there is a regulatory neuronal circuit between the small and the large bowel. To verify this hypothesis the present study investigated: (i) the distribution, chemical coding and routing of caudal mesenteric ganglion (CaMG) neurons participating in an intestinointestinal reflex pathway involving ileal descending neurons and viscerofugal colonic neurons and (ii) possible changes in the neuroarchitecture of this pathway evoked by chemically induced ileitis in juvenile pigs (n = 16). Methods Combined retrograde tract tracing and transections of the intermesenteric or caudal colonic nerves were applied. In addition, double immunostainings was used to investigate the chemical coding of retrogradely labeled CaMG neurons and intraganglionic nerve terminals apposed to them, under normal and inflammatory conditions. Key Results The majority of the ileum‐projecting neurons were found in the caudal part of CaMG. Disruption of particular nerve pathways resulted in diminished number of retrogradely labeled neurons, ipsilateral to the side of manipulation. In normal pigs, ileum‐projecting CaMG neurons stained for tyrosine hydroxylase, dopamine‐β‐hydroxylase, neuropeptide Y (NPY), somatostatin and galanin (GAL). The number and chemical coding of the neurons in the inflamed animals were similar to those observed in the normal pigs. However, in the inflamed pigs, the number of NPY‐, GAL‐ or substance P‐positive nerve terminals supplying retrogradely labeled neurons was increased. Conclusions & Inferences The present results suggest that inflammatory processes of the porcine ileum are able to induce changes in the intraganglionic architecture of a sympathetic ganglion located at discrete distance from the affected bowel segment.     

Cytoarchitecture and visual receptive neurons in the Wulst of the Japanese quail (Coturnix coturnix japonica)

The cellular organization of the Wulst was studied in Nissl- and Golgi-stained brain sections in order to identify the visual receptive neurons. Golgi-impregnated neurons were divided into four types according to their soma size, dendritic configuration, and density of spine distribution. Type I neurons, the largest cells in the Wulst, have long, straight dendrites with many spines. Type II neurons are medium-sized cells with long, straight dendrites. These dendrites have numerous spines. Type III neurons are medium-sized or small cells with spine-free dendrites. Type IV neurons, the smallest cells in the Wulst, have short dendrites with sparse spines. The projections of the nucleus dorsolateralis anterior thalami pars lateralis (DLL) to the Wulst were determined by the Fink-Heimer method. After lesions of the DLL, degenerating terminals are seen in a dorsolateral portion of the nucleus intercalatus hyperstriatum accessorium where the types II, III, and IV neurons are distributed. Postsynaptic elements to the DLL axons were identified by reconstruction of electron microscopic serial sections. Most of the postsynaptic elements were dendritic spines of the type II and IV neurons and a few were dendritic shafts of the type III neurons.     

Neuronal connections in the primary auditory cortex: an electrophysiological study in the cat

Neuronal connections in the primary auditory cortex (AI) of the cat were studied electrophysiologically by using intracellular recording techniques. Fast-conducting fibers from the medial geniculate nucleus (MG) projected monosynaptically onto AI neurons in layers III-VI (mainly in layer IV), whereas slow-conducting MG-fibers projected monosynaptically onto AI neurons in layer I. AI neurons which received monosynaptic inputs from the auditory association cortices (AII and Ep) and/or from the contralateral AI were distributed in all layers of the AI; the commissural fibers from the contralateral AI were divided into fast- and slow-conducting ones. AI neurons were categorized into seven types: type I neurons which received monosynaptic inputs from slow-conducting MG-fibers were located in layer I. Type II neurons which received polysynaptic inputs from the MG were located in layers II-VI. Type III neurons which sent their axons to the AII or Ep were mainly located in layer III. Type IV neurons which sent their axons to the contralateral AI were located mainly in layer III. Type V neurons which received monosynaptic inputs from fast-conducting MG-fibers were located mainly in layer IV. Type VI neurons which projected onto the inferior colliculus were located in the upper part of the layer V. Type VII neurons which projected onto the MG were located in layers V and VI.     

Intracellular recording and injection study of corticospinal neurons in the rat somatosensory cortex: effect of prenatal exposure to ethanol

The effects of prenatal exposure to ethanol on the structure and function of corticospinal neurons was investigated. The subjects were the 3-4-month-old offspring of hooded rats fed a nutritionally balanced liquid diet containing 6.7% (v/v) ethanol (Et), pair-fed a nutritionally matched isocaloric diet (Ct), or fed chow and water (Ch). Corticospinal neurons in primary somatosensory cortex were examined by intracellularly recording and filling cells that were driven by antidromic stimulation of the pyramidal decussation. In the control rats, corticospinal neurons comprised a homogeneous morphophysiological population. Morphologically, all of the antidromically driven cells examined were pyramidal neurons with cell bodies in layer Vb. The dendrites of these neurons were spinous and branched within layers I, IV, and V. Their axons arborized within layers IV, V, and VI and some collaterals extended laterally for distances up to 2.6 mm from the cell body. The mean conduction latency was 3.6 and 3.4 msec for Ch- and Ct-treated rats, respectively. In Et-treated rats, corticospinal neurons constituted a heterogeneous population. The laminar distribution of the corticospinal neurons in Et-treated rats was broad; the cell bodies of labeled neurons were in layers II, IV, V, and VI. The dendrites of layer Vb neurons were spinous; however, many of the spines appeared dysmorphic and the density of spines was significantly greater (32%) in Et-treated rats than in Ct-treated rats. Although the dendritic branching pattern for layer Vb neurons was similar to that described for the controls, a Sholl analysis showed that the complexity and extent of their dendritic trees were significantly greater in Et-treated rats. The axons of all layer Vb neurons in Et-treated rats had long horizontal processes that arborized in layers IV-VI, and some neurons also had an array of collaterals that ascended to layer I. The mean conduction latency for layer Vb neurons was 3.9 msec. The structure and function of ectopic neurons (those in layers II, IV, Va, Vc, and VI) in Et-treated rats differed markedly from those of the layer Vb neurons. Morphologically, the dendritic and axonal fields of these neurons were narrower than for the layer Vb neurons, and the ectopic neurons had a mean conduction latency of 7.1 msec. The heterogeneity of the population of corticospinal neurons in Et-treated rats may result from the effects of ethanol on early events in neuronal development such as neuronal generation and migration.     

Retinal ganglion cells in two teleost species,Sebastiscus marmoratus and Navodon modestus

Distribution patterns of ganglion cells in the retina were examined in Nissl-stained retinal whole mounts of Sebastiscus and Navodon. The existence of area centralis in the temporal retina in both species suggests binocular vision. In Navodon, another high density area was found in the nasal retina, and a dense band of ganglion cells was observed along the horizontal axis between the two high-density areas. There is an obvious trend for the ganglion cell size to increase as the density decreases. The total number of ganglion cells was estimated to be about 45 × 10⁴ in Sebastiscus and 87 × 10⁴ in Navodon, whereas the total number of optic nerve fibers was about 35 × 10⁴ and 70 × 10⁴, respectively. The retinal ganglion cells labeled with HRP were classified into six types according to such morphological characteristics as size, shape, and location of the soma as well as dendritic arborization pattern. Type I cells have a small round or oval soma in the ganglion cell layer and a small dendritic field in the inner plexiform layer. Type II cells are similar to type I cells, but the dendrites arborize more closely to the ganglion cell layer in the innermost region of the inner plexiform layer. Type III cells have a medium-sized round soma in the ganglion cell layer, and the dendrites extend in an extremely wide area in the inner plexiform layer with few branches. Type IV cells have a large soma which is located in the ganglion cell layer. Dendrites emanate from the soma in all directions, branching out several times within a rather small region in the innermost part of the inner plexiform layer. Type V cells have large somata of various shapes, usually dislocated to the inner plexiform or granular layer. The dendrites extend in every direction and occupy an extremely large area in the inner plexiform layer. Type VI cells have the largest somata, which are also dislocated to the inner plexiform or granular layer. Type VI cells have a characteristic triangular or fan-shaped dendritic field. Soma size and the axon diameter are intimately linked, that is, small somata of type I and II cells give off thin axons, and large somata of type V and VI give off thick axons. Medium-sized somata of type III cells or large somata of type IV cells, which have rather small dendritic fields, give off medium-sized axons. The histograms of the soma areas in the whole retina are quite similar to the histograms of the diameters of the optic nerve fibers.     

Intracortical connectivity of layer VI pyramidal neurons in the somatosensory cortex of normal and barrelless mice

In mice, barrels in layer IV of the somatosensory cortex correspond to the columnar representations of whisker follicles. In barrelless (BRL) mice, barrels are absent, but functionally, a columnar organization persists. Previously we characterized the aberrant geometry of thalamic projection of BRL mice using axonal reconstructions of individual neurons. Here we proceeded with the analysis of the intracortical projections from layer VI pyramidal neurons, to assess their contribution to the columnar organization. From series of tangential sections we reconstructed the axon collaterals of individual layer VI pyramidal neurons in the C2 barrel column that were labelled with biocytin [controls from normal (NOR) strain, 19 cells; BRL strain, nine cells]. Using six morphological parameters in a cluster analysis, we showed that layer VI neurons in NOR mice are distributed into four clusters distinguished by the radial and tangential extent of their intracortical projections. These clusters correlated with the cortical or subcortical projection of the main axon. In BRL mice, neurons were distributed within the same four clusters, but their projections to the granular and supragranular layers were significantly smaller and their tangential projection was less columnar than in NOR mice. However, in both strains the intracortical projections had a preference for the appropriate barrel column (C2), indicating that layer VI pyramidal cells could participate in the functional columnar organization of the barrel cortex. Correlative light and electron microscopy analyses provided morphometric data on the intracortical synaptic boutons and synapses of layer VI pyramidal neurons and revealed that projections to layer IV preferentially target excitatory dendritic spines and shafts.     

Early postnatal development of cholecystokinin-immunoreactive structures in the visual cortex of the cat

The early postnatal development of cholecystokinin-immunoreactive (CCK-ir) neurons was analyzed in visual areas 17 and 18 of cats aged from postnatal day 0 to adulthood. Neurons were classified mainly by axonal criteria. According to their chronology of appearance neurons are grouped into three neuronal populations. The first population consists of five cell types which appear perinatally in areas 17 and 18. Four of them have axons terminating in layer VI. Neurons with columnar dendritic fields of layers IV and V display a conspicuous dendritic arborization with the long dendrites always arranged parallel to each other. This way they form a vertically oriented dendritic column. The neurons differentiate at around P 2 and are present until the end of the second postnatal week. They disappear possibly by degeneration and cell death. Multipolar neurons of layer VI have long dendrites and axonal domains of up to 800 micron in diameter. Three percent of these neurons send out two axons instead of only one. Neurons differentiate at P 0 and the cell type persists into adulthood. Bitufted to multipolar neurons of layer V constitute a frequent type; 10% of these cells issue two axons. They differentiate at P 2 and the type survives into adulthood. Bitufted to multipolar neurons of layers II/III appear at P 2 and send their axons into layer VI. So, early postnatally an axonal connection from superficial cortical layers to layer VI is established. The cell type persists into adulthood. The fifth cell type of the first population is constituted by the neurons of layer I with intralaminar axons which differentiate at P 2. Although they derive from the early marginal zone, the cell type survives into adulthood. The second population consists of two cell types which appear around the end of the second and during the third postnatal week in areas 17 and 18. Multipolar neurons of layer II have horizontally or obliquely arranged basket axons which, during the second postnatal month, form patches of high fiber and terminal density along the layer I/II border. Neurons with descending main axons issuing horizontal and oblique collaterals of layers II-IV form broad axonal fields. The third population in area 17 is constituted by three cell types: Bitufted neurons with axons descending in form of loose bundles of layers II/III differentiate during the fifth postnatal week. Small basket cells of layers II/III with locally restricted axonal plexuses and somewhat larger basket cells of layer IV appear during the sixth and seventh week.(ABSTRACT TRUNCATED AT 400 WORDS)     

Effect of testosterone on input received by an identified neuron type of the canary song system: a Golgi/electron microscopy/degeneration study

Combinations of the Golgi stain, anterograde degeneration, and electron microscopy are used to further characterize the hormone-sensitive "type IV" neuron of the forebrain nucleus robustus archistriatalis (RA) of adult female canaries. Anterograde degeneration was used to "stain," at the electron-microscopic level, the axon terminals of neurons projecting to RA from hyperstriatum ventralis, pars caudalis (HVc) and from the lateral magnocellular nucleus of the anterior neostriatum (L-MAN). The HVc neurons projecting to RA type IV cells form synapses predominantly on the dendritic spines of those cells, while L-MAN neurons that project to RA type IV cells form a 2.5:1 mixture of shaft and spine synapses. There were about 1000 synapses from HVc neurons (about 30% of all spine synapses) on typical type IV cells and about 50 synapses from L-MAN neurons. Earlier work had shown that in female canaries the dendrites of type IV neurons of the avian song control nucleus RA increase in total length after systemic testosterone treatment, and that this increase in dendritic length was accompanied by the development of malelike song. We now show that testosterone treatment also increases the number of dendritic spines present in type IV neurons. Presumably this is accompanied by an increase in the number of synaptic inputs received by type IV cells. Earlier evidence suggested that the testosterone-induced addition of extra dendritic length to type IV cells occurred at existing dendritic tips. We tested the hypothesis that these added peripheral ends received a special subset of inputs, which might then account for the change in behavior, and found it to be false. Mapping and counts of degenerating synapses resulting from lesion of HVc and L-MAN suggest that under the influence of hormone, new synapses are added throughout the dendritic tree, with no special distribution or change in ratio of inputs occurring at the tip of dendrites. Under the influence of testosterone, each type IV cell may receive only "more of the same" inputs it received before onset of treatment. We speculate on how such changes in circuitry may relate to song stability and learning.     

A Golgi study of the monkey paraventricular nucleus: neuronal types, afferent and efferent fibers

The neuronal organization of the paraventricular nucleus (PVN) was examined in Golgi impregnations of adult monkey. Results showed that at least six types of neurons could be identified in the nucleus on the basis of morphological features of the somata, dendrites, and axons. Four types of neurons with sparse to densely spined cell bodies and dendrites exhibited long axons and included large neurons (types I and II), medium-sized to large neurons (type III), and small to medium-sized cells (type IV). Axons of type I, III, and IV neurons had different diameters and were followed out of the PVN. Axon collaterals that arborized within the PVN were seen on the axons of types III and IV cells. Two types of interneurons with small somata were also found. One (type V) exhibited varicose dendrites and a profusely arborizing local axon. The other cell (type VI) had recurved dendrites with long appendages and no impregnated axon. Afferent fibers were also identified. Type 1 was a fine-caliber axon that coursed long distances in the PVN and exhibited numerous short branches. Additional observations suggested that type 1 afferents originated from the stria terminalis. The other afferent axon (type 2) was thicker and gave rise to terminal arborizations containing clusters of small swellings. The efferent fibers of the PVN were also examined in impregnations of the paraventriculosupraopticohypophysial tract. Fibers formed an extensive plexus as they coursed ventrally and passed through the lateral hypothalamus. Axons coursing more laterally in the tract were much larger than those more medially located. Our findings show a diverse organization of neuronal types within the monkey PVN with evidence for intrinsic connections through axon collaterals of efferent neurons and the locally arborizing axons of interneurons. Correlations are proposed between morphological subtypes of neurons seen in this Golgi study and the known functional output pathways of the PVN.     

Morphology of normal and deafferented neurons in the chick ectomamillary nucleus

Neurons in the ectomamillary nucleus (EMN) undergo both atrophy and cell death following eye removal at hatching. It is not known whether all EMN neurons are affected uniformly by transneuronal atrophy or whether cell loss is an artifact due to misidentification of atrophied neurons as glia. In a preliminary morphological study, four types of neurons were found in the EMN by using the rapid Golgi method: A large multipolar neuron (type I); two medium-sized spindle-shaped neurons, one possessing many dendritic branches (type II) and the other possessing few dendritic branches (type III); and a small round neuron (type IV). Horseradish peroxidase (HRP) was then injected into two of the EMN projection fields in enucleated chicks in order to label retrogradely as many EMN neurons as possible. Types, I, II, and III neurons were identified both in the control and experimental EMN. The three types of backfilled neurons showed different degrees of transneuronal atrophy ranging from 12 to 47%. The type IV neuron, which could not be backfilled, was inferred to atrophy by 33%. Substantial differences in transneuronal atrophy, therefore, exist among the different types of neurons within the same nucleus. Since no glialike neurons could be retrogradely labeled it was concluded that there is a true neuron loss in the EMN following eye removal rather than mistaken identification of neurons as glia.     

FlCRhR/cyclic AMP signaling in myenteric ganglia and calbindin-D28 intrinsic primary afferent neurons involves adenylyl cyclases I, III and IV

The aims of this study were to improve insight into cAMP signaling in myenteric neurons and glia and identify the adenylyl cyclase (AC) isoforms expressed in myenteric ganglia of the guinea-pig small intestine. An increase in the intracellular cAMP levels was measured indirectly by an increase in the 520 nm/580 nm fluorescence emission ratio of the protein kinase A fluorosensor FlCRhR. Forskolin or pituitary adenylyl cyclase activating peptide caused an increase in cAMP levels in cell somas and neurites and elicited a slow EPSP-like response in myenteric AH/Type 2 neurons, whereas the inactive form of forskolin was without these effects. Glia displayed similar cAMP responses. Immunoblot analysis showed that AC I, III and IV were present in myenteric ganglia, with AC I being detected as two bands of 160 kDa and 185 kDa, AC III as two bands near 220 kDa, and AC IV as two bands of greater than 220 kDa. Pretreatment with N-ethylmaleimide and N-glycosidase F revealed an AC IV band at 115 kDa. Preabsorption with specific blocking peptides prevented detection of AC I or AC IV immunoreactive proteins. In ganglia which expressed strong AC IV immunoreactivity, no immunoreactive bands were detected for AC II, AC V/VI, AC VII or AC VIII. The amount of AC isoforms expressed in myenteric ganglia followed the order of AC IV&z.Gt;III>I. Immunofluorescent labeling studies revealed that AC I, AC III and AC IV were variably expressed in myenteric neurons and glia of the duodenum, jejunum and ileum. In the guinea-pig ileum, AC I, III and IV immunoreactivities were respectively present in 26%, 58% and 89% of calbindin-D28-colabeled myenteric neurons. These findings suggest that (1) AC I, AC III and AC IV variably contribute to cAMP signaling in myenteric ganglia, (2) AC I, AC III and AC IV may be differentially expressed in distinct subsets of calbindin-D28 neurons which may represent intrinsic primary afferent myenteric neurons. Our study also provides direct evidence for activation of cAMP-dependent protein kinase.     

Interlaminar connections and pyramidal neuron organisation in the visual cortex,area 17, of the Macaque monkey

The patterns of arborisation of apical dendrites of different varieties of pyramidal neurons in area 17 differ and are characteristic for each cell type. They appear to serve as a means of collating within one neuron information derived directly from several different laminae. These different patterns of apical dendrite arborisation provide dendritic links which relate closely to the laminar distribution of axons of the spiny stellate neurons as well as the pyramidal neurons themselves. The axons of spiny stellate neurons lying in laminae IVCβ and IVA (Lund, '73)—Which receive information from parvocellular geniculate layers — project heavily to the lower half of lamina III (IIIB) and to a narrow zone at the top of lamina V (VA); laminae IIIB and VA are in turn linked by a specific variety of pyramidal neuron, with basal dendritic field in lamina VI, whose apical dendrite has marked lateral branching only in laminae VA and IIIB (where it terminates). Pyramidal neurons with basal dendritic field in laminae VA (with vestigial apical dendrite) or in IIIB have recurrent axon projections to lamina IIIA and above (the descending axon projection of lamina IIIB pyramids is principally to lamina VA itself). The pyramidal neurons of laminae IIIA and above have axons which distribute in the same upper laminae as their dendtritic fields and a descending axon projection to lamina VB. Pyramidal neurons with basal dendritic field on lamina VB have an apical dendrite which, if not vestigal, arborises in IIIA or above; their axons in some cases project to the superior colliculus or may be exclusively, or in addition, recurrent, distributing collaterals within laminae VB, VI and in IIIA or above; one variety of pyramidal neuron with basal dentritic field in lamina VI makes a dentritic link with these same regions, its apical dendrite arborising first within lamina VB and then in lamina IIIA and above. Axons of spiny stellate neurons of lamina IVCα (which receives the projection of the magnocellular layers of the lateral geniculate nucleus) as well as distributing widely within lamina IVCα also contribute to laminae IVB and VA; a link is again made by a specific variety of pyramidal neuron, with basal dendtritic field in lamina VI, which shows branching to its apical dendtrite only in laminae VA and as a terminal arborisation in IVCα. Another variety of pyramidal neuron with basal dendtric field in lamina VI has apical dendritic arborisation only in lamina IVB. The pyramidal neurons with basal dendritic field in lamina IVB and apical dendrite arborising in lamina IIIB and above, also contribute axonal collatetrals to lamina IIIA and above; their horizontal axon collaterals, together with the axons of spiny stellate neurons of laminae IVCα and IVB, form the horizontal fiber band of lamina IVB (to which the axons of laminae III and II pyramidal neurons do not contribute. The descending axon projection of the spiny stellate and pyramidal neurons of lamina IVB appears to be principally to lamina VI. The pattern of branching of pyramidal neuron apical dendrites is therefore neither random nor a continuum of one basic pattern; instead it is a series of separate patterns, each spatially distributed in a highly specific and unique fashion relating to the patterns of projection of afferent information through the cortex.     

Multimodal responses of taste neurons in the frog nucleus tractus solitarius

The responses of 216 neurons in the nucleus tractus solitarius (NTS) of the American bullfrog were recorded following taste, temperature, and tactile stimulation. Cells were classified on the basis of their responses to 5 taste stimuli: 0.5 M NaCl, 0.0005 M quinine-HCl (QHCl), 0.01 M acetic acid, 0.5 M sucrose, and deionized water (water). Neurons showing excitatory responses to 1, 2, 3, or 4 of the 5 kinds of taste stimuli were named Type I, II, III, or IV, respectively. Cells whose spontaneous rate was inhibited by taste and/or tactile stimulation of the tongue were termed Type V. Type VI neurons were excited by tactile stimulation alone. Of the 216 cells, 115 were excited or inhibited by taste stimuli (Types I-V), with 35 being Type I, 34 Type II, 40 Type III, 2 Type IV and 4 Type V. The remaining 101 cells were responsive only to tactile stimulation (Type VI). Of those 111 cells excited by taste stimulation (Types I-IV), 106 (95%) responded to NaCl, 66 (59%) to acetic acid, 44 (40%) to QHCl, 10 (9%) to water, and 9 (8%) to warming. No cells responded to sucrose. Of the 111 cells of Types I-IV, 76 (68%) were also sensitive to mechanical stimulation of the tongue. There was some differential distribution of these neuron types within the NTS, with more narrowly tuned cells (Type I) being located more dorsally in the nucleus than the more broadly tuned (Type III) neurons. Cells responding exclusively to touch (Type VI) were also more dorsally situated than those responding to two or more taste stimuli (Types II and III).     

Neurons of the dorsal lateral geniculate nucleus of the albino rat.

Light and electron microscopic observations were made on the dorsal lateral geniculate nucleus (DLGN) of 33 young adult male albino rats. Three variants of the Golgi silver impregnation technique were employed in the light microscopic studies. Neurons were classified into three categories based on location, dendritic pattern, and dendritic appendages. Type 1 and type 3 neurons were distributed throughout the DLGN. Type 2 neurons were located in the superficial zone. Dendritic appendages of type 1 and type 2 neurons indicated these cells may function as geniculo-cortical relay neurons. The type 3 neurons had lobulated dendritic appendages and an axon that terminated withinthe nucleus. Type 3 neurons may represent Golgi-type-II interneurons. Camera lucida drawings, photomicrographs, and electronmicrographs illustrate the characteristics ofthe three cell types. The literature on ultrastructural and neurophysiological findings may substantiate the presence of three neuronal types. Initially, the rat DLGN does not appear as elaborately organized as the nucleus observed in cats and primates; however, there are notable similarities in neuronal morphology and synaptology.     

Ultrastructural synaptic organization of axon terminals in the ventral part of the cat oral pontine reticular nucleus

In an attempt to contribute to the current knowledge of the brainstem reticular formation synaptic organization, the ultrastructure and distribution of synaptic terminal profiles on neurons in the ventral part of the oral pontine reticular nucleus (vRPO), the rapid eye movement (REM) sleep-induction site, were studied quantitatively. Terminals with asymmetric contacts and rounded vesicles were classified according to vesicle density as type I or II (high or low density, respectively). The area, apposed perimeter length, and mitochondrial area of type I terminals, on average, were significantly smaller than those of type II terminals. Type III and IV terminals had symmetric contacts and oval and/or flattened vesicles; type III terminals formed synapses between them and on initial axons. Type V and VI terminals showed characteristics intermediate to those of asymmetric and symmetric synapses. Interestingly, some terminal features were related to both terminal area and postsynaptic dendritic diameter. The percentages of different synapses sampled on somata were as follows: asymmetric synapses (usually formed by type II terminals; mean +/- S.D.), 26.4% +/- 3%; symmetric synapses, 46.7% +/- 5.2%; and intermediate synapses, 26.9% +/- 6.1%. The percentages of different synapses sampled on dendrites were asymmetric synapses, 62.1% +/- 9%; symmetric synapses, 25.6% +/- 8.1%; and intermediate synapses, 12.3% +/- 1.7%. Comparison between large- and small-diameter dendrites revealed that the percentages of symmetric synapses and type II terminals decreased, whereas the percentages of type I terminals increased as postsynaptic dendritic diameters became smaller. Synaptic density was approximately four times lower on somata than on dendrites. The vRPO synaptic organization reflects some patterns that are similar to those found in other regions of the central nervous system as well as specific synaptic patterns that are probably related to its functions: the generation and maintenance of REM sleep and the control of eye movement or limb muscle tone.     

FlCRhR/cyclic AMP signaling in myenteric ganglia and calbindin-D28 intrinsic primary afferent neurons involves adenylyl cyclases I, III and IV

The aims of this study were to improve insight into cAMP signaling in myenteric neurons and glia and identify the adenylyl cyclase (AC) isoforms expressed in myenteric ganglia of the guinea-pig small intestine. An increase in the intracellular cAMP levels was measured indirectly by an increase in the 520 nm/580 nm fluorescence emission ratio of the protein kinase A fluorosensor FlCRhR. Forskolin or pituitary adenylyl cyclase activating peptide caused an increase in cAMP levels in cell somas and neurites and elicited a slow EPSP-like response in myenteric AH/Type 2 neurons, whereas the inactive form of forskolin was without these effects. Glia displayed similar cAMP responses. Immunoblot analysis showed that AC I, III and IV were present in myenteric ganglia, with AC I being detected as two bands of 160 kDa and 185 kDa, AC III as two bands near 220 kDa, and AC IV as two bands of greater than 220 kDa. Pretreatment with N-ethylmaleimide and N-glycosidase F revealed an AC IV band at 115 kDa. Preabsorption with specific blocking peptides prevented detection of AC I or AC IV immunoreactive proteins. In ganglia which expressed strong AC IV immunoreactivity, no immunoreactive bands were detected for AC II, AC V/VI, AC VII or AC VIII. The amount of AC isoforms expressed in myenteric ganglia followed the order of AC IVIII>I. Immunofluorescent labeling studies revealed that AC I, AC III and AC IV were variably expressed in myenteric neurons and glia of the duodenum, jejunum and ileum. In the guinea-pig ileum, AC I, III and IV immunoreactivities were respectively present in 26%, 58% and 89% of calbindin-D₂₈—colabeled myenteric neurons. These findings suggest that (1) AC I, AC III and AC IV variably contribute to cAMP signaling in myenteric ganglia, (2) AC I, AC III and AC IV may be differentially expressed in distinct subsets of calbindin-D₂₈ neurons which may represent intrinsic primary afferent myenteric neurons. Our study also provides direct evidence for activation of cAMP-dependent protein kinase.     

Quantitative Golgi study of anatomically identified subdivisions of motor thalamus in the rat

A Golgi study of neurons in the ventroanterior-ventrolateral complex (VAL) and ventromedial (VM) nucleus in the dorsal thalamus of rats was performed. To facilitate the delineation of subdivisions of these nuclei, some animals received injections of horseradish peroxidase (HRP) into the afferent and efferent fields of VAL and VM, and alternate sections were processed for the histochemical detection of HRP. As an adjunct to subjective observations, a multivariate statistical analysis of morphometric variables was performed to provide an objective assessment of neuronal morphology. All Golgi-stained neurons in VAL and VM were tentatively identified as projection neurons; no cells with morphological features commonly ascribed to thalamic interneurons were impregnated. Four classes of morphologically distinct neurons were identified in VAL. Type 1 neurons, the most commonly impregnated cell, were found throughout the extent of VAL and resembled "tufted" or "multipolar bush" neurons described previously in many thalamic nuclei. The remaining three neuronal types differed in a number of morphometric parameters and were differentially distributed throughout VAL. Type 2 neurons, distinguished in part by dendritic spine morphology and elongated bipolar dendritic fields, were found only in the rostral sector of the dorsal division of VAL (VALD). Type 3 neurons, characterized by a large and evenly distributed dendritic field, were situated in rostral VAL (all subdivisions). Type 4 neurons had small soma and dendritic dimensions and were located in the ventromedial aspect of the ventral division of VAL (VALV) adjacent to VM. In contrast, the vast majority of neurons in VM were considered to be a single morphological class (similar in form to type 4 neurons in VAL), although a rarely impregnated second type of neuron was also observed. The apparent scarcity of interneurons in VAL and VM is consistent with previous evidence that the synaptic organization of motor thalamus in the rat is markedly different from that of higher-order mammals. Speculation about the functional attributes of the neuronal types in VAL and VM is necessarily restricted to considerations of afferent and efferent relations, since "motor modality" functions of neurons in these nuclei have yet to be elucidated.     

Localization of the type VI voltage-gated sodium channel protein in human CNS

The cellular distribution of the type VI human voltage-gated sodium channel (Type VI) was examined in selected human brain regions. Antibodies designed to be specific to rat and human Type VI were raised against a synthetic peptide from the predicted NH2-terminal of the protein, and used for an immunohistochemical investigation. Immunoblot experiments showed that purified antibodies specifically detected the presence of Type VI in transfected cells and human brain membrane preparations. Immunohistochemistry on perfusion fixed human tissue revealed a predominantly somato-dendritic distribution of Type VI in major output neurons of the cerebellum, cerebral cortex and hippocampus. The observed localisation of this channel may reflect an important role in the integration of synaptic input in the human CNS.