Transport Of Wheat Germ Agglutinin Research Articles

Localization of sympathetic and parasympathetic neurons innervating pancreas and spleen in the cat

The localization of sympathetic and parasympathetic neurons innervating the pancreas and spleen was studied in the cat utilizing retrograde transport of wheat germ agglutinin conjugated horseradish peroxidase (WGA-HRP). Injection of WGA-HRP into the pancreas resulted in retrograde labeling in the whole of the solar plexus, while injection of WGA-HRP into the spleen also resulted in heavy labeling in the celiac ganglia bilaterally. Only a few labeled neurons were distributed in the superior mesenteric ganglion. With respect to parasympathetic innervation, HRP-labeled pancreatic and splenic neurons were found throughout the rostrocaudal extent of the dorsal motor nucleus of the vagus nerve (DMV) bilaterally. Although pancreatic neurons in the DMV were mainly observed in limits rostral to the obex, splenic neurons were centered at the level of the obex.

The synaptic interrelationships between primary afferent terminals, cuneothalamic relay neurons and GABA-immunoreactive boutons in the rat cuneate nucleus

The present study described an ultrastructural synaptic configurations between primary afferent terminals (PATs), cuneothalamic relay neurons (CTNs) and GABA-immunoreactive (GABA-IR) boutons in the cuneate nucleus of rats using cervicothoracic dorsal rhizotomies, retrograde transport of wheat germ agglutinin conjugated with horseradish peroxidase complex (WGA-HRP) and anti-GABA immunogold labelling methods. With this procedure, direct synaptic relationships between the PATs, CTNs and GABA-IR boutons have been demonstrated. The most remarkable feature was the observation whereby an immunogold-labelled GABA-IR bouton was presynaptic to a WGA-HRP labelled dendrite of CTN and a degenerating PAT; the same PAT was in turn presynaptic to the HRP-labelled dendrite. This was evident in ten out of a total of 133 synaptic configurations that were closely scrutinized. Results of this study support the concept that GABA-IR boutons are not only involved in presynaptic inhibition on the primary afferent input to the cuneothalamic relay neurons, but also exert a simultaneous postsynaptic inhibition on these cells.

Glutamate immunoreactivity of insular cortex afferents to the nucleus tractus solitarius in the rat: a quantitative electron microscopic study.

Corticosolitary axons and their terminals were labeled by the anterograde transport of wheat germ agglutinin conjugated to horseradish peroxidase, after injections into the rat insular cortex. The ultrastructure of these cortical afferents was analysed in the medial and commissural subnuclei of the nucleus tractus solitarius. Cortical terminals had a mean area of 0.36 microns 2, and were among the smallest terminals in the nucleus. They made single, asymmetric synaptic contacts with thin dendritic stems or with spines. The average diameter of the dendrites postsynaptic to cortical axons was 0.59 microns, and significantly smaller (P < 0.01, Kolmogorov-Smirnov test) than the mean (0.87 microns) of the population of dendrites in the same region of the nucleus tractus solitarius. Cortical boutons contained closely packed round and clear synaptic vesicles of diameter ca. 28 nm, a few mitochondria, and no dense core vesicles. Postembedding immunogold analysis showed that the anterogradely labeled cortical axon terminals were immunoreactive to glutamate, but not to GABA. Cortical afferents had on average four times the glutamate immunoreactivity (assessed by gold particle density) than local dendrites or terminals making symmetric synaptic contacts. Similarly, most of the unlabeled axon terminals participating in asymmetric synaptic contacts were highly enriched in glutamate immunoreactivity, suggesting that glutamate may be a most prevalent transmitter in the nucleus tractus solitarius. Terminals immunoreactive to GABA always made symmetric synapses, mostly with dendritic shafts and perikarya. We concluded that insular cortex axons made single, asymmetric synaptic contacts with thin, probably distal dendrites in the nucleus tractus solitarius. Cortical terminals are immunoreactive to glutamate, and morphologically different from primary afferents and from terminals immunoreactive to GABA.

Evidence for glutamate as a neurotransmitter in spinothalamic tract terminals in the posterior region of owl monkeys

Previous studies have suggested that glutamate is a neurotransmitter in ascending somatosensory pathways to the thalamus. The present study examined with quantitative immunohistochemical methods the presence of glutamate in spinothalamic tract terminals of owl monkeys (Aotus trivirgatus). Such terminals in the posterior region, in which a nucleus was recently identified as a specific pain and temperature relay in macaques and humans, were labeled by anterograde transport of wheat germ agglutinin conjugated to horseradish peroxidase, injected into the spinal dorsal horn. Glutamate-like immunoreactivity was demonstrated with a postembedding immunogold procedure using a well-characterized glutamate antiserum. Quantitative analysis of the immunogold labeling demonstrated that the spinothalamic tract terminals contained more than twice the tissue average of glutamate-like immunoreactivity. Enrichment of glutamate-like immunoreactivity was also found in terminals of presumed cortical origin. Presynaptic dendrites, cell bodies and non-vesicle-containing dendrites displayed low levels of glutamate-like immunoreactivity. A strong positive correlation (r = 0.69; P < 0.0001) was found between the density of synaptic vesicles and the density of gold particles in spinothalamic tract terminals, in contrast to a weak negative relationship (r = -0.28; P = 0.089) present in GABAergic presynaptic dendrites. These data provide strong evidence that the gold labeling in the spinothalamic tract terminals represents transmitter labeling, implying that glutamate is a neurotransmitter for ascending nociceptive and thermoreceptive information in primates.

Early decline and late restoration of spinal cord binding and transganglionic transport of isolectin B4 from Griffonia simplicifolia I after peripheral nerve transection or crush

Isolectin B4 from Griffonia simplicifolia I (B4) has a high binding affinity to a large population of unmyelinated primary sensory neurons (Wang et al., Neuroscience 62 (1994) 539-551). Using immunohistochemical techniques, binding and transganglionic transport of B4 in the spinal cord was investigated, both at short and long survival times, after sciatic nerve transection and ligation or crush in the adult rat. Nerve transection and ligation resulted in nearly complete disappearance of B4 immunolabelling in the sciatic nerve territory of the superficial dorsal horn after B4 binding, as well as after transganglionic transport of B4 by 2 weeks postinjury. Partial recovery of both B4 binding and B4 transport was found by 8 months, and nearly complete recovery by 16 months, indicating that reappearance of B4 binding is not critically dependent on peripheral reinnervation. Crush injury made by jeweller's forceps resulted in partial depletion of binding and transport by 2 weeks and a nearly complete recovery by 10 weeks. The results show that binding and transganglionic transport of B4 can be used to label dorsal horn connections of unmyelinated primary afferents during the process of regeneration after crush injury. Furthermore, as B4 binding and transport recover at long survival times in the absence of reestablished peripheral connections, the same techniques can be used to study central primary afferent connections at long survival times after nerve transection. Binding and transganglionic transport of B4 offer alternatives to the use of previous techniques such as transganglionic transport of wheat germ agglutinin conjugated horseradish peroxidase (WGA-HRP) to study central connections of fine primary afferents after injury.

Local projections of GABAergic neurons in the dentate gyrus and CA1 region in the rat hippocampal formation

Using retrograde transport of wheat germ agglutinin conjugated colloidal gold (WGA-gold) combined with immunoreactivity for glutamate decarboxylase (GAD), a specific synthesizing enzyme for γ-aminobutyric acid (GABA), local projections of GABAergic neurons in the dentate gyrus and CAI were examined. In the hilus of the dentate gyrus, it was found that GABAergic neurons in the granule cell layer projected to the ipsilateral upper leaf of the molecular layer, with a mediolateral extension of more than 1.2 mm and a rostrocaudal extension of over 0.8 mm. Non-GABAergic neurons in nearly the entire hilar area were found to project to the ipsilateral upper leaf of the molecular layer. In the dorsal CAI region, GABAergic neurons in the stratum pyramidale and radiatum converged onto the ipsilateral stratum pyramidal/oriens, with a mediolateral extension of over 1 mm and a rostrocaudal extension of over 0.7 mm. These results provide direct evidence that in both the dentate gyrus and CAI, GABAergic interneurons from a fairly large field converge onto a very small target area. This suggests that the output signals from GABAergic neurons in the dentate gyrus and CAI, and non-GABAergic neurons in the dentate gyrus, may propagate beyond the anatomical limits contained in conventional slice preparations of the hippocampal formation.

Differences in the connectivity of rat pudendal motor nuclei as revealed by retrograde transneuronal transport of wheat germ agglutinin.

Bilateral coordinated activation of pudendal motoneurons is an essential component of penile reflexes in male rats. However, little is known about the intraspinal organization of these reflexes. In the present study, retrograde transneuronal transport of wheat germ agglutinin (WGA) was used to examine the organization of spinal motoneurons and putative interneurons mediating penile reflexes in adult male rats. Injection of WGA into the ventral bulbospongiosus muscle resulted in direct retrograde labeling of motoneurons in the ipsilateral dorsomedial (DM) nucleus and transneuronal labeling of ipsilateral and contralateral DM motoneurons. Motoneurons in the ipsilateral and contralateral dorsolateral (DL) nuclei were not labeled. WGA-labeled putative interneurons were observed bilaterally, primarily in the ventromedial spinal gray matter extending dorsally to the central canal and the dorsal gray commissure. The number of transneuronally labeled putative interneurons increased with longer survival times. Injection of WGA into the ischiocavernosus muscle resulted in direct retrograde labeling of motoneurons in the medial subdivision of the ipsilateral DL nucleus. However, no WGA labeling was detected in motoneurons in the lateral subdivision of the ipsilateral DL nucleus, the contralateral DL nucleus, or the DM nuclei at any of the survival times studied (1-7 days). Only a small number of transneuronally labeled putative interneurons was observed in the ventrolateral gray matter at longer survival times (3-7 days). Thus, marked differences were observed between the DM and DL nuclei with respect to the transneuronal transport of WGA. These results are discussed with respect to the organization of the spinal circuits that mediate pudendal motor reflexes.

GABAergic boutons establish synaptic contacts with the soma and dendrites of cuneothalamic relay neurons in the rat cuneate nucleus.

This study investigates the synaptic relation between gamma-aminobutyric acid-immunoreactive (GABA-IR) and cuneothalamic relay neurons (CTNs) in the rat cuneate nucleus. Retrograde transport of wheat germ agglutinin conjugated with horseradish peroxidase complex (WGA-HRP) was used to label CTNs while anti-GABA immunogold serum was used for the detection of GABA-IR boutons associated with CTNs. With these procedures, immunogold-labelled GABA-IR boutons were found to form axosomatic, axodendritic and axospinous synapses with the WGA-HRP-labelled but immunonegative CTNs. Quantitative estimation showed that the mean ratios of GABA-IR to GABA-immunonegative boutons making synaptic contacts with somata, proximal dendrites, and distal dendrites were 47.9%, 49.1% and 34.7%, respectively. Statistical analysis showed that the incidence of GABA-IR boutons on the somata and proximal dendrites of CTNs was significantly higher than on the distal dendrites. Our results indicate that GABA is the primary inhibitory neurotransmitter in the cuneate nucleus, thereby emphasizing the importance of postsynaptic inhibition on cuneothalamic relay neurons.

Transient cortical pathways in the pyramidal tract of the neonatal ferret.

Anterograde transport of wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP) was used to study transient axons from the visual cortex in the pyramidal tract. Injections at birth restricted to the visual cortex labeled axons in the vicinity of the pontine nuclei. Two to eight days after birth, axons from the occipital cortex were found posterior to the pontine nucleus, their caudalmost stable target. Transient corticospinal axons from the presumptive primary visual cortex did not grow caudal to the pyramidal decussation. Innervation of more distal targets preceded innervation of proximal targets. Innervation of the pontine nucleus is initiated around 68 hours after birth, when the transient extension in the medullary pyramidal tract has attained its maximum caudal extent. Innervation of the superior colliculus begins 9 days after birth. Retrograde tracers were used to follow the developmental changes in the cortical distribution of the parent neurons giving rise to axons in the pyramidal tract. In the adult, labeled neurons following injection of retrograde tracer in the pyramidal tract occupied less than a third of the neocortex and were centred on the anterior part of the coronal and spleniocruciate gyri. In the immature brain, labeled neurons covered more than two-thirds of the neocortex. Areal density measurements in the neonate showed that peak labeling was centred in the anterior coronal and spleniocruciate gyri, where corticospinal cells in the adult are located. There was a marked rostral-caudal gradient so that labeled neurons were very scarce towards the occipital pole. These results, showing transient neocortical axons in the pyramidal tract in a carnivore, suggest that this may be a common feature of mammalian development. The finding that the adult pattern of corticospinal projections does not emerge from a uniform distribution is discussed with respect to the areal specification of cortical connectivity.

Glutamatergic and cholinergic projections to the pontine inhibitory area identified with horseradish peroxidase retrograde transport and immunohistochemistry.

Previous studies in our laboratory have shown that microinjection of acetylcholine and non-N-methyl-D-aspartate (NMDA) glutamate agonists into the pontine inhibitory area (PIA) induce muscle atonia. The present experiment was designed to identify the PIA afferents that could be responsible for these effects, by use of retrograde transport of wheat germ agglutinin conjugated horseradish peroxidase (WGA-HRP), glutamate immunohistochemistry and NADPH-diaphorase staining techniques. Experiments were performed in both decerebrate and intact cats. Dense retrograde WGA-HRP labelling was found in neurons in the periaqueductal gray (PAG) and mesencephalic reticular formation (MRF) at the red nucleus (RN) level, ventral portion of paralemniscal tegmental field (vFTP), retrorubral nucleus (RRN), contralateral side of PIA (cPIA), pontis reticularis centralis caudalis (PoC), and most rostral portion of the nucleus parvicellularis (NPV) and nucleus praepositus hypoglossi (PH) at the level of the pontomedullary junction; moderate labelling was seen in pedunculopontine nucleus, pars compacta (PPNc), laterodorsal tegmental nucleus (LDT), superior colliculus (SC), MRF and PAG at the level caudal to RN, medial and superior vestibular nuclei, and principle sensory trigeminal nucleus (5P); and light labelling was seen in dorsal raphe (DR) and locus coeruleus complex (LCC). The projection neurons were predominantly ipsilateral to the injection site, except for both vFTP and RRN, which had more projection cells on the contralateral side. Double labelled WGA-HRP/NADPH-d neurons could be found in PPNc and LDT. Double labelled WGA-HRP/glutamatergic neurons could be seen at high densities in MRF, RRN, vFTP, and cPIA, moderate densities in SC, LDT, PPNc, PoC, and NPV, and low densities in PH, 5P, DR, LCC, and PAG.(ABSTRACT TRUNCATED AT 250 WORDS)

Synaptic relationships between gaba-immunoreactive boutons and primary afferent terminals in the rat cuneate nucleus

The present study examined the synaptic relation between the primary afferent terminals and intrinsic neuronal elements in the rat cuneate nucleus. For this purpose, experimental degeneration after multiple cervicothoracic dorsal rhizotomies or anterograde transport of wheatgerm agglutinin conjugated to horseradish peroxidase were used to identify the primary afferent terminals, while immunogold postembedding staining was employed to identify the GABA-immunoreactive boutons. The combined procedure allowed us to demonstrate a direct synaptic relationship between the primary afferent terminals and GABA-immunoreactive boutons. At least two types of synaptic relation were observed between the primary afferent terminals, identified by their degenerating features or labeled by wheatgerm agglutinin conjugated to horseradish peroxidase, and the immunogold-labeled GABA-immunoreactive boutons (i) a GABA-immunoreactive bouton making a simple presynaptic contact with the primary afferent terminal; and (ii) a synaptic glomerular complex in which the centrally located primary afferent terminal was postsynaptic to a GABA-immunoreactive bouton and presynaptic to dendrites closely associated with it; both terminals were sometimes presynaptic to a common dendrite. It is speculated from this study that the incoming impulses from the forelimb area are modulated by the GABA-immunoreactive boutons in the cuneate nucleus of the rat.

Differential spinal projections of subregions in the forelimb area of the motor cortex in the cat

Anterograde transport of wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP) was used to examine the topography of projections from the forelimb area of motor cortex to the cervical spinal cord in the cat. Tracer was injected in sites in the rostrolateral (RL-MCx) and caudolateral (CL-MCx) subregions concerned with the distal forelimb. Whereas both subregions projected throughout the cervical cord, with the greatest density of label present in the cervical enlargement, the dorso-ventral distributions were different for the two injection sites. Injections in RL-MCx produced labeling in the lateral portions of laminae VI, VII, and VIII in the upper cervical segments. This corresponds to the locations of propriospinal neurons that project to forelimb motor nuclei used in reaching [Exp. Brain Res., 42 (1981) 299–318]. In the cervical enlargement, labeling was present in laminae V, VI, VII, and part of VIII. At all levels examined, the density of labeling was greatest in the intermediate zone. After CL-MCx injection, labeling was concentrated in the dorsal horn both in the upper cervical segments and in the cervical enlargement. These findings suggest that the two motor cortical subregions project to different propriospinal and interneuronal systems in the cervical cord and support the idea that the two subregions play different roles in controlling forelimb movements.

Distribution of cerebellothalamic and nigrothalamic projections in the dog: a double anterograde tracing study.

The distribution of nigrothalamic and cerebellothalamic projections was investigated in the dog by a double labeling strategy combining the anterograde transport of wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP) and tritiated amino acids. Following tritiated amino acid injections into the substantia nigra pars reticulata (SNr) and WGA-HRP injections into the contralateral cerebellar nuclei, we found that the nigrothalamic and cerebellothalamic afferents distribute to three main targets: the central portion of the ventral anterior nucleus (VA) and the ventral lateral nucleus (VL), the internal medullary lamina (IML) region, which includes the paralaminar VA, the mediodorsal nucleus (MD) and the central lateral nucleus (CL), and finally the ventromedial nucleus (VM). We observed three distribution patterns of labeled fibers: a) Dense single label was observed in the central portion of VA following the SNr injections and in VL following the cerebellar nuclei injections. b) A complementary pattern consisting of alternating foci of nigral and cerebellar label was found in the IML region. This pattern was also observed in the caudal intralaminar nuclei where cerebellar label predominated in the centrum medianum (CM), while the parafascicular nucleus (Pf) primarily contained nigral label. c) An overlapping pattern of autoradiographic and WGA-HRP label was found in the lateral half of the VM. Overall, the distribution of nigrothalamic and cerebellothalamic projections was widespread throughout much of rostrocaudal thalamus. However, the pattern of projections varied along a continuum from lateral to medial thalamus. In lateral thalamus, nigral and cerebellar projections distributed to separate nuclei while in medial thalamus, the projection pattern changed to focal and complementary in the IML and overlapping in VM. Taken together, these thalamic projections may constitute crucial links in different functional channels involved in alerting and orienting mechanisms associated with motor behavior. Our findings also suggest that the organization of motor thalamic afferents in the dog shares similarities with the segregated and parallel circuitry characteristic of primates as well as with the overlapping and converging circuits of rodents and other carnivores.

Spinothalamic and propriospinal neurones in the upper cervical cord of the rat: terminations of primary afferent fibres on soma and primary dendrites.

Experiments were performed on rats to determine whether primary afferents from the upper cervical region terminate directly on spinothalamic and propriospinal neurones. The central terminations of primary afferents from the upper cervical region were identified by diffusely filling their axons with horseradish peroxidase. Spinothalamic neurones or propriospinal neurones were identified in the same experimental animals by using retrograde transport of wheat germ agglutinin conjugated to horseradish peroxidase. Approximately 3-11% of spinothalamic cells in laminae 4-6 of spinal segments C2-4 received apparent synaptic contacts from primary afferents on the soma or primary dendrites. Approximately 18-36% of propriospinal neurones with axons descending to lower thoracic or lumbar levels received apparent synaptic contacts on the soma or primary dendrites. These data provide anatomical evidence that spinothalamic and long propriospinal neurones in the upper cervical cord are excited directly by primary afferents. The data also help to clarify the neural circuitry underlying somatic sensation and reflex movements evoked by neck receptors.

Topographic organization of subcortical projections to the anterior thalamic nuclei in the rat

Subcortical projections to the anterior thalamic nuclei were studied in the rat, with special reference to projections from the mammillary nuclei, by retrograde and anterograde transport of wheat germ agglutinin conjugated to horseradish peroxidase. The medial mammillary nucleus (MM) projects predominantly ipsilaterally to the entire anterior thalamic nuclei, whereas the lateral mammillary nucleus projects bilaterally to the anterodorsal nucleus (AD) of the anterior thalamic nuclei. A topographic relationship was recognized between the MM and the anterior thalamic nuclei. The dorsal region of the pars mediana of the MM projects to the interanteromedial nucleus (IAM), whereas the ventral region projects to the rostral part of the anteromedial nucleus (AM). The dorsal and the ventral regions of the pars medialis project to the dorsomedial part of the AM at its caudal and rostral levels, respectively. The dorsomedial region of the pars lateralis projects to the ventral AM. The ventrolateral region of the pars lateralis projects to the ventral part of the anteroventral nucleus (AV) in such a manner that rostral cells project rostrally and caudal cells project caudally. The pars basalis projects predominantly ipsilaterally to the dorsolateral AV and bilaterally to the AD. The rostrolateral region of the pars posterior projects to the lateral AV, whereas the medial and the caudal regions of the pars posterior project to the dorsomedial AV. The rostrodorsal part of the nucleus reticularis thalami was found to project to the anterior thalamic nuclei; cells located rostrally in this part project to the IAM and AM, whereas cells located caudodorsally project to the AV and AD. The laterodorsal tegmental nucleus projects predominantly ipsilaterally to the AV, especially to its dorsolateral part. The present study demonstrates that subdivisions of the subcortical structures are connected to the subnuclei of the anterior thalamic nuclei, with a clear-cut topography arranged in the dorsoventral and the rostrocaudal dimensions.

Trigeminocerebellar projections to the posterior lobe in the cat, as studied by anterograde transport of wheat germ agglutinin-horseradish peroxidase.

Cerebellar projections of the nucleus interpolaris and oralis of the spinal trigeminal nucleus were studied in the cat by anterograde transport of wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP). Injections of WGA-HRP into these nuclei labeled many mossy fiber terminals mainly ipsilaterally in the rostral folium of lobule IX (IXa or IXa + b), the simple lobule, the anterior part (sublobule A) of the paramedian lobule and the posterior part of crus II. Labeled terminals were also seen in the anterior lobe, lobules VI and VII, the anterior part of crus I, and the paraflocculus dorsalis. Projection fields in the horizontal plane of lobules were reconstructed from a series of transverse sections through each folium of lobule IX, the paramedian lobule, and the posterior part of crus II on the ipsilateral side. In sublobule IXa + b, labeled terminals were distributed in five longitudinal areas extending along the apicobasal axis of the sublobule. These five areas were located in the apical two-thirds of the ipsilateral half of the sublobule. Labeled terminals were distributed in five longitudinal areas in sublobule A (the rostral part) of the paramedian lobule. In the posterior part of crus II, four aggregations of labeled terminals were present in cross sections through a lobule. They were distributed in the apicobasal extent of the lobules. The present study indicates that the projection fields of trigeminocerebellar fibers are longitudinally arranged along the apicobasal axis of the cerebellar lobules.

The primate dorsal spinothalamic tract: evidence for a specific termination in the posterior nuclei (Po/SG) of the thalamus

The spinothalamic tract in primates and other mammals arises primarily from cells in lamina 1 of the dorsal horn, from lamina V cells and to a lesser extent from other laminae. Most of the neurons of lamina I respond only to noxious mechanical or thermal stimuli. Spinothalamic tract (STT) cells of lamina V tend to respond to both innocuous and noxious stimuli. Recent studies have suggested that the classical STT in the anterolateral quadrant (ALQ) contains primarily the axons of lamina V cells and that the axons of lamina I cells travel more dorsally in the dorsolateral quadrant (DLQ) to constitute the dorsal spinothalamic tract (DSTT). Using the anterograde transport of wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP) injected into the spinal cord in conjunction with a contralateral anterolateral cordotomy, we have found there is a substantial projection of the DSTT to the posterior nuclei of the caudal-ventral thalamus, designated Po/SG. This projection is almost entirely abolished when the lesion includes the area of spinal cord white matter at the level of the denticulate ligament. Larger lesions that destroy the ALQ and much of the lateral column white matter, but that spare the dorsolateral column white matter in the region of the corticospinal tract, abolish all transport of WGA-HRP to the thalamus. We conclude that the spinothalamic pathway in the non-human primate encompasses a continuous fiber bundle that extends dorsally to include the region of lateral column white matter opposite the denticulate ligament and that the more dorsal aspect of this pathway projects primarily to Po/SG of thalamus.

Retinal projections in the house musk shrew, Suncus murinus, as determined by anterograde transport of WGA-HRP.

Retinal projections in the house musk shrew (Suncus murinus) were determined by the anterograde transport of wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP). Unilateral injection of WGA-HRP into the vitreous body resulted in the terminal labeling of the optic projections in the suprachiasmatic nucleus (SCH), the ventral (CGLv) and dorsal (CGLd) lateral geniculate nuclei, the intergeniculate leaflet (IGL), the pretectum, the superficial layers of the superior colliculus (CS), and the dorsal terminal nucleus (DTN) of the accessory optic system (AOS). Labeling of the SCH was bilateral, with ipsilateral predominance, and covered the whole dorsoventral extent of the nucleus. Immunohistochemical studies revealed that VIP-like immunoreactive neurons and fibers were present in almost all parts of the SCH. No hypothalamic regions other than the SCH received the optic fibers. The ipsilateral projections to the CGLv, CGLd, and IGL were sparse, and a considerable number of uncrossed retinal fibers were found in the pretectal olivary nucleus. No retinal projections to the lateral posterior thalamic nucleus (LP) were found. Ipsilateral optic fibers projected sparsely to the medial part of the CS. The AOS consisted of a small DTN with a very few crossed retinal projections but no lateral and medial terminal nuclei. In addition, the AOS had no inferior fascicle.

Gracile projection to the cat medial accessory olive: Ultrastructural termination patterns and convergence with spino‐olivary projection

The caudal medial accessory subdivision of the inferior olive (cMAO) receives information from the hindlimb from both the gracile nucleus and the lumbosacral spinal cord. This study determined which elements in cMAO serve as the postsynaptic targets of the gracile projection and whether these elements also receive input from the lumbosacral spinal cord. Gracile axons were labeled in cats by anterograde transport of wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP), visualized with tetramethylbenzidine. Convergence of gracile and lumbosacral axons was evaluated by labeling in the same animal, one pathway by WGA-HRP and the other by degeneration. In cMAO, gracile axons synapse with equal probability on dendritic spines and distal dendritic shafts. This termination pattern contrasts markedly with that of other somatosensory inputs to the inferior olive and may account for the greater heterogeneity in responses to somatosensory stimuli displayed by neurons in cMAO. The distal dendritic shafts receiving gracile input were more likely than dendritic spines to receive convergent input from putative inhibitory synapses. The most likely source of these inhibitory synapses is the parasolitary nucleus, a structure that has been shown by others to receive input from the cerebellum. Thus the parasolitary nucleus may serve as an inhibitory relay between the cerebellum and cMAO. The dendritic spines in cMAO that receive input from the gracile nucleus often receive additional input from the lumbosacral spinal cord. This convergence of somatosensory axons on dendritic spines may provide a mechanism through which the unusually complex receptive fields of neurons in cMAO are generated.

Central projections of cervical primary afferent fibers in the guinea pig: An HRP and WGA/HRP tracer study

The central course and the projections of the first and the second cervical dorsal root ganglia and of suboccipital muscle primary afferent fibers in the guinea pig were studied by means of anterograde transport of wheat germ agglutinin conjugated to horseradish peroxidase (WGA/HRP) or aqueous solution of horseradish peroxidase (HRP). Injections of WGA/HRP into the second cervical dorsal root ganglion produced labeling in the dorsal and ventral horns. Within the spinal cord, the largest amount of HRP reaction product was found within the lateral third of the substantia gelatinosa and within the central cervical nucleus. The main area of termination in the medulla was the external cuneate nucleus. However, HRP reaction product was also found within the medial and inferior vestibular nuclei, cell group x, the perihypoglossal nuclei, the nucleus of the solitary tract, and the nucleus of the spinal trigeminal tract. Descending fibers could be detected as caudal as spinal segment T5. Injections of WGA/HRP into the first cervical dorsal root ganglion produced heavy terminal label within the central cervical nucleus but not within the substantia gelatinosa. Again, the external cuneate nucleus was the main area of termination within the medulla. Label could not be observed within the vestibular nuclear complex or within the spinal trigeminal nucleus. Injections of aqueous HRP into the suboccipital muscles produced heavy transganglionic label within the central cervical nucleus, whereas the substantia gelatinosa totally lacked terminal label. Ascending proprioceptive fibers reached the external cuneate nucleus and group x. Scanty projections could be detected within the vestibular nuclei as well as within the perihypoglossal nuclei except for the nucleus prepositus hypoglossi. Label was absent in the spinal trigeminal nucleus.