Injections Of Wheat Germ Agglutinin-horseradish Peroxidase Research Articles

Adult rat motor cortex connections to thalamus following neonatal and juvenile frontal cortical lesions: WGA-HRP and amino acid studies.

Frontal cortex was removed in 1- and 30-day-old rats. When both groups reached 90 days of age, the forelimb motor/sensory cortex in the unlesioned hemisphere was injected with wheat germ agglutinin-horseradish peroxidase (WGA-HRP) or tritiated leucine. Thalamic neurons were retrogradely labeled only ipsilateral to the WGA-HRP injection site in both neonatally and juvenile-lesioned subjects. Ventrolateral (VL), ventromedial (VM), centromedial (CM), centrolateral (CL), parafascicular (PF), posteromedial (POm), and posterior (PO) thalamic nuclei were labeled. This and the demonstration of only ipsilateral thalamocortical connections at birth helped explain the marked thalamic atrophy which developed ipsilateral to neonatal frontal cortex lesions. Death of thalamic neurons after neonatal removal of their normal cortical target could be due to their failure to sprout into the opposite cortex because that cortex was already innervated by the opposite thalamus at birth. Leucine motor/sensory cortex injections in both neonatally and juvenile-lesioned subjects labeled the ipsilateral VL, VM, CM, CL, PF, POm, and PO thalamic nuclei; contralateral CM, CL, and PF thalamic nuclei; ipsilateral medial, ventral, and lateral pontine nuclei; and parts of the contralateral pontine nuclei. The ipsilateral connections were always more robust than the contralateral connections. The contralateral corticothalamic and corticopontine projections, however, were much more numerous and widespread in neonatally compared to juvenile-lesioned subjects. The greater sparing of some motor functions said to occur in neonatal compared to adult motor cortex-lesioned subjects could be due to the plasticity of corticothalamic, corticopontine, and other corticofugal pathways, but not to the plasticity of thalamocortical pathways.

The cerebellar nucleo-olivary and olivo-cerebellar nuclear projections in the cat as studied with anterograde and retrograde transport in the same animal after implantation of crystalline WGA-HRP. II. The fastigial nucleus.

The bidirectional connections between the inferior olive and the fastigial nucleus were studied by means of anterograde and retrograde transport after implantation of crystalline wheat germ agglutinin-horseradish peroxidase (WGA-HRP) complex into the fastigial nucleus. The fastigio-olivary fibres terminate in the caudal half of the medial accessory olive, nucleus beta and the dorsal cap, and the olivo-fastigial projection has its origin within the same olivary regions. A topical arrangement is indicated for both pathways. The lateral part of the medial accessory olive appears to be connected with the lateral part of the fastigial nucleus, while the medial part of the medial accessory olive appears to be connected with more medial fastigial regions. Retrogradely labelled olivo-fastigial neurons were often located within the terminal field of anterogradely labelled fastigio-olivary fibres, indicating that the olivo-fastigial and fastigio-olivary projections are at least in part reciprocally organized. The findings are discussed and related to previous studies on the olivo-cerebellar nuclear and cerebellar nucleo-olivary pathways. Some methodological considerations are made, and comments are made concerning the active area for uptake and transport from the stained area at the WGA-HRP injection site.

Connections between the cerebellum and hypothalamus in the tree shrew ( Tupaia glis)

Following injections of a wheat germ agglutinin-horseradish peroxidase (WGA-HRP) conjugate into representative areas of cerebellar cortex of tree shrew ( Tupaia glis) retrogradely labeled cells were found in posterior, lateral and dorsal hypothalamic areas and in the lateral mammillary nucleus. These represent monosynaptic hypothalamocerebellar cortical projections. Anterogradely labeled axons were also traced into various areas of the contralateral hypothalamus subsequent to injections of WGA-HRP into the cerebellar nuclei. These results identify a direct cerebellar nucleohypothalamic pathway. These hypothalamocerebellar and cerebellohypothalamic connections represent potential circuits through which the cerebellum may interact with visceral centers.

The onset and development of descending pathways to the spinal cord in the chick embryo.

The ontogenetic development of afferent (supraspinal and propriospinal) as well as efferent (ascending) fiber connections of the spinal cord was examined following the injection of horseradish peroxidase (HRP) or wheat germ agglutinin HRP (WGA-HRP) into the cervical and lumbar spinal cords (or brains) of embryos ranging in age from 4 to 14 days of incubation. A few cells were first reliably retrogradely labelled in the pontine reticular formation on embryonic day (E) 4 and E5 following the injection of WGA-HRP into the cervical and lumbar spinal cord, respectively. Propriospinal projections to the lumbar spinal cord, originating from brachial spinal cord, were found by E5, and from the cervical spinal cord by E5.5. Ascending fibers arising from neurons in the lumbar spinal cord could be followed to rostral mesencephalic levels in E5 embryos. Thus, the earliest supraspinal, propriospinal, and ascending fiber connections appear to be formed almost simultaneously. Retrogradely labelled cells were found in the raphe, reticular, vestibular, interstitial, and hypothalamic nuclei in E5.5 embryos following lumbar injections of WGA-HRP. Except for neurons in cerebellar nuclei, all the cell groups of origin that project to the cervical spinal cord of posthatching chicks were also retrogradely labelled by E8. There was a delay in the time of appearance of the projections from various regions of the brain stem to the lumbar versus the cervical spinal cord, ranging from 0.5 to 7 days, but typically of about 3 days duration. A large number of cells located in the ventral hypothalamic region, just dorsal to the optic chiasma, were found to be labelled following cervical HRP injection between E6 and E10. These cells may represent transient projections that are present only during embryonic stages since no labelled cells were found in this region in the newly-hatched chick.

Evidence of collateral axonal projections to the superior olivary complex.

In this study we investigated the collateral axonal projections to the superior olivary complex using the combined anterograde and retrograde transport of wheat-germ agglutinin conjugated with horseradish peroxidase. Small injections of this tracer were placed in the lateral or medial superior olivary nuclei in cats, and the location of anterograde label in the alternate nuclei of the superior olivary complex was determined. Injections of [3H]leucine were also placed in these nuclei for control purposes. After wheat-germ agglutinin-horseradish peroxidase injections in the lateral superior olivary nucleus anterograde label was observed bilaterally in the medial superior olivary nuclei. Likewise, after injections in the medial superior olivary nucleus anterograde label was observed in the contralateral medial and lateral superior olivary nuclei. The topography of the anterograde label was always precise and varied predictably as a function of the injection site. Most retrogradely labeled cells were located in the ipsilateral anteroventral cochlear nucleus and the medial nucleus of the trapezoid body. Various interpretations of the data are considered. Our primary conclusion is that cells in the anteroventral cochlear nucleus are a major source of collaterals to both the ipsilateral and contralateral nuclei of the superior olivary complex.

Light and electron microscopic demonstration of hypothalamic projections to the parabrachial nuclei in the cat

Hypothalamic connections with the parabrachial nuclei in the cat were studied at light and electron microscopic levels following wheat germ agglutinin-horseradish peroxidase injections into the parabrachial nuclei and electrolytic lesions in the hypothalamus. The greatest concentration of retrogradely labeled neurons occurred in the paraventricular nucleus. Labeled neurons were also seen within the preoptic, anterior, lateral, dorsomedial and ventromedial hypothalamic nuclei. Hypothalamic lesions resulted in the degeneration of terminals forming axosomatic and axodendritic synapses in the parabrachial nuclei, particularly its lateral division. These findings support the idea that hypothalamic connections to specific regions of the parabrachial nuclei may underlie the topographical functional organization demonstrated for these brainstem nuclei.

Reciprocal parabrachial-cortical connections in the rat

The projection from the parabrachial nucleus (PB) to the cerbral cortex in the rat was studied in detail using the autoradiographic method for tracing anterograde axonal transport and the wheat germ agglutinin-horseradish peroxidase (WGA-HRP) method for both anterograde and retrograde tracing. PB innervates layers I, V and VI of a continuous sheet of cortex extending from the posterior insular cortex caudally, through the dorsal agranular and the granular anterior insular cortex and on rostrally into the lateral prefrontal cortex. Within the prefrontal area, PB fibers innervate primarily layer V of the ventrolateral cortex caudally, but more rostrally the innervated region includes progressively more dorsal portions of the prefrontal area, until by the frontal pole the entire lateral half of the hemisphere is innervated. This projection originates for the most part in a cluster of neurons in the caudal ventral part of the medial PB subdivision, although a few neurons in the adjacent parts of the PB, the Kolliker-Fuse nucleus and the subcoeruleus region also participate. After injection of WGA-HRP into the PB region, retrogradely labeled neurons were found in layer V of the same cortical areas which receive PB inputs. The importance of this monosynaptic reciprocal brainstem-cortical projection as a possible anatomical substrate for the regulation of cortical arousal is discussed.