Intracortical connections between neuron groups in the somatosensory cortex studied by the retrograde horseradish peroxidase transport method in rats

Short corticocortical connections between specialized groups of neurons (so-called barrels) were studied in the somatosensory cortex. After microinjections of horseradish peroxidase into a definite "barrel" labeled neurons were found in nearby groups within a radius of up to 400 µ. Labeled neurons were located chiefly in cortical layers V and III; 90% of them were pyramidal cells. Intracortical connection of labeled neurons were 1.6 times more numerous than thalamocortical connections. It is postulated that connections between neighboring cortical neuron groups are effected through their output cells, i.e., through pyramidal neurons of layers V and III.     

Ultrastructural organization of the geniculo-cortical neurons demonstrated by retrograde axonal transport of horseradish peroxidase

The ultrastructural organization of geniculo-cortical relay neurons projecting to the primary auditory cortex (field 22) was studied in the cat by the method of retrograde axonal transport of horseradish peroxidase. The labeled neurons appear to be a medium-sized cells containing a large amount of profiles of vacuolar systems as well as organelles involved in catabolic processes. These cells differ from small unmarked neurons in having a narrow band scanty cytoplasm. Only a few axo-somatic synapses are found on the labeled neurons, the majority of afferent impulsation is perceived by their dendrites. The function of relay neurons is discussed.     

Study of afferent connections of the visual cortex in the ventral bank of the cruciate sulcus in cats by the method of retrograde axonal transport of horseradish peroxidase

To study the possible pathways along which visual signals reach a visual zone discovered by the writers in the cat frontal cortex in the ventral bank of the cruciate sulcus, horseradish peroxidase was injected into a site previously identified by physiological experiments. Stained neurons were discovered in visual areas of the cortex (lateral suprasylvian and ectosylvian), in the parietal cortex (areas 5 and 7), and also in small numbers in the prefrontal and limbic cortex. Stained neurons were found in the following nuclei in the thalamus: n. medialis dorsalis, intralaminar nuclei (nn. centralis lateralis, paracentralis, centralis medialis), nn. ventralis medialis, anteromedialis, and reuniens. Many stained neurons were found in the claustrum and a few in the substantia grisea centralis in the midbrain. The principal sources of inputs to the cortical area investigated are thus centers of the visual system or parts of the brain directly connected with it.Institute for Problems in Information Transmission, Academy of Sciences of the USSR, Moscow. Brain Institute, All-Union Mental Health Research Center, Academy of Medical Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 17, No. 1, pp. 43–49, January–February, 1985.     

Facilitated ultracytochemical demonstration of retrograde axonal transport of horseradish peroxidase in peripheral nerve

p-Phenylenediamine/pyrocatechol mixture (PPD-PC) was evaluated as a reagent for the ultracytochemical demonstration of retrograde axonal transport of horseradish peroxidase (HRP). HRP crystals were applied to the proximal stumps of the severed infraorbital nerves in rats. After 48 h the rats were sacrificed by perfusion, and the trigeminal ganglia ipsilateral to the severed nerves were processed for HRP cytochemistry and then prepared for electron microscopy. PPD-PC was rapidly oxidized in HRP-labeled neurons to form a dark brown-black osmiophilic reaction product which was more readily visible than the DAB product in the sections. This facilitated selection by light microscopy of areas in the epoxy wafers for ultrathin sectioning. In thin sections viewed under the electron microscope, the osmicated electron opaque PPD-PC reaction product was present in membrane-bound structures including smooth endoplasmic reticulum and granules of various sizes. The PPD-PC reaction product formed after 10-min incubation appeared to be more electron opaque than the DAB reaction product formed after 20 min. PPD-PC was found to be much less readily oxidized than DAB by endogenous hemoproteins. This methodology facilitated the ultracytochemical localization of HRP in neurons following retrograde axonal transport.     

Demonstration of the neurosecretory hypothalamo-rhombencephalic junction in rats by the retrograde axonal transport of horseradish peroxidase]

The retrograde transport of horseradish peroxidase (HRP) was used to demonstrate the neurosecretory hypothalamo-hindbrain connection of the rat. Following HRP injections into the region of the dorsal columns nuclei labeled cells were observed in the caudal part of the paraventricular nucleus and in the lateral hypothalmic area. Hypothalamo-hindbrain projections are predominantly uncrossed.     

Discovery of the sources of some descending forebrain systems by the retrograde axonal transport of horseradish peroxidase method

The location of neurons forming fiber systems descending into the brain-stem reticular formation, red nucleus, and relay nuclei of the dorsal columns was studied in cats by the retrograde axonal transport of horseradish peroxidase method. The cortical projection regions, structures of the limbic system, and the hypothalamus were shown to form fiber systems that descend to the brain stem, whereas the orbito-frontal cortex is the chief source of cortico-reticular projections. The possible functional role of these descending systems in the central control of somatic and visceral functions is discussed.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 11, No. 3, pp. 218–226, May–June, 1979.     

The demonstration of recurrent motor axon collaterals in the chick embryo by using horseradish peroxidase axonal transport]

Motoneurons were labelled by retrograde axonal transport of HRP applied to transected spinal nerves in 9-11-day chick embryos in the in vitro spinal cord preparation. Recurrent motor axon collaterals were revealed in 17 of 48 motor axons which could be followed in the edge regions of labelled motoneuronal pools. The results, coupled with author's earlier electrophysiological data, provide further evidence for the presence of the Renshaw inhibition in the avian spinal cord.     

Afferent connections of cat facial nucleus; a study using retrograde axonal transport of horseradish peroxidase

Neuronal populations in the brainstem and spinal cord — the sources of fiber pathways to the facial nucleus — were investigated in adult cats by microiontophoretically injecting horseradish peroxidase into restricted areas of the facial nucleus. Projections were identified from thenucleus nervi hypoglossi, nucleus praepositus hypoglossi, nucleus raphe pallidus, nucleus intercalatus, medial nucleus of the solitary tract, dorsal motor nucleus of the vagus, neurons of genu of the facial nerve, ipsilateral red nucleus, and reticular formation of the midbrain to the facial nucleus. Projections from a number of other brain structures to the facial nucleus also received confirmation. A topographic map was drawn up, showing how brainstem and spinal cord afferents are distributed in the facial nucleus.L. A. Orbeli Institute of Physiology, Academy of Sciences of the Armenian SSR, Erevan. Translated from Neirofiziologiya, Vol. 18, No. 1, pp. 35–45, January–February, 1986.     

Hypophysiotropic neurons in the goldfish hypothalamus demonstrated by retrograde transport of horseradish peroxidase

Summary The horseradish-peroxidase (HRP) technique was used to visualize the cell bodies of axons projecting to the goldfish pituitary. Following intravenous injections of HRP, HRP reaction products were observed in axons of the rostral pars distalis, proximal pars distalis, neurointermediate lobe, pituitary stalk and in axons coursing from the pituitary into the hypothalamus. HRP-labelled cells in the brain were localized in two regions only — the nucleus preopticus (NPO) pars magnocellularis and pars parvocellularis, and the nucleus lateralis tuberis (NLT) of the hypothalamus. These observations suggest that the NPO and NLT are the source of the neurosecretory innervation of the goldfish pituitary.     

Localization of sources of thalamic inputs into the sensorimotor cortex in the rabbit using retrograde axonal transport technique

It was shown that the rabbit sensorimotor cortex received afferent fibers from neurons located in the specific, nonspecific, and association thalamic nuclei using the retrograde axonal transport technique. The distribution, dimensions, and shape of the somata of relay neurons spread through the thalamic nuclei were analyzed. The total number of neurons sending out thalamo-sensorimotor-cortical fibers was calculated and the coordinates of loci with the highest density of these cells in each thalamic nucleus were identified. Multipolar and stellate cells with somata measuring 12–20 µm and 10–15 µm in diameter, respectively, prevailed amongst relay neurons. Amongst the specific nuclei, the majority of afferent fibers are sent out by the ventrolateral, ventral anterior, and anterior ventral nuclei. A comparable number of afferent fibers are sent out by the mediodorsal and paracentral nuclei; these split up among the association nuclei and paracentral nuclei, respectively. It is suggested that afferents from many different groups of thalamic nuclei are essential for the sensorimotor cortex to participate in thalamocortical interaction.Institute of Higher Nervous Activity and Neurophysiology, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 19, No. 1, pp. 87–94, January–February, 1987.     

Olivary projections from the pretectal region in the cat studied with horseradish peroxidase and tritiated amino acids axonal transport

The organization of the projection from the pretectal region to the inferior olive in the cat was studied with autoradiographic and horseradish peroxidase (HRP) methods. After injections of HRP into the olive in six cats, cells were labeled ipsilaterally in the anterior pretectal nucleus (NPA), the posterior pretectal nucleus (NPP), the nucleus of the optic tract (NOT), and the dorsal terminal nucleus of the accessory optic tract (DTN). In three experiments, tritiated amino acids were injected into those parts of the pretectal region which contained labeled cells in the HRP experiments, and the projections to the olive were plotted. Both NPA and NPP projected to the rostral half of the dorsal accessory olive, the rostromedial margin of the ventral lamella, and the lateral part of the ventrolateral outgrowth. NOT projected to the caudal half of the dorsal cap, while DTN projected to both the dorsal cap and nucleus beta. The projections are entirely ipsilateral.     

Superior sensitivity of conjugates of horseradish peroxidase with wheat germ agglutinin for studies of retrograde axonal transport.

We have compared the retrograde axonal transport of horseradish peroxidase (HRP), to the retrograde transport of HRP conjugated with wheat germ agglutinin (WGA). Morphometric studies have shown that WGA-HRP conjugates were 40 times more sensitive than free HRP, in the tracing of retrograde connections from the rat submandibular gland to the superior cervical ganglion. Also, WGA-HRP was more sensitive than free HRP in the tracing of retrograde connections from the rat tongue to the hypoglossal nucleus. Our findings with WGA-HRP are consistent with the observations by Schwab et al. who reported (-125I) WGA is a highly sensitive retrograde tracer (Brain Research 152:145, 1978 (22)).     

Projection of the celiac plexus to the afferent centers demonstrated by the horseradish peroxidase retrograde transport method

Using the horseradish peroxidase (HP) retrograde method for ascertaining connections of the celiac plexus of the white rat with various afferent centers, HP-marked neurocytes have been revealed in caudal nodes of the vagus nerves and in spinal nodes at the Th4-L2 level. Negative results have been obtained at investigation of the cervical spinal nodes and intramural nodes in the cat ileocecal part. Similar data are obtained, when connections of the celiac plexus with the same area of the cat gut are investigated. Therefore, the problem on interrelations of the celiac plexus with the proper afferent centers of the diaphragmatic+ nerve and the second type cells of Dogel in the cat intramural ganglia is still disputable.