Observations of HRP labeling following injection through a chronically implanted cannula--a method to avoid diffusion of HRP into injured fibers

The spatial relationship between the cerebral cortex and fiber trajectory through the corpus callosum of the cat

We related fiber trajectory through the feline corpus callosum to the site of fiber origin in the cortical mantle and to functional modality. The cortical fields which contribute axons to the different portions of the corpus callosum were revealed by applying horseradish peroxidase (HRP) to the cut ends of selected groups of callosal axons in twelve adult cats. Overall, the application of HRP at progressively more caudal positions in the corpus callosum labels fields of neurons at successively more caudal positions in the cerebral cortex. Comparison of these data to functionally distinct cortical zones shows that the callosal body conveys a mixture of fibers arising from functionally diverse regions of the cerebrum, whereas portions of the rostral and caudal ends appear to be essentially unimodal, conveying motor and visual signals, respectively.

The substantia innominata complex and the peripeduncular nucleus in orofacial dyskinesia: a pharmacological and anatomical study in cats

It has been shown that orofacial dyskinesia, i.e. a syndrome of abnormal involuntary movements of the facial muscles, can be elicited from the sub-commissural part of the globus pallidus and the adjoining dorsal parts of the extended amygdala in cats. Until now it is unknown whether the peripeduncular nucleus, which receives input from these structures according to anterograde tracing studies, plays a role in the funneling of orofacial dyskinesia to lower output stations. In the present study the connection of the subcommissural part of the globus pallidus and dorsal parts of the extended amygdala with the peripeduncular nucleus was investigated anatomically, using cholera toxin subunit B as a retrograde tracer, and functionally, using intracerebral injections of GABAergic compounds. The anatomical data show that the sub-commissural part of the globus pallidus and dorsal parts of the extended amygdala were marked by cholera toxin sub-unit B-immunoreactive cells following injections of this retrograde tracer into the peripeduncular nucleus. Thus, it could be confirmed that the peripeduncular nucleus receives input from the sub-commissural part of the globus pallidus and dorsal parts of the extended amygdala. Still, the orofacial dyskinesia elicited by local injections of the GABA antagonist picrotoxin (500 ng/0.5 microliters) into the sub-commissural part of the globus pallidus and dorsal extended amygdala was only in part attenuated by local injections of the GABA agonist muscimol (100 ng/l microliters) into the peripeduncular nucleus. Only the number of tongue protrusions was significantly attenuated, but not that of the ear and cheek movements. Furthermore, tongue protrusions, but no additional oral movements, were elicited by picrotoxin injections (375-500 ng) into the peripeduncular nucleus.(ABSTRACT TRUNCATED AT 250 WORDS)

Afferent and efferent connections of the cholinoceptive medial pontine reticular formation (region of the ventral tegmental nucleus) in the cat

Following minor concussive brain injury when there is an otherwise general suppression of CNS activity, the ventral tegmental nucleus of Gudden (VTN) demonstrates increased functional activity (32). Electrical or pharmacological activation of a cholinoceptive region in this same general area of the medial pontine tegmentum contributes to certain components of reversible traumatic unconsciousness, including postural atonia (31, 32, 45). Therefore, in an effort to examine the neuroanatomical basis of the behavioral suppression associated with a reversible traumatic unconsciousness, the afferent and efferent connections of the VTN and putative cholinoceptive medial pontine reticular formation (cmPRF) were studied in the cat using the retrograde horseradish peroxidase (HRP), HRP/choline acetyltransferase (ChAT) double-labeling immunohistochemistry, and anterograde HRP and autoradiographic techniques. Based upon retrograde HRP labeling, the principal afferents to the VTN region of the cmPRF originated from the medial and lateral mammillary nuclei, and lateral habenular nucleus, and to a lesser extent from the interpeduncular nucleus, lateral hypothalamus, dorsal tegmental nucleus, superior central nucleus, and contralateral nucleus reticularis pontis caudalis. Other afferents, which were thought to have been labeled through spread of HRP into the medial longitudinal fasciculus (MLF), adjacent paramedian pontine reticular formation, or uptake by transected fibers descending to the inferior olive, included the nucleus of Darkschewitsch, interstitial nucleus of Cajal, zona incerta, prerubral fields of Forel, deep superior colliculus, nucleus of the posterior commissure, nucleus cuneiformis, ventral periaqueductal gray, vestibular complex, perihypoglossal complex, and deep cerebellar nuclei. In HRP/ChAT double labeling studies, only a very small number of cholinergic VTN afferent neurons were found in the medial parabrachial region of the dorsolateral pontine tegmentum, although the pedunculopontine and laterodorsal tegmental nuclei contained numerous single-labeled ChAT-positive cells. Anterograde HRP and autoradiographic findings demonstrated that the VTN gave rise almost exclusively to ascending projections, which largely followed the course of the mammillary peduncle (16,21) and medial forebrain bundle, or the tegmentopeduncular tract (4). The majority of fibers ascended to terminate in the medial and lateral mammillary nuclei, interpeduncular complex (especially paramedian subnucleus), ventral tegmental area, lateral hypothalamus, and the medial septum in the basal forebrain. Labeling that joined the mammillothalamic tract to terminate in the anterior nuclear complex of the thalamus was thought to occur transneuronally. Some projections were also observed to nucleus reticularis pontis oralis and caudalis, superior central nucleus, and dorsal tegmental nucleus adjacent to the VTN...

The frontal eye field and prefrontal cortex project to the paramedian pontine reticular formation in the cat

Transcannular microinjections of horseradish peroxidase were made into the paramedian pontine reticular formation (PPRF) in adult cats to identify regions of the cerebral cortex having direct influence on this important center for the production of saccadic eye movements. The majority of retrogradely labeled cortico-(ponto)reticular neurons were located in lamina V of the dorsomedial precruciate shoulder cortex and presylvian sulcal cortex, the medial and lateral frontal eye fields of the cat respectively. In most cases, labeled cells also extended into the gyrus proreus, the cat prefrontal cortex.

The ultrastructural identification of reticulo-hypoglossal axon terminals anterogradely labeled with horseradish peroxidase

Injections of horseradish peroxidase (HRP) or wheat-germ agglutinin-horseradish peroxidase (WGA-HRP) into the nucleus reticularis parvocellularis (RPc) produced anterograde labeling of axon terminals within the hypoglossal nucleus. Based on morphological parameters of vesicle population, membrane specializations, and postsynaptic articulations, two types of axon terminals derived from neurons in RPc end on hypoglossal neurons. More than half of the terminals contained spherical vesicles (S-type), established asymmetrical membrane specializations and contacted proximal and medium-sized dendrites. The remaining labeled terminals had flattened vesicles (F-type), symmetrical membrane densities and apposed medium and small dendrites. The morphological differences expressed in the two types of terminals may reflect physiological and/or pharmacological differences in the action of RPc neurons on motoneurons in the hypoglossal nucleus.

Afferents to a midbrain periaqueductal grey region involved in the 'defence reaction' in the cat as revealed by horseradish peroxidase. I. The telencephalon

Horseradish peroxidase injections were made at sites, within the midcollicular portion of the midbrain periaqueductal grey region (PAG), at which both electrical stimulation and subsequent microinjections of excitatory amino acids elicited defensive behaviour. Since excitatory amino acids depolarize cell bodies and dendrites located in the vicinity of the injection site but not axons of passage, the injections were centred within a PAG region known to contain neurones whose excitation elicited defensive behaviour. The telencephalic afferents to these sites were then determined. Sixty percent of the labelled telencephalic neurones were found in the frontal cortex, specifically in the medial frontal cortex along the banks of the rostral two-thirds of the cruciate sulcus, primarily area 6 and area 4, and the medial frontal cortex ventral to area 6 (area 32). Twenty-five percent of the labelled telencephalic neurones were found in the orbito-insular cortex while 8% were found in the parietal cortex surrounding the anterior ectosylvian sulcus. Although the functional significance of these projections remains to be established, available data suggest that these projections to the PAG arise from frontal 'oculomotor' and motor cortices, a polysensory insular cortical region and somatosensory, visual and auditory parietal cortical areas.

Afferents to a midbrain periaqueductal grey region involved in the 'defense reaction' in the cat as revealed by horseradish peroxidase. II. The diencephalon

Horseradish peroxidase injections were made at the same sites, within the midcollicular portion of the midbrain periaqueductal grey region (PAG), at which electrical stimulation and microinjections of excitatory amino acids elicited defensive behaviour. The diencephalic afferents to these sites were then studied. Seventy eight percent of the labelled diencephalic neurons were found within the tuberal portion of the hypothalamus, specifically in 3 regions: (a) the ventromedial hypothalamic nucleus and adjacent perifornical area; (b) the region of the tuber cinereum, ventral and medial to the ventromedial hypothalamic nucleus; (c) the region of paraventricular and parvocellular hypothalamic nuclei. A control injection of HRP at a site, in the tegmentum immediately adjacent to the PAG, at which electrical stimulation elicited defensive behaviour, but excitatory amino acid injections did not, suggested that the extensive labelling of neurones within the tuberal region of the hypothalamus was specific to the HRP injections being made at PAG sites at which excitatory amino acid injections elicited defensive behaviour.

Temporal pattern of HRP spread from an iontophoretic deposit site and description of a new HRP-gel implant method

In the course of examining afferents to ventromedial hypothalamic (VMH) neurons using horseradish peroxidase (HRP), we needed to know how close to an iontophoretic deposit site neurons could be proved to be retrogradely labeled. In evaluating cells near but clearly outside HRP deposit sites visualized after a 24-hour survival period, for example, neurons which had been filled with HRP by somal or dendritic uptake could not be treated as retrogradely labeled and thus would not add to studies of intrahypothalamic connections. Rats were given standardized iontophoretic applications of HRP into VMH (continuous positive current 0.25 mu amp for 1 minute) and sacrificed after 5 or 15 minutes, 1, 4, 8, 12, or 24 hours in order to examine the pattern of HRP spread. The chromogen was tetramethylbenzidine. The volume of the application site visualized at 24 hours was less than 10% of maximum site size, which occurred at 1 hour. Since the cells located within the maximal spread boundary are candidates for nonretrograde labeling, HRP data on local connections obtained even from small iontophoretic deposits must be evaluated in the light of the demonstrated expansion and subsequent contraction of the application site. These results may also hold implications for the precision with which distant connections can be examined using the HRP retrograde method, as sites that appear discrete when visualized after 24-hour survival may have overlapped at shorter times post-iontophoresis. Incorporation of retrograde tracers into polyacrylamide gels provides an effective alternative to pressure injection or iontophoresis of aqueous tracer solutions. We describe a method for filling micropipettes with HRP-polyacrylamide gel. The pipettes are then implanted into brain sites to provide a confined pool of HRP. With postimplantation survival of 24 hour or longer, this method produces sites comparable in size to iontophoretic sites examined at 24 hours and results in improved retrograde labeling. Some results obtained with this method concerning the afferent connections of the dorsomedial hypothalamus are described.

Supramedullary afferents of the nucleus raphe magnus in the rat: a study using the transcannula HRP gel and autoradiographic techniques

Afferents of the nucleus raphe magnus (NRM) were retrogradely labelled by using a transcannula HRP gel technique in conjunction with tetramethylbenzidine neurohistochemistry to determine the sources of inputs to the nucleus which could potentially influence the descending antiociceptive raphe-spinal system. Large numbers of HRP-labelled neurons were seen in the frontal cortex, dorsomedial nucleus of the hypothalamus, zona incerta, nucleus parafascicularis prerubralis (NPfPr), pretectum, dorsal and lateral periaqueductal gray, nucleus cuneiformis (NC), deep superior colliculus (dSC), a paraoculomotor cell group which may be the medial accessory nucleus of Bechterew, dorsal column nuclei, and spinal trigeminal nucleus. Smaller numbers of labelled cells were also observed in the preoptic area, nucleus of Darkschewitsch, ventral peri(third)ventricular gray, nucleus reticularis pontis oralis and caudalis, medial and lateral vestibular nuclei, and a subdivision of the hypoglossal nucleus. Confirmational anterograde autoradiographic studies were performed by injecting tritiated leucine into two of the principal sources of afferents to NRM: NPfPr, and dSC/NC. The results are compared with control HRP gel implants in the inferior olive, spinal cord, nucleus reticularis paragigantocellularis, and medial facial nucleus. Comments are also made concerning the parcellation of the ventromedial medulla and the possible role of both NRM and its afferents in central analgesic mechanisms.

Uptake of horseradish peroxidase by axons of passage and its modification by poly-L-ornithine and dimethylsulphoxide

It has been shown that transected axons of passage in the optic tract can take up horseradish peroxidase (HRP) and transport it back to the cell bodies. This effect is considerably reduced if the HRP is injected from a small-tipped micropipette 6-12 h after insertion into the injection site. HRP is not taken up by uninjured axons of passage. The use of poly-L-ornithine and dimethylsulphoxide dramatically increases the numbers of labeled cells. These numbers are undiminished after 6-12 h waiting periods. From this and from calculation it is clear that much of this effect must occur via uninjured axons. These substances should not be used in any situation where it is important not to label axons of passage. If other HRP conjugates and additives have the same effect as those described here, the results of experiments with these substances should be interpreted with caution.

A transcannula method for subcortical HRP gel implants: inferior olive afferents in the rat

A technique for using horseradish peroxidase in a polyacrylamide gel form for subcortical implants is described. In order to prevent uptake along the injection tract, the solid HRP gel pellet is delivered through a pre-implanted cannula to the target site. The appreciable advantages of using the HRP-transcannula technique are discussed in conjunction with a description of the afferents to the inferior olivary complex in the rat. The principal sources of afferents were the ipsilateral prerubral parafascicular nucleus, contralateral lateral cerebellar nucleus and dorsal column nuclei.

The organization of afferent projections to the midbrain periaqueductal gray of the rat

The retrograde transport technique was utilized in the present study to investigate the afferent projections to the periaqueductal gray of the rat. Iontophoretic injections of horseradish peroxidase were made into the periaqueductal gray of 22 experimental animals and into regions adjacent to the periaqueductal gray in 6 control animal. Utilization of the retrograde transport method permitted a quantitative analysis of the afferent projections not only to the entire periaqueductal gray, but also to each of its four intrinsic subdivisions. The largest cortical input to this midbrain region arises from areas 24 and 32 in the medial prefrontal cortex. The basal forebrain provides a significant input to the periaqueductal gray and this arises predominantly from the ipsilateral lateral and medial preoptic areas and from the horizontal limb of the diagonal band of Broca. The hypothalamus was found to provide the largest descending input to the central gray. Numerous labeled cells occurred in the ventromedial hypothalamic nucleus, the lateral hypothalamic area, the posterior hypothalamic area, the anterior hypothalamic area, the perifornical nucleus and the area of the tuber cinereum. The largest mesencephalic input to the periaqueductal gray arises from the nucleus cuneiformis and the substantia nigra. The periaqueductal gray was found to have numerous intrinsic connections and contained a significant number of labeled cells both above and below the injection site in each case. Other structures containing significant label in the midbrain and isthmus region included the nucleus subcuneiformis, the ventral tegmental area, the locus coeruleus and the parabrachial nuclei. The medullary and pontine reticular reticular formation provide the largest input to the periaqueductal gray from the lower brain stem. The midline raphe magnus and superior central nucleus also supply a significant fiber projection to the central gray. Both the trigeminal complex and the spinal cord provide a minor input to this region of the midbrain. The sources of afferent projections to the periaqueductal gray are extensive and allow this midbrain region to be influenced by motor, sensory and limbic structures. In addition, evidence is provided which indicates that the four subdivisions of the central gray receive differential projections from the brain stem as well as from higher brain structures.

Neural damage following retrochiasmatic knife cuts in the rat

In order to define neuronal damage produced by sham, frontal and frontolateral hypothalamic knife cuts known to effect neuroendocrine and behavioral variables, we designed a retractable knife capable of delivering horseradish peroxidase as a cut was being produced. Damaged neurons filled with homogeneous reaction product were found in virtually all hypothalamic nuclei. A similar distribution of damage was produced by frontolateral (FLC), frontal (FC) or sham cuts--the primary differences being the greater density of damaged neurons in hypothalamic nuclei and labeling of the ventral tegmental area of Tsai in FLC and FC animals. The difference between FC and FLC animals was primarily one of degree of damage. The amount of damage produced by the sham surgery is consistent with the idea that sham surgeries produce endocrine dysfunctions intermediate between frontal cut animals and unoperated controls. It is interesting to note that a number of nuclei damaged by these surgeries provide aminergic innervation to the hypothalamus.

Cortical projections to visual centres in the rat: an HRP study

We have investigated the relationships of the visual cortex to other visual centres in the rat: namely the lateral geniculate nucleus, the visually responsive part of the thalamic reticular nucleus and the superior colliculus. We injected horseradish peroxidase iontophoretically so as to restrict the injectate to each of the regions, and reacted sections using 3 different procedures. Areas 17, 18 and 18a project to both dorsal and ventral lateral geniculate nucleus as well as to the visually responsive part of the thalamic reticular nucleus and superior colliculus. Pyramidal cells in lamina VI project to the dorsal lateral geniculate nucleus and to the thalamic reticular nucleus, whereas cells of origin of the projection to the superior colliculus lie in lamina V; cells in lamina V also project to ventral lateral geniculate nucleus. The implications of these findings are discussed, particularly in terms of the functional relationships between the visual cortex, lateral geniculate nucleus and visual thalamic reticular nucleus.

Thalamic connections with limbic cortex. I. Thalamocortical projections

The thalamocortical projections to limbic cortex in the cat have been studied with retrograde and anterograde axonal transport techniques. Five limbic cortical areas were identified on the basis of cytoarchitecture. The five areas are the anterior limbic area, the cingular area, the dorsal and ventral retrosplenial areas, and the presubiculum. Each of these cortical areas received small injections of horseradish peroxidase, and the afferent thalamic nuclei were identified by retrograde labelling of cells. The cortical projection of each of the anterior thalamic nuclei and the lateral dorsal nucleus was determined autoradiographically. Each of the anterior thalamic nuclei and the lateral dorsal nucleus projects to limbic cortex by two pathways. One group of fibers leaves the rostral thalamus by the fornix, pierces the corpus callosum, joins the cingulate fasciculus to reach limbic cortex. The other group travels through the lateral thalamic peduncle and internal capsule. The anterior ventral nucleus projects primarily to the dorsal retrosplenial area, particularly to layer I, the deep portion of layer II, and superficial portion of layer III. Sparse projections also exist to the ventral retrosplenial area, the cingular area, and the presubiculum. Very sparse projections to the anterior limbic area are seen. The anterior dorsal nucleus projects primarily to the ventral retrosplenial area, particularly layers I, the deep portion of layer II, and superficial layer III. sparse projections exist to the dorsal retrosplenial area and presubiculum, but apparently no projections exist to the cingular or anterior limbic area. The anterior medial nucleus projects primarily to layers I and superficial III of the ventral retrosplenial area. sparse projections exist to each of the other limbic cortical areas. The lateral dorsal nucleus projects extensively onto limbic cortex. Prominent projections occur to layer I, the external granular layer and lamina dessicans of the presubiculum, layers I and III-IV of the dorsal retrosplenial area, and layers I, III, and IV of the cingular area. Sparse projections occur to the ventral retrosplenial area and the anterior limbic areas. Thalamocortical projections also originate in the midline and intralaminar nuclei including the central medial, reuniens, rhomboid, paracentral, central lateral, and central dorsal nuclei. These data indicate that the anterior thalamic nuclei project upon limbic cortex in a complex manner. Further, the projections to limbic cortex from the anterior nuclei overlap with projections from the lateral dorsal nucleus. This overlap of thalamic projections onto limbic cortex suggests a convergence of information from nonprimary sensory systems with information from the classical limbic system.

A new method for application of horseradish peroxidase into a restricted area of the brain

A new method for horseradish peroxidase (HRP) application into the very restricted area of the brain was developed. Crystalline HRP was packed into the tips of fine micropipettes having tip size of about 50 micrometer in outer diameter. The HRP micropipettes were stereotaxically implanted into the globus pallidus of rats. After survival period of 6 to 48 hours, brain was excised and HRP distribution was investigated following conventional procedures. The diffusion area of HRP at the application site was restricted within the limits of 200--250 micrometer in diameter completely inside the globus pallidus. It was known that the slowly solubilized crystalline HRP was taken up by the nerve terminals in the globus pallidus, and transported retrogradely to the cell bodies in the pars compacta of substantia nigra, indicating the existence of nigro-pallidal projections.

The topographical organization and laminar origin of some cortico-amygdaloid connections

Injections of horseradish peroxidase were made into the basolateral nuclei of the amygdaloid complex in cats. It was shown that the periamygdaloid cortex immediately below the rhinal sulcus and extending medially to the amygdaloid fissure projects to the lateral nucleus. The rest of the periamygdaloid cortex medial to the amygdaloid fissure and including the cortical nucleus of the amygdala projects primarily to the basomedial nucleus. These cortico-amygdaloid projections originate in the deeper one-third of the cortex. No projections from the neocortex could be demonstrated.

Uptake sites of horseradish peroxidase after injection into peritoneal structures: defining some pitfalls

Following injection of horseradish peroxidase (HRP) either into the jejunal wall or the peritoneal cavity, neurons in the dorsal motor nucleus of the vagus nerve, celiac, nodose and spinal ganglia, and ventral and lateral horns of the spinal cord from the mid-thoracic to lumbar segments were labeled. When HRP was injected into the wall of the exteriorized gut, neurons of the spinal cord were not labeled. Furthermore, there was a significant decrease in the number of labeled neurons in the dorsal motor nucleus and ganglia examined. These results indicate that HRP injected into the intestinal wall could leak into the peritoneal cavity and be taken up and transported to neuronal cell bodies by nerve fibers not terminating in the injection area. The leakage of HRP to nearby abdominal structures and its subsequent uptake by nerve fibers is attributed to the lack of a diffusion barrier across the surfaces of the intestinal wall and the abdominal structures. It is suggested that in applying the HRP techniques for the study of neuronal connections in the peripheral nervous system, it is essential that carefully pla-ned control experiments be undertaken which can overcome the problem of mislabeling due to diffusion from the injection site.