Connections of the tectum of the rattlesnake Crotalus viridis: an HRP study.

We have studied the connections of the tectum of the rattlesnake by tectal application of horseradish peroxidase. The tectum receives bilateral input from nucleus lentiformis mesencephali, posterolateral tegmental nuclei, anterior tegmental nuclei and periventricular nuclei; ipsilateral input from nucleus geniculatus pretectalis, and lateral geniculate nucleus pars dorsalis; and contralateral input from dorso-lateral posterior tegmental nucleus and the previously undescribed nucleus reticularis caloris (RC). RC is located on the ventro-lateral surface of the medulla and consists of large cells 25--45 micrometer in diameter. Efferent projections from the tectum can be traced to the ipsilateral nucleus lentiformis mesencephali, the ipsilateral lateral geniculate region, anterior tegmental region and a wide bilateral area of the neuropil of the ventral tegmentum and ventral medualla. We have not found any direct tectal projections from the sensory trigeminal nuclei including the nucleus of the lateral descending trigeminal tract (LTTD). We suggest that in the rattlesnake, RC is the intermediate link connecting LTTD to the tectum.     

The accessory optic system of rodents: a whole-mount HRP study

The three-dimensional fiber pathways of the accessory optic system in three species of rodents (rat, golden hamster, guinea pig) were examined on whole-mounted preparations of the diencephalon and the midbrain, without sectioning, by anterograde labeling of retinal axons with horseradish peroxidase (HRP). HRP histochemical studies on the serial coronal sections were also done. In this study, only the accessory optic system on the side contralateral to the eye injection of HRP was clearly detected. The rat accessory optic system consisted of the inferior fasciculus, the superior fasciculus, the medial terminal nucleus, the lateral terminal nucleus, and the dorsal terminal nucleus. After the inferior fasciculus arrived at the ventromedial border of the cerebral peduncle, some fibers from the inferior fasciculus ran caudally to the medial terminal nucleus. The remaining fibers from the inferior fasciculus further proceeded dorsocaudally on the surface of the cerebral peduncle and left the inferior fasciculus at various levels of the cerebral peduncle to be mixed up with the fibers from the superior faciculus. The golden hamster accessory optic system also consisted of the inferior fasciculus, the superior fasciculus, the medial terminal nucleus, the lateral terminal nucleus, and the dorsal terminal nucleus. However, all fibers of the inferior fasciculus ran caudally on the lateral surface of the hypothalamus or along the ventromedial border of the cerebral peduncle to terminate at the medial terminal nucleus. The guinea pig accessory optic system and rat accessory optic system were similar, but the posterior fibers of the superior fasciculus decreased in number, and the dorsal terminal nucleus and the posterior portion of the lateral terminal nucleus were not observed in the guinea pig accessory optic system.     

Connections of the parietal lobe

The efferent connections of the posterior parietal cortex were studied in rhesus monkeys subjected to selective lesions of the superior and inferior parietal lobules, which correspond approximately to Brodmann's areas 5 and 7, respectively.

Following ablations of either the superior or inferior parietal lobule, axon degeneration, stained with the Nauta and Fink-Heimer methods, was traced into the extreme, external, and internal capsules, and into the cerebral peduncle. This degeneration extended into the ipsilateral insular cortex, cingulate gyrus, prefrontal and premotor cortices, and the precentral and postcentral gyri. In addition to these connections, the superior lobule sends fibers to the ipsilateral inferior parietal lobule and superior temporal gyrus, and via the corpus callosum to the contralateral superior and inferior parietal lobules, whereas the inferior parietal lobule sends fibers to the ipsilateral superior parietal lobule and to the contralateral superior and inferior parietal lobules. A prominent fiber system to the ipsilateral temporal lobe degenerates following lesions in the inferior parietal lobule (area 7); in such cases fiber degeneration appears in the superior, middle and inferior temporal convolutions, and in the fusiform and parahippocampal gyri.

Both lobules evidently project to the claustrum and body of the caudate nucleus. Both, moreover, have massive efferent connections with the dorsal two-thirds of the putamen. By contrast, no evidence of projections from the parietal cortex to the globus pallidus was found in any of the cases studied.

A further subcortical projection from the posterior parietal cortex involves the nucleus reticularis thalami and the nucleus lateralis posterior thalami. The inferior lobule projects directly to the nucleus lateralis dorsalis and to the mediodorsal region of the nucleus lateralis posterior that closely adjoins two thalamic cell groups: the n. lateralis dorsalis and the intralaminar nucleus centralis lateralis. The superior parietal lobule, by contrast, projects massively to a ventrolateral district of the nucleus lateralis posterior.

Parietosubthalamic connections could be traced from areas 5 and 7 to the zona incerta and fields H₂ and H of Forel, but evidence for terminal connections with the n. subthalamicus (Luys) could not be foud.

Both areas 5 and 7 project massively to the pretectal area and the deeper layers of the superior colliculus. This parieto-mesencephalic connection is amplified by a fiber connection from the inferior parietal lobule (area 7) to the lateral, densocellular region of the circumaqueductal gray matter. No evidence of parietal corticonigral fibers connections was found. Finally, both parietal lobules were found to project to the pontine nuclei.

Speculations regarding the associative functions of the parietal lobules at the cortical and subcortical levels are presented, with particular emphasis upon the possible significance of the projections from the inferior parietal lobule to insular, cingulate and temporal regions of the cortex.     

Afferents to the optic tectum of the leopard frog: an HRP study.

Following unilateral HRP injections in the optic tectum of Rana pipiens, HRP-positive cells were seen in three pretectal nuclei: bilaterally in the dorsal posterior nucleus; in the dorsal half of the ipsilateral posterior nucleus; and ipsilaterally in the large-called pretectal nucleus. HRP-positive cells were also seen ipsilaterally in the anterodorsal, posterodorsal and posteroventral tegmental fields, the nucleus isthmi, and the dorsal gray columns of the cervical spinal cord; bilaterally in the suprapeduncular nucleus, a paramedian cell group dorsal to the interpeduncular nucleus; and in the deep layers of the contralateral tectum. In addition, evidence for a bilateral ventral preopto-tectal projection was seen in half the experimental animals. No tectal afferents from telencephalic or rostal thalamic areas were seen. Both the ascending and descencing tectal efferent fibers were also filled with reaction product. The pale reaction indicative of terminating tectal efferents was seen in the dorsal pretectum, partially overlapping the lateral nucleus and uncinate neuropil; in the core of nucleus isthmi; and in the superior olive.     

Reticulo-olivary circuits: An intracellular HRP study in the rat

Intracellular recordings were obtained from medullary reticular neurons subsequent to electrical stimulation of the ipsilateral or contralateral inferior cerebellar peduncle (ICP) and/or the midbrain. After recording physiological data, the neurons were intracellularly injected with horseradish peroxidase (HRP). Thirty-four HRP filled neurons were subjected to light microscopic analysis. They could be divided into two general groups: those which extend dendritic processes into the neuropil of the inferior olivary complex (n = 19); and those that have no anatomical relationship to the inferior olive (n = 15). These two populations of reticular neurons differ in their distribution, morphological characteristics and physiological responses. Neurons which extend dendritic processes into the inferior olive are located within 200 microns of the dorsal border of this nuclear complex, between the exiting fibers of the XIIth nerve and the raphe. The cell bodies are located in the nucleus reticularis gigantocellularis and are fusiform or multipolar in shape. Their dendrites extend for long distances in the mediolateral direction; are thin and relatively spine-free except at their distal tips where spines and varicose appendages are evident. Physiologically, midbrain stimulation elicits a fast rising hyperpolarization which is identified as an inhibitory postsynaptic potential. However, only rarely is a response observed subsequent to stimulation of either the ipsilateral or contralateral ICP. Dendrites from 4 neurons from the first group of reticular cells were analyzed at the ultrastructural level. Based on random and serial thin sections, the following features were noted: they contain numerous mitochondria when compared to olivary dendrites; they contribute to the postsynaptic elements within olivary synaptic clusters (glomeruli); and they exhibit focal clusters of synaptic vesicles although conventional synaptic complexes have not been observed. Reticular neurons of the second group, those that do not extend dendritic processes into the inferior olive, are located either lateral to the XIIth nerve or at distances greater than 200 microns from the dorsal border of the inferior olivary complex. Their cell bodies and dendrites are comparable morphologically to the reticular neurons whose dendrites do arborize in the inferior olive. However, rarely are the distal tips of their dendrites characterized by spines or varicose appendages. Physiologically, this population of reticular neurons respond to midbrain stimulation with a low amplitude, short latency depolarizing potential which is interrupted by a hyperpolarizing potential.(ABSTRACT TRUNCATED AT 400 WORDS)     

Connections between the frontal eye field and pretectum in the monkey: An anterograde/retrograde study using HRP GEL and TMB neurohistochemistry

Horseradish peroxidase (HRP) gel implants in the frontal eye field (FEF) of macaque monkeys, processed with tetramethylbenzidine (TMB) neurohistochemistry and studied with darkfield microscopy, demonstrated bidirectional HRP labeling of the afferents and efferents of this cortical area. It was evident that among the entire scope of its inputs, the FEF received a prominent afferent projection from the nucleus of the optic tract (NOT, nucleus limitans) and the suprageniculate nucleus, and projected to a medial subdivision of NOT, sublentiform nucleus, nucleus of the pretectal area, nucleus of the posterior commissure, and the rostral periaqueductal gray. The directafferent projections to FEF from NOT could provide a route for visual inputto reach FEF via the pretectum without first going to the visual cortex. The efferents probably represent the pathway through which FEF influences pupillary dynamics known to accompany, or occur independently of, eye movements.     

Galanin-immunoreactive neuronal system and colocalization with serotonin in the optic lobe and peduncle complex of the octopus (Octopus vulgaris)

Immunohistochemical techniques were used to investigate the distribution of galanin-like immunoreactivity and colocalization with serotonin (5-HT) in the optic lobe and peduncle complex of the octopus, Octopus vulgaris. Galanin immunoreactive (Gal-IR) fibers, but not cells, were seen in the plexiform layer of the optic lobe cortex. Gal-IR cells were scattered in the cell-islands of the optic lobe medulla and Gal-IR varicose fibers were observed to be abundant in the neuropil surrounding the islands. All Gal-IR cells were immunoreactive for 5-HT, and a few cells showed only 5-HT-like immunoreactivity. In the peduncle lobe, no Gal-IR cells were seen in the basal zone or spine, but in the basal zone, many Gal-IR fibers were seen. In the anterior olfactory lobule, only a few pyramidal Gal-IR cells were observed in the cell layer, and their apical processes were traced to the central neuropil. In the median olfactory lobule, ovoid Gal-IR cells were scattered in the peripheral cell layer. All Gal-IR cells in the anterior and median olfactory lobules showed 5-HT-like immunoreactivity. In the posterior olfactory lobule, ovoid and triangular Gal-IR cells were scattered in the cell layer. Some of them showed 5-HT-like immunoreactivity. Western blot analysis indicated an Gal-IR band at approximately 15.4 kDa. These results suggest the association of galanin-like substance and 5-HT with the visual system of octopus and that the main form of the octopus galanin might have a different molecular weight from vertebrate galanins.     

Pre- and postsynaptic excitation and inhibition at octopus optic lobe photoreceptor terminals; implications for the function of the 'presynaptic bags'

Synaptic transmission was examined in the plexiform zone of Octopus vulgaris optic lobes using field-potential recording from optic lobe slices. Stimulation of the optic nerve produced pre- and postsynaptic field potentials. Transmission was abolished in calcium-free seawater, L- glutamate or the AMPA/Kainate receptor blocker CNQX (EC(50), 40 microm), leaving an intact presynaptic field potential. ACh markedly reduced or blocked and d-tubocurarine augmented both pre- and postsynaptic field potentials, while alpha-bungarotoxin and atropine were without effect. Paired-pulse stimulation showed short-term depression of pre- and postsynaptic components with a half-time of recovery of approximately 500 ms. The depression was partially relieved in the presence of d-tubocurarine (half-time of recovery, 350 ms). No long-term changes in synaptic strength were induced by repetitive stimulation. A polyclonal antibody raised against a squid glutamate receptor produced positive staining in the third radial layer of the plexiform zone. No positive staining was observed in the other layers. Taking into account previous morphological data and our results, we propose that the excitatory terminations of the photoreceptors are in the innermost layer of the plexiform zone where the transmitter is likely to be glutamate and postsynaptic receptors are AMPA/kainate-like. Thus, the function of the terminal bags is to provide a location for a presynaptic cholinergic inhibitory shunt. The results imply that this arrangement provides a temporal filter for visual processing and enhances the perception of moving vs. stationary objects.     

The subfrontal lobe and touch learning in the octopus.

Octopuses with the supraoesophageal lobes of the brain divided longitudinally can be taught to discriminate using the arms on either side. If there is no further lesion the two sides behave alike. Lesions limited to one side did not affect the performance of the contralateral, "control" side. Lesions made in the vertical (n=7) lobes led to a slight drop in the quality of performance in training to take a smooth sphere, in discrimination training (rough vs. smooth spheres) and in subsequent extinction and transfer tests. After removal of the median inferior frontal lobe (n = 10) there were somewhat greater effects in the same direction. Much larger effects followed interference with the subfrontal lobe (n = 20). Removal of parts from this always led to a marked loss of capacity for touch learning, broadly dependent on the amount of tissue removed. Removal of the whole of the subfrontal lobe (n = 6) produced animals that showed, at best, only very slight signs of learning. Such animals can adjust their overall level of response as a result of training but they seem incapable of adjusting response levels to two objects independently. These results are discussed in relation to the function of the subfrontal lobe as a memory store.     

The gyri of the octopus vertical lobe have distinct neurochemical identities

The cephalopod vertical lobe is the largest learning and memory structure known in invertebrate nervous systems. It is part of the visual learning circuit of the central brain, which also includes the superior frontal and subvertical lobes. Despite the well‐established functional importance of this system, little is known about neuropil organization of these structures and there is to date no evidence that the five longitudinal gyri of the vertical lobe, perhaps the most distinctive morphological feature of the octopus brain, differ in their connections or molecular identities. We studied the histochemical organization of these structures in hatchling and adult Octopus bimaculoides brains with immunostaining for serotonin, octopus gonadotropin‐releasing hormone (oGNRH), and octopressin‐neurophysin (OP‐NP). Our major finding is that the five lobules forming the vertical lobe gyri have distinct neurochemical signatures. This is most prominent in the hatchling brain, where the median and mediolateral lobules are enriched in OP‐NP fibers, the lateral lobule is marked by oGNRH innervation, and serotonin immunostaining heavily labels the median and lateral lobules. A major source of input to the vertical lobe is the superior frontal lobe, which is dominated by a neuropil of interweaving fiber bundles. We have found that this neuropil also has an intrinsic neurochemical organization: it is partitioned into territories alternately enriched or impoverished in oGNRH‐containing fascicles. Our findings establish that the constituent lobes of the octopus superior frontal–vertical system have an intricate internal anatomy, one likely to reflect the presence of functional subsystems within cephalopod learning circuitry. J. Comp. Neurol. 523:1297–1317, 2015. © 2015 Wiley Periodicals, Inc.     

Galanin-immunoreactive neuronal system and colocalization with serotonin in the optic lobe and peduncle complex of the octopus (Octopus vulgaris)

Immunohistochemical techniques were used to investigate the distribution of galanin-like immunoreactivity and colocalization with serotonin (5-HT) in the optic lobe and peduncle complex of the octopus, Octopus vulgaris. Galanin immunoreactive (Gal-IR) fibers, but not cells, were seen in the plexiform layer of the optic lobe cortex. Gal-IR cells were scattered in the cell-islands of the optic lobe medulla and Gal-IR varicose fibers were observed to be abundant in the neuropil surrounding the islands. All Gal-IR cells were immunoreactive for 5-HT, and a few cells showed only 5-HT-like immunoreactivity. In the peduncle lobe, no Gal-IR cells were seen in the basal zone or spine, but in the basal zone, many Gal-IR fibers were seen. In the anterior olfactory lobule, only a few pyramidal Gal-IR cells were observed in the cell layer, and their apical processes were traced to the central neuropil. In the median olfactory lobule, ovoid Gal-IR cells were scattered in the peripheral cell layer. All Gal-IR cells in the anterior and median olfactory lobules showed 5-HT-like immunoreactivity. In the posterior olfactory lobule, ovoid and triangular Gal-IR cells were scattered in the cell layer. Some of them showed 5-HT-like immunoreactivity. Western blot analysis indicated an Gal-IR band at approximately 15.4 kDa. These results suggest the association of galanin-like substance and 5-HT with the visual system of octopus and that the main form of the octopus galanin might have a different molecular weight from vertebrate galanins.     

Afferent and efferent connections of cerebellar lobe C1 of the mormyrid fish Gnathonemus petersi: an HRP study

The corpus of the highly developed cerebellum of the weakly electric fish Gnathonemus petersi is differentiated into four lobes, numbered C1 to C4. The present paper deals with the extrinsic connections of the rostralmost lobe C1. Relevant nuclei were studied in normal histological material and HRP injections were placed in lobe C1, the neighbouring pedunculus valvulae, and the brainstem. The largest number of afferents to lobe C1 originates from the nucleus lateralis valvulae, a large nucleus of tightly packed small cells in the dorsal midbrain tegmentum. In Gnathonemus this nucleus encompasses nine subdivisions, of which the rostral, caudal, and exterolateral parts project in particular to lobe C1. Larger neurons in the dorsal midbrain tegmentum and presumed mesencephalic trigeminal neurons project to C1 as well. In the rhombencephalon, afferents to lobe C1 arise from the first funicular nucleus, the lateral reticular nucleus, and the inferior olive. Efferents of lobe C1 have been found to arise from a peculiar cell type in the Purkinje cell layer (so-called eurydendroid neurons) and to project predominantly to the nucleus of the fasciculus longitudinalis medialis, the nucleus reticularis superius and medius, and the trigeminal motor nucleus. Additional small projections terminate in the tectum mesencephali and in the nucleus reticularis inferior. Compared with other parts of the mormyrid cerebellum as well as with the cerebellum of other teleosts, the connections of lobe C1 appear to be quite restricted and specialized. In this respect the connections with the trigeminal nerve via the first funicular nucleus, the mesencephalic trigeminal nucleus, and the trigeminal motor nucleus are of particular interest. The absence of central cerebellar nuclei intercalated in the efferent cerebellar connections, in combination with the presence of a precerebellar nucleus (lateralis valvulae) involved in the afferent cerebellar connections, represents a remarkable difference between teleosts and other vertebrate classes.     

Afferent and efferent connections of cerebellar lobe C3 of the mormyrid fish Gnathonemus petersi: an HRP study

The present paper is devoted to the extrinsic connections of lobe C3 of the highly differentiated corpus cerebelli of the electric fish Gnathonemus petersi. For this purpose, HRP injections or gels were placed in distinct parts of lobe C3 or its peduncle, in the pretectal region, and in the eye. Moreover, the presence of serotonin and tyrosine-hydroxylase was studied with immunohistochemical methods. The afferent connections of the rostral and caudal part of lobe C3 appear to differ considerably. Although both parts receive comparable projections from two pretectal nuclei (termed nucleus geniculatus and dorsal anterior pretectal nucleus) and the inferior olive, they receive projections from different parts of the nucleus lateralis valvulae, a large cell mass in the midbrain tegmentum, composed of small, tightly packed neurons. The caudal part of lobe C3 receives a projection from the most rostromedial cap of cells of this nucleus, whereas the rostral cap of lobe C3 receives efferents from the neighboring, more caudolateral, zone of cells of the nucleus lateralis valvulae. The caudal part of lobe C3, but not its rostral part, receives an additional projection from a nucleus in the isthmus region, termed nucleus Q. This nucleus sends a collateral projection to the torus longitudinalis. The efferents of both parts of lobe C3 project to slightly different parts of the midbrain tegmentum and the nucleus reticularis superior, and originate at least partly from eurydendroid cells. None of the nuclei and fiber tracts labeled could be shown to contain serotonin or catecholamines. The connections of lobe C3, as revealed by the present study, are compared with those of other parts of the mormyrid cerebellum and with those of the corpus cerebelli of other teleosts, with emphasis on the homology and functional significance of pretectocerebellar connections, the topical order in the cerebellar projections of the nucleus lateralis valvulae, and the relations between the cerebellum and torus longitudinalis. Comparison of the cerebellar connections in different teleostean species suggests that the strong development and the considerable differentiation of the cerebellum of mormyrids are related to at least two types of changes in the extrinsic connections, i.e.: a redistribution or parcelling of connections and the development of connections specific for mormyrids.     

Nucleus of the tractus solitarius projections to the olfactory tubercle: An HRP study

Labelled cells were found in the nucleus of the tractus solitarius (NTS) after horseradish peroxidase injections in the olfactory tubercle (OT) of the rat. These results suggest a direct pathway from the NTS to the OT. The importance of this pathway in a neural circuit related to autonomic functions is discussed.     

Monocular and binocular optic inputs to salamander pretectal neurons: intracellular recording and HRP labelling study

Intracellular recordings and horseradish peroxidase injections were performed in the pretectum and adjacent tegmentum of Salamandra salamandra, while both optic nerves were electrically stimulated. In approximately half of the recorded units no spikes could be evoked but rather graded postsynaptic potentials. The latter type morphologically showed features of interneurons. From a total of 48 recorded units, nearly 60% were excited only by the contralateral optic nerve, whereas approximately 40% were binocular. For the most part (10/19) the binocular cells were excited by the contralateral and inhibited by the ipsilateral optic nerve. Fewer neurons (7/19) received excitatory inputs from both optic nerves. The latency distribution of the monocular cells shows a maximum of 20-30 ms. The same maximum exists for the contralateral inputs to the binocular cells, whereas the ipsilateral inputs to these units were nearly as frequent with latencies of 20-30 and 40-50 ms. Since neurons with the short ipsilateral latencies always had parts of their dendrites within the ipsilateral ocular projection field, a feature which was lacking in the cells with long ipsilateral latencies, it is possible that the longer latencies are due to indirect ipsilateral inputs. Efferents of labelled dorsal pretectal cells reach the contralateral pretectum via the posterior commissure, the basal optic neuropil of the accessory optic system and the tegmental white substance. More ventrally located cells often reach the pretectal and the basal optic neuropil with their dendrites. Axons of this type descend to the medulla oblongata via the medial longitudinal fasciculus.     

An autoradiographic and HRP study of vestibulocollic pathways in the pigeon

This study examines the connections underlying the vestibulocollic system in the adult pigeon by using retrogradely transported horseradish peroxidase (HRP) to identify neck muscle motoneurons in one set of animals, and transneural anterograde transport of tritiated proline-fucose to delineate the descending medial (MVST) and lateral (LVST) vestibulospinal tracts in a second set of animals. Correlations of location and distribution of HRP-labeled motoneurons and autoradiographically labeled fiber tracts and terminal fields were performed between the two sets of experiments. The right biventer cervicis and complexus neck muscles were subdivided into rostral and caudal halves in ten animals and HRP injected into only half of one of the two muscles in each experiment. Following a 16–48-hour survival, the brain was fixed by intracarotid catheterization and perfusion and the HRP in the brain sections reacted with the tetramethylbenzidine (TMB) blue reaction process. Three groups of HRP-labeled motoneurons were identified in the ipilateral ventral horn of the upper cervical spinal cord: a ventromedial and ventrolateral group within lamina VIII innervating the biventer cervicis and the more rostral part of the complexus muscle, and a dorsolateral group of motoneurons within lamina VII innervating the caudal part of the complexus muscle. The dorsolateral motoneurons with their HRP-labeled axons leaving the cord through the dorsal root are homologous to the spinal accessory nucleus of mammals. Labeled motoneurons were also noted in the ipsilateral medulla adjacent to the medial longitudinal fasiculus (ELM) in a location previously identified as the hy-poglossal nucleus. Additional experiments were performed in which HRP was injected directly into the base of the tongue. The resultant HRP-labeled hypoglossal motoneurons were separate and dorsolateral to the collic motoneurons. Descending vestibulospinal projections from one vestibular labyrinth were identified autoradiographicalry (ARG) by transneural anterograde transport of ³H-proline-fucose injected into the left labyrinthine endolytine endolymph in five animals. Heavily labeled MVST fibers were observed crossing the midline of the brain to enter and descend in the contralateral ELM. Labeled MVST fibers were noted to leave the contralateral FLM and surround the previously identified collie motoneurons in the medulla with intense terminal fields suggestive of synaptic contact. Labeled MVST fibers in the contralateral ventral funiculus of the cord were also noted to innervate the HRP-identified ventromedial and ventrolateral cervical motoneurons, but not the dorsolateral motoneurons in lamina VII. Ipsilateral (left) descending MVST and LVST fibers were less heavily labeled at all levels in the medulla and upper cervical cord. Labeled ipsilateral (left) vestibulospinal fibers were also observed to leave the lateralmost aspect of the left ventrolateral funiculus in the upper cervical cord to terminate among left ventrolateral motoneurons. Our findings are compared and contrasted with previous studies of vestibulocollic pathways.     

Connections of the olfactory bulb and nucleus olfactorius anterior in the hedgehog (Erinaceus europaeus): fluorescent tracers and HRP study

The projections of the main olfactory bulbs (MOBs) and the dorsal part of the anterior olfactory nucleus (NOA) in the hedgehog (Erinaceus europaeus) have been studied by fluorescent tracers and the horseradish peroxidase method (HRP), respectively, to reveal the pattern of labeling from these structures. After different dye injections in both MOBs, labeled cells were present in the following structures: tenia tecta, vertical limb of the diagonal band of Broca, and medial septal nucleus in the ipsilateral injection site; and the NOA, piriform cortex, nucleus of the lateral olfactory tract, horizontal limb of the diagonal band of Broca, posterolateral cortical amygdaloid nucleus, anterior amygdaloid area, and dorsal raphe nucleus in both hemispheres. Structures showing double-labeled cells were the NOA, horizontal limb of the diagonal band of Broca, nucleus of the lateral olfactory tract, anterior amygdaloid area, and posterolateral cortical amygdaloid nucleus. After HRP injections in the dorsal part of the NOA, labeled cells were distributed in the NOA, nucleus of the lateral olfactory tract, posterolateral cortical amygdaloid nucleus, piriform cortex, horizontal and vertical limbs of the diagonal band of Broca, mitral cell layer of the MOB, tenia tecta, anterior amygdaloid area, and the contralateral NOA. We suggest that the contralateral projection nuclei to the MOB of the hedgehog, unusual in other mammals, and the large number of cells with axonal collaterals projecting to both hemispheres, may be a strategy in these animals to bilaterally integrate brain functions at the expense of its reduced corpus callosum.