Norepinephrine innervation of the cochlear nuclei by locus coeruleus neurons in the rat

Summary The cochlear nuclei (CN) contain a moderate concentration of norepinephrine (445±20 ng/g tissue) with dopamine levels (46±14 ng/g) that are low and within the precursor range expected for a norepinephrine (NE) terminal system. Lesion and horseradish peroxidase (HRP) experiments indicate that this innervation is bilateral and arises from fusiform and multipolar neurons in the locus coeruleus.Autoradiographic and fluorescence histochemical experiments demonstrate that locus coeruleus fibers reach the ipsilateral ventral cochlear nuclei via a rostral pathway that projects from the rostral locus coeruleus laterally through the brain stem to the rostral tip of the ventral nuclei. This pathway is located dorsal to the motor and spinal trigeminal nuclei and ventral to the middle cerebellar peduncle. Descending coeruleo-cochlear fibers travel between the fourth ventricle and the vestibular nuclei to enter the acoustic striae. These fibers innervate both the dorsal and ventral nuclei. Contralateral locus fibers reach the CN by crossing in the pontine central gray at the rostral border of the fourth ventricle and by decussating with the fibers of the mesencephalic trigeminal nucleus ventral to the medial longitudinal fasciculus. The bilateral locus coeruleus innervation of the cochlear nuclei comprises a highly collateralized network of varicose axons which are not topographically organized. Unlike the cochlear nerve fibers in the CN which form specific projections, the locus coeruleus afferents to these sensory nuclei are diffuse and non-specific.     

The organization of the crossed geniculogeniculate pathway of the rat: a Phaseolus vulgaris-leucoagglutinin study.

The intergeniculate leaflet of the thalamus is known to give rise to neuronal projections to the suprachiasmatic nuclei and the rostral part of the pineal gland. Via these projections the intergeniculate leaflet is considered to play a role in regulation of circadian rhythms. Iontophoretic injections of the anterograde tracer Phaseolus vulgaris-leucoagglutinin were placed in various subnuclei of the lateral geniculate nucleus in order to study the topographical organization of the crossed geniculogeniculate pathway in the rat. Injections involving neurons in the intergeniculate leaflet or the medial subpart of the ventral nucleus (which presumably is part of the intergeniculate leaflet of the thalamus too) gave rise to labeled nerve fibers in the opposite lateral geniculate nucleus. The axons contained in this pathway were followed either medially via the posterior commissure, or via the optic tracts and optic chiasm, to the contralateral hemisphere. In the contralateral lateral geniculate nucleus, the intergeniculate leaflet was most densely innervated, but a substantial innervation of the ventral lateral geniculate nucleus was observed as well. Only a few labeled fibers were observed in the dorsal subnucleus. However, the dense innervation of the contralateral intergeniculate leaflet not only covered the small zone between the dorsal and ventral nuclei, but also a dorsomedial part of the ventral nucleus that merged caudally with the lateral part of the zona incerta. In the remaining part of the ventral nucleus, single Phaseolus vulgaris-leucoagglutinin-labeled fibers surrounded specific cells. The demonstration of a divergent projection between the intergeniculate leaflet and specific subparts of the contralateral geniculate nuclei indicates that the two lateral geniculate nuclei are regulating each other. The function of this pathway is suggested to be related to the regulation of circadian rhythmicity, but experimental evidence for this hypothesis is still lacking.     

Locus coeruleus projections to the dorsal motor vagus nucleus in the rat.

The origin of the noradrenergic innervation of the preganglionic autonomic nuclei in the medulla oblongata and spinal cord is still controversial. In this investigation descending connections of the locus coeruleus to the dorsal motor vagus nucleus in the rat are studied with Phaseolus vulgaris leucoagglutinin and horseradish peroxidase as neuroanatomical tracers. Locus coeruleus projections in the motor vagus nucleus are found in the medial part at rostral levels and in the lateral part at intermediate levels of this nucleus. The terminal labeling in the lateral intermediate part of the vagus nucleus appears in an area where possibly preganglionic parasympathetic cardiac neurons are located, suggesting that the locus coeruleus might be involved in regulation of cardiovascular functions. After small iontophoretic injections of horseradish peroxidase in the motor vagus nucleus, retrogradely labeled cells are found in the ventral part of the locus coeruleus and occasionally in the dorsal part of the nucleus. The results show that the locus coeruleus-dorsal motor vagus nucleus pathway may participate in the inhibition of the cardiac preganglionic neurons in the dorsal motor vagus nucleus by the hypothalamic paraventricular nucleus.     

Immunohistochemical demonstration of regionally selective projections from locus coeruleus to the vestibular nuclei in rats

Summary This study describes a regionally selective projection of tyrosine hydroxylase and dopamine -hydroxylase-immunoreactive fibers from locus coeruleus (LC) and the A4 region of nucleus subcoeruleus to the vestibular nuclear complex in Long-Evans and Sprague-Dawley rats. These fibers travel in two distinct pathways. A lateral descending noradrenergic bundle provides input from LC to the superior vestibular nucleus (SVN), the cochlear nuclei, and the cerebellar cortex. A medial descending noradrenergic bundle provides input to the lateral vestibular nucleus (LVN), medial vestibular nucleus (MVN), and the inferior vestibular nucleus (IVN) before continuing on to the cochlear and cerebellar nuclei. The terminal plexus of these fibers varies markedly across these vestibular nuclear regions. Immunoreactive axons form a dense plexus around somata and proximal dendrites of Deiters' neurons in dorsal LVN. The axon plexus is less dense in SVN and ventral LVN, and relatively sparse in MVN and IVN. This regional selectivity of noradrenergic innervation suggests that central adrenergic systems may selectively modulate vestibulospinal reflexes at the level of the vestibular nuclear complex.     

Fastigial nucleus projections in the midbrain and thalamus in dogs

Efferent connections to midbrain and thalamus from portions of the cerebellar fastigial nucleus were investigated using autoradiographic techniques. Bipolar stimulating electrodes were placed in the fastigial nucleus of anesthetized beagles and the area which produced maximal increases in blood pressure and heart rate was localized in each dog. A mixture of [3H]leucine and [3H]proline (4:1) was injected into that area and autoradiograms were prepared. Injections filled the rostral and various parts of the caudal fastigial nucleus. The rostral-caudal extent of injection sites were mapped in the horizontal plane from sequential coronal, thionin-stained sections and "primary" and "secondary" injection zones were defined according to specific criteria. Labeled axons reached the mesencephalon via the contralateral uncinate fasiculus. Ascending fibers assembled in a diffuse contingent at the prerubral level adjacent to the ventrolateral periaqueductal gray. The heaviest projections were contralateral to the injection site, but ipsilateral terminals were observed as well. In the midbrain, axons entered the contralateral and ipsilateral superior colliculus to branch repeatedly and terminate in the deep and intermediate layers. Additional terminals were observed bilaterally in the nuclei of the posterior commissure and pretectal areas at the midbrain-diencephalic junction. In the thalamus, labeled axons formed into three groups which terminated in: the contralateral paraventricular complex and medial dorsal nucleus; the contralateral central medial, paracentral, parafasicular and central lateral nuclei, and the contralateral ventral medial and ventral lateral nuclei. There was a sparse projection to the ipsilateral ventral lateral nucleus. The contralateral projection to the ventral medial and ventral lateral nuclei was marked by dense clusters of label ventral to the internal medullary lamina extending, in the dorsal ventral lateral nucleus, to its rostral pole. Projections to specific somesthetic thalamus or the hypothalamus were not observed. These ascending projections in the canine brain generally conform to those described in other nonprimate mammals. The fastigial nucleus presumably provides information concerning equilibrium and body proprioception to the superior colliculus and to thalamic nuclei including both specific motor relay and "nonspecific" midline and intralaminar nuclei, much the same as reported in the cat. The projection to the ventral medial and ventral lateral thalamic nuclei terminate in areas known to participate in the control of axial and proximal limb muscle activity.(ABSTRACT TRUNCATED AT 400 WORDS)     

Projections from the rat cuneiform nucleus to the A7, A6 (locus coeruleus), and A5 pontine noradrenergic cell groups

Stimulation of neurons in the cuneiform nucleus (CnF) produces antinociception and cardiovascular responses that could be mediated, in part, by noradrenergic neurons that innervate the spinal cord dorsal horn. The present study determined the projections of neurons in the CnF to the pontine noradrenergic neurons in the A5, A6 (locus coeruleus), and A7 cell groups that are known to project to the spinal cord. Injections of the anterograde tracer, biotinylated dextran amine in the CnF of Sasco Sprague-Dawley rats labeled axons located near noradrenergic neurons that were visualized by processing tissue sections for tyrosine hydroxylase-immunoreactivity. Anterogradely labeled axons were more dense on the side ipsilateral to the BDA deposit. Both A7 and A5 cell groups received dense projections from neurons in the CnF, whereas locus coeruleus received only a sparse projection. Highly varicose anterogradely labeled axons from the CnF were found in close apposition to dendrites and somata of tyrosine hydroxylase-immunoreactive neurons in pontine tegmentum. Although definitive evidence for direct pathways from CnF neurons to the pontine noradrenergic cell groups requires ultrastructural analysis, the results of the present studies provide presumptive evidence of direct projections from neurons in the CnF to the pontine noradrenergic neurons of the A7, locus coeruleus, and A5 cell groups. These results support the suggestion that the analgesia and cardiovascular responses produced by stimulation of neurons in the CnF may be mediated, in part, by pontine noradrenergic neurons.     

大白鼠海马传入纤维的来源——HRP法研究

本研究用25只雌性成年大白鼠,体重150～250g。将33％的HRP(Sigma Ⅵ)分别注射于右侧背海马或腹海马区,在下列各核区发现有HRP标记细胞。 1.本侧:内侧隔核、上乳头体核、下乳头丘脑束核、中缝背核、正中中缝核、蓝斑、内嗅皮层、斜角带和上丘等。 2.对侧:海马的CA_3区、CA_4区和蓝斑。     

Effects of eye-enucleation on substance P-immunoreactive fibers of some retinorecipient nuclei of the rat in relation to their origin from the superior colliculus.

We have previously shown that retinal deafferentation causes a decrease in immunoreactive dendrites of substance P-positive neurons of the superficial superior colliculus of the rat. Since some retinorecipient thalamic and pretectal nuclei are putative targets for substance P-containing cells of the superior colliculus, the present study attempted to ascertain whether substance P-immunoreactive fibers in these nuclei are also affected by retinal denervation. We found that unilateral eye removal produced a progressive increase in fibrous substance P immunoreactivity in the nucleus of the optic tract, lateral posterior nucleus, and lateral geniculate nucleus of the side contralateral to the enucleation. On the other hand, unilateral lesions to the superficial layers of the superior colliculus produced a dramatic reduction in substance P immunoreactivity in the ipsilateral nucleus of the optic tract, lateral posterior nucleus, and dorsal and ventral lateral geniculate nuclei. In bilaterally enucleated animals, unilateral lesion to the superior colliculus produced, as expected, loss of immunoreactive fibers only in the lateral posterior nucleus and the retinorecipient nuclei ipsilateral to the lesion. These results suggest that transneuronal changes in the distribution of substance P in collicular neurons observed after enucleation could be reflected in their projections to the other primary visual centers and to the lateral posterior nucleus.     

Neocortical connections in fetal cats

The major extrinsic projections to and from visual and auditory areas of cerebral cortex were examined in fetal cats between 46 and 60 days of gestation (E46-E60) using axonal transport of horseradish peroxidase either alone or in combination with tritiated proline. Projections to visual cortex from the dorsal lateral geniculate nucleus and lateral-posterior/pulvinar complex exist by E46, and those from the contralateral hemisphere, claustrum, putamen, and central lateral nucleus of the thalamus are present by E54-E56. In addition, cells in the medial geniculate nucleus project to auditory cortex by E55. At E54-E56 efferent cortical projections reach the contralateral hemisphere, claustrum, putamen, lateral-posterior/pulvinar complex and reticular nucleus of the thalamus. Cells in visual cortex also project to the dorsal and ventral lateral geniculate nuclei, pretectum, superior colliculus and pontine nuclei, and cells in auditory cortex project to the medial geniculate nucleus. Except for interhemispheric projections, all pathways demonstrated are ipsilateral, and projections linking cerebral cortex with claustrum, dorsal lateral geniculate nucleus and lateral-posterior/pulvinar complex are reciprocal. The reciprocal projections formed with the dorsal lateral geniculate nucleus, lateral-posterior/pulvinar complex and the claustrum show a greater degree of topological organization compared to the projections formed with the contralateral hemisphere and superior colliculus, which show little or no topological order. Therefore, the results of the present study show that the major extrinsic projections of the cat's visual and auditory cortical areas with subcortical structures are present by the eighth week of gestation, and that the origins and terminations of many of these projections are arranged topologically.     

Subcortical projections to the lateral geniculate body in the rat

Summary The subcortical projections to the lateral geniculate body (LGB) in the rat were studied by means of discrete HRP iontophoretic deposits in the dorsal or the ventral LGB; the labelling was compared to that resulting from HRP deposits in neighboring nuclei.After injecting HRP in the dorsal LGB, labelled cells appeared bilaterally in the ventral LGB, pretectum, superior colliculus, lateral groups of the dorsal raphe nucleus and locus coeruleus. Ipsilaterally, labelled cells were found in the lateral posterior thalamus, nucleus of the posterior commissure and deep mesencephalic reticular nucleus.After injecting HRP into the ventral LGB, labelled cells were observed bilaterally in the pretectum, superior colliculus and dorsal raphe nucleus (lateral groups). Contralateral labelling appeared in the ventral LGB and parabigeminal nucleus. Ipsilateral labelling was found in the zona incerta, lateral posterior thalamus, lateral and medial mesencephalic reticular formation, vestibular and dorsal tegmental nuclei.These findings provide evidence of subcortical projections to the LGB arising in visually-related areas as well as extravisual areas, which might be related to the LGB boutons that survive complete cortical and retinal ablations.     

Efferent projections of nucleus locus coeruleus: topographic organization of cells of origin demonstrated by three-dimensional reconstruction

The present study examines the spatial distribution within rat locus coeruleus of neurons projecting to particular brain regions. In order to accurately recreate, in digital and pictorial formats, the spatial distribution of neurons for the entire nucleus locus coeruleus, three-dimensional reconstructions were created which specified the location of each individual Nissl-stained locus coeruleus cell in each of five nuclei. Dynamic computerized displays were visually analyzed and statistically compared. The nuclei from different brains were found to be strikingly similar in density and distribution of cells. In order to determine whether the cells of origin for particular locus coeruleus projections were clustered within the nucleus, reconstructions were created of the distributions of cells labeled by injections of a retrograde tracer, horseradish peroxidase, into particular terminal regions. Groups consisting of animals with injections into the same target areas were visually and statistically compared. The cells of origin of most efferent projections were found to be spatially organized within locus coeruleus. Specifically, projections to both the dorsal and ventral hippocampus originated solely from the dorsal segment of the nucleus, while spinal cord projections originated from ventral-posterior locus coeruleus. Cells of origin of cerebral and cerebellar cortical efferents, as well as hypothalamic efferents, exhibited less clustering, although reliable differences in distribution were observed. The most striking example of clustered cells of origin was exhibited by the large norepinephrine-containing cells constituting the anterior pole of locus coeruleus which were labeled only by hypothalamic injections. This analysis of spatial organization within locus coeruleus is unique in its utilization of a defined control group, experimental groups consisting of strictly defined replications, accurate three-dimensional reconstruction, and statistical comparisons. The demonstrated spatial heterogeneity of locus coeruleus neurons with respect to efferent projections can now be compared to the spatial distributions of other cellular characteristics such as soma morphology, colocalized transmitters and physiological properties. Presumably, such spatial segregation reflects the operation of functionally important organizing principles within the nucleus.     

Retinofugal projections of an echolocating megachiropteran

The projection leading from the eye and the nuclear targets of the projection to the brainstem were identified in an echolocating megachiropteran (Rousettus aegyptiacus) following unilateral intraocular injections of radioactive amino acids. In the hypothalamus, the projection ended bilaterally in suprachiasmatic nuclei. In the ventral thalamus, it ended bilaterally in external and internal divisions of the ventral lateral geniculate nuclei. In the dorsal thalamus, the projection terminated bilaterally in the dorsal lateral geniculate nuclei and contralaterally in the lateral posterior nucleus. Input from the two eyes was segregated to laminae in the lateral division of the dorsal lateral geniculate nucleus. The contralateral projection ended in the dorsolateral and ventral portions of lamina 1, in lamina 2, the ventral portions of lamina 3, and an interlaminar fiber plexus. The ipsilateral projection ended in the dorsomedial portion of lamina 1, the dorsal portion of lamina 3, and the most superficial portion of lamina 1. Contralateral and ipsilateral input to the medial division of the dorsal lateral geniculate nucleus was for the most part segregated. The projection to the pretectum terminated in nuclei of the optic tract, pretectal olivary nuclei, and posterior pretectal nuclei. Although the input to the pretectal nuclei was bilateral, the contralateral projection was greater. The contralateral projection to the superior colliculus terminated throughout the rostral-caudal extent of the superficial gray layer. The ipsilateral projection to the superior colliculus ended in the superficial gray layer in the middle one-third of the superior colliculus only. On the contralateral side the projection to the outer portion of the superficial gray layer was especially heavy. The superior fascicle of the accessory optic tract was identified. It was traced to dorsal, lateral, and medial accessory optic nuclei. These results indicate that the visual system of Rousettus is more extensive than that of the echolocating microchiroptera and that it is similar to that described for nonecholocating Pteropus.     

猫丘脑中央外侧核的皮质下传入联系

本实验用HRP逆行性轴浆运输技术,对猫丘脑中央外侧核的传入纤维联系及其局部定位关系进行了观察。投射至丘脑中央外侧核尾侧区的主要核团包括:外侧膝状体腹核背侧带、丘脑网状核特别是它的背侧部、上丘深层,以同侧为主。板内核、丘脑下部外侧区和黑质网状部神经元的轴突终止在同侧丘脑中央外侧核吻侧区。丘脑中央外侧核全长的传入起自脑干网状结构和前庭神经核,呈双侧投射。前者以同侧为主,后者以对侧占优势。同侧未定带,顶盖前区、动眼神经核周围的细胞群、对侧三叉神经感觉主核、楔束核、薄束核以及小脑齿状核内也含有少量标记细胞。我们还观察到HRP注射中心区位于中央外侧核并扩散至丘脑腹前核者,同侧脚内核含大量HRP阳性细胞,而Gudden被盖腹侧核内充满密集的标记终末。这些结果表明,丘脑中央外侧核可能涉及多种感觉和运动功能。     

下丘脑外侧核乙酰胆碱酯酶阳性神经元的传入联系

为也观察下丘脑外侧核乙酰胆碱酯酶阳性神经元的传入纤维联系。方法；采用ＨＲＰ与Ａｃｈｅ相结合的双标记方法，对１７只大鼠下丘脑外侧核进行了逆行追踪研究。结果；在下列核团观察到ＨＲＰ－ＡｃｈＥ双标记细胞；斜角带核垂直支腹侧部，斜角带核水平支隔内侧核，中缝背核，蓝斑，臂旁核，下丘脑前核，对侧下丘脑外侧核，小脑间位核及小脑齿状核。     

Quantitative evaluation of crossed and uncrossed projections from basal ganglia and cerebellum to the cat thalamus

Quantitative and qualitative analysis of crossed vs uncrossed projections from the substantia nigra, entopeduncular nucleus and individual cerebellar nuclei to the thalamus was undertaken in nine adult cats using retrograde labeling with horseradish peroxidase and fluorescent dyes. The results indicate that about 90% of entopeduncular nucleus neurons and 50% of substantia nigra neurons give rise to ipsilateral projections to the thalamus whereas the contralateral component of these projections originates from about 10 and 7% neurons of entopeduncular nucleus and substantia nigra, respectively. Some of the fibers constituting the contralateral component are represented by branching axon collaterals of the neurons projecting ipsilaterally. In the basal ganglia thalamic projection, its minor component (contralateral) targets the ventral anterior and ventral medial nuclei the same as its major component (ipsilateral). However, some preferential distribution of the contralateral projections to the ventral medial nucleus appears to exist. In regard to the cerebellothalamic projections it was found that about 90% of neurons located in the dentate and interpositus nuclei and 50% of neurons in the fastigial nucleus project to the contralateral thalamus while 16% of dentate nucleus neurons and 40% of fastigial nucleus neurons give rise to the ipsilateral cerebellothalamic projections. A considerable number of ipsilateral cerebellothalamic fibers are represented by divergent axon collaterals of the same neurons projecting to the contralateral thalamus. The cerebellothalamic projections from all cerebellar nuclei including the fastigial nucleus are targeted primarily to the ventral lateral nucleus both contra- and ipsilaterally. The ventral medial nucleus receives bilateral input from the fastigial nucleus which originates from about one quarter of the thalamus projecting neurons in this nucleus. Of all other cerebellar nuclei only the dentate nucleus projects to the ventral medial nucleus and this projection is exclusively contralateral.     

Distribution of catecholamines in the brain stem and spinal cord of the lizard Varanus exanthematicus: an immunohistochemical study based on the use of antibodies to tyrosine hydroxylase

Antibodies to tyrosine hydroxylase were used to study the distribution of nerve cells, fibers and terminals, containing catecholamines, in the lizard Varanus exanthematicus, by means of the indirect immunofluorescence technique. Tyrosine hydroxylase-containing cell bodies occurred in the hypothalamus, the ventral and dorsal tegmentum mesencephali, the substantia nigra, the isthmic reticular formation, in and ventrolaterally to the locus coeruleus, in the nucleus tractus solitarii and in a lateral part of the nucleus reticularis inferior. In addition tyrosine hydroxylase-containing cell bodies were found throughout the spinal cord, ventral to the central canal. Tyrosine hydroxylase-immunoreactive terminal areas in the brain stem were seen in the nucleus interstitialis of the fasciculus longitudinalis medialis, the nucleus raphes superior, the locus coeruleus, several parts of the reticular formation and the nucleus descendens nervi trigemini. Ascending catecholaminergic pathways could be traced from the ventral mesencephalic tegmentum as well as from the dorsal isthmic tegmentum rostralwards, through the lateral hypothalamus. These pathways correspond to the mesostriatal and isthmocortical projections respectively, as described in mammals. Furthermore, ascending catecholaminergic fibers could be traced from the catecholaminergic cell groups in the medulla oblongata to the isthmus, where they intermingle with the locus coeruleus neurons. These pathways correspond to the medullohypothalamic projection and to the dorsal periventricular system in mammals. Descending catecholaminergic fibers to the spinal cord pass via the dorsomedial part of the lateral funiculus, and mainly terminate in the dorsal horn. The results obtained in the present study have been placed in a comparative perspective, which illustrates the constancy of catecholaminergic innervation throughout phylogeny.     

Retinal projections to the subcortical visual system in congenic albino and pigmented rats

The primary visual pathway in albino mammals is characterized by an increased decussation of retinal ganglion cell axons at the optic chiasm and an enhanced contralateral projection to the dorsal lateral geniculate nucleus. In contrast to the primary visual pathway, little is known about the organization of retinal input to most nuclei of the subcortical visual system in albino mammals. The subcortical visual system is a large group of retinorecipient nuclei in the diencephalon and mesencephalon. These areas mediate a range of behaviors that include both circadian and acute responses to light. We used a congenic strain of albino and pigmented rats with a mutation at the c locus for albinism (Fischer 344-c/+; LaVail MM, Lawson NR (1986) Development of a congenic strain of pigmented and albino rats for light damage studies. Exp Eye Res 43:867-869) to quantitatively assess the effects of albinism on retinal projections to a number of subcortical visual nuclei including the ventral lateral hypothalamus (VLH), ventral lateral preoptic area (VLPO), olivary pretectal nucleus (OPN), posterior limitans (PLi), commissural pretectal area (CPA), intergeniculate leaflet (IGL), ventral lateral geniculate nucleus (vLGN) and superior colliculus (SC). Following eye injections of the neuroanatomical tracer cholera toxin-beta, the distribution of anterogradely transported label was measured. The retinal projection to the contralateral VLH, PLi, CPA and IGL was enhanced in albino rats. No significant differences were found between albino and pigmented rats in retinal input to the VLPO, OPN and vLGN. These findings raise the possibility that enhanced retinofugal projections to subcortical visual nuclei in albinos may underlie some light-mediated behaviors that differ between albino and pigmented mammals.     

Retinofugal projections in the rufous horseshoe bat, Rhinolophus rouxi

Summary The retinal projections in the horseshoe bat were studied with anterograde transport of wheat germ agglutinin conjugated to horseradish peroxidase. Retinal fibers clearly terminate bilaterally in the lateral geniculate nuclei, superior colliculus, pretectal area, and nucleus of the optic tract. The suprachiasmatic nucleus and the lateral terminal nucleus of the accessory optic tract receive extremely weak, though bilateral retinal input. No projections to medial and dorsal accessory optic nuclei were found. There was a limited retinal projection to the ipsilateral dorsal geniculate nucleus. The focus of the ipsilateral projection corresponded to a less densely labeled region on the contralateral side. In this study an ipsilateral retinal projection to the anterior superior colliculus is documented for the first time in a Microchiropteran bat. In the contralateral superior colliculus retinal fibers terminate in a patch-like pattern at caudal levels.Abbreviations BSC brachium of the SC - CH optic chiasm - CP cerebral peduncle - IGL intergeniculate leaflet - dLGN dorsal lateral geniculate nucleus - vLGN ventral lateral geniculate nucleus: d dorsal, i intermediate, v ventral subdivision - LTN lateral terminal nucleus of accessory optic system - MGN medial geniculate nucleus - NOT nucleus of the optic tract - NSCH suprachiasmatic nucleus - ON optic nerve - OT optic tract - PA pretectal area - PON pretectal olivary nucleus - Rh.r. Rhinolophus rouxi - SC superior colliculus     

Descriptive and functional neuroanatomy of locus coeruleus-noradrenaline-containing neurons involvement in bradykinin-induced antinociception on principal sensory trigeminal nucleus

The present study was carried out in Wistar rats, using the jaw-opening reflex and dental pulp stimulation, to investigate noradrenaline- and serotonin-mediated antinociceptive circuits. The effects of microinjections of bradykinin into the principal sensory trigeminal nucleus (PSTN) before and after neurochemical lesions of the locus coeruleus noradrenergic neurons were studied. Neuroanatomical experiments showed evidence for reciprocal neuronal pathways connecting the locus coeruleus (LC) to trigeminal sensory nuclei and linking monoaminergic nuclei of the pain inhibitory system to spinal trigeminal nucleus (STN). Fast blue (FB) injections in the locus coeruleus/subcoeruleus region retrogradely labeled neurons in the contralateral PSTN and LC. Microinjections of FB into the STN showed neurons labeled in both ipsilateral and contralateral LC, as well as in the ipsilateral Barrington's nucleus and subcoeruleus area. Retrograde tract-tracing with FB also showed that the mesencephalic trigeminal nucleus sends neural pathways towards the ipsilateral PSTN, with outputs from cranial and caudal aspects of the brainstem. In addition, neurons from the lateral and dorsolateral columns of periaqueductal gray matter also send outputs to the ipsilateral PSTN. Microinjections of FB in the interpolar and caudal divisions of the STN labeled neurons in the caudal subdivision of STN. Microinjections in the STN interpolar and caudal divisions also retrogradely labeled serotonin- and noradrenaline-containing nucleus of the brainstem pain inhibitory system. Finally, the gigantocellularis complex (nucleus reticularis gigantocellularis/paragigantocellularis), nucleus raphe magnus and nucleus raphe pallidus also projected to the caudal divisions of the STN. Microinjections of bradykinin in the PSTN caused a statistically significant long-lasting antinociception, antagonized by the damage of locus coeruleus-noradrenergic neuronal fibres with (N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine) (DSP4), a neurotoxin that specifically depleted noradrenaline from locus coeruleus terminal fields. These data suggest that serotonin- and noradrenaline-containing nuclei of the endogenous pain inhibitory system exert a key-role in the antinociceptive mechanisms of bradykinin and the locus coeruleus is crucially involved in this effect.