The nuclei of origin of monoaminergic, peptidergic, and cholinergic afferents to the cat nucleus reticularis magnocellularis: a double-labeling study with cholera toxin as a retrograde tracer

Iontophoretic application of unconjugated cholera toxin B subunit (CTb) combined with immunohistochemistry of neurochemical substances: a method for transmitter identification of retrogradely labeled neurons

In this report, we demonstrate that cholera-toxin B subunit (CTb) is a very sensitive retrograde tracer in the central nervous system when recognized by streptavidin-peroxidase immunohistochemistry. We further show that: (1) injection of a small volume of CTb gives rise to small sharply defined injection sites limited to the cell group of interest associated with the labeling of all the known afferent projections, (2) CTb is taken up, and anterogradely as well as retrogradely transported in damaged but not intact fibers of passage, (3) CTb can be applied iontophoretically, allowing us to study the afferents to small cell groups without any evidence of tissue necrosis in the sites and therefore without artefactual labeling due to uptake by damaged fibers of passage, (4) the use of 4% paraformaldehyde fixative ideally suited for the preservation of most neural antigens, the addition of a 48 h colchicine treatment and the development of a double immunohistochemical method allow the biochemical characterization of the cell of origin of particular pathways in the CNS, (5) CTb is also anterogradely transported with an extensive filling of axons and axon terminals and thereby opens up the possibility of identifying simultaneously the afferents as well as the efferents of the group of cells studied and finally (6) the very long conservation of the preparation, the possibility of counterstaining it and of making camera lucida drawings allow easy and precise localization of the retrogradely labeled cells.

Nuclei of origin of monoaminergic, peptidergic, and cholinergic afferents to the cat trigeminal motor nucleus: a double-labeling study with cholera-toxin as a retrograde tracer

The aim of the present study was to determine the brainstem afferents and the location of neurons giving rise to monoaminergic, cholinergic, and peptidergic inputs to the cat trigeminal motor nucleus (TMN). This was done in colchicine treated animals by using a very sensitive double immunostaining technique with unconjugated cholera-toxin B subunit (CT) as a retrograde tracer. After CT injections in the TMN, retrogradely labeled neurons were most frequently seen bilaterally in the nuclei reticularis parvicellularis and dorsalis of the medulla oblongata, the alaminar spinal trigeminal nucleus (magnocellular division), and the adjacent pontine juxtatrigeminal region and in the ipsilateral mesencephalic trigeminal nucleus. We further observed that inputs to the TMN arise from the medial medullary reticular formation (the nuclei retricularis magnocellularis and gigantocellularis), the principal bilateral sensory trigeminal nucleus, and the dorsolateral pontine tegmentum. In addition, the present study demonstrated that the TMN received 1) serotonergic afferents, mainly from the nuclei raphe obscurus, pallidus, and dorsalis; 2) catecholaminergic afferent projections originating exclusively in the dorsolateral pontine tegmentum, including the Kölliker-Fuse, parabrachialis lateralis, and locus subcoeruleus nuclei; further, that 3) methionin-enkephalin-like inputs were located principally in the medial medullary reticular formation (nuclei reticularis magnocellularis and gigantocellularis and nucleus paragigantocellularis lateralis), in the caudal raphe nuclei (Rpa and Rob) and the dorsolateral pontine tegmentum; 4) substance P-like immunoreactive neurons projecting to the TMN were present in the caudal raphe and Edinger-Westphal nuclei; and 5) cholinergic afferents originated in the whole extent of the nuclei reticularis parvicellularis and dorsalis including an area located ventral to the nucleus of the solitary tract at the level of the obex. In the light of these anatomical data, the present report discusses the possible physiological involvement of TMN inputs in the generation of the trigeminal jaw-closer muscular atonia occurring during the periods of paradoxical sleep in the cat.

Somatodendritic morphology of on- and off-cells in the rostral ventromedial medulla

The rostral ventromedial medulla (RVM) contains two classes of physiologically defined neurons, on-cells and off-cells, that are implicated in nociceptive modulation. In a continuing effort to detail the neural circuitry that underlies the activity of these two distinct neuronal types, the somatodendritic morphology of on- and off-cells was studied in the cat, rat, and ferret. In lightly anesthetized animals, on-cells increased and off-cells decreased their discharge rate during a withdrawal reflex evoked by noxious stimuli. Following their physiological characterization by using intracellular recording, on- and off-cells were injected with either horseradish peroxidase or biocytin and their somatodendritic arborizations were examined. Labeled on- and off-cells included fusiform and stellate cells of all sizes as well as large multipolar neurons. Although the somatic shape of both on- and off-cells in RVM was heterogeneous, off-cells tended to be fusiform neurons whose long axis was oriented mediolaterally. The dendritic domains of both on- and off-cells extended bilaterally past the lateral edge of the trapezoid body or pyramid and ventrally to, and sometimes including, the trapezoid body or pyramid. In contrast to their extensive mediolateral spread, the dendritic domains of both cell types were limited to the ventral half of the reticular formation and were compressed along the rostrocaudal axis. The dendritic arbor of individual on- and off-cells extended well beyond the cytoarchitectonic boundaries of any single nuclear region, within the domain delineated as the RVM. The spatial domains of the dendritic arbors of on- and off-cells are further evidence that the on- and off-cells throughout the RVM constitute an integrated unit in the modulation of nociceptive transmission.

Monosynaptic projection from the pedunculopontine tegmental nuclear region to the reticulospinal neurons of the medulla oblongata. An electron microscope study in the cat

The magnocellular reticular nucleus (MRN) of the cat was observed electron microscopically following the combined application of kainic acid into the pedunculopontine tegmental nuclear region (PPN region) and horseradish peroxidase conjugated to wheat germ agglutinin (WGA-HRP) into the spinal cord. Some degenerating axon terminals arising from the PPN region were found to make synaptic contacts with retrogradely HRP-labeled reticulospinal neurons in the MRN.

Injection of a cholinergic agonist in the dorsolateral pontine tegmentum of cats affects the posturokinetic responses to cortical stimulation

Microinjection into the dorsolateral pontine tegmentum of the muscarinic agonist bethanechol, leading to activation of cholinoceptive pontine reticular formation (pRF) neurons and the related medullary inhibitory reticulospinal system, did not modify the threshold, latency and amplitude of the forelimb flexion elicited by unilateral stimulation of the corresponding motor cortex. However, the remaining limbs which displayed a diagonal pattern of postural adjustments showed a dissociation of their postural responses in 2 components: the early component of central origin greatly decreased in amplitude, while the late component attributed to reflex mechanism triggered by the unbalance brought about by the flexion movement increased. Further evidence indicated that the pRF system intervenes in the gain regulation of the early postural responses during the cortically induced limb movement.

Immunohistochemical study of choline acetyltransferase-immunoreactive processes and cells innervating the pontomedullary reticular formation in the rat

The present study was undertaken to examine the cholinergic innervation of the brainstem reticular formation in an effort to understand the potential role of cholinergic neurons in processes of sensory-motor modulation and state control. The cholinergic cells and processes within the pontomedullary reticular formation were studied in the rat by application of peroxidase-antiperoxidase immunohistochemistry with silver intensification for choline-acetyltransferase (ChAT). ChAT-immunoreactive cells were located in the pontomesencephalic tegmentum within the laterodorsal and pedunculopontine tegmental (LDT and PPT) nuclei, where they numbered approximately 3,000 on each side and were scattered in the midline, medial, and lateral medullary reticular formation, where they numbered approximately 10,000 in total on each side. The cholinergic neurons within the reticular formation were commonly medium in size and gave rise to multiple dendrites that extended for considerable distances within the periventricular gray or the reticular formation, as is typical of other isodendritic reticular neurons. A prominent innervation of the entire pontomedullary reticular formation was evident by varicose ChAT-immunoreactive fibers that often surrounded large noncholinergic reticular neurons in a typical perisomatic pattern of termination, suggesting a potent influence of the cholinergic innervation on pontomedullary reticular neurons. The contribution of the pontomesencephalic cholinergic neurons to the innervation of the medial medullary and lateral pontine reticular formation was studied by retrograde transport of horseradish peroxidase conjugated wheat germ agglutinin (WGA-HRP) in combination with ChAT immunohistochemistry. A proportion of the cholinergic neurons within the laterodorsal tegmental nucleus (pars alpha) and the pedunculopontine tegmental nucleus were retrogradely labelled on the ipsilateral (10-15%) and contralateral (5-10%) sides from the medial medullary reticular formation, indicating a significant contribution to the cholinergic innervation of this region, which, however, also appeared to derive in part from intrinsic medullary cholinergic neurons. The major fiber system by which the medial medullary reticular formation was reached by the pontomesencephalic cholinergic neurons appeared to correspond to the lateral tegmentoreticular tract. Fibers passed from these cholinergic cells ventrally through the lateral pontine tegmentum, in the region of the subcoeruleus, where they also appeared to innervate by fibres en passage the noncholinergic neurons of the region. A significant proportion of the pontomesencephalic cholinergic neurons were retrogradely labelled from the lateral pontine tegmentum.(ABSTRACT TRUNCATED AT 400 WORDS)

Cholera toxin B-gold, a retrograde tracer that can be used in light and electron microscopic immunocytochemical studies

The purpose of this study was to test whether a new retrograde tracer, the B subunit of cholera toxin conjugated to colloidal gold particles (CTB-gold), was taken up and transported by neurons in the central nervous system of the rat. Retrograde transport of CTB-gold was assessed from axon terminals, from damaged nerve fibers, and from axons of passage. For light microscopy, CTB-gold was visualized by silver intensification; for electron microscopy, sections were silver-intensified with or without subsequent gold toning. Retrogradely transported CTB-gold was detected in neurons after survival times of 12 hours to 42 days and appeared as black punctate deposits in perikarya and proximal dendrites at the light microscope level. Ultrastructurally, the deposits were usually associated with lysosomes. Injections of CTB-gold into the caudal ventrolateral medulla or into the lateral horn of the spinal cord gave small well-defined injection sites and resulted in retrograde labelling in medullary neurons in the same locations as similarly placed injections of wheat germ agglutinin-horseradish peroxidase. When injected into the superior cervical ganglion, CTB-gold was transported to nerve cell bodies in the spinal cord, but application of CTB-gold to the cut cervical sympathetic trunk did not label neurons in the spinal cord. Injection of CTB-gold into the nodose ganglion retrogradely labelled neurons in the dorsal motor nucleus of the vagus and the nucleus ambiguus. CTB-gold was not transported anterogradely from injections sites within the medulla. Nerve fibers and cell bodies containing neuropeptides, monoamines, or neurotransmitter-synthesizing enzymes were readily immunostained after silver intensification of retrogradely transported CTB-gold. Immunoreactivity for neuropeptides and enzymes was also demonstrated ultrastructurally after silver intensification and gold toning. These results show that CTB-gold is retrogradely transported from nerve terminals and fibers of passage but not from damaged axons. CTB-gold gives well-localized injection sites and persists in neurons for weeks. Transported CTB-gold is easily visualized and its detection is compatible with light and electron microscopic immunocytochemistry. These properties make CTB-gold a valuable tool for studying the connectivity and neurochemistry of pathways in the central nervous system.

Lower brainstem afferents to the cat posterior hypothalamus: a double-labeling study

Using a double-immunostaining technique with cholera toxin (CT) as a retrograde tracer, the authors examined the cells of origin and the histochemical nature of lower brainstem afferents to the cat posterior hypothalamus. The posterior hypothalamus, in particular the lateral hypothalamic area, receives substantial afferent projections from: substantia nigra, peripeduncular nucleus, ventral tegmental area, periaqueductal grey, mesencephalic reticular formation, peribrachial region including the locus coeruleus complex, rostral raphe nuclei and the rostral part of the nucleus magnus. In addition, a moderate number of retrogradely labeled neurons was found in: Edinger-Westphal nucleus, nucleus reticularis pontis oralis, nucleus reticularis magnocellularis, caudal lateral bulbar reticular formation around the nucleus ambiguus and lateral reticular nucleus and the nucleus of the solitary tract. The posterior hypothalamus receives: 1) dopaminergic inputs from A8, A9 and A10 cell groups; 2) noradrenergic inputs from A6 and A7 pontine, as well as A1 and A2 bulbar cell groups; 3) adrenergic inputs from C1 cell group in the caudal medulla; 4) serotoninergic inputs from the rostral raphe nuclei (B6, B7 and B8 cell groups); 5) cholinergic inputs from the peribrachial region of the dorsal pontine tegmentum as well as from the nucleus reticularis magnocellularis of the medulla; 6) peptidergic inputs such as methionine-enkephalin, substance P, corticotropin-releasing factor and galanin that originate mainly in the mesencephalic periaqueductal grey, the dorsal raphe nucleus and the peribrachial region of the dorsal pontine tegmentum.

Monoaminergic, peptidergic, and cholinergic afferents to the cat facial nucleus as evidenced by a double immunostaining method with unconjugated cholera toxin as a retrograde tracer

Using a sensitive double immunostaining technique with unconjugated cholera-toxin B subunit as a retrograde tracer, the authors determined the nuclei of origin of monoaminergic, peptidergic, and cholinergic afferent projections to the cat facial nucleus (FN). The FN as a whole receives substantial afferent projections, with relative subnuclear differences, from the following areas: 1) the perioculomotor areas, the contralateral paralemniscal region, and the mesencephalic reticular formation dorsal to the red nucleus; 2) the ipsilateral parabrachial region and the nucleus reticularis pontis, pars ventralis; and 3) the nuclei reticularis parvicellularis, magnocellularis, ventralis, and dorsalis of the medulla. In addition, the present study demonstrated that the lateral portion of the FN receives specific projections from the contralateral medial and olivary pretectal nuclei and the ipsilateral reticular formation of the pons. It was also found that the FN receives: 1) serotoninergic inputs mainly from the nuclei raphe obscurus, pallidus, magnus, and the caudal ventrolateral bulbar reticular formation; 2) catecholaminergic afferent projections from the A7 noradrenaline cell group located in the Kölliker-Fuse, parabrachialis lateralis, and locus subcoeruleus nuclei; 3) methionin-enkephalin-like inputs originating in the pretectal complex, the nucleus paragigantocellularis lateralis and the caudal raphe nuclei; 4) substance P-like afferent projections mainly from the Edinger-Westphal complex and the caudal raphe nuclei; and 5) cholinergic afferents from an area located ventral to the nucleus of the solitary tract at the level of the obex. In the light of these anatomical data, the present report discusses the physiological significance of FN inputs relevant to tonic and phasic events occurring at the level of the facial musculature during the period of paradoxical sleep in the cat.

Simultaneous immunohistochemical demonstration of intra-axonally transported markers and neuropeptides in the peripheral nervous system of the guinea pig

Projections and peptide neurotransmitter/neuromodulator content of autonomic and visceral afferent neurons of the guinea pig were studied after application of the subunit B of cholera toxin (CTB) with or without horseradish peroxidase (HRP) as retrograde and anterograde tracers and subsequent immunohistochemical processing for double staining using antibodies raised to CTB, HRP and various neuropeptides. The results demonstrate that substance P (SP)- and calcitonin gene-related peptide (CGRP)-containing dorsal root ganglion cells project to the pylorus as well as to the celiac superior mesenteric and stellate ganglia as demonstrated with both retrograde and anterograde transport methodology. Binding studies revealed that a small number of the CTB-binding dorsal root ganglion cells contains immunoreactivity to SP and CGRP. The majority of the CTB-binding cells is SP- and CGRP-negative and terminate in the deeper parts of the dorsal horn. After injection of CTB conjugated to HRP (B-HRP) into the nodose ganglion, both motor and sensory elements were labeled in the medulla oblongata. Some of the CTB labeled vagal sensory nerve fibers in the nucleus tractus solitarii (NTS) were also found to contain immunoreactivity to SP or CGRP. The tracer was also transported through the peripheral branch of the nodose ganglion cells and labeled terminals in the esophagus.

Long-lasting insomnia induced by preoptic neuron lesions and its transient reversal by muscimol injection into the posterior hypothalamus in the cat

In order to analyse the role of the anterior hypothalamus in the regulation of the sleep-waking cycle we made bilateral neuronal lesions at different levels of the anterior hypothalamus in cats, by means of microinjections of a cell-specific neurotoxin:ibotenic acid. These lesions resulted in severe insomnia in eight cats. This insomnia was characterized by a large decrease or even disappearance of paradoxical sleep and deep slow wave sleep and, to a lesser extent, by a decrease of light slow wave sleep, for 2-3 weeks. In the other five animals, we observed a large reduction of deep slow wave sleep (0-40% of control level), but a less intensive decrease of time spent in paradoxical sleep (50-75% of control level) and no marked effect on light slow wave sleep. During the first 3-6 postoperative days we also noticed hyperthermia in all cats; thereafter, the animals presented only a slight increase in brain temperature which did not appear to trigger the sleep impairment. Histological analysis of the different lesions revealed that the insomnia could be attributed to neuronal cell body destruction in the mediobasal part of the anterior hypothalamus covering; the medial preoptic area and a narrow portion of the lateral preoptic area as well as a restricted part of the anterior hypothalamic nucleus. In order to investigate the putative role of the posterior hypothalamic structures in the mechanism of insomnia after lesion of the mediobasal preoptic area neurons we injected an agonist of GABA into the ventrolateral part of the posterior hypothalamus to locally depress the neuronal activity. The bilateral intracerebral microinjection of muscimol (0.5-5 micrograms) induced a transient intensive hypersomnia (slow wave sleep and paradoxical sleep). These findings indicate that neuronal cell loss in the mediobasal preoptic area induced a long lasting insomnia. Thus, it may be hypothesized that the integrity of this structure is necessary for sleep appearance. Finally, our data are in keeping with an intrahypothalamic regulation of the sleep-waking cycle.