Understanding the Experience and Impacts of Brain Fog in Chronic Pain: A Scoping Review

Introduction

Approximately 15% to 40% of persons with chronic pain as a primary disorder experience brain fog. Prior research has investigated the etiology of "brain fog" in conditions in which pain presents as a key feature (e.g., fibromyalgia). However, it remains understudied in the context of chronic 10 musculoskeletal pain. Following current scoping review guidelines, we obtained stakeholder input from patient and health care professionals (HCPs) to define this phenomenon. Specific aims of this review were to (1) identify factors contributing to brain fog, (2) identify the functional correlates of brain fog and assessments used to measure them, and (3) establish a definition of brain fog that can be employed by researchers and HCPs to advance research and care.

Methods

A scoping review was conducted using recommendations of the Joanna Briggs Institute methodology of scoping reviews and the Levac et al methodology. Embase, Cinahl, PsycINFO, and Medline was searched to identify relevant sources. Findings were verified with patient and healthcare professionals.

Results

We identified four 15 key features of brain fog: perceived variability, subjective cognitive dysfunction, participation limitations, and changes in functional activities. We developed a model of brain fog illustrating the overlapping categories of contributors to brain fog in chronic musculoskeletal pain: (1) neuroanatomical and neurophysiological, (2) mental health/emotional, and (3) environmental/lifestyle.

Conclusion

The results of this scoping review conclude that the inconsistency in research regarding brain fog in 20 chronic musculoskeletal pain is obstructing a clear understanding of the phenomenon and therefore may be impeding persons with chronic pain and brain fog from receiving optimal care.

Monoaminergic and Peptidergic Innervation of the Intermedio-Lateral Horn of the Spinal Cord

In the rat the monoaminergic and neuropeptidergic innervation of the sympathetic visceral nuclei of the entire thoracic spinal cord has been analysed in serial horizontal sections using immunocytochemistry. Tyrosine hydroxylase (TH), Phenyl-ethanolamine-N-methyl-transferase (PNMT), 5-hydroxytryptamine (5-HT), substance P (SP) and enkephalin (ENK) immunoreactive (IR) nerve terminals form tufts of plexa with strong IR in the principal part of the intermediolateral nucleus (ILp) with the terminals in an extraperikaryal location. High densities of these strongly IR terminals are also found in the principal part of the intercalated nucleus (ICp) and in the paraependymal part of the intercalated nucleus (ICpe). The various types of IR nerve terminals also form rostro-caudally oriented and latero-medially oriented strands of strongly IR nerve terminals at regular intervals within each segment. Outside these sympathetic nuclei the terminals are absent or only weakly to moderately IR. The similar pattern of monoamine and peptide innervation of the putative preganglionic sympathetic neurons along the entire thoracic spinal cord may be related to the general three dimensional architecture of the preganglionic multipolar neurons. Thus, these inputs tend to cover the entire surface area of the preganglionic neurons in a uniform way. Some heterogeneities have been observed for the TH, PNMT and neuropeptide Y (NPY) innervation which may contribute to a differential control of sympathetic preganglionic neurons. It is suggested that the unique features of the descending monoaminergic or peptidergic neurons to sympathetic spinal nuclei are related to a demand for maintained transmission upon prolonged activation in these cardiovascular systems, allowing the maintenance of cardiovascular homeostasis.

Monoaminergic and Peptidergic Innervation of the Intermedio-Lateral Horn of the Spinal Cord

In the rat the monoamine and neuropeptide innervation of the sympathetic visceral nuclei has been analysed using retrograde tracing and single and double immunolabelling procedures. When combined with tyrosine hydroxylase (TH), 5-hydroxytryptamine (5-HT) and enkephalin (ENK) immunocytochemistry, somata and dendrites of many preganglionic sympathetic neurons projecting to the coeliac ganglion visualized by retrograde tracing are found in close association with strands and plexa of strongly TH, 5-HT or ENK immunoreactive (IR) nerve terminals, while others have only a minor association with strong TH, 5-HT and ENK immunoreactivities, suggesting that a differential control of preganglionic sympathetic neurons is possible. Experiments with double immunolabelling procedures give further support to a direct innervation of preganglionic sympathetic neurons by TH, 5-HT and ENK IR nerve terminals. In conclusion, the present results open up the possibility for differential regulation of the preganglionic sympathetic neurons according to the Sherringtonian concept of spatial occlusion and facilitation in a pool of motoneurons.

Comparative study of fluoxetine, sibutramine, sertraline and dexfenfluramine on the morphology of serotonergic nerve terminals using serotonin immunohistochemistry

We compared the effects of treatment with high doses of fluoxetine, sibutramine, sertraline, and dexfenfluramine for 4 days on brain serotonergic nerve terminals in rats. Methylenedioxymethamphetamine (MDMA) and 5,7-dihydroxytryptamine (5,7-DHT) were used as positive controls because both compounds deplete brain serotonin. Food intake and body weight changes were also monitored and yoked, pair-fed animals were used to control for possible changes in morphology due to nutritional deficits. Fluoxetine, sibutramine, sertraline and dexfenfluramine all produced a significant reduction in body weight. Fluoxetine, sibutramine and sertraline treatment resulted in no depletion of brain serotonin but produced morphological abnormalities in the serotonergic immunoreactive nerve network. In contrast, dexfenfluramine and MDMA depleted brain serotonin and produced morphological changes in the serotonin nerve network. These results indicate that even though fluoxetine, sibutramine and sertraline do not deplete brain serotonin, they do produce morphological changes in several brain regions (as identified by serotonin immunohistochemistry). Dexfenfluramine and MDMA, on the other hand, markedly deplete brain serotonin and also produce morphological changes. Collectively, these results lend support to the concept that all compounds acting on brain serotonin systems, whether capable of producing serotonin depletion or not, could produce similar effects on the morphology of cerebral serotonin systems.

Immunohistochemical detection of active transforming growth factor-beta in situ using engineered tissue

The biological activity of transforming growth factor-beta 1 (TGF-beta) is governed by dissociation from its latent complex. Immunohistochemical discrimination of active and latent TGF-beta could provide insight into TGF-beta activation in physiological and pathological processes. However, evaluation of immunoreactivity specificity in situ has been hindered by the lack of tissue in which TGF-beta status is known. To provide in situ analysis of antibodies to differentiate between these functional forms, we used xenografts of human tumor cells modified by transfection to overexpress latent TGF-beta or constitutively active TGF-beta. This comparison revealed that, whereas most antibodies did not differentiate between TGF-beta activation status, the immunoreactivity of some antibodies was activation dependent. Two widely used peptide antibodies to the amino-terminus of TGF-beta, LC(1-30) and CC(1-30) showed marked preferential immunoreactivity with active TGF-beta versus latent TGF-beta in cryosections. However, in formalin-fixed, paraffin-embedded tissue, discrimination of active TGF-beta by CC(1-30) was lost and immunoreactivity was distinctly extracellular, as previously reported for this antibody. Similar processing-dependent extracellular localization was found with a neutralizing antibody raised to recombinant TGF-beta. Antigen retrieval recovered cell-associated immunoreactivity of both antibodies. Two antibodies to peptides 78-109 showed mild to moderate preferential immunoreactivity with active TGF-beta only in paraffin sections. LC(1-30) was the only antibody tested that discriminated active from latent TGF-beta in both frozen and paraffin-embedded tissue. Thus, in situ discrimination of active versus latent TGF-beta depends on both the antibody and tissue preparation. We propose that tissues engineered to express a specific form of a given protein provide a physiological setting in which to evaluate antibody reactivity with specific functional forms of a protein.

Maturation of brain stem neurons involved in respiratory rhythmogenesis: biochemical, bioelectrical and morphological properties

Neonatal and adult respiratory-related functions of brain stem were compared using in vivo or in vitro approaches. The control of inspiratory off-switch by glutamate-like neurotransmitters was found active at birth. However, neurons from the nucleus tractus solitarius (NTS) are immature at birth because they present growth cones and the transient potassium current appears progressively during the first week of life in association with modification of the dendritic tree. These data support the hypothesis that the mechanisms of respiratory rhythmogenesis are different at birth and in the adult.

Two distinct phases characterize maturation of neurons in the nucleus of the tractus solitarius during early development: morphological and electrophysiological evidence

We have used electrophysiology and light microscopy of intracellularly labeled neurons in the nucleus of the tractus solitarius (nTS) in brainstem slices of the newborn rat (P0 to P6) to examine the functional and morphological correlation of their development. Three-dimensional reconstruction of neurons injected intracellularly with biocytin, following electrophysiological recording, revealed a close correspondence between morphological immaturity (appearing as polarization of the dendritic tree) and the absence of a ramp-like voltage trajectory at the offset of hyperpolarizing current injections-IA negativity (8 of the 8 cells examined showed this correlation). These morphologically polarized IA negative neurons showed preferential dendritic sprouting in two diametrically opposite poles of the perikaryon. The orientation of the polarity differed according to the rostrocaudal location of the neuron. The appearance of a polarized dendritic tree during the first (immature) phase was transient and closely coincident with IA negativity. Following the development of adult-like electrophysiological characteristics, i.e., IA positivity, nucleus of the tractus solitarius neurons showed remarkably different morphological features (9 of 10 cells). These included a wide-spread branching of the dendritic tree in all directions, giving it a bushy appearance (cell body to dendrite ratio of 1:40). Numerous dendritic spines, growth cones on both dendrites and axons, and axon collateralization were present during both phases and indicate that nTS neurons during the two phases of early development demonstrate dynamic features of growth and maturation. The development of adult-like electrophysiological characteristics, i.e., IA positivity, progressively increased in the postnatal period. During the later part of the first postnatal week, twice as many neurons showed IA positivity in days P3 to P6 as compared with days P0 to P2. These results reveal the dynamic nature of neurons in the nTS during early development and illustrate the close link between morphology and functional characteristics in this region. We suggest that the establishment of adult-like morphology can be modified by appropriate environmental clues provided to nTS neurons during the initial (immature) phase of early postnatal development.

Early ontogeny of the vagus nerve: an analysis of the medulla oblongata and cervical spinal cord of the postnatal rat

Retrograde transport of cholera toxin conjugated with horseradish peroxidase in the postnatal rat has revealed remarkable features of dendritic fields of vagal motor neurons in the medulla oblongata and cervical spinal cord during the period of early development (0-10 days). At birth, vagal motor neurons in the dorsal motor nucleus of the vagus, nucleus ambiguus, nucleus retroambigualis, nucleus dorsomedials and the spinal nucleus of the accessory nerve are small with relatively few, unbranched processes. The span of the dendritic tree is much smaller than that found in adult animals. By the postnatal Day 2 there are marked changes in the soma as well as in the dendritic tree of these neurons. There is dispersion of the cell bodies within the neuropil as well as an expansion of the total area of the brain stem occupied by these motor neurons and their dendritic processes which show extensive growth and branching. By postnatal Day 3 the most extensive proliferation of these neurons is seen and appears to represent the peak of dendritic growth of vagal motor neurons such that the area occupied by the dendritic tree of a single neuron is three times that seen in an adult rat. This proliferation gradually decreased during the subsequent seven days of early development (i.e. Days 4-10) so that by Day 10 the dendritic span of vagal motor neurons was reduced to about twice the adult size. This growth progressively decreased from Days 10 to 30 at which time adult levels were reached. Ultrastructural examination of these horseradish peroxidase labeled dendrites showed a positive correlation between the number of dendritic processes and the number of axo-dendritic synapses. This was accompanied by an increase in the number of identifiable synaptic junctions. These morphological complexities observed during the period of early development of vagal motor neurons indicate that the vagus nerve undergoes dramatic changes during the period of early development including the establishment of numerous synaptic contacts between vagal afferents and efferents in the brainstem. A number of these changes occur in developing dendritic fields of vagal motor neurons during the first three days of neonatal life. It is reasonable to assume that developmental abnormalities during this "critical period" could produce significant functional changes in the pattern of respiration as well as in the control of airway smooth muscle.

Reversible, short-lasting, and dose-dependent effect of (+)-fenfluramine on neocortical serotonergic axons

Dextrofenfluramine [+)-fenfluramine) is the dextro-optical isomer of the racemic compound (+/-)-fenfluramine. This compound stimulates the release of serotonin (5-HT) and blocks its re-uptake in serotonergic nerve terminals. (+)-Fenfluramine and its nor metabolite which have been localized in significant amounts in the rat brain are useful anorectic agents in animals. In humans, (+)-fenfluramine is used as an anti-obesity agent when administered orally in doses of 0.25 mg/kg/twice a day. Studies in some animal species (such as the rat and monkey, but not mice) using high doses of (+)-fenfluramine (administered subcutaneously) have shown long-term neurochemical and immunocytochemical effects in selected brain regions. In the present study we used the rat to determine the mechanism underlying the anorectic effect of orally administered (+)-fenfluramine. The rat was selected because long-term effects of (+)-fenfluramine have been previously described in this species. In addition, a variety of other aspects of orally administered (+)-fenfluramine have been addressed in this study. For example, how long does the depletion of 5-HT in the nerve terminals last following cessation of the drug treatment? i.e. is the effect reversible? Is this depletion of 5-HT and the resultant abnormal morphology of 5-HT-immunoreactive nerve terminals seen at high doses dose-dependent? Since some of these questions relate to morphological evaluation of this drug in brain 5-HT systems, we have examined this system as part of our ongoing effort to examine brain monoaminergic systems under perturbed conditions. We have used a morphological (immunocytochemical) approach to answer these questions. The primary function of this study was to evaluate the effects of short-term exposure (4 days) to varying doses of orally administered (+)-fenfluramine on 5-HT-immunoreactive nerve terminals in the frontal cortex of the rat. The frontal cortex was selected because it contains a homogeneous population of nerve fibers and terminals unlike other cortical regions, the hippocampus, striatum and the hypothalamus where a mixed population of coarse and fine fibers has been described. Since the previously reported effect of fenfluramine on 5-HT nerve terminals was the appearance of coarse fibers, the region of cortex selected for this study showed no coarse fibers in the pair-fed control. This essential feature of control regions has not been used in previous studies on this subject. The present study demonstrates that (+)-fenfluramine produces a dose-dependent reduction in 5-HT immunoreactivity of 5-HT nerve terminals in the neocortex of adult rats.(ABSTRACT TRUNCATED AT 400 WORDS)

Comparative evaluation of oral prostaglandin E2 & intravenous oxytocin for induction of labour

Oral prostaglandin E2 tablets (group I) and iv Oxytocin (group II) were evaluated in 120 randomly selected women subjected to induction of labour. In group I, 60 women received oral prostaglandin E2 tablets in incremental doses from 0.5-1.5 mg hourly, depending upon the parity and Bishop score of the patient. Group II women received oxytocin iv in 5 per cent dextrose, starting at a rate of 2 mU/min and gradually increasing to a maximum of 64 mU/min. Overall success rate in group I (prostaglandin E2) and group II (intravenous oxytocin) was 85 and 93.3 per cent respectively (P greater than 0.05). In the favourable group (Bishop score 6-13) the induction delivery interval (IDI) for group I and group II was 8.86 h and 7.95 h respectively (P greater than 0.05), while in the unfavourable group (Bishop score less than or equal to 5), the IDI for the respective groups were 13.42 h and 10.11 h (P less than 0.05). Side effects with prostaglandin E2 were mostly mild gastrointestinal ones. A significantly higher incidence of foetal distress was observed with intravenous oxytocin (15%) as compared to prostaglandin E2 (3.33%). Oral prostaglandin E2 was thus found to be a better alternative to intravenous oxytocin in multiparous women with favourable Bishop score (greater than 6) and in those in whom fluid retention is to be avoided (e.g., conditions like toxemias, renal disease).

Rapidly adapting pulmonary receptor afferents: I. Arborization in the nucleus of the tractus solitarius

The organization of axon collaterals, preterminal processes, and presumptive synaptic boutons of single physiologically identified rapidly adapting receptor (RAR) pulmonary afferent fibers was examined following the intraaxonal application of wheat germ agglutinin conjugated with horseradish peroxidase (WGA-HRP). The RAR axons were injected 200-300 microns lateral to the nucleus of the tractus solitarius (nTS) at a number of different rostrocaudal levels in seven individual experiments. The trajectories of the stained axons were reconstructed from individual 50-microns-thick serial sections. The rostrocaudal extent, as well as the distribution of the trajectory of each RAR afferent, was reconstructed from every section by using a camera lucida attachment. In this first of two papers, we describe the pattern of organization of bouton terminals of RAR afferents related to cytoarchitectonically distinct subnuclei of the nTS. In the companion paper, morphological details of the fine structure of these synaptic boutons and axonal branches are described in different subnuclei in order to illustrate morphological differences in these functionally distinct regions. A number of significant findings have resulted from this light microscopic study. The central process of a single RAR afferent fiber arborized in the medulla oblongata over a considerable distance in the rostrocaudal plane (2.5 mm rostral to 1.4 mm caudal to the obex). A single RAR afferent fiber terminated in numerous bouton terminals (range 500-1,050), and these terminals arose from over 400 segments of branches of the parent injected axon. A small number of en passant bouton terminals were found. There appeared to be a remarkable degree of consistency in the subnuclei of the nTS where these terminals arborized. The dorsal and dorsolateral subnuclei of the nTS received 144-647 bouton terminals. The second-largest concentration of bouton terminals of RAR afferents was found in the intermediate (nI) subnucleus of the nTS. No labeled bouton terminal was found in the ventral and ventrolateral subnuclei of the nTS. This finding is in sharp contrast to the terminations of SAR afferents which terminated predominantly in the ventral and ventrolateral nuclei of the nTS, the interstitial nucleus of the nTS, and the nI. The parent RAR axon could be traced as far rostrally as 2.5 mm, even though the region of terminal arborization could not be followed beyond 0.8 mm. The destination of this rostrally projecting RAR afferent could not be determined in this study.(ABSTRACT TRUNCATED AT 400 WORDS)

Rapidly adapting pulmonary receptor afferents: II. Fine structure and synaptic organization of central terminal processes in the nucleus of the tractus solitarius

The nucleus of the tractus solitarius (nTS) is a site for termination of primary afferents originating from a variety of different visceral sensory endings (Kalia and Mesulam: J. Comp. Neurol. 193:523-553, '80). The light and electron microscopic evaluation of bouton terminals of slowly adapting lung stretch (SAR) afferent fibers originating from the tracheobronchial tree has been described previously (Kalia and Richter: J. Comp. Neurol. 241:503-520, 521-535, '85). The companion article (Kalia and Richter: J. Comp. Neurol. 273:000-000, '88) describes details of the light microscopic organization of a second group of pulmonary afferents, the rapidly adapting receptors (RARs), that are known to signal transient volume changes in airways (Sellick and Widdicombe: J. Physiol. (Lond.) 203: 359-381, '69; Q.J. Exp. Physiol. 55:153-163, '70). Terminals from RAR afferents are concentrated within two specific subnuclear groups of the nTS (dnTS and nI) and are distributed over 4 mm of the medulla oblongata rostrocaudally. Within the nTS, axon collaterals of RAR afferents remain myelinated up to a diameter of 0.4-1.0 microns. Preterminal processes are always unmyelinated and range in diameter from 0.15 to 0.3 microns. Bouton terminals (1.0-2.0 microns) are of both the en passant and end terminal varieties. The synaptic profiles formed by 143 bouton terminals of RAR afferents, were examined in uninterrupted sequential sections and are described in this paper. All the bouton terminals examined under the electron microscope were found to contain clear, round synaptic vesicles. Boutons made synaptic contact with different profiles in each of the two subnuclei (dnTS and nI) examined. Contacts were usually asymmetrical (type I) containing clear, round synaptic vesicles 35-50 nm in diameter. In the dorsal subnucleus of the nTS (dnTS), the synaptic arrangement of RAR boutons did not appear to be complex. The RAR bouton terminal was usually located in juxtaposition to unlabeled axon terminals of similar morphological characteristics. Typically, the RAR bouton terminal made synaptic contact with a medium-sized spiny dendrite. No axosomatic contacts involving RAR afferents were observed in this subnucleus. In the intermediate subnucleus of the nTS (nI), the most common synaptic arrangement of RAR bouton terminals was in the form of a "glomerulus," which was formed by five to seven different types of neuronal profiles surrounding the labeled RAR bouton terminal.(ABSTRACT TRUNCATED AT 400 WORDS)

Neuropeptide Y-immunoreactive perikarya and nerve terminals in the rat medulla oblongata: relationship to cytoarchitecture and catecholaminergic cell groups

The aim of this study was to examine details of the distribution of neuropeptide Y (NPY)-immunoreactive perikarya and nerve terminals in the medulla oblongata in relation to cytoarchitectonically and functionally distinct catecholaminergic regions. The immunoperoxidase method was combined with Nissl staining to determine nuclear boundaries of transmitter-identified nerve cell bodies and to examine the relationship between populations of NPY-immunoreactive neurons and catecholaminergic cell groups (A1, A2, C1, C2, and C3) in serial sections. Previous studies using immunofluorescence have described the existence of NPY catecholaminergic immunoreactive nerve cell bodies in the brainstem. No information is currently available with regard to details of the distribution of these peptidergic neurons and nerve terminals in the functional subnuclear units of the medulla oblongata. In this study we have delineated the anatomical association of NPY immunoreactivity with cardiovascular function. Neuropeptide Y-immunoreactive neurons were found located in close association with noradrenergic neurons of the A1 cell group in the caudal ventrolateral medulla oblongata, where they were usually found located dorsal to the lateral reticular nucleus (LRt). A second population of NPY-immunoreactive neurons was found located medial to the A1 cell group in the ventral subdivision of the reticular nucleus of the medulla (MdV). Neuropeptide Y-immunoreactive neurons in the rostral medulla were found located in regions corresponding to the principal distribution of adrenergic neurons in the C1, C2, and C3 cell groups. In the dorsomedial medulla (A2 region) NPY-immunoreactive neurons were localized in the area postrema (ap) and in a number of subnuclei of the nucleus of the tractus solitarius (nTS), i.e., the dorsal parasolitary region (dPSR), the dorsal strip (ds), the periventricular region (PVR), and the ventral parasolitary region (vPSR). The location of NPY-immunoreactive perikarya and nerve terminals in the dorsal subnuclei of the nTS, i.e., the dPSR and ds, is of particular significance, since this distribution corresponds with the location of small adrenergic neurons as well as with the site of termination of aortic and carotid sinus nerve afferent fibers. NPY-immunoreactive neurons in the dorsomedial medulla are ideally situated for receiving monosynaptic input from baroreceptor afferents and could play a key role in the central integration of cardiovascular reflexes.

Evidence for discrete alterations in central cardiovascular catecholamine and neuropeptide Y immunoreactive neurons in aged male rats and in genetically hypertensive male rats of the Lyon strain

A computer-assisted morphometrical and microdensitometrical analysis has been performed on cardiovascular noradrenaline (NA), adrenaline (A) and neuropeptide (Y (NPY) neurons in adult and 24-month-old male rats and on hypotensive (LL), normotensive (LN) and hypertensive (LH) male rats of the Lyon strain using the indirect immunoperoxidase procedures. It was found that in NPY/phenylethanolamine-N-methyltransferase (PNMT) costoring neurons of the CI area of the rostral medulla oblongata NPY-like immunoreactivity showed a more marked reduction than the PNMT immunoreactivity. Furthermore, within the parvocellular part of the paraventricular hypothalamic nucleus. NPY immunoreactive nerve terminal profiles were much more affected than the PNMT immunoreactive profiles during aging as revealed by a marked reduction in the number of profiles and by a marked reduction of absorbency values in the microdensitometrical analysis. Thus, in the NPY/PNMT costoring neurons of the A C1 group of the ventrolateral medulla projecting, for example, to the hypothalamus, the peptide transmission line may have a special vulnerability to the aging processes which may contribute to the development of hypertension in old people in view of a vasodepressor role of many central NPY/PNMT neurons. An extensive morphometrical and microdensitometrical analysis of the various catecholamine (CA) cell groups of the medulla oblongata of the LL, LN and LH rats of the Lyon strain was performed. In a comparison between LL and LH rats the A2 cell group of the LH strain showed a trend for an increase in the mean tyrosine hydroxylase (TH) immunoreactive cell body area and the C3 group showed a significant increase in the number of PNMT immunoreactive profiles.(ABSTRACT TRUNCATED AT 250 WORDS)

Ganglioside-induced regeneration and reestablishment of axonal continuity in spinal cord-transected rats

In this study we examined the effect of chronic GM-1 ganglioside treatment on the reestablishment of axonal continuity and functional recovery in spinal cord-transected rats. Previous studies have shown that chronic treatment with GM-1 ganglioside is effective in producing regeneration of lesioned mesostriatal dopaminergic neurons in the central nervous system [1, 2]. In addition, GM-1 ganglioside advances peripheral nerve regeneration following nerve crush injury [12]. Axonal continuity was determined by the ability of the spinal cord to transport horseradish peroxidase across the region of transection. Comparisons between ganglioside-treated and saline-treated controls showed that ganglioside treatment resulted in the reestablishment of axonal continuity between the spinal cord distal to the level of the transection and the brainstem. Saline-treated controls showed little evidence of axonal continuity between these two regions. Thus gangliosides induce reestablishment of axonal continuity and thereby could advance functional recovery in rats following spinal cord transection.

Morphology of physiologically identified slowly adapting lung stretch receptor afferents stained with intra-axonal horseradish peroxidase in the nucleus of the tractus solitarius of the cat. I. A light microscopic analysis

The present series of experiments was designed to study the organization of preterminal processes and synaptic boutons of single physiologically identified slowly adapting receptor (SAR) pulmonary stretch afferent fibers. Intra-axonally injected horseradish peroxidase-wheat germ agglutinin (HRP-WGA) conjugate was used as the label. In the first paper, we describe the pattern of arborization of axon collaterals from single physiologically identified SAR afferent fibers evident in the various subnuclei of the nucleus of the tractus solitarius (nTS). In the second paper, details are presented regarding the ultrastructure of these synaptic boutons and axon collaterals. A number of significant findings resulted from this study: (1) A single lung stretch SAR afferent fiber arborized over a considerable distance rostrocaudally in the brain stem (1,700-2,100 microns). (2) A single lung stretch SAR afferent fiber terminated as hundreds of bouton terminals (650-1,180). (3) There was a remarkable consistency in the subnuclei of the nTS that received these terminal arborizations of SAR afferents. (4) The ventral (vnTS), intermediate (nI), ventrolateral (vlnTS), and interstitial (ni) subnuclei of the nTS were the only regions of the nTS receiving bouton terminals of SAR afferent fibers. (5) Under the light microscope the pattern of termination of SAR afferents was similar in all the axons studied in this series. (6) The injected parent axon in each case could be followed in the TS at all levels and remained consistent with regard to position and orientation and could be traced rostrally to levels as far as 3.5 mm rostral to the obex whereas the region of terminal arborization was located around 1.7-2.1 mm rostral to the obex. This pattern indicates that a single lung stretch SAR afferent fiber descends caudally upon entering the nTS. In the cat vagal afferent fibers are known to enter the medulla at levels between 0.5 mm and 3.2 mm rostral to the obex (Kalia and Mesulam, '80a). The results of the light microscopic analysis presented in this article indicate that lung stretch (SAR) afferents from the lungs and tracheobronchial tree have distinctly localized patterns of distribution in the nTS. In addition, these findings support the concept that representation of pulmonary afferents in the medulla is constituted by a differentiated distribution of nerve terminals in the various subnuclei of the nTS. Modality-specific localization (SAR afferents in this case) appears to be predominant in the nTS. The widespread rostrocaudal distribution of the terminal field of a single lung stretch SAR afferent is remarkable.(ABSTRACT TRUNCATED AT 400 WORDS)

Morphology of physiologically identified slowly adapting lung stretch receptor afferents stained with intra-axonal horseradish peroxidase in the nucleus of the tractus solitarius of the cat. II. An ultrastructural analysis

The nucleus of the tractus solitarius is a site for termination of primary afferents originating from a variety of visceral receptors. The localization of bouton terminals of slowly adapting lung stretch (SAR) afferent fibers originating from the tracheobronchial tree have been described in the companion paper (Kalia and Richter, '85). The most conspicuous finding regarding the location of SAR terminals is that they are concentrated within specific subnuclear groups of the nucleus of the tractus solitarius (nTS) and are distributed widely in the rostrocaudal plane of the medulla oblongata. These light microscopic features have provided us with valuable information with regard to the organization of visceral afferents in the central nervous system. The synaptic profiles formed by the 476 bouton terminals of these HRP-labeled afferents have been described in this paper in serial thin sections. All of the bouton terminals examined under the electron microscope were found to contain round synaptic vesicles. Synaptic boutons (1.0-3.0 microns in diameter) were usually of the en passant variety and made contact with different structures depending upon the subnucleus which was examined. In the ventral (v) and the ventrolateral (vl) subnuclei of the nTS, asymmetrical (type I) synaptic contacts containing round, clear synaptic vesicles of 35-50 microns in diameter were found and these contacts were made with (1) the soma of cell bodies located in that subnucleus; (2) spiny dendrites in that nucleus; (3) vesicle-containing axon terminals that were presynaptic to the HRP-labeled bouton terminal; and (4) vesicle-containing dendrites in which the HRP profile was presynaptically located. The terminal axon remained myelinated till the last 1 micron before the bouton terminal was formed. There was no distinct, unmyelinated portion of the terminal axon. The synaptic bouton received axon-axonal synapses from unlabeled bouton terminals containing round, clear vesicles. This is the first report of the localization of these afferent fibers as well as of the regional variations in the ultrastructure of boutons of physiologically identified terminals. It appears likely that the lung stretch afferent fibers, by having axon-axonal as well as axon-somatic contact in the ventral, ventrolateral, and intermediate subnuclei of the nTS, can interact in a variety of different ways in this region. The significance of these features in relation to the precise influence of respiratory afferents on central respiratory mechanisms needs to be evaluated further.

Somatostatin induced apnoea: prevention by central and peripheral administration of the opiate receptor blocking agent naloxone

Somatostatin (SRIF) (6 nmol) given intracisternally (i.c.) into the alpha-chloralose anaesthetized rat has recently been shown to cause apnoea with a latency of 5-10 minutes (Kalia et al. 1984a). The apnoea produced by SRIF is very rapid, irreversible and leads to the death of the animal. In view of the existence of SRIF nerve cell bodies and terminals in medullary respiratory nuclei such as the ventral and ventrolateral subnuclei of the nucleus of the tractus solitarius (nTS) (Kalia et al. 1984b, Johanson et al. 1984), we have proposed the existence of somatostatinergic mechanisms in the respiratory nuclei of the medulla oblongata involved in mediating apnoeic conditions (Kalia et al. 1984a). In the present study, we have analysed whether the SRIF induced apnoea could be counteracted by a previous i.c. administration of the highly selective alpha 2-adreno-receptor blocking agent RX 781094 (2-(2-(I,4 benzodioxanyl]2-imi-dazoline HCl) (Doxey et al. 1983), or an opiate receptor blocking agent such as naloxone. Thus, both alpha 2-adrenoreceptor agonists and opiates induce respiratory depression, and opiates in high doses cause apnoea (Bolme et al. 1974, Hassen et al. 1982, Sitsen et al. 1982). In addition, catecholamine (CA) and enkephalin immuno-reactive nerve terminal networks exist in high densities within the nucleus tractus solitarius (nTS) of the medulla oblongata and may therefore interact with somatostatin nerve terminals in regulation of respiratory activity (Kalia et al. 1984b).

Rat medulla oblongata. III. Adrenergic (C1 and C2) neurons, nerve fibers and presumptive terminal processes

The goal of this study was to define the cytoarchitectonic relationships between the catecholaminergic cell groups (the C1 and C2) in the rostral medulla oblongata of the rat. Immunocytochemistry was combined with Nissl staining to determine the nuclear boundaries in this region of the brain stem. In addition, the morphological characteristics of neurons in the C1 and C2 cell groups were determined and the relationship between these populations of neurons and their caudaul counterparts (A1 and A2 cell groups) was established (Kalia et al., '85a). The results indicate that the C1 and C2 cell groups are distributed over a wide region of the rostral medulla. The location of these adrenergic neurons is related to a number of nuclear groups in this region. This finding was remarkably consistent in all the animals studied in this series. In addition, adrenergic nerve fibers were found to be distributed over a large region of the medullary reticular formation. There was homogeneity in the morphology of the C1 and C2 cell groups. These rostrally located adrenergic neurons did not share morphological features in common with the recently described (Kalia et al., '85a) caudally located adrenergic neurons in the dorsal region of the nucleus of the tractus solitarius. These striking anatomical features of the adrenergic C1 and C2 cell groups support the proposal that adrenergic neurons in the rostral medulla oblongata play an important role in the integration of visceral functions (Fuxe et al., '80).

Rat medulla oblongata. II. Dopaminergic, noradrenergic (A1 and A2) and adrenergic neurons, nerve fibers, and presumptive terminal processes

The aim of this study was to determine the anatomical relationships between catecholaminergic neurons and cytoarchitectonically defined nuclei in the caudal medulla oblongata. Previous studies have demonstrated the existence of noradrenergic cell bodies (designated as the A1 and A2 cell groups) in the caudal medulla oblongata of the rat (Dahlström and Fuxe, '64), including the nTS. There is no information currently available with regard to details of the distribution of these noradrenergic neurons in the functionally distinct subnuclei of the medulla oblongata. In this study the location of catecholamine-synthesizing enzymes was examined in the serial sections of the caudal medulla oblongata of the rat: tyrosine hydroxylase (TH), dopamine-beta-hydroxylase (DBH), and phenylethanolamine N-methyl transferase (PNMT). The immunoperoxidase method of Sternberger ('79) was used to demonstrate the location of immunoreactive neurons, nerve fibers, and presumptive terminal processes. This was followed by Nissl staining of the same sections to localize accurately the immunoreactivity. Noradrenergic neurons (TH- and DBH-positive and PNMT-negative) were localized in a number of subnuclei of the nucleus of the tractus solitarius (nTS), the area postrema (ap), and in the dorsal motor nucleus of the vagus (dmnX). The distribution of these noradrenergic cells was different at different rostrocaudal levels. In addition, adrenergic neurons (TH-, DBH-, and PMNT-positive) were identified dorsal to the tractus solitarius (TS), in the dorsal strip region (ds), the periventricular region (PVR), the dorsal parasolitarius region (dPSR), and the dmnX (rostral to obex). In addition, dopaminergic neurons (TH-positive and DBH- and PNMT-negative) were found in the ap and dmnX. The A1 cell group in the ventrolateral medulla consisted almost exclusively of noradrenergic neurons (TH- and DBH-positive and PNMT-negative). These results indicate that in the rat the A2 cell group is a mixed population of catecholaminergic neurons that are localized in well-defined regions of the dorsal medulla oblongata. The distribution of these neurons is very specific both in terms of rostrocaudal levels and cytoarchitectonic subdivisions of regions of the medulla known to be involved in central autonomic control. This supports the hypothesis that monoaminergic neurons in the dorsal medulla play important roles in the central regulation of visceral function.

Rat medulla oblongata. IV. Topographical distribution of catecholaminergic neurons with quantitative three-dimensional computer reconstruction

We examined serial 40 micron vibratome, immunoperoxidase-stained sections of the medulla with tyrosine hydroxylase (TH), dopamine-beta-hydroxylase (DBH), and phenylethanolamine N-methyltransferase (PNMT) antisera followed by Nissl staining to locate catecholaminergic neurons in cytoarchitectonic regions followed by a three-dimensional (3D) computer reconstruction of these cell groups to determine their spatial organization. Overlay drawings of low and high power photomicrographs showing cell bodies and nuclear boundaries were entered into a digital computer storage system. Every section in the series was plotted to yield an accurate representation of regional densities of cells and location of nuclei, as revealed by two-dimensional plots of individual sections as well as three-dimensional plots of groups of sections. Data files were scanned in a number of ways to obtain total cell counts of TH-, DBH-, and PNMT-immunoreactive cells within a designated area or cell counts of only one type of immunoreactive cell. This combination of data manipulation produced the following results: (1) A1 group is a homogeneous population of noradrenergic neurons at levels caudal to the obex, and at the obex it is mixed with adrenergic cells. The dimensions of the A1 cell group are 1.3 X 2.7 mm, extending from -2.5 to +0.2. Part of this cell group lies in the lateral reticular nucleus. (2) A2 group is not purely noradrenergic as previously suspected. It is a very mixed cell group containing mainly dopaminergic neurons in the area postrema (periventricular region) and the dorsal motor nucleus of the vagus, mainly noradrenergic neurons in the medial subnucleus of the nucleus of the tractus solitarius (nTS), mainly adrenergic neurons in the dorsal strip and dorsal subnucleus of the nucleus of the tractus solitarius, and a mixture of all three catecholaminergic neurons in the other subnuclei of the nTS. The dimensions of this group are 0.4 X 3 mm extending from -2.7 to +0.3. (3) C1 group is a homogeneous population of adrenaline cells extending from +1 to +2.5 with dimensions of 1.5 X 1.5 mm and consisting of scattered neurons some of which occupy the gigantocellular reticular nucleus. (4) C2 group is a homogeneous population of adrenaline neurons extending from +1 to +3 with dimensions of 2.5 X 3 mm. Accurate visual imaging and quantitation of the spatial organization of medullary catecholaminergic neurons within the classical anatomical framework of cytoarchitecture provides an enhanced comprehension of the organization of this region of the central nervous system.

Rat medulla oblongata. I. Cytoarchitectonic considerations

The goal of this study was to define the detailed cytoarchitecture of the medulla oblongata of the rat in order to accurately localize immunocytochemically distinct populations of neurons in this region. The cytoarchitectonic features of this region of the rat brain stem were examined in 40 micron thick serial sections of celloidin embedded brains blocked in the Horsley-Clarke stereotaxic plane. These sections were stained with cresyl violet and examined at a number of different magnifications with a variety of different intensities of staining to demonstrate particular features of the cells in this region. High magnification photomicrographs of this material revealed characteristic features of the various populations of cells. The results illustrate that the cytoarchitecture of the medulla oblongata of the rat changes remarkably within very short distances in the rostrocaudal direction. These changes indicate the need to study the anatomy and immunocytochemistry of this region in detailed serial sections. The ventral reticular formation of the rat medulla is cytoarchitectonically complex. Nuclear groups such as the lateral reticular nucleus (LRt) contain a number of cytoarchitectonically distinct subnuclei, as does the dorsally located nucleus of the tractus solitarious (nTS) (Kalia and Sullivan, '82). These nuclei occupy a considerable length of the medulla and terminate abruptly at the pontomedullary boundary. A number of other cytoarchitectonic features of the medulla were examined and the detailed characteristics were defined.

Distribution of neurophysin II immunoreactive nerve fibers within the subnuclei of the nucleus of the tractus solitarius of the rat

The location of neurophysin II immunoreactive nerve fibers and preterminal processes has been examined in various functionally distinct subnuclei of the nucleus of the tractus solitarius (nTS) using the indirect immunofluorescence method for immunocytochemistry combined with cytoarchitectonic identification. The nTS is responsible for integrating respiratory and autonomic reflex activity: the vlnTS, vnTS, ni and nI are associated with respiratory activity; the dlnTS and dnTS are important sites for the integration of baroreceptor and chemoreceptor activity; the ncom, dnTS and dlnTS integrate cardiac afferent activity and the mnTS mediates both cardiovascular and gastrointestinal effects. At levels caudal to the obex, the ncom contained the largest number of neurophysin II immunoreactive nerve fibers and the mnTS and dmnX contained moderate neurophysin II immunoreactivity. At levels rostral to the obex the region of the dorsal medulla adjacent to the mnTS and dnTS (PVR and dPSR) showed the densest immunoreactivity and the mnTS, dmnX and vPSR showed moderate immunoreactivity. At the rostral pole of the nTS, neurophysin II immunoreactive nerve terminals were seen in the dendritic regions of cells in dmnX and mnTS. This selective distribution of neurophysin II immunoreactive nerve terminals in the cardiovascular and gastrointestinal subnuclei of the nTS implicates a direct, descending, hypothalamic, oxytocin-neurophysin II containing pathway interacting with these nTS functions. These results confirm the hypothesis (Sawchenko and Swanson) that descending neurophysin II immunoreactive pathways represent an important neuronal system for the hypothalamic regulation of cardiovascular (vasomotor) and gastrointestinal nuclei in the brainstem.

Somatostatin-induced apnea: interaction with hypoxia and hypercapnea in the rat

The effects of hypoxia and hypercapnea in the production of somatostatin (SRIF)-induced apnea were studied during rebreathing experiments. Hypoxia and hypercapnea resulted in a shortening of the latency of SRIF-induced apnea. In order to exclude the effect of stimulation of central chemoreceptors by mock-CSF solution, control experiments using mock-CSF in combination with hypoxia and hypercapnea were done. No apnea could be produced by the mock-CSF in combination with hypoxia and hypercapnea. The shortening of apneic latency from 480 +/- 8 s (S.E.M.) to 148 +/- 30 s with the addition of a chemostimulus (hypoxia and hypercapnea) in SRIF-induced respiratory depression demonstrates that chemostimulation interacts with the centrally originating apnea to enhance its apneic response.

Evidence for the existence of putative dopamine-, adrenaline- and noradrenaline-containing vagal motor neurons in the brainstem of the rat

A combined technique utilizing retrograde transport of horseradish peroxidase (HRP) combined with immunocytochemistry using antibodies raised against tyrosine hydroxylase (TH), dopamine beta-hydroxylase (DBH) and phenylethanolamine N-methyl transferase (PNMT) has been used to characterize monoaminergic neurons located within the region of the brainstem vagal motor nucleus. TH-immunoreactive (IR) but not DBH-IR and PNMT-IR neurons were double labelled predominantly at the caudal-most pole of the dorsal motor nucleus of the vagus (dmnX), whereas double-labelled PMNT and DBH plus TH-IR neurons extended from levels just rostral to the obex to 1-2 mm rostrally in the medial and lateral poles of the dmnX, respectively. The presence of putative dopamine (DA), noradrenaline (NA) and adrenaline (A) neurons in topographically distinct regions of the dmnX implicates, DA, NA and A in the modulation of cholinergic transmission at the level of parasympathetic ganglia in discrete parts of the thoracic and abdominal viscera.

Somatostatin produces apnea and is localized in medullary respiratory nuclei: a possible role in apneic syndromes

Immunocytochemical studies on the nucleus of the tractus solitarius and adjacent areas of the dorsal medulla of the rat demonstrate the existence of somatostatin immunoreactive nerve cell bodies and nerve terminals within the ventrolateral and ventral subnuclei of the nucleus of the tractus solitarius. Injections of somatostatin (6 nmol in 10 microliters) into the cisterna magna of chloralose-anesthetized rats produced an apnea with a latency of 5-7 min. This apnea was preceded by slow deep breathing, a reduction in heart rate and fall of arterial blood pressure. The apnea was usually irreversible leading to death of the animal. These respiratory and cardiovascular effects of somatostatin were not abolished either by bilateral vagotomy or by low decerebration (below the inferior colliculus). It is suggested that activation of somatostatin receptors linked to neurons in medullary respiratory nuclei might be responsible for the inhibition of respiratory neuronal activity and thus may mediate apneic conditions.

Distribution of neuropeptide immunoreactive nerve terminals within the subnuclei of the nucleus of the tractus solitarius of the rat

The location of substance P, enkephalin and somatostatin (SRIF), and neurophysin II immunoreactive nerve terminals and preterminal processes in the caudal part of the nucleus of the tractus solitarius (nTS) was examined by the indirect immunofluorescence method for immunocytochemistry combined with cytoarchitectural identification of nuclear subgroups in the same tissue. In 22 Sprague-Dawley rats we examined 14-micrometers-thick serial sections of the dorsal medulla at levels from 1 mm caudal to 2 mm rostral to the obex. These sections were incubated with substance P, enkephalin, somatostatin, and neurophysin II antisera. All four peptides were examined in each case and five typical levels (two caudal and three rostral to the obex) were selected for comparison of terminal distribution between peptides. All sections were photographed under the fluorescence microscope and then counter-stained with cresyl violet. This method of analysis revealed distinct patterns of neuropeptide immunoreactivity in the subnuclei of the nTS that varied according to the level of the section. The nTS is responsible for integrating respiratory, cardiovascular (baroreceptor and cardiac), and gastrointestinal functions. The ventrolateral subnucleus (Vl)nTS, ventral subnucleus (v)nTS, interstitial subnucleus (ni)nTS, and intermediate subnucleus (nI)nTS are the major respiratory subnuclei with vlnTS and vnTS prominently associated with pulmonary afferents, ni associated with laryngeal afferents, and nI with tracheal afferents. The vlnTS, vnTS, and ni showed a moderate density of somatostatin-positive nerve terminals, scattered substance P and enkephalin immunoreactivity, and no neurophysin II-positive terminals. The nI showed moderate density of substance P immunoreactive nerve terminals. The subnuclei of the nTS receiving baroreceptor and chemoreceptor afferents--dorsolateral and dorsal (dl and d) subnuclei of nTS--showed scattered substance P immunoreactive nerve terminals. The commissural nucleus of nTS (ncom), which receives most of the cardiac afferents, showed a moderate density of enkephalin-positive immunoreactive nerve terminals. The medial subnucleus (m)nTS at levels rostral to the obex, the primary site for the termination of gastrointestinal afferents, showed substance P immunoreactivity in moderate amounts and weak immunoreactivity for all the other neuropeptides. An important result of these experiments was the observation that regions of the medulla adjacent to the nTS, i.e., the ventral parasolitarius region (vPSR), dorsal (d)PSR, and the periventricular region (PVR) showed the densest amounts of immunoreactive nerve terminals.(ABSTRACT TRUNCATED AT 400 WORDS)

Transmitter and peptide systems in areas involved in the control of blood pressure

The distribution of catecholamine neurons in the dorsal vagal complex is described on the basis of indirect immunofluorescence histochemistry using antisera to three enzymes in the catecholamine synthesis, tyrosine hydroxylase, dopamine-beta-hydroxylase and phenylethanolamine-N-methyltransferase, allowing differentiation between dopamine, noradrenaline and adrenaline cells. In addition attention was focused on the occurrence of two peptides, neuropeptide Y (NPY) and neurotensin in this region. It could be established that they partly were present in subpopulations of the A2/C2 catecholamine neurons. The significance of this coexistence of a peptide and a catecholamine is discussed.

Evaluation of regeneration of nerve and reinnervation of skeletal muscle in the hibernating ground squirrel

The retrograde transport of HRP was used to determine the status of axonal transport in the peroneal and sciatic nerves of hibernating and nonhibernating ground squirrels following crush of the peroneal nerve at 10 to 12 mm (SNS) or sciatic nerve at 33 to 35 mm (LNS) from its entrance into the extensor muscle. The ability of the proximal segment to reestablish axonal continuity and thus neuromuscular transmission was also studied. Two weeks to 3 months after nerve crush the extensor muscles were injected with HRP. We found that during hibernation no axonal transport across the site of crush was seen even after 3 months and that regeneration of the nerve during this period was minimal. Evidence of slight regeneration seen at 90 days could be due to periods of awaking of the animals during their natural hibernation cycle. In these animals HRP deposits were seen only in the nerve distal to crush, i.e., between crush site and muscle. In the nonhibernating squirrels, axoplasmic flow was reestablished at the site of injury as early as 2 weeks after crush, and HRP could be detected in the spinal cord in motoneurons of the ipsilateral ventral horn at spinal levels L3 to L5. In one hibernating animal the peroneal nerve was crushed at the distal site (SNS) and also the spinal cord was injured by dropping a weight. After nerve crush and the spinal cord injury the hibernating state could not be maintained and the animal stayed awake 22 days. The time course of regeneration of the nerve in that animal was similar to that seen in nonhibernating squirrels. After nerve crush in nonhibernating animals, reaction product was also found in sensory cell bodies of dorsal root ganglia as well as in terminals in the substantia gelatinosa of the spinal cord at the same levels. Thus, the axonal transport occurs in hibernating and non-hibernating squirrels in both sensory and motor nerve fibers. The extensor muscle fibers of the hibernating squirrels showed substantial membrane depolarization 90 days after crush. Action potentials from these fibers could be obtained from 15 to 35 days only through stimulating the nerve segment distal to the crush. Stimulation of the proximal nerve segment did not evoke muscle activity. These results demonstrate that nerve regeneration was nearly abolished during hibernation and that blockade of axonal transport continued across a region of nerve crush for the duration of the hibernating period.

Ganglioside-induced acceleration of axonal transport following nerve crush injury in the rat

The role of gangliosides in the re-establishment of neuronal continuity was examined in rats whose peroneal nerve had been crushed by a standardized procedure. Neuronal continuity was determined by the ability of the nerve to transport horseradish peroxidase retrogradely back to the spinal cord. The number of retrogradely labeled neurons provided an index of the degree of axonal transport that was re-established. Comparison of ganglioside-treated animals with saline-treated controls showed that ganglioside treatment advanced the re-establishment of retrograde axonal transport by 3 days.

Brainstem projections of sensory and motor components of the vagus nerve in the rat

The sensory and motor connections of the cervical vagus nerves and of its inferior ganglion (nodose ganglion) have been traced in the medulla and upper cervical spinal cord of 16 male Wistar rats by using horseradish peroxidase (HRP) neurohistochemistry. The use of tetramethyl benzidine (TMB) as the substrate for HRP permitted the visualization of transganglionic and retrograde transport in sensory nerve terminals and perikarya, respectively. The vagus nerve in the rat enters the medulla in numerous fascicles with points of entry covering the entire lateral aspect of the medulla extending from level +4 to -6 mm rostrocaudal to the obex. Fascicles of vagal sensory fibers enter the dorsolateral aspect of the medulla and travel to the tractus solitarius (TS) which was labeled for over 8.8 mm in the medulla. The caudal extent of the TS receiving vagal projections was found in lamina V of the cervical spinal cord (C1 to C2). Sensory terminal fields could be visualized bilaterally in the nucleus of the tractus solitarius (nTS), area postrema (ap) and dorsal motor nucleus of the vagus nerve (dmnX). The ipsilateral projection to the nTS and the dmnX was heavier than that found on the contralateral side. The area postrema was intensely labeled on both sides. Motor fibers from HRP-labeled perikarya in the dmnX travel ventromedially in a distinct fascicle and subsequently subdivide into a number of small fiber bundles that traverse the medullary reticular formation in the form of a fine network of HRP-labeled fibers. As these fibers from the dmnX approach the ventrolateral aspect of the medulla they are joined by axons from the nucleus ambiguus (nA), nucleus retroambigualis (nRA) and the retrofacial nucleus (nRF). These latter fibers form hairpin loops in the middle of the reticular formation to accompany the axons from the dmnX exiting from the medulla in a ventrolateral location. HRP-labeled perikarya, in contrast to transganglionically transported HRP in sensory terminals in the nTS, were visualized on one side only, thus indicating that motor control via the vagus nerve is exerted only by motor neurons located ipsilaterally. Sensory information on the other hand, diverges to many nuclear subgroups located on both sides of the medulla.

Differential uptake of peroxidase (HRP) and peroxidase-lectin (HRP-WGA) conjugate injected in the nodose ganglion of the cat

A comparison was made of the uptake and consequent axonal transport of peroxidase and peroxidase-lectin conjugate injected in low concentrations (0.167%) in the nodose ganglion of cats. At the light microscopic level horseradish peroxidase (HRP)-wheat germ agglutinin (WGA) intensely labeled only central terminal fields of vagal afferents (anterograde), while free HRP only labeled perikarya in vagal motor nuclei (passing retrograde). Low concentrations of these proteins, in addition to normal diffusion equilibria, permit a differential distribution of those species demonstrating some affinity for cell membranes. We attribute these differences in the uptake of HRP and HRP-WGA to the selective affinity of WGA for cell surface receptors (n-acetyl glucosamine) on the plasma membrane. This results in a greater number of WGA molecules coupled to HRP being internalized in any given endocytotic event compared to free HRP. The fractionation of efferent and passing fiber populations within a nodosal injection site can be discriminated with these different preparations.

Neurohistochemical methods in tracing central respiratory mechanisms

Neurohistochemical methods using the retrograde and transganglionic transport of horseradish peroxidase (HRP) have been used to examine differences in the topographic representation in the brainstem of airway stretch receptors in the extrathoracic trachea and intrathoracic trachea of the cat. HRP neurohistochemistry has also been used to trace connections between brainstem respiratory nuclei, e.g., the inspiratory region of the nucleus of the tractus solitarius (nTS). Microiontophoretic deposits of HRP in functionally homogeneous neuronal populations of the medulla, the inspiratory neuronal group of the ventrolateral nTS, permit the examination of specific anatomical projections; distinct differences between the subnuclei of the nTS receiving projections from the extrathoracic and intrathoracic trachea could be identified. The afferents from the extrathoracic trachea (trachealis muscle stretch receptors) terminate in the main inspiratory subnucleus of the nTS, the ventrolateral nTS, whereas an identical region of the intrathoracic trachea sends its afferents to the dorsolateral nTS. The possible functional effects of such topographic differences are discussed. The inspiratory neuronal population in the ventrolateral nTS receives afferent projections from the contralateral rostral ventrolateral medulla. These afferent projections originate in a recently identified location in the rostral end of the nucleus ambiguous lying ventral to the retrofacial nucleus. This region has been identified as a site for respiratory related activity, which is expiratory in nature and anatomically distinct from the nucleus ambiguus and the retrofacial nucleus. This region has been identified as the Bötzinger complex, which corresponds to a collection of expiratory neurons in the rostral medulla.

Carotid sinus nerve projections to the brain stem in the cat

The distribution of carotid sinus nerve (CNS) afferent and efferent fibers in the brain stem was examined in eight cats using horseradish peroxidase (HRP) neurohistochemistry. The transganglionic transport of HRP yielded dense extraperikaryal labeling within the nucleus of the tractus solitarius (nTS). Labeling was also present in the area postrema (ap) and in the region of the nucleus ambiguus (nA). The nTS labeling was bilateral, the ipsilateral side being more intense. Within the nTS, the labeling was not uniform, being heaviest in the dorsal, dorsolateral and commissural subnuclei. Moderate labeling was seen in the ventrolateral nTS. In the region of the obex, HRP labeled fibers could be followed from the nTS to the region of the nA, where extraperikaryal labeling could be seen. HRP labeled perikarya were found in the rostral pole of nA. In two controls, the CSN was sectioned close to its junction to the glossopharyngeal nerve just prior to HRP injection. In both cases, no labeling was found in either the petrosal ganglion or brain stem.

Brain stem localization of vagal preganglionic neurons

The central distribution of vagal preganglionic neurons has been examined using the retrograde transport of horseradish peroxidase (HRP). In 27 adult cats, the entire vagus nerve was exposed to HRP. In 13 other cats we examined the brain stem following microinjections of HRP (10 microliter) into individual visceral organs - lung, heart and stomach. Comparison of individual cases led to the conclusion that different patterns exist for each visceral organ. The preganglionic (parasympathetic) innervation of the entire vagus nerve arises from the dorsal motor nucleus of the vagus (dmnX), nucleus ambiguus (nA), nucleus retroambigualis (nRA), nucleus dorso-medialis (ndm), spinal nucleus of the accessory (nspA) and from the reticular formation between the dmnX and nA. Axons arising from the nA do not traverse the medulla laterally; rather they are initially directed dorso-medially toward the dmnX where they bend at right angles and accompany axons of neurons in the dmnX. The motor nuclei innervating the lungs, heart and stomach are dmnX, the nA and nRA: the dmnX contributes fibers to the heart, lungs and stomach from a region of 10 mm of medulla rostrocaudally; the nA contributes efferents to the 3 viscera studied from the entire 6 mm contributing vagal efferents; the nRA contributes efferents to the stomach in addition to providing innervation to the larynx and trachea (see 19). The area postrema (ap) receives afferent input from the lungs, heart and stomach, as indicated by extraperikaryal grains of HRP reaction product resulting from transganglionically transported HRP (through the ganglion nodosum). Sensory terminal labeling in the various subnuclei of the nucleus of the tractus solitarius (nTS) was also examined and it was found that no specific region of the medulla is devoted to receiving input from any one visceral organ; rather the rostro-caudal extent of vagal afferent terminals in the medulla spans the entire length of the medulla. Differences between the central representation of different viscera seemed to lie within the organization of the nuclear subgroups of the nTS.

Brain stem projections of sensory and motor components of the vagus complex in the cat: I. The cervical vagus and nodose ganglion

The motor and sensory connections of the cervical vagus nerve and of its inferior ganglion (nodose ganglion) have been traced in the medulla oblongata of 32 adult cats with the neuroanatomical methods of horseradish peroxidase (HRP) histochemistry and amino acid autoradiography (ARG). In 14 of these subjects, an aqueous solution of HRP was applied unilaterally to the central end of the severed cervical vagus nerve. In 13 other cases, HRP was injected directly into the nodose ganglion. Three of these 13 subjects had undergone infranodose vagotomy 6 weeks prior to the HRP injection. A mixture of tritiated amino acid was injected into the nodose ganglion in five additional cats. The retrograde transport of HRP yielded reaction product in nerve fibers and perikarya of parasympathetic and somatic motoneurons in the medulla oblongata. Furthermore, a tetramethyl benzidine (TMB) method for visualizing HRP enabled the demonstration of anterograde and transganglionic transport, so that central sensory connections of the nodose ganglion and of the vagus nerve could also be traced. The central distribution of silver grain following injections of tritiated amino acids in the nodose ganglion corresponded closely with the distribution of sensory projections demonstrated with HRP, thus confirming the validity of HRP histochemistry as a method for tracing these projections. The histochemical and autoradiographic experiments showed that the vagus nerve enters the medulla from its lateral aspect in multiple fascicles and that it contains three major components--axons of preganglionic parasympathetic neurones, axons of skeletal motoneurons, and central processes of the sensory neurons in the nodose ganglion. Retrogradely labeled neurons were seen in the dorsal motor nucleus of X(dmnX), the nucleus ambiguus (nA), the nucleus retroambigualis (nRA), the nucleus dorsomedialis (ndm) and the spinal nucleus of the accessory nerve (nspA). The axons arising from motoneurons in the nA did not traverse the medulla directly laterally; rather, all of these axons were initially directed dorsomedially toward the dmnX, where they formed a hairpin loop and then accompanied the axons of dmnX neurons to their points of exit. Afferent fibers in the vagus nerve reached most of the subnuclei of the nTS bilaterally, with the more intense labeling being found on the ipsilateral side. Labeling of sensory vagal projections was also found in the area postrema of both sides and around neurons of the dmnX. These direct sensory projections terminating within the dmnX may provide an anatomical substrate for vagally mediated monosynpatic reflexes. Following deefferentiation by infranodose vagotomy 6 weeks prior to HRP injections into the nodose ganglion, a number of neurons in the dmnX were still intensely labeled with the HRP reaction product. The axons of these HRP-labeled perikarya may constitute the bulbar component of the accessory nerve.

Brain stem projections of the aortic nerve in the cat: a study using tetramethyl benzidine as the substrate for horseradish peroxidase

The intra-axonal transport of horseradish peroxidase (HRP) has been used to trace the nodose ganglion and brain stem projections of a physiologically distinct nerve - the aortic depressor nerve - following electrophysiological identification. Tetramethyl benzidine (TMB) has been used as the substrate for demonstrating the centrally transported HRP15, 16. This sensitive method for horseradish peroxidase histochemistry has permitted the visualization of the central projections of aortic nerve afferents and has also provided information regarding the anatomical localization of cell bodies of these sensory nerve fibers within the nodose ganglion. This study demonstrates the usefulness of using TMB as a substrate for HRP histochemistry in anatomical studies where the detection of anterogradely transported HRP is an essential prerequisite. The uptake of HRP from the cut central ends of sensory nerve fibers and the transport of this enzyme to the sensory ganglion and subsequently into the central processes of these sensory neurons have made possible this study of the central projections of a functionally distinct peripheral nerve. Information has been provided by this study that cell bodies of aortic nerve afferent fibers are localized in the rostrolateral pole of the nodose ganglion. Dense central projections of sensory terminals of aortic afferents have been found in the dorsolateral and medial subdivisions of the nucleus of the tractus solitarius. These central projections of aortic afferents extend for 6 mm rostrocaudally in the medulla with the densest projection being found at the level of the obex. These projections are bilateral at all rostrocaudal levels. This anatomical demonstration of the dorsolateral and medial subdivisions of the nucleus of the tractus solitarius confirms earlier reports based on electrophysiological studies. Of particular interest in this study is the new observation that there exists a dense projection of aortic nerve afferents to the area postrema. The possible physiological implications of a direct input of peripheral chemoreceptor afferents to a region of central chemosensitivity are discussed. The complete absence of any retrogradely labeled cell body in the brain stem from exposure of the aortic nerve to horseradish peroxidase is noteworthy. This indicates that the aortic nerve is purely afferent in function and that reflex control of afferent activity in the aortic nerve is not mediated by brain stem neurons projecting down the same nerve.

Tissue culture of adult human neurons

Dissociated neurons from adult human trigeminal and superior cervical ganglia were cultured in vitro for more than 2 months. Immediately after dissociation by incubation in 0.06% collagenase for 15--18 h, the cultures consisted of single neurons or clumps of neurons and degenerating fragments of myelinated or non-myelinated axons. After 7--10 days, bipolar Schwann cells, large neurons and fine nerve fibers were observed. Electron microscopic examination of these neurons revealed all the ultrastructural features of healthy adult neurons including those of lipofuscin pigments. By electrophysiological technique, extracellular recording to action potentials generated by these neurons were obtained indicating the neurons were alive and healthy. The availability of adult human neurons in culture should provide a model system for investigation related to the pathomechanism of lipofuscin formation and aging in general.