Immunohistochemical localization of putative neurotransmitters within the feline nucleus tractus solitarii

Key role of 5-HT3 receptors in the nucleus tractus solitarii in cardiovagal stress reactivity

Serotonin plays a modulatory role in central control of the autonomic nervous system (ANS). The nucleus tractus solitarii (NTS) in the medulla is an area of viscerosomatic integration innervated by both central and peripheral serotonergic fibers. Influences from different origins therefore trigger the release of serotonin into the NTS and exert multiple influences on the ANS. This major influence on the ANS is also mediated by activation of several receptors in the NTS. In particular, the NTS is the central zone with the highest density of serotonin₃ (5-HT₃) receptors. In this review, we present evidence that 5-HT₃ receptors in the NTS play a key role in one of the crucial homeostatic responses to acute and chronic stress: inhibitory modulation of the parasympathetic component of the ANS. The possible functional interactions of 5-HT₃ receptors with GABA_A and NK₁ receptors in the NTS are also discussed.

Mechanism of the inhibitory effect of electroacupuncture on experimental arrhythmias

Clinical observations reported that acupuncture can alleviate several kinds of arrhythmias. To explore its efficacy and mechanism, we have studied the electroacupuncture (EA) inhibition on experimental arrhythmias in rabbits since 1980s and analyzed its mechanism. These studies were mostly conducted in the Department of Physiology, Shanghai Medical University; recently the mechanism of acupuncture's effect on arrhythmias was analyzed in the School of Medicine, University of California, Irvine, which involves the following: (1)the inhibitory effect of EA on ventricular extrasystoles can be induced by hypothalamic defense area stimulation: a low-current and low-frequency stimulation of the median nerve underneath acupoints P 5 or deep peroneal nerve underneath S 36 can activate arcuate nucleus-ventral periaqueductal gray -nuclei raphe pathway and release endorphin, enkephaline, gamma-aminobutyric acid (GABA), 5-hydroxytryptamine (5-HT), etc., thus inhibiting the rostral ventrolateral medulla (rVLM), decreasing sympathetic outflow, and alleviating ventricular extrasystoles; (2) the bradycardia induced by stimulation of aortic depressor nerve can be blocked by stimulation of superficial radial nerve (underneath LI 6-7) or superficial peroneal nerve (underneath G37-39): these stimulations activate the rVLM release opioids and GABA to inhibit nucleus tractus solitarius and vagal nuclei, and block vagal bradycardia. These experimental data explore the mechanism of acupuncture's effect on arrhythmias and are useful for clinical application.

Neuroactive substances in the dorsal vagal complex of the medulla oblongata: nucleus of the tractus solitarius, area postrema, and dorsal motor nucleus of the vagus

The distributions of classical and putative neurotransmitters within somata and fibres of the dorsal vagal complex are reviewed. The occurrence within the dorsal medulla oblongata of receptors specific for some of these substances is examined, and possible functional correlations of the specific neurochemicals with respect to their distribution within the dorsal vagal complex are discussed. Many of the known transmitters and putative transmitters are represented in the dorsal vagal complex, particularly within various subnuclei of the nucleus of the solitary tract, the main vagal afferent nucleus. In a few cases, some of these have been examined in detail, particularly with respect to their possible mediation of cardiovascular or gastrointestinal functions. For example, the catecholamines, substance P and angiotensin II in the nucleus of the solitary tract have all been strongly implicated as playing a role in the central control of cardiovascular function. Other neurotransmitters or putative transmitters may be involved as well, but probably to a lesser extent. Similarly, the roles in the dorsal vagal complex of dopamine, the endorphins and cholecystokinin in control of the gut have been studied in some detail. Future investigations of the distributions of and electrophysiological parameters of neurotransmitters at the cellular level should provide much needed clues to advance our knowledge of the correlations between anatomical distributions of specific neurochemicals and physiological functions mediated by them.

Beyond the central pattern generator: amine modulation of decision-making neural pathways descending from the brain of the medicinal leech

The biological mechanisms of behavioral selection, as it relates to locomotion, are far from understood, even in relatively simple invertebrate animals. In the medicinal leech, Hirudo medicinalis, the decision to swim is distributed across populations of swim-activating and swim-inactivating neurons descending from the subesophageal ganglion of the compound cephalic ganglion, i.e. the brain. In the present study, we demonstrate that the serotonergic LL and Retzius cells in the brain are excited by swim-initiating stimuli and during spontaneous swim episodes. This activity likely influences or resets the neuromodulatory state of neural circuits involved in the activation or subsequent termination of locomotion. When serotonin (5-HT) was perfused over the brain, multi-unit recordings from descending brain neurons revealed rapid and substantial alterations. Subsequent intracellular recordings from identified command-like brain interneurons demonstrated that 5-HT, especially in combination with octopamine, inhibited swim-triggering neuron Tr1, as well as swim-inactivating neurons Tr2 and SIN1. Although 5-HT inhibited elements of the swim-inactivation pathway, rather than promoting them, the indirect and net effect of the amine was a reliable and sustained reduction in the firing of the segmental swim-gating neuron 204. This modulation caused cell 204 to relinquish its excitatory drive to the swim central pattern generator. The activation pattern of serotonergic brain neurons that we observed during swimming and the 5-HT-immunoreactive staining pattern obtained, suggest that within the head brain 5-HT secretion is massive. Over time, 5-HT secretion may provide a homeostatic feedback mechanism to limit swimming activity at the level of the head brain.

Immunohistochemical distribution of tachykinins in the CNS of the lamprey Petromyzon marinus

The presence of tachykinins in the CNS of vertebrates has been known for many decades, and numerous studies have described their distribution in mammals. Tachykinins were also reported in the CNS of lampreys using immunohistochemistry, chromatography, and radioimmunoassay methods, but the use of substance P (SP)-specific antibodies to reveal those tachykinins could have led to an underestimation of their number in this genus. Therefore, we carried out a new immunohistochemical study on Petromyzon marinus using a commercial polyclonal antibody that binds not only to mammalian SP, but also to other neurokinins. This antibody labeled all previously described lamprey tachykinin-containing neuronal populations, but more important, labeled new populations in several parts of the brain. These include the dorsal gray of the rostral spinal cord, the dorsal column nuclei, the octavolateral area, the nucleus of the solitary tract, the medial rhombencephalic reticular formation, the lateral tegmentum of the rostral rhombencephalon, the torus semicircularis, the optic tectum, the habenula, the mammillary area, the dorsal thalamic area, the lateral hypothalamus, and the septum area. Preabsorption experiments confirmed the binding of the antibody to neurokinins and allowed us to propose that the CNS of P. marinus contains at least two different tachykinins.

Substance P in the baroreceptor reflex: 25 years

Twenty-five years ago, very little was known about chemical communication in the afferent limb of the baroreceptor reflex arc. Subsequently, considerable anatomic and functional data exist to support a role for the tachykinin, substance P (SP), as a neuromodulator or neurotransmitter in baroreceptor afferent neurons. Substance P is synthesized and released from baroreceptor afferent neurons, and excitatory SP (NK1) receptors are activated by baroreceptive input to second-order neurons. SP appears to play a role in modulating the gain of the baroreceptor reflex. However, questions remain about the specific role and significance of SP in mediating baroreceptor information to the central nervous system (CNS), the nature of its interaction with glutaminergic transmission, the relevance of colocalized agents, and complex effects that may result from mediation of non-baroreceptive signals to the CNS.

Depletion of substance P and glutamate by capsaicin blocks respiratory rhythm in neonatal rat in vitro

The specific role of the neuromodulator substance P (SP) and its target, the neurokinin 1 receptor (NK1R), in the generation and regulation of respiratory activity is not known. The preBötzinger complex (preBötC), an essential site for respiratory rhythm generation, contains glutamatergic NK1R-expressing neurones that are strongly modulated by exogenously applied SP or acute pharmacological blockade of NK1Rs. We investigated the effects of capsaicin, which depletes neuropeptides (including SP) and glutamate from presynaptic terminals, on respiratory motor output in medullary slice preparations of neonatal rat that generate respiratory-related activity. Bath application of capsaicin slowed respiratory motor output in a dose- and time-dependent manner. Respiratory rhythm could be restored by bath application of SP or glutamate transporter blockers. Capsaicin also evoked dose-dependent glutamate release and depleted SP in fibres within the preBötC. Our results suggest that depletion of SP (or other peptides) and/or glutamate by capsaicin causes a cessation of respiratory rhythm in neonatal rat slices.

Direct injection of substance P-antisense oligonucleotide into the feline NTS modifies the cardiovascular responses to ergoreceptor but not baroreceptor afferent input

Substance P (SP) is released from the feline nucleus tractus solitarius (NTS) in response to activation of skeletal muscle afferent input. However, there are differing results about SP release from the rostral NTS in response to baroreceptor afferent input. An anti-sense oligonucleotide to feline SP (SP-asODN) was injected directly into the rostral NTS of chloralose-anesthetized cats to determine whether blood pressure or heart rate responses to ergoreceptor activation (muscle contraction) or baroreceptor unloading (carotid artery occlusion) were sensitive to SP knockdown. Control injections included either buffer alone or a scrambled-sequenced oligonucleotide (SP-sODN). Both muscle contractions and carotid occlusions were performed 3, 6 and 12 h after the completion of the oligonucleotide injections. The cardiovascular responses to contractions were significantly attenuated 3 and 6 h after SP-asODN, but not by the injection of the SP-sODN. The cardiovascular responses to contractions returned to control levels 12 h post anti-sense injection. No detectable release of SP (using antibody-coated microprobes) was measured 3 and 6 h after SP-asODN injections and the expression of SP-immunoreactivity (SP-IR) in the NTS was significantly attenuated, as determined by immunohistochemistry procedures. In contrast, neither the injection of SP-asODN nor the s-ODN attenuated the cardiovascular responses to carotid occlusions, or altered the pattern of release of SP from the brainstem. Injection of the SP-sODN did not affect the expression of SP-IR. These results suggest that the SP involved with mediating the peripheral somatomotor signal input to the rostral NTS comes from SP-containing neurons within the NTS. Our results also suggest that SP in the rostral NTS does not play a direct role in mediating the cardiovascular responses to unloading the carotid baroreceptors. We suggest that the SP released during isometric contractions excites an inhibitory pathway modulating baroreceptor input, thus contributing to the increase in mean blood pressure.

Substance P release in the feline nucleus tractus solitarius during ergoreceptor but not baroreceptor afferent signaling

Substance P (SP) is associated with metabo- and mechanoreceptor afferent fibers ('ergoreceptors') in skeletal muscle as well as the afferent fibers from carotid sinus baroreceptors. Afferent activity from each of these are at least partially integrated in the nucleus tractus solitarius (NTS). The purpose of this study was to determine whether SP was released from the NTS during acute reflex-induced changes in blood pressure caused by stimulating these receptors. Both the muscle pressor response and the baroreflex were studied in adult cats anaesthetized with alpha-chloralose. SP antibody-coated microprobes were used to measure the possible release of SP from the NTS. The muscle pressor response caused a release of immunoreactive SP-like substances (irSP) from the rostral medial NTS, as well as the dorsal motor nucleus (DMV) and lateral tegmental field (FTL). This release was not dependent on intact afferent input from the carotid sinus nerve, but was a function of activation of muscle ergoreceptors, since no irSP was released in response to stimulation of the motor nerves after the muscle was paralyzed. There was no detectable release of irSP from the mNTS during carotid artery occlusions (baroreceptor unloading). Baroreceptor activation, induced by the i.v. injection of the vasoconstrictor, phenylephrine, did not cause the release of irSP from the mNTS above resting baseline levels. These data suggest that SP is involved with the mediation of the afferent signal from muscle ergoreceptor fibers in the medial NTS. SP is not involved with the mediation of baroreceptor afferent signaling in the medial NTS. The release of SP in response to ergoreceptors activation may function to excite an inhibitory pathway which inhibits baroreflex signals that would tend to reduce the blood pressure and heart rate during the muscle pressor response.

Immunohistochemical distribution of enkephalin, substance P, and somatostatin in the brainstem of the leopard frog, Rana pipiens

The brainstems of frogs contain many of the neurochemicals that are found in mammals. However, the clustering of nuclei near the ventricles makes it difficult to distinguish individual cell groups. We addressed this problem by combining immunohistochemistry with tract tracing and an analysis of cell morphology to localize neuropeptides within the brainstem of Rana pipiens. We injected a retrograde tracer, Fluoro-Gold, into the spinal cord, and, in the same frog, processed adjacent sections for immunohistochemical location of antibodies to the neuropeptides enkephalin (ENK), substance P (SP), and somatostatin (SOM). SOM+ cells were more widespread than cells containing immunoreactivity (ir) to the other substances. Most reticular nuclei in frog brainstem contained ir to at least one of these chemicals. Cells with SOM ir were found in nucleus (n.) reticularis pontis oralis, n. reticularis magnocellularis, n. reticularis paragigantocellularis, n. reticularis dorsalis, the optic tectum, n. interpeduncularis, and n. solitarius. ENK-containing cell bodies were found in n. reticularis pontis oralis, n. reticularis dorsalis, the nucleus of the solitary tract, and the tectum. The midbrain contained most of the SP+ cells. Six nonreticular nuclei (griseum centrale rhombencephali, n. isthmi, n. profundus mesencephali, n. interpeduncularis, torus semicircularis laminaris, and the tectum) contained ir to one or more of the substances but did not project to the spinal cord. The descending tract of V, and the rubrospinal, reticulospinal, and solitary tracts contained all three peptides as did the n. profundus mesencephali, n. isthmi, and specific tectal layers. Because the distribution of neurochemicals within the frog brainstem is similar to that of amniotes, our results emphasize the large amount of conservation of structure, biochemistry, and possibly function that has occurred in the brainstem, and especially in the phylogenetically old reticular formation.

Vaginocervical stimulation-induced release of classical neurotransmitters and nitric oxide in the nucleus of the solitary tract varies as a function of the oestrus cycle

The effects of vaginocervical stimulation (VCS) on glutamate (GLU), aspartate (ASP), gamma-aminobutyric acid (GABA), noradrenaline (NA), arginine (ARG) and nitric oxide (NO) (citrulline) release in the nucleus of the solitary tract (nTS) were measured in anaesthetised female rats as a function of the oestrus cycle. During pro-oestrus/oestrus (P/E), but not during met-oestrus/di-oestrus (M/D), VCS significantly increased concentrations of NA, ASP, GLU, NO (citrulline) and GABA, but not ARG. Basal NA concentrations were also increased in P/E. These effects were prevented by bilateral section of either the vagus nerve or pelvic and hypogastric nerves. Vagotomy also significantly decreased basal NO concentrations in M/D and P/E while pelvic and hypogastric nerve section significantly increased GABA concentrations. Our results therefore confirm that the nTS is a relay structure for the visceral afferents sending information from the uterus into the central nervous system. The ability of VCS to trigger classical transmitter release and NO in the female is influenced by the stage of the oestrous cycle and is routed both via the vagus and pelvic/hypogastric nerves.

Effects of somatostatin on the control of breathing in humans

1. Somatostatin depresses the ventilatory response to hypoxia (AHVR). This study sought to determine whether somatostatin also reduced the peripheral chemoreflex sensitivity to hypercapnia, and if so, whether this was related to the reduction in AHVR. 2. Nine subjects completed the study. AHVR and the ventilatory responses to hypercapnia under both hyperoxic and hypoxic conditions were assessed both without and with an infusion of somatostatin (0.5 BsBs5mgBs5 h-1). Peripheral (fast) and central (slow) responses to hypercapnia were distingushed by use of a multi-frequency binary sequence input in end-tidal PCO2 (PET,CO2) that included 13 steps into and out of hypercapnia. 3. The acute ventilatory response to a reduction in end-tidal PO2 (PET,O2) from 100 to 50 Torr (at a PET, CO2 of +1.5-2.0 Torr above normal) was reduced from (mean +/- s.e.m. ) 16.4 +/- 3.3 to 9.5 +/- 3.2 l min-1 (P < 0.005, Student's t test) by somatostatin. The magnitude of the ensuing hypoxic ventilatory decline was unaltered (8.8 +/- 2.7 l min-1 in control vs. 8.0 +/- 2. 9 l min-1 with somatostatin). 4. The peripheral chemoreflex sensitivity to CO2 in hypoxia was reduced from 2.42 +/- 0.36 to 1.18 +/- 0.20 l min-1 Torr-1 (P < 0.005) with somatostatin. The reduction under hyperoxic conditions from 0.75 +/- 0.34 to 0.49 +/- 0.09 l min-1 Torr-1 did not reach significance. Central chemoreflex sensitivity to CO2 was unchanged. Changes in peripheral chemoreflex sensitivity to CO2 in hypoxia correlated with changes in AHVR. 5. We conclude that peripheral chemoreflex sensitivity to CO2 is reduced by somatostatin, probably via the same mechanism as that by which somatostatin exerts its effects on AHVR.

Skeletal muscle afferent fibres release substance P in the nucleus tractus solitarii of anaesthetized cats

1. The tachykinin substance P was recovered from the commissural subdivision of the nucleus tractus solitarii (cNTS) using in vivo microdialysis during activation of cardiorespiratory and skeletal muscle receptors in thirteen chloralose-anaesthetized cats. 2. Tetanic muscle contraction was evoked by stimulating L7-S1 ventral roots (n = 7). Electrically induced muscle contraction increased mean arterial pressure (MAP) by 55 +/- 10 mmHg and heart rate by 29 +/- 6 beats min-1. During contraction the dialysate concentration increased 154 % above resting control levels (from 0.217 +/- 0.009 to 0.546 +/- 0.023 fmol (100 microl)-1, control vs. contraction, P < 0.05). 3. Loss of cardiorespiratory input following disruption of the carotid sinus and vagus nerves significantly blunted, but did not abolish, the increase in substance P during muscle contraction (from 0.247 +/- 0.022 to 0.351 +/- 0.021 fmol (100 microl)-1, control vs. contraction, P < 0.05). Approximately 44 % of the substance P release during contraction was independent of cardiorespiratory input transmitted by carotid sinus and vagus nerves. 4. To determine the contribution of cardiorespiratory related neural input on substance P release, an intravascular balloon positioned in the thoracic aorta was inflated to increase arterial pressure (n = 6). Balloon inflation increased MAP by 50 +/- 5 mmHg and substance P increased from 0.251 +/- 0.025 to 0.343 +/- 0. 028 fmol (100 microl)-1 (control vs. balloon inflation, P < 0.05). This increase was completely abolished following interruption of vagal and carotid sinus nerves (from 0.301 +/- 0.012 to 0.311 +/- 0. 014 fmol (100 microl)-1, control vs. balloon inflation). This finding shows that neural input from cardiorespiratory receptors (primarily arterial baroreceptors) accounted for 37 % of the total substance P release during muscle contraction. 5. The findings from this study demonstrate that activation of skeletal muscle receptors and cardiorespiratory receptors (predominantly arterial baroreceptors) increases the extraneuronal concentration of substance P in the cNTS. Because substance P release was not completely abolished during muscle contraction following disruption of carotid sinus and vagus nerves it is proposed that: (1) afferent projections from contraction-sensitive skeletal muscle receptors may release substance P in the NTS; (2) neural input from muscle receptors activates substance P-containing neurones within the NTS; and (3) convergence of afferent input from skeletal muscle receptors and arterial baroreceptors onto substance P-containing neurones in the cNTS facilitates the release of substance P. The role of tachykininergic modulation of cardiorespiratory input is discussed.

The enkephalinergic innervation of the genioglossus musculature in the rat: implications for the respiratory control of the tongue

This study sought to determine if the enkephalinergic (ENK) innervation of the hypoglossal nucleus (nXII) in the rat was organized differentially for the control of the genioglossus musculature whose activity is essential in maintaining the patency of the upper airway. Immunocytochemical results revealed that the genioglossus motoneuron pool, comprising the ventrolateral subcompartment of the nXII, was consistently and heavily labeled throughout its rostrocaudal dimension. Labeling was characterized by dense focal clustering throughout the neuropil, and by the appearance of numerous perisomatic-like profiles. Similarly, the ventromedial subcompartment mainly rostrally, and the dorsal compartment caudally, whose motoneurons control the caudal intrinsic protrusor and rostral retrusor muscles, respectively, were also consistently labeled. While these results demonstrate that the genioglossus musculature is targeted by ENK inputs, they also suggest that other selected musculature of the tongue is controlled by ENK. It is argued that the innervation pattern identified in the present study is consistent with a functional role for ENK in the respiratory control of the tongue.

Direct synaptic projections to esophageal motoneurons in the nucleus ambiguus from the nucleus of the solitary tract of the rat

Neurons of the nucleus of the solitary tract (NTS) serve as interneurons in swallowing. We investigated the synaptology of the terminals of these neurons and whether they project directly to the esophageal motoneurons in the compact formation of the nucleus ambiguus (AmC). Following wheat germ agglutinin conjugated horseradish peroxidase (WGA-HRP) injection into the NTS, many anterogradely labeled axodendritic terminals were found in the neuropil of the AmC. The majority of labeled axodendritic terminals (89%) contained round vesicles and made asymmetric synaptic contacts (Gray's type I), but a few (11%) contained pleomorphic vesicles and made symmetric synaptic contacts (Gray's type II). More than half of the labeled terminals contacted intermediate dendrites (1-2 microm diameter). There were no retrogradely labeled medium-sized motoneurons, but there were many retrogradely labeled small neurons having anterogradely labeled axosomatic terminals. A combined retrograde and anterograde transport technique was developed to verify the direct projection from the NTS to the esophageal motoneurons. After the esophageal motoneurons were retrogradely labeled by cholera toxin subunit B conjugated HRP, the injection of WGA-HRP into the NTS permitted ultrastructural recognition of anterogradely labeled axosomatic terminals contacting directly labeled esophageal motoneurons. Serial sections showed that less than 20% of the axosomatic terminals were labeled in the esophageal motoneurons. They were mostly Gray's type I, but a few were Gray's type II. In the small neurons, more than 30% of axosomatic terminals were labeled, which were exclusively Gray's type I. These results indicate that NTS neurons project directly not only to the esophageal motoneurons, but also to the small neurons which have bidirectional connections with the NTS.

Cardiovascular effects of neurotensin microinjections into the nucleus of the solitary tract

Neurotensin (NT) immunoreactivity and binding sites have been demonstrated to be extensively distributed throughout the caudal nucleus of the solitary tract (NTS). In this study, the cardiovascular effects of microinjecting the tridecapeptide neurotensin (NT) or its analogues NT 1-8 and [D-Trp11]NT into NTS were investigated in the chloralose-anesthetized, paralyzed and artificially ventilated rat. Microinjection of NT (10 pmol) elicited decreases in arterial pressure (AP) (-34 +/- 3 mm Hg) and heart rate (HR) (-28 +/- 2 beats/min), whereas microinjection of equimolar amounts of the NT fragment NT 1-8 elicited a significantly smaller depressor response (-14 +/- 3 mm Hg), but the bradycardic (-22 +/- 4 beats/min) response was similar in magnitude to that elicited by NT. On the other hand, microinjection of [D-Trp11]NT did not elicit cardiovascular responses from sites in NTS. In addition, the prior injection of [D-Trp11]NT into cardiovascular responsive sites in the NTS did not significantly reduce the AP or HR response to NT. The depressor response elicited by NT was not affected by bilateral vagotomy but was abolished by either C1-C2 spinal cord transection or the i.v. administration of the nicotinic receptor blocker hexamethonium bromide. The cardiac slowing was partially attenuated by either bilateral vagotomy (-19 +/- 2 beats/min), i.v. administration of atropine methyl bromide (-17 +/- 4 beats/min), i.v. administration of hexamethonium bromide (-11 +/- 4 beats/min) or by spinal cord transection (-12 +/- 3 beats/min), and completely abolished after total autonomic blockade or by combined bilateral vagotomy and spinal cord transection. These data have demonstrated that within a restricted region of the caudal NTS NT activates neurons that contribute to vasodepressor responses as a result of sympatho-inhibition and to bradycardia responses as a result of vagal excitation and sympatho-inhibition. Furthermore, these data suggest that NT may act as a neurotransmitter or modulator in central cardiovascular reflex pathways.

Augmented release of serotonin by adenosine A2a receptor activation and desensitization by CGS 21680 in the rat nucleus tractus solitarius

Rat dorsomedial medullary brain segments containing primarily nucleus tractus solitarius (NTS) were employed for slice superfusion studies of electrically evoked [3H]serotonin ([3H]5-HT) release. Individual slices loaded with [3H]5-HT were stimulated two times, S1 and S2, at 3 Hz, 25 mA, 2 ms pulses for 1 min. Control NTS slices had a S2/S1 ratio of 0.94 (+/- 0.02). Superfusion of tissue slices with 0.1 nM to 100 nM 2-p-(2-carboxyethyl)-phenethylamino-5'-N-ethylcarboxamidoadenosine (CGS 21680), a selective adenosine A2a receptor agonist, for 5 min prior to the S2 stimulus produced a significant concentration-dependent increase in the S2/S1 fractional release ratio which was maximal (37.2% increase, P < 0.01) at 1.0 nM. However, superfusion of tissue slices with CGS 21680 over the same concentration range for 20 min prior to the S2 stimulus did not significantly alter the S2/S1 ratio from control release ratios. The augmented release of [3H]5-HT mediated by 1.0 nM CGS 21680 with 5 min tissue exposure was abolished by 1.0 nM 9-chloro-2-(2-furanyl)-5, 6-dihydro-[1,2,4]-triazolo[1,5-c]quinazolin-5-imine (CGS 15943) as well as by 100 nM 8-(3-chlorostyryl)caffeine (CSC), both A2a receptor antagonists, but not by 1.0 nM 8-cyclopentyl-1,3,-dipropylxanthine (DPCPX), the A1 receptor antagonist. These results indicate that CGS 21680 augmented the evoked release of [3H]5-HT in the NTS by way of activation of presynaptic adenosine A2a receptors. It was also apparent that this population of adenosine A2a receptors in the NTS desensitized within 20 min since the augmenting action of CGS 21680 on evoked transmitter release was not evident at the longer time interval.

The dorsal vagal complex of the ferret: anatomical and immunohistochemical studies

To further the understanding of gastrointestinal function in this species, and in particular to advance our own work concerning central emetic pathways, the cytoarchitecture and the distribution of eight neurochemicals were studied in the ferret dorsal vagal complex (DVC; area postrema, nucleus of the solitary tract [nTS] and dorsal motor nucleus of the vagus). The cytoarchitectural features of this region in the ferret were similar to those seen in other species; however, the ferret possesses a particularly large and distinct subnucleus gelatinosus of the nTS. Dense calcitonin gene-related peptide-immunoreactivity was found in the gelatinous, interstitial and commissural subnuclei of the nTS, with lesser amounts in other regions of the DVC. Enkephalin-immunoreactivity of varying densities was found throughout the DVC. Moderate to dense galanin-immunoreactivity was observed throughout the DVC, with the exception of the subnucleus gelatinosus of the nTS, from which it was virtually absent. Dense neuropeptide Y-immunoreactivity was observed in the subnucleus gelatinosus and interstitial subnucleus, with moderate staining in other regions of the DVC. Neurotensin immunoreactivity was very sparse or absent. Immunoreactivity for serotonin was sparsely distributed throughout the DVC. Moderate somatostatin-immunoreactivity was observed over a large portion of the DVC, but was virtually absent from the gelatinosus and interstitial subnuclei. Substance P immunoreactivity was observed throughout the DVC and was particularly dense in the dorsal/dorsolateral subnucleus and the dorsal aspects of the medial and commissural subnuclei. In terms of its cytoarchitecture the DVC of the ferret is more similar to the cat than the rat, especially with regard to the area postrema and the subnucleus gelatinosus of the nTS. The distribution of neuroactive substances was largely similar to other species; however, differences were present particularly in patterns of immunoreactivity for enkephalin, serotonin, neuropeptide Y and somatostatin.

GABAergic neurons in rat nuclei of solitary tracts receive inhibitory-type synapses from amygdaloid efferents lacking detectable GABA-immunoreactivity

Gamma-aminobutyric acid (GABA) is a prominent inhibitory transmitter in both the central nucleus of the amygdala (Ce) and the medial nuclei of the solitary tracts (mNTS). These regions are reciprocally connected by anatomical pathways mediating the coordinated visceral responses to emotional stress. To further determine whether GABA is present in the amygdaloid efferents or their targets in the mNTS, we combined peroxidase labeling of Phaseolus vulgaris leucoagglutinin (PHA-L) or biotinylated dextran amine (BDA) anterogradely transported from the Ce with immunogold-silver detection of antibodies against GABA in the rat mNTS. By light microscopy, peroxidase labeling for either PHA-L or BDA was seen in varicose processes, whereas immunogold-silver labeling for GABA was detected in perikarya and processes throughout the rostrocaudal mNTS. The intermediate mNTS at the level of the area postrema, a region receiving mainly cardiorespiratory and gastric visceral afferents, were examined by electron microscopy. In this region, anterograde labeling was observed exclusively in unmyelinated axons and axon terminals. These terminals lacked detectable GABA-immunoreactivity, but formed symmetric synapses that are associated with inhibition. The targets of the anterogradely labeled terminals were medium-sized dendrites both with and without GABA-labeling. These dendrites often also received convergent input from terminals that were intensely GABA-immunoreactive. We conclude that visceral activation accompanying emotional response to stress is likely to involve inhibition of GABAergic neurons in the mNTS by non-GABA-containing amygdaloid efferents. Furthermore, our results indicate that the inhibition of these GABAergic neurons may be further augmented by release of GABA from other converging terminals in the mNTS.

The broad-spectrum anti-emetic activity of the novel non-peptide tachykinin NK1 receptor antagonist GR203040

1. Following our earlier observations that the tachykinin NK1 receptor antagonist CP-99,994 is an effective anti-emetic in ferrets, we have examined the anti-emetic effects of a more potent and novel NK1 receptor antagonist, GR203040, against various emetic stimuli in the ferret, dog and house musk shrew (Suncus murinus). 2. In ferrets, GR203040 (0.1 mg kg-1 s.c. or i.v.) is effective against emesis induced by radiation, cisplatin, cyclophosphamide, copper sulphate, ipecacuanha or morphine. 3. In animals in which emesis had been established with cisplatin, GR203040 (1 mg kg-1 s.c.) was fully effective as an interventional treatment. No further emesis was seen in animals treated with GR203040 whilst saline-treated animals continued to vomit. 4. GR203040 (0.1 mg kg-1 s.c.) retains anti-emetic efficacy in the ferret, even when given as a 6 h pretreatment, indicating that this compound has a long duration of action. The compound is also effective orally at the same dose, when given as a 90 min pretreatment. 5. GR203040 (0.1 mg kg-1 i.v.) is fully effective against ipecacuanha-induced emesis in the dog. 6. GR203040 is effective against motion- and cisplatin-induced emesis in Suncus murinus. These effects were seen at doses an order of magnitude greater than those shown to be effective against cisplatin in the ferret. 7. In conclusion, GR203040 is a novel anti-emetic agent, and the broad spectrum of anti-emetic activity, together with activity observed in three species, suggests that this compound is worthy of clinical investigation.

The pattern of excitatory inputs to the nucleus tractus solitarii evoked on stimulation in the hypothalamic defence area in the cat

1. In anaesthetized, paralysed and artificially ventilated cats, recordings have been made in the nucleus tractus solitarii (NTS) to assess further the role of this nucleus in mediating the cardiorespiratory responses that are elicited on stimulation within the hypothalamic defence area (HDA). 2. The responses of NTS neurones to stimulation in the hypothalamus were assessed, as were their patterns of evoked response to electrical stimulation of the sinus (SN), aortic (AN), superior laryngeal (SLN) and vagus (VN) nerves. 3. Stimulation in the HDA affected the activity of 110 NTS neurones (85 studied in intracellular and 25 studied in extracellular recordings). The present study focused on those sixty-eight neurones that were excited by such stimulation (51 intracellular recordings and 17 extracellular recordings). 4. Of the sixty-eight neurones that were excited by HDA stimulation, seven revealed no changes in membrane potential or evoked discharge (2 neurones) but the stimulus facilitated the excitatory effects of stimulating either (or both) the SN and SLN. An additional group of neurones showed powerful excitatory responses to HDA stimulation (15 studied with extracellular and 35 with intracellular recording). Evoked EPSPs had onset latencies in the range of 1-30 ms. Of those thirty-five neurones displaying EPSPs, twenty-six were shown to receive convergent inputs on nerve stimulation. In nine neurones the early EPSP in response to HDA stimulation was followed by an IPSP. 5. In a further group of neurones HDA stimulation elicited a long-lasting IPSP, but this was not analysed further because its features have been described in detail in earlier studies from this laboratory. 6. The patterns of response of several neurones excited by stimulation in the HDA are consistent with them forming a group of NTS interneurones that mediate the hypothalamically evoked cardiovascular responses, including modulation of reflex function, which is a major feature of cardiorespiratory control. This possibility is discussed in the light of the present physiological observations and descriptions of an intrinsic NTS group of GABA-containing neurones that have been suggested to fulfil such a role.

Raphe nuclei in three cartilaginous fishes, Hydrolagus colliei, Heterodontus francisci, and Squalus acanthias

The vertebrate reticular formation, containing over 30 nuclei in mammals, is a core brainstem area with a long evolutionary history. However, not all reticular nuclei are equally old. Nuclei that are widespread among the vertebrate classes are probably ones that evolved early. We describe raphe nuclei in the reticular formation of three cartilaginous fishes that diverged from a common ancestor over 350 million years ago. These fishes are Hydrolagus colliei, a holocephalan, Squalus acanthias, a small-brained shark, and Heterodontus francisci, a large-brained shark. Nuclear identification was based on immunohistochemical localization of serotonin and leu-enkephalin, on brainstem location, and on cytoarchitectonics. Raphe nuclei are clustered in inferior and superior cell groups, but within these groups individual nuclei can be identified: raphe pallidus, raphe obscurus, and raphe magnus in the inferior group and raphe pontis, raphe dorsalis, raphe centralis superior, and raphe linearis in the superior group. Hydrolagus lacked a dorsal raphe nucleus, but the nucleus was present in the sharks. The majority of immunoreactive cells are found in the superior group, especially in raphe centralis superior, but immunoreactive cells are present from spinal cord to caudal mesencephalon. The distribution and cytoarchitectonics of serotoninergic and enkephalinergic cells are similar to each other, but raphe nuclei contain fewer enkephalinergic than serotoninergic cells. The cytoarchitectonics of immunoreactive raphe cells in cartilaginous fishes are remarkably similar to those described for raphe nuclei in mammals; however, the lack of a raphe dorsalis in Hydrolagus indicates that either it evolved later than the other raphe nuclei or it was lost in holocephalan fishes.

Distribution and developmental expression of octopamine-immunoreactive neurons in the central nervous system of the leech

Octopamine, a biogenic amine analogous to norepinephrine, plays an important role in the orchestration and modulation of invertebrate behavior. In the leech, the behavioral actions of octopamine have been demonstrated; however, identification of octopaminergic neurons had not been determined by using immunohistochemical techniques. Thus, we used an antibody highly specific to octopamine to examine the distribution of octopamine-immunoreactive neurons in the segmental ganglia of American and European medicinal leeches (Macrobdella decora and Hirudo medicinalis). One pair of octopamine-immunoreactive neurons was located in the dorsolateral ganglionic region of anterior ganglia 1-6 and posterior ganglia 15-21. No corresponding octopamine-immunoreactive neurons were found in midbody ganglia 7-14. Using Neutral Red staining in combination with intracellular Neurobiotin injections and octopamine immunostaining, we determined the identity of the dorsolateral octopamine-immunoreactive cells. The dorsolateral octopamine-immunoreactive neuron (the DLO) was not cell 21, the only previously reported Neutral Red staining neuron in the dorsolateral position. We also determined that the Leydig neuron was not octopamine immunoreactive in either of the two medicinal leech species. Octopamine immunostaining in the sex ganglia revealed hundreds of immunoreactive neurons in sexually mature leeches. Such neurons were not observed in juvenile leeches. The developmental time course of octopamine immunoreactivity in the dorsolateral octopamine-immunoreactive neurons was also investigated by staining embryonic Hirudo medicinalis. Octopamine expression occurred relatively late as compared with the detectable onset of serotonin expression. Octopamine expression in the dorsolateral octopamine-immunoreactive cells was not detectable at early to mid-embryonic stages, and must commence during late embryonic to early juvenile stages. The identification of octopamine-immunoreactive cells now sets the stage for further investigations into the functional role of octopamine in leech behavior and the development of behavior.

Glycine elicits release of acetylcholine from the nucleus tractus solitarii in rat

Previous studies have suggested that cardiovascular responses elicited by injection of glycine into the nucleus tractus solitarii (NTS) depend upon interactions between glycinergic and cholinergic neuronal elements in NTS. Release of acetylcholine in response to glycine is one such interaction that has been shown in slices of hippocampus and striatum. In this study we sought to test the hypothesis that glycine causes release of acetylcholine from neurotransmitter stores in NTS. We compared release from NTS with that from adjacent hypoglossal nucleus and from caudate nucleus. Release of radiolabeled acetylcholine was determined in vitro after incubating NTS with [3H]choline. Exposure of NTS and caudate nucleus, but not hypoglossal nucleus, to glycine caused release of acetylcholine in a calcium-dependent manner that varied with concentration of glycine in the incubation medium. The maximally effective concentration (1 mM) of glycine elicited 136% increases over basal levels. Glycine did not elicit release of [3H]acetylcholine from tissue when calcium ion had been removed from the bath. Acetylcholine also was not released if tissue was incubated with either strychnine (10 microM) or hemicholinium-3 (1 mM) prior to exposure to glycine (1 mM). Thus, glycine, acting at strychnine-sensitive receptors in NTS, elicits release of acetylcholine from a portion of locally synthesized neurotransmitter stores.

Distribution of substance P-like immunoreactive neurons and terminals throughout the nucleus of the solitary tract in the human brainstem

The anatomical distribution of substance P-like immunoreactivity across the subnuclear divisions of the nucleus of the solitary tract has been examined in the human medulla oblongata. A differential distribution of neurons, fibres, and terminals was observed throughout the ten subnuclear divisions of this nucleus. Substance P-like immunoreactive neurons were observed most frequently in the nucleus gelatinosus, with moderate numbers in the medial, intermediate subnuclei and very few in the commissural, ventral, dorsal, and dorsolateral subnuclei. The paracommissural, ventrolateral, and interstitial subnuclei did not contain substance P-like-immunoreactive neurons. These neurons were typically bipolar and moderate-sized to large, except for the neurons in the nucleus gelatinosus, which were substantially smaller. The highest densities of fibres and terminals were observed in the gelatinosus, medial, and intermediate nuclei, with moderate densities in the paracommissural and dorsal subnuclei. Sparse substance P-like-immunoreactive fibres and terminals were seen in the ventral and interstitial nuclei as well as within the solitary tract. The dorsolateral nucleus was characterized by a light distribution of fibres and terminals, except for a dense aggregation along its lateralmost border. A prominent innervation of pigmented neurons by substance P-like-immunoreactive terminals and fibres was also observed in the dorsolateral nucleus. The results reveal that the subnuclear complexity of the nucleus of the solitary tract is richly reflected by its differential pattern of substance P-like-immunoreactive structures.

Nucleus of the solitary tract and dorsal motor nucleus of the vagus nerve of the pigeon: localization of peptide and 5-hydroxytryptamine immunoreactive fibers

The distribution of peptide and serotonin fibers in the nucleus of the solitary tract (NTS) and the dorsal motor nucleus of the vagus nerve (DMNX) in the pigeon (Columba livia) was investigated immunocytochemically. This information was correlated with the viscerotopic organization of the nuclei and with central NTS circuitry to suggest the role of the neurochemical containing fibers in the regulation of organ function. The distribution of fibers containing cholecystokinin (CCK), calcitonin gene-related peptide (CGRP), enkephalin (ENK), neuropeptide Y (NPY), neurotensin (NT), substance P (SP), somatostatin (SS), vasoactive intestinal peptide (VIP), and 5-hydroxytryptamine (5-HT) was determined. Each substance had a distinct distribution within the subnuclei of NTS-DMNX, but certain generalities can be deduced. In the DMNX, fibers immunoreactive for ENK, NT, and SP were found in greatest concentration, while CGRP and 5-HT immunoreactive fibers were the least dense. This suggests that ENK, NT, and SP may have a significant modulatory effect on gastrointestinal functions. In the NTS overall, ENK, NT, SP, and VIP fibers were found in high density, CCK, NPY, SS, and 5-HT fibers were found in moderate density, and CGRP fibers were found in low density. However, some individual NTS subnuclei were found to contain moderate to high concentrations of each of the substances, including CGRP. Fibers containing CCK, ENK, NT, SP, SS, and VIP in the medial dorsal NTS subnuclei may regulate gastroesophageal functions. The caudal part of subnucleus lateralis parasolitarius did not contain most of the substances, which suggests that pulmonary function is not modulated by these neurochemicals. The boundaries of a subnucleus could sometimes be demarcated by a change in density of immunoreactive fibers between adjacent subnuclei. This was particularly evident in NTS subnuclei medialis dorsalis anterior centralis and lateralis parasolitarius, and in DMNX subnucleus posterior dorsalis magnocellularis. The selective distribution of peptide and serotonin immunoreactive fibers in various subnuclei of NTS-DMNX suggests that these substances may be differentially involved in neural circuits that mediate cardiovascular and gastrointestinal functions.

Somatostatin and the lung

Lung carcinoma is the most common cause of death in the western world and is increasing particularly among women. Despite significant developments in our understanding of the molecular biology of this disease our ability to treat the various subtypes of lung cancer has been at a relative standstill for the past decade. Novel approaches to the therapy of lung tumours are required. Recent work has evaluated the potential role of somatostatin and its analogues in the treatment of lung cancer. Experimental evidence has demonstrated that lung tumours, in particular small cell lung cancer (SCLC), may express somatostatin. The significance of this expression has not yet been evaluated. Somatostatin receptors have been demonstrated on between 50-75% of SCLC cell lines and fresh tumour samples studied to date. Using radiolabelled somatostatin analogues SCLC tumours may be detected and localised in patients through scintigraphic imaging techniques. Studies have shown that SCLC cell line clonal proliferation may be inhibited in vitro with somatostatin analogues suggesting that the somatostatin receptors are functional. In-vivo growth inhibition studies have likewise yielded encouraging results with growth inhibition of somatostatin receptor positive SCLC xenografts and receptor negative SCLC and non-small cell lung cancer cell line xenografts. These latter result suggests that somatostatin analogues may inhibit tumour growth by indirect as well as direct means. These findings have laid the ground for formal clinical trials in the future.

Ontogeny of proenkephalin mRNA and enkephalin peptide expression in the cerebellar cortex of the rat: spatial and temporal patterns of expression follow maturational gradients in the external granular layer and in Purkinje cells

Proenkephalin mRNA and peptide products were examined in developing cells of the postnatal rat cerebellar cortex using in situ hybridization and immunocytochemistry. On day 7, proenkephalin mRNA was first detected as discrete cellular labeling in Golgi cells and as a diffuse hybridization signal over the Purkinje cell layer. On day 14, proenkephalin mRNA and peptide products primarily appeared in distinct subpopulations of Purkinje cells present in the posterior and lateral cerebellum. Similarly, in the external granular layer (EGL), enkephalin immunoreactivity was present only in the posterior and lateral portions of the cerebellum on day 14. However, proenkephalin mRNA was not detected in enkephalin-immunoreactive EGL cells. On day 21, the subset of Purkinje cells that expressed proenkephalin mRNA and peptides were distributed more uniformly throughout the cerebellum. On day 28, a few enkephalin-immunoreactive Purkinje cells were uniformly present throughout the cerebellum, but proenkephalin mRNA was not detected in most of these cells. The spatial gradients in proenkephalin mRNA expression evident in the Purkinje cells of younger rats were no longer present in 28-day-old rats. These findings are important, because endogenous opioids such as enkephalin have been previously shown to inhibit the growth of Purkinje cell dendrites and dendritic spines, and inhibit the rate of mitosis in EGL neuroblasts. Cells do not develop at uniform rates within the cerebellum. There are regional differences in the timing of the formation of the EGL, and in the morphogenesis of Purkinje cells. In conjunction with previous work, the present findings suggest that during development, the pattern of enkephalin immunoreactivity in Purkinje and EGL cells closely follows the spatial and temporal gradients of maturation in both these cell types. The emergence and disappearance of enkephalin immunoreactivity in Purkinje and EGL cells is spatially and temporally related, and coincides with proenkephalin mRNA expression in Purkinje cells. Thus, the transient and coordinated appearance of enkephalin in cerebellar Purkinje and EGL cells may contribute to regional differences in the rate of cerebellar maturation, and may help synchronize the developmental interactions between these two cell types.

Distribution of tachykinin- and opioid-expressing neurons in the hamster solitary nucleus: an immuno- and in situ hybridization histochemical study

In several sensory systems, tachykinin- and opioid-expressing neurons functionally interact and influence the processing of afferent information. To determine whether a similar relationship exists for the processing of general and special (gustatory) visceral afferent information, the present study mapped the distributions of these two neuronal phenotypes within the nucleus of the solitary tract (NST) of the hamster by employing a combination of immuno- and in situ hybridization histochemistry (ISHH). The hamster was chosen because it is frequently used as a model in taste studies, yet there is a relative dearth of data about peptide expression or the classical neurotransmitters in the brainstem of this animal. The immunohistochemical analyses employed 2 highly selective antisera directed towards the prototypical tachykinin and opioid peptides, i.e. substance P (SP) and methionine enkephalin (ENK), respectively. Intense staining of fibers and preterminal/terminal puncta was concentrated in the rostral pole or gustatory zone of the NST. SP-, but not ENK-like immunoreactivity was also observed in long courses of axon bundles traversing the brainstem enroute to the NST. Local application of colchicine engendered the appearance of a moderate number of SP-positive somata that were mostly clustered in the medial, central and intermediate subnuclei, as well as being scattered throughout the remainder of the NST, including the gustatory zone. A low number of isolated ENK-positive somata were also observed throughout the NST. The somal areas of the SP- and ENK-positive somata averaged 86.3 and 81.8 microns 2, respectively. The ISHH studies were performed using 2 selective oligodeoxynucleotide probes with complementary sequences to mRNAs encoding gamma-preprotachykinin (PPT) and preproenkephalin (PPE) molecules. Overall, the cellular expression of PPT mRNA within the NST corresponded both in distribution and in number to those identified by immunohistochemical analyses using anti-SP serum. In contrast, ISHH analyses monitored a significantly greater number of PPE-expressing somata in the medial, central, intermediate and ventrolateral nuclei than were ENK immunoreactive. These findings indicate that tachykinin and opioid peptide phenotypes are represented in neurons throughout the hamster NST and suggest a functional role for PPT- and PPE-related peptide forms in the modulation of afferent general visceral and gustatory information.

Improvements for the anatomical characterization of insect neurons in whole mount: the use of cyanine-derived fluorophores and laser scanning confocal microscopy

The optical sectioning capability of the laser scanning confocal microscope was utilized to image dye-filled neurons within whole-mounted insect ganglia. Specific pterothoracic interneurons, in the moth Manduca sexta, were retrogradely filled with Neurobiotin and subsequently visualized with a monoclonal anti-biotin conjugated with one of the following fluorophores: fluorescein, and the newly developed cyanines, Cy3.18 (Cy3) and Cy5.18 (Cy5). Overall, the Cy5 fluorophore was best suited for imaging insect neurons within ganglia. This new methodology allowed us to identify and characterize morphologically a collection of descending multisegmental interneurons with large or small diameter somata. A variety of larger molecular weight (10,000 daltons) tracers was also used to examine the possibility of nonselective filling of neurons with Neurobiotin, possibly through gap junctions. We also investigated the usefulness of Cy3 and Cy5 as fluorophores for transmitter immunostaining of neurons in whole mount. Neurons immunoreactive for serotonin and the neuropeptides, FMRFamide and SCPB, were imaged in the brain and the pterothoracic ganglion. The central projections of some of these immunoreactive neurons were imaged in their entirety.

GABA-like immunoreactivity in the gustatory zone of the nucleus of the solitary tract in the hamster: light and electron microscopic studies

The distribution of GABA-like immunoreactive (GABA-LI) somata was studied in the gustatory zone of the nucleus of the solitary tract (NST) in the hamster in order to identify putative inhibitory circuitry in gustatory processing. Immunoreactive somata were located throughout the gustatory NST, in accordance to the distribution of large and small types of neurons as determined in previous morphometric studies. Consequently, GABA-LI somata were mostly found in the dorsal two-thirds of the gustatory zone. Such somata were mostly ovoid in shape and possessed somal areas that averaged 85.5 +/- 2.8 microns 2 (12.7 x 8.4 microns). A narrow range of somal areas (50-125 microns 2) suggested a single functional group. At the electron microscopic level, 18% of the neurons encountered were immunoreactive and their nuclei always possessed deeply invaginated boundaries. This morphological feature indicated that GABA-LI neurons are smaller members of the most common class of neurons within the gustatory NST. Because GABA is often implicated as the neurotransmitter of small inhibitory local circuit neurons, these findings indicate a possible inhibitory aspect to the processing of taste information at the level of the first relay in the brainstem.

Effects of vagotomy on neurotransmitter receptors in the rat dorsal vagal complex

The dorsal vagal complex contains many different neurotransmitter receptors. The cyto-architectural localizations of some of these receptors remain largely unknown. In rats, vagotomy was performed to destroy vagal afferents terminating in the nucleus of the solitary tract and to produce chromatolysis of preganglionic motoneurons in the dorsal motor nucleus of the vagus. Quantitative receptor autoradiography was then employed to determine the effect of vagotomy upon the distribution of receptors for thyrotropin-releasing hormone, substance P, and serotonin within individual regions and subnuclei of the entire dorsal vagal complex. Vagotomy reduced the concentrations of thyrotropin-releasing hormone and substance P, but not serotonin1A, or serotonin1B, receptors in the dorsal motor nucleus of the vagus. Within the nucleus of the solitary tract, substance P receptors were reduced in only the medial and central subnuclei after vagotomy. In contrast, no effect was observed upon the concentrations of thyrotropin-releasing hormone, serotonin1A, or serotonin1B receptors in any subnuclei of the solitary tract following vagotomy. These results suggest that in the dorsal motor nucleus of the vagus, thyrotropin-releasing hormone and substance P receptors are localized upon vagal preganglionic motoneurons, while serotonin1A and serotonin1B receptors are present upon interneurons or other neuronal elements. These results also suggest that thyrotropin-releasing hormone, substance P, serotonin1A, and serotonin1B receptors in the nucleus of the solitary tract are localized upon internuncial neurons in the nucleus of the solitary tract.

Behavioral studies of emetic sensitivity in the ferret

The ferrets' responsiveness to several known and putative emetic agents was evaluated using a variety of agents that were injected subcutaneously and/or intravenously. Apomorphine was consistently emetic at relatively high doses (100 micrograms/kg) when injected subcutaneously in large male ferrets (> or = 1.4 kg). The responsiveness to apomorphine was anomalous in that subcutaneous injections produced a more consistent response than intravenous ones. In addition, ferrets rapidly become tolerant or tachyphylactic to subcutaneously administered apomorphine. Area postrema ablation, but not abdominal vagotomy, rendered ferrets refractory to the emetic effects of apomorphine. This species, relative to dog and humans, proved to be insensitive to a variety of pharmacologic agents including angiotensin II, gastrin, histamine, Leu-enkephalin, neurotensin, serotonin, and vasopressin. Cisplatin elicited forceful retching and emesis. Emetic responses were obtained with substance P and Met-enkephalin in individual animals but were inconsistent. Sensitivity to DAGO [D-Ala2,MePhe4,Gly-ol5 enkephalin] was variable. Results of this study indicate that the ferret is not an optimal model for all forms of emesis.

Which fluorophore is brightest? A comparison of the staining obtained using fluorescein, tetramethylrhodamine, lissamine rhodamine, Texas red, and cyanine 3.18

There are several red-emitting fluorophores available for immunofluorescence studies, including tetramethylrhodamine, lissamine rhodamine, Texas Red, and cyanine 3.18; however, it is unclear which of these is best. The present study compared the brightness of these fluorophores to that of fluorescein. Staining was attempted using a primary antibody raised against serotonin and a secondary antibody that was conjugated with either fluorescein or one of the red fluorophores. The intensity of staining was determined densitometrically. It was found that a conjugate of cyanine 3.18 provided significantly brighter staining that conjugates of any of the other fluorophores, including fluorescein. It is concluded that cyanine 3.18 should be useful for multicolor fluorescence experiments and that it may be the brightest fluorophore available for single-color fluorescence immunocytochemistry.

Morphology of identified preganglionic neurons in the dorsal motor nucleus of the vagus

To determine the degree of variation of neuronal morphology both within and between the subnuclei of the dorsal motor nucleus of the vagus (dmnX), structural features of the preganglionic neurons of each of the five primary subnuclei in the rat dmnX were characterized quantitatively. Each of the columnar subnuclei was separately labeled by application of the retrograde tracer fast blue to its corresponding subdiaphragmatic vagal branch. Fixed brain slices of 100 microns thickness were then prepared in coronal, sagittal, and horizontal orientations. Next, randomly selected fast blue labeled neurons (n = 1,256) were injected with Lucifer yellow, drawn with camera lucida, and digitized. For each cell, three features of the perikaryon and twelve of the dendritic tree were measured. Dorsal motor nucleus neurons with up to eight primary dendrites, 30 dendritic segments, and seventh order dendritic branches were observed. Throughout the dmnX, the dendrites of preganglionic neurons were preferentially oriented in the horizontal plane. Consistent with an organizing role for the columnar subnuclei, most dendrites remained within their column of origin. However, between 5 and 30% of the neurons in each of the columns projected dendrites into adjacent dmnX subnuclei or other brainstem nuclei, including the nucleus of the solitary tract (NTS). The cyto- and dendroarchitectural analyses revealed systematic gradations in morphology, although they did not support the idea that the dmnX was composed of multiple distinct preganglionic types. The most parsimonious interpretation of the data is that dmnX motorneurons are variants of a single prototype, with dendrites varying widely in length and degree of ramification. The extent of an individual preganglionic neuron's dendritic field was predicted by three factors: the cell's rostrocaudal position within the dmnX, its location within a transverse plane (i.e., its coronal position within or ectopic to the dmnX), and its subnucleus of origin. Neurons at rostral and midlongitudinal levels of each column had more extensive dendritic arbors than those at caudal levels. Ectopic neurons had more extensive dendritic fields than similar cells in the corresponding columns; in fact, of all vagal preganglionic neurons, ectopics had the most extensive dendritic fields. Somata and dendrites of celiac column neurons were more extensive than those of hepatic and gastric column cells. These differential regional distributions of vagal preganglionics suggest that their structure and function are correlated.

Immunohistochemical localization of serotonin, leu-enkephalin, tyrosine hydroxylase, and substance P within the visceral sensory area of cartilaginous fish

We examined the distribution of immunoreactivity to serotonin (5-HT), leu-enkephalin (LENK), tyrosine-hydroxylase (TH), and substance P (SP) within the primary visceral sensory region of cartilaginous fish. Two genera of sharks, Squalus and Heterodontus, a skate, Raja, a ray, Myliobatis, and a holocephalian, Hydrolagus, were used. Cranial nerves, VII, IX, and X enter the visceral sensory complex from the lateral aspect and divide it into lobes. Based on sagittally cut sections, there are four lobes in Hydrolagus and five in Squalus, corresponding to the number of gill arches. The neurochemicals are differentially distributed within each lobe. LENK+ and 5-HT+ fibers are located in all regions within the visceral sensory complex. SP+ fibers are extremely dense in a dorsolateral subdivision and do not extend as far ventrally as 5-HT+ and LENK+ fibers. The lobes lack 5-HT+ cells, but contain a few LENK+ and SP+ cells. Many TH+ cells are distributed in dorsomedial portions of the complex, but there are few TH+ fibers. Thus, the visceral sensory area of cartilaginous fish contains several divisions that can be distinguished by their neurochemical content.

Fine distribution of substance P-like immunoreactivity in the dorsal nucleus of the vagus nerve in cats

The ultrastructure of substance P (SP)-immunoreactive elements in the cat dorsal motor nucleus of the vagus nerve was examined using pre- and post-embedding immunocytochemical procedures. Substance P-like immunoreactivity was observed in axon terminals and axon fibres which were mostly unmyelinated. Quantitative data showed that at least 16% of axon terminals contained SP. Their mean diameter was larger than that of their non-immunoreactive counterparts. Most (83%) SP-containing terminals were seen to contact dendrites but some were observed adjoining soma or entirely embedded in the cytoplasm of vagal neurons (4.5%). Only 0.5% were observed to contact soma of internuerons. A few immunoreactive axon terminals (4%) were observed in contact with non-immunoreactive axon terminals. Round agranular vesicles and numerous dense core vesicles were visible in most SP-containing axon terminals (84.6%). The immunogold procedure showed the preferential subcellular location of SP to be dense core vesicles. In 32.4% of cases, SP-containing terminals were involved in synaptic contacts that were generally of the asymmetrical Gray type 1 and mainly apposed dendrites. The theoretical total of synaptic contacts was 74.5% and this suggests the existence of weak non-synaptic SP innervation involving approximately 25% of SP-containing axon terminals. No axo-axonic synapses were observed in the dorsal vagal nucleus. These results support the hypothesis that SP found in the dorsal vagal nucleus originates partly from vagal afferents and is involved in direct modulation of visceral functions mediated by vagal preganglionic neurons.

Calcitonin gene-related peptide immunoreactivity in the nucleus of the tractus solitarius and the carotid receptors of the cat originates from peripheral afferents

The presence and distribution of the calcitonin gene-related peptide was studied, using immunohistochemical techniques, in carotid receptors, in the nodose and glossopharyngeal ganglia and in the nucleus tractus solitarii of the cat. Seventy-seven per cent of the 42% of the nodose ganglion cells were labeled. Fine, sparsely branched immunoreactive terminal axonal arborizations were found in the carotid body; they disappeared after petrosal ganglionectomy. The intense immunoreactivity present in fibers in the commissural, medial, interstitial, gelatinosus, dorsal, intermediate and rostral gustatory subnuclei of the nucleus tractus solitarius was drastically reduced after removal of the ipsilateral nodose and petrosal ganglia. The central distribution of the immunoreactive axons, the morphology of the terminals in the carotid receptors and their dependence on an intact peripheral innervation are consistent with the idea that in the cat the calcitonin gene-related peptide is present in a high proportion of the primary visceral afferents, most of them unmyelinated.

Serotonin-, substance P- and tyrosine hydroxylase-like immunoreactive neurons projecting from the midbrain periaqueductal gray to the nucleus tractus solitarii in the rat

Serotonin-, substance P- and tyrosine hydroxylase-like immunoreactive neurons in the midbrain periaqueductal gray (PAG) were observed to send their axons to the nucleus tractus solitarii in the rat by the retrograde horseradish peroxidase tracing method combined with the immunocytochemical technique. These neurons were most frequently observed in the ventrolateral subnucleus and ventral portion of the medial subnucleus of the PAG at the entire rostrocaudal levels.

Up-regulation of substance P binding sites in the vagus nerve projection area of the cat brainstem after nodosectomy. A quantitative autoradiographic study

Substance P (SP) regulates visceral functions in the nucleus of the solitary tract (NST) area. High affinity SP binding sites labelled with [3H]SP or [125I]SP show a heterogeneous distribution in the cat medulla with high densities in the rostral and dorso-caudal parts of both the median subnucleus of NST and the dorsal motor nucleus (DMN). We previously observed a significant loss of SP immunoreactivity in the vagal area of the cat after an ipsilateral nodosectomy. It was thus important to study the correlated plasticity of SP binding in the context of the regulation of receptor function. Whichever labelled ligand was used, a unilateral nodose excision was followed by an ipsilateral increase in SP binding in the NST (200%) and the DMN (300%) after 30 days of survival. This increase was region-specific and did not match exactly the decrease in SP immunoreactivity following nodosectomy. This SP receptor density up-regulation could be due to long-term deprivation of SP afferent fibres in the NST and partly in the DMN. In the latter the increase of SP receptors occurred in both the cytoplasm of large neurons and the neuropile and did not affect the glia. The up-regulation phenomenon seems to be specific for SP receptors in the cat (at least in the DMN) and may constitute a reactive mechanism against the injury of axotomy of DMN neurons.

[The nucleus tractus solitarius: neuroanatomic, neurochemical and functional aspects]

The nucleus tractus solitarii (NTS) has long been considered as the first central relay for gustatory and visceral afferent informations only. However, data obtained during the past ten years, with neuroanatomical, biochemical and electrophysiological techniques, clearly demonstrate that the NTS is a structure with a high degree of complexity, which plays, at the medullary level, a key role in several integrative processes. The NTS, located in the dorsomedial medulla, is a structure of small size containing a limited number of neurons scattered in a more or less dense fibrillar plexus. The distribution and the organization of both the cells and the fibrillar network are not homogeneous within the nucleus and the NTS has been divided cytoarchitectonically into various subnuclei, which are partly correlated with the areas of projection of peripheral afferent endings. At the ultrastructural level, the NTS shows several complex synaptic arrangements in form of glomeruli. These arrangements provide morphological substrates for complex mechanisms of intercellular communication within the NTS. The NTS is not only the site of vagal and glossopharyngeal afferent projections, it receives also endings from facial and trigeminal nerves as well as from some renal afferents. Gustatory and somatic afferents from the oropharyngeal region project with a crude somatotopy within the rostral part of the NTS and visceral afferents from cardiovascular, digestive, respiratory and renal systems terminate viscero-topically within its caudal part. Moreover the NTS is extensively connected with several central structures. It projects directly to multiple brain regions by means of short connections to bulbo-ponto-mesencephalic structures (parabrachial nucleus, motor nuclei of several cranial nerves, ventro-lateral reticular formation, raphe nuclei...) and long connections to the spinal cord and diencephalic and telencephalic structures, in particular the hypothalamus and some limbic structures. The NTS is also the recipient of several central afferent inputs. It is worth to note that most of the structures that receive a direct projection from the NTS project back to the nucleus. Direct projections from the cerebral cortex to the NTS have also been identified. These extensive connections indicate that the NTS is a key structure for autonomic and neuroendocrine functions as well as for integration of somatic and autonomic responses in certain behaviors. The NTS contains a great diversity of neuroactive substances. Indeed, most of the substances identified within the central nervous system have also been detected in the NTS and may act, at this level, as classical transmitters and/or neuromodulators.(ABSTRACT TRUNCATED AT 400 WORDS)

SP-like immunoreactivity in the primary trigeminal neurons projecting to the nucleus tractus solitarii

Using the double-labeling method of retrograde transport of HRP combined with PAP immunocytochemistry, the neurons containing SP-like immunoreactivity (SPLI) of the trigeminal nerve projecting to the nucleus tractus solitarii (NTS) were examined. HRP-SP double-labeled neurons in the trigeminal ganglion, mainly small or middle-sized, were found after the NTS or the lingual nerve was injected with HRP followed by SP-immunoreaction. These findings demonstrate that the projection of the trigeminal nerve to the NTS contains SPLI.

Localization of serotonin, tyrosine hydroxylase, and leu-enkephalin immunoreactive cells in the brainstem of the horn shark, Heterodontus francisci

In previous studies on reptiles and elasmobranchs, we determined that some reticular groups are either absent or may be displaced compared to their locations in mammals. For example, nucleus raphe dorsalis, the largest serotoninergic cell group in mammals, is not present in rays, skates, or guitarfish. In the present study, we chose heterodontid sharks, a sister group to these batoids, for an out-group comparison of this and other characters. We identified cells in the brainstem of Heterodontus francisci by use of antibodies against tyrosine hydroxylase, serotonin, or leu-enkephalin and compared the distribution of these nuclei to descriptions in mammals and other elasmobranchs. The majority of tyrosine hydroxylase-positive cells were found in the midbrain tegmentum (A8-A10) and the hypothalamus. In addition, putative A1, A2, A5, A7 (noradrenergic) groups were found in the metencephalon and myelencephalon. Serotonin-positive cells were found in raphe nuclei and scattered lateral to the raphe. We identified probable homologues to raphe pallidus, raphe obscurus, raphe magnus, and raphe centralis superior (B8) cell groups, which have been described in mammals. A cluster of cells dorsomedial to the medial longitudinal fasciculus was identified as raphe dorsalis. The distributions of leu-enkephalin and serotonin immunoreactive cells were similar to each other, but the tyrosine-hydroxylase immunoreactive cells rarely intermingle with the former two immunoreactive cell types. Other reticular groups that contained both serotonin- and leu-enkephalin-positive cells included reticularis (r.) ventralis, r. magnocellularis, r. paragigantocellularis lateralis, r. pontis caudalis, and r. pontis oralis medialis and lateralis. Thus, this shark contains many of the major brainstem raphe and catecholaminergic cell groups described for rats, but the relative distribution of the immunopositive cell groups differs in mammals and cartilaginous fish.

Enhanced in vivo release of substance P in the nucleus tractus solitarii during hypoxia in the rabbit: role of peripheral input

In the adult, pentobarbitone-anaesthetized rabbit, the in vivo release of substance P-like immunoreactivity was measured in the nucleus tractus solitarii using microdialysis and radioimmunoassay. Increased 160 +/- 16%) extracellular concentrations of substance P-like immunoreactivity were observed during hypoxic provocations of 9% O2 in N2 which also resulted in an increase in phrenic nerve activity. In bilateral carotid sinus nerve-denervated animals no enhanced release of substance P was seen in response to hypoxic challenges (105 +/- 6%) and the phrenic nerve activity was not significantly affected. Perfusion of the nucleus tractus solitarii region with the dopamine agonist, apomorphine (10(-5) M) resulted in a significant decrease in the extracellular level of substance P. These results provide further evidence that substance P is involved in the mediation of the hypoxic drive inputs from the peripheral chemoreceptors. The interactions of apomorphine with substance P release might also suggest a presynaptic modulation of substance Pergic neurons by dopamine in the nucleus tractus solitarii.

Anatomical distribution of substance P-immunoreactive neurons in human brainstem during the first postnatal year

The localization of substance P (SP)-immunoreactive structures in the infant brainstem was investigated by immunohistochemistry using the peroxidase antiperoxidase technique. SP-immunoreactive structures are widely distributed throughout the brainstem region. SP-immunoreactive cell bodies are prominent in the superior colliculis, the central grey, the nucleus tractus solitarius and the reticular formation. A high density of SP-immunoreactive fibers is found in the nucleus tractus solitarius, the trigeminal nucleus and the dorsal horn of the spinal cord. Large SP-immunoreactive fibers are seen in the substantia nigra. In the present study, we also investigated the development of substance P-immunoreactive fibers in the infant brainstem during the first postnatal year. We note a qualitative increase in the density of SP-immunoreactivity in some brainstem regions such as colliculus superior and substantia nigra with respect to age.