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PubMed1980

Neural pathways mediating the prolactin secretory response to acute neurogenic stress in the male rat.

Adult male rats, intact (N) or bearing complete, anterior or posterior hypothalamic deafferentations (CHD, AHD or PHD, respectively), or bilateral medial forebrain bundle (MFB) lesions, were acutely exposed to visual or audiogenic stimulation. At 2, 4, 10 or 30 min following stress onset the animals were decapitated and trunk blood was collected for prolactin (PRL) determinations. Basal serum PRL levels were found to be similar in all groups. In N animals, exposure to both modalities resulted in rapid and marked PRL secretory responses. These responses were totally abolished in the CDH group. In AHD rats, no significant elevation in serum PRL concentration was found upon stress exposure. In PHD animals, the PRL secretory responses were only slightly attenuated when compared with the N group. In MFB-lesioned rats, a marked elevation in serum PRL concentrations was recorded following visual stimulation; contrary thereto, the PRL secretory response following audiogenic stress was markedly attenuated. These data (1) describe the temporal aspects of the PRL secretory response to acute exposure to neurogenic stresses in the male rat, and (2) demonstrate that these PRL responses are elicited via a neural pathway impinging upon the medial basal hypothalamus from the rostral direction.

Acoustic Stimulation↗
PubMed1988

Afferent neural pathways in cough and reflex bronchoconstriction.

Cough and bronchoconstriction are airway reflexes that protect the lung from inspired noxious agents. These two reflexes can be evoked both from the larynx and tracheobronchial tree and also from some extrarespiratory sites. Within the airways, certain sites are particularly sensitive to stimulation of cough (larynx and points of proximal airway branching), whereas bronchoconstriction can be triggered from the whole of the tracheobronchial tree. In the larynx, "irritant" receptors with myelinated afferents mediate cough and bronchoconstriction. Little seems to be known about laryngeal nonmyelinated afferents and their reflexes. In the tracheobronchial tree and lung, slowly adapting stretch receptors (SARs) and rapidly adapting stretch receptors (RARs) have opposing effects on airway tone, the former mediating bronchodilation and the latter bronchoconstriction. In cough, on the other hand, they operate concurrently, a mediatory role for RARs and a facilitatory role for SARs. C-fiber endings (bronchial and pulmonary) mediate bronchoconstriction. Inhalation of so-called "selective" C-fiber stimulants induces cough, but excitation of RARs has not been eliminated, and the possibility also exists that the cough is secondary to other lung actions mediated by these nerve endings. Although cough and bronchoconstriction may be mediated by the same type of receptor, they seem to have separate afferent neural pathways.

Afferent Pathways↗
PubMed2001

Identification of efferent neural pathways from the lamina terminalis activated by blood-borne relaxin.

The ovarian hormone relaxin, in addition to its role in pregnancy, exerts an action on the brain to influence oxytocin and vasopressin secretion, water drinking, and cardiovascular function. Intravenous (i.v.) infusion of relaxin causes an acute water drinking response, confirming its role as a dipsogenic hormone. The aim of this study was to determine whether neurones in the lamina terminalis, which project to the hypothalamic paraventricular and supraoptic nuclei, are activated by elevated levels of circulating relaxin in conscious rats. Immunocytochemistry combined with retrograde neuronal tracing with cholera toxin B subunit conjugated to cholera toxin B (CTB-gold) was used to identify populations of neurones responding with elevated cells of Fos protein to i.v. relaxin administration and which project to these specific hypothalamic sites. Neurones exhibiting Fos were present in the outer parts of the subfornical organ (SFO), the dorsal part of the organum vasculosum (OVLT), the supraoptic nucleus and the paraventricular nucleus. These did not occur in control rats with i.v. infusions of isotonic saline. Approximately 90% of neurones concentrated in the outer parts of the SFO and in the dorsal OVLT showed both retrogradely transported CTB-gold and Fos in response to i.v. infusion of relaxin. These data support a role for relaxin acting on the brain to regulate body fluid and electrolyte homeostasis by activating neural pathways subserving water drinking, vasopressin and oxytocin secretion.

Animals↗
PubMed2004

Ghrelin enhances gastric motility through direct stimulation of intrinsic neural pathways and capsaicin-sensitive afferent neurones in rats.

BACKGROUND: Ghrelin may stimulate gastric motility via the vagal nerve pathway. However, the mechanism of ghrelin-induced changes in gastrointestinal motility has not yet been clearly defined. The present study was designed to investigate whether ghrelin accelerates gastric emptying via capsaicin-sensitive afferent neurones and directly affects the enteric neuromuscular function. METHODS: Gastric emptying of nutrient solids was assessed after intravenous administration of saline or ghrelin in conscious rats. The effects of ghrelin on gastric emptying were also examined in rats pretreated with capsaicin. Gastric emptying and intestinal transit of non-caloric liquids were evaluated using 51Cr solution. The effects of ghrelin on spontaneous contractile activities of isolated strips from stomach and jejunum were also investigated and the influence of ghrelin on motor responses to carbachol and electrical field stimulation was examined. RESULTS: Ghrelin significantly accelerated gastric emptying of both nutrient solids and non-caloric liquids in conscious rats. The intestinal transit of non-caloric liquids was also enhanced by ghrelin. Pretreatment with capsaicin prevented the ghrelin-induced acceleration of gastric emptying of nutrient solids. Ghrelin did not modulate spontaneous and carbachol-induced contractions of strips of gastric body, gastric antrum and jejunum. However, electrical field stimulation-induced contractions were significantly enhanced by ghrelin in the gastric body. CONCLUSIONS: The results suggest that the stimulatory effects of ghrelin on gastric motility are mediated by direct stimulation of the enteric neural pathway and capsaicin-sensitive afferent neurones.

Afferent Pathways↗
PubMed2006

Noradrenergic and cholinergic neural pathways mediate stress-induced reactivation of colitis in the rat.

Evidence to date suggests that stress-induced exacerbation or relapse of intestinal inflammation in inflammatory bowel disease requires both activation of the autonomic nervous system and the activation of the immune system by the presence of previously encountered luminal antigens. The aim of the present study was to further explore these associations and to determine the role of the autonomic nervous in modulating the intestinal inflammatory response to stress. Rats healed from an initial dinitrobenzene sulfonic acid-induced colitis were given a non-colitic dose of dinitrobenzene sulfonic acid (dissolved in saline) or 0.9% saline intra-rectally and then subjected to restraint stress. Cardiac sympathovagal balance was assessed by power spectral analysis of heart rate variability data collected from telemetric electrocardiogram recordings before, during and post stress. Only rats that were stressed and received dinitrobenzene sulfonic acid showed an inflammatory relapse characterized by significant macroscopic damage and elevated myeloperoxidase activity associated with a significant infiltration of mucosal and submucosal T lymphocytes. No difference in inflammatory markers was observed in animals that received intra-rectal saline and restraint stress. Rats subjected to stress and intra-rectal dinitrobenzene sulfonic acid demonstrated an increase in sympathetic activity with a nearly four fold increase in LF:HF ratio during stress and a significant increase in heart rate. Shortly after cessation of stress, the LF:HF ratio decreased significantly, returning to baseline levels, however the heart rate remained significantly elevated over baseline levels following stress, but decreased to a level that was significantly lower than during stress. The stress/dinitrobenzene sulfonic acid-induced relapses were preventable by pre-treating rats with hexamethonium (a nicotinic cholinergic ganglion blocking agent) or the co-administration of atropine (a muscarinic cholinoceptor antagonist) and bretylium (a noradrenergic ganglion blocking agent), but was not prevented when either atropine or bretylium were administered alone. This study utilizes an established model of chemically induced colitis that when integrated with stress results in relapsing inflammatory bowel disease. Moreover, this study demonstrates that noradrenergic and cholinergic neural pathways mediate the stress response critical for the relapse of colitis.

Acute Disease↗
PubMed1994

Substance P activates rat colonic motility via excitatory and inhibitory neural pathways and direct action on muscles.

We studied effects of nicotinic, muscarinic, serotoninergic, dopaminergic, adrenergic, vasoactive intestinal peptide (VIP) antagonists, VIP, nitric oxide-synthase inhibitors and stimulators alone and in combination with tetrodotoxin on substance P (SP)-stimulated intraluminal tone of the isolated proximal, middle and distal rat colon. Tetrodotoxin significantly enhanced SP-stimulated intraluminal tonic pressure in the distal, but not in the middle and proximal colon. N omega-nitro-L-arginine methylester enhanced SP stimulation in all colonic segments, whereas L-arginine inhibited it partially and D-arginine did not affect it. Atropine and hexamethonium partially inhibited SP stimulation of the middle and distal colon. Tetrodotoxin completely abolished the effects of L-arginine, atropine and/or hexamethonium on SP stimulation. Propranolol, phentolamine, reserpine, telenzepine, naloxone, Mr 2266, a VIP antagonist (H9935) and ketanserin did not affect SP-induced colonic muscle stimulation. VIP strongly reduced SP-stimulated intraluminal pressure in all colonic segments. VIP(10-28), a putative VIP antagonist, produced similar inhibition of SP-stimulated intraluminal tonic pressure, but did not affect N omega-nitro-L-arginine methylester-induced enhancement of SP-stimulated intraluminal pressure in any segments. It is concluded that in the isolated rat colon SP-stimulated intraluminal pressure (mainly generated by circular muscles) by a direct action on colonic muscles over the whole colonic length and by simultaneous activation of neural cholinergic excitatory pathways in the middle and distal, of noncholinergic excitatory pathways in the proximal colonic segment, and by activation of nitric oxide-dependent inhibitory neural pathways. VIP seems not to be directly involved in this inhibitory pathway.

Animals↗
PubMedDate not supplied

The contribution of neural pathways to blood volume homeostasis in the subhuman primate.

Studies are presented which indicate that the neural components of an atrio-renal reflex appear to be present in the primate and thus presumably in man. However, this reflex does not appear to contribute importantly to blood volume homeostasis in the primate. It is our hypothesis that it is the high-pressure baroreceptors, i.e., those in the carotid sinus and those in the aortic arch which play the major role in the neural control of blood volume in the primate and thus in man. This apparent evolutionary change in the importance of high pressure vs. low pressure receptors in the neural modulation of blood volume may be related to the assumption of an upright or semi-upright posture.

Animals↗
PubMed1987

Neural pathways that mediate the effects of afferent stimuli on paraventricular nucleus multiunit activity in freely moving rats.

The direct involvement of the hypothalamic paraventricular nucleus (PVN) in the control of adrenocortical secretion is now generally accepted. In order to contribute to our understanding of the electrical activity of cells in this region during adrenocortical activation, we have recorded multiunit electrical activity (MUA) in response to acute neural stimuli in freely moving male rats and have examined the pathways involved. Photic, acoustic, olfactory, and sciatic nerve stimulation all increased PVN MUA by between 130% and 250%. These responses were selectively blocked, according to the stimulus modality tested, by radiofrequency lesions of central neural structures. Thus PVN responses to photic stimulation were blocked by lesions of the suprachiasmatic nuclei and reduced by mammillary peduncle lesions but were unaffected by lesions of the bed nuclei of the stria terminalis. Responses to acoustic stimulation were blocked by lesions of the mammillary peduncles but not by those placed in the suprachiasmatic nuclei, the septum, or the bed nuclei of the stria terminalis. Lesions of the septum blocked the response to sciatic nerve stimulation but did not affect the response to olfactory stimulation with amyl acetate fumes, which was blocked by lesions of the bed nuclei of the stria terminalis. The data confirm those obtained in endocrine studies concerning the neural pathways involved in the transmission of neural stimuli that produce adrenocortical activation.

Acoustic Stimulation↗
PubMed1994

H3 receptors: modulation of histamine-stimulated neural pathways influencing electrogenic ion transport in the guinea pig colon.

The role of H3 receptors in neurally-evoked recurrent increases in chloride ion secretion evaluated from changes in short-circuit current (Isc) was examined during application of histamine or histamine analogs. Muscle-stripped or whole thickness segments of distal colon were set up in flux chambers. Histamine and dimaprit, an H2 receptor agonist, caused recurrent increases in Isc. Dimaprit-evoked recurrent responses were reduced by the H3 receptor agonists, N alpha-methylhistamine and R alpha-methylhistamine, and the inhibition was reversed by the H3 receptor antagonist, burimamide. Histamine-evoked recurrent increases in Isc were enhanced by the H3 receptor antagonists burimamide and thioperamide. The results indicate that H3 receptors play an inhibitory role in histamine-evoked, neurally-mediated recurrent increases in Isc in guinea pig colon.

Animals↗
PubMed2004

Alcohol activates a sucrose-responsive gustatory neural pathway.

A strong positive association exists between the ingestion of alcohol and sweet-tasting solutions. The neural mechanisms underlying this relationship are unknown, although recent data suggest that gustatory substrates are involved. Here, we examined the role of sweet taste receptors and central neural circuits for sugar taste in the gustatory processing of ethanol. Taste responses to ethanol (3, 5, 10, 15, 25, and 40% vol/vol) and stimuli of different taste qualities (e.g., sucrose, NaCl, HCl, and quinine-HCl) were recorded from neurons of the nucleus of the solitary tract in anesthetized rats prior to and after oral application of the sweet receptor blocker gurmarin. The magnitude of ethanol-evoked activity was compared between sucrose-responsive (n = 21) and sucrose-unresponsive (n = 20) neurons and the central neural representation of ethanol taste was explored using multivariate analysis. Ethanol produced robust concentration-dependent responses in sucrose-responsive neurons that were dramatically larger than those in sucrose-unresponsive cells. Gurmarin selectively and similarly inhibited ethanol and sucrose responses, leaving NaCl, HCl, and quinine responses unaltered. Across-neuron patterns of response to ethanol were most similar to those evoked by sucrose, becoming increasingly more so as the ethanol concentration was raised. Results implicate taste receptors for sucrose as candidate receptors for ethanol and reveal that alcohol and sugar taste are represented similarly by gustatory activity in the CNS. These findings have important implications for the sensory and reward properties of alcohol.

Action Potentials↗
PubMed2006

The role of galanin in modulating stress-related neural pathways.

Galanin is a 29 or 30 amino acid peptide with a close anatomical and neurophysiological relationship with neural systems mediating stress. In rodent behavioral studies, the consequences of galanin activity on stress-related behaviors such as anxiety-like and depression-like behavior varies according to site of administration and behavioral assay used. However, galaninergic systems remain a promising novel target for new antianxiety and antidepressant drugs. Current work attempting to delineate which galanin receptor subtypes mediate which effects of galanin will undoubtedly inform the development of these drugs. Further, the well-established deleterious effects of galanin on cognitive function provide support for galanin as a novel link between stress, anxiety and memory. This link suggests that galaninergic drugs could provide a novel therapeutic option for psychopathologies, such as post-traumatic stress syndrome, in which abnormal memory and emotion are intertwined.

Animals↗
PubMed2006

Transneuronal tracing of neural pathways that regulate hindlimb muscle blood flow.

Despite considerable interest in the neural mechanisms that regulate muscle blood flow, the descending pathways that control sympathetic outflow to skeletal muscles are not adequately understood. The present study mapped these pathways through the transneuronal transport of two recombinant strains of pseudorabies virus (PRV) injected into the gastrocnemius muscles in the left and right hindlimbs of rats: PRV-152 and PRV-BaBlu. To prevent PRV from being transmitted to the brain stem via motor circuitry, a spinal transection was performed just below the L2 level. Infected neurons were observed bilaterally in all of the areas of the brain that have previously been shown to contribute to regulating sympathetic outflow: the medullary raphe nuclei, rostral ventrolateral medulla (RVLM), rostral ventromedial medulla, A5 adrenergic cell group region, locus coeruleus, nucleus subcoeruleus, and the paraventricular nucleus of the hypothalamus. The RVLM, the brain stem region typically considered to play the largest role in regulating muscle blood flow, contained neurons infected following the shortest postinoculation survival times. Approximately half of the infected RVLM neurons were immunopositive for tyrosine hydroxylase, indicating that they were catecholaminergic. Many (47%) of the RVLM neurons were dually infected by the recombinants of PRV injected into the left and right hindlimb, suggesting that the central nervous system has a limited capacity to independently regulate blood flow to left and right hindlimb muscles.

Animals↗
PubMed1984

A bilateral model for central neural pathways in vestibuloocular reflex.

It is argued that vestibular internuclear commissural pathways are functionally important in the vestibuloocular reflex (VOR), particularly since they appear to be modulated during nystagmus. A bilateral approach to VOR modeling is essential to an effective study of the effects of commissural connections on response dynamics. A bilateral model of the VOR central pathways is proposed, with three main postulates: neural filters (NF) on each side of the brain stem, each linked to tonic cells in the ipsilateral vestibular nuclei in negative feedback loops; strong coupling between these bilateral loops by reciprocal commissural connections that significantly affect response dynamics; and modulation of this coupling by inhibitory burst neurons during fast phases. Mathematical analysis of this model shows that the NF need not be good integrators. During slow-phase operation, commissural pathways provide a positive-feedback effect that improves the effective integration function of the bilateral system beyond that of the NF in each side. Analysis suggests that the time constant of the NF might even be as small as that of the eye plant (approximately 0.24 s), so that the NF might be considered to be internal models of the eye plant rather than pseudointegrators. In the model, modulation of commissural gains by burst cells is shown to be sufficient to cause the system to switch between a compensatory position-tracking mode (slow phases) and an anticompensatory velocity-tracking mode (fast phases) during nystagmus. The model simulates a number of behavioral and neurophysiological findings, such as a) tonic vestibular nuclei (VN) cells have sensitivities and decay times larger than primary vestibular fibers, and their response polarity may reverse after section of superficial commissural fibers; b) effective VOR integration deteriorates after cerebellectomy or commissurectomy; c) peak fast-phase eye velocity is modulated by the vestibular signal as well as by fast-phase amplitude. The model accounts for the modulation of central VN responses during nystagmus and, as a result, simulations strongly imply that envelopes of slow-phase eye velocity or smoothed central firing rates will depend on fast-phase strategy and, hence, may not always yield accurate estimates of VOR dynamics. Similarly, the model predicts that "apparent" disassociation between central and ocular responses may occur because of interactions during nystagmus, despite appropriate behavior within slow-phase segments (since VN responses are not simple estimates of eye velocity).(ABSTRACT TRUNCATED AT 400 WORDS)

Eye↗