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PubMed1984

Behavioural and biochemical studies with the benzamide sulpiride in rats.

We have studied the effects of the benzamide, sulpiride, on dopamine transmission using a functional approach combining brain dialysis experiments with behavioural studies utilising rotational and holeboard models. In the 6-OH-dopamine-rotational model, both apomorphine and pergolide induced a dose-dependent contralateral rotation. However, sulpiride blocks very effectively the pergolide responses whilst it inhibits poorly the apomorphine rotation. Further studies using the same model suggest different receptor mechanisms distinctly distributed in the striata of rats and involving different efferent pathways. A dialysis tube was implanted into the left striatum of rats in order to study changes in dopamine release after influencing dopamine autoreceptors. Apomorphine produced a decrease of dopamine release which was reversed by sulpiride. The dopamine autoreceptor regulation of exploratory behaviour has been studied using an automatic holeboard device. Apomorphine and pergolide inhibited locomotion in an dose-dependent manner. This inhibition was selectively reversed by sulpiride but not by cis-flupenthixol. The dialysis provided also another possibility to study the functional regulation of DA systems. It has been suggested that sulpiride most effectively blocks the dopamine receptors localized presynaptically on cortico-striatal glutamate afferent neurons. We have compared the effects of cis-flupenthixol and sulpiride on glutamate and GABA release as measured by dialysis in the striata of rats. We found no clearcut effect after cis-flupenthixol, while sulpiride caused a significant change in glutamate release.

Animals↗
PubMed1983

Prostaglandin-mediated inhibition of noradrenaline release. VII. Effect of indomethacin on some cardiovascular reflexes in man.

The effect of indomethacin, a prostaglandin (PG) synthesis inhibitor, on some cardiovascular reflexes was studied in healthy subjects. Heart rate (HR) and respiratory sinus arrhythmia (RSA) in the basal state and during carotid stimulation (neck suction), Valsalva ratio, and changes in heart rate and blood pressure (BP) during an orthostatic test were measured before and one hour after administration of indomethacin (1.5 mg/kg). The efficacy of the PG synthesis inhibitor was monitored by analysis of platelet aggregation induced by arachidonic acid. Following indomethacin no change was observed in basal HR. Carotid stimulation depressed the HR and this effect was of the same amplitude before and after indomethacin. The amplitude of RSA was not affected by indomethacin, either in the basal state or during carotid stimulation. The Valsalva ratio and the changes in HR and BP during the orthostatic test were similar before and after the drug. Circulating levels of noradrenaline were unaffected by indomethacin. These data demonstrate that inhibition of PG bioformation in man does not affect major cardiovascular reflexes. Consequently they disfavour the hypothesis that endogenously formed PG would be involved in the normal activity of the afferent, central or efferent pathways for cardiovascular regulation.

Adult↗
PubMed1989

Renal denervation does not prevent dehydration-induced natriuresis in sheep.

Normal sheep or sheep in which the renal nerves had been extirpated were deprived of water for 2 days in order to determine whether changes in renal nerve activity contribute to natriuresis during water deprivation. Both groups of sheep showed a considerable natriuresis throughout the period of water deprivation and increases in plasma osmolality and plasma Na concentration. Renal denervation, as indicated by the absence of catecholamine fluorescence in kidney sections, was extensive. Previous experiments have suggested cerebral involvement in the induction of dehydration-induced natriuresis. The present results indicate that the efferent pathway mediating this cerebral influence on renal sodium excretion does not involve the renal nerves, suggesting a hormonal mechanism as the likely pathway.

Animals↗
PubMed1995

The role of limbic structures in the modulation of ACTH responses following adrenalectomy.

The role of the HIPP, DF, and the lateral SPT as well as of the central AMG nucleus in ACTH hypersecretion following Adex, was studied in male rats. In animals with bilateral dorsal hippocampectomy, DF section, or SPT lesions there was a much greater increase in ACTH hypersecretion when compared to Adex alone. Implants of CS in the paraventricular nucleus of the hypothalamus prevented the rise in serum ACTH following Adex, and this effect was reversed by hippocampectomy. Bilateral lesions in the AMG prevented the Adex-induced rise of serum ACTH. These results indicate that the dorsal HIPP and its efferent pathways to the hypothalamus have normally an inhibitory effect on Adex-induced ACTH secretion. Their removal permits an elevated ACTH hypersecretion as well as attenuation of the CS feedback effect. The central AMG nucleus, which has a facilitatory effect on the hypothalamopituitary-adrenocortical axis, can also modulate ACTH secretion following Adex.

Adrenalectomy↗
PubMed1984

Effect of limb ischaemia on blood pressure and the blood pressure-heart rate reflex in the rat.

The effects of bilateral hind-limb ischaemia on blood pressure and on the blood pressure-heart rate reflex have been studied in the rat. Limb ischaemia increased blood pressure and decreased the elevation and slope of the regression line describing the relationship between heart period (H.P.) and mean arterial pressure (M.A.P.). Nociceptive afferents from muscle receptors using long fibre tracts in the anterolateral part of the spinal cord seem to be responsible for the changes seen. The changes in the blood pressure-heart rate reflex were mediated by a combination of vagal inhibition and sympathetic activation. The efferent pathway for the pressor effect was in the sympathetic outflow. Central catecholaminergic neurones were involved in the pressor effect of limb ischaemia but not in the changes in the blood pressure-heart rate reflex. Electrolytic lesions in the posterior hypothalamus attenuated the inhibition of the reflex and it is suggested that neurones in the defence area may be activated by limb ischaemia. The interaction between limb ischaemia and the H.P.-M.A.P. relationship was not affected by opioid antagonists. After the period of ischaemia there was an increase in the elevation of the regression line describing the relationship between H.P. and M.A.P. which was secondary to the fall in body temperature characteristic of this phase of the response to injury.

Afferent Pathways↗
PubMed1966

Analysis of some central actions of nicotine injected into the cerebral ventricles of cats.

1. In unanaesthetized cats intraventricular injections of 2.5-10 mug nicotine produced blinking, narrowing of the palpebral fissures, retching, vomiting and asynchronous twitching of the ears. With larger doses (30-100 mug) the ear twitching was interrupted for a short time by laying back of the ears. Respiration first became laboured and deep, then rapid and shallow following which panting occurred. There was salivation, loud calling, micturition and defaecation. With still larger doses (300-1000 mug) there was torticollis, ataxia and blind charging sometimes followed by a clonic-tonic convulsion.2. In cats anaesthetized with chloralose only some of these effects followed the intraventricular injection of nicotine, i.e. the ear response, respiratory changes and salivation. In addition, the pinna reflex was facilitated.3. The ear response and the facilitation of the pinna reflex did not occur on perfusion of nicotine from a lateral ventricle to aqueduct. They result from an action on superficial structures in the cervical cord between C1 and C2. Applied to this region of the cord, nicotine produced the ear response within 10-60 sec, sometimes in concentrations as low as 1/100,000. Applied below C2, nicotine was ineffective.4. Transecting the cord below C2 or cutting the dorsal and ventral roots of C1, C2 and C3 bilaterally did not affect the ear response produced by topical application or by intraventricular injection of nicotine. Transection of the cord above C1 abolished it.5. Hexamethonium applied to the cervical cord between C1 and C2 inhibited the ear response and the facilitation of the pinna reflex whether produced by nicotine applied topically or injected intraventricularly.6. The salivation and the respiratory changes produced by intraventricular injections of nicotine did not occur when nicotine was perfused from a lateral ventricle to the aqueduct. They result from an action of the nicotine on structures situated superficially in the brain stem. Nicotine had no sialogogue or respiratory effect when applied to the region of the cord at which it produced an ear response, but perfused through the subarachnoid space from interpeduncular fossa to cisterna magna or injected into the subarachnoid space alongside the brain stem, it produced these effects.7. Hexamethonium perfused from interpeduncular fossa to cisterna magna inhibited the salivary secretion as well as the respiratory changes produced by nicotine similarly applied.8. The efferent pathway for the salivation is parasympathetic since it no longer occurred after cutting the chorda-lingual nerve or after intravenous atropine.9. Intravenous injections of nicotine also produced the ear response with facilitation of the pinna reflex, salivation and hyperventilation in the anaesthetized cat, but only the ear response and facilitation of the pinna reflex are central effects. The salivation and hyperventilation following intravenous injection are due to peripheral actions of nicotine.

Journal Article↗
PubMed1970

Observations on the mechanism of salicylate-induced antipyresis.

1. Fever has been produced in conscious rabbits, first, by injection of leucocyte pyrogen into the lateral cerebral ventricle and, second, by local cooling of the hypothalamus.2. Both intravenous and intraventricular salicylate produce antipyresis during an established fever due to intraventricular leucocyte pyrogen. This is incompatible with the hypothesis that salicylate acts by interfering with the passage of leucocyte pyrogen from the circulation into the hypothalamus.3. Intravenous sodium salicylate has no effect on the fever due to local cooling of the hypothalamus. This suggests that salicylates do not act on central or peripheral efferent pathways involved in thermoregulation.

Animals↗
PubMed1973

The ponto-medullary area integrating the defence reaction in the cat and its influence on muscle blood flow.

1. In anaesthetized cats the effects were investigated of electrical stimulation of regions in the caudal mesencephalon, pons and medulla on muscle blood flow, skin blood flow and arterial blood pressure.2. It was found that within the dorsal part of the well known pressor area there is a narrow strip, 2.5 mm lateral from the mid line, starting ventral to the inferior colliculus and ending in the medulla close to the floor of the IV ventricle, from which vasodilatation in skeletal muscles is selectively obtained. This strip is quite separate from the more ventral, efferent pathway for active vasodilatation running from the hypothalamic and rostral mesencephalic ;defence centre'.3. As in the case of the hypothalamic and rostral mesencephalic ;defence centre', the muscle vasodilatation obtained from the caudal strip is accompanied not only by a rise of arterial blood pressure, but also by tachycardia, vasoconstriction in the skin, pupillary dilatation and piloerection.4. Stimulation, restricted to the caudal strip, via implanted electrodes in unanaesthetized animals, produced a behavioural response resembling the defence reaction. The strip, therefore, is probably a caudal extension of the ;defence centre'.5. Unlike the vasodilatation elicited from the more rostral part of the ;defence centre' in the hypothalamus and mesencephalon, the muscle vasodilatation obtained on stimulation of the caudal strip was resistant to atropine, but was blocked by guanethidine.6. It is suggested that during naturally occurring defence reactions in the normal animal the ponto-medullary area is activated together with the hypothalamo-mesencephalic area, inhibition of vasoconstrictor tone then accompanying activation of the vasodilator nerve fibres in skeletal muscle.

Animals↗
PubMed1976

The responses of human muscle spindle endings to vibration during isometric contraction.

1. An human subjects, vibration of amplitude 1-5 mm and frequency 20-220 Hz was applied to the tendons of muscles in the leg to examine the effects on the discharge of primary and secondary endings during manoeuvres designed to alter the level of fusimotor drive. 2. In four experiments, the peroneal nerve was completely blocked with lidocaine proximal to the recording site in order to de-efferent spindle endings temporarily. The responses to muscle stretch and vibration, as seen in multi-unit recordings and in single unit recordings, were similar during the block as in the relaxed state prior to the block. Thus, these experiments provided no evidence for a functionally effective resting fusimotor drive. 3. The responses to vibration of nine primary endings and four secondary endings were examined during isometric voluntary contractions of the receptor-bearing muscles. Providing that the endings were responding submaximally in the relaxed state, voluntary contraction enhanced the response to vibration, suggesting co-activation of the fusimotor system sufficient to compensate for mechanical unloading. Unloading effects were observed during contractions of neighbouring synergistic muscles, indicating a close spatial relationship between the co-activated skeletomotor and fusimotor outflows. 4. Recordings were obtained from ten primary endings and seven secondary endings during isometric reflex contractions resulting from the vibratory stimulus (TVR contractions). For twelve endings, the appearance of the tonic vibration reflex in the receptor-bearing muscle resulted in a significant decrease in the response to vibration, suggesting that the endings were unloaded by the extrafusal contraction. On voluntary suppression of the reflex contraction spindle responses reverted to their previous levels. 5. These results suggest that the tonic vibration reflex, like the tendon jerk reflex, operates predominantly or exclusively on alpha motoneurones and that it does not utilize the same cortically originating efferent pathways as are used in the performance of voluntary contractions.

Action Potentials↗
PubMed1977

Intracerebroventricular taurine in rabbits: effects of normal body temperature, endotoxin fever and hyperthermia produced by PGE1 and amphetamine.

1. Intracerebroventricular (I.C.V.) injections of taurine into rabbits resting at an ambient temperature (Ta) of 10 degrees or 23 degrees C caused hypothermia but at 30 degrees C ambient temperature, rectal temperature was unchanged. 2. An I.C.V. bolus of 0=5 mg taurine immediately followed by a slow infusion of taurine (0-01--0-2 mg/min) into rabbits at 23 degrees C ambient temperature caused sedation and peripheral vasodilation and blocked the febrile response to Salmonella typhosa endotoxin (1 microng/kg i.v.). Sustained fevers, characteristic of fevers caused by central administration of pyrogens, developed after taurine infusions were stopped. Control infusions of taurine at the same rates in the same rabbits when they were afebrile had little effect on rectal temperature. 3. An I.C.V. injection of 0-5 mg taurine reduced the hyperthermia caused by prostaglandin E1 (PGE1; 2 microng) given I.C.V. A dose of 5-0 mg not only blocked PGE1 hyperthermia but also caused marked hypothermia. 4. Bilateral injections of taurine into the preoptic/anterior hypothalamic region, at sites where injections of Salmonella typhosa endotoxin caused long-lasting fevers, had no effect on rectal temperature. Similar injections into the reticular substance of the medulla oblongata, in the region believed to be concerned with a secondary temperature control function, were also without effect on body temperature. 5. Taurine (0-5 and 5-0 mg, I.C.V.) had no consistent effect on hyperthermia induced by amphetamine (2 mg/kg, I.V.) 6. We conclude that the hypothermic effect of taurine is not due to an action on the central neurone pool or pools concerned with the integrative control of thermoregulatory effectors. This amino acid appears to inhibit neuronal activity in efferent pathways which control peripheral vasomotor tone and heat production and to depress the level of arousal. Taurine delays the onset and extends the duration of endotoxin-induced fever, perhaps by two separate action: by inhibiting activity in central thermoregulatory pathways and by promoting accumulation of endogenous pyrogen in the brain.

Amphetamines↗
PubMed1979

Left ventricular inotropic responses to stimulation of carotid body chemoreceptors in anaesthetized dogs.

1. Dogs were anaesthetized with chloralose and artificially ventilated. The regions of both carotid bifurcations were vascularly isolated and perfused at constant pressure with arterial blood or with venous or hypoxic blood. 2. Inotropic responses were assessed by measuring the maximum rate of change of left ventricular pressure (dP/dtmax) with aortic pressure and heart rate held constant. 3. Stimulation of the chemoreceptors with venous blood from the inferior vena cava resulted in a decrease in dP/dtmax from 510 +/- 27 kPa.s-1 to 418 +/- 21 kPa.s-1 (mean +/- S.E.): a change of 17.9 +/- 1.0% 4. In experiments in which the oxygen tension of the blood perfusing the carotid chemoreceptors was decreased in steps between 10 and 3 kPa, by use of an oxygenator, graded responses of dP/dtmax were obtained at each step. 5. The inotropic responses to chemoreceptor stimulation were abolished by raising carotid pressure. 6. The inotropic responses were abolished either by crushing both carotid bodies or both ansae subclaviae, indicating that the reflex originates from the carotid bodies and that the efferent pathway is in the cardiac sympathetic nerves.

Animals↗
PubMed2003

Gastrointestinal-projecting neurones in the dorsal motor nucleus of the vagus exhibit direct and viscerotopically organized sensitivity to orexin.

Orexin (hypocretin)-containing projections from lateral hypothalamus (LH) are thought to play an important role in the regulation of feeding behaviour and energy balance. In rodent studies, central administration of orexin peptides increases food intake, and orexin neurones in the LH are activated by hypoglycaemia during fasting. In addition, administration of orexins into the fourth ventricle or the dorsal motor nucleus of the vagus (DMV) has been shown to stimulate gastric acid secretion and motility, respectively, via vagal efferent pathways. In this study, whole-cell recordings were obtained from DMV neurones in rat brainstem slices to investigate the cellular mechanism(s) by which orexins produce their gastrostimulatory effects. To determine whether responsiveness to orexins might be differentially expressed among distinct populations of preganglionic vagal motor neurones, recordings were made from neurones whose projections to the gastrointestinal tract had been identified by retrograde labelling following apposition of the fluorescent tracer DiI to the gastric fundus, corpus or antrum/pylorus, the duodenum or caecum. Additionally, the responses of neurones to orexins were compared with those produced by oxytocin, which acts within the DMV to stimulate gastric acid secretion, but inhibits gastric motor function. Bath application of orexin-A or orexin-B (30-300 nM) produced a slow depolarization, accompanied by increased firing in 47 of 102 DMV neurones tested, including 70 % (30/43) of those that projected to the gastric fundus or corpus. In contrast, few DMV neurones that supplied the antrum/pylorus (3/13), duodenum (4/18) or caecum (1/13) were responsive to these peptides. The depolarizing responses were concentration dependent and persisted during synaptic isolation of neurones with TTX or Cd2+, indicating they resulted from activation of postsynaptic orexin receptors. They were also associated with a small increase in membrane resistance, and in voltage-clamp recordings orexin-A induced an inward current that reversed near the estimated equilibrium potential for K+, indicating the depolarization was due in large part to a reduction in K+ conductance. Orexins did not affect synaptically evoked excitation, but did reduce membrane excitability in a subset of gastric-projecting DMV neurones by enhancing GABA-mediated synaptic input. Lastly, although many DMV neurones responded to orexins and oxytocin with excitation, for the most part these peptides modulated excitability of distinct populations of gastric-projecting vagal motor neurones. These results indicate that orexins act preferentially within the DMV to directly excite vagal motor neurones that project to gastric fundus and corpus. In this way, release of endogenous orexins from descending hypothalamic projections into the DMV may mediate the increase in gastric acid secretion and motor activity associated with the cephalic phase of feeding.

Action Potentials↗
PubMed2003

Arterial baroreflex control of muscle blood flow at the onset of voluntary locomotion in mice.

To assess the role of arterial baroreflex control in muscle blood flow (MBF) and voluntary locomotion, mean arterial pressure (MAP), MBF, and electromyograms (EMGs) were measured in freely moving mice before (CNT) and after blocking the afferent or efferent pathway of arterial baroreflexes, carotid sinus denervation (CSD), or intraperitoneal administration of phentolamine (BLK), respectively. MAP was measured through a catheter placed in the femoral artery. MBF was measured with a needle-type laser-Doppler flowmeter and recorded through a low-pass filter with an edge frequency of 0.1 Hz. The frequency and duration of locomotion were judged from EMG recordings in the hindlimb. These probes were implanted at least 2 days before the measurements. Muscle vascular conductance (MVC = MBF/MAP) in all groups started to rise within 1 s after the onset of locomotion, but the increasing rate in CSD and BLK was significantly higher than in CNT for the first 9 s (P < 0.001). MAP in CSD and BLK significantly decreased below the baseline within 1 s and this was highly correlated with the increase in MVC for the first 9 s (R2 = 0.842, P < 0.001), whereas MAP in CNT increased significantly 8 s after the onset of locomotion. Although the total period of movement in a free-moving state for 60 min was not significantly different between CNT and CSD (P > 0.1), the frequency of movement with a short duration of 0.1-0.4 min was higher in CSD than in CNT (P < 0.001), which was highly correlated with the reduction in MAP accompanying each period of movement (R2 = 0.883, P < 0.01). These results suggest that arterial baroreflexes suppress vasodilatation in contracting muscle to maintain MAP at the onset of voluntary locomotion, and are necessary to continue a given duration of locomotion in mice.

Adrenergic alpha-Antagonists↗
PubMed2002

betaAR signaling required for diet-induced thermogenesis and obesity resistance.

Excessive caloric intake is thought to be sensed by the brain, which then activates thermogenesis as a means of preventing obesity. The sympathetic nervous system, through beta-adrenergic receptor (betaAR) action on target tissues, is likely the efferent arm of this homeostatic mechanism. To test this hypothesis, we created mice that lack the three known betaARs (beta-less mice). beta-less mice on a Chow diet had a reduced metabolic rate and were slightly obese. On a high-fat diet, beta-less mice, in contrast to wild-type mice, developed massive obesity that was due entirely to a failure of diet-induced thermogenesis. These findings establish that betaARs are necessary for diet-induced thermogenesis and that this efferent pathway plays a critical role in the body's defense against diet-induced obesity.

Adipose Tissue, Brown↗
PubMed1981

Spatial localization after strabismus surgery: evidence for inflow.

Strabismics pointed to targets (without sight of the hand) before and again after surgery that altered the position of the deviating eye in its orbit. Patients having this surgery for the first time were able to use proprioceptively derived information about the surgically altered eye position. In contrast, patients who had similar operations, but on muscles that had been operated on one or more times in the past, were apparently deprived of this information. The important afference may be supplied by the tendon organs.

Afferent Pathways↗
PubMed1977

Postural changes in plasma renin activity and responses to vasoactive drugs in a case of Shy-Drager syndrome.

A male aged 47 years with gross autonomic insufficiency as part of the Shy-Drager syndrome is described. He did not sweat normally when warmed, and his circulatory responses to mental arithmetic, the Valsalva manoeuvre, and head-up tilt were abnormal indicating severe sympathetic failure. During head-up tilt there was a rise in plasma renin activity and plasma aldosterone. It is argued that plasma renin activity is not dependent on sympathetic nervous activity and may be mediated by renal baroreceptors. These rises may help sustain the blood pressure in such patients during repeated head-up tilts. Infusions of L-noradrenaline and angiotension produced greater hypertension, and injections of isoprenaline greater hypotension than in controls. Although it is difficult to exclude the possibility that one factor in this may be hypersensitivity of receptors in blood vessel walls, the principal factor is likely to be the absence of those baroreflexes of which the efferent pathways are in the sympathetic nervous system.

Angiotensin II↗