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PubMed1989

In-vivo blockage of neutrophil migration by LPS is mimicked by a factor released from LPS-stimulated macrophages.

The present study was performed to determine the effect of an intravenous injection of the macrophage-derived neutrophil chemotactic factor (MNCF) (Cunha & Ferreira 1986) on neutrophil migration to rat peritoneal cavities, which were challenged with chemotactic stimuli. Macrophage monolayers stimulated by LPS release a factor (MW greater than 10,000 D) which, when injected intravenously, blocked neutrophil migration in carrageenin-induced peritonitis. This inhibition was dependent on dose and lasted more than 2 h. It was not due to neutropaenia, hypotension or LPS contamination. Neutrophil migration induced by LPS, MNCF, the Gram-negative bacterium Pseudomonas aeruginosa was also blocked by intravenous administration of the factor. Intravenous injection of recombinant interleukin 1 beta or tumour necrosis factor-alpha, present in the samples of the factor, failed to reproduce the described inhibitory effect on neutrophil migration. The release of this factor by LPS-stimulated macrophage monolayers was inhibited by dexamethasone but not by indomethacin. It is suggested that the failure of neutrophils to migrate during septicaemia may be the result of a continuous release of chemotactic factors in the circulation, particularly of the macrophage-derived neutrophil chemotactic factor(s).

Animals↗
PubMed1984

The beta-adrenoceptor-blocking drug propranolol prevents secretion of immunoreactive beta-endorphin and alpha-melanocyte-stimulating hormone in response to certain stress stimuli.

Handled female Wistar rats were exposed to one of the following stress stimuli: restraint, electric foot shocks, passive avoidance situation, ether, or nembutal anesthesia followed by ip formalin or laparotomy. Trunk blood was collected 2-4 min after initiation of the stress stimulus for the determination of immunoreactive beta-endorphin (beta-ENDi), ACTH (ACTHi), and alpha-MSH (alpha-MSHi). All stressors evoked a rapid increase of circulating beta-ENDi to 0.75-2.10 ng/ml. All except passive avoidance situation also induced a rapid increase of plasma ACTHi to 0.45-0.70 ng/ml, whereas plasma alpha-MSHi increased after ether and restraint to 0.18-0.40 ng/ml but was not affected by formalin stress. To study the involvement of a beta-adrenoceptor mechanism in stress-induced peptide secretion, rats were treated with D-propranolol or L-propranolol 40 min before stress exposure. Propranolol did not prevent the increase of plasma ACTHi to any of the stressors studied. L-Propranolol but not its inactive D-isomer reduced (restraint, passive avoidance) or abolished (electric foot shocks) the increase in plasma beta-ENDi but did not affect the beta-ENDi response to other stressors (ether, formalin, laparotomy). Similarly, L-propranolol attenuated the alpha-MSHi response to restraint but not to ether stress. To discriminate between corticotroph or melanotroph origin of beta-ENDi released during stress, rats were treated with dexamethasone or were subjected to neurointermediate lobectomy (4 weeks). Neurointermediate lobectomy did not affect basal or stress-induced plasma ACTHi but resulted in undetectable alpha-MSHi levels. It largely prevented the beta-ENDi response to restraint stress (propranolol sensitive) but had little effect on the beta-ENDi response to formalin stress (propranolol insensitive). Conversely, dexamethasone prevented stress-induced ACTHi response without affecting plasma alpha-MSHi. The beta-ENDi response to restraint stress (propranolol sensitive) was not changed but the response to formalin stress (propranolol insensitive) was largely prevented by dexamethasone. These results show that the intermediate lobe is the main source of beta-ENDi secreted during exposure to stressors with a high emotional impact. Since intermediate lobe peptide secretion induced by such stimuli can be prevented by beta-adrenoceptor blockade, we speculate that stress-induced discharge of catecholamines, possibly from the adrenal medulla, is the trigger signal for peptide secretion from the melanotrophs during this type of stress.

Adrenocorticotropic Hormone↗
PubMed1986

Synergistic activation of rat supraoptic neurosecretory neurons by noxious and hypovolemic stimuli.

The effects of saphenous nerve stimulation on discharge activity of supraoptic neurosecretory (NS) cells were studied in anesthetized rats. Of 112 supraoptic neurosecretory cells, 62 exhibited a 'phasic' discharge pattern. The nerve stimulation transiently excited 46 of these 62 'phasic' units, as well as 35 of the 50 remaining 'non-phasic' units. No appreciable blood pressure change was noted using PSTHs with 1-ms resolution. Though the nerve stimulation also evoked a flexor reflex of the ipsilateral hind limb, blockage of the hind limb movement with gallamine did not alter the amplitude of the supraoptic cell excitation. The threshold of the nerve stimulation was higher for the excitation than for the flexor reflex. Effects of hypovolemic and hyperosmotic stimuli on discharge activity of 'phasic' cells during saphenous nerve stimulation were studied to find a possible interaction between these stimuli. Hemorrhage potentiated the transient excitation evoked by the nerve stimulation in all of the 8 'phasic' cells tested, while no such effect was seen after an injection of hypertonic sodium chloride solution in the 7 'phasic' cells tested. These electrophysiological data suggest that hypovolemic and noxious stimuli potentiate VP secretion in a synergistic manner but that hyperosmotic and noxious stimuli do not.

Animals↗
PubMed1984

Induction of the rectoanal reflex by electric stimulation. A diagnostic aid for Hirschsprung's disease.

We induced the rectoanal reflex electrically in three groups of children, following rectal dilatation with a balloon. In normal children, and in children with constipation or ileus due to causes other than Hirschsprung's disease, the rectoanal reflex was induced by electric stimulation as well as by dilatation of the rectum with a balloon. In children with Hirschsprung's disease, however, no typical reflex was obtained by either of these stimuli. Since electric stimulation does not dilate the rectum, passive dilatation of the anus or shift of the probe along with balloon expansion does not take place, so no false-positive reflex is elicited. Electric current, moreover, is capable of providing a constant quantifiable stimulus. We have demonstrated the induction of the rectoanal reflex by electric stimulation alone; distention of the circular muscle of the rectum does not appear necessary for the induction of this reflex.

Anal Canal↗
PubMed1983

Fatigue considerations of muscle contractile force during high-frequency stimulation.

In a model for control of muscle force, wherein an induced background tetanus is attenuated by concurrent indirect stimulation at frequencies in the 0.6- to 10-kHz range, evaluation was made for effects on muscle fatigue of differing rates of the tetanic and high-frequency stimuli. Relatively little fatigue, and yet nearly the complete range of attenuation, were favored by lower frequencies of both these stimuli, e.g., tetanic stimulation at 50 Hz and a blocking frequency of 600 Hz.

Animals↗
PubMed1978

[Participation of interoceptive afferent signals in the polymodal reactions of superior colliculus neurons in cats].

Stimulation of the vagal nerve in unanesthetized immobilized cats evoked marked responses in 43% of neurons of the superior colliculus. In 60% of the responses the changes in the spike activity were of tonic character. After stimulation with single stimuli inhibitory effects prevailed; in half of cases distinct initial inhibition of discharges lasting for 180-1700 ms was observed. Phasic responses with an initial period of activity occurred only in 9-11% of neurons. On the contrary somatic stimuli provoked mainly phasic reactions of activation type. Most of the investigated neurons were bimodal and often the time pattern of the responses depended on the modality of stimulation.

Animals↗
PubMed1992

The effect of changing somatostatin tone on the pituitary growth hormone and thyroid-stimulating hormone responses to their respective releasing factor stimuli.

Somatostatin (SS) inhibits GH and TSH secretion, but its role in modulating their pulsatility is unclear. We studied GH and TSH responses to GH-releasing hormone (GHRH) and TRH stimulation upon a variable background infusion of saline, SS-(1-14) at 20 and 100 micrograms/m2.h, and oral pyridostigmine (30 and 60 mg) in six adult males. Basal GH levels were unaffected by SS-(1-14). Deconvolution analysis of serum GH values demonstrated that the pituitary responded to two GHRH stimuli 90 min apart without attenuation of the second response. The higher dose of SS-(1-14) significantly blunted the first GH response; second GH responses were further attenuated by both SS-(1-14) doses. Maximum GH release and "switch-off" rates for both stimuli were reduced without changes in the 50% secretion time. Pyridostigmine enhanced the first GH response to GHRH with an increase in the GH release rate; second GH responses were not augmented. GH secretion was prolonged by pyridostigmine, although the 50% secretion time remained unchanged. Peak stimulated serum TSH was attenuated by both SS-(1-14) doses, but pyridostigmine had no effect. All other TSH parameters examined were unaffected. We conclude that the GH response to GHRH is dependent on SS tone, but that the thyrotroph is not tonically inhibited by SS. SS attenuates the rate of GH release without changing the duration of secretion and appears important in terminating GH secretion.

Adult↗
PubMed1985

Learning and integration of rewarding and aversive stimuli in the rat lateral hypothalamus.

Single neuron activity was recorded in the lateral hypothalamus (LHA) and lateral preoptic-anterior hypothalamic area (IPOA-AHA) of the rat during discrimination learning of cue tones that predicted glucose or intracranial self-stimulation as rewarding stimuli, or electric shock or tail pinch as aversive stimuli, using identical behavior, licking. Rewarding and aversive stimuli had opposite effects on the same LHA neurons, but had the same effects on IPOA-AHA neurons. Neurons in the LHA that differentiated between reward and aversion acquired discrimination of the respective cue tones, while IPOA-AHA neurons responded in the same way to cue tones whether they preceded reward or aversion. The results suggest reward- and aversion-related integrative functions in the LHA and arousal or attentional functions in the IPOA-AHA.

Animals↗
PubMed1984

[The conduction of optic nerve fibers using different visual patterns].

The Authors have studied the behaviour of checkerboard pattern visual evoked potential (VEP) latencies by using different spatial frequency stimuli and different stimulating visual fields in order to demonstrate whether spatial frequency might constitute a parameter capable of exciting different retinal regions like different stimulus fields. According to the recent literature low spatial frequency stimuli generate VEP with latencies which are significantly shorter than high spatial frequency stimuli, making this method more reliable for the differentiation of macular and peripheral retinal fields.

Adult↗
PubMed2005

The anterior cingulate cortex contains distinct areas dissociating external from self-administered painful stimulation: a parametric fMRI study.

The anterior cingulate cortex (ACC) has a pivotal role in human pain processing by integrating sensory, executive, attentional, emotional, and motivational components of pain. Cognitive modulation of pain-related ACC activation has been shown by hypnosis, illusion and anticipation. The expectation of a potentially noxious stimulus may not only differ as to when but also how the stimulus is applied. These combined properties led to our hypothesis that ACC is capable of distinguishing external from self-administered noxious tactile stimulation. Thermal contact stimuli with noxious and non-noxious temperatures were self-administered or externally applied at the resting right hand in a randomized order. Two additional conditions without any stimulus-eliciting movements served as control conditions to account for the certainty and uncertainty of the impending stimulus. Calculating the differences in the activation pattern between self-administered and externally generated stimuli revealed three distinct areas of activation that graded with perceived stimulus intensity: (i) in the posterior ACC with a linear increase during external but hardly any modulation for the self-administered stimulation, (ii) in the midcingulate cortex with activation patterns independent of the mode of application and (iii) in the perigenual ACC with increasing activation during self-administered but decreasing activation during externally applied stimulation. These data support the functional segregation of the human ACC: the posterior ACC may be involved in the prediction of the sensory consequences of pain-related action, the midcingulate cortex in pain intensity coding and the perigenual ACC is related to the onset uncertainty of the impending stimuli.

Adult↗
PubMed1984

The effect of eccentricity and colour on negativity in pattern onset visual evoked potentials.

The effects of stimulus size, eccentricity and colour on the amplitudes of N100 and N130 were investigated in pattern onset VEPs. For black-and-white pattern stimulation, the first set of stimuli was derived from a full dartboard pattern. Central stimulation of various extents was produced by patterns with reduced number of outer rings and for eccentric stimuli a number of central rings were removed from the full pattern. It was found that amplitude of N100 was maximal in VEPs to central stimuli and that it was greatly reduced when eccentric stimulation was applied. The amplitude of N130 showed no significant change in relation to the type of stimulus. When checkerboard stimuli of identical configuration were used for black-and-white pattern stimulation instead of dartboards, systematic changes in peak latencies of N100 were observed in relation to check size. In VEPs to centrally presented small checks the emergence of an early negative peak preceding N100 was recorded at 75 msec. In VEPs to coarse checkerboards presented centrally N100 was often observed with a delayed peak latency of 110 msec. Changes in N130 were not regular when checkerboards with different check sizes were presented centrally. For eccentric checkerboard stimulation, both negative peaks N100 and N130 were revealed. Their peak latencies were similar to those observed in the case of dartboard paracentral stimulation. In VEPs to patterns projected through red or blue filters, regular changes were observed in both negative peaks. Introduction of the red filter led to enhancement of the N100 amplitude in VEPs to dartboard and to checkerboards with fine checks, but it caused no effect on N100 in the VEPs to coarse checkerboards. Introduction of the blue filter led to a decrease in the N100 amplitude in VEPs to dartboard and fine checkerboards and to a slight increase of N100 in VEPs to coarse checkerboards. Changes in N130 were observed only when the blue filter was introduced and they corresponded to those which take place when the level of illumination changes from photopic to mesopic.

Color Perception↗
PubMed1986

Functional characterization of preganglionic neurons projecting in the lumbar splanchnic nerves: vasoconstrictor neurons.

Lumbar preganglionic neurons, which project in the lumbar splanchnic nerves and which probably have a vasoconstrictor function (visceral vasoconstrictor, VVC neurons), were analyzed for their discharge patterns. The responses of these neurons to the following natural stimuli were tested: stimulation of arterial baroreceptors, arterial chemoreceptors and visceral afferents from the urinary bladder, the colon and the mucosal skin of the anus. Forty-nine preganglionic neurons were classified as VVC neurons. They showed the following characteristics: the ongoing activity of the VVC neurons exhibited pronounced cardiac rhythmicity and correlated with the cycle of the artificial ventilation. Stimulation of arterial baroreceptors, produced by increase of blood pressure or by increase of pressure in an isolated carotid blind sac, led to inhibition of activity in VVC neurons. Unloading of arterial baroreceptors, produced by decrease of blood pressure, led to an increase in VVC neuron activity. Stimulation of arterial chemoreceptors by bolus injections of CO2-enriched saline solution, close to a carotid glomus, led to a weak excitation of VVC neurons. Stimulation of arterial chemoreceptors by systemic hypoxia led to weak excitation and/or to depression of activity in VVC neurons. Stimulation of visceral afferents from urinary bladder and colon by isovolumetric contractions and distensions of the organs had no effect on most VVC neurons. Anal stimulation also did not induce reflexes in the majority of the VVC neurons. Some 14% of the VVC neurons (7 from 49) were excited by at least one of the visceral stimuli in the same manner as the motility-regulating (MR) neurons. This investigation shows that preganglionic neurons, probably involved in regulation of vascular resistance in colon and pelvic organs, are functionally a distinct population of neurons with some interesting functional overlap with the motility-regulating neurons.

Animals↗
PubMed1986

Hypothalamic neuron involvement in integration of reward, aversion, and cue signals.

The lateral hypothalamus (LHA) is involved in integrative functions related to emotion, reward, aversion, and learning. It is, however, unclear whether the medial forebrain bundle (MFB) forms a substrate common to the anterior and posterior hypothalamic areas or whether information regarding rewarding and aversive stimuli converges on and is integrated by the same hypothalamic neuron. In the present study, unit activity in the LHA and lateral preoptic-anterior hypothalamic area (lPOA-AHA) of the rat was recorded during discrimination learning of cue tone stimuli (CTS) that predicted glucose or intracranial self-stimulation (ICSS) as rewarding stimuli, or electric shock or tail pinch as aversive stimuli, using identical behavior, licking. We examined functional differences between the LHA and lPOA-AHA. In positive reinforcement experiments a rat was rewarded by glucose or ICSS only when it licked a spout presented in front of its mouth. The threshold current for ICSS was used. In negative reinforcement experiments an aversive stimulus, either electric shock or tail pinch was applied if the rat did not lick the spout. The strengths of electric shock and tail pinch were selected to produce an avoidance ratio less than 20-30%, averaged in all trials. The activity of 507 LHA and 249 lPOA-AHA neurons was analyzed during both glucose and ICSS trials. The effects of both glucose and ICSS on the same LHA or lPOA-AHA neuron were usually in the same direction, i.e., either both excitatory or both inhibitory. Of 143 LHA and 44 lPOA-AHA neurons that responded to both rewards, the responses of 117 (81.8%) LHA and 35 (79.5%) lPOA-AHA neurons to both stimuli were similar. The activity of 131 LHA and 153 lPOA-AHA neurons was analyzed in both electric shock and tail pinch trials. The effects of both electric shock and tail pinch on the same LHA or lPOA-AHA neuron were usually in the same direction. Of 29 LHA and 27 lPOA-AHA neurons that responded to both aversive stimuli, the responses of 28 (96.6%) LHA and 25 (92.6%) lPOA-AHA neurons to both were similar. The activity of 170 LHA and 195 lPOA-AHA neurons in response to both rewarding glucose and/or ICSS stimulation and aversive electric shock and/or tail pinch was analyzed. About one-third of the neurons in each area were reward specific (57/170 in LHA; 63/195 in lPOA-AHA), whereas relatively few were aversion specific in each area (21/170 in LHA; 15/195 in lPOA-AHA).(ABSTRACT TRUNCATED AT 400 WORDS)

Acoustic Stimulation↗
PubMed2001

Can estrogen influence the response to noxious stimuli?

STUDY OBJECTIVES: To evaluate estrogen-induced alternations in noxious stimuli response. DESIGN: Randomized, prospective, double-blind study. SETTINGS: Tertiary-care academic medical center. PATIENTS: 40 ASA physical status I and II women at the beginning and conclusion of an in vitro fertilization stimulation cycle. INTERVENTIONS: Stimuli were applied to the fingers of the dominant hand via a Basile Analgesy-Meter, which applied increasing pressure (g/cm(2)) in a continuous fashion, and ice water immersion. MEASUREMENTS: Serum hormonal concentrations and responses to noxious (pressure and cold thermal) stimuli were studied. MAIN RESULTS: Estrogen and progesterone concentrations changed from 377 +/- 323.42 pg/mL to 2078.05 +/- 1175.92 pg/mL (p < 0.001) and 1.20 +/- 0.56 to 1.03 +/- 0.35 ng/mL (p = NS), respectively. Although no significant difference was noted in the response to pressure (16.92 +/- 4.41 to 17.85 +/- 4.95 g/cm(2)), a significant reduction in the tolerance to ice water immersion (34.18 +/- 28.29 to 24.05 +/- 23.02 s) was observed. CONCLUSIONS: High estrogen concentrations are associated with significantly lower tolerance to cold, but not pressure stimuli.

Adult↗
PubMed1984

Stimulatory and inhibitory effects of prostaglandin E2 on prolactin release in the domestic fowl.

In vivo prolactin secretion was increased in immature cockerels 20-30 min after the intravenous administration of prostaglandin (PG) E2 at a dose of 200 micrograms/kg. The addition of PGE2 to incubation medium had no direct effect on the release of pituitary prolactin during short-term (3-hr) culture, but augmented the stimulatory effect of hypothalamic tissue on prolactin secretion. The stimulatory effect of serotonin, noradrenaline, acetylcholine, and histamine on hypothalamus-induced prolactin release was also increased when pituitaries were coincubated with 10(-7)M PGE2, as was the stimulatory effect of thyrotrophin-releasing hormone (TRH) and hypothalamic extract (HE). The long-term (24-hr) preincubation of pituitaries with 10(-7)M PGE2 reduced the responsiveness of the prolactin-secreting cells to TRH or HE stimulation. PGE2 treatment also reduced the stimulatory effect of hypothalamic tissue on prolactin release and diminished the stimulatory effect of serotonin on hypothalamus-induced prolactin secretion. A 24-hr preincubation of hypothalamic tissue with 10(-7)M PGE2 also reduced its stimulatory effect on prolactin release when subsequently incubated with control pituitary glands. These results demonstrate that PGE2 initially stimulates in vivo and in vitro prolactin secretion in the fowl, possibly by increasing the release of hypothalamic prolactin-releasing activity and/or by increasing pituitary sensitivity to provocative stimuli. Chronic PGE2 stimulation appears to result in a reduction in pituitary responsiveness to stimulatory influences and in the release of hypothalamic-releasing activity.

Acetylcholine↗
PubMed1989

[Neuronal reactions of the reticular nucleus and adjacent thalamus structures in the cat to natural stimulation in a chronic experiment].

Spike responses of 104 neurons of the nucleus reticularis thalami (R) and neighbouring thalamic nuclei to the acoustic stimuli, tactile and visual stimulation were studied in the chronic experiment. 29% of neurons responded to the acoustic stimulation and 11% of them were not specific to different acoustic stimuli. The minimal latency of the excitation to the acoustic stimulation was 12-37 ms and that of the inhibition--18-27 ms. The duration of the excitation in response to the acoustic stimulation was 50-250 ms and that of inhibition--27-190 ms. 16% of R neurons responded to the stimulation of different sensory systems. The majority of R neurons showed excitation in response to different stimuli and only 4-10% of neurons showed inhibition.

Animals↗
PubMed2005

External inferior colliculus integrates trigeminal and acoustic information: unit responses to trigeminal nucleus and acoustic stimulation in the guinea pig.

The external nucleus of the inferior colliculus (ICx) receives ascending projections from both auditory and somatosensory nuclei. In the guinea pig, both the spinal trigeminal nucleus (TN) and the cochlear nucleus converge in the ventrolateral region of ICx. We investigated the function of trigeminal-collicular pathways by electrically stimulating the TN while recording unit responses from ICx. Pairing electrical stimulation with acoustic stimuli allowed us to investigate the function of converging auditory and somatosensory inputs, i.e. multisensory integration. Unit responses were recorded from ICx using a multi channel, single shank electrode. Electrical stimulation of the TN produced small changes above or below spontaneous rate, but resulted in significant suppression or enhancement of sound-evoked responses. Multisensory integration has been demonstrated in the dorsal cochlear nucleus (DCN), superior colliculus and sensory cortices and may play a role in plasticity that occurs after sensory deprivation.

Acoustic Stimulation↗