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At least 19 recordsLinked to original sources
PubMed1977

[Increase in stability of isolated tissues and proteins caused by the action of chemical stimulants].

Chemical agents in subtoxic concentrations prolongate the survival time of living muscles and the time of contractile ability of glycerinated muscles. They preserve also the native property of actomyosine over the control time. The increase of resistance of living muscles and their models may be explained by stabilization of proteins or of their complexes. It is accompanied by the change of the indices of the functional state of the living muscle--by the decrease of the binding of vital dyes, by the hyperpolarization, by reducing the consumption of O2 and by the conservation of the quantity of SH groups at the high level.

Actomyosin↗
PubMed1994

[Brainstem mechanisms of vocalization analyzed by electrical stimulation and chemical stimulation of sodium glutamate in cats].

The functional connection between the midbrain and the lower brain structures which organize vocalization was investigated in cats. To induce vocalization, repetitive electrical stimulation (0.2ms, 10-300 microA, 100Hz, lasting for 5 to 10s) was delivered to the caudal part of the ventrolateral periaqueductal gray (PAG), adjacent reticular formation (RF) or the pontine call site (PCS) which is located in the ventrolateral pontine RF. In Ketamine-anesthetized cats (n = 12), the stimulus threshold was the lowest in the ventrolateral PAG, and the stimulus threshold within the RF near the PAG tended to be higher than that in the PAG. In the effective RF area, the stimulus threshold was lower in the ventral area than that in the dorsal area. The effective area extended from the PAG through the RF to the PCS. The stimulus threshold around the PCS was the lowest in all animals. The size of the effective area was about 1 to 1.5mm in diameter within the PAG and the RF, and was wider than that in the PCS, which was about 0.5 to 1.0mm in diameter. There was a tendency for a wider effective area to correlate with a higher stimulus threshold. These results suggest that axons from the PAG area pass through the nearby RF and then compose a narrower fiber bundle in the PCS. In unanesthetized decerebrate cats (n = 5), a microinjection of glutamate, (2M sodium glutamate dissolved in 0.1M phosphate buffer (pH = 7.4)), was made with a glass micropipette (tip outer diameter: 200 microns) attached to a microsyringe with a polyethylene tube.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1979

A modification of the dialytrode for simultaneous CNS recording and chemical stimulation.

Currently, chemical stimulation of the brain is done either with a single cannula that is inserted at the time the drug is delivered or with two cannulae that permit perfusion of the area of interest. The dialytrode is a push-pull cannula consisting of two concentric tubes, a porous membrane covering the tip of the tubing and a platinum wire loop that extends around the membrane and is used for EEG recordings. Studies with the dialytrode indicate that while the membrane is relatively impermeable to bacteria, molecules the size of neurotransmitters pass easily through the membrane. Therefore, the dailytrode is well suited for chronic chemical stimulation studies.

Amygdala↗
PubMed1995

Effect of chemical stimulation of the dorsal raphe nucleus on cerebral blood flow in rat.

We have previously shown that electrical stimulation of the dorsal raphe nucleus (DRN) can increase or decrease cerebral blood flow (CBF). We now sought to determine whether the CBF responses are mediated by DRN neurons or fibers of passage. In anesthetized rat, the DRN was stimulated chemically (L-glutamate, kainate) and CBF in parietal cortex was measured by laser-Doppler flowmetry. Microinjection of kainate (5 nmol), but not L-glutamate, into DRN increased CBF (28 +/- 22%; P < 0.05). Decreased CBF to DRN stimulation was not observed. We conclude that stimulation of DRN neurons increases CBF.

Animals↗
PubMed1999

Measurement of corneal sensitivity to mechanical and chemical stimulation with a CO2 esthesiometer.

PURPOSE: To develop an instrument to measure corneal sensitivity. Mechanical stimulation was performed with increasing air flow. Chemical stimulation consisted of local pH decreases induced by a mixture of air and CO2 at different concentrations. METHODS: Air and 98.5% CO2 were mixed with an electronic, proportional-direction control valve to obtain gas mixtures from 0% to 80% CO2. The regulated outflow of gas was carried to a probe mounted on a slit lamp holder, where it was warmed and its CO2 concentration monitored. An electronic valve directed gas pulses of controlled duration to the cornea. Corneal stimulation was performed in 17 young human subjects. The intensity of the experienced sensation was recorded in a continuous visual analog scale (VAS). To obtain threshold values and intensity-response curves, 3-second pulses were applied. For mechanical stimulation, air pulses of increasing flow were used. For chemical stimulation, gas mixtures of increasing CO2 concentration at subthreshold flow and CO2 in stepped increases of 5% was applied. RESULTS: Mechanical and chemical stimulation of the cornea evoked a brief sensation of irritation. Mechanical threshold (flow values) varied among subjects but were reproducible within each subject and were higher with warmed air. The magnitude of the sensation increased proportionally to the flow of air. The mean chemical stimulation threshold (CO2 concentration) was 25% +/- 3%. Increases in CO2 concentration from 10% to 80% augmented proportionally the intensity of the evoked sensation. CONCLUSIONS: The gas esthesiometer, which combines variable air flow and CO2 concentrations, permits application to the cornea of mechanical stimuli of controlled force and pH reductions of increasing magnitude. This instrument may be useful in a separate exploration of mechanical and chemical sensitivity of the cornea in human subjects.

Adult↗
PubMed1998

Responses of neurons in the parabrachial region of the rat to electrical stimulation of the superior laryngeal nerve and chemical stimulation of the larynx.

The responsiveness of the parabrachial region to electrical stimulation of the superior laryngeal nerve was first examined in anesthetized rats. Action potentials were recorded in 30 parabrachial sites by single and train electrical pulses to the superior laryngeal nerve. The average latency, from the onset of stimulation to the first action potentials, was 9.9 ms (range, 6.5-18.8 ms). The responsiveness of parabrachial neurons to chemical stimulation of the laryngeal region was next examined using anesthetized, immobilized, and artificially ventilated rats in which the chorda tympani and glossopharyngeal nerves were bilaterally sectioned. Taste stimuli were applied to the laryngeal region through a tracheal tube and rinsed with 0.15 NaCl. A total of 66 responses were recorded from 26 neurons. The most effective stimulus for these neurons was 0.03 M hydrochloric acid, followed by 0.01 M quinine hydrochloride, 0.5 M sodium chloride, 0.5 M sucrose, and distilled water. Seven responses were derived from 0.15 NaCl. These neurons were mainly located in a posterodorsolateral part of the parabrachial nucleus. These results suggest that chemical signals from the laryngeal region are transmitted to the parabrachial nucleus through the superior laryngeal nerve.

Action Potentials↗
PubMed1978

Chemical stimulation of single human fungiform taste papillae: sensitivity profiles and locus of stimulation.

Psychophysical responses to chemical stimulation of single human fungiform taste papillae were obtained from 40 papillae in four subjects. Effects of solution concentration and locus of stimulation were examined for nine test compounds. Sensitivity profiles constructed for individual papillae showed that single fungiform papillae mediate more than a single taste quality. In addition, the chemical sensitivities of individual papillae were reflected in their thresholds for all compounds, and correlation coefficients between recognition thresholds were no greater for similar than for dissimilar tasting compounds. No differences in mediation of quality were found as a function of locus of stimulation on the papilla, although sensitivity was found to be greater on the dorsal surface than on the sides. The data were discussed within the context of previous studies of response characteristics of single papilla.

Adolescent↗
PubMed1981

Modulation by the hypothalamus of glucagon and insulin secretion in rabbits: studies with electrical and chemical stimulations.

The effects of electrical and chemical stimulations of the hypothalamus on the plasma levels of glucagon, insulin, and glucose were studied in undisturbed and free-moving rabbits. Electrical stimulation of the ventromedial hypothalamic nucleus (VMH) caused a marked increase in the circulating level of glucagon coincident with a rapid rise in the glucose level. The level of insulin did not increase during VMH stimulation, but increased after cessation of stimulation. Electrical stimulation of the lateral hypothalamic nucleus (LHN), on the other hand, did not alter the plasma level of either hormone. Microinjection of a minute amount of acetylcholine into the VMH led to a rapid increase in plasma glucagon, with a gradual rise in plasma glucose, but no significant change in the insulin level. The responses of glucagon and glucose to acetylcholine were almost completely blocked by previous treatment of the VMH with hexamethonium, but not with atropine. Microinjections of epinephrine and norepinephrine into the VMH also caused rises in the levels of both glucagon and insulin, although the effects of norepinephrine were much less than those of epinephrine. Injections of dopamine, serotonin, and gamma-aminobutyric acid had no effect. Chemical stimulation of the LHN only with epinephrine induced a preferential rise in the insulin level without any significant change in the levels of glucagon and glucose. It is concluded that the actions of acetylcholine in the VMH, probably though activation of nicotinic receptor, and of epinephrine in the LHN are important for hypothalamic modulation of the selective releases of glucagon and insulin, respectively. (Endocrinology 108: 605, 1981)

Acetylcholine↗
PubMed1991

Chemical stimulation of the ventrolateral medullary depressor area decreases ipsilateral cerebral blood flow in anesthetized rats.

In anesthetized (chloralose and urethane), paralyzed and artificially ventilated rats, the neurons in the ventrolateral medullary depressor area (VLDA) were chemically stimulated by microinjections of L-glutamate (2.5-5 nmole in 100 nl of 0.9% sodium chloride solution) and the cerebral blood flow (CBF) was determined using a combination of labeled microspheres (57Co, 113Sn and 46Sc). Unilateral chemical stimulation of the VLDA (n = 11) produced a significant (P less than 0.05) decrease in CBF of the cerebral cortex ipsilateral to the stimulated VLDA; the CBF was 41 +/- 5 (mean +/- S.E.M.) and 29 +/- 4 ml.min-1.(100 g)-1 before and during the chemical stimulation of VLDA. The decrease in CBF was not due to the decrease in arterial blood pressure (ABP) caused by the chemical stimulation of the VLDA because the CBF during the chemical stimulation of the VLDA was significantly smaller (P less than 0.01) than the CBF during controlled hemorrhagic hypotension (n = 10). In another group of rats (n = 6), moderate hypertension was induced by blood transfusion. Unilateral chemical stimulation of the VLDA in these rats decreased ABP but it remained within normotensive range. A significant (P less than 0.05) decrease in CBF (from 46 +/- 12 to 29 +/- 7 ml.min-1.(100 g)-1) and a significant (P less than 0.01) increase in cerebrovascular resistance (from 2.7 +/- 0.4 to 4.3 +/- 0.6 mmHg per [ml.min-1.(100 g)-1]) was observed in the ipsilateral cerebral cortex of these rats. Chemical stimulation of the VLDA did not affect the reactivity of the cerebral vessels to hypercapnea (n = 5).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1995

Morphine, 5-HT2 and 5-HT3 receptor antagonists reduce c-fos expression in the trigeminal nuclear complex following noxious chemical stimulation of the rat nasal mucosa.

Noxious chemical stimulation of the rat nasal mucosa induces the expression of the immediate early gene c-fos in trigeminal brainstem neurons. In the present study, we applied the irritant mustard oil (1%) into the left nostril of urethane anesthetized rats. Immunohistochemical methods were used to evaluate the expression of Fos protein in the trigeminal subnuclei interpolaris and caudalis and to test the effects of putative analgesics that might depress synaptic transmission in neurons related to nociception. For this purpose, morphine (3 mg/kg and 10 mg/kg), the 5-HT2 antagonist ketanserin (0.5 mg/kg and 5 mg/kg) and the 5-HT3 antagonist ICS 205-930 (0.1 mg/kg and 1 mg/kg) were administered intravenously prior to noxious stimulation. Pretreatment with any of the three compounds reduced Fos-like immunoreactivity. The effect of morphine was reversible with naloxone. The reduction of the expression of Fos-like immunoreactivity by exogenous morphine speaks in favour of an opioidergic link in the modulation of orofacial pain in the trigeminal nuclei. The effects of the 5-HT receptor antagonists are most likely mediated via 5-HT2 and 5-HT3 receptors located on primary afferent fibres.

Animals↗
PubMed1998

Autoradiographic determination of local cerebral blood flow and local cerebral glucose utilization during chemical stimulation of the nucleus tractus solitarii of anesthetized rats.

This study was conducted to determine whether the decrease in cerebral blood flow (CBF) observed during chemical stimulation of the nucleus tractus solitarius (NTS) can be explained by a decrease in cerebral metabolism. In anesthetized (urethane and chloralose), paralyzed and artificially ventilated rats, neurons in the NTS were chemically stimulated by microinjection of L-glutamate. Local cerebral blood flow (LCBF) and local cerebral glucose utilization (LCGU) were quantified in 43 brain structures by quantitative autoradiographic techniques using [14C]iodoantipyrine and 2-[14C]deoxyglucose, respectively. During chemical stimulation of the NTS (n = 6), LCBF decreased significantly in 32 of the 43 structures investigated when compared to either a control group with artificial cerebrospinal fluid injection (n = 6), or a controlled hemorrhage group (n = 5). In the controlled hemorrhage group, blood pressure was decreased to a degree comparable to that induced by microinjection of L-glutamate into the NTS. Mean blood flow of all structures investigated was significantly (P < 0.01) lower in the stimulation group than that in the control group and in the hemorrhage group. No significant differences in LCGU were observed between the three investigated groups in all structures examined except for an increase in LCGU in the chemically stimulated NTS site. It is concluded that the decrease in LCBF measured in most brain structures during chemical stimulation of the NTS is not caused by a decrease in LCGU in these structures and may therefore be explained by neurogenic influences on brain vessels.

Animals↗
PubMed1997

Role of spinal GABA receptors in depressor responses to chemical stimulation of the A5 area in normal and hypertensive rats.

Chemical stimulation of neurons in the pontine A5 area by microinjection of L-glutamate lowers arterial blood pressure. The mechanism of this 'A5 depressor response' is not well-established. Here, we examine the involvement of spinal cord gamma-aminobutyric acid (GABA) receptors in this depressor response in normotensive Wistar-Kyoto rats (WKY) and spontaneously hypertensive rats (SHR). Experiments were conducted in male WKY and age-matched SHR anaesthetised with sodium pentobarbitone and chloral hydrate. An intrathecal catheter was implanted with the tip located between T9 and L2. Three days later, rats were re-anaesthetised and 10 nl of 40 mM L-glutamate was injected into the A5 area before, during and after, blockade of spinal cord GABA-A receptors by intrathecal injection of bicuculline methiodide (1 mM in 10 microliters phosphate-buffered saline). Injection of L-glutamate (10, 20, 40, 80 mM in 10 nl) produced depressor responses that were similar in WKY (n = 6) and SHR (n = 6). Intrathecal injection of bicuculline elicited a pressor response that was greater in SHR (n = 7, 28.5 +/- 7.6% increase in mean arterial pressure) than WKY (n = 11, 11.6 +/- 3.6%, p < 0.05). After bicuculline, the depressor response to injection of L-glutamate into the A5 area was eliminated in both WKY (n = 7) and SHR (n = 6). Intrathecal injection of vehicle had no effect on either resting arterial blood pressure or the depressor response to A5 stimulation. Basal blood pressure and control responses to A5 stimulation were fully restored by around 90 min after bicuculline injection in each animal. In separate groups of rats, intrathecal injection of muscimol elicited depressor responses that were greater in SHR (n = 6, -32.0 +/- 6.2%) than WKY (n = 6, -17.3 +/- 1.5%, p < 0.05). Our results suggest that the A5 depressor response is due to a projection from the A5 area to the spinal cord. This projection acts directly, or through a spinal interneuron and uses GABA as a neurotransmitter. Furthermore, our results indicate a hyper-responsiveness to GABA-A receptor stimulation in SHR since intrathecal bicuculline elicited much greater increases and intrathecal muscimol elicited much greater decreases, in blood pressure in SHR than in WKY. Finally, it seems likely that the A5-spinal depressor pathway is less effective in SHR than WKY under physiological conditions since chemical stimulation of the A5 area with L-glutamate produced a comparable depressor response in both strains.

Animals↗
PubMed1997

Cerebral extracellular lactate concentration and blood flow during chemical stimulation of the nucleus tractus solitarii in anesthetized rats.

The extracellular lactate concentration and blood flow in the cerebral cortex of urethane-anesthetized, paralyzed and artificially ventilated rats were monitored continuously and simultaneously using an enzyme electrode and a laser Doppler flowmeter (LDF), respectively, during chemical stimulation of the nucleus tractus solitarii (NTS) by microinjection of L-glutamate (1.7 nmol 50 nl). Chemical stimulation of the NTS significantly decreased the arterial blood pressure (ABP) from 85 +/- 17 to 68 +/- 14 mmHg, heart rate from 418 +/- 13 to 402 +/- 19 beats x min(-1) and cerebral blood flow (CBF) by 17.9 +/- 6.2% (P < 0.001). However, chemical stimulation of the NTS significantly increased the lactate concentration by 58.9 +/- 17.3 microM (P < 0.001). Barostat maneuver, which held systemic ABP constant during chemical stimulation of the NTS attenuated the responses in CBF and lactate concentration by 30 and 27%, respectively. The onset of the increase in lactate concentration was delayed about 19 s after that of the CBF decrease. Circulatory lactate produced no significant change in the cerebral extracellular lactate concentration. These results indicate that chemical stimulation of the NTS induces an increase in extracellular lactate concentration in the cerebral cortex through a decrease in CBF via cerebral vasoconstriction.

Animals↗
PubMed1990

Chemical stimulation of the nucleus tractus solitarii decreases cerebral blood flow in anesthetized rats.

In anesthetized (chloralose and urethane), paralyzed and artificially ventilated rats, the neurons in the nucleus tractus solitarius (NTS) were chemically stimulated by microinjections of L-glutamate and the cerebral blood flow (CBF) was determined using a combination of labeled microspheres (either 57Co, 113Sn and 46Sc or 141Ce, 85Sr and 46Sc). Unilateral chemical stimulation of the NTS (n = 14) decreased CBF significantly in most brain areas. The decrease in CBF was not due to the decrease in arterial blood pressure (ABP) because the CBF of the whole cerebral cortex during the chemical stimulation of the NTS was significantly smaller (P less than 0.05) than the CBF during controlled hemorrhagic hypotension (n = 10). In another group of rats (n = 6), moderate hypertension was induced by blood transfusion. Unilateral chemical stimulation of the NTS in these rats decreased ABP but it remained within normotensive range. A significant (P less than 0.05) decrease in CBF (from 62 +/- 28 (mean +/- S.D.) to 48 +/- 23 ml.min-1.(100 g)-1) and increase in cerebrovascular resistance (from 1.9 +/- 1.2 to 2.6 +/- 1.2 mm Hg per [ml.min-1.(100 g)-1]) was observed in the whole cerebral cortex of these rats. Chemical stimulation of the NTS did not affect the reactivity of the cerebral vessels to hypercapnea (n = 5). These results suggest that the cell bodies within the NTS may play a role in the control of cerebral circulation.

Animals↗
PubMed1996

Spinal cord lactate concentration during chemical stimulation of the nucleus tractus solitarii in anesthetized rats.

This study was conducted to determine the mechanism of spinal cord blood flow (SCBF) decrease following the nucleus tractus solitarii (NTS) activation. In urethane-anesthetized, paralyzed and artificially ventilated rats, neurons in the NTS were chemically stimulated by microinjection of L-glutamate (1.7 nmol; 50 nl) and the lactate concentration, one of indicators of local neuronal metabolism, in the spinal cord was monitored in real time using an enzyme electrode. Before the chemical stimulation study, the responses of the enzyme electrode and its specificity were tested in vitro and in vivo. The electrode responded to step changes in lactate concentration and a calibration plot and regression line were obtained in vitro. The lactate concentration was significantly (P < 0.01) increased during induced apnea in vivo (n = 8). The lactate concentration in the spinal cord was not significantly changed by chemical stimulation of the NTS when arterial blood pressure (ABP) remained above the lower limit of spinal cord autoregulation (n = 21). When chemical stimulation of the NTS decreased ABP to below the lower limit of autoregulation (n = 18), the lactate concentration in the spinal cord was significantly (P < 0.01) increased. This may only be due to hypotensive effects because the lactate concentration was also significantly (P < 0.01) increased when the ABP was passively decreased below the lower limit of autoregulation by controlled hemorrhage in intact (n = 11) and sinoaortic denervated rats (n = 10). Intravenous lactate injection produced no significant increase in the current from the enzyme electrode in the spinal cord (n = 4). Using the electrode with inactivated enzyme solution, the current from the electrode did not change with the increase in lactate in the spinal cord. These findings indicate that the enzyme electrode can detect rapid changes of lactate, a product of anaerobic metabolism. These results also indicate that the spinal cord vasoconstrictor response elicited by chemical stimulation of the NTS, which was performed above the lower limit of spinal cord autoregulation in our previous study, may be due to neurogenic regulatory mechanism, but not to the secondary effects of changes in metabolism.

Anesthesia↗
PubMed1992

Microwave-stimulated chemical fixation of whole eyes.

BACKGROUND: Microwave-stimulated chemical fixation has been used successfully to rapidly prepare nonocular tissue for processing and paraffin embedding. METHOD: This same technique was adapted to fix whole eyes using a common domestic microwave oven. Histologic sections were compared with sections from globes that were fixed in a traditional manner. RESULTS: Histologic sections and histochemical and immunohistochemical staining of eyes treated with microwave-stimulated chemical fixation in 10% neutral-buffered formalin were comparable in quality to eyes fixed in 10% neutral-buffered formalin at room temperature for 48 hours. CONCLUSION: Because microwave irradiation accelerates the most time-consuming part of preparing whole eyes for light microscopy, the technique enhances laboratory efficiency. The technique is particularly well suited for ensuring adequate fixation of globes when histologic diagnosis is needed in less than 48 hours.

Animals↗