Physiology & behavior
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Physiology & behavior · Aug 1997
Ventromedial hypothalamus lesions increase the dipsogenic responses and reduce the pressor responses to median preoptic area activation.
In this study, we investigated the participation of adrenergic receptors of the median preoptic area (MnPO) and the participation of ventromedial hypothalamus (VMH) in angiotensin II-(ANG II)-induced water intake and pressor responses. Male rats with sham or electrolytic VMH lesions and a stainless steel cannula implanted into the MnPO were used. Noradrenaline, clonidine (an alpha2-adrenergic receptor agonist), or phenylephrine (an alpha1-adrenergic receptor agonist) injected into the MnPO of sham-lesioned rats reduced water ingestion induced by ANG II injected into the same area. ⋯ The pressor response induced by ANG II injected into the MnPO was reduced in VMH-lesioned rats, whereas the pressor response induced by clonidine was abolished. Previous treatment with noradrenaline and phenylephrine into the MnPO of sham-lesioned rats produced a pressor response, and a hypotensive response was obtained with the previous administration of noradrenaline, phenylephrine or isoproterenol into the MnPO of VMH-lesioned rats. These results show that VMH is essential for the dipsogenic and pressor responses induced by adrenergic and angiotensinergic activation of the MnPO in rats.
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Physiology & behavior · Mar 1997
Cholinergic and GABAergic modulation of self-stimulation of lateral hypothalamus and ventral tegmentum: effects of carbachol, atropine, bicuculline, and picrotoxin.
This study aimed at investigating the effects of modulators of acetylcholine-muscarinic (ACh-M) and GABAA. B-receptors in the lateral hypothalamus and ventral tegmentum on the electrical self-stimulation evoked from these regions. In each Wistar rat, a bipolar electrode and an ipsilateral insulated cannula-cum-electrode were implanted chronically in the right hemisphere. ⋯ On the contrary, changes in ICSS of LH-MFB following Ach-M receptor ligands do not influence the ICSS of VTA-SN. The direct effects of GABA-receptor antagonists have shown disassociation because ICSS of LH-MFB was more sensitive to bicuculline, whereas the ICSS of VTA-SN was more sensitive to picrotoxin. Thus, the cholinergic and GABAergic mechanisms of the self-stimulation of lateral hypothalamus and ventral tegmentum are different.
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This study was designed to compare the renal effects of sedation with alphaxalone-alphadolone, etomidate, propofol, midazolam, fentanyl-fluanisone, and thiopental in rats. The sedative dose was defined as the highest dose that abolished the escape response without affecting the righting reflex. Female Wistar rats were chronically catheterized with a jugular vein catheter, and urine flow rate and renal clearances of inulin (glomerular filtration rate = GFR), sodium, and lithium (used as an index of proximal tubular function) were measured in the conscious, unrestrained state (n = 107 experiments). ⋯ Propofol and fentanyl-fluanisone reduced fractional lithium excretion by 9-13%. Only alphaxalone-alphadolone, etomidate, and midazolam produced sedation without affecting renal function in rats. Because midazolam produced the most consistent degree of sedation, we conclude that midazolam is the least confounding sedative agent for renal function studies in conscious rats.
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Physiology & behavior · Mar 1996
Comparative Study Clinical TrialSensitization and desensitization to capsaicin and menthol in the oral cavity: interactions and individual differences.
It was reported in a recent study that, like capsaicin, menthol is capable of producing a desensitization to sensory irritation in the oral cavity. Whereas capsaicin is known to be able to cross-desensitize with other chemical irritants, no such information exists for menthol. To address this question, the first experiment was designed to reveal whether cross-desensitization would occur between menthol and capsaicin. ⋯ The latter outcome was investigated in a second experiment in which the effect of capsaicin desensitization on the perception of physical as well as chemical (menthol) cooling was measured when the stimuli were presented as oral rinses. No desensitization was found for either form of stimulation, which implied the apparent desensitization of coolness in Experiment I may have been due to the difficulty of discriminating sensations of cold from sensations of chemical irritation. The overall findings are discussed in terms of the complex sensory and perceptual interactions that take place within the chemesthetic modality.
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Physiology & behavior · Feb 1996
A noninvasive method for studying quantitatively heat-evoked nocifensive hindlimb withdrawal reflexes in lightly anesthetized rats.
We have developed a noninvasive method for studying quantitatively the magnitude of hindlimb withdrawal reflexes induced by noxious heat in lightly anesthetized rats. The amplitude, latency, and duration of the hindlimb withdrawal was determined by a very small piezoceramic device placed on the hamstring muscle while the glabrous skin of the hindpaw was stimulated using a feedback-controlled contact thermostimulator. ⋯ The sensitivity of the method was verified using morphine, which produced a dose-related (3.5-7.0 mg/kg) attenuation of all these response components. The use of a piezoceramic device for measuring the withdrawal response provides a quantitative, noninvasive method for evaluating the magnitude of various components of the nocifensive withdrawal reflexes induced by noxious stimuli in lightly anesthetized rats.