Inhibition by topically applied clonidine and guanfacine on the pressor response to stimulation of the locus coeruleus in cats.
نویسنده
چکیده
There is considerable evidence that a adrenergic mechanisms within medulla and hypothalamus play a role in cardiovascular regulation (1-4). Apart from the action on medullary mechanisms, clonidine has been reported to elicit hypotension by an action on hypothalamic a-adrenergic receptors and the possible mechanism of action of the drug applied into the hypothalamus has hitherto been discussed in relation to the descending pathways from the hypothalamus to the medullary cardiovascular control system (3, 5-8). Contrary to this, there has been no available report referring to an effect of clonidine on the ascending noradrenergic pathway from the locus coeruleus (LC) to the posterior hypothalamus (HPA), which is assumed to be involved in regulation of arterial blood pressure (9, 10). In addition, it is not clear whether clonidine acts either as an a-adrenergic agonist at the presynaptic receptor or as an a-adrenergic antagonist at the postsynaptic receptor (3, 11). Guanfacine, N-amidino-2-(2,6-dichloro phenyl) acetamide HCI, which resembles clonidine in chemical structure, appears to produce its hypotensive effects as a result of presynaptic a-adrenoceptor stimulation at central sympathetic control systems, though the possible site of central action of the drug has not yet been defined (12, 13). Thus, it was of interest to investigate an effect of clonidine and guanfacine injected into HPA on the pressor response to electrical stimu lation of the LC. Cats of either sex weighing 2.2-3.5 kg were anesthetized with a-chloralose-ure thane. After tracheotomy, the left carotid artery was catheterized for measurement of the blood pressure with a pressure transducer. A coaxial electrode was stereo taxically inserted into right or left LC (P2, L2, H-2) according to the atlas of Berman (14) for electrical stimulation with square wave pulses of 1 msec duration at 250 Hz, 3-5 V for 10 sec. Before the drug application, the LC was stimulated electrically three or four times every 10 min to elicit nearly a constant pressor response (a rise of the mean arterial blood pressure), and three pressor responses were averaged for the control. Then, a drug solution was injected into HPA (F 9.5, L 0.8, H-2.5) at a rate of 1 /d/30 sec with a microsyringe of 1 al introduced through the guide cannula which was cemented to the skull, and the LC was stimulated to evoke a pressor response 10, 30, 60 and 90 min after injection. The drug effect was estimated by comparing the pressor responses before and after injection …
منابع مشابه
Effect of phasic electrical locus coeruleus stimulation on inhibitory and excitatory receptive fields of layer V barrel cortex neurons in male rat
Introduction: It is believed that Locus Coeruleus (LC) influences the sensory information processing. However, its role in cortical surround inhibitory mechanism is not understood. In this experiment, using controlled mechanical displacement of whiskers we investigated the effect of phasic electrical stimulation of LC on response of layer V barrel cortical neurons in anesthetized rat. Methods: ...
متن کاملEffect of sensory deprivation and Locus Coeruleus (LC) electrical stimulation on the response properties of layer IV barrel cortex neurons in male rats
Introduction: Barrel cortex of rodents is responsible for sensory information processing from muzzle whiskers. Locus coeruleus (LC) as the main source of norepinephrine (NE) in the cortex, is effective on the sensory information processing. Methods: Rats were divided to 2 groups. One group underwent sensory deprivation (P4) and the other group served as control and did not undergo sensory d...
متن کاملThe effects of locus coeruleus electrical stimulation on brain waves of morphine dependent rats
Introduction: Opiates cause dependency via affect on central nervous system. Locus coeruleus nucleus is a main group of noradrenergic neurons in the brain that plays an important role in the expression of opioid withdrawal signs. During opioid withdrawal, brain waves change in addition to physical and behavioral signs. In this study, we examined the effects of locus coeruleus electrical sti...
متن کاملRole of Orexin-A receptors within the Locus Coeruleus in the antinociception induced by microinjection of carbachol into the lateral hypothalamus
Introduction: Previous studies have shown that stimulation of lateral hypothalamus (LH) produces antinociception. Orexin-A (OXA) receptor is strongly expressed in the nucleus locus coeruleus (LC) and orexinergic fibers densely project from LH to LC. In this study, we assessed the role of LC and its OXA receptors in antinociceptive response induced by LH chemical stimulation in the rat. Meth...
متن کاملStudy of interaction between opioid and ?-2 adrenergic systems in analgesic effect of oxytocin in locus coeruleus nucleus
Introduction: Oxytocin is a active neuropeptide of central nervous system. In this study the effects of naloxone (opioid receptor antagonist) and yohimbine (α-2 adrenergic receptor antagonist) on analgesic effect of oxytocin applied into the locus coeruleus (LC) nucleus were investigated. Methods: Adult male Wistar rats were used. Animals divided into different groups receiving saline, oxy...
متن کاملذخیره در منابع من
با ذخیره ی این منبع در منابع من، دسترسی به آن را برای استفاده های بعدی آسان تر کنید
برای دانلود متن کامل این مقاله و بیش از 32 میلیون مقاله دیگر ابتدا ثبت نام کنید
ثبت ناماگر عضو سایت هستید لطفا وارد حساب کاربری خود شوید
ورودعنوان ژورنال:
- Japanese journal of pharmacology
دوره 31 5 شماره
صفحات -
تاریخ انتشار 1981