• The Korean Journal of Physiology
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• v.25 no.2
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• pp.201-209
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• 1991

The rostral ventrolateral medulla (RVLM) has been established recently as a sympathoexcitatory area. The present study was conducted to investigate whether the somatosympathetic pressor and/or depressor responses are mediated through RVLM in cats anesthetized with ${\alpha}-chloralose$. An occipital craniectomy was performed and ventrolateral medulla were stimulated either electrically or chemically to evoke changes in arterial blood pressure. And then the effect of lesions in the ventrolateral medulla on the changes in blood pressure elicited by the peripheral nerve stimulation was observed. Followings are the results obtained: 1) Pressor areas were found in the ventrolateral medulla, lateral reticular nucleus and rostral dorsal area. 2) Depressor areas were found mainly in the ventrolateral medulla rostral to the pressor areas. 3) Some areas showed biphasic responses: a depressor response to lower frequency and a pressor response to higher frequency stimulation. 4) After electrical lesion in pressor area in RVLM, the somatosympathetic pressor response was abolished or depressed markedly. The somatosympathetic depressor response, however, remained after the lesion. 5) Electrical lesion in the depressor area abolished somatosympathetic depressor response. From the above results it is concluded that somatosympathetic pressor response is mediated through RVLM, while somatosympathetic depressor response is not mediated through RVLM.

• The Korean Journal of Pharmacology
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• v.23 no.2
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• pp.77-85
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• 1987

This study was carried out to determine the role of cholinoceptors in the ventrolateral medulla on central control of blood pressure (BP) and heart rate (HR). In rats anesthetized with urethane and paralyzed, microinjections of the neuroexcitatory amino acid L-glutamate (300 ng/site) were performed to functionally identity the vasopressor area (VLPA) and the vasodepressor area (VLDA) in the ventrolateral medulla oblongata. 1. The bilateral microinjection of carbachol (300 ng/site) into the VLPA produced significantly an increase in BP and HR which was not blocked by bilateral pretreatment of hexamethoium ($4\;{\mu}g/site$). 2. The bilateral microinjection of physostigmine (200 ng/site) and oxotremorine (300 ng/site) into the VLPA produced significantly an increase in BP respectively. 3. The bilateral microinjection of atropine ($4\;{\mu}g/site$) into the VLPA produced significantly a decrease in BP and HR. 4. The bilateral micro injection of acetylcholine (500 ng/site) and dimethylphenylpiperazinium (500 ng/site) into the VLDA produced significantly a decrease in BP and HR respectively. 5. The depressor and bradycardiac responses elicited by the bilateral microinjection of acetylcholine (500 ng/site) into the VLDA were blocked by bilateral pretreatment of hexamethonium ($4\;{\mu}g/site$). The results suggest that the activation of cholinoceptors in VLPA produce hypertensive and tachycardiac responses which may be mediated by muscarinic receptors, and the activation of cholinoceptors in VLDA produce hypotensive and bradycardiac responses which may be mediated by nicotinic receptors.

• The Korean Journal of Physiology and Pharmacology
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• v.1 no.6
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• pp.639-645
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• 1997

The purpose of the present study is to determine the role of muscarinic cholinergic receptors of posterior hypothalamus in the central blood pressure regulation when respiration is controlled. In anesthetized and artificially ventilated rats, vasodepressor response was evoked by injection of L-glutamate(10 nmol) neuroexcitatory amino acid into the posterior hypothalamic area. The injection of $carbachol(0.5{\sim}8\;nmol)$ into the same area induced dose-dependent vasodepressor and bradycardic responses. Pretreatment with atropine(4 nmol) completely blocked the vasodepressor response to carbachol(2 nmol). In contrast, in spontaneously breathing rats, the injection of carbachol(8 nmol) into the posterior hypothalamic area induced the vasopressor and tachycardic responses. These results suggest that the muscarinic cholinergic receptors in the posterior hypothalamic area primarily play an inhibitory role in the central regulation of blood pressure and heart rate.

• The Korean Journal of Physiology
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• v.27 no.2
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• pp.185-197
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• 1993

The rostral ventrolateral medulla (RVLM) includes vasopressor neurons, which transmit activation signals to the intermediolateral nucleus (IML) of the spinal cord, where the preganglionic sympathetic nucleus is located, to raise arterial blood pressure (BP). However, controversy exists as to the possible depressor area in the RVLM and the pathway involved. The present study persued evidence far the location of depressor neurons and the pathway by simultaneously observing changes in BP and the firing rate (FR) of cardiovascular neurons (CVNs) in the RVLM during the somatosympathetic reflex (SSR) elicited by peripheral nerve stimulation, since CVNs are known to contribute to the generation of the sympathetic nerve discharge. In 42 cats, anaesthetized with $\alpha-chloralose$, single unit recording was performed, using carbon filament electrodes inserted into the RVLM, enabling estimation of the post R wave unit histogram (PR-UNlT) and the spike triggered average of sympathetic nerve discharge (STA-SND), allowing identification of CVNs. Antidromic stimulation of spinal $T_2$ segment was followed to determine whether the identified CVN projects axonal endings to the spinal cord (reticulospinal neuron). The sciatic nerve was electrically stimulated at $A\delta-intensity$ (1 mA, 0.1 ms), 1 Hz and C-intensity (10 mA, 0.5 ms), 20 Hz to elicit the depressor, and pressor responses of the SSR, respectively. Simultaneous measurement of CVN firing rate was made. Experimental results are summarized as follows. 1) 20 out of 98 CVNs had axonal projections to the spinal cord and 17 out of 98 CVNs showed FR changes during SSR. 2) Response patterns of FR and BP during SSR were classified into 8 types. 3) These 8 different response patterns could be further classified into those from pressor and depressor neurons. These results demonstrate that some CVNs were identifiable as reticulospinal neurons responding to anti-dromic stimulation and that CVNs operating as depressor neurons as well as pressor neurons exist in the RVLM, both of which are involved with SSR mediation. Therefore, evidence was found that an independent depressor pathway might be involved in the mediation of SSR.