Harumi Hotta

Acupuncture Affects Regional Blood Flow in Various Organs

In this review, our recent studies using anesthetized animals concerning the neural mechanisms of vasodilative effect of acupuncture-like stimulation in various organs are briefly summarized. Responses of cortical cerebral blood flow and uterine blood flow are characterized as non-segmental and segmental reflexes. Among acupuncture-like stimuli delivered to five different segmental areas of the body; afferent inputs to the brain stem (face) and to the spinal cord at the cervical (forepaw), thoracic (chest or abdomen), lumbar (hindpaw) and sacral (perineum) levels, cortical cerebral blood flow was increased by stimuli to face, forepaw and hindpaw. The afferent pathway of the responses is composed of somatic groups III and IV afferent nerves and whose efferent nerve pathway includes intrinsic cholinergic vasodilators originating in the basal forebrain. Uterine blood flow was increased by cutaneous stimulation of the hindpaw and perineal area, with perineal predominance. The afferent pathway of the response is composed of somatic group II, III and IV afferent nerves and the efferent nerve pathway includes the pelvic parasympathetic cholinergic vasodilator nerves. Furthermore, we briefly summarize vasodilative regulation of skeletal muscle blood flow via a calcitonin gene-related peptide (CGRP) induced by antidromic activation of group IV somatic afferent nerves. These findings in healthy but anesthetized animals may be applicable to understanding the neural mechanisms improving blood flow in various organs following clinical acupuncture.

Aging of the autonomic nervous system and possible improvements in autonomic activity using somatic afferent stimulation

There are significant age‐related changes in autonomic nervous system function that are responsible for an impaired ability to adapt to environmental or intrinsic visceral stimuli in the elderly. We review data on changes in autonomic nervous system regulation of cardiovascular and urinary function, as well as data on strategies to improve function. There are data showing alterations in peripheral and central autonomic nerve activity, and decreases in neurotransmitter receptor action that lead to diminished autonomic reactivity (e.g. blood pressure and cerebral blood flow regulation) and poorly coordinated autonomic discharge (e.g. bladder function). Simple strategies for autonomic function improvement and increasing cortical blood flow include walking and somatic afferent stimulation (e.g. stroking skin or acupuncture) to increase sympathetic, parasympathetic and central cholinergic activity. Geriatr Gerontol Int 2010; 10 (Suppl. 1): S127–S136.

Sympathetic and parasympathetic regulation of the uterine blood flow and contraction in the rat

The effects of electrical stimulation of hypogastric sympathetic and pelvic parasympathetic nerves on uterine blood flow and contraction in anesthetized female non-pregnant normal cycling rats were examined. Electrical stimulation of the efferent pelvic nerve with supramaximal intensity induced marked increase of uterine blood flow accompanied by uterine contraction. On the other hand, the stimulation of efferent hypogastric nerve caused decrease of uterine blood flow accompanied by uterine contraction. These responses could only be elicited with stimulus intensity above the threshold for unmyelinated C fibers in both the hypogastric and pelvic nerves. Intravenous administration of atropine (0.5 mg/kg) totally blocked the response of uterine contraction elicited by pelvic and hypogastric nerve stimulation and also the increase of blood flow induced by pelvic nerve stimulation. Intravenous administration of phenoxybenzamine (0.5 mg/kg) blocked the decreased response of uterine blood flow induced by hypogastric nerve stimulation. It was concluded that uterine blood flow and contraction were regulated by both the parasympathetic and sympathetic nerves, but in different manners; blood flow is regulated reciprocally (1) by parasympathetic vasodilators mainly via activation of muscarinic cholinergic receptors, and (2) by sympathetic vasoconstrictors via activation of alpha-adrenergic receptors; contraction is produced by activation of both parasympathetic and sympathetic nerves via muscarinic cholinergic receptors.

Effects of age on cholinergic vasodilation of cortical cerebral blood vessels in rats

The present study examined the age-related changes in the cholinergic vasodilative system originating in the nucleus basalis of Meynert (NBM) and projecting to the cerebral cortex using Wistar rats of three different ages; young adult (4-7 months), old (24-25 months), and very old (32-42 months) rats. The vasodilative responses in frontal and parietal cortices, measured by laser Doppler flowmetry, induced by electrical stimulation of NBM without blood pressure response were well maintained in old rats, but declined significantly in very old rats. Extracellular acethylcholine (ACh) release in both cortices collected by a microdialysis technique showed both basal levels and response to NBM stimulation to be well maintained in both old and very old rats. The vasodilative cerebral blood flow response elicited by stimulation of the muscarinic ACh receptors, using their agonist, arecoline, was also well maintained in old and very old rats. Considering the present data and our previous finding that the cerebral cortical vasodilative response to activation of the nicotinic ACh receptors using their agonist, nicotine, was markedly reduced in very old rats (Neurosci. Lett., 228 (1997) 203), it was concluded that the age-related decline of nicotinic ACh receptor activity was a cause of the decline of the vasodilative responses elicited by NBM stimulation in very old rats. This result suggests that a reduction of the cholinergic vasodilative system in very old rats due to decreased activity of the nicotinic ACh receptor may cause insufficient blood flow in the cortex when the cortical neurons require.

Effects of the 5-HT1 receptor agonists sumatriptan and CP 93,129 on dural arterial flow in the rat

The blood flow in and around the medial meningeal artery (dural arterial flow) was recorded in the exposed parietal dura mater encephali of the anesthetized rat using laser Doppler flowmetry. Local electrical stimulation of the dura mater (pulses of 0.5 ms delivered at 7.5-17.5 V and 5 or 10 Hz for 30 s) caused temporary increases in dural arterial flow. The effects of the 5-HT1 receptor agonists sumatriptan and CP 93,129 on the basal flow and the electrically evoked increases in flow were examined. Topical administration of undiluted sumatriptan (12 mg/ml) lowered the basal and the evoked flow by 20% on average. Systemic (i.v.) administration of sumatriptan (0.24, 0.72 and 3.6 mumol/kg) caused a short-lasting reduction of the evoked flow increases only at the higher doses while the basal flow was not significantly altered. Systemic administration of CP 93, 129 (0.46 and 4.6 mumol/kg) caused no significant changes of the basal and the evoked flow. At a dose of 23 mumol/kg CP 93,129 lowered the basal flow by 20% and the evoked flow by 30% for 20 min. The systemic arterial pressure was not significantly altered by sumatriptan and CP 93,129 within the whole range of doses. It is suggested that sumatriptan and CP 93,129 at high doses exert inhibitory effects on those fine afferent nerve fibers which release the calcitonin gene-related peptide, since this neuropeptide mediates the evoked increases in dural arterial flow.

Effects of aging on numbers, sizes and conduction velocities of myelinated and unmyelinated fibers of the pelvic nerve in rats

The effects of aging on the conduction velocities, numbers and sizes of the myelinated and unmyelinated fibers of the pelvic nerve in Wistar rats, aged 3-9 and 30-37 months were examined using electrophysiological and ultrastructural techniques. The myelinated fibers did not show significant age-related changes in the maximum conduction velocities (9.7 +/- 1.1 m/s in adult vs. 11.0 +/- 1.5 m/s in aged rats), the number of fibers (662 +/- 27 vs. 625 +/- 56) and distribution of fiber diameters. In aged rats, the unmyelinated fibers did not show a significant change in maximum conduction velocity (1.5 +/- 0.1 m/s vs. 1.5 +/- 0.1 m/s), but showed a significant decrease in the number of fibers (4133 +/- 114 vs. 3113 +/- 456), specifically of fibers smaller than 0.7 microm in diameter. It is concluded that myelinated fibers of the pelvic nerve in rats preserve their conduction ability and fiber population during aging, but unmyelinated fibers, particularly fibers with smaller diameters decrease in number. Unmyelinated fibers with larger diameters maintain their conduction ability and numbers with aging.

The effect of walking on regional blood flow and acetylcholine in the hippocampus in conscious rats

Recent studies in our laboratory have demonstrated that stimulation of the septal complex (i.e., the medial septal nucleus and the nucleus of the diagonal band) increases extracellular acetylcholine (ACh) release and, consequently, results in an increase in regional cerebral blood flow in the hippocampus (Hpc CBF) via activation of the nicotinic ACh receptors (nAChRs) [Neurosci. Lett. 107 (1989) 135; Neurosci. Lett. 112 (1990a) 263]. The present study aimed to examine the effects of walking on Hpc CBF, measured by laser Doppler flowmetry, in conscious rats. Walking at a moderate speed (4 cm/s) on a treadmill for 30 s produced increases in Hpc CBF and mean arterial pressure (MAP), reaching 107 +/- 1% and 105 +/- 1% of the prewalking control values, respectively. Walking for 3 min produced an increase in ACh release in the extracellular space of the hippocampus. The increase in Hpc CBF during walking was attenuated by mecamylamine (abbreviated as MEC here; 2 mg/kg, i.v.), a nAChR antagonist permeable to the blood-brain barrier (BBB), but not by hexamethonium (denoted as C6 here; 20 mg/kg, i.v.), a nAChR antagonist impermeable to the BBB, while the walking-induced increase in MAP was abolished by either agent. The response of Hpc CBF and MAP were not altered by atropine (abbreviated as ATR here; 0.5 mg/kg, i.v.), a muscarinic AChR antagonist permeable to the BBB. The increase in Hpc CBF during walking was attenuated by N(omega)-nitro-L-arginine methyl ester (L-NAME, 3 and 30 mg/kg, i.v.), a nitric oxide synthase (NOS) inhibitor, and the reduced responses were reversed following the intravenous (i.v.) administration of a physiological precursor of NO, L-arginine (600 mg/kg). The results suggest that the increase in Hpc CBF during walking is independent of MAP and attributable at least to activation of the nAChRs by the cholinergic vasodilator nerves projecting to the hippocampus and to production of NO in the hippocampus.

Uterine contractility and blood flow are reflexively regulated by cutaneous afferent stimulation in anesthetized rats.

The effects of cutaneous mechanical afferent stimulation of various skin areas on uterine contractility and blood flow were examined in anesthetized non-pregnant rats. The contractility of the uterus was measured by the balloon method in the uterus. The uterine blood flow was measured by laser Doppler flowmetry. Noxious pinching stimulation of the perineum for 1 min induced an abrupt contraction of the uterus during stimulation. Pinching of a hindpaw or perineum and innocuous brushing of the perineum for 1 min increased uterine blood flow. Stimulation of other skin areas produced no changes in uterine contractility or blood flow. Most uterine responses were abolished by severance of the pelvic nerves, which innervated the uterus. The activity of pelvic parasympathetic efferent nerves to the uterus increased following perineal pinching. All these cutaneous stimulation-induced responses of uterine contractility, blood flow and pelvic efferent nerve activity still existed, and were even augmented, after acute spinalization. These results indicate that cutaneous mechanical sensory stimulation can regulate uterine contractility and blood flow by a segmental spinal reflex mechanism via uterine parasympathetic efferent nerves.

Vagus nerve stimulation-induced bradyarrhythmias in rats

The autonomic consequences of seizures can be severe. Death can follow from autonomic overactivity that causes a parasympathetically mediated bradyarrhythmia. We studied the cardiovascular consequences of unilateral and bilateral stimulation of the distal segments of transected vagus nerve in rats anesthetized with urethane. The range of stimulation rates tested is comparable to the firing rates observed in vagus nerve during seizures. There was a consistent inverse relation between stimulus rate and heart rate with nodal block appearing at 5-10 Hz and minimum HR levels (cardiac standstill) occurring at 50 Hz. Cardiac standstill could last many seconds. Blood pressure during VNS was maintained during lower frequency VNS, but collapsed at frequencies > or =20 Hz to dramatically impair ventricular filling. Recovery of heart rate and blood pressure after VNS was rapid. In the presence of sympathetic co-activation (pharmacological or hypercapnia and/or hypoxia), mean arterial pressure was better maintained and there was much better ventricular filling, but cardiac performance was worse (e.g. ejection fraction derived from echocardiography). The combination of sympathetic and parasympathetic overactivity was sometimes associated with prolonged (> or =20 s) apneic periods during VNS. We conclude that an abrupt increase in parasympathetic activity on the order of 5 times the background of parasympathetic tone can produce transient bradyarrhythmias, and increases on the order of 20 times can produce cardiac standstill, sometimes accompanied by apnea. Our findings suggest that parasympathetically mediated bradyarrhythmia must be accompanied by airway obstruction to sustain parasympathetic overactivity and produce hypoxia to ultimately cause death.

Mechanism of the reflex inhibition of heart rate elicited by acupuncture-like stimulation in anesthetized rats

Acupuncture or acupuncture-like stimulation applied to different body areas can modify autonomic nerve activity to various organs, including gut, bladder, adrenal medulla, and the heart. We studied the reflex bradycardia in response to insertion into the skin and underlying muscles and twisting of an acupuncture needle in pentobarbital-anesthetized rats. We found that acupuncture-like stimulation of forelimb, hindlimb, chest, and abdomen all produced significant heart rate decreases. Rate minima were reached at the end of the 60-second stimulation episode and significant bradycardia persisted for about 40 s after stimulation ended. Heart rate decreases were paralleled by decreases in cardiac sympathetic nerve activity, and could be produced by electrical stimulation of group IV muscle afferent fibers (tibial nerve). Electrical stimulation of the tibial nerve at rates as low as 0.1-2 Hz was effective for eliciting heart rate decreases. Nerve fiber groups were defined by stimulation of and recording from tibial nerve. Activation of groups I, II, or III fiber was ineffective for eliciting the reflex bradycardia. Sympathectomy, high spinal transection, or infusion of the GABA(A) receptor antagonist, bicuculline, into the cisterna magna were all effective for disrupting the reflex bradycardia. Vagotomy and opioid receptor blockade were ineffective for disrupting the reflex pathway. We conclude that the reflex pathway to decrease heart rate by acupuncture-like stimulation consists of mainly group IV muscle afferent fibers whose activity (even very low rate of activity) leads to the activation of GABA-ergic neurons in the brainstem and an inhibition of sympathetic outflow to the heart.