Harue Suzuki

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.

Increases in adrenal catecholamine secretion and adrenal sympathetic nerve unitary activities with aging in rats

Changes in sympathoadrenal medullary functions with age were investigated using urethane-chloralose anesthetized Wistar rats between about 100-900 days after birth. Although secretion rates of adrenaline and noradrenaline from the adrenal gland under resting conditions varied widely among animals, they gradually increased after 300 days and reached a level 2-4 times higher at 800-900 days compared with that of 100 days. Sympathetic nerve efferent unitary activity at resting conditions was also increased during aging in a manner similar to the catecholamine secretion rates.

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.

A- and C-reflexes elicited in cardiac sympathetic nerves by single shock to a somatic afferent nerve include spinal and supraspinal components in anesthetized rats.

The spinal and supraspinal components of both A- and C-reflexes were studied in the somato-cardiac sympathetic reflex discharges elicited by a single electrical shock either to a spinal (T3-4) afferent nerve or to a limb (tibial) afferent nerve in urethane anesthetized rats. In central nervous system (CNS) intact rats, a single shock to a T3-4 spinal afferent nerve produced early and late A-reflex discharges with latencies of 20 +/- 1 ms and 62 +/- 6 ms, respectively, and a C-reflex with a latency of 136 +/- 9 ms in a cardiac sympathetic efferent nerve. After spinalization at the first cervical level, stimulation of the same spinal afferent nerve produced an A-reflex with the same latency as the early A-reflex in CNS-intact rats and a C-reflex with a latency of 86 +/- 3 ms. The amplitude of the early A-reflex became augmented after spinal transection. On the other hand, a single shock to a tibial afferent nerve evoked an A-reflex discharge with a latency of 41 +/- 2 ms and a C-reflex discharge with a latency of 210 +/- 13 ms in CNS-intact rats. These A- and C-reflexes elicited by stimulation of a tibial afferent nerve were not observed after spinalization. It was concluded that cardiac sympathetic A- and C-reflex discharges evoked by stimulation of a segmental spinal afferent nerve in CNS-intact rats are of spinal and supraspinal origin, and those evoked by tibial nerve stimulation are of supraspinal origin. The spinal reflex pathway is segmentally organized, because the spinal reflex is evoked only when stimulation is delivered to afferent nerves close to the cardiac sympathetic outflow segments. With the CNS intact, the spinal reflex component is depressed by descending inhibitory pathways originating in the brain.

Undiminished reflex responses of adrenal sympathetic nerve activity to stimulation of baroreceptors and cutaneous mechanoreceptors in aged rats

Reflex responses of adrenal sympathetic nerve activity to stimulation of baroreceptor and cutaneous mechanoreceptors were compared in young adult (4 months old) and aged (26 months old) rats, under strictly controlled conditions for anesthesia, respiration and body temperature. Under these conditions the reflex depression to baroreceptor stimulation and cutaneous brushing and reflex excitation to cutaneous pinching were quite well maintained during aging.

Reflex responses in adrenal sympathetic nerves to stimulation of glucoreceptors and chemoreceptors in aging rats

The age-related changes in the sensitivity of reflex responses of adrenal sympathetic nerve activity following stimulation of glucoreceptors and arterial chemoreceptors were investigated in young adult rats 4-5 months old and aged rats 24-26 months old. The sensitivity of the inhibitory reflex responses to stimulation of glucoreceptors and the sensitivity of excitatory reflex responses to systemic hypoxia with end-tidal O2 concentration at 8% and 6% were well maintained in the same ranges in aged rats as in young adult rats. The sensitivity of the excitatory reflex responses to mild systemic hypoxia with end-tidal O2 concentration at 10% increased slightly but significantly in aged rats compared with that in young adult rats.

Direct recording of total catecholamine secretion from the adrenal gland in response to splanchnic nerve stimulation in rats

A new method for the continuous recording of catecholamine (CA) secretion from the adrenal gland in rats in response to splanchnic nerve stimulation was developed. The method consists of in situ perfusion of the adrenal gland and direct continuous recording of released total CA by an electrochemical detector (ECD). Splanchnic nerve stimulation evoked current responses in a stimulus frequency dependent manner. The amounts of total CA released was linearly related to peak amplitude and to the total integrated output current for various current responses, indicating that the ECD current response in this system represents a highly reliable parameter of the secretory process in the adrenal gland. This system has the advantage of directly and continuously monitoring total CA secretion from the adrenal gland in situ.

Modulation of Calcitonin, Parathyroid Hormone, and Thyroid Hormone Secretion by Electrical Stimulation of Sympathetic and Parasympathetic Nerves in Anesthetized Rats

The thyroid and parathyroid glands are dually innervated by sympathetic (cervical sympathetic trunk [CST]) and parasympathetic (superior laryngeal nerve [SLN]) nerve fibers. We examined the effects of electrical stimulation of efferent or afferent nerve fibers innervating the thyroid and parathyroid glands on the secretion of immunoreactive calcitonin (iCT), parathyroid hormone (iPTH), 3,3′,5-triiodothyronine (iT3), and thyroxine (iT4) from the thyroid and parathyroid glands. In anesthetized and artificially ventilated rats, thyroid venous blood was collected. The rate of hormone secretion from the glands was calculated from plasma hormone levels, measured by ELISA, and the flow rate of thyroid venous plasma. SLNs or CSTs were stimulated bilaterally with rectangular pulses with a 0.5-ms width. To define the role of unmyelinated nerve fibers (typically efferent), the cut peripheral segments were stimulated at various frequencies (up to 40 Hz) with a supramaximal intensity to excite all nerve fibers. The secretion of iCT, iT3, and iT4 increased during SLN stimulation and decreased during CST stimulation. iPTH secretion increased during CST stimulation, but was not affected by SLN stimulation. To examine the effects of selective stimulation of myelinated nerve fibers (typically afferent) in the SLN, intact SLNs were stimulated with a subthreshold intensity for unmyelinated nerve fibers. iCT, iT3, and iT4 secretion increased during stimulation of intact SLNs at 40 Hz. These results suggest that excitation of myelinated afferents induced by low intensity and high frequency stimulation of intact SLNs promotes secretion of CT and thyroid hormones from the thyroid gland, potentially via reflex activation of parasympathetic efferent nerve fibers in the SLN.

Inhibitory effects of a new, potent, centrally acting muscle relaxant, (4S,5R)-4-(2-methylpropyl)-3-]3-(perhydroazepin-1-yl)propyl[-5-phenyl-1,3-oxazolidin-2-one (NC-1200) on micturition contractions of the bladder in rats

The effect of the centrally acting muscle relaxant, (4S,5R)-4-(2-methylpropyl)-3-[3-(perhydroazepin-1-yl)propyl]-5- phenyl-1,3-oxazolidin-2-one (NC-1200) on micturition contractions of the urinary bladder was tested in anesthetized rats with the intention of using it clinically to depress vesical micturition contractions. Rhythmic micturition contractions of the bladder were produced by expanding a balloon inserted in the bladder. Efferent nerve activity of the pelvic and hypogastric branches of the bladder was recorded. Both the vesical micturition contractions and the rhythmic burst discharges of the pelvic efferent nerve were inhibited by the i.v. administration of NC-1200 (1-10 mg/kg) in a dose-dependent manner. Hypogastric efferent nerve activity and ganglionic synaptic transmission from the pelvic preganglionic neurons to their postganglionic neurons innervating the bladder were not influenced significantly by the i.v. administration of NC-1200. No inhibitory effect on vesical smooth muscle was observed. From these results we concluded that NC-1200 inhibits the micturition contraction by inhibiting pelvic efferent nerve activity and that this inhibitory effect of NC-1200 originates mainly in the central nervous system.

Age-Related Changes in Neuromodulatory Control of Bladder Micturition Contractions Originating in the Skin

The brainstem is essential for producing micturition contractions of the urinary bladder. Afferent input from perineal skin evoked by gentle mechanical stimulation inhibits micturition contractions by decreasing both ascending and descending transmissions between the brainstem and spinal cord. Dysfunction of this inhibitory mechanism may be one cause of the increase in the prevalence of overactive bladder in old age. The aim of this study was to examine effect of aging on function of skin afferent fibers that inhibit bladder micturition contractions in rats. We used anesthetized male rats in three different age groups: young adult (4–5 months old), middle aged (6–9 months old), and aged (27–30 months old). The bladder was expanded to produce isovolumetric rhythmic micturition contractions. Skin afferent fibers were activated for 1 min either by electrical stimulation (0.5 ms, 0.2–10 V, 0.1–10 Hz) of the cutaneous branch of the pudendal nerve (CBPN) or by gentle mechanical skin stimulation with an elastomer roller. When skin afferent nerves were activated electrically, micturition contractions were inhibited in a similar manner in all age groups, with long latency inhibition induced by excitation of Aβ fibers and short latency inhibition by additional Aδ and C fiber excitation (at 1–10 Hz). On the contrary, when skin afferent nerves were activated mechanically by rolling, latency of inhibition following rolling stimulation was prolonged in aged rats. Single unitary afferent nerve activity of low-threshold mechanoreceptors (LTMs) from the cutaneous nerve was recorded. The discharge rate during rolling was not significantly reduced in Aβ units but was much lower in Aδ and C units in aged rats (0.4 and 0.5 Hz, respectively) than in young adult rats (3 and 7 Hz). These results suggest that the neural mechanism that inhibits bladder micturition contractions by skin afferent input is well maintained in old age, but the early inhibition by gentle skin stimulation is decreased because of reduced responses of Aδ- and C-LTMs.