Interaction of visceral and somatic afferentation at the level of postsynaptic spinal cord elements.

The interaction of visceral and somatic afferentation at the level of postsynaptic spinal cord elements was studied in cats. The effect of conditioning stimuli on the propriospinal (PS) and suprasegmental (SS) component of the tested unit responses was compared. Afferentation from the splanchnic nerve completely inhibited the SS component of somatomotor motoneuronal responses; the PS component was only partly inhibited. Inhibition persisted even after the conditioning stimulus-induced changes in the membrane potential of the motoneurones had disappeared. The activity of the interneurones responsing synchronously with the SS component of the efferent discharges was also completely inhibited in the same intervals. The inhibitory effect of splanchnic afferentation on the PS component of interneuronal discharges evoked by the stimulation of somatic afferents was significantly less effective. The results of interaction for test responses from the cutaneous and muscular nerves was the same. When splanchnic responses were tested during conditioning from somatosensory areas, inhibitory control was found to be reciprocal. The authors discuss the question of the structures and mechanisms participating in functional relations between the autonomic and somatic nervous system in the spinal cord.     

Site on inhibition of the spino-bulbo-spinal reflex on stimulation of the anterior lobe of the cerebellum.

The effect of stimulation of the anterior lobe (AL) of the cerebellum on spinobulbo-spinal (SBS) reflex activity evoked by somatic and splanchnic afferentation was studied in chloralose-anaesthetized cats. Unit activity synchronous with the SBS component of the efferent discharge was observed at the level of motoneurons, descending axons of the dorsolateral and ventral funiculi and neurones of the reticular formation (RF). Conditioning stimulation of the AL inhibited this unit activity. Reticular formation units influenced from the AL had direct contact with segmental structures; these results showed that disappearance of the SBS reflex during AL conditioning is associated with the depressant effect of the cerebellar cortex on the reticular formation.     

Maturation of central autonomic control of the circulation

Postnatal maturation of central neural regulation of cardiovascular function is being examined in developing swine. Three major types of investigations have been undertaken: 1) alterations of inputs from visceral and somatic afferents, e.g., baroreceptor manipulation, stimulation of sciatic nerves; 2) stimulation of central vasoactive sites; 3) subjecting the animals to the stresses of hemorrhage, hypoxia, or hypercapnia. Our findings indicate that cardiovascular reflexes mature at different postnatal ages. For example, the J-receptor reflex had almost the adult pattern of response at birth, whereas the Bezold-Jarisch reflex had a markedly delayed postnatal maturation. Recordings of spontaneous discharge in a major efferent sympathetic supply, i.e., the greater splanchnic nerve, have indicated that neural innervation to the adrenal medulla and splanchnic vasculature is present at birth in piglets.     

Medullary substrate and differential cardiovascular responses during stimulation of specific acupoints

Electroacupuncture (EA) at P5-P6 acupoints overlying the median nerve reduces premotor sympathetic cardiovascular neuronal activity in the rostral ventral lateral medulla (rVLM) and visceral reflex pressor responses. In previous studies, we have noted different durations of influence of EA comparing P5-P6 and S36-S37 acupoints, suggesting that point specificity may exist. The purpose of this study was to evaluate the influence of stimulating P5-P6 (overlying the median nerve), LI4-L7 (overlying branches of the median nerve and the superficial radial nerve), LI6-LI7 (overlying the superficial radial nerve), LI10-LI11 (overlying the deep radial nerves), S36-S37 (overlying the deep peroneal nerves), or K1-B67 (overlying terminal branches of the tibial nerves) specific acupoints, overlying deep and superficial somatic nerves, on the excitatory cardiovascular reflex and rVLM responses evoked by stimulation of chemosensitive receptors in the cat's gallbladder with bradykinin (BK) or direct splanchnic nerve (SN) stimulation. We observed point-specific differences in magnitude and duration of EA inhibition between P5-P6 or LI10-LI11 and LI4-L7 or S36-S37 in responses to 30-min stimulation with low-frequency, low-current EA. EA at LI6-LI7 and K1-B67 acupoints as well as direct stimulation of the superficial radial nerve did not cause any cardiovascular or rVLM neuronal effects. Cardiovascular neurons in the rVLM, a subset of which were classified as premotor sympathetic cells, responded to brief (30 s) stimulation of the SN as well as acupoints P5-P6, LI10-LI11, LI4-L7, S36-S37, LI6-LI7, or K1-B67, or underlying somatic pathways in a fashion similar to the reflex responses. In fact, we observed a significant linear relationship (r(2) = 0.71) between the evoked rVLM response and reflex change in mean arterial blood pressure. In addition, EA stimulation at P5-P6 and LI4-L7 decreased rVLM neuronal activity by 41 and 12%, respectively, for >1 h, demonstrating that prolonged input into the medulla during stimulation of somatic nerves, depending on the degree of convergence, leads to more or less inhibition of activity of these cardiovascular neurons. Thus EA at acupoints overlying deep and superficial somatic nerves leads to point-specific effects on cardiovascular reflex responses. In a similar manner, sympathetic cardiovascular rVLM neurons that respond to both visceral (reflex) and somatic (EA) nerve stimulation manifest graded responses during stimulation of specific acupoints, suggesting that this medullary region plays a role in site-specific inhibition of cardiovascular reflex responses by acupuncture.     

Renorenal reflexes: interaction between efferent and afferent renal nerve activity.

In rats, stimulation of renal mechanoreceptors by increasing ureteral pressure results in a contralateral inhibitory renorenal reflex response consisting of increases in ipsilateral afferent renal nerve activity, decreases in contralateral efferent renal nerve activity, and increases in contralateral urine flow rate and urinary sodium excretion. Mean arterial pressure is unchanged. To study possible functional central interaction among the afferent renal nerves and the aortic and carotid sinus nerves, the responses to renal mechanoreceptor stimulation were compared in sinoaortic denervated rats and sham-denervated rats before and after vagotomy. In contrast to sham-denervated rats, there was an increase in mean arterial pressure in response to renal mechanoreceptor stimulation in sinoaortic-denervated rats. However, there were no differences in the renorenal reflex responses among the groups. Thus, our data failed to support a functional central interaction among the renal, carotid sinus, and aortic afferent nerves in the renorenal reflex response to renal mechanoreceptor stimulation. Studies to examine peripheral interaction between efferent and afferent renal nerves showed that marked reduction in efferent renal nerve activity produced by spinal cord section at T6, ganglionic blockade, volume expansion, or stretch of the junction of superior vena cava and right atrium abolished the responses in afferent renal nerve activity and contralateral renal function to renal mechanoreceptor stimulation. Conversely, increases in efferent renal nerve activity caused by thermal cutaneous stimulation increased basal afferent renal nerve activity and its responses to renal mechanoreceptor stimulation. These data suggest a facilitatory role of efferent renal nerves on renal sensory receptors.     

Efferent activity in the phrenic nerve during startle reflex in chloralose anesthetized cats

Efferent activity was investigated in the phrenic nerve during startle reflex manifesting as somatic nerve discharges (lower intercostal nerves and the nerve endings) in chloralose anesthetized cats. Inhibition (usually of short duration, lasting 23–36 msec) of inspiration activity was found to be the main component of response in the phrenic nerve in the shaping of "low threshold" startle reflex produced by acoustic and tactile stimuli and stimulation of low threshold peripheral afferents. Reflex discharge prevailed amongst the response patterns produced in the phrenic nerve by stimulating high threshold afferents, i.e., early (propriospinal) and late (suprasegmental, arising from stimulating intercostal nerve) or late only (when stimulating the hindlimb nerves). Two patterns of late response could be distinguished, one on inspiration (found in roughly 3 out of 4 experiments) and other on exhalation — the respiratory homologs of somatic startle reflex. Response pattern is described throughout the respiratory cycle. Structure and respiratory modulation of reflex responses produced in the phrenic nerve by stimulating bulbar respiratory structure are also examined. Possible neurophysiological mechanisms underlying phrenic response during the shaping of startle reflex are discussed.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 19, No. 4, pp. 473–482, July–August, 1987.     

The effect of stimulation of Golgi tendon organs and spindle receptors from hindlimb extensor muscles on supraspinal descending inhibitory mechanisms

Experiments were performed in precollicular decerebrate cats to investigate whether proprioceptive volleys originating from Golgi tendon organs and muscle spindles may activate supraspinal descending inhibitory mechanisms. Conditioning stimulation of the distal stump of ventral root filaments of L7 or S1 leading to isometric contraction of the gastrocnemius-soleus (GS) muscle inhibited the monosynaptic reflex elicited by stimulation of the ipsilateral plantaris-flexor digitorum and hallucis longus (Pl-FDHL) nerve. The amount and the time course of this Golgi inhibition were greatly increased by direct cross-excitation of the intramuscular branches of the group Ia afferents due to ephaptic stimulation of the sensory fibers, which occurred when a large number of a fibers had been synchronously activated. The postsynaptic and the presynaptic nature of these inhibitory effects, as well as their segmental origin, have been discussed. In no instance, however, did the stimulation of Golgi tendon organs elicit any late inhibition of the test monosynaptic reflex, which could be attributed to a spino-bulbo-spinal (SBS) reflex. Conditioning stimulation of both primary and secondary endings of muscle spindles, induced by dynamic stretch of the lateral gastrocnemius-soleus (LGS) muscle, was unable to elicit any late inhibition of the medial gastrocnemius (MG) monosynaptic reflex. The only changes observed in this experimental condition were a facilitation of the test reflex during the dynamic stretch of the LGS, followed at the end of the stimulus by a prolonged depression. These effects however were due to segmental interactions, since they persisted after postbrachial section of the spinal cord. Intravenous injection of an anticholinesterase, at a dose which greatly potentiated the SBS reflex inhibition produced by conditioning stimulation of the dorsal root L6, did not alter the changes in time course of the test reflex induced either by muscle contraction or by dynamic muscle stretch. Conditioning stimulation of a muscle nerve activated the supraspinal descending mechanism responsible for the inhibitory phase of the SBS reflex only when the high threshold group III muscle afferents (innervating pressure-pain receptors) had been recruited by the electric stimulus. This finding contrasts with the great availability of the system to the low threshold cutaneous afferents. The proprioceptive afferent volleys originating from Golgi tendon organs as well as from both primary and secondary endings of muscle spindles, contrary to the cutaneous and the high threshold muscle afferent volleys, were apparently unable to elicit not only a SBS reflex inhibition, but also any delayed facilitation of monosynaptic extensor reflexes attributable to inhibition of the cerebellar Purkinje cells.     

Spinal GABA(A) receptors do not mediate the sympathetic baroreceptor reflex in the rat

Activation of baroreceptors causes efferent sympathetic nerve activity (SNA) to fall. Two mechanisms could account for this sympathoinhibition: disfacilitation of sympathetic preganglionic neurons (SPN) and/or direct inhibition of SPN. The roles that spinal GABA and glycine receptors play in the baroreceptor reflex were examined in anesthetized, paralyzed, and artificially ventilated rats. Spinal GABA(A) receptors were blocked by an intrathecal injection of bicuculline methiodide, whereas glycine receptors were blocked with strychnine. Baroreceptors were activated by stimulation of the aortic depressor nerve (ADN), and a somatosympathetic reflex was used as control. After an intrathecal injection of vehicle, there was no effect on any measured variable or evoked reflex. In contrast, bicuculline caused a dose-dependent increase in arterial pressure, SNA, phrenic nerve discharge, and it significantly facilitated the somatosympathetic reflex. However, bicuculline did not attenuate either the depressor response or sympathoinhibition evoked after ADN stimulation. Similarly, strychnine did not affect the baroreceptor-induced depressor response. Thus GABA(A) and glycine receptors in the spinal cord have no significant role in baroreceptor-mediated sympathoinhibition.     

Why the ovotestis of Helix aspersa is innervated

Although Schmalz described the innervation of the ovotestis in pulmonate snails as early as 1914, no functions have been attributed to it. In H. aspersa, the intestinal nerve branches profusely within the ovotestis and terminates in the walls of the acini and in the sheath surrounding the early portion of the hermaphroditic duct. We found both sensory and motor functions for this innervation. Significantly, there is a tonic sensory discharge generated by the mechanical pressure of growing oocytes, and the level of tonic afferent activity is strongly correlated with the number of ripe oocytes; this is probably a permissive signal that gates ovulation. Tactile stimulation of the ovotestis causes a phasic sensory discharge and a pronounced cardio activation. Also, an efferent discharge is elicited in the ovotestis branch of the intestinal nerve. To study the motor consequences of efferent activity, the ovotestis branch was electrically stimulated. We found that such stimulation evokes peristaltic contractions of the initial portion of the hermaphroditic duct and increases beat frequencies of the cilia that line the interior of the duct. These effects could facilitate the transport of oocytes down the duct. Still other functions of afferent activity are implied by changes in the spontaneous activity of mesocerebral cells following nerve stimulation. Putative sensory neurons and putative motoneurons have been identified in the visceral and right parietal ganglia.     

Differential responses of regional sympathetic activity and blood flow to visceral afferent stimulation

The sympathetic nervous system is essential for the cardiovascular responses to stimulation of visceral afferents. It remains unclear how the reflex-evoked sympathetic output is distributed to different vascular beds to initiate the hemodynamic changes. In the present study, we examined changes in regional sympathetic nerve activity and blood flows in anesthetized cats. Cardiovascular reflexes were induced by either electrical stimulation of the right splanchnic nerve or application of 10 microg/ml of bradykinin to the gallbladder. Blood flows were measured using colored microspheres or the Transonic flow meter system. Sympathetic efferent activity was recorded from the left splanchnic, inferior cardiac, and tibial nerves. Stimulation of visceral afferents decreased significantly blood flows in the celiac (from 49 +/- 4 to 25 +/- 3 ml/min) and superior mesenteric (from 35 +/- 4 to 23 +/- 2 ml/min) arteries, and the vascular resistance in the splanchnic bed was profoundly increased. Consistently, stimulation of visceral afferents decreased tissue blood flows in the splanchnic organs. By contrast, activation of visceral afferents increased significantly blood flows in the coronary artery and portal vein but did not alter the vascular resistance of the femoral artery. Furthermore, stimulation of visceral afferents increased significantly sympathetic efferent activity in the splanchnic (182 +/- 44%) but not in the inferior cardiac and tibial nerves. Therefore, this study provides substantial new evidence that stimulation of abdominal visceral afferents differentially induces sympathetic outflow to the splanchnic vascular bed.     

Analysis of afferent,central, and efferent components of the baroreceptor reflex in mice

Studies of genetically modified mice provide a powerful approach to investigate consequences of altered gene expression in physiological and pathological states. The goal of the present study was to characterize afferent, central, and efferent components of the baroreceptor reflex in anesthetized Webster 4 mice. Baroreflex and baroreceptor afferent functions were characterized by measuring changes in renal sympathetic nerve activity (RSNA) and aortic depressor nerve activity (ADNA) in response to nitroprusside- and phenylephrine-induced changes in arterial pressure. The data were fit to a sigmoidal logistic function curve. Baroreflex diastolic pressure threshold (P(th)), the pressure at 50% inhibition of RSNA (P(mid)), and baroreflex gain (maximum slope) averaged 74 +/- 5 mmHg, 101 +/- 3 mmHg, and 2.30 +/- 0.54%/mmHg, respectively (n = 6). The P(th), P(mid), and gain for the diastolic pressure-ADNA relation (baroreceptor afferents) were similar to that observed for the overall reflex averaging 79 +/- 9 mmHg, 101 +/- 4 mmHg, and 2.92 +/- 0.53%/mmHg, respectively (n = 5). The central nervous system mediation of the baroreflex and the chronotropic responsiveness of the heart to vagal efferent activity were independently assessed by recording responses to electrical stimulation of the left ADN and the peripheral end of the right vagus nerve, respectively. Both ADN and vagal efferent stimulation induced frequency-dependent decreases in heart rate and arterial pressure. The heart rate response to ADN stimulation was nearly abolished in mice anesthetized with pentobarbital sodium (n = 4) compared with mice anesthetized with ketamine-acepromazine (n = 4), whereas the response to vagal efferent stimulation was equivalent under both types of anesthesia. Application of these techniques to studies of genetically manipulated mice can be used to identify molecular mechanisms of baroreflex function and to localize altered function to afferent, central, or efferent sites.     

Renorenal reflexes: neural and functional responses

Evidence supporting the existence of renorenal reflexes is reviewed. Renal mechanoreceptors (MR) and afferent renal nerve fibers are localized in the corticomedullary region and in the wall of the renal pelvis. Stimulating renal MR by increased ureteral pressure (increases UP) or increased renal venous pressure (increases RVP) and renal chemoreceptors (CR) by retrograde ureteropelvic perfusion with 0.9 M NaCl results in increased ipsilateral afferent renal nerve activity (ARNA) in a variety of species. However, renorenal reflex responses to renal MR and CR differ among species. In the dog, stimulating renal MR results in a modest contralateral excitatory renorenal reflex response with contralateral renal vasoconstriction that is integrated at the supraspinal level. Renal CR stimulation is without effect on systemic and renal function. However, in the rat the responses to renal MR and CR stimulation are opposite to those of the dog. Increased ureteral pressure, renal venous pressure, or retrograde ureteropelvic perfusion with 0.9 M NaCl each results in a receptor-specific contralateral inhibitory renorenal reflex response. The afferent limb consists of increased ipsilateral ARNA and the efferent limb of decreased contralateral efferent RNA with contralateral diuresis and natriuresis. The renorenal reflex responses to MR and CR stimulation are integrated at the supraspinal level.     

Effects of transections and electrical coagulations in the medulla oblongata upon the activities in the respiratory muscles of the crucian carp (author's transl)]

The following conclusions may be drawn from the results in this work. The respiratory cycles are formed by the neuronal machinery in the reticular formation under the posterior part of the vagal motor nucleus. The motor neurones or the neuronal networks composing the motor nucleus of the respiratory muscles tonically discharge the action potentials, when the neurones or the networks are released from the inhibitory influences of the interneurones connecting the neuronal machinery to the motor neurones. Furthermore, the interneurones probably generate the tonic discharges after removing the inhibitory influences of the other interneurones or the neuronal machinery on them. A reflex mouth closing is elicited by a mechanical stimulus applying on the upper lip. The motor neurones of the m. adductor mandibulae are activated via only one synapse in the reflex. The reflex action potentials recorded from the motor nerve reduce in amplitude at the resting phase of the nerve in the respiratory cycles. These results suggest that the respiratory motor neurones are by nature spontaneous generators of the tonic action potentials and, in the time of the normal breathing, the tonic activity is interrupted by an inhibitory influence of the neuronal machinery generating the respiratory cycles.     

Activity of lateral line efferents in the axolotl (Ambystoma mexicanum)

Summary Activity of efferent fibers was recorded from the ramus ophthalmicus superficialis of the head lateral line nerve and the ramus medialis of the trunk lateral line nerve of the axolotl Ambystoma mexicanum. Baseline activity and activity evoked by sensory stimuli were examined. Electrical stimulation of selected branches was used to determine the conduction velocity and the branching pattern of efferent fibers. The influence of lesions at different levels in the CNS on efferent activity was studied.Up to 5 units with baseline activity were found in a single ramus of the lateral line nerve. Discharge rates were variable and highly irregular; they differed between units of the same branch. Bursting activity occurred in 62% of the units. Movements of the animal were accompanied by activity in up to 8 efferent units in a single nerve.Efferent activity could be elicited or modified by stimulation of visual, labyrinthine, somatosensory, and lateral line systems. Stimulation of the electrosensory system had no effect. Individual efferent neurons innervated different fields in the lateral line periphery. Conduction velocities of efferent fibers ranged from 5 to 12 m/s.Efferent units received input from various sources at different brain levels up to the diencephalon. These in puts determined the baseline activity. The mechanosensory input was mediated at the medullary level.Abbreviations r.m. ramus medialis - r.o.s. ramus ophthalmicus superficialis - r.s. ramus superior     

Activation of latent efferent sympathetic fibers in a viscero-visceral reflex circle under conditions of visceral pain in rats

Activation of “silent” efferent fibers due to stimulation of the mesenteric nerve within a definite frequency range is described; the effect is supposed to result from sensitization in reflex circles related to visceral pain. Neirofiziologiya/Neurophysiology, Vol. 38, No. 4, pp. 368–369, July–August, 2006.     

Mechanisms of reflex bladder activation by pudendal afferents

Activation of pudendal afferents can evoke bladder contraction or relaxation dependent on the frequency of stimulation, but the mechanisms of reflex bladder excitation evoked by pudendal afferent stimulation are unknown. The objective of this study was to determine the contributions of sympathetic and parasympathetic mechanisms to bladder contractions evoked by stimulation of the dorsal nerve of the penis (DNP) in α-chloralose anesthetized adult male cats. Bladder contractions were evoked by DNP stimulation only above a bladder volume threshold equal to 73 ± 12% of the distension-evoked reflex contraction volume threshold. Bilateral hypogastric nerve transection (to eliminate sympathetic innervation of the bladder) or administration of propranolol (a β-adrenergic antagonist) decreased the stimulation-evoked and distension-evoked volume thresholds by -25% to -39%. Neither hypogastric nerve transection nor propranolol affected contraction magnitude, and robust bladder contractions were still evoked by stimulation at volume thresholds below the distension-evoked volume threshold. As well, inhibition of distention-evoked reflex bladder contractions by 10 Hz stimulation of the DNP was preserved following bilateral hypogastric nerve transection. Administration of phentolamine (an α-adrenergic antagonist) increased stimulation-evoked and distension-evoked volume thresholds by 18%, but again, robust contractions were still evoked by stimulation at volumes below the distension-evoked threshold. These results indicate that sympathetic mechanisms contribute to establishing the volume dependence of reflex contractions but are not critical to the excitatory pudendal to bladder reflex. A strong correlation between the magnitude of stimulation-evoked bladder contractions and bladder volume supports that convergence of pelvic afferents and pudendal afferents is responsible for bladder excitation evoked by pudendal afferents. Further, abolition of stimulation-evoked bladder contractions following administration of hexamethonium bromide confirmed that contractions were generated by pelvic efferent activation via the pelvic ganglion. These findings indicate that pudendal afferent stimulation evokes bladder contractions through convergence with pelvic afferents to increase pelvic efferent activity.     

Super-long latent somato-sympathetic response in non-anesthesized decerebrate frogs

Somato-sympathetic reflex responses were studied by recording the activity of the renal sympathetic efferents following excitation of sciatic nerve A-afferents in immobilized decerebrated frogs before and during viadril-induced anesthesia. Apart from A-response reported in anesthetized frogs and consisting of excitatory and inhibitory components, in non-anesthetized frogs reflex discharge with a latency over 2 sec was revealed. Unlike the former one, this response disappeared after intravenous injection of viadril. In the same frogs intravenous injection of viadril converted pressor reflexes in response to stimulation of sciatic nerve A-afferents into depressor ones. A-response with superlong latency is assumed to reflect the excitation of those central structures that are responsible for the development of pressor reflexes to somatic A-fiber stimulation. In this respect the described somato-sympathetic A-response seems to be analogous to the very late A-response in the mammals.     

电刺激家兔迷走神经中枢端诱导的黑-伯反射中的非联合型学习现象

本文旨在研究电刺激家兔迷走神经诱导的黑-伯（Hering-Breuer,HB）反射中的学习和记忆现象。选择性电刺激家兔迷走神经中枢端（频率10～100Hz,强度20～60μA,波宽0．3ms,持续60s）,观察对膈神经放电的影响。以不同频率电刺激家兔迷走神经可模拟HB反射的两种成分,即类似肺容积增大所致抑制吸气的肺扩张反射和类似肺容积缩小所致加强吸气的肺萎陷反射。（1）长时高频（≥40Hz,60s）电刺激迷走神经可模拟呼吸频率减慢,呼气时程延长的肺扩张反射。随着刺激时间的延长,膈神经放电抑制的程度逐渐衰减,表现为呼吸频率的减慢（主要由呼气时程延长所致）在刺激过程中逐渐减弱或消失,显示为适应性或“习惯化”的现象;刺激结束时呼吸运动呈现反跳性增强,表现为一过性的呼气时程缩短,呼吸频率加快,然后才逐渐恢复正常。长时低频（〈40Hz,60s）电刺激迷走神经可模拟呼吸频率加快、呼气时程缩短的肺萎陷反射。随着刺激时间的延长,膈神经放电增强的程度逐渐衰减,同样表现出“习惯化”现象;刺激结束后,膈神经放电不是突然降低,而是继续衰减,表现为呼气时程逐渐延长,呼吸频率逐渐减慢,直至恢复到前对照水平,表现了刺激后的短时增强效应。（2）HB反射的适应性或“习惯化”程度反向依赖于刺激强度和刺激频率,表现为随着刺激强度和频率的增加,膈神经放电越远离正常基线水平,即爿惯化程度减弱。结果表明,家兔HB反射具有“习惯化”这一非联合型学习现象,反映与其有关的呼吸神经元网络具有突触功能的可翅性,呼吸的中枢调控反射具有一定的适应性。     

Cholinergic transmission at mechanosensory afferents in the crayfish terminal abdominal ganglion

Electrical stimulation of mechanosensory afferents innervating hairs on the surface of the exopodite in crayfish Procambarus clarkii (Girard) elicited reciprocal activation of the antagonistic set of uropod motor neurones. The closer motor neurones were excited while the opener motor neurones were inhibited. This reciprocal pattern of activity in the uropod motor neurones was also produced by bath application of acetylcholine (ACh) and the cholinergic agonist, carbamylcholine (carbachol). The closing pattern of activity in the uropod motor neurones produced by sensory stimulation was completely eliminated by bath application of the ACh blocker, d-tubocurarine, though the spontaneous activity of the motor neurones was not affected significantly. Bath application of the acetylcholinesterase inhibitor, neostigmine, increased the amplitude and extended the time course of excitatory postsynaptic potentials (EPSPs) of ascending interneurones elicited by sensory stimulation. These results strongly suggest that synaptic transmission from mechanosensory afferents innervating hairs on the surface of the tailfan is cholinergic.Bath application of the cholinergic antagonists, dtubocurarine (vertebrate nicotinic antagonist) and atropine (muscarinic antagonist) reversibly reduced the amplitude of EPSPs in many identified ascending and spiking local interneurones during sensory stimulation. Bath application of the cholinergic agonists, nicotine (nicotinic agonist) and oxotremorine (muscarinic agonist) also reduced EPSP amplitude. Nicotine caused a rapid depolarization of membrane potential with, in some cases, spikes in the interneurones. In the presence of nicotine, interneurones showed almost no response to the sensory stimulation, probably owing to desensitization of postsynaptic receptors. On the other hand, no remarkable changes in membrane potential of interneurones were observed after oxotremorine application. These results suggest that ACh released from the mechanosensory afferents depolarizes interneurones by acting on receptors similar to vertebrate nicotinic receptors.Abbreviations ACh cetylcholine - mns motor neurones - asc int ascending interneurone     

Synaptic interactions between nonspiking local interneurones in the terminal abdominal ganglion of the crayfish

Nonspiking local interneurones are the important premotor elements in arthropod motor control systems. We have analyzed the synaptic interactions between nonspiking interneurones in the crayfish terminal (6th) abdominal ganglion using simultaneous intracellular recordings. Only 15% of nonspiking interneurones formed bi-directional excitatory connections. In 77% of connections, however, the nonspiking interneurones showed a one-way inhibitory interaction. In these cases, the presynaptic nonspiking interneurones received excitatory synaptic inputs from the sensory afferents innervating hairs on the surface of the uropods and the postsynaptic nonspiking interneurones received inhibitory synaptic inputs that were partly mediated by the inputs to the presynaptic nonspiking interneurones. The membrane hyperpolarization of the postsynaptic nonspiking interneurones mediated by the presynaptic nonspiking interneurones was reduced in amplitude when the hyperpolarizing current was injected into the postsynaptic interneurones, or when the external bathing solution was replaced with one containing low calcium and high magnesium concentrations. The role of these interactions in the circuits controlling the movements of the terminal appendages is discussed.Abbreviations AL antero-lateral - epsp excitatory postsynaptic potential - ipsp inhibitory postsynaptic potential - PL postero-lateral