Divergent projections of catecholaminergic neurons in the nucleus of the solitary tract to limbic forebrain and medullary autonomic brain regions.
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The nucleus of the solitary tract (NTS) is a critical structure involved in coordinating autonomic and visceral activities. Previous independent studies have demonstrated efferent projections from the NTS to the nucleus paragigantocellularis (PGi) and the central nucleus of the amygdala (CNA) in rat brain. To further characterize the neural circuitry originating from the NTS with postsynaptic targets in the amygdala and medullary autonomic targets, distinct green or red fluorescent latex microspheres were injected into the PGi and the CNA, respectively, of the same rat. Thirty-micron thick tissue sections through the lower brainstem and forebrain were collected. Every fourth section through the NTS region was processed for immunocytochemical detection of tyrosine hydroxylase (TH), a marker of catecholaminergic neurons. Retrogradely labeled neurons from the PGi or CNA were distributed throughout the rostro-caudal segments of the NTS. However, the majority of neurons containing both retrograde tracers were distributed within the caudal third of the NTS. Cell counts revealed that approximately 27% of neurons projecting to the CNA in the NTS sent collateralized projections to the PGi while approximately 16% of neurons projecting to the PGi sent collateralized projections to the CNA. Interestingly, more than half of the PGi and CNA-projecting neurons in the NTS expressed TH immunoreactivity. These data indicate that catecholaminergic neurons in the NTS are poised to simultaneously coordinate activities in limbic and medullary autonomic brain regions. (+info)
Effect of electroacupuncture at Sibai on the gastric myoelectric activities of denervated rats.
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AIM: To explore the mechanism of the exciting effects of electro-acupuncture (EA) at Sibai on the gastric myoelectric activities. METHODS: A total of 32 rats were randomly divided into four groups. Through intraperitoneal injection with atropine (the anti-cholinergic agent by blockade of muscarinic receptors), hexamethonium (automatic nerve ganglion-blocking agent) and reserpine (anti-adrenergic agent by depleting the adrenergic nerve terminal of its norepinephrine store), effects of EA at Sibai on the gastric myoelectric activities of the denervated rats were observed. RESULTS: After intraperitoneal injection of atropine and hexamethonium, the average amplitude and ratio of period to time in the phase of high activity of gastric myoelectric slow wave, and the average numbers of the peaks of gastric myoelectric fast wave were significantly decreased (P<0.01, P<0.05, P<0.01), while after intraperitoneal injection of reserpine, the aforementioned three parameters were increased (P<0.01, P<0.05, P<0.01). EA at Sibai point partially relieved the inhibitory effect of atropine and hexamethonium on the gastric myoelectric activities in the rats (P<0.05 or P>0.05). CONCLUSION: Cholinergic and adrenergic nervous systems and autonomic nerve ganglion participate in the peripheral passage of the controlling effects of EA at Foot Yangming Channel on gastrointestinal tract. (+info)
The purpose of this study was to determine the role of transient receptor potential vanilloid type 1 (TRPV1) receptor in modulating neuronal activity of the dorsolateral periaqueductal gray (dl-PAG) through excitatory and inhibitory synaptic inputs. First, whole cell voltage-clamp recording was performed to obtain the spontaneous miniature excitatory postsynaptic currents (mEPSCs) and inhibitory postsynaptic currents (mIPSCs) of the dl-PAG neurons. As 1 microM of capsaicin was applied into the perfusion chamber, the frequency of mEPSCs was increased from 3.21 +/- 0.49 to 5.64 +/- 0.64 Hz (P < 0.05, n = 12) without altering the amplitude and the decay time constant of mEPSCs. In contrast, capsaicin had no distinct effect on mIPSCs. A specific TRPV1 receptor antagonist, iodo-resiniferatoxin (i-RTX, 300 nM), decreased the frequency of mEPSCs from 3.51 +/- 0.29 to 2.01 +/- 0.2 Hz (P < 0.05, n = 8) but did not alter the amplitude and decay time. In addition, i-RTX applied into the chamber abolished the effect of capsaicin on mEPSC of the dl-PAG. In another experiment, spontaneous action potential of the dl-PAG neurons was recorded using whole cell current-clamp methods. Capsaicin significantly elevated the discharge rate of the dl-PAG neurons from 3.03 +/- 0.38 to 5.96 +/- 0.87 Hz (n = 8). The increased firing activity was abolished in the presence of glutamate N-methy-D-aspartate (NMDA) and non-NMDA antagonists, 2-amino-5-phosphonopentanoic acid, and 6-cyano-7-nitroquinoxaline-2,3-dione. The results from this study provide the first evidence indicating that activation of TRPV1 receptors increases the neuronal activity of the dl-PAG through selective potentiation of glutamatergic synaptic inputs. (+info)
Cranial visceral afferent pathways through the nucleus of the solitary tract to caudal ventrolateral medulla or paraventricular hypothalamus: target-specific synaptic reliability and convergence patterns.
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Cranial visceral afferents activate central pathways that mediate systemic homeostatic processes. Afferent information arrives in the brainstem nucleus of the solitary tract (NTS) and is relayed to other CNS sites for integration into autonomic responses and complex behaviors. Little is known about the organization or nature of processing within NTS. We injected fluorescent retrograde tracers into two nuclei to identify neurons that project to sites involved in autonomic regulation: the caudal ventrolateral medulla (CVLM) or paraventricular nucleus of the hypothalamus (PVN). We found distinct differences in synaptic connections and performance in the afferent path through NTS to these neurons. Anatomical studies using confocal and electron microscopy found prominent, primary afferent synapses directly on somata and dendrites of CVLM-projecting NTS neurons identifying them as second-order neurons. In brainstem slices, afferent activation evoked large, constant latency EPSCs in CVLM-projecting NTS neurons that were consistent with the precise timing and rare failures of monosynaptic contacts on second-order neurons. In contrast, most PVN-projecting NTS neurons lacked direct afferent input and responded to afferent stimuli with highly variable, intermittently failing synaptic responses, indicating polysynaptic pathways to higher-order neurons. The afferent-evoked EPSCs in most PVN-projecting NTS neurons were smaller and unreliable but also often included multiple, convergent polysynaptic responses not observed in CVLM-projecting neurons. A few PVN-projecting NTS neurons had monosynaptic EPSC characteristics. Together, we found that cranial visceral afferent pathways are structured distinctly within NTS depending on the projection target. Such, intra-NTS pathway architecture will substantially impact performance of autonomic or neuroendocrine reflex arcs. (+info)
Environmental noise alters gastric myoelectrical activity: Effect of age.
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AIM: To evaluate the effect of age and acoustic stress on gastric myoelectrical activity (GMA) and autonomic nervous system function. METHODS: Twenty-one male subjects (age range 22-71 years, mean 44 years) were recruited and exposed, in random order, to three auditory stimuli (Hospital noise, conversation babble and traffic noise) after a 20-min baseline. All periods lasted 20 min and were interspersed with a 10 min of recovery. GMA was obtained using a Synectics Microdigitrapper. Autonomic nerve function was assessed by monitoring blood pressure and heart rate using an automatic recording device. RESULTS: Dominant power tended to decrease with increase of age (P < 0.05). The overall percentage of three cycle per minute (CPM) activity decreased during exposure to hospital noise (12.0%, P <0.05), traffic noise (13.9%, P < 0.05), and conversation babble (7.1%). The subjects in the younger group (< 50 years) showed a consistent reduction in the percentage of 3 CPM activity during hospital noise (22.9%, P < 0.05), traffic noise (19.0%, P < 0.05), and conversation babble (15.5%). These observations were accompanied by a significant increase in bradygastria: hospital noise (P < 0.05) and traffic noise (P < 0.05). In contrast, the subjects over 50 years of age did not exhibit a significant decrease in 3 CPM activity. Regardless of age, noise did not alter blood pressure or heart rate. CONCLUSION: GMA changes with age. Loud noise can alter GMA, especially in younger individuals. Our data indicate that even short-term exposure to noise may alter the contractility of the stomach. (+info)
Diversity of sympathetic vasoconstrictor pathways and their plasticity after spinal cord injury.
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Sympathetic vasoconstrictor pathways pass through paravertebral ganglia carrying ongoing and reflex activity arising within the central nervous system to their vascular targets. The pattern of reflex activity is selective for particular vascular beds and appropriate for the physiological outcome (vasoconstriction or vasodilation). The preganglionic signals are distributed to most postganglionic neurones in ganglia via synapses that are always suprathreshold for action potential initiation (like skeletal neuromuscular junctions). Most postganglionic neurones receive only one of these "strong" inputs, other preganglionic connections being ineffective. Pre- and postganglionic neurones discharge normally at frequencies of 0.5-1 Hz and maximally in short bursts at <10 Hz. Animal experiments have revealed unexpected changes in these pathways following spinal cord injury. (1) After destruction of preganglionic neurones or axons, surviving terminals in ganglia sprout and rapidly re-establish strong connections, probably even to inappropriate postganglionic neurones. This could explain aberrant reflexes after spinal cord injury. (2) Cutaneous (tail) and splanchnic (mesenteric) arteries taken from below a spinal transection show dramatically enhanced responses in vitro to norepinephrine released from perivascular nerves. However the mechanisms that are modified differ between the two vessels, being mostly postjunctional in the tail artery and mostly prejunctional in the mesenteric artery. The changes are mimicked when postganglionic neurones are silenced by removal of their preganglionic input. Whether or not other arteries are also hyperresponsive to reflex activation, these observations suggest that the greatest contribution to raised peripheral resistance in autonomic dysreflexia follows the modifications of neurovascular transmission. (+info)
Baseline vagal tone predicts BOLD response during elicitation of grief.
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Previous studies of the relationship between autonomic and central nervous system activity using fMRI have primarily utilized cognitive, motor or conditioning tasks. The present study investigated the association between the regional brain activity during the evocation of grief and baseline parasympathetic activity. Eight right-handed women who had experienced the death of a loved one in the past 18 months were scanned during the presentation of personalized pictures and words that evoked grief and had a measure of baseline parasympathetic activity taken. Greater posterior cingulate cortex (PCC) activity was associated with lower parasympathetic activity (eg more arousal). Connectivity has been demonstrated between the ventral PCC (vPCC) and the subgenual ACC (sACC), which then projects to the autonomic nuclei. In the present study, functional connectivity analysis revealed a positive correlation between vPCC and sACC/orbitofrontal cortical activity. Additionally, bilateral cuneus and parahippocampus were associated with higher baseline parasympathetic tone, important to visual perception in emotional processing and episodic memory respectively. Future studies should compare differences between central and peripheral arousal in complicated and non-complicated grief. (+info)
Sympathetic activity and spatial dispersion of repolarization (DOR) have been implicated as mechanisms that promote arrhythmia vulnerability; yet there are no direct measurements of the effects of autonomic nerve stimulation on DOR. Rabbit hearts were perfused in a Langendorff apparatus with full sympathetic and parasympathetic innervation and were optically mapped to measure action potential durations and DOR (apex-base) over the left ventricles. DOR was measured under sinus rhythm, during bilateral sympathetic nerve stimulation (SNS) and right and/or left vagus nerve stimulation and was compared with DOR during isoproterenol (100 nmol/L) or acetylcholine (1 micromol/L) infusion. In sinus rhythm, repolarization started at the apex and systematically progressed toward the base. SNS (10 to 15 Hz) increased DOR by 29% (from Deltaaction potential duration=17+/-0.7 to -22+/-1.6 ms, n=6) and reversed DOR as the direction of repolarization from apex-->base in sinus rhythm shifted to base-->apex in 5 to 15 seconds after SNS. DOR flipped back to its sinus rhythm DOR pattern 115+/-15 seconds after the interruption of SNS. During right or left vagus nerve stimulation, there was no change in the direction of DOR, but bilateral vagus nerve stimulation increased and reversed DOR to base-->apex direction. Infusion of isoproterenol or acetylcholine increased DOR but did not alter the direction of repolarization sequences. These findings demonstrate that bilateral autonomic activity (SNS or vagus nerve stimulation) cause reversible shifts of apex-base DOR and that the spatial heterogeneities of autonomic effects on the ventricles are most likely attributable to a greater innervation at the base than the apex of the heart. (+info)