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PubMed2004

New roles for cysteine and transsulfuration enzymes: production of H2S, a neuromodulator and smooth muscle relaxant.

The enzymes of the transsulfuration pathway also have the capacity to catalyze the desulfhydration of cysteine. Recent studies demonstrate a role of the transsulfuration enzymes, cystathionine gamma-lyase and cystathionine beta-synthase, in catalyzing the desulfhydration of cysteine in brain and smooth muscle. The H2S produced from cysteine functions as a neuromodulator and smooth muscle relaxant. In glutamatergic neurons, the production of H2S by cystathionine beta-synthase enhances N-methyl-D-aspartate (NMDA) receptor-mediated currents. In smooth muscle cells, H2S produced by cystathionine gamma-lyase enhances the outward flux of potassium by opening potassium channels, leading to hyperpolarization of membrane potential and smooth muscle relaxation.

Animals↗

PubMed2006

The absorption, metabolism, and excretion of the novel neuromodulator RWJ-333369 (1,2-ethanediol, [1-2-chlorophenyl]-, 2-carbamate, [S]-) in humans.

RWJ-333369 (1,2-ethanediol, [1-2-chlorophenyl]-, 2-carbamate, [S]-; CAS Registry Number 194085-75-1) is a novel neuromodulator in clinical development for the treatment of epilepsy. To study the disposition of RWJ-333369, eight healthy male subjects received a single oral dose of 500 mg of (14)C-RWJ-333369. Urine, feces, and plasma were collected for analysis for up to 1 week after dosing. Radioactivity was mainly excreted in urine (93.8 +/- 6.6%) and much less in feces (2.5 +/- 1.6%). RWJ-333369 was extensively metabolized in humans, since only low amounts of parent drug were excreted in urine (1.7% on average) and feces (trace amounts). The major biotransformation pathways were direct O-glucuronidation (44% of the dose), and hydrolysis of the carbamate ester followed by oxidation to 2-chloromandelic acid, which was subsequently metabolized in parallel to 2-chlorophenyl glycine and 2-chlorobenzoic acid (mean percentage of the dose for the three acids together was 36%). Other routes were chiral inversion followed by O-glucuronidation (11%), and aromatic hydroxylation in combination with sulfate conjugation (5%). In plasma, unchanged drug accounted for 76.5% of the total radioactivity, with the R-enantiomer and the O-glucuronide of the parent drug as the only measurable plasma metabolites. With the use of very sensitive liquid chromatography-tandem mass spectrometry techniques, only traces of aromatic (pre)mercapturic acid conjugates were detected in urine (each <0.3% of the dose), suggesting a low potential for reactive metabolite formation. In conclusion, the disposition of RWJ-333369 in humans is characterized by virtually complete absorption, extensive metabolism, and unchanged drug as the only significant circulating species.

Administration, Oral↗

PubMed1983

Purinergic neurotransmission and neuromodulation.

Conflicting views abound on the peripheral neurotransmitter and neuromodulator roles of purine compounds. Substantial organ- and species-related variations have become apparent. There is, however, a body of compelling evidence for such roles, if not so broad and ubiquitous as those envisioned (7) for the central nervous system. The variations may in part be attributable to the neuroeffector synaptic geometry. The transmitter concentration found at the postsynaptic membrane drops precipitously with increase in the synaptic cleft (85). Where the cleft is narrow, a purine may serve as the primary or sole transmitter (purinergic nerve) and presynaptic modulator. Alternatively, from nonpurinergic (e.g. adrenergic) nerves a purine may be released, possibly ATP by exocytosis, to act as a cotransmitter. It may also serve as pre- and post-synaptic modulator, potentially with a contribution from postsynaptic release (Figure 1). The purine could conceivably diffuse and affect other varicosities. Where the cleft is wide, the postsynaptic concentration of the neurogenic purine may be too low to permit a transmitter or postsynaptic modulator function. The concentration of the nonpurine transmitter may also be insufficient to elicit a significant postsynaptic purine release. The neuronally released purine may, however, presynaptically exert inhibition of transmitter release much as in a narrow cleft. It seems, therefore, that the origin of synaptic purines and their function, be it transmitter, cotransmitter, or modulator, are dictated at least in part by the characteristics of the purine pools, purinergic receptors, and synaptic configuration, which await further assessment.

Adenosine↗

PubMed1991

gamma-Aminobutyric acid is a neuromodulator in sinus node of guinea pig heart.

A possible neurotransmitter role for gamma-aminobutyric acid (GABA) in the sinus node of guinea pig heart was examined. Among right atrium, left atrium, right ventricle, left ventricle, and sinus node, the highest amount of the endogenous GABA was found in the sinus node (1,240.6 +/- 120.8 nmol/g protein). The neuronal uptake of [3H]GABA was also the highest in the sinus node and kinetic analysis of the [3H]GABA uptake system in the sinus node showed one saturable component (Km = 17.3 microM, Vmax = 2.18 nmol.g protein-1.10 min-1). Autoradiography of [3H]GABA demonstrated heavy labeling of [3H]GABA in the nonmyelinated nerve fibers within the sinus node compared with findings in the atrial muscle. Electrical transmural stimulation evoked a Ca(2+)-dependent tetrodotoxin-sensitive release of [3H]GABA from the isolated sinus node preloaded with [3H]GABA in the presence of beta-alanine, thereby indicating that the [3H]GABA in the nerve is released from nerve terminals following electrical stimulation. These results provide evidence for the neuromodulator role of GABA in the sinus node of the guinea pig.

Animals↗

PubMed1995

Neuromodulation of ion transport in porcine distal colon: NPY reduces secretory actions of leukotrienes.

Electrical transmural stimulation (ETS) was used to examine the neuroregulation of electrolyte transport in the porcine distal colon. ETS of the colonic mucosa-submucosa mounted in Ussing chambers produced rapid and transient increases in short-circuit current (Isc) that were inhibited 36% by serosal bumetanide, suggesting that a portion of the response may be attributed to Cl secretion. ETS actions were dependent upon stimulus intensity and frequency and were inhibited by tetrodotoxin and omega-conotoxin. Prazosin and pyrilamine had no effect on the mucosal responses to ETS, whereas atropine reduced the responses by 32%. Neuropeptide Y (NPY) also reduced the mucosal responses to ETS up to 60% (half-maximal effective concentration = 17 nM). In addition, the effects of leukotriene C4, previously shown to stimulate Cl secretion via a neuronal pathway, were also inhibited by NPY. These results indicate that cholinergic submucosal neurons play a role in the regulation of epithelial ion transport and that NPY acts as an inhibitory neuromodulator, particularly on leukotriene-sensitive neurons in the porcine distal colon.

Animals↗

PubMed2005

Regulation of synaptic vesicles pools within motor nerve terminals during short-term facilitation and neuromodulation.

The reserve pool (RP) and readily releasable pool (RRP) of synaptic vesicles within presynaptic nerve terminals were physiologically differentiated into distinctly separate functional groups. This was accomplished in glutamatergic nerve terminals by blocking the glutamate transporter with dl-threo-beta-benzyloxyaspartate (TBOA; 10 microM) during electrical stimulation with either 40 Hz of 10 pulses within a train or 20- or 50-Hz continuous stimulation. The 50-Hz continuous stimulation decreased the excitatory postsynaptic potential amplitude 60 min faster than for the 20-Hz continuous stimulation in the presence of TBOA (P < 0.05). There was no significant difference between the train stimulation and 20-Hz continuous stimulation in the run-down time in the presence of TBOA. After TBOA-induced synaptic depression, the excitatory postsynaptic potentials were rapidly (<1 min) revitalized by exposure to serotonin (5-HT, 1 microM) in every preparation tested (P < 0.05). At this glutamatergic nerve terminal, 5-HT promotes an increase probability of vesicular docking and fusion. Quantal recordings made directly at nerve terminals revealed smaller quantal sizes with TBOA exposure with a marked increase in quantal size as well as a continual appearance of smaller quanta upon 5-HT treatment after TBOA-induced depression. Thus 5-HT was able to recruit vesicles from the RP that were not rapidly depleted by acute TBOA treatment and electrical stimulation. The results support the notion that the RRP is selectively activated during rapid electrical stimulation sparing the RP; however, the RP can be recruited by the neuromodulator 5-HT. This suggests at least two separate kinetic and distinct regulatory paths for vesicle recycling within the presynaptic nerve terminal.

Amino Acid Transport System X-AG↗

PubMed2006

Network architecture, receptive fields, and neuromodulation: computational and functional implications of cholinergic modulation in primary auditory cortex.

Two fundamental issues in auditory cortical processing are the relative importance of thalamocortical versus intracortical circuits in shaping response properties in primary auditory cortex (ACx), and how the effects of neuromodulators on these circuits affect dynamic changes in network and receptive field properties that enhance signal processing and adaptive behavior. To investigate these issues, we developed a computational model of layers III and IV (LIII/IV) of AI, constrained by anatomical and physiological data. We focus on how the local and global cortical architecture shape receptive fields (RFs) of cortical cells and on how different well-established cholinergic effects on the cortical network reshape frequency-tuning properties of cells in ACx. We identify key thalamocortical and intracortical circuits that strongly affect tuning curves of model cortical neurons and are also sensitive to cholinergic modulation. We then study how differential cholinergic modulation of network parameters change the tuning properties of our model cells and propose two different mechanisms: one intracortical (involving muscarinic receptors) and one thalamocortical (involving nicotinic receptors), which may be involved in rapid plasticity in ACx, as recently reported in a study by Fritz and coworkers.

Acoustic Stimulation↗

PubMed1993

Differential neuromodulation of calcium currents by norepinephrine in rat sympathetic neurons.

1. Differences in the neuromodulation of Ca2+ currents between superior cervical ganglion (SCG) and more caudal paravertebral ganglion (PVG) neurons acutely isolated from the same rats were investigated using the whole-cell patch-clamp technique. 2. Norepinephrine (NE) induced a concentration-dependent inhibition of Ca2+ currents in both SCG and PVG neurons. The concentration producing 50% inhibition (IC50) for NE estimated from concentration-response curves was similar between SCG and PVG neurons but the maximal inhibition estimated from the concentration-response curve for PVG neurons was decreased compared with that of SCG neurons. 3. Tail current activation curves of both SCG and PVG neurons in the absence and presence of NE (5 microM) could be fitted to a double Boltzmann equation. In the presence of NE, the activation curves for both SCG and PVG neurons were shifted toward more depolarized potentials. The magnitude of the shift was greater in SCG than in PVG neurons, which could be accounted for by a greater decrease (P < 0.05) in the fractional amplitude of the first current component of SCG neurons (delta 1.4 +/- 0.4 nA, mean +/- SE, 39%) compared with that of PVG neurons (delta 0.9 +/- 0.1 nA, 16%). 4. Ca2+ current density, expressed as maximal tail current amplitude normalized to cell capacitance, was greater in PVG neurons than that in SCG neurons. 5. In SCG neurons, a saturating concentration of omega-conotoxin GVIA (omega-CgTx) produced a greater decrease of Ca2+ current amplitude at +20 mV (77.4 +/- 1.9%) than in PVG neurons (71.2 +/- 1.5%, P < 0.05). 6. After pretreatment with 15 microM omega-CgTx, NE still decreased the Ca2+ currents in both populations of neurons; however, the inhibition was greater in SCG neurons (31.1 +/- 3.4%) than in PVG neurons (12.8 +/- 3.6%, P < 0.01). 7. The dihydropyridine Ca2+ channel "agonist" Bay K 8644 (10 microM) prolonged Ca2+ tail currents in both SCG and PVG neurons. After normalizing to cell capacitance, there was no significant difference in Bay K 8644-induced tail current amplitude between the two populations of neurons. Moreover, NE (5 microM) increased the prolonged Ca2+ tail current amplitude induced by Bay K 8644 (10 microM) by 44.7 +/- 13.5% in SCG and 41.9 +/- 11.9% in PVG neurons. 8. Under control conditions, Ca2+ currents were facilitated by a depolarizing conditioning pulse (50 ms to +100 mV) in both PVG neurons (29.2 +/- 5.1%) and SCG neurons (20.1 +/- 4.0%).(ABSTRACT TRUNCATED AT 400 WORDS)

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗

PubMed2001

Intrinsic optical signals in respiratory brain stem regions of mice: neurotransmitters, neuromodulators, and metabolic stress.

In the rhythmic brain stem slice preparation, spontaneous respiratory activity is generated endogenously and can be recorded as output activity from hypoglossal XII rootlets. Here we combine these recordings with measurements of the intrinsic optical signal (IOS) of cells in the regions of the periambigual region and nucleus hypoglossus of the rhythmic slice preparation. The IOS, which reflects changes of infrared light transmittance and scattering, has been previously employed as an indirect sensor for activity-related changes in cell metabolism. The IOS is believed to be primarily caused by cell volume changes, but it has also been associated with other morphological changes such as dendritic beading during prolonged neuronal excitation or mitochondrial swelling. An increase of the extracellular K(+) concentration from 3 to 9 mM, as well as superfusion with hypotonic solution induced a marked increase of the IOS, whereas a decrease in extracellular K(+) or superfusion with hypertonic solution had the opposite effect. During tissue anoxia, elicited by superfusion of N(2)-gassed solution, the biphasic response of the respiratory activity was accompanied by a continuous rise in the IOS. On reoxygenation, the IOS returned to control levels. Cells located at the surface of the slice were observed to swell during periods of anoxia. The region of the nucleus hypoglossus exhibited faster and larger IOS changes than the periambigual region, which presumably reflects differences in sensitivities of these neurons to metabolic stress. To analyze the components of the hypoxic IOS response, we investigated the IOS after application of neurotransmitters known to be released in increasing amounts during hypoxia. Indeed, glutamate application induced an IOS increase, whereas adenosine slightly reduced the IOS. The IOS response to hypoxia was diminished after application of glutamate uptake blockers, indicating that glutamate contributes to the hypoxic IOS. Blockade of the Na(+)/K(+)-ATPase by ouabain did not provoke a hypoxia-like IOS change. The influences of K(ATP) channels were analyzed, because they contribute significantly to the modulation of neuronal excitability during hypoxia. IOS responses obtained during manipulation of K(ATP) channel activity could be explained only by implicating mitochondrial volume changes mediated by mitochondrial K(ATP) channels. In conclusion, the hypoxic IOS response can be interpreted as a result of cell and mitochondrial swelling. Cell swelling can be attributed to hypoxic release of neurotransmitters and neuromodulators and to inhibition of Na(+)/K(+)-pump activity.

6-Cyano-7-nitroquinoxaline-2,3-dione↗

PubMed2006

An ethics perspective on transcranial magnetic stimulation (TMS) and human neuromodulation.

This paper concerns the ethics of human neuromodulation using transcranial magnetic stimulation (TMS). We examine the challenges of modulating the brain with TMS through the research ethics lens and in clinical medicine for treating frank pathology, primarily in psychiatric diseases. We also consider contemporary issues raised in the neuroethics literature about managing unexpected findings, and relate these to TMS and to other frontier neurotechnology that is becoming openly available in the public domain. We argue that safety and informed consent are of paramount importance for TMS, but that personal values and sociocultural factors must also be considered when examining the promise of this technology and applications that ought to be highlighted for extra precautions.

Brain↗

PubMedDate not supplied

Categorical and prolonged potentials are evoked when brief, intermediate-intensity flashes stimulate horseshoe crab lateral eye photoreceptors during octopamine neuromodulation.

Octopamine, a major efferent neurotransmitter in the lateral eye of the horseshoe crab (Limulus polyphemus), has previously been shown to modulate photoreceptor responses evoked by long flashes. Quantification of these data indicates that this modulation produced a genuine increase in sensitivity to light which cannot be entirely due to an increase in optical efficiency consequent on an anatomical alteration. Other previous studies demonstrated that extrinsic current can modulate Limulus lateral eye photoreceptor cells by inducing a bistable membrane potential with two distinct states. The present study was therefore undertaken to find out if octopamine could modulate visual responses by inducing prolonged and bistable polarization shifts similar to those demonstrated in several other neural systems. Intracellular microelectrodes were used to execute an electrophysiological study of the receptor potentials evoked in the lateral eye of Limulus when brief (20-ms) flashes were delivered while 50 microM octopamine perfused dark-adapted photoreceptors. The combined chemical and optical stimuli prolonged photoreceptor responses to light to the degree that they often exceeded the duration of the brief stimulus by hundreds of milliseconds. Moreover, these prolonged potentials were clearly bistable because they were categorical--either a prolongation was perceptually clear-cut and present or it was not, with no intermediate patterns being observed. During seawater control perfusions, such prolongations were absent. This appears to be the first demonstration of such categorical and prolonged potentials in a photoreceptor neuron. This finding particularly suggests that efferent-driven neuromodulation can enable the development of a persisting short-term representation of a brief stimulus, with this representation being retained at the most distal possible neural site.

Animals↗

PubMed2001

Buttock placement of the implantable pulse generator: a new implantation technique for sacral neuromodulation--a multicenter study.

OBJECTIVE: In the standard operation procedure for sacral neuromodulation, the implantable pulse generator (IPG) is implanted in a subcutaneous pocket at the lower part of the anterior abdominal wall. This procedure requires a long operation time and three incisions. With the IPG in the abdominal wall, some patients complain of displacement or pain at the IPG site postoperatively. By modifying the technique of placement of the IPG, these disadvantages are overcome. METHODS: Between August 1999 and July 2000, 39 patients underwent a buttock implant of the IPG. In 2 of these patients the position of the IPG was changed from abdominal region to the buttock. During follow-up, complications concerning the operation and location of the IPG were compared to the published literature. RESULTS: Operation time is reduced in all patients by approximately 1 h. No repositioning of the patient is required during surgery. Only a short subcutaneous tunnel is required to connect the lead to the IPG. Pain at the level of the IPG was noted in 10% of the patients, which needed no further treatment. No infections were seen and the IPG did not displace postoperatively. CONCLUSION: Buttock placement of the IPG in sacral nerve stimulation leads to shorter operation time; only two incisions are needed instead of three and a shorter subcutaneous tunnel is needed. Using this technique there are less complications and a lower re-operation rate.

Adult↗

PubMedDate not supplied

Neuronal nitric oxide synthase-immunoreactivity. A neuromodulating system independent of peripheral nasal gland denervation in guinea pig nasal mucosal tissue after treatment with botulinum toxin type A.

The influence of botulinum toxin type A (BTA) on cellular mechanisms has not been studied in much detail. Since nitric oxide (NO) is of increasing interest as a neuromodulator in the innervation of the nose, its localization was examined in the nasal mucosa of guinea pigs treated with BTA or saline. Neuronal nitric oxide synthase-immunoreactivity (nNOS-IR) was found around vessels and nasal glands. Immunoreactivity was seen in the respiratory epithelium, in the periost and the osteocytes of the turbinate bone. A distinct interindividual difference in the strength of nNOS-IR was obvious among the animals, but there was no difference in the strength of immunoreactivity between the animals treated with BTA or saline. NO might therefore contribute to the regulation of vascular tone, glandular function, respiratory epithelial cell function and bone metabolism. BTA does not seem to influence the processes regulated and modulated by NO. This may represent a benefit for the application of BTA.

Animals↗

PubMedDate not supplied

Percutaneous peripheral neuromodulation in the treatment of fecal incontinence.

BACKGROUND/AIMS: To assess the results of peripheral neuromodulation for the treatment of fecal incontinence (FI) resulting from uninhibited rectal contraction (URC) or uninhibited anal sphincter relaxation (UASR). METHODS: The work comprised 32 patients (age 38.2 +/- 6.7 years; 22 women) with FI in whom conventional therapy had failed before enrollment in the study. Twenty-six had URC and 6 UASR. Peripheral neurostimulation was effected by posterior tibial nerve stimulation using a Stoller Afferent Nerve Stimulator (UroSurge, Coralville, lowa, USA). The needle was introduced into the skin cephalad to the medial malleolus. Stimulation (parameters: 0.5-10 mA, 200 micros, 20 Hz) was performed every other day for 4 weeks. Functional assessment was done by a questionnaire (incontinence score: 0-20) and physiologic studies. RESULTS: Group 1: 17 patients (13 URC, 4 UASR) had FI improvement, recording a mean score of 1.7 of 20. Group 2: 10 patients (8 URC, 2 UASR) had fair improvement (score 8.6). Group 3: 5 patients had poor results (score 14.8). Rectometric recording showed improvement in groups 1 and 2. Recurrence of symptoms occurred in 8 patients; 6 improved after retreatment. CONCLUSIONS: A percutaneous access to the S(3) spinal region was achieved through the posterior tibial nerve. Improvement of FI was achieved in 78.2%. The technique is simple, easy, without complications and cost-effective. It can be done as an outpatient procedure or by the patient at home. The results need to be reproduced on a large number of patients.

Adult↗

PubMed2005

Evolution of neuromodulation.

Neuromodulation, as defined as the use of electrical stimulation by implanted stimulators to treat various neurological conditions, has developed gradually from long experience with electrical stimulation of the nervous system. Indications are still evolving, and the field is advancing at an ever increasing rate.

Deep Brain Stimulation↗

PubMed2005

Sacral neuromodulation for urinary retention in a kidney-transplant patient.

Bladder outlet obstruction can negatively affect renal function in the kidney transplant population. Functional obstruction represents a clinical challenge as conventional treatments are either ineffective or not recommended. Sacral neuromodulation was successfully used in functional voiding dysfunction in a kidney transplant patient. This is the first case to be reported in the literature.

Electric Stimulation Therapy↗

PubMed1987

Histaminergic neuromodulation of the release of vasopressin.

In an attempt to clarify the nature of histaminergic neuromodulation of the vasopressinergic system, several studies under different experimental paradigms were carried out. L-Histidine loads (8 mmol/kg, i.p.) induced a marked increase in histamine (HA) in the anterior (AHR) and posterior (PHR) hypothalamic regions, the median eminence (ME) and adenohypophysis (Ah) with no apparent effect on the concentration of HA in the neurohypophysis (Nh), as measured by high-performance liquid chromatography. These findings correlated with decreases in vasopressin (VP) levels in the AHR and ME, accompanied by increases of the neuropeptide in the PHR and Ah. Intraperitoneal injections of HA (6 mumol/kg), resulted in a significant (p less than 0.005) rise in VP levels in the PHR, ME and Ah. HA induced an elevation of VP in the prefrontal cortex (PFC) from 6.23 +/- 2.02 to 43 +/- 4.05 microU/mg, as well as a 60% reduction in neurohypophyseal VP. These HA-induced VP responses were abolished by both mepyramine (3 mumol/kg) and famotidine (4 mumol/kg) in the PHR and PFC. Mepyramine suppressed the HA-induced VP response in the Ah and enhanced it in the Nh, while famotidine did the opposite. When alpha-fluoromethylhistidine (FMH), an irreversible inhibitor of histidine decarboxylase, was administered at doses of 100 mg/kg/day (i.p.), hypothalamic HA levels fell by 40-45% after 1 h, by 50% after 3 h, and by 65-80% after 24 h in adrenalectomized rats. In the same conditions, but after a week of treatment with FMH, the VP response to adrenalectomy was clearly impaired.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1996

Surface localization of sacral foramina for neuromodulation of bladder function. An anatomical study.

A method is described for percutaneous localization of the sacral foramina, for neuromodulation of bladder function. We carried out an anatomical study of 5 male and 5 female human cadaver pelves. Using the described surface markings, needles were placed percutaneously into all sacral foramina from nine different angles. Paths of needle entry were studied by subsequent dissection. We observed that although it was possible to enter any sacral foramen at a wide range of insertion angles, the incidence of nerve root/vascular penetration increased with increasing angle of needle entry. Also, the incidence of nerve root penetration was higher with the medial approach compared with lateral entry. The insertion of a needle into the S1 foramen was associated with a higher incidence of nerve root penetration and presents a potential for arterial haemorrhage. On the other hand the smaller S3 and S4 nerve roots were surrounded by venous plexuses, presenting a potential source of venous haemorrhage during procedures. Our study suggests a new method for identifying the surface markings of sacral foramina and it describes the paths of inserted needles into the respective foramina. In addition, it has highlighted some potential risk factors secondary to needle insertion.

Electric Stimulation↗