Reduction In Discharge Rate Research Articles

Rainfall Dependency and Water quality Assessment of springs of three villages of Rudraprayag District: An analysis of veins of Uttarakhand Himalaya

A spring is a crevice in the substrate that forms naturally and allows water to pour out directly from the earths subsurface. Every major river in the country has a system of springs that serve as a symbolic representation of its source. But this very fundamental source of many resources is in peril. The problem is mainly related with the reduced discharge rate of water from the spring. The reason of truncate discharge rate is variability in the rainfall pattern in the recharge area due to the climate change over the years.To ensure the quality and security of the public's water supply, regular quality assessments of drinking water sources are required. In consequence, this study not only analyse the rainfall dependency of springs but also evaluated the spring water quality for drinking, using water quality index, in three villages located in Jakholi block of Rudraparayag district, Uttarakhand. The ten foremost physiochemical elements that regulate water quality—Nitrate, Fluoride, Iron, pH, Turbidity, Chloride, Residual Chlorine, Magnesium, sulphate, and Hardness—were investigated to ensure compliance with guidelines defined by the Bureau of Indian Standards IS: 12500:2012. After examining the data, it became apparent that all of the indicators pointed to acceptable water quality, making it ideal for drinking. However, because of its low discharge and great reliance on rainfall, its position is getting more detrimental.

Evaluation and selection of eutectic salts combined with metal foams for applications in high-temperature latent heat thermal energy storage

This study presents a systematic process for selecting eutectic salts for use in latent heat thermal energy storage (LHTES), and provides experimental evidence regarding their performance. One primary goal was to identify the most suitable eutectic salt for use with metallic foams over a temperature range of 450 °C–500 °C. Twenty one eutectic salts were preselected for comparison. The performance and cost-effectiveness of each were evaluated based on the Ragone relation, enabling a fair comparison of each salt's heat storage capacity and power density relative to cost. As a result, MgCl-NaCl, CaCl2-NaCl, and FLiNaK were selected as the most promising candidates. Subsequently, experiments were performed to demonstrate the compatibility of the selected salts with metal foams while the copper and aluminum foams were immersed in the salts at 550 °C for 120 h. Combining C10100 (copper alloy) foam with CaCl2-NaCl was observed to generate the least surface corrosion due to oxidation. The charge/discharge performance and thermal stability of CaCl2-NaCl, both with and without the copper foam, were also tested to confirm the feasibility of this combination. The capsule with the copper foam showed enhanced performance (a 13 % reduced discharge rate) in comparison to the capsule without copper foam. The melting point of the CaCl2-NaCl remained unchanged for 300-h duration of the cyclic melting/solidification experiments, and no thermal stability issues were observed.

Unbalanced sediment transport by tidal power generation in Lake Sihwa

An in-situ observational study was conducted to understand the sediment transport processes disturbed by the flood generation type of Sihwa tidal power plant (TPP). A surface mooring was deployed in Lake Sihwa (inside of TPP) to collect time-series data of the current velocity and suspended sediment concentration (SSC). A TPP with a capacity of 254 MW has four sequential phases (power generation–standby–drain–standby) of operation. The SSC during power generation was one order of magnitude higher than that during drain, which led to heavily unbalanced sediment fluxes. The total residual sediment flux was always negative (into the lake), which was attributed to the mean advection processes associated with the discharge. Over 18 day mooring period, 78.28 tons m−1 of sediment was delivered to the lake. The source of delivered sediment might be attributed to more local resuspension than the sediment inflow through the gates of TPP. Since the maximum sediment influx during power generation occurred within the water head difference of 4–6 m, the reduction in discharge rate can be a possible measure for solving the sediment accumulation within Lake Sihwa.

Discharge and mixing of moisture coal particles in silos

ABSTRACT Due to the limit of traditional models, a revised mathematical model was adopted to describe the movement of packing powder in silos. The model could be used in the area of coal particles with moisture content concerned based on continuum method. The accuracy of the model was validated by comparing with experimental results from the aspects of discharge rate, the flow pattern and the ash content at outlet. With the model, it was also found that the flow pattern was converted from mass flow (θ= 15°) to funnel flow (θ= 45°, 60°) with the half opening angle increasing. Furthermore, the increase of the moisture content led to the transition from mass flow (x=6.91%) to funnel flow (x=14.68%). And the reduction of discharge rate had the same effect when G was converted from 11.46kg/s to 2.86kg/s. Besides, the transformation of flow pattern brought differences of the granular mixing process in silos, which was indicated by the ash content at outlet and Mixing Index. Compared with the mass flow, the mixing degree got more intensive for the funnel flow.

P23-F Re-examining the origin of medium latency reflex response of soleus using single motor units

Background This study is inquiring the origin of the medium latency reflex response (MLR) that occurs in soleus muscle when common peroneal nerve is electrically stimulated. Material and methods In total, 23 SingleMUs from 9 males were obtained. During SMU recruitment, 308 ± 141 stimuli were delivered. We investigated the duration of the inhibitory postsynaptic potential (IPSP) and excitatory postsynaptic potential (EPSP). Results Common peroneal nerve stimulation resulted in M-response at SEMG of TA muscle and MLR in SOL-SEMG as well as accumulation of SMUs between 50 and 120 ms after the stimulus. A reduction in firing probability of SMUs was also observed and the reduction in discharge rate continued much longer than the spike reduction probability in PSTH and CUSUM. This reduction in discharge rate was followed by an increased discharge rate of SMUs. Duration of the IPSP obtained at PSF, 24.5 ± 6.3 ms, and the duration of EPSP, i.e. MLR, in PSF was found as 119.3 ± 54.3 The latency of EPSP was found higher in PSF and SEMG as 68.3 ± 9.9 ms and 74.5 ± 9.7 ms, than PSTH and MMU which were 56.3 ± 4.6 ms and 57.6 ± 4.2 ms, respectively. Conclusions There was a genuine Ia reciprocal inhibition followed by a stretch-induced reflex response in the SOL. The first response was due to the well-known Ia-IPSP pathway connecting antagonist muscles and the second response, the so-called MLR in the literature, was an indirect stretch reflex response caused by the M-response in the TA muscle. This Project (3135) was supported by Akdeniz University Scientific Research Unit .

Seismic induced flow disruption of Gandll K'in Gwaay.yaay thermal springs, Gwaii Haanas National Park Reserve, Canada

The October 28, 2012 magnitude 7.8 Haida Gwaii earthquake disrupted flow of the only thermal springs in the Haida Gwaii archipelago of western Canada. Springs of the Gandll K'in Gwaay.yaay geothermal system ceased discharge at existing outlets and spring pools drained empty. Subsequent visits to the remote site documented return of flow at the lowest elevation discharge points, although at a greatly reduced discharge rate. Over time thermal water discharge was renewed at higher elevations and the total discharge rate increased.To understand better how seismic activity affected the spring flow, at a site ∼30 km distant from the epicentre, a study was initiated to inform development of a conceptual model of the thermal system. Stable isotope data show that thermal waters discharging at Gandll K'in Gwaay.yaay originate in deep circulation of meteoric waters, where they are heated by the normal increase in ground temperature with depth. Geothermal gradients in the region are relatively low, and aqueous geothermometry suggests that circulation depths of the system are ∼3.6 km. There is no significant difference in overall water geochemistry from before and after the earthquake, either suggesting that the flow path was clogged, or that changes in water pressure in the recharge zone have reduced the overall system drive. We propose a conceptual model, suggesting that the earthquake induced a drop in the water table of the recharge zone, reducing the driving force of the flow system, leading to flow cessation. As the water table returned back to normal elevations the spring system has begun to return to pre-earthquake discharge patterns. This interpretation is consistent with traditional knowledge of the site, were oral history records previous earthquake induced flow cessations and subsequent returns of spring flow.

Midazolam is effective to reduce cortical network activity in organotypic cultures during severe cholinergic overstimulation with soman

Intoxication with organophosphorus compounds can result in life-threatening organ dysfunction and refractory seizures. Sedation or hypnosis is essential to facilitate mechanical ventilation and control seizure activity. The range of indications for midazolam includes both hypnosis and seizure control. Since benzodiazepines cause sedation and hypnosis by dampening neuronal activity of the cerebral cortex, we investigated the drug’s effect on action potential firing of cortical neurons in brain slices. Extensive cholinergic overstimulation was induced by increasing acetylcholine levels and simultaneously treating the slices with soman to block acetylcholinesterase activity. At control conditions midazolam reduced discharge rates (median/95% confidence interval) from 8.8 (7.0–10.5) Hz (in the absence of midazolam) to 2.2 (1.4–2.9) Hz (10 μM midazolam) and 1.6 (0.9–2.2) Hz (20 μM midazolam). Without midazolam, cholinergic overstimulation significantly enhanced neuronal activity to 13.1 (11.0–15.2) Hz. Midazolam attenuated firing rates during cholinergic overstimulation to 6.5 (4.8–8.2) Hz (10 μM midazolam) and 4.1 (3.3–6.0) Hz (20 μM midazolam), respectively. Thus, high cholinergic tone attenuated the drug’s efficacy only moderately. These results suggest that midazolam is worth being tested as a promising drug to induce sedation and hypnosis in patients suffering from severe organophosphorous intoxication.

Use of telehealth in the management of non-critical emergencies in rural or remote emergency departments: A systematic review

Background Telehealth has been used extensively in emergency departments to improve healthcare provision. However, its impact on the management of non-critical emergency presentations within rural and remote emergency department settings has not been adequately explored. The objective of this systematic review is to identify how telehealth has been used to assist in the management of non-critical presentations in rural and remote emergency departments and the outcomes. Methods Articles were identified through database searches of CINAHL, Cochrane, MEDLINE (OVID), Informit and SCOPUS, as well as the screening of relevant article reference and citation lists. To determine how telehealth can assist in the management of non-critical emergencies, information was extracted relating to telehealth programme model, the scope of service and participating health professionals. The outcomes of telehealth programmes were determined by analysing the uptake and usage of telehealth, the impact on altering a diagnosis or management plan as well as patient disposition including patient transfer, discharge, local hospital admission and rates of discharge against medical advice. Results Of the 2532 identified records, 15 were found to match the eligibility criteria and were included in the review. Uptake and usage increased for telehealth programmes predominantly utilised by nursing staff with limited local medical support. Teleconsultation conservatively altered patient diagnosis or management in 18–66% of consultations. Although teleconsultation was associated with increased patient transfer rates, unnecessary transfers were reduced. Simultaneously, an increase in local hospital admission was noted and fewer patients were discharged home. Discharge against medical advice rates were low at 0.9–1.1%. Conclusion The most widely implemented hub-and-spoke telehealth model could be incorporated into existing referral frameworks. Telehealth programmes may assist in reducing unnecessary patient transfer and secondary overtriage, while increasing the capacity of emergency department staff to diagnose and manage patients locally, which may translate into increased local hospital admission and reduced discharge rates following teleconsultation.

Impact of intensive groundwater exploitation on an unprotected covered karst aquifer: a case study in Kermanshah Province, western Iran

Islam Abad region, located in the southwestern of Kermanshah Province, is a karst region where over-exploitation from the deep karst water resources has directly affected the water balance of the whole area. Using a combination of geophysical investigations and analysis of well log data and other relevant hydrogeological studies, we looked for the actual relationship between over-exploitation from deep-water wells, penetrated into the covered karst aquifer, and the drying out of some of the main karst springs throughout the study area. In total, 20 piezometric wells and 4 main karst springs have been chosen for groundwater monitoring network. By integrating GIS processing system and a classical water balance method together with hydrogeology and hydrogeochemical spatial maps, critical zones of human impacts on groundwater resources, made by water extraction for agricultural demand, were identified. Results show that water balance in the Islam Abad basin is in clear disequilibrium, since 2.15 mcm of water depletes from the main aquifers of the study area, annually. This volume of water shortage has resulted in a 7 m groundwater level decline in the last decade, which caused both drying out and reduction in discharge rate of some of the main karst springs throughout the study area. Depths of penetration of deep-water wells into the covered karst aquifer vary from 1 to 93 m. Hydrogeochemical evaluations, including ion relations and hydrogeochemical diagrams, show interactions between karst and alluvium aquifers. Results showed a broad connection between these two resources and, therefore any pressure on alluvium aquifer will affect the karst aquifer, especially by excessive deep-water wells drilling in mutual alluvial and covered karst aquifers.

FV 6. Striatal Microcircuit alterations in a mouse model of preclinical parkinsonism

Objective During recent years, extensive studies in different genetic model systems have complemented conventional toxin-based dopamine depletion approaches and significantly advanced our pathophysiological understanding of familial Parkinson’s disease (PD) from a molecular level to human clinical practice. One of the particular strengths of genetic models is that they open experimental windows to hitherto inaccessible presymptomatic periods in PD, allowing for an investigation of functional changes and adaptive mechanisms during very early phases of this complex neurodegenerative disorder. Mice with a loss-of-function mutation in the parkin-encoding PARK2 gene (a frequent cause of young-onset, autosomal recessive PD) display no motor symptoms, show no appreciable dopaminergic neurodegeneration but exhibit abnormalities of striatal dopaminergic neurotransmission and impaired signalling at the cortico-striatal synapse. Here, we set out to determine whether and how loss of parkin function affects neuronal activity in cortex-basal ganglia networks in vivo. Methods To dissect the cortico-striato-pallidal circuitry in this premanifest model of PD, we performed simultaneous microelectrode recordings in motor cortex, striatum and globus pallidus of anesthetized parkin-mutant mice and controls. Results Based on electrophysiological criteria of striatal single unit activity, we identified several presumably different striatal cell types: Medium spiny projection neurons (pMSN), tonically active neurons (pTAN – corresponding to cholinergic interneurons) and fast spiking interneurons (pFSI – a subpopulation of GABAergic interneurons). In transgenic mice, pTANs displayed significantly increased activity levels, while pFSIs showed reduced discharge rates compared to controls. Furthermore, we found evidence for a disrupted functional connectivity within the striatal FSI microcircuit. In line with the absence of motor symptoms, we observed no changes in the ongoing discharge characteristics of transgenic pMSNs and pallidal neurons. Phase locking analysis revealed elevated and phase-shifted phase coupling to slow (1–3 Hz) cortical local field potential oscillations. Unexpectedly, local field potentials recorded from striatum and globus pallidus of parkin-mutant mice robustly exhibited amplified beta oscillations. Notably, the subgroup of pFSIs showed a selective enhancement of phase coupling to these beta oscillations. Conclusions Our findings suggest that loss of parkin function leads to amplifications of synchronized cortico-striatal oscillations in multiple frequency ranges and an intrastriatal reconfiguration of interneuronal circuits. This presymptomatic disarrangement of striatal dynamic functional connectivity may precede nigrostriatal neurodegeneration and predispose to imbalance of striatal outflow accompanying symptomatic PD.

Estimating discharge rates of oily wastes and deterrence based on aerial surveillance data collected in western Canadian marine waters

Illegal discharge of waste oil from ships is a major source of mortality for seabirds globally. Using linear and log-linear regression, we explored the relationship between detection rates of marine oily discharges and surveillance effort at different time scales, based on data collected in the Canadian Pacific Ocean by the National Aerial Surveillance Program (NASP) from 1997 to 2006. We introduce an approach for quantifying reductions in discharge rates with increased surveillance while controlling appropriately for surveillance effort, as standard linear correction for effort can introduce considerable bias. Despite low probabilities of detection (0.088–1.1%), we found evidence for reduced discharge rates with increasing surveillance effort for data summarized monthly and bimonthly in region A, which is closest to the NASP base airport. Using residuals derived from the best-fit log-linear models, we found detected discharge rates declined annually (−[0.070spills/month]×year).

Comparison of power and EMG during 6-s all-out cycling between young and older women

To investigate the effects of ageing on the neural control strategies governing sprint cycling on a friction-loaded cycle-ergometer, 10 older (aged 70–83yr) and 8 young (aged 19–35yr) healthy women completed seven 6-s all-out cycling trials against varying loads. Root mean square (RMS), median frequency and muscle fibre conduction velocity were determined from the vastus lateralis of the dominant limb during each pedal stroke. Peak power was 43% lower in the older group compared to the younger (p < 0.001) and was accompanied by a significantly lower RMS (p < 0.05). No differences were observed in the other electromyography (EMG) parameters between the groups (p > 0.05). ΔRMS from the first to the sixth second during each trial was found to increase significantly with the development of power output in both groups (p < 0.05). For the first time during an all-out 6-s cycle trial, it has been demonstrated that older women's lower mechanical power output was accompanied by a significantly lower RMS, which indicates a decline in either the number of active of motor units or a reduced discharge rate. Hence, changes in motor units can be regarded as a contributory factor to the decline of muscle power with advancing age. Overall, though, similar neural strategies are adopted in both younger and older populations.

Activation of cortical interneurons during sleep: an anatomical link to homeostatic sleep regulation?

Although slow wave activity in the EEG has been linked to homeostatic sleep regulation, the neurobiological substrate of sleep homeostasis is not well understood. Whereas cortical neurons typically exhibit reduced discharge rates during slow wave sleep (SWS), a subpopulation of GABAergic interneurons, which express the enzyme neuronal nitric oxide synthase (nNOS), has recently been found to be activated during SWS. The extent of activation of these nNOS neurons is proportional to homeostatic sleep 'drive'. These cells are an exception among cortical interneurons in that they are projection neurons. We propose that cortical nNOS neurons are positioned to influence neuronal activity across widespread brain areas. They could thus provide a long-sought anatomical link for understanding homeostatic sleep regulation.

Effects of pharmacological entopeduncular manipulations on idiopathic dystonia in the dt sz mutant hamster

The pathophysiology of idiopathic dystonias is still unknown, but it is regarded as a basal ganglia disorder. Previous experiments in the dt(sz) hamster, a model of primary paroxysmal dystonia, demonstrated reduced discharge rates and an abnormal pattern within the entopeduncular nucleus (EPN), a basal ganglia output structure. To clarify if this is based on abnormal gamma-aminobutyric acid(GABA)ergic or glutamatergic input, microinjections into the EPN were done in mutant hamsters in the present study. The GABA(A) receptor antagonists pentylenetetrazole and bicuculline exerted moderate antidystonic effects, while previous systemic administrations worsened dystonia in the dt(sz) mutant. GABA-potentiating drugs, i.e., the GABA(A) receptor agonist muscimol and the GABA transporter inhibitor 1,2,5,6-tetrahydro-1-[2-[[(diphenylmethylene)amino]oxy]ethyl]-3-pyridinecarboxy-lic acid (NNC-711), which are known to improve dystonia after systemic treatment in mutant hamsters, did not exert significant effects after EPN injections, but NNC-711 tended to increase the severity at the highest dose (2.5 ng bilateral). The NMDA receptor antagonist D(-)-2-amino-5-phosphopentanoic acid (AP-5) retarded the onset of a dystonic attack. However, this effect was not dose dependent and the AMPA receptor antagonist 2,3-dihydroxy-6-nitro-7-sulfamoylbenzol(f)quinoxaline (NBQX) alone or in combination with AP-5 and NNC-711, also failed to show any effects on dystonia. The present data do not provide clear evidence for an enhanced striatal GABAergic input or a reduced glutamatergic activation of the EPN via the subthalamic nucleus, i.e., more pronounced antidystonic effects of GABA(A) receptor antagonists and stronger prodystonic effects of GABAmimetics and glutamate receptor antagonists were expected. Nevertheless, previously found changes in entopeduncular activity probably play a critical pathophysiological role in dystonic hamsters.

Ultrastructural localization and function of dopamine D1‐like receptors in the substantia nigra pars reticulata and the internal segment of the globus pallidus of parkinsonian monkeys

The motor symptoms of Parkinson's disease (PD) are commonly attributed to striatal dopamine loss, but reduced dopamine innervation of basal ganglia output nuclei, the internal globus pallidus (GPi) and the substantia nigra pars reticulata (SNr) may also contribute to symptoms and signs of PD. Both structures express dopamine D1 and D5 receptors under normal conditions, and we have recently demonstrated that their local activation reduces neuronal discharge rates and enhances bursts and oscillatory activity in both nuclei of normal monkeys [M.A. Kliem et al. (2007)J. Neurophysiol., 89, 1489-1500]. Here, we determined the ultrastructural localization and function of D1-like receptors in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated parkinsonian monkeys. In both normal and MPTP-treated monkeys, most of the D1 and D5 receptor immunoreactivity was associated with unmyelinated axons, but we also found significant postsynaptic D5 receptor immunostaining in dendrites of GPi and SNr neurons. A significant proportion of axonal D1 immunostaining was bound to the plasma membrane in both normal and MPTP-treated monkeys. Local microinjections of the D1/D5 receptor agonist SKF82958 significantly reduced discharge rates in GPi and SNr neurons, while they increased burst firing and oscillatory activity in the 3-15-Hz band in SNr, but not in GPi, of parkinsonian monkeys. Together with our recent findings from normal monkeys, these data provide evidence that functional D1/D5 receptors are expressed in GPi and SNr in both normal and parkinsonian states, and that their activation by endogenous dopamine (under normal conditions) or dopamine receptor agonists (in parkinsonism) may regulate basal ganglia outflow.

Atropine increases sevoflurane potency in cortical but not spinal networks during cholinergic overstimulation

In the event of mass destruction with nerve agents a number of victims can be expected to suffer from symptoms of cholinergic overstimulation due to intoxication as well as from physical trauma. Since previous studies have demonstrated that cholinesterase inhibitors may reverse general anaesthesia in humans this scenario raises the question of how these patients can be anaesthetised in order to enable surgical interventions. A likely reason for this reversal is a reduction of anaesthetic potency by acetylcholine as observed for volatile anaesthetics in vitro. In order to test whether a combination of cholinergic antagonists with general anaesthetics improves their potency, we investigated the effects of clinically relevant concentrations of atropine on sevoflurane potency in cortical and spinal slice cultures during cholinergic overstimulation. As the spinal cord and neocortex are important substrates for general anaesthetics cultured spinal and cortical tissue slices were obtained from embryonic and newborn mice, respectively. Drug effects were assessed by extracellular voltage recordings of spontaneous action potential activity. Application of acetylcholine elevated spontaneous activity in neocortical and spinal slices. Atropine (10 nM) reduced discharge rates and reversed the increase of spontaneous activity induced by acetylcholine. In the presence of acetylcholine and atropine sevoflurane caused a concentration-dependent decrease of neuronal activity in neocortical (EC 50 = 0.35 ± 0.33 MAC) and spinal slices (EC 50 = 0.43 ± 0.03 MAC). Comparing our results with previous studies which investigated the effects of acetylcholine on anaesthetic potency it is concluded that small concentrations of atropine increase sevoflurane potency in cortical networks during cholinergic overstimulation. Thus, in a clinical setting, we recommend that anaesthetic drugs should be co-applied with atropine for adequate performance of general anaesthesia.

Motor Unit Recruitment Strategies Are Altered during Deep-Tissue Pain

Muscle pain is associated with decreased motor unit discharge rate during constant force contractions. As discharge rate is a determinant of force, other adaptations in strategy must explain force maintenance during pain. Our aim was to determine whether motor unit recruitment strategies are altered during pain to maintain force despite reduced discharge rate. Motor unit discharge behavior was recorded in two muscles, one with (quadriceps) and one without [flexor pollicis longus (FPL)] synergists. Motor units were recruited during matched low-force contractions with and without experimentally induced pain, and at higher force without pain. A total of 52 and 34 units were recorded in quadriceps and FPL, respectively, during low-force contractions with and without pain. Of these, 20 quadriceps and 9 FPL units were identified during both trials. The discharge rate of these units reduced during pain in both muscles [quadriceps: 8.7 (1.5) to 7.5 (1.3) Hz, p < 0.001; FPL: 11.9 (1.5) to 10.0 (1.7) Hz, p < 0.001]. All remaining units discharged only with or without pain, but not in both conditions. Only one-third of the additional units recruited during pain (quadriceps n = 7/19, FPL n = 3/15) were those expected given orderly recruitment of the motor unit pool as determined during higher-force contractions. We conclude that reduced motor unit discharge rate with pain is accompanied by changes in the population of units used to maintain force. The recruitment of new units is partly inconsistent with generalized inhibition of the motoneuron pool predicted by the "pain adaptation" theory, and provides the basis for a new mechanism of motor adaptation with pain.

Motoneurone recruitment is altered with pain induced in non-muscular tissue

Motoneurone discharge rate is reduced despite the maintenance of force when pain is induced via injection of hypertonic saline into muscle. Two aspects require consideration. First, hypertonic saline may have direct effects on axons other than small diameter pain fibres including the motoneurones that innervate the painful muscle. Second, it is unclear how force is maintained, when motoneurone discharge rate is decreased. We aimed to determine; (1) if motoneurone discharge rate is reduced during force-matched tasks when pain is induced in non-muscle tissue (to exclude direct effects on motoneurones) and (2) if the reduction of discharge rate is associated with additional changes in motoneurone recruitment over multiple muscle regions. Motoneurone discharge was recorded in the quadriceps with eight pairs of fine-wire electrodes. Seven subjects performed 30-s low-level, force-matched contractions before and during anterior knee pain, which was induced by a bolus (0.25ml) injection of 5% hypertonic saline into the infra-patellar fat pad. In total, 119 motor units were identified. Of these, 34 were identified both before and during pain. The discharge rate of these units decreased during pain from 8.9(1.5) to 7.2(1.4)Hz (P<0.0001). In addition, 31 units were recruited in the no-pain condition but not during pain, when 53 new units were recruited. These changes coincided with a large variability in gross muscle activity measures between muscle regions. These data confirm that motoneurone recruitment is altered when direct effects of saline on motoneurones are excluded. Recruitment of additional motor units may explain force maintenance despite reduced discharge rate of some units.

Activation of Nigral and Pallidal Dopamine D1-Like Receptors Modulates Basal Ganglia Outflow in Monkeys

Studies of the effects of dopamine in the basal ganglia have focused on the striatum, whereas the functions of dopamine released in the internal pallidal segment (GPi) or in the substantia nigra pars reticulata (SNr) have received less attention. Anatomic and biochemical investigations have demonstrated the presence of dopamine D1-like receptors (D1LRs) in GPi and SNr, which are primarily located on axons and axon terminals of the GABAergic striatopallidal and striatonigral afferents. Our experiments assessed the effects of D1LR ligands in GPi and SNr on local gamma-aminobutyric acid (GABA) levels and neuronal activity in these nuclei in rhesus monkeys. Microinjections of the D1LR receptor agonist SKF82958 into GPi and SNr significantly reduced discharge rates in GPi and SNr, whereas injections of the D1LR antagonist SCH23390 increased firing in the majority of GPi neurons. D1LR activation also increased bursting and oscillations in neuronal discharge in the 3- to 15-Hz band in both structures, whereas D1LR blockade had the opposite effects in GPi. Microdialysis measurements of GABA concentrations in GPi and SNr showed that the D1LR agonist increased the level of the transmitter. Both findings are compatible with the hypothesis that D1LR activation leads to GABA release from striatopallidal or striatonigral afferents, which may secondarily reduce firing of basal ganglia output neurons. The antagonist experiments suggest that a dopaminergic "tone" exists in GPi. Our results support the finding that D1LR activation may have powerful effects on GPi and SNr neurons and may mediate some of the effects of dopamine replacement therapies in Parkinson's disease.

Study of CA1 place cell activity and exploratory behavior following spatial and nonspatial changes in the environment

Changes in the spatial arrangement or identity of objects inside a familiar environment induce reexploration. The present study looks at modifications of place cell activity during such renewed exploration. Hungry rats foraged for food in a cylinder with a salient cue card attached to the wall and with two distinct objects at fixed positions on the floor relative to each other and to the cue card. Once a set of CA1 place cells was recorded in this standard configuration, additional sessions were done after two kinds of manipulation. In the first, the two objects were rotated as a rigid set 90 degrees counterclockwise around the cylinder center while leaving the cue card in place; this was considered a spatial change. The effects of rotating the objects were different for fields near the objects (near fields) and fields far from the objects (far fields). Object rotation altered most near fields in complex ways, including remapping and cessation of firing. Near fields that remained intact after object rotation underwent unpredictable rotations that frequently departed considerably from the expected value of 90 degrees CCW. In contrast, the only change induced in far fields was a reduction of discharge rate on day 1, but not day 2, exposures of the rat to the rotated objects. The effects on both near and far fields were reversed when the objects were returned to their standard position. In the second manipulation, substitution of one of the two familiar objects with a novel object, a nonspatial change, had no detectable effect on place cell activity, regardless of field location. The sensitivity of hippocampal place cells to spatial changes but not to nonspatial changes is in agreement with earlier results showing that hippocampal lesions abolish reexploration after spatial but not after nonspatial object manipulations. The fact that reexploration is accompanied by place cell changes after spatial but not nonspatial changes reinforces the role that the hippocampus is believed to play in navigational computing and is perfectly compatible with the idea that another brain structure, likely perirhinal cortex, is responsible for object recognition.