Gene count from target sequence capture places three whole genome duplication events in Hibiscus L. (Malvaceae)

Background

The great diversity in plant genome size and chromosome number is partly due to polyploidization (i.e. genome doubling events). The differences in genome size and chromosome number among diploid plant species can be a window into the intriguing phenomenon of past genome doubling that may be obscured through time by the process of diploidization. The genus Hibiscus L. (Malvaceae) has a wide diversity of chromosome numbers and a complex genomic history. Hibiscus is ideal for exploring past genomic events because although two ancient genome duplication events have been identified, more are likely to be found due to its diversity of chromosome numbers. To reappraise the history of whole-genome duplication events in Hibiscus, we tested three alternative scenarios describing different polyploidization events.

Results

Using target sequence capture, we designed a new probe set for Hibiscus and generated 87 orthologous genes from four diploid species. We detected paralogues in > 54% putative single-copy genes. 34 of these genes were selected for testing three different genome duplication scenarios using gene counting. All species of Hibiscus sampled shared one genome duplication with H. syriacus, and one whole genome duplication occurred along the branch leading to H. syriacus.

Conclusions

Here, we corroborated the independent genome doubling previously found in the lineage leading to H. syriacus and a shared genome doubling of this lineage and the remainder of Hibiscus. Additionally, we found a previously undiscovered genome duplication shared by the /Pavonia and /Malvaviscus clades (both nested within Hibiscus) with the occurrences of two copies in what were otherwise single-copy genes. Our results highlight the complexity of genomic diversity in some plant groups, which makes orthology assessment and accurate phylogenomic inference difficult.

A case of distal limb arterial tortuosity and dilation: observations and potential clinical significance

Arterial tortuosity describes variation via bending of the arterial wall and has been noted in several arteries throughout the body. Tortuous blood vessels can cause nerve compression, as well as present difficulties to surgeons and radiologists. Here we present an unusual case of multi-vessel arterial tortuosity discovered in 78-year-old Hispanic male cadaver, independent of systemic pathology. The left ulnar and right tibial arteries were dissected, and using calibrated digital calipers, their external and internal diameters were measured both at the origin site and at the site of greatest dilation. Both wall thickness and the number of inflection points were also measured. Six bends were noticed in the ulnar artery and its diameter measured 8.11 mm at its widest, with a wall thickness of 0.88mm. On the lower extremity, the right tibial artery had three bends and its diameter measured 4.86 mm at its widest, with a wall thickness of 1.32 mm. This uncommon tortuosity is not only more prone to laceration during surgery, but the bending and thickening can be mistaken for tumors. Finally, fluid dynamics can be altered, resulting in an impact on blood pressure in the extremities. Thus, raising awareness is crucial to prevent both symptoms and iatrogenic complications.

The pitfalls of biodiversity proxies: Differences in richness patterns of birds, trees and understudied diversity across Amazonia

Most knowledge on biodiversity derives from the study of charismatic macro-organisms, such as birds and trees. However, the diversity of micro-organisms constitutes the majority of all life forms on Earth. Here, we ask if the patterns of richness inferred for macro-organisms are similar for micro-organisms. For this, we barcoded samples of soil, litter and insects from four localities on a west-to-east transect across Amazonia. We quantified richness as Operational Taxonomic Units (OTUs) in those samples using three molecular markers. We then compared OTU richness with species richness of two relatively well-studied organism groups in Amazonia: trees and birds. We find that OTU richness shows a declining west-to-east diversity gradient that is in agreement with the species richness patterns documented here and previously for birds and trees. These results suggest that most taxonomic groups respond to the same overall diversity gradients at large spatial scales. However, our results show a different pattern of richness in relation to habitat types, suggesting that the idiosyncrasies of each taxonomic group and peculiarities of the local environment frequently override large-scale diversity gradients. Our findings caution against using the diversity distribution of one taxonomic group as an indication of patterns of richness across all groups.

How the past impacts the future: modelling the performance of evolutionarily distinct mammals through time

How does past evolutionary performance impact future evolutionary performance? This is an important question not just for macroevolutionary biologists who wish to chart the phenomena that describe deep-time changes in biodiversity but also for conservation biologists, as evolutionarily distinct species-which may be deemed 'low-performing' in our current era-are increasingly the focus of conservation efforts. Contrasting hypotheses exist to account for the history and future of evolutionarily distinct species: on the one hand, they may be relicts of large radiations, potentially 'doomed' to extinction; or they may be slow-evolving, 'living fossils', likely neither to speciate nor go extinct; or they may be seeds of future radiations. Here, we attempt to test these hypotheses in Mammalia by combining a molecular phylogenetic supertree with fossil record occurrences and measuring change in evolutionary distinctness (ED) at different time slices. With these time slices, we modelled future ED as a function of past ED. We find that past evolutionary performance does indeed have an impact on future evolutionary performance: the most evolutionarily isolated clades tend to become more evolutionarily distinct with time, indicating that low-performing clades tend to remain low-performing throughout their evolutionary history. This article is part of a discussion meeting issue 'The past is a foreign country: how much can the fossil record actually inform conservation?'

phylotaR: An Automated Pipeline for Retrieving Orthologous DNA Sequences from GenBank in R

The exceptional increase in molecular DNA sequence data in open repositories is mirrored by an ever-growing interest among evolutionary biologists to harvest and use those data for phylogenetic inference. Many quality issues, however, are known and the sheer amount and complexity of data available can pose considerable barriers to their usefulness. A key issue in this domain is the high frequency of sequence mislabeling encountered when searching for suitable sequences for phylogenetic analysis. These issues include, among others, the incorrect identification of sequenced species, non-standardized and ambiguous sequence annotation, and the inadvertent addition of paralogous sequences by users. Taken together, these issues likely add considerable noise, error or bias to phylogenetic inference, a risk that is likely to increase with the size of phylogenies or the molecular datasets used to generate them. Here we present a software package, phylotaR that bypasses the above issues by using instead an alignment search tool to identify orthologous sequences. Our package builds on the framework of its predecessor, PhyLoTa, by providing a modular pipeline for identifying overlapping sequence clusters using up-to-date GenBank data and providing new features, improvements and tools. We demonstrate and test our pipeline’s effectiveness by presenting trees generated from phylotaR clusters for two large taxonomic clades: Palms and primates. Given the versatility of this package, we hope that it will become a standard tool for any research aiming to use GenBank data for phylogenetic analysis.

A roadmap for global synthesis of the plant tree of life

Providing science and society with an integrated, up-to-date, high quality, open, reproducible and sustainable plant tree of life would be a huge service that is now coming within reach. However, synthesizing the growing body of DNA sequence data in the public domain and disseminating the trees to a diverse audience are often not straightforward due to numerous informatics barriers. While big synthetic plant phylogenies are being built, they remain static and become quickly outdated as new data are published and tree-building methods improve. Moreover, the body of existing phylogenetic evidence is hard to navigate and access for non-experts. We propose that our community of botanists, tree builders, and informaticians should converge on a modular framework for data integration and phylogenetic analysis, allowing easy collaboration, updating, data sourcing and flexible analyses. With support from major institutions, this pipeline should be re-run at regular intervals, storing trees and their metadata long-term. Providing the trees to a diverse global audience through user-friendly front ends and application development interfaces should also be a priority. Interactive interfaces could be used to solicit user feedback and thus improve data quality and to coordinate the generation of new data. We conclude by outlining a number of steps that we suggest the scientific community should take to achieve global phylogenetic synthesis.

Protecting Free-Living Dormice: Molecular Identification of Cestode Parasites in Captive Dormice (Muscardinus avellanarius) Destined for Reintroduction

The success of any population translocation programme relies heavily on the measures implemented to control and monitor the spread of disease. Without these measures, programmes run the risk of releasing immunologically naïve species or, more dangerously, introducing novel infectious agents to native populations. As a precaution, a reintroduction programme for the common or hazel dormouse, Muscardinus avellanarius, in England screens dormice before release following captive breeding. Using PCR sequencing of a range of genes, we tested whether the same species of tapeworm(s) were present in captive and free-living dormice. Whilst only Rodentolepis straminea were identified in free-living dormice, cestode ova found in a captive individual produced a molecular match closely related to Hymenolepis microstoma and a previously unrecorded Rodentolepis species. To prevent putting at risk the free-living population, we recommended the continued treatment of dormice showing tapeworm infection before release. Our work demonstrates how molecular techniques can be used to inform reintroduction programmes, reduce risk from disease and increase chances of reintroduction success.

Phylogenetic factorization of compositional data yields lineage-level associations in microbiome datasets

Marker gene sequencing of microbial communities has generated big datasets of microbial relative abundances varying across environmental conditions, sample sites and treatments. These data often come with putative phylogenies, providing unique opportunities to investigate how shared evolutionary history affects microbial abundance patterns. Here, we present a method to identify the phylogenetic factors driving patterns in microbial community composition. We use the method, "phylofactorization," to re-analyze datasets from the human body and soil microbial communities, demonstrating how phylofactorization is a dimensionality-reducing tool, an ordination-visualization tool, and an inferential tool for identifying edges in the phylogeny along which putative functional ecological traits may have arisen.

treeman: an R package for efficient and intuitive manipulation of phylogenetic trees

Background

Phylogenetic trees are hierarchical structures used for representing the inter-relationships between biological entities. They are the most common tool for representing evolution and are essential to a range of fields across the life sciences. The manipulation of phylogenetic trees—in terms of adding or removing tips—is often performed by researchers not just for reasons of management but also for performing simulations in order to understand the processes of evolution. Despite this, the most common programming language among biologists, R, has few class structures well suited to these tasks.

Results

We present an R package that contains a new class, called TreeMan, for representing the phylogenetic tree. This class has a list structure allowing phylogenetic trees to be manipulated more efficiently. Computational running times are reduced because of the ready ability to vectorise and parallelise methods. Development is also improved due to fewer lines of code being required for performing manipulation processes.

Conclusions

We present three use cases—pinning missing taxa to a supertree, simulating evolution with a tree-growth model and detecting significant phylogenetic turnover—that demonstrate the new package’s speed and simplicity.

Electronic supplementary material

The online version of this article (doi:10.1186/s13104-016-2340-8) contains supplementary material, which is available to authorized users.

The database of the PREDICTS (Projecting Responses of Ecological Diversity In Changing Terrestrial Systems) project

The PREDICTS project-Projecting Responses of Ecological Diversity In Changing Terrestrial Systems (www.predicts.org.uk)-has collated from published studies a large, reasonably representative database of comparable samples of biodiversity from multiple sites that differ in the nature or intensity of human impacts relating to land use. We have used this evidence base to develop global and regional statistical models of how local biodiversity responds to these measures. We describe and make freely available this 2016 release of the database, containing more than 3.2 million records sampled at over 26,000 locations and representing over 47,000 species. We outline how the database can help in answering a range of questions in ecology and conservation biology. To our knowledge, this is the largest and most geographically and taxonomically representative database of spatial comparisons of biodiversity that has been collated to date; it will be useful to researchers and international efforts wishing to model and understand the global status of biodiversity.

Distribution and population structure of the anther smut Microbotryum silenes-acaulis parasitizing an arctic-alpine plant

Cold-adapted organisms with current arctic-alpine distributions have persisted during the last glaciation in multiple ice-free refugia, leaving footprints in their population structure that contrast with temperate plants and animals. However, pathogens that live within hosts having arctic-alpine distributions have been little studied. Here, we therefore investigated the geographical range and population structure of a fungus parasitizing an arctic-alpine plant. A total of 1437 herbarium specimens of the plant Silene acaulis were examined, and the anther smut pathogen Microbotryum silenes-acaulis was present throughout the host's geographical range. There was significantly greater incidence of anther smut disease in more northern latitudes and where the host locations were less dense, indicating a major influence of environmental factors and/or host demographic structure on the pathogen distribution. Genetic analyses with seven microsatellite markers on recent collections of 195 M. silenes-acaulis individuals revealed three main genetic clusters, in North America, northern Europe and southern Europe, likely corresponding to differentiation in distinct refugia during the last glaciation. The lower genetic diversity in northern Europe indicates postglacial recolonization northwards from southern refugia. This study combining herbarium surveys and population genetics thus uniquely reveals the effects of climate and environmental factors on a plant pathogen species with an arctic-alpine distribution.

Global effects of land use on local terrestrial biodiversity

Human activities, especially conversion and degradation of habitats, are causing global biodiversity declines. How local ecological assemblages are responding is less clear--a concern given their importance for many ecosystem functions and services. We analysed a terrestrial assemblage database of unprecedented geographic and taxonomic coverage to quantify local biodiversity responses to land use and related changes. Here we show that in the worst-affected habitats, these pressures reduce within-sample species richness by an average of 76.5%, total abundance by 39.5% and rarefaction-based richness by 40.3%. We estimate that, globally, these pressures have already slightly reduced average within-sample richness (by 13.6%), total abundance (10.7%) and rarefaction-based richness (8.1%), with changes showing marked spatial variation. Rapid further losses are predicted under a business-as-usual land-use scenario; within-sample richness is projected to fall by a further 3.4% globally by 2100, with losses concentrated in biodiverse but economically poor countries. Strong mitigation can deliver much more positive biodiversity changes (up to a 1.9% average increase) that are less strongly related to countries' socioeconomic status.

The PREDICTS database: a global database of how local terrestrial biodiversity responds to human impacts

Biodiversity continues to decline in the face of increasing anthropogenic pressures such as habitat destruction, exploitation, pollution and introduction of alien species. Existing global databases of species’ threat status or population time series are dominated by charismatic species. The collation of datasets with broad taxonomic and biogeographic extents, and that support computation of a range of biodiversity indicators, is necessary to enable better understanding of historical declines and to project – and avert – future declines. We describe and assess a new database of more than 1.6 million samples from 78 countries representing over 28,000 species, collated from existing spatial comparisons of local-scale biodiversity exposed to different intensities and types of anthropogenic pressures, from terrestrial sites around the world. The database contains measurements taken in 208 (of 814) ecoregions, 13 (of 14) biomes, 25 (of 35) biodiversity hotspots and 16 (of 17) megadiverse countries. The database contains more than 1% of the total number of all species described, and more than 1% of the described species within many taxonomic groups – including flowering plants, gymnosperms, birds, mammals, reptiles, amphibians, beetles, lepidopterans and hymenopterans. The dataset, which is still being added to, is therefore already considerably larger and more representative than those used by previous quantitative models of biodiversity trends and responses. The database is being assembled as part of the PREDICTS project (Projecting Responses of Ecological Diversity In Changing Terrestrial Systems – http://www.predicts.org.uk). We make site-level summary data available alongside this article. The full database will be publicly available in 2015.

Schizophrenia disorders, substance abuse and prior offending in a sequential series of 435 homicides

OBJECTIVE

To examine the relationship between committing homicide, the presence of schizophrenia, substance misuse and past criminality.

METHOD

The study employed a data linkage design, using contacts recorded on two statewide databases, one of which recorded public mental health services contacts and the second of which recorded contacts with the police. The estimated rates of schizophrenia disorders, substance abuse and criminal convictions found among a population of 435 homicide offenders were contrasted with estimated rates in two composite comparison samples.

RESULTS

Of the 435 offenders, 38 (8.7%) had been diagnosed with a schizophrenia disorder, which was RR 13.11 (95% CI 9.14-18.80) times more likely than a comparison sample. Rates of known substance abuse between homicide offenders with and without schizophrenia and community-dwelling residents with schizophrenia did not differ significantly. However, these rates were higher than those found in the general community. A similar pattern emerged for comparisons regarding offending histories between these same groups.

CONCLUSION

The association between homicidal violence and having a schizophrenia disorder cannot be explained away simply on the basis of either comorbid substance abuse or prior criminal offending.

Adrenergic receptors modulate motoneuron excitability, sensory synaptic transmission and muscle spasms after chronic spinal cord injury

The brain stem provides most of the noradrenaline (NA) present in the spinal cord, which functions to both increase spinal motoneuron excitability and inhibit sensory afferent transmission to motoneurons (excitatory postsynaptic potentials; EPSPs). NA increases motoneuron excitability by facilitating calcium-mediated persistent inward currents (Ca PICs) that are crucial for sustained motoneuron firing. Spinal cord transection eliminates most NA and accordingly causes an immediate loss of PICs and emergence of exaggerated EPSPs. However, with time PICs recover, and thus the exaggerated EPSPs can then readily trigger these PICs, which in turn produce muscle spasms. Here we examined the contribution of adrenergic receptors to spasms in chronic spinal rats. Selective activation of the α(1A) adrenergic receptor with the agonists methoxamine or A61603 facilitated Ca PIC and spasm activity, recorded both in vivo and in vitro. In contrast, the α(2) receptor agonists clonidine and UK14303 did not facilitate Ca PICs, but did decrease the EPSPs that trigger spasms. Moreover, in the absence of agonists, spasms recorded in vivo were inhibited by the α(1) receptor antagonists WB4010, prazosin, and REC15/2739, and increased by the α(2) receptor antagonist RX821001, suggesting that both adrenergic receptors were endogenously active. In contrast, spasm activity recorded in the isolated in vitro cord was inhibited only by the α(1) antagonists that block constitutive receptor activity (activity in the absence of NA; inverse agonists, WB4010 and prazosin) and not by the neutral antagonist REC15/2739, which only blocks conventional NA-mediated receptor activity. RX821001 had no effect in vitro even though it is an α(2) receptor inverse agonist. Our results suggest that after chronic spinal cord injury Ca PICs and spasms are facilitated, in part, by constitutive activity in α(1) adrenergic receptors. Additionally, peripherally derived NA (or similar ligand) activates both α(1) and α(2) adrenergic receptors, controlling PICs and EPSPs, respectively.

Locomotion after spinal cord injury depends on constitutive activity in serotonin receptors

Following spinal cord injury (SCI) neurons caudal to the injury are capable of rhythmic locomotor-related activity that can form the basis for substantial functional recovery of stepping despite the loss of crucial brain stem-derived neuromodulators like serotonin (5-HT). Here we investigated the contribution of constitutive 5-HT(2) receptor activity (activity in the absence of 5-HT) to locomotion after SCI. We used a staggered hemisection injury model in rats to study this because these rats showed a robust recovery of locomotor function and yet a loss of most descending axons. Immunolabeling for 5-HT showed little remaining 5-HT below the injury, and locomotor ability was not correlated with the amount of residual 5-HT. Furthermore, blocking 5-HT(2) receptors with an intrathecal (IT) application of the neutral antagonist SB242084 did not affect locomotion (locomotor score and kinematics were unaffected), further indicating that residual 5-HT below the injury did not contribute to generation of locomotion. As a positive control, we found that the same application of SB242084 completely antagonized the muscle activity induced by exogenous application of the 5-HT(2) receptor agonists alpha-methyl-5-HT (IT). In contrast, blocking constitutive 5-HT(2) receptor activity with the potent inverse agonist SB206553 (IT) severely impaired stepping as assessed with kinematic recordings, eliminating most hindlimb weight support and overall reducing the locomotor score in both hind legs. However, even in the most severely impaired animals, rhythmic sweeping movements of the hindlimb feet were still visible during forelimb locomotion, suggesting that SB206553 did not completely eliminate locomotor drive to the motoneurons or motoneuron excitability. The same application of SB206553 had no affect on stepping in normal rats. Thus while normal rats can compensate for loss of 5-HT(2) receptor activity, after severe spinal cord injury rats require constitutive activity in these 5-HT(2) receptors to produce locomotion.

Apamin-sensitive calcium-activated potassium currents (SK) are activated by persistent calcium currents in rat motoneurons

Low voltage-activated persistent inward calcium currents (Ca PICs) occur in rat motoneurons and are mediated by Cav1.3 L-type calcium channels (L-Ca current). The objectives of this paper were to determine whether this L-Ca current activates a sustained calcium-activated potassium current (SK current) and examine how such SK currents change with spinal injury. For comparison, the SK current that produces the postspike afterhyperpolarization (mAHP) was also quantified. Intracellular recordings were made from motoneurons of adult acute and chronic spinal rats while the whole sacrocaudal spinal cord was maintained in vitro. Spikes/AHPs were evoked with current injection or ventral root stimulation. Application of the SK channel blocker apamin completely eliminated the mAHP, which was not significantly different in chronic and acute spinal rats. The Ca PICs were measured with slow voltage ramps (or steps) with TTX to block sodium currents. In chronic spinal rats, the PICs were activated at -58.6 +/- 6.0 mV and were 2.2 +/- 1.2 nA in amplitude, significantly larger than in acute spinal rats. Apamin significantly increased the PIC, indicating that there was an SK current activated by L-Ca currents (SK(L) current), which ultimately reduced the net PIC. This SK(L) current was not different in acute and chronic spinal rats. The SK(AHP) and the SK(L) currents were activated by different calcium currents because the mAHP/SK(AHP) was blocked by the N, P-type calcium channel blocker omega-conotoxin MVIIC and was resistant to the L-type calcium channel blocker nimodipine, whereas the L-Ca and SK(L) currents were blocked by nimodipine. Furthermore, the SK(AHP) current activated within 10 ms of the spike, whereas the SK(L) current was delayed approximately 100 ms after the onset of the L-Ca current, suggesting that the SK(L) currents were not as spatially close to the L-Ca currents. Finally, the SK(L) and the L-Ca currents were poorly space clamped, with oscillations at their onset and hysteresis in their activation and deactivation voltages, consistent with currents of dendritic origin. The impact of these dendritic currents was especially pronounced in 15% of motoneurons, where apamin led to uncontrollable L-Ca currents that could not be deactivated, even with large hyperpolarizations of the soma. Thus, although the SK(L) currents are fairly small, they play a critical role in terminating the dendritic L-Ca currents.

Expression of L-type calcium channel alpha(1)-1.2 and alpha(1)-1.3 subunits on rat sacral motoneurons following chronic spinal cord injury

In the presence of the monoamines serotonin and norepinephrine, motoneurons readily generate large persistent inward currents (PICs). The resulting plateau potentials amplify and sustain motor output. Monoaminergic input to the cord originates in the brainstem and the sharp reduction in monoamine levels that occurs following acute spinal cord injury greatly decreases motoneuron excitability. However, recent studies in the adult sacral cord of the rat have shown that motoneurons reacquire the ability to generate PICs and plateau potentials within 1-2 months following spinal transection. Ca(v)1.3 L-type calcium channels are involved in generating PICs in both healthy and injured animals. Additionally, expression of Ca(v)1.2 and Ca(v)1.3 L-type calcium channels is altered in several pathological conditions. Therefore, in this paper we analyzed the expression of L-type calcium channel alpha(1) subunits within the motoneuron pool following a complete transection of the spinal cord at the level of the sacral vertebra (S)2 segment. The analysis was done both caudally (S4 segment) and rostrally [thoracic vertebra (T)6 segment] from the injury site. The S4 segment was significantly reduced in diameter when compared with control animals, and this reduction was more evident in the white matter. Ca(v)1.2 alpha(1) subunit expression significantly increased (26%) in the motoneuron pool located caudally but not rostrally from the injury site. In contrast, the expression of Ca(v)1.3 alpha(1) subunit remained unchanged in both S4 and T6 segments. The differential expression of the two alpha(1) subunits in spinal injury suggests that Ca(v)1.2 and Ca(v)1.3 channels have different functions in neuronal adaptation following spinal cord injury.

Serotonin facilitates a persistent calcium current in motoneurons of rats with and without chronic spinal cord injury

In the months after spinal cord transection, motoneurons in the rat spinal cord develop large persistent inward currents (PICs) that are responsible for muscle spasticity. These PICs are mediated by low-threshold TTX-sensitive sodium currents (Na PIC) and L-type calcium currents (Ca PIC). Recently, the Na PIC was shown to become supersensitive to serotonin (5-HT) after chronic injury. In the present paper, a similar change in the sensitivity of the Ca PIC to 5-HT was investigated after injury. The whole sacrocaudal spinal cord from acute spinal rats and spastic chronic spinal rats (S2 level transection 2 mo previously) was studied in vitro. Intracellular recordings were made from motoneurons and slow voltages ramps were applied to measure PICs. TTX was used to block the Na PIC. For motoneurons of chronic spinal rats, a low dose of 5-HT (1 microM) significantly lowered the threshold of the Ca PIC from -56.7 +/- 6.0 to -63.1 +/- 7.1 mV and increased the amplitude of the Ca PIC from 2.4 +/- 1.0 to 3.0 +/- 0.73 nA. Higher doses of 5-HT acted similarly. For motoneurons of acute spinal rats, low doses of 5-HT had no significant effects, whereas a high dose (about 30 microM) significantly lowered the threshold of the L-Ca PIC from -58.5 +/- 14.8 to -62.5 +/- 3.6 mV and increased the amplitude of the Ca PIC from 0.69 +/- 1.05 to 1.27 +/- 1.1 nA. Thus Ca PICs in motoneurons are about 30-fold supersensitive to 5-HT in chronic spinal rats. The 5-HT-induced facilitation of the Ca PIC was blocked by nimodipine, not by the I(h) current blocker Cs(+) (3 mM) or the SK current blocker apamin (0.15 microM), and it lasted for hours after the removal of 5-HT from the nCSF, even increasing initially after removing 5-HT. The effects of 5-HT make motoneurons more excitable and ultimately lead to larger, more easily activated plateaus and self-sustained firing. The supersensitivity to 5-HT suggests the small amounts of endogenous 5-HT below the injury in a chronic spinal rat may act on supersensitive receptors to produce large Ca PICs and ultimately enable muscle spasms.

Endogenous monoamine receptor activation is essential for enabling persistent sodium currents and repetitive firing in rat spinal motoneurons

The spinal cord and spinal motoneurons are densely innervated by terminals of serotonin (5-HT) and norepinephrine (NE) neurons arising mostly from the brain stem, but also from intrinsic spinal neurons. Even after long-term spinal transection (chronic spinal), significant amounts (10%) of 5-HT and NE (monoamines) remain caudal to the injury. To determine the role of such endogenous monoamines, we blocked their action with monoamine receptor antagonists and measured changes in the sodium currents and firing in motoneurons. We focused on persistent sodium currents (Na PIC) and sodium spike properties because they are critical for enabling repetitive firing in motoneurons and are facilitated by monoamines. Intracellular recordings were made from motoneurons in the sacrocaudal spinal cord of normal and chronic spinal rats (2 mo postsacral transection) with the whole sacrocaudal cord acutely removed and maintained in vitro (cords from normal rats termed acute spinal). Acute and chronic spinal rats had TTX-sensitive Na PICs that were respectively 0.62 +/- 0.76 and 1.60 +/- 1.04 nA, with mean onset voltages of -63.0 +/- 5.6 and -64.1 +/- 5.4 mV, measured with slow voltage ramps. Application of 5-HT2A, 5-HT2C, and alpha1-NE receptor antagonists (ketanserin, RS 102221, and WB 4101, respectively) significantly reduced the Na PICs, and a combined application of these three monoamine antagonists completely eliminated the Na PIC, in both acute and chronic spinal rats. Likewise, reduction of presynaptic transmitter release (including 5-HT and NE) with long-term application of cadmium also eliminated the Na PIC. Associated with the elimination of the Na PIC in monoamine antagonists, the motoneurons lost their ability to fire during slow current ramps. At this point, the spike evoked by antidromic stimulation was not affected, suggesting that activation of the transient sodium current was not impaired. However, the spike evoked after a slow ramp depolarization was slightly reduced in height and rate-of-rise, suggesting decreased sodium channel availability as a result of increased channel inactivation. These results suggest that endogenous monoamine receptor activation is critical for enabling the Na PIC and decreasing sodium channel inactivation, ultimately enabling steady repetitive firing in both normal and chronic spinal rats.

5-HT2 receptor activation facilitates a persistent sodium current and repetitive firing in spinal motoneurons of rats with and without chronic spinal cord injury

We examined the modulation of persistent inward currents (PICs) by serotonin (5-HT) in spinal motoneurons of normal and chronic spinal rats. PICs are composed of both a TTX-sensitive persistent sodium current (Na PIC) and a nimodipine-sensitive persistent calcium current (Ca PIC), and we focused on quantifying the Na PIC (and its action on the total PIC), which is known to be critical in enabling repetitive firing. Intracellular recordings were made from motoneurons of the whole sacrocaudal spinal cord of normal adult rats after the cord was acutely transected at the S2 spinal level (acute spinal rat condition), removed from the animal, and then maintained in vitro. In vitro motoneuron recordings were likewise made from rats that had a sacral spinal transection 2 mo previously (chronic spinal rats). In motoneurons from acute spinal rats, moderately high doses of 5-HT (> or = 10 microM), or the 5-HT2 receptor agonist DOI (> or = 30 microM), significantly increased the total PIC, hyperpolarized the PIC onset voltage, and hyperpolarized the spike threshold, whereas lower doses had no effect. Both 5-HT and DOI specifically increased the Na PIC portion of the total PIC (tested with nimodipine blocking the Ca PIC). Additionally, 5-HT, but not DOI, depolarized the resting membrane potential (Vm) and increased the input resistance (Rm) in a dose-dependent manner. Therefore 5-HT2 receptor activation facilitated the Na PIC, whereas other 5-HT receptors modulated Vm and Rm. Motoneurons of chronic spinal rats responded to 5-HT and DOI in the same way, but with larger responses and at much lower doses (0.3-1 microM), thus exhibiting a 30-fold supersensitivity to 5-HT. Specifically the Na PIC was supersensitive to 5-HT2 receptor activation with DOI. Also, Rm and Vm were supersensitive to 5-HT. Consistent with the known critical role of the Na PIC in repetitive firing, enhancement of the Na PIC by DOI or 5-HT facilitated the repetitive firing evoked by steady current injection and enabled repetitive firing in a subpopulation of motoneurons of acute spinal rats that were initially unable to produce sustained repetitive firing. We suggest that after spinal transection, residual endogenous spinal sources of 5-HT help facilitate the Na PIC and repetitive firing. With chronic injury, the developed 5-HT supersensitivity more than compensates for lost brain stem 5-HT, so that the Na PIC is large and motoneurons are very excitable, thus contributing to spasticity.

Persistent sodium currents and repetitive firing in motoneurons of the sacrocaudal spinal cord of adult rats

Months after sacral spinal transection in rats (chronic spinal rats), motoneurons below the injury exhibit large, low-threshold persistent inward currents (PICs), composed of persistent sodium currents (Na PICs) and persistent calcium currents (Ca PICs). Here, we studied whether motoneurons of normal adult rats also exhibited Na and Ca PICs when the spinal cord was acutely transected at the sacral level (acute spinal rats) and examined the role of the Na PIC in firing behavior. Intracellular recordings were obtained from motoneurons of acute and chronic spinal rats while the whole sacrocaudal spinal cord was maintained in vitro. Compared with chronic spinal rats, motoneurons of acute spinal rats were more difficult to activate because the input resistance was 22% lower and resting membrane potential was hyperpolarized 4.1 mV further below firing threshold (-50.9 +/- 6.2 mV). In acute spinal rats, during a slow voltage ramp, a PIC was activated subthreshold to the spike (at -57.2 +/- 5.0 mV) and reached a peak current of 1.11 +/- 1.21 nA. This PIC was less than one-half the size of that in chronic spinal rats (2.79 +/- 0.94 nA) and usually was not large enough to produce bistable behavior (plateau potentials and self-sustained firing not present), unlike in chronic spinal rats. The PIC was composed of two components: a TTX-sensitive Na PIC (0.44 +/- 0.36 nA) and a nimodipine-sensitive Ca PIC (0.78 +/- 0.82 nA). Both were smaller than in chronic spinal rats (but with similar Na/Ca ratio). The presence of the Na PIC was critical for normal repetitive firing, because no detectable Na PIC was found in the few motoneurons that could not fire repetitively during a slow ramp current injection and motoneurons that had large Na PICs more readily produced repetitive firing and had lower minimum firing rates compared with neurons with small Na PICs. Furthermore, when the Na PIC was selectively blocked with riluzole, steady repetitive firing was eliminated, even though transient firing could be evoked on a rapid current step and the spike itself was unaffected. In summary, only small Ca and Na PICs occur in acute spinal motoneurons, but the Na PIC is essential for steady repetitive firing. We discuss how availability of monoamines may explain the variability in Na PICs and firing in the normal and spinal animals.

Effects of baclofen on spinal reflexes and persistent inward currents in motoneurons of chronic spinal rats with spasticity

In the months after spinal cord injury, motoneurons develop large voltage-dependent persistent inward currents (PICs) that cause sustained reflexes and associated muscle spasms. These muscle spasms are triggered by any excitatory postsynaptic potential (EPSP) that is long enough to activate the PICs, which take > 100 ms to activate. The PICs are composed of a persistent sodium current (Na PIC) and a persistent calcium current (Ca PIC). Considering that Ca PICs have been shown in other neurons to be inhibited by baclofen, we tested whether part of the antispastic action of baclofen was to reduce the motoneuron PICs as opposed to EPSPs. The whole sacrocaudal spinal cord from acute spinal rats and spastic chronic spinal rats (with sacral spinal transection 2 mo previously) was studied in vitro. Ventral root reflexes were recorded in response to dorsal root stimulation. Intracellular recordings were made from motoneurons, and slow voltage ramps were used to measure PICs. Chronic spinal rats exhibited large monosynaptic and long-lasting polysynaptic ventral root reflexes, and motoneurons had associated large EPSPs and PICs. Baclofen inhibited these reflexes at very low doses with a 50% inhibition (EC50) of the mono- and polysynaptic reflexes at 0.26 +/- 0.07 and 0.25 +/- 0.09 (SD) microM, respectively. Baclofen inhibited the monosynaptic reflex in acute spinal rats at even lower doses (EC50 = 0.18 +/- 0.02 microM). In chronic (and acute) spinal rats, all reflexes and EPSPs were eliminated with 1 microM baclofen with little change in motoneuron properties (PICs, input resistance, etc), suggesting that baclofen's antispastic action is presynaptic to the motoneuron. Unexpectedly, in chronic spinal rats higher doses of baclofen (20-30 microM) significantly increased the total motoneuron PIC by 31.6 +/- 12.4%. However, the Ca PIC component (measured in TTX to block the Na PIC) was significantly reduced by baclofen. Thus baclofen increased the Na PIC and decreased the Ca PIC with a net increase in total PIC. By contrast, when a PIC was induced by 5-HT (10-30 microM) in motoneurons of acute spinal rats, baclofen (20-30 microM) significantly decreased the PIC by 38.8 +/- 25.8%, primarily due to a reduction in the Ca PIC (measured in TTX), which dominated the total PIC in these acute spinal neurons. In summary, baclofen does not exert its antispastic action postsynaptically at clinically achievable doses (< 1 microM), and at higher doses (10-30 microM), baclofen unexpectedly increases motoneuron excitability (Na PIC) in chronic spinal rats.

Spastic long-lasting reflexes of the chronic spinal rat studied in vitro

Over the months following sacral spinal cord transection in adult rats, a pronounced spasticity syndrome emerges in the affected tail musculature, where long-lasting muscle spasms can be evoked by low-threshold afferent stimulation (termed long-lasting reflex). To develop an in vitro preparation to examine the neuronal mechanisms underlying spasticity, we removed the whole sacrocaudal spinal cord of these spastic chronic spinal rats (>1 mo after S(2) sacral spinal transection) and maintained it in artificial cerebral spinal fluid in a recording chamber. The ventral roots were mounted on monopolar recording electrodes in grease, and the reflex responses to dorsal root stimulation were recorded and compared with the reflexes seen in the awake chronic spinal rat. When the dorsal roots were stimulated with a single pulse, a long-lasting reflex occurred in the ventral roots, with identical characteristics to the long-lasting reflex in the awake spastic rat tail. The reflex response was low threshold (T), short latency, long duration ( approximately 2 s), and enhanced by repeated stimulation. Brief high-frequency stimulation trains (0.5 s, 100 Hz, 1.5 x T) evoked even longer duration responses (5-10 s), with repeated bursts of activity that were similar to the repeated muscle spasms evoked in awake rats with stimulation trains or manual skin stimulation. Stimulation of a given dorsal root evoked long-lasting reflexes in both the ipsilateral and contralateral ventral roots. Long-lasting reflexes did not occur in the sacrocaudal spinal cord of acute spinal rats (S(2) transection), which is similar to the areflexia seen in awake acute spinal rats. However, long-lasting reflexes could be made to occur in the acute spinal rat by altering K(+) (7 mM) or Mg(2+) (0 mM) concentrations, or by application of high doses of the neuromodulators norepinephrine (NE, >20 microM) or serotonin (5-HT, >20 microM). In chronic spinal rats, much lower doses of these neuromodulators (0.1 microM) enhanced the long-lasting reflexes, suggesting a denervation supersensitivity to 5-HT and NE following injury. Higher doses of NE or 5-HT produced a paradoxical inhibition of the long-lasting reflexes. The high dose inhibition by NE was mimicked by the alpha(2)-adrenergic receptor agonist clonidine but not the alpha(1)-adrenergic receptor agonist methoxamine. In summary, the sacral spinal in vitro preparation offers a new approach to the study of spinal cord injury and analysis of antispastic drugs.

Spastic Long-Lasting Reflexes in the Awake Rat After Sacral Spinal Cord Injury

Following chronic sacral spinal cord transection in rats the affected tail muscles exhibit marked spasticity, with characteristic long-lasting tail spasms evoked by mild stimulation. The purpose of the present paper was to characterize the long-lasting reflex seen in tail muscles in response to electrical stimulation of the tail nerves in the awake spastic rat, including its development with time and relation to spasticity. Before and after sacral spinal transection, surface electrodes were placed on the tail for electrical stimulation of the caudal nerve trunk (mixed nerve) and for recording EMG from segmental tail muscles. In normal and acute spinal rats caudal nerve trunk stimulation evoked little or no EMG reflex. By 2 wk after injury, the same stimulation evoked long-lasting reflexes that were 1) very low threshold, 2) evoked from rest without prior EMG activity, 3) of polysynaptic latency with >6 ms central delay, 4) about 2 s long, and 5) enhanced by repeated stimulation (windup). These reflexes produced powerful whole tail contractions (spasms) and developed gradually over the weeks after the injury (≤52 wk tested), in close parallel to the development of spasticity. Pure low-threshold cutaneous stimulation, from electrical stimulation of the tip of the tail, also evoked long-lasting spastic reflexes, not seen in acute spinal or normal rats. In acute spinal rats a strong C-fiber stimulation of the tip of the tail (20 × T) could evoke a weak EMG response lasting about 1 s. Interestingly, when this C-fiber stimulation was used as a conditioning stimulation to depolarize the motoneuron pool in acute spinal rats, a subsequent low-threshold stimulation of the caudal nerve trunk evoked a 300–500 ms long reflex, similar to the onset of the long-lasting reflex in chronic spinal rats. A similar conditioned reflex was not seen in normal rats. Thus there is an unusually long low-threshold polysynaptic input to the motoneurons (pEPSP) that is normally inhibited by descending control. This pEPSP is released from inhibition immediately after injury but does not produce a long-lasting reflex because of a lack of motoneuron excitability. With chronic injury the motoneuron excitability is increased markedly, and the pEPSP then triggers sustained motoneuron discharges associated with long-lasting reflexes and muscle spasms.

Differential distribution of interneurons in the neural networks that control walking in the mudpuppy (Necturus maculatus) spinal cord

Locomotor behavior is believed to be produced by interneuronal networks that are intrinsically organized to generate the underlying complex spatiotemporal patterns. In order to study the temporal correlation between the firing of individual interneurons and the pattern of locomotion, we utilized the spinal cord-forelimb preparation from the mudpuppy, in which electrophysiological recordings of neuronal activity were achieved during walking-like movement of the forelimb induced by bath application of N-methyl- D-aspartate (NMDA). Intra- and extracellular recordings were made in the C2 and C3 segments of the spinal cord. These segments contain independent flexor and extensor centers for the forelimb movement about the elbow joint during walking. Among the 289 cells recorded in the intermediate gray matter (an area between the ventral and dorsal horns) of the C2 and C3 segments, approximately 40% of the cells fired rhythmically during "walking." The firing rates were 6.4+/-0.4 impulses/s (mean +/- SE). These rhythmically active cells were classified into four types based on their phase of activity during a normalized step cycle. About half the rhythmic cells fired in phase with either the flexor (F) or extensor (E) motoneurons. The rest fired in the transitions between the two phases (F-->E and E-->F). Longitudinal distributions of the four types of interneurons along the spinal cord were in agreement with observations that revealed distinct but overlapping flexor and extensor centers for walking. Some cells triggered short-latency responses in the elbow flexor or extensor muscles and may be last-order interneurons. These observations suggest that there is a differential distribution of phase-specific interneurons in the central pattern generator of the mudpuppy spinal cord for walking.

Alpha-amino acid phenolic ester derivatives: novel water-soluble general anesthetic agents which allosterically modulate GABA(A) receptors

In the search for a novel water-soluble general anesthetic agent the activity of an alpha-amino acid phenolic ester lead, identified from patent literature, was markedly improved. In addition to improving in vivo activity in mice, good in vitro activity at GABA(A) receptors was also conferred. Within the series of compounds good enantioselectivity for both in vitro and in vivo activity was found, supporting a protein-mediated mechanism of action for anesthesia involving allosteric modulation of GABA(A) receptors. alpha-Amino acid phenolic ester 19, as the hydrobromide salt Org 25435, was selected for clinical evaluation since it retained the best overall anesthetic profile coupled with improved stability and water solubility. In the clinic it proved to be an effective intravenous anesthetic in man with rapid onset of and recovery from anesthesia at doses of 3 and 4 mg/kg.

Plateau potentials in sacrocaudal motoneurons of chronic spinal rats, recorded in vitro

Intracellular recordings were made from sacrocaudal tail motoneurons of acute and chronic spinal rats to examine whether plateau potentials contribute to spasticity associated with chronic injury. The spinal cord was transected at the S2 level, causing, over time, exaggerated long-lasting reflexes (hyperreflexia) associated with a general spasticity syndrome in the tail muscles of chronic spinal rats (1-5 mo postinjury). The whole sacrocaudal spinal cord of chronic or acute spinal rats was removed and maintained in vitro in normal artificial cerebral spinal fluid (ACSF). Hyperreflexia in chronic spinal rats was verified by recording the long-lasting ventral root responses to dorsal root stimulation in vitro. The intrinsic properties of sacrocaudal motoneurons were studied using intracellular injections of slow triangular current ramps or graded current pulses. In chronic spinal rats, the current injection triggered sustained firing and an associated sustained depolarization (plateau potential; 34/35 cells; mean, 5.5 mV; duration >5 s; normal ACSF). The threshold for plateau initiation was low and usually corresponded to an acceleration in the membrane potential just before recruitment. After recruitment and plateau activation, the firing rate changed linearly with current during the slow ramps [63% of cells had a linear frequency-current (F-I) relation] despite the presence of the plateau. The persistent inward current (I(PIC)) producing the plateau and sustained firing was estimated to be on average 0.8 nA as determined by the reduction in injected current needed to stop the sustained firing [DeltaI = -0.8 +/- 0.6 (SD) nA], compared with the current needed to start firing (I = 1.7 +/- 1.5 nA; 47% reduction). In motoneurons of acute spinal rats, plateaus were rarely seen (3/22), although they could be made to occur with bath application of serotonin. In motoneurons of chronic spinal rats there were no significant changes in the mean passive input resistance, rheobase or amplitude of the spike afterhyperpolarization (AHP) as compared with acute spinal rats. However, there were significant increases in AHP duration and initial firing rate at recruitment and decreases in minimum firing rate and F-I slope. We suggest that the higher initial firing rate resulted from the plateau activation at recruitment and the lower F-I slope resulted from an increase in active conductance during firing, due to I(PIC). Brief dorsal root stimulation also triggered a plateau and sustained discharge (long-lasting reflexes; 2-5 s) in motoneurons of chronic (but not acute) spinal rats. When the plateau was eliminated by a hyperpolarizing current bias, the reflex response was significantly shortened (to 1 s). Thus plateaus contributed substantially to the long-lasting reflexes in vitro and therefore should contribute significantly to the corresponding exaggerated reflexes and spasticity in awake chronic spinal rats.

Evidence for plateau potentials in tail motoneurons of awake chronic spinal rats with spasticity

Motor units of segmental tail muscles were recorded in awake rats following acute (1-2 days) and chronic (>30 days) sacral spinal cord transection to determine whether plateau potentials contributed to sustained motor-unit discharges after injury. This study was motivated by a companion in vitro study that indicated that after chronic spinal cord injury, the tail motoneurons of the sacrocaudal spinal cord exhibit persistent inward currents (I(PIC)) that cause intrinsically sustained depolarizations (plateau potentials) and firing (self-sustained firing). Importantly, in this companion study, the plateaus were fully activated at recruitment and subsequently helped sustain the firing without causing abrupt nonlinearities in firing. That is, after recruitment and plateau activation, the firing rate was modulated relatively linearly with injected current and therefore provided a good approximation of the input to the motoneuron despite the plateau. Thus in the present study, pairs of motor units were recorded simultaneously from the same muscle, and the firing rate (F) of the lowest-threshold unit (control unit) was used as an estimate of the synaptic input to both units. We then examined whether firing of the higher-threshold unit (test unit) was intrinsically maintained by a plateau, by determining whether more synaptic input was required to recruit the test unit than to maintain its firing. The difference in the estimated synaptic input at recruitment and de-recruitment of the test unit (i.e., change in control unit rate, DeltaF) was taken as an estimate of the plateau current (I(PIC)) that intrinsically sustained the firing. Slowly graded manual skin stimulation was used to recruit and then de-recruit the units. The test unit was recruited when the control unit rate was on average 17.8 and 18.9 Hz in acute and chronic spinal rats, respectively. In chronic spinal rats, the test unit was de-recruited when the control unit rate (re: estimated synaptic input) was significantly reduced, compared with at recruitment (DeltaF = -5.5 Hz), and thus a plateau participated in maintaining the firing. In the lowest-threshold motor units, even a brief stimulation triggered very long-lasting firing (seconds to hours; self-sustained firing). Higher-threshold units required continuous stimulation (or a spontaneous spasm) to cause firing, but again more synaptic input was needed to recruit the unit than to maintain its firing (i.e., plateau present). In contrast, in acute spinal rats, the stimulation did not usually trigger sustained motor-unit firing that could be attributed to plateaus because DeltaF was not significantly different from zero. These results indicate that plateaus play an important role in sustaining motor-unit firing in awake chronic spinal rats and thus contribute to the hyperreflexia and hypertonus associated with chronic injury.

Activity of hindlimb motor units during locomotion in the conscious rat

This paper compares the activity of hindlimb motor units from muscles mainly composed of fast-twitch muscle fibers (medial and lateral gastrocnemius: MG/LG, tibialis anterior: TA) to motor units from a muscle mainly composed of slow-twitch muscle fibers (soleus: SOL) during unrestrained walking in the conscious rat. Several differences in the activation profiles of motor units from these two groups of muscles were observed. For example, motor units from fast muscles (e.g., MG/LG and TA) fired at very high mean frequencies of discharge, ranging from 60 to 100 Hz, and almost always were recruited with initial doublets or triplets, i.e., initial frequencies >/=100 Hz. In contrast, the majority of SOL units fired at much lower mean rates of discharge, approximately 30 Hz, and had initial frequencies of only 30-60 Hz (i.e., there were no initial doublets/triplets >/=100 Hz). Thus the presence of initial doublet or triplets was dependent on the intrinsic properties of the motor unit, i.e., faster units were recruited with a doublet/triplet more often than slower units. Moreover, in contrast to units from the slow SOL muscle, the activity of single motor units from the fast MG/LG muscle, especially units recruited midway or near the end of a locomotor burst, was unrelated to the activity of the remainder of the motoneuron pool, as measured by the corresponding gross-electromyographic (EMG) signal. This dissociation of activity was suggested to arise from a compartmentalized recruitment of the MG/LG motoneuron pool by the rhythm-generating networks of the spinal cord. In contrast, when comparing the rate modulation of simultaneously recorded motor units within a single LG muscle compartment, the frequency profiles of unit pairs were modulated in a parallel fashion. This suggested that the parent motoneurons were responsive to changes in synaptic inputs during unrestrained walking, unlike the poor rate modulation that occurs during locomotion induced from brain stem stimulation. In summary, data from this study provide evidence that the firing behavior of motor units during unrestrained walking is influenced by both the intrinsic properties of the parent motoneuron and by synaptic inputs from the locomotor networks of the spinal cord. In addition, it also provides the first extensive description of motor-unit activity from different muscles during unrestrained walking in the conscious rat.

Gi/Go couple met-enkephalin to inhibition of cholinergic and beta-adrenergic stimulation of lacrimal secretion

PURPOSE

To determine whether G-protein-mediated inhibition of secretion by met-enkephalin involves cyclic adenosine monophosphate (cAMP)-dependent events and to identify the G proteins that couple met-enkephalin to inhibition of lacrimal secretion.

METHODS

Secretion of protein was measured in 3-day primary cultures of rabbit lacrimal acini exposed to vehicle, the cholinergic agonist carbachol (Cch), the beta-adrenergic agonist isoproterenol (Isop), vasoactive intestinal peptide (VIP), or forskolin (FSK) with or without the enkephalin analog D-ala2-met-enkephalinamide (DALA). In separate experiments, cells were pretreated with pertussis toxin or polyclonal antibodies against the alpha subunits of Gi/Go to determine the physiologic role of G proteins in met-enkephalin inhibition of the release of lacrimal protein. Adenylyl cyclase (AC) activity was measured by a cAMP-dependent protein kinase binding assay in lacrimal membranes in response to the same agonists used in the secretion studies.

RESULTS

Cch resulted in a significant increase in protein release from cultured lacrimal acini. Increased secretion also occurred with Isop, VIP, and FSK. Cch- and Isop-stimulated secretion was inhibited by DALA to near-basal values. However, DALA did not inhibit VIP- or FSK-stimulated secretion. The inhibitory effect of DALA on Cch and Isop stimulation of secretion was reversed by pertussis toxin. Inhibition of Cch-stimulated secretion was blocked by antibody specific to a common peptide sequence of Gialpha1 and Gialpha2 but was not blocked by anti-Gialpha1 antibody. The inhibitory effect on Cch-stimulated secretion was also blocked by anti-Gialpha3 and anti-Goalpha. Similar experiments resulted in a reversal of DALA inhibition of beta-adrenergic stimulation of secretion by immunoneutralization of Gialpha1/2 and Goalpha but not by immunoneutralization of Gialpha1 or Gialpha3. VIP, Isop, and FSK significantly stimulated AC. However, Cch had no effect on the activity of the enzyme. In addition, DALA had no effect on AC activity under any conditions.

CONCLUSIONS

These results show that enkephalin inhibition of cholinergic and beta-adrenergic stimulation of secretion is mediated by Gi2, Gi3, and Go. The effector coupled by the G proteins is not AC. However, we suggest a role for met-enkephalin in G-protein-coupled modulation of ion channels important for cholinergic and beta-adrenergic stimulation of lacrimal secretion.

Alpha(2) adrenoceptor agonists as potential analgesic agents. 1. (Imidazolylmethyl)oxazoles and -thiazoles

A series of (imidazolylmethyl)oxazoles and -thiazoles were prepared and evaluated as alpha(2) adrenoceptor agonists. These compounds were also tested in in vivo paradigms that are predictive of analgesic activity. Variations in both the imidazole and thiazole portions of the molecule were investigated. Some of the more potent compounds such as 22, 26, 45, and 53 displayed alpha(2) receptor binding in the 10-20 nM range and also had significant antinociceptive activity in the mouse abdominal irritant test (MAIT).

Activation patterns of hindlimb motor units in the awake rat and their relation to motoneuron intrinsic properties

The activity of hindlimb motor units from the lateral gastrocnemius and tibialis anterior muscles in the awake rat was compared during locomotion and during slow, sinusoidal muscle stretch. The majority of units were activated with high initial frequencies and often commenced firing with an initial doublet or triplet, even when activated by slow muscle stretch. The high firing rates at recruitment occurred without jumps in the firing rates of other concurrently activated units, the firing rate profiles of which were used as a measure of the net synaptic drive onto the motoneuronal pool. This suggested that the sharp recruitment jumps were not due to an abrupt increase in synaptic drive but rather due to intrinsic properties of the motoneuron. In addition, motor units that were activated phasically by the muscle stretch fired more action potentials during muscle shortening than during muscle lengthening, resulting in rightwardly skewed, asymmetrical firing profiles. In contrast, when the same units fired tonically during the imposed muscle stretch, the frequency profiles were modulated symmetrically and no nonlinearities were observed. Tonically firing units were modulated symmetrically throughout a wide range of firing frequencies, and discrete jumps in rate (i.e., bistable firing) were not observed. The sharp recruitment jumps during locomotion and muscle stretch are proposed to have resulted from the additional depolarization produced by the activation of plateau potentials at recruitment. Likewise, the sustained activation of plateaus subsequent to recruitment may have produced the prolonged firing of the motor units during sinusoidal muscle stretch.

Mediated priming in younger and older adults

This paper reports the result of a lexical decision experiment in which the primes were either directly related to their targets, mediated, or unrelated. Mediated primes are indirectly related to their targets through a single connecting link (e.g., PASTURE-COW-MILK). Older and younger adult subjects responded to each letter string in a continuous lexical decision task, deciding whether each string was a word or a nonword. The results indicated that both younger and older subjects benefited from the mediated primes, as well as from the directly related primes. The results are discussed in relation to issues of age changes in processing speed.

Spasticity in rats with sacral spinal cord injury

We have investigated sacral spinal cord lesions in rats with the goal of developing a rat model of muscular spasticity that is minimally disruptive, not interfering with bladder, bowel, or hindlimb locomotor function. Spinal transections were made at the S2 sacral level and, thus, only affected the tail musculature. After spinal transection, the muscles of the tail were inactive for 2 weeks. Following this initial period, hypertonia, hyperreflexia, and clonus developed in the tail, and grew more pronounced with time. These changes were assessed in the awake rat, since the tail is readily accessible and easy to manipulate. Muscle stretch or cutaneous stimulation of the tail produced muscle spasms and marked increases in muscle tone, as measured with force and electromyographic recordings. When the tail was unconstrained, spontaneous or reflex induced flexor and extensor spasms coiled the tail. Movement during the spasms often triggered clonus in the end of the tail. The tail hair and skin were extremely hyperreflexive to light touch, withdrawing quickly at contact, and at times clonus could be entrained by repeated contact of the tail on a surface. Segmental tail muscle reflexes, e.g., Hoffman reflexes (H-reflexes), were measured before and after spinalization, and increased significantly 2 weeks after transection. These results suggest that sacral spinal rats develop symptoms of spasticity in tail muscles with similar characteristics to those seen in limb muscles of humans with spinal cord injury, and thus provide a convenient preparation for studying this condition.

Synaptic activation of plateaus in hindlimb motoneurons of decerebrate cats

Intracellular recordings were made from hindlimb motoneurons in decerebrate cats to study how synaptic inputs could affect the threshold at which plateau potentials are activated with current injections through the recording microelectrode in the cell body. This study was prompted by recent evidence that the noninactivating inward currents that regeneratively produce the plateau potentials arise (partly) from dendritic conductances, which may be relatively more accessible to synaptic input than to current injected into the soma. Initially, cells were studied by injecting a slow triangular current ramp intracellularly to determine the threshold for activation of the plateau. In cells where the sodium spikes were blocked with intracellular QX314, plateau activation was readily seen as a sudden jump in membrane potential, which was not directly reversed as the current was decreased. With normal spiking, the plateau activation (the noninactivating inward current) was reflected by a steep and sustained jump in firing rate that was not directly reversed as the current was decreased. Importantly, the threshold for plateau activation (at 34 Hz on average) was significantly above the recruitment level (13 Hz on average). When tonic synaptic excitation [excitatory postsynaptic potentials (EPSPs)] was provided either by stretching the triceps surae muscle or by stimulating its nerve at a high frequency, the threshold for plateau activation by intracellular current injection was significantly lowered (by 12 Hz or 5.8 mV on average, without and with QX314, respectively). Conversely, tonic synaptic inhibition [inhibitory postsynaptic potentials (IPSPs)], provided by appropriate nerve stimulation, significantly raised the plateau threshold (by 19 Hz or 7.6 mV on average). These effects were graded with the intensity of tonic EPSPs and IPSPs. Strong enough EPSPs brought the plateau threshold down sufficiently that it was activated by the intracellular current soon after recruitment. A further increase in tonic EPSPs recruited the cell directly, and in this case the plateau was activated at or before recruitment. The finding that synaptic excitation can produce plateau activation below the recruitment level is of importance for the interpretation of its function. With this low-threshold activation, the plateau potentials are likely important in securing an effective recruitment to frequencies that produce significant force generation and would subsequently have no further affect on the frequency modulation, other than to provide a steady depolarizing bias that would help to sustain firing (cf. self-sustained firing). Additional jumps in frequency after recruitment (i.e., bistable firing) would not be expected.

Decerebration by global ischemic stroke in rats

In this study we present a fast and simple technique to decerebrate rats. By injecting polyvinylsiloxane (PVS) into both common carotid arteries we occluded the circle of Willis and all cerebral arteries, thereby completely interrupting the blood supply to the cerebrum. High viscosity PVS was used so that it only entered the large arteries, and did not pass into the capillary beds. This procedure reliably resulted in an anemic decerebration, without interfering with the blood supply to the brainstem. Long-term survival was achieved by reducing intracranial pressure by the application of steroids and/or opening the skull.

Short-term plasticity in hindlimb motoneurons of decerebrate cats

Cat hindlimb motoneurons possess noninactivating voltage-gated inward currents that can, under appropriate conditions, regeneratively produce sustained increments in depolarization and firing of the cell (i.e., plateau potentials). Recent studies in turtle dorsal horn neurons and motoneurons indicate that facilitation of plateaus occurs with repeated plateau activation (decreased threshold and increased duration; this phenomenon is referred to as warm-up). The purpose of the present study was to study warm-up in cat motoneurons. Initially, cells were studied by injecting a slow triangular current ramp intracellularly to determine the threshold for activation of the plateau. In cells where the sodium spikes were blocked with intracellular QX314, plateau activation was readily seen as a sudden jump in membrane potential, which was not directly reversed as the current was decreased (cf. hysteresis). With normal spiking, the plateau activation (the noninactivating inward current) was reflected by a steep and sustained jump in firing rate, which was not directly reversed as the current was decreased (hysteresis). Repetitive plateau activation significantly lowered the plateau activation threshold in 83% of cells (by on average 5 mV and 11 Hz with and without QX314, respectively). This interaction between successive plateaus (warm-up) occurred when tested with 3- to 6-s intervals; no interaction occurred at times >20 s. Plateaus initiated by synaptic activation from muscle stretch were also facilitated by repetition. Repeated slow muscle stretches that produced small phasic responses when a cell was hyperpolarized with intracellular current bias produced a larger and more prolonged responses (plateau) when the bias was removed, and the amplitude and duration of this response grew with repetition. The effects of warm-up seen with intracellular recordings during muscle stretch could also be recorded extracellularly with gross electromyographic (EMG) recordings. That is, the same repetitive stretch as above produced a progressively larger and more prolonged EMG response. Warm-up may be a functionally important form of short-term plasticity in motoneurons that secures efficient motor output once a threshold level is reached for a significant period. Finally, the finding that warm-up can be readily observed with gross EMG recordings will be useful in future studies of plateaus in awake animals and humans.

Gi2 and Gi3 couple met-enkephalin to inhibition of lacrimal secretion

PURPOSE

The intent of this study was to identify the pertussis toxin-sensitive G proteins that couple met-enkephalin to the inhibition of cholinergically stimulated secretion in rabbit lacrimal gland acini.

METHODS

The authors detected G proteins in membranes from freshly isolated glands, freshly isolated acini, and cultured lacrimal acini from rabbits by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and immunoblotting. Antibodies against the alpha subunits of Gi1, Gi1 and Gi2, or Gi3 were used in cultured acini permeabilized by streptolysin-O to determine the role of the G proteins in met-enkephalin inhibition of cholinergic stimulation of lacrimal acinar protein release.

RESULTS

Western blot analysis showed the presence of the alpha subunits of Gi2 and Gi3, but not Gi1, in all three membrane preparations. The met-enkephalin analog D-Ala2-methionine enkephalinamide (DALA) inhibited cholinergic stimulation of secretion by cultured rabbit acinar cells to near basal levels. Inhibition of secretion by DALA was blocked by insertion of antibody to a peptide sequence common to Gialpha1 and Gialpha2, but was not blocked by antibody against a specific Gialpha1 sequence. The inhibitory effect of DALA also was blocked by antibody to a Gialpha3 sequence. At low doses of anti-Gialpha1/2 and anti-Gialpha3 in combination, the effect on reversal of inhibition was additive. However, at higher doses, the effect of the combination was no greater than the effect of either antibody alone.

CONCLUSIONS

These results demonstrate that met-enkephalin inhibition of cholinergic secretion is mediated by way of the pertussis toxin-sensitive G proteins Gi2 and Gi3 in cultured rabbit lacrimal acini. Because the effects of the G proteins are not additive, the intracellular events distal to G protein activation most likely converge at some point before exocytosis.

Identification, localization, and modulation of neural networks for walking in the mudpuppy (Necturus maculatus) spinal cord

We tested the hypothesis that the neural networks for walking in the mudpuppy can be divided into a flexor and an extensor center, each of which contains collections of interneurons localized in the vicinity of their motoneuron pools. Combining a battery of techniques, we identified and localized the elbow flexor center and its motoneuron pool in the C2 segment and the elbow extensor center and its motoneuron pool in the C3 segment. Rhythmic flexion or extension of the limb in isolation could be induced by continuous trains of current pulses of the C2 or C3 segments, respectively. Independent activation could also occur after application of glutamate receptor agonist NMDA. Part of segment C2 in isolation generated rhythmic elbow flexor bursts, whereas part of segment C3 in isolation generated rhythmic elbow extensor bursts. An isolated region spanning the C3 roots generated both flexor and extensor bursts. The step cycle was modulated in a phase-dependent manner by stimulation of the dorsal roots, the ventral roots, or either of the two centers. The effects of ventral root stimulation were removed by deafferentation to block reafferent input attributable to muscle contraction induced by the stimulation. We conclude that the neural networks for walking contain at least a flexor and an extensor generator that are localized in close apposition to the motoneuron pools, that the two centers can work independently despite the fact that there are reciprocal inhibitory interconnections between them, and that sensory input interacts with the spinal neural networks to reset the ongoing walking rhythm in a phase-dependent manner.

Self-sustained firing of human motor units

Motoneurons of invertebrates and vertebrates can continue to fire repetitively after being activated by a brief, excitatory synaptic input (self-sustained firing). This firing behavior is due to the activation of intrinsic, voltage-gated currents which produce sustained regenerative depolarizations (plateau potentials) of the cell. Examination of these intrinsic cellular properties has been performed in reduced animal preparations and it is unknown if such self-sustained firing occurs in motoneurons of the intact human. In this paper, we present evidence of this in the human by using a technique of dual motor unit recordings. Subjects were instructed to maintain a constant dorsiflexion effort, and the common synaptic input (e.g. descending drive) onto the tibialis anterior (TA) motoneuron pool was monitored by recording the firing frequency of a low threshold 'control' unit. Once the firing rate of the control unit was constant, vibration of the TA tendon recruited a second 'test' unit which continued to fire after the vibration (i.e. synaptic input) was removed, even though the firing rate of the control unit (and thus, the common drive) remained the same or decreased. Self-sustained firing of motoneurons such as this may reduce the need for prolonged synaptic input when constant muscle activation is required (e.g. for postural tone).

Effect of sensory denervation on the structure and physiologic responsiveness of rabbit lacrimal gland

PURPOSE

This work was conducted to determine the effects of unilateral trigeminal ganglion ablation on lacrimal gland structure and secretory activity.

METHODS

Adult male New Zealand rabbits underwent unilateral thermocoagulation of the ophthalmic division of the trigeminal ganglion. Sensory denervation was affirmed by anatomic inspection of the lesion and transmission electron microscopy (TEM) of the lacrimal gland innervation. Eight to 10 days after the procedure, the intraorbital lacrimal glands were removed from both sides. To compare the physiologic competence of the intact and denervated glands, freshly isolated gland fragments from the paired intact and denervated glands were stimulated with carbachol (100 microM), isoproterenol (10 microM), phorbol-12,13-dibutyrate (PDBu, 10 microM), forskolin (40 microM), or vehicle. Total secreted protein was measured at 30 or 60 min after the establishment of baseline values. Intact and denervated glands also were examined by light and TEM, and the morphologic appearance of the acinar structures as well as the appearance of nerves innervating the gland after denervation were assessed. Similar experiments were conducted with animals that underwent unilateral superior cervical ganglionectomy.

RESULTS

Tissues from sensory denervated glands released significantly more protein than did tissues from innervated glands in response to in vitro stimulation by carbachol or isoproterenol but not in response to PDBu or forskolin. Microscopy showed that the acinar cells that had undergone sensory denervation showed a massive accumulation of secretory granules. The secretory granules filled the entire cytoplasmic space and displaced the ellipsoidal nuclei to the extreme periphery. Examination of segments of nerves revealed numerous unmyelinated axons, a few small-diameter myelinated axons, and a large amount of nerve degeneration after sensory denervation. In contrast to the effects of sensory denervation, sympathetic denervation did not alter either the acinar appearance or secretory responsiveness of the gland.

CONCLUSION

Loss of the considerable sensory innervation from the trigeminal ganglion has pronounced effects on the pharmacologic responsiveness and the structure of the lacrimal gland. The effects of sensory innervation on the gland may be mediated through two possible pathways: direct input to the gland or control of the preganglionic parasympathetic pathway.

One step is not enough: making better use of association norms to predict cued recall

Cued recall is strongly affected by the strength of the preexisting connection between the test cue and the information to be recalled, the target. In all past work, preexisting cue-to-target strength has been measured by the probability that the cue produced the target in free association. This paper presents four experiments showing that this use of such norms underestimates the strength of the connection and that a more accurate estimate can be obtained by incorporating indirect as well as direct connections in the estimate. Experiments 1 and 2 showed that in extralist cued recall both the strength and number of two-step indirect connections facilitate recall. Experiment 3 showed that three-step connections have negligible effects. Experiment 4 used an intralist task in which cue and target are first studied together, and the results showed once again that indirect connections can affect recall. In all of these experiments, indirect connections had an effect on recall that was larger when direct cue-to-target strength was weak than when it was strong. Implications for using association norms in research are described, and an algorithm for using association norms to measure cue-to-target strength is proposed.

Recollective and automatic uses of memory

Three cued-recall experiments examined the effects of learning conditions and set size on recollective and automatic uses of memory. Words were studied under different conditions and had either small or large preexisting associative sets. Results based on the process-dissociation procedure showed that learning conditions and set size influenced recollective uses of memory, whereas only set size influenced automatic uses. Other results indicated that process-dissociation and direct-indirect test procedures produce similar results. The findings suggest that the relative contributions of recently acquired information and preexisting information depend on how memory is being used. Recollective uses of memory are affected by the nature of recent study and by what such study activates in long-term memory. In contrast, automatic uses of memory are more affected by what the test cue automatically activates than by what has been learned during recent study.

Positive force feedback control of muscles

This study was prompted by recent evidence for the existence of positive force feedback in feline locomotor control. Our aim was to establish some basic properties of positive force feedback in relation to load compensation, stability, intrinsic muscle properties, and interaction with displacement feedback. In human subjects, muscles acting about the wrist and ankle were activated by feedback-controlled electrical stimulation. The feedback signals were obtained from sensors monitoring force and displacement. The signals were filtered to mimic transduction by mammalian tendon organ and muscle spindle receptors. We found that when muscles under positive force feedback were loaded inertially, they responded in a stable manner with increased active force. The activation attenuated the muscle stretch (yield) that would otherwise occur in the absence of feedback. With enough positive force feedback gain, yield could actually reverse. This behavior, which we termed the affirming reaction, was reminiscent of the mammalian positive supporting reaction, a postural response elicited by contact of the foot with the ground. Muscles under positive force feedback remained stable, even when the loop gain (Gf) was set at levels of 2 or 3. In a linear system, if Gf > 1, instability occurs when the loop is closed. On further investigation, we found that Gf changed with joint angle: it declined as the load-bearing muscle actively shortened. We inferred that in closed-loop operation, the active muscles always shortened until Gf approached unity. In other words, the length-tension curve of active muscle ensures stability even when force-related excitation of motoneurons is very large. Concomitant negative displacement feedback reinforced and stabilized load compensation up to a certain gain, beyond which instability occurred. In further trials we included delays of up to 40 ms in the positive force feedback pathway, to model the delays recently described for tendon organ reflexes in cat locomotion. Contrary to expectations, this did not destabilize the loop. Indeed, when instability was deliberately evoked by setting displacement feedback gain high, delays in the positive force feedback pathway actually stabilized control. The stabilization of positive force feedback by inherent properties of the neuromuscular system increases the functional scope to be expected of feedback from force receptors in biological motor control. Our results provide a rationale for the delayed excitatory action of Ib heteronymous input on extensor motoneurons in cat locomotion.

Implications of positive feedback in the control of movement

In this paper we review some theoretical aspects of positive feedback in the control of movement. The focus is mainly on new theories regarding the reflexive role of sensory signals from mammalian tendon organ afferents. In static postures these afferents generally mediate negative force feedback. But in locomotion there is evidence of a switch to positive force feedback action. Positive feedback is often associated with instability and oscillation, neither of which occur in normal locomotion. We address this paradox with the use of analytic models of the neuromuscular control system. It is shown that positive force feedback contributes to load compensation and is surprisingly stable because the length-tension properties of mammalian muscle provide automatic gain control. This mechanism can stabilize control even when positive feedback is very strong. The models also show how positive force feedback is stabilized by concomitant negative displacement feedback and, unexpectedly, by delays in the positive feedback pathway. Other examples of positive feedback in animal motor control systems are discussed, including the beta-fusimotor system, which mediates positive feedback of displacement. In general it is seen that positive feedback reduces the sensitivity of the controlled extremities to perturbations of posture and load. We conclude that positive force feedback can provide stable and effective load compensation that complements the action of negative displacement and velocity feedback.

Gs and Gq/11 couple vasoactive intestinal peptide and cholinergic stimulation to lacrimal secretion

PURPOSE

The intent of this study was to determine the physiological role of selected G proteins in receptor-mediated protein release by lacrimal acini.

METHODS

The role of G proteins in lacrimal secretion was determined in tissues obtained from the lacrimal glands of adult male New Zealand White rabbits. Pertussis toxin treatment of primary acinar cultures and permeabilization of cultured acini with streptolysin-O and insertion of GDP beta S or antibodies against the alpha subunit of Gs or Gq/11 were used to determine the role of G proteins in vasoactive intestinal peptide (VIP) and carbachol-stimulated lacrimal secretion. Gs and Gq/11 were identified in lacrimal membranes obtained from freshly isolated lacrimal gland fragments, freshly isolated acini, and cultured acini by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and immunoblotting.

RESULTS

Permeabilization by streptolysin-O and introduction of guanosine thiodiphosphate into cultured acini blocked stimulation of protein released by either 100 nM VIP or 100 microM carbachol by approximately 50%. Exposure of cultured acini to 100 ng/ml pertussis toxin for 36 to 48 hours did not affect stimulated release by either agonist, indicating that the guanosine triphosphate-dependent actions of VIP and carbachol are mediated through pertussis toxin-insensitive G proteins. Pertussis toxin-insensitive G proteins in lacrimal membranes obtained from freshly isolated glands, freshly isolated acini, and cultured acini were identified with polyclonal antibodies to the alpha subunits of Gs and Gq/11. Immunoblotting of lacrimal membranes with anti-Gs alpha antiserum showed two immunoreactive bands at 44 and 47 kDa. Anti-Gq/11 alpha antiserum detected a single band at 46 kDa in similar membrane preparations. Anti-Gs alpha antiserum reduced the secretory response to VIP by 64% and to carbachol by 37%. Introduction of anti-Gq/11 alpha antiserum reduced the response to carbachol by 70%; however, the response to VIP was unchanged. Simultaneous introduction of both antisera caused no further reduction of VIP-stimulated release than did anti-Gs alpha antiserum alone. However, simultaneous introduction of both anti-Gs alpha and anti-Gq/11 alpha antisera resulted in complete inhibition of the effects of carbachol on protein release by cultured acini.

CONCLUSIONS

These results show that VIP receptor activation of lacrimal protein release is mediated through Gs, whereas cholinergic stimulation involves both Gs and Gq/11. From the authors' results, the authors conclude that Gs links VIP receptor activation to adenylyl cyclase and cyclic adenosine 3'-5' monophosphate production and the ultimate release of protein by acinar cells and that Gq/11 links muscarinic receptor activation to phospholipase C and IP3 and diacylglycerol accumulation, which also leads to protein release. Furthermore, it is hypothesized that Gs has an additional role in the regulation of vesicular traffic and exocytosis.

Measurement of rigidity in Parkinson's disease

Clinical assessment of rigidity in parkinsonian patients is largely qualitative. The reliability and validity of the assessments are sometimes in doubt. Several "engineering" methods of quantifying rigidity have been described, but none has been adopted into general clinical practice. A possible reason is that these methods differ in crucial aspects from the clinical exam. We therefore tackled the problem by monitoring the clinical exam itself, using small sensors to measure the forces and displacements applied. Limb impedance (Z) was computed using parameter identification methods and compared to raters' verbalized ratings of rigidity based on a 5-point scale: the Unified Parkinson's Disease Rating System. The qualitative and quantitative estimates of impedance covaried over a fourfold range, depending on the forces imposed and the subject's motor set. Raters differed by up to 1 full point in their mean qualitative ratings and sometimes disagreed on whether levodopa reduced rigidity. This was not due to any significant differences in the overall range of rigidity they evoked, but rather to the way they scored this range [the ratio of mean rating to mean impedance (R/Z) varied between raters and subjects]. On the other hand, the R/Z ratio was reproducible over separate sets of ratings and may therefore serve to convert measured impedance into a standardized rating. Our results indicate that the current clinical exam may be too abbreviated to detect the sometimes quite small reductions in rigidity after levodopa. We conclude that a device that conveniently quantifies the clinical assessment of rigidity is now available and will lead to more standardized protocols for rating rigidity in the near future.