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Biomedical subjects

R D Hawkins

Publications and source records attributed to R D Hawkins.

At least 37 records · Page 2Linked to original sources
PubMed1998

A preliminary assessment of professional footballers' awareness of injury prevention strategies.

Players from five English professional football clubs completed a questionnaire containing 52 items relating to injury prevention practices and advice received on these issues. Responses were received from 55 players, which represents a mean response of 11 (4) and a response rate of 38 (14)% from each club (means (SD)). The main deficiencies in awareness of injury prevention strategies for players were identified as: use of shin pads during training, carbohydrate intake before and after training and after matches, cool downs after training and matches, and flexibility work. These deficiencies indicate a need for wider education of players in current injury prevention strategies.

Adult↗
PubMed1998

An examination of the frequency and severity of injuries and incidents at three levels of professional football.

OBJECTIVE: To assess the risk of injury to professional footballers during European international and English Premier and First Division league matches. METHODS: Videotaped recordings of 29, 49, and 93 matches from the 1996 European Championship, 1996/1997 English Premier season and 1994 to 1997 English First Division seasons respectively were analysed. During each match, several relevant variables, including the number of fouls, injuries, time of incident, player identity, and injury mechanism, were recorded. RESULTS: Significantly more free kicks were awarded during international matches than during league matches; however, there were no significant differences between the numbers of free kicks awarded over the three First Division seasons assessed. Between 1.7 and 3.0% of fouls resulted in a player requiring treatment for injury, but only 15-28% of all injuries resulted from foul play. In all "non-foul" situations, in which injury resulted, at least 60% still involved player to player contact. No significant differences in injury frequency were observed between playing positions or match halves. CONCLUSIONS: The results equate to a total of 808 players per season from the estimated 2600 players in the four English professional football leagues sustaining a match injury that caused them to miss at least one game. The large number of underlying "non-injury" incidents is identified as the reason for this level of injury rather than a higher ratio of "injury" to "non-injury" incidents in professional football compared with other occupations.

Analysis of Variance↗
PubMed1998

Morphological changes associated with long-term potentiation.

Long-term potentiation (LTP) is a long-lasting form of synaptic plasticity induced by brief repetitive afferent stimulation that is thought to be associated with learning and memory. It is most commonly studied in the hippocampus where it may last for several weeks, and involves the synthesis of new proteins that might play a structural role. In this review we summarize the evidence in favor of modifications of neuronal architecture during LTP. We focus our attention on changes occurring at the level of single synapses, including components of postsynaptic dendrites (dendritic spines, the postsynaptic density, and synaptic curvature), of presynaptic terminals, and the formation of new synapses. We conclude that although many morphological changes at various sites have been observed during LTP, there is no definitive proof in favor of structural changes associated with LTP. However, morphological modifications remain a valid candidate for mechanisms of learning and memory.

Animals↗
PubMed1997

A simplified preparation for relating cellular events to behavior: mechanisms contributing to habituation, dishabituation, and sensitization of the Aplysia gill-withdrawal reflex.

To relate cellular events to behavior in a more rigorous fashion, we have developed a simplified preparation for studying the gill-withdrawal reflex of Aplysia, in which it is relatively easy to record the activity of individual neurons during simple forms of learning. Approximately 84% of the reflex in this preparation is mediated through the single motor neuron LDG1, so that changes in the firing of LDG1 can account for most of the changes in behavior. We have used this preparation to investigate cellular mechanisms contributing to habituation, dishabituation, and sensitization by recording evoked firing, the complex postsynaptic potential (PSP), and the monosynaptic component of the complex PSP in LDG1. Our results suggest that habituation is largely attributable to depression at sensory neuron synapses. By contrast, dishabituation and sensitization involve several mechanisms at different loci, including facilitation at sensory neuron synapses, enhancement in the periphery (perhaps attributable to post-tetanic potentiation at the neuromuscular junction), and both facilitation and inhibition of excitatory and inhibitory interneurons. Moreover, these different mechanisms contribute preferentially at different times after training, so that information processing in the neuronal circuit for the reflex is distributed not only in space but also in time. Nonetheless, our results also suggest that the neuronal circuit is not a highly distributed neural network. Rather, plasticity of the reflex can evidently be accounted for by several specific mechanisms and loci of plasticity in a defined neural circuit, including a limited number of neurons, some of which make a large contribution to the behavior.

Animals↗
PubMed1997

A simplified preparation for relating cellular events to behavior: contribution of LE and unidentified siphon sensory neurons to mediation and habituation of the Aplysia gill- and siphon-withdrawal reflex.

We have begun to analyze several elementary forms of learning in a simple preparation consisting of the isolated mantle organs and abdominal ganglion of Aplysia. Previous studies suggested that plasticity at siphon sensory neuron synapses contributes to habituation and dishabituation of the gill- and siphon-withdrawal reflex in this preparation. We next wished to identify the sensory neurons that participate in the reflex and examine their plasticity more directly. To investigate the contribution of the LE siphon mechanosensory cells, we recorded from them and gill or siphon motor neurons during the same siphon stimulation that has been used in behavioral experiments in this preparation. Our results indicate that the LE cells make a substantial contribution to the evoked response in the motor neurons under these conditions, but they suggest that other as yet unidentified siphon sensory neurons with lower thresholds and shorter latencies also contribute. In addition, we find that homosynaptic depression of monosynaptic postsynaptic potentials (PSPs) from LE sensory cells makes an important contribution to habituation of the response in the motor neurons. To investigate plasticity of PSPs from the unidentified sensory neurons, we recorded the PSP that was produced in a motor neuron by water-movement stimulation of the siphon, which does not cause firing of LE cells. Our results suggest that PSPs from the unidentified sensory neurons and the LE neurons undergo similar plasticity during habituation and dishabituation training. These results support the idea that plasticity at synapses of both LE and unidentified sensory neurons contributes to habituation and dishabituation of the reflex response in this preparation.

Animals↗
PubMed1997

Involvement of pre- and postsynaptic mechanisms in posttetanic potentiation at Aplysia synapses.

Posttetanic potentiation (PTP) is a common form of short-term synaptic plasticity that is generally thought to be entirely presynaptic. Consistent with that idea, PTP of evoked excitatory postsynaptic potentials at Aplysia sensory-motor neuron synapses in cell culture was reduced by presynaptic injection of a slow calcium chelator and was accompanied by an increase in the frequency but not the amplitude of spontaneous excitatory postsynaptic potentials. However, PTP was also reduced by postsynaptic injection of a rapid calcium chelator or postsynaptic hyperpolarization. Thus, PTP at these synapses is likely to involve a postsynaptic induction mechanism in addition to the known presynaptic mechanisms.

1-Octanol↗
PubMed1997

Carbohydrate intake and recovery of intermittent running capacity.

The purpose of the present study was to examine the influence of an increased carbohydrate intake on the recovery of endurance running capacity after exhaustive intermittent running. Six male subjects were randomly assigned to two dietary recovery conditions, each involving two running tests separated by 22 hr. The protocol comprised a prolonged, intermittent, high-intensity shuttle run test (I-HI). One week later subjects repeated the I-HI on consecutive days under different dietary conditions. During the 22-hr recovery, either the carbohydrate intake of the subjects was increased (CHO) or they ate an isocaloric diet by supplementing their normal diet with extra protein and fat (CON). Intermittent running capacity was improved when subjects increased their carbohydrate intake to 10 g.kg-1 bm during the 22-hr recovery between trials, but an isocaloric diet without additional carbohydrate did not bring about the same improvements.

Adult↗
PubMed1997

Developing a health surveillance strategy for professional footballers in compliance with UK health and safety legislation.

The need for health surveillance for professional footballers has been assessed against criteria specified in UK health and safety legislation. As footballers suffer from chronic injuries under normal playing conditions, professional football clubs have a requirement to implement health surveillance programmes to protect their players. A health surveillance programme, based on benchmarking a player's fitness and addressing the issues of pre-recruitment, pre-season, during-season, post-season, and rehabilitation assessment, is proposed.

Athletic Injuries↗
PubMed1996

Mice expressing activated CaMKII lack low frequency LTP and do not form stable place cells in the CA1 region of the hippocampus.

To relate different forms of synaptic plasticity to the formation and maintenance of place cells in the hippocampus, we have recorded place cells in freely behaving, transgenic mice that express a mutated Ca2+-independent form of CaM Kinase II. These mice have normal long-term potentiation (LTP) at 100 Hz, but they lack LTP in response to stimulation at 5-10 Hz and are impaired on spatial memory tasks. In these transgenic mice, the place cells in the CA1 region have three important differences from those of wild types: they are less common, less precise, and less stable. These findings suggest that LTP in the 5-10 Hz range may be important for the maintenance of place-field stability and that this stability may be essential for the storage of spatial memory.

Action Potentials↗
PubMed1996

Long-term potentiation is reduced in mice that are doubly mutant in endothelial and neuronal nitric oxide synthase.

Nitric oxide (NO) has been implicated in hippocampal long-term potentiation (LTP), but LTP is normal in mice with a targeted mutation in the neuronal form of NO synthase (nNOS-). LTP was also normal in mice with a targeted mutation in endothelial NOS (eNOS-), but LTP in stratum radiatum of CA1 was significantly reduced in doubly mutant mice (nNOS-/eNOS-). By contrast, LTP in stratum oriens was normal in the doubly mutant mice. These results provide the first genetic evidence that NOS is involved in LTP in stratum radiatum and suggest that the neuronal and endothelial forms can compensate for each other in mice with a single mutation. They further suggest that there is also a NOS-independent component of LTP in stratum radiatum and that LTP in stratum oriens is largely NOS independent.

Animals↗
PubMed1996

Nitric oxide acts directly in the presynaptic neuron to produce long-term potentiation in cultured hippocampal neurons.

Nitric oxide (NO) has been proposed to act as a retrograde messenger during long-term potentiation (LTP) in the CA1 region of hippocampus, but the inaccessibility of the presynaptic terminal has prevented a definitive test of this hypothesis. Because both sides of the synapse are accessible in cultured hippocampal neurons, we have used this preparation to investigate the role of NO. We examined LTP following intra- or extracellular application of an NO scavenger, an inhibitor of NO synthase, and a membrane-impermeant NO donor that releases NO only upon photolysis with UV light. Our results indicate that NO is produced in the postsynaptic neuron, travels through the extracellular space, and acts directly in the presynaptic neuron to produce long-term potentiation, supporting the hypothesis that NO acts as a retrograde messenger during LTP.

Animals↗
PubMed1996

Control of memory formation through regulated expression of a CaMKII transgene.

One of the major limitations in the use of genetically modified mice for studying cognitive functions is the lack of regional and temporal control of gene function. To overcome these limitations, a forebrain-specific promoter was combined with the tetracycline transactivator system to achieve both regional and temporal control of transgene expression. Expression of an activated calcium-independent form of calcium-calmodulin-dependent kinase II (CaMKII) resulted in a loss of hippocampal long-term potentiation in response to 10-hertz stimulation and a deficit in spatial memory, a form of explicit memory. Suppression of transgene expression reversed both the physiological and the memory deficit. When the transgene was expressed at high levels in the lateral amygdala and the striatum but not other forebrain structures, there was a deficit in fear conditioning, an implicit memory task, that also was reversible. Thus, the CaMKII signaling pathway is critical for both explicit and implicit memory storage, in a manner that is independent of its potential role in development.

Amygdala↗
PubMed1996

Mice lacking the gene encoding tissue-type plasminogen activator show a selective interference with late-phase long-term potentiation in both Schaffer collateral and mossy fiber pathways.

The gene encoding tissue-type plasminogen activator (t-PA) is an immediate response gene, downstream from CREB-1 and other constitutively expressed transcription factors, which is induced in the hippocampus during the late phase of long-term potentiation (L-LTP). Mice in which the t-PA gene has been ablated (t-PA-/-) showed no gross anatomical, electrophysiological, sensory, or motor abnormalities but manifest a selective reduction in L-LTP in hippocampal slices in both the Schaffer collateral-CA1 and mossy fiber-CA3 pathways. t-PA-/- mice also exhibit reduced potentiation by cAMP analogs and D1/D5 agonists. By contrast, hippocampal-dependent learning and memory were not affected in these mice, whereas performance was impaired on two-way active avoidance, a striatum-dependent task. These results provide genetic evidence that t-PA is a downstream effector gene important for L-LTP and show that modest impairment of L-LTP in CA1 and CA3 does not result in hippocampus-dependent behavioral phenotypes.

Animals↗
PubMed1996

Nitric oxide acts as a retrograde messenger during long-term potentiation in cultured hippocampal neurons.

We examined long-term potentiation (LTP) at synapses between hippocampal neurons in dissociated cell culture following presynaptic, postsynaptic, or extracellular application of a nitric oxide (NO) scavenger, an inhibitor of NO synthase, and a membrane-impermeant NO donor that releases NO only upon photolysis with UV light. Our results indicate that NO is produced in the postsynaptic neuron, travels through the extracellular space, and acts directly in the presynaptic neuron to produce long-term potentiation, supporting the hypothesis that NO acts as a retrograde messenger during LTP.

Animals↗
PubMed1996

Risk assessment in professional football: an examination of accidents and incidents in the 1994 World Cup finals.

OBJECTIVE: To assess the risks to footballers' health and safety during competitive international matches, with identification of the most common causes of injury. METHODS: Videos of 44 of the 52 matches played during the 1994 World Cup finals staged in the USA were analysed. During each match, several relevant variables were recorded, including the number of fouls, injuries, treatments, times of incidents, identity of players treated or injured, and the injury mechanism. Additional information on players' injuries was obtained from the extensive media coverage of the event. RESULTS: Only 29% of injuries resulted from foul play, whereas 71% of injuries to players occurred where no foul play was adjudged by the referee to have taken place (P < 0.01). Defenders were found to be proportionately subjected to a greater risk of injury than other players (P < 0.05). Fifteen per cent of all injuries were judged to be at least moderate, resulting in the player missing at least one match. Frequency of moderate injury was 1026 injuries per 100,000 hours played. CONCLUSIONS: The major causes of injuries during international football matches were not found to be associated with foul play, as judged by the referees. However, in those cases where injuries occurred without a foul being committed, almost 50% involved player to player contact. This gives some cause for concern and is worth further investigation.

Adult↗
PubMed1995

Activity-dependent long-term enhancement of transmitter release by presynaptic 3',5'-cyclic GMP in cultured hippocampal neurons.

Long-term potentiation (LTP) in hippocampus is a type of synaptic plasticity that is thought to be involved in learning and memory. Several lines of evidence suggest that LTP involves 3',5'-cyclic GMP (cGMP), perhaps as an activity-dependent presynaptic effector of one or more retrograde messengers (refs 2-12, but see ref. 13). However, previous results are also consistent with postsynaptic effects of cGMP. This is difficult to test in hippocampal slices, but more rigorous tests are possible in dissociated cell culture. We have therefore developed a reliable method for producing N-methyl-D-aspartate (NMDA) receptor-dependent LTP at synapses between individual hippocampal pyramidal neurons in culture. We report that inhibitors of guanylyl cyclase or of cGMP-dependent protein kinase block potentiation by either tetanic stimulation or low-frequency stimulation paired with postsynaptic depolarization. Conversely, application of 8-Br-cGMP to the bath or injection of cGMP into the presynaptic neuron produces activity-dependent long-lasting potentiation. The potentiation by cGMP involves an increase in transmitter release that is in part independent of changes in the presynaptic action potential. These results support a presynaptic role for cGMP in LTP.

Action Potentials↗
PubMed1995

Impairment of spatial but not contextual memory in CaMKII mutant mice with a selective loss of hippocampal LTP in the range of the theta frequency.

We assessed hippocampal-dependent memory in mice with a Ca(2+)-independent form of CaMKII generated by the introduction of an aspartate at amino acid 286. The CaMKII-Asp-286 mice show normal LTP at high frequency stimulation, but in the 5-10 Hz range, they show a shift in the frequency-response curve favoring LTD. This range of frequencies is similar to the theta rhythm, which is associated with exploration in rodents. Using the Barnes maze to assess spatial memory, we found the transgenic mice could not learn to navigate to a specific location using spatial cues. In contrast, one line of transgenic mice performed normally in contextual fear conditioning, a task that is also hippocampal dependent. This dissociation between spatial and contextual memory suggests that even though both require the hippocampus, they may be mediated by different synaptic mechanisms.

Animals↗