Sensitization, asthma and allergic disease in young soccer players.

BACKGROUND: The aim of this study was to identify the prevalence of allergic disease in young soccer players compared to age-matched students and to evaluate if this prevalence changes as the intensity of training increases. METHODS: A modified ECRHS questionnaire was administered to 194 soccer players divided by age as Beginners (8-11 years), Juniors (12-16 years) and Under 21 (17-20 years) to evaluate the prevalence of allergic diseases and symptoms as well as drug consumption. Subjects with a positive personal history of allergic diseases underwent skin prick and/or patch tests. Age-matched students (n = 136) were used as a control group. RESULTS: The prevalence of allergic diseases was 34.5% in soccer players and 31.6% in control subjects (n.s.). Skin sensitization to inhalant allergens was detected in 14.4% of symptomatic soccer players and in 19.2% of control students (n.s.). Patch tests were positive in 35.7% of soccer players and 23.0% of controls with allergic dermatitis (n.s.). The prevalence of allergic diseases did not significantly change in relation to the intensity of training. Although the relative prevalence of sensitization to perennial allergens and asthma was less frequent in soccer players than in controls, and the occurrence of exercise-induced bronchoconstriction was similar in the two groups, soccer players used twice as many anti-allergic and anti-asthmatic drugs as control students. CONCLUSIONS: An increasingly intensive training programme is not associated with greater risk of allergic disease in soccer players. Therapy regimens of allergic athletes and exercisers should be monitored more closely to guarantee adequate treatment yet avoid inappropriate drug use and doping practices.

Sensory feedback and central afferent interaction in the muscle receptor organ of the crab, Carcinus maenas.

1. An interaction exists between two proprioceptive afferent neurons innervating the thoracic-coxal muscle receptor organ (TCMRO) of the crab, Carcinus maenas. Intracellular recordings were made from the extraganglionic regions of the afferents in order to characterize this interaction and its effects on sensory feedback. 2. A current-induced depolarization of the nonspiking T fiber of the TCMRO results in a depolarization of the P fiber, a small-diameter (7 microns) neuron innervating the same receptor. This interaction is graded in amplitude, and may result in a single action potential being superimposed on the graded response of the P fiber. A hyperpolarization of the T fiber has a smaller effect on the P fiber than a depolarization of similar amplitude. The interaction is rectified in a T- to P-fiber direction, and has a minimum central delay of approximately 3.6 ms. 3. The site of the interaction between the afferents is situated centrally, within the thoracic ganglion. Action potentials evoked in the P fiber by a T-fiber depolarization propagate actively and antidromically to the periphery. 4. Central modulation of the interaction occurs, because the amplitude of a T-fiber-induced depolarization is reduced in the P fiber during centrally generated spontaneous bursts of activity in the motoneurons of basal leg muscles. 5. Because of the interaction between T and P fibers, action potentials recorded from the peripheral portion of the P fiber during receptor stretch may be either orthodromic, resulting directly from the effects of the stretch on the sensory endings of the P fiber, or antidromic, resulting from the central input from the T fiber. 6. The T- to P-fiber interaction may serve to extend the dynamic sensitivity range of the P fiber, in particular by amplifying its sensory response at short receptor lengths and low velocities of stretch.

Sensory characteristics of the P afferent neurone of the crab thoracic-coxal muscle receptor organ.

Intracellular recordings were made from the P fibre, the smallest of the three afferent neurones innervating the thoracic-coxal muscle receptor organ of the crab (Carcinus maenas). While the two larger afferents are nonspiking, the response of the P fibre to a trapezoidal change in receptor muscle length consists of a single action potential signalling the onset of stretch superimposed on a graded amplitude receptor potential. The P fibre is sensitive to the velocity of the applied stretch, but is insensitive to static joint position, stretch amplitude and the velocity of the release phase. The presence and amplitude of the action potential depends on the initial length of the receptor muscle, the tension caused by efferent activation of the receptor muscle prior to receptor stretch, and on the velocity of stretch. Length constant (1.9 mm) and specific membrane resistance (76 K omega x cm2) values obtained for the P fibre, together with its small diameter (7 microns) suggest that this neurone is less well adapted to conveying passive signals to the thoracic ganglion than are the S and T fibres. It is likely that the P fibre complements the length sensitivity of the S fibre and the tension and velocity sensitivity of the T fibre by signalling the onset of receptor stretch via single action potentials.

Interaction between afferent neurones in a crab muscle receptor organ.

Two of the three mechanoreceptor neurones which innervate the crab thoracic-coxal muscle receptor organ are non-spiking. The third, the small diameter P neurone, employs graded amplitude receptor potentials with either spikes or graded amplitude active membrane responses superimposed. An excitatory synaptic connection between one of the larger non-spiking afferents and the P neurone has now been detected within the thoracic ganglion. This novel connection between two afferents innervating the same receptor strand effectively extends the dynamic sensitivity range of the P neurone.

Blockage of synaptic release by brief hyperpolarizing pulses in the neuromuscular junction of the crayfish.

1. Synaptic currents were evoked at the neuromuscular junction of the deep extensor abdominal muscle of the crayfish by direct depolarization of motor nerve endings. 2. Quantal content and time course of neurotransmitter release were determined from delay histograms of unitary release events recorded with a macropatch clamp technique. 3. Synaptic facilitation was elicited by pairing depolarizing pulses at intervals ranging from 10 to 200 ms. At 14 degrees C the duration of facilitation was about 50 ms. Reducing activity of the Nao(+)-Cai2+ exchange by lowering [Na+]o by 50% resulted in prolonged facilitation, which lasted approximately 150 ms. 4. Normalized synaptic delay histograms at normal [Na+]o and 50% [Na+]o were the same for the first and the facilitated second response, indicating that activity of the Na(+)-Ca2+ exchange does not determine the time course of release. 5. The application of a hyperpolarizing post-pulse after the first depolarizing stimulus reduced release and altered its time course to a similar extent both in normal and in 50% [Na+]o. However, it did not affect the level and the time course of release of the facilitated response. 6. A hyperpolarizing post-pulse given after the first and second pulses of a pair reduced release to the same extent for the two depolarizing pulses. 7. These results indicate that whereas manipulations thought to increase [Ca2+]i (i.e. reducing activity of the Nao(+)-Cai2+ exchange or facilitation) affect the quantal content, they do not influence the time course of release. However, changes of membrane potential do affect the quantal content, and more importantly the time course of release, thus suggesting a contributory role of membrane potential in the control of synaptic release.

Action potentials in a 'non-spiking' neurone: graded responses and spikes in the afferent P fibre of the crab thoracic-coxal muscle receptor organ.

The small diameter P neurone (7 microns) is here characterized as an afferent of the crab thoracic-coxal muscle receptor organ (TCMRO), in addition to the S and T neurones (50-60 microns). The P neurone employs both passively conducted, graded amplitude receptor potentials and, superimposed upon these, either graded active membrane responses or constant amplitude action potentials. Intracellularly recorded receptor potential waveforms reflect the dynamic component of stretch more strongly than receptor length, while action potentials at the onset of stretch accentuate the phasic response characteristics of this neurone.

Positive feedback to a muscle receptor stabilized by concurrent self-inhibition.

The two non-spiking afferent neurones (T and S fibres) of the crab's thoracic-coxal muscle receptor organ mediate antagonistic reflex controls upon the specific receptor motoneurone (Rm1). Depolarization of the 'in-series' T fibre, by receptor muscle stretch or intracellular current injection, reflexly excites Rm1, whereas length- or current-induced S fibre depolarization inhibits Rm1. The latter, autogenetic negative feedback stabilizes the concurrent positive feedback over the physiological range of receptor muscle lengths.