Rapid activation, desensitization, and resensitization of synaptic channels of crayfish muscle after glutamate pulses

Completely desensitizing excitatory channels were activated in outside-out patches of crayfish muscle membrane by applying glutamate pulses with switching times of approximately 0.2 ms for concentration changes. Channels were almost completely activated with 10 mM glutamate. Maximum activation was reached within 0.4 ms with greater than or equal to 1 mM glutamate. Channel open probability decayed with a time constant of desensitization of 2 ms with 10 mM glutamate and more rapidly at lower glutamate concentrations. The rate of beginnings of bursts (average number of beginnings of bursts per time bin) decayed even faster but approximately in proportion to the glutamate concentration. The dose-response curve for the channel open probability and for the rate of bursts had a maximum double-logarithmic slope of 5.1 and 4.2, respectively. Channels desensitized completely without opening at very low or slowly rising glutamate concentrations. Desensitization thus originates from a closed channel state. Resensitization was tested by pairs of completely desensitizing glutamate pulses. Sensitivity to the second pulse returned rapidly at pulse intervals between 1 and 2 ms and was almost complete with an interval of 3 ms. Schemes of channel activation by up to five glutamate binding steps, with desensitization by glutamate binding from closed states, are discussed. At high agonist concentrations bursts are predominantly terminated by desensitization. Quantal currents are generated by pulses of greater than 1 mM glutamate, and their decay is determined by the duration of presence of glutamate and possibly by desensitization

Does strabismus surgery improve quality and mood, and what factors influence this?

Aims To establish the impact of adult strabismus surgery on clinical and psychosocial well-being and determine who experiences the greatest benefit from surgery and how one could intervene to improve quality of life post-surgery. Methods A longitudinal study, with measurements taken pre-surgery and at 3 and 6 months post-surgery. All participants completed the AS-20 a disease specific quality of life scale, along with measures of mood, strabismus and appearance-related beliefs and cognitions and perceived social support. Participants also underwent a full orthoptic assessment at their preoperative visit and again 3 months postoperatively. Clinical outcomes of surgery were classified as success, partial success or failure, using the largest angle of deviation, diplopia and requirement for further therapy. Results 210 participants took part in the study. Strabismus surgery led to statistically significant improvements in psychosocial and functional quality of life. Those whose surgery was deemed a partial success did however experience a deterioration in quality of life. A combination of clinical variables, high expectations, and negative beliefs about the illness and appearance pre-surgery were significant predictors of change in quality of life from pre- to post-surgery. Conclusions Strabismus surgery leads to significant improvements in quality of life up to 6 months postoperatively. There are however a group of patients who do not experience these benefits. A series of clinical and psychosocial factors have now been identified, which will enable clinicians to identify patients who may be vulnerable to poorer outcomes post-surgery and allow for the development of interventions to improve quality of life after surgery

Herbivorous reptiles and body mass: Effects on food intake, digesta retention, digestibility and gut capacity, and a comparison with mammals

Differences in the allometric scaling between gut capacity (with body mass, BM1.00) and food intake (with BM0.75) should theoretically result in a scaling of digesta retention time with BM0.25 and therefore a higher digestive efficiency in larger herbivores. This concept is an important part of the so-called ‘Jarman-Bell principle’ (JBP) that explains niche differentiation along a body size gradient in terms of digestive physiology. Empirical data in herbivorous mammals, however, do not confirm the scaling of retention time, or of digestive efficiency, with body mass. Here, we test these concepts in herbivorous reptiles, adding data of an experiment that measured food intake, digesta retention, digestibility and gut capacity in 23 tortoises (Testudo graeca, T. hermanni , Geochelone nigra, G. sulcata, Dipsochelys dussumieri) across a large BM range (0.5-180 kg) to a literature data collection. While dry matter gut fill scaled to BM1.07 and dry matter intake to BM0.76, digesta mean retention time (MRT) scaled to BM0.17; the scaling exponent was not significantly different from zero for species > 1 kg. Food intake level was a major determinant of MRT across reptiles and mammals. In contrast to dietary fibre level, BM was not a significant contributor to dry matter digestibility in a General Linear Model. Digestibility coefficients in reptiles depended on diet nutrient composition in a similar way as described in mammals. Although food intake is generally lower and digesta retention longer in reptiles than in mammals, digestive functions scale in a similar way in both clades, indicating universal principles in herbivore digestive physiology. The reasons why the theoretically derived JBP has little empirical support remain to be investigated. Until then, the JBP should not be evoked to explain niche differentiation along a body size axis in terms of digestive physiology

Comparing life expectancy of three deer species between captive and wild populations

Life in zoological gardens provides a number of benefits to captive animals, resulting in an artificial reduction of the “struggle for life” compared to their free-ranging counterparts. These advantages should result in a higher chance of surviving from one year to the next, and thus in longer average life expectancies for captive animals, given that the biological requirements of the species are adequately met. Here, we compare the life expectancy of captive and free-ranging populations of three deer species (reindeer Rangifer tarandus, red deer Cervus elaphus, and roe deer Capreolus capreolus). Whereas captive reindeer and red deer had life expectancies equal to or longer than free-ranging individuals, the life expectancy of captive roe deer was shorter than that of free-ranging animals. These results support the impression that roe deer are difficult to keep in zoos, whereas reindeer and red deer perform well under human care. We suggest that the mean life expectancy of captive populations relative to that of corresponding free-ranging populations is a reliable indicator to evaluate the husbandry success of a species in captivity

Chemosensory properties of murine nasal and cutaneous trigeminal neurons identified by viral tracing

BACKGROUND: Somatosensation of the mammalian head is mainly mediated by the trigeminal nerve that provides innervation of diverse tissues like the face skin, the conjunctiva of the eyes, blood vessels and the mucouse membranes of the oral and nasal cavities. Trigeminal perception encompasses thermosensation, touch, and pain. Trigeminal chemosensation from the nasal epithelia mainly evokes stinging, burning, or pungent sensations. In vitro characterization of trigeminal primary sensory neurons derives largely from analysis of complete neuronal populations prepared from sensory ganglia. Thus, functional properties of primary trigeminal afferents depending on the area of innervation remain largely unclear. RESULTS: We established a PrV based tracing technique to identify nasal and cutaneous trigeminal neurons in vitro. This approach allowed analysis and comparison of identified primary afferents by means of electrophysiological and imaging measurement techniques. Neurons were challenged with several agonists that were reported to exhibit specificity for known receptors, including TRP channels and purinergic receptors. In addition, TTX sensitivity of sodium currents and IB4 binding was investigated. Compared with cutaneous neurons, a larger fraction of nasal trigeminal neurons showed sensitivity for menthol and capsaicin. These findings pointed to TRPM8 and TRPV1 receptor protein expression largely in nasal neurons whereas for cutaneous neurons these receptors are present only in a smaller fraction. The majority of nasal neurons lacked P2X(3 )receptor-mediated currents but showed P2X(2)-mediated responses when stimulated with ATP. Interestingly, cutaneous neurons revealed largely TTX resistant sodium currents. A significantly higher fraction of nasal and cutaneous afferents showed IB4 binding when compared to randomly chosen trigeminal neurons. CONCLUSION: In conclusion, the usability of PrV mediated tracing of primary afferents was demonstrated. Using this technique it could be shown that compared with neurons innervating the skin nasal trigeminal neurons reveal pronounced chemosensitivity for TRPM8 and TRPV1 channel agonists and only partially meet properties typical for nociceptors. In contrast to P2X(3 )receptors, TRPM8 and TRPV1 receptors seem to be of pronounced physiological relevance for intranasal trigeminal sensation