Many representations of sensory stimuli in the neocortex are arranged as topographic maps. These cortical maps are not fixed, but show experience-dependent plasticity. For instance, sensory deprivation causes the cortical area representing the deprived sensory input to shrink, and neighbouring spared representations to enlarge, in somatosensory, auditory or visual cortex. In adolescent and adult animals, changes in cortical maps are most noticeable in the supragranular layers at the junction of deprived and spared cortex. However, the cellular mechanisms of this experience-dependent plasticity are unclear. Long-term potentiation and depression have been implicated, but have not been proven to be necessary or sufficient for cortical map reorganization. Short-term synaptic dynamics have not been considered. We developed a brain slice preparation involving rat whisker barrel cortex in vitro. Here we report that sensory deprivation alters short-term synaptic dynamics in both vertical and horizontal excitatory pathways within the supragranular cortex. Moreover, modifications of horizontal pathways amplify changes in the vertical inputs. Our findings help to explain the functional cortical reorganization that follows persistent changes of sensory experience.

The muscle of Lawrence (MOL) is a bilaterally symmetrical muscle spanning the tergite of the fifth abdominal segment of adult male Drosophila melanogaster. It is not, however, a general feature of male-specific development within the subfamily Drosophilinae. Of 95 species surveyed within this subfamily, 67 exist with no MOL at all. By drawing comparisons with published cladograms of species relatedness, three conclusions regarding the evolutionary history of the MOL are made: (i) The MOL predates the major radiations of the genus Drosophila, given its presence in earlierbranching Chymomyza and Scaptodrosophila; the MOL has been subsequently excluded in at least one present species of each of these two primitive genera. First described in Drosophila melanogaster, the muscle of Lawrence (MOL) is a large, bilaterally symmetrical muscle spanning the fifth tergite of the abdomen of adult males; it does not develop in females (1). Oddly, the MOL eluded decades of extensive genetic and biological investigation in D. melanogaster, including the definitive survey of adult musculature by Miller in 1950 (2). Only in 1984 was this muscle's existence first revealed with the report of Lawrence (the muscle's eponym) and Johnston (1), showing that formation of the MOL is sex-specific and is associated with developmental cues in the fifth abdominal segment (A5) of the male; homeotic mutations transforming either A4 or A6 to A5 induce the development of a MOL in the transformed segment (1, 3).Development of the MOL depends not on the sex of its progenitor myoblasts, but rather the sex of the contacting motoneuron in A5. If the motoneuron is male, the MOL develops; if the motoneuron is female, the MOL fails to develop (3). Ablation of the ingrowing motoneuron in a male correspondingly blocks MOL development (4). Although use of the MOL to the adult male fly is unknown, other interesting observations have accumulated regarding its general biology, including genetic evidence that its development requires normal expression of fruitless (fru) (5, 6), a gene identified by its involvement in adult male courtship behavior (7) and as a sex determination gene that acts late in development (8, 9). In addition, formation of the MOL in A5 involves recruitment of the relatively rare 79B actin (10).To gain insight into the evolutionary history of this muscle, we have analyzed its appearance within the subfamily Drosophilinae. Surprisingly, of 95 species surveyed, 67 have no MOL at all. By comparing our observations with generally accepted cladograms of species relatedness within the Drosophilinae (11-24), we provide evidence that the MOL was an existing feature of primitive forms within the early radiation of the subfamily. Also stemming from that comparison is our conclusion that several independent genetic exclusions of this muscle have occurred during the subsequent radiation of MOL-containing lines. This makes the MOL a rare example of an anatomical structure that has undergone independent, repeated loss among closely related evolut...

Background:To increase the understanding of the physiological mechanisms by which massage therapy produces health benefits such as pain relief and anxiety reduction, the relationship between specific elements of massage and physiological outcomes must be addressed.Purpose: The effects on resting muscular activity of applying varying levels of pressure during massage were investigated.Methods: In this clinical crossover study, conducted in a simulated clinical setting, human subjects (n = 25; mean age: 34.1 years) received 3 different levels of massage pressure to the legs. A licensed therapist applied pressure to the rectus femoris in a distal-to-proximal direction. Each volunteer received the 3 levels of pressure in 2 different orders-increasing (IP) and decreasing pressures (DP)-separated by at least 4 weeks. Surface electromyography (EMG) was used to measure muscle activity levels at baseline and after each pressure level.Results: During the trials of IP, EMG did not vary significantly [Greenhouse-Geisser corrected analysis of variance F(1.71 df) = 0.30, p = 0.71]. During the trials of DP, EMG varied significantly [Greenhouse-Geisser corrected analysis of variance F(1.58 df) = 4.49, p = 0.03], with the largest variation, an increase of 235%, noted between baseline activity and activity after deep pressure. After application of light pressure, activity returned to baseline levels. Interestingly, the overall levels of force required to achieve subjective pressure levels as reported by the client were higher in the DP protocol than in the IP protocol (p < 0.02).Conclusions: These results suggest that the physiological response of the muscle depends on the pattern of applied pressure during massage. That finding is consistent with a mechanism by which light-or moderate-pressure massage (or a combination) may reduce the gain of spinal nociceptive reflexes. As those reflexes are elevated in chronic pain syndromes, pressure variation provides a possible mechanism for the relief of chronic pain by massage therapy.