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Motoneuronal persistent inward currents (PICs) are facilitated by neuromodulatory inputs but are highly sensitive to local inhibitory circuits. Estimates of PICs are reduced by group Ia reciprocal inhibition, and increased with the diffuse actions of neuromodulators released during remote muscle contraction. However, it remains unknown how motoneurons function in the presence of simultaneous excitatory and inhibitory commands. To probe this topic, we investigated motor unit discharge patterns and estimated PICs during voluntary co‐contraction of ankle muscles, which simultaneously demands the contraction of agonist–antagonist pairs. Twenty participants performed triangular ramps of both co‐contraction (simultaneous dorsiflexion and plantar flexion) and isometric dorsiflexion to a peak of 30% of their maximum muscle activity from a maximal voluntary contraction. Motor unit spike trains were decomposed from high‐density surface EMG activity recorded from tibialis anterior using blind source separation algorithms. Voluntary co‐contraction altered motor unit discharge rate characteristics. Discharge rate at recruitment and peak discharge rate were modestly reduced (∼6% change; P < 0.001; d = 0.22) and increased (∼2% change; P = 0.001, d = −0.19), respectively, in the entire dataset but no changes were observed when motor units were tracked across conditions. The largest effects during co‐contraction were that estimates of PICs (ΔF) were reduced by ∼20% (4.47 vs. 5.57 pulses per second during isometric dorsiflexion; P < 0.001, d = 0.641). These findings suggest that, during voluntary co‐contraction, the inhibitory input from the antagonist muscle overcomes the additional excitatory and neuromodulatory drive that may occur due to the co‐contraction of the antagonist muscle, which constrains PIC behaviour. Key points: Voluntary co‐contraction is a unique motor behaviour that concurrently provides excitatory and inhibitory synaptic input to motoneurons.Co‐contraction of agonist–antagonist pairs alters agonist motor unit discharge characteristics, consistent with reductions in persistent inward current magnitude. [ABSTRACT FROM AUTHOR]

Muscle spasms are common in chronic spinal cord injury (SCI), posing challenges to rehabilitation and daily activities. Pharmacological management of spasms mostly targets suppression of excitatory inputs, an approach known to hinder motor recovery. To identify better targets, we investigated changes in inhibitory and excitatory synaptic inputs to motoneurons as well as motoneuron excitability in chronic SCI. We induced either a complete or incomplete SCI in adultmice of either sex and divided those with incomplete injury into low or high functional recovery groups. Their sacrocaudal spinal cords were then extracted and used to study plasticity below injury, with tissue from naive animals as a control. Electrical stimulation of the dorsal roots elicited spasm-like activity in preparations of chronic severe SCI but not in the control. To evaluate overall synaptic inhibition activated by sensory stimulation, we measured the rate-dependent depression of spinal root reflexes. We found inhibitory inputs to be impaired in chronic injury models. When synaptic inhibition was blocked pharmacologically, all preparations became clearly spastic, even the control. However, preparations with chronic injuries generated longer spasms than control. We then measured excitatory postsynaptic currents (EPSCs) in motoneurons during sensory-evoked spasms. The data showed no difference in the amplitude of EPSCs or their conductance among animal groups. Nonetheless, we found that motoneuron persistent inward currents activated by the EPSCs were increased in chronic SCI. These findings suggest that changes in motoneuron excitability and synaptic inhibition, rather than excitation, contribute to spasms and are better suited for more effective therapeutic interventions. [ABSTRACT FROM AUTHOR]

We aimed to further the understanding of the low rates of sun protection in young women at risk for skin cancer. Six-hundred-sixty-one daily diary entries were received via text message over 14 days from 56 young women at moderate to high risk of developing skin cancer. Women reported whether or not they used sun protection and also listed what their reasons were for using protection or not using sun protection each day. Multi-level modeling was used to examine the influence of study variables when predicting daily sun protection or lack of protection. The number of days in which sun protection was reported was positively associated with 'habit' and 'prevention' as reasons for protection and negatively associated with 'not-needed' and 'unprepared' as reasons for non-protection. Self-reported sun protection increased over the 14-day study period. Results of this study suggest the potential value of interventions aimed at motives for sun-protection behaviors., Author(s): M. V. Auerbach [sup.1] [sup.2] , C. J. Heckman [sup.1] [sup.3] , S. Darlow [sup.1] [sup.4] Author Affiliations: (Aff1) 0000 0004 0456 6466, grid.412530.1, Cancer Prevention and Control Program, [...]

The study's purpose was to select/refine measures assessing psychosocial constructs associated with skin cancer risk/protective behaviors. Cognitive interviewing was conducted with twenty participants locally, and a survey was conducted with 965 adults aged 18-25 years at moderate to high risk of developing skin cancer, recruited nationally online. Psychosocial measures assessed variables from the Integrative Model of Behavior Prediction. As a result of expert review and cognitive interviewing, items were removed, added, and/or made simpler, more personal, consistent, and less ambiguous. A factor analysis resulted in 14 scales and adequate model fit. Internal reliability and test-retest reliability was acceptable to good. Correlations among the psychosocial and behavioral variables were generally significant and in expected directions, demonstrating convergent validity. We have refined measures that assess important psychosocial constructs associated with skin cancer-related behaviors, that research participants can understand and complete successfully, and that are reliable and demonstrate evidence for validity., Author(s): C. J. Heckman [sup.1] , E. Handorf [sup.1] , S. D. Darlow [sup.1] , A. L. Yaroch [sup.2] , S. Raivitch [sup.1] Author Affiliations: (1) Fox Chase Cancer Center, [...]

Noninvasive recordings of motor unit (MU) spike trains help us understand how the nervous system controls movement and how it adapts to various physiological conditions. The majority of participants in human and nonhuman animal physiology studies are male, and it is assumed that mechanisms uncovered in these studies are shared between males and females. However, sex differences in neurological impairment and physical performance warrant the study of sex as a biological variable in human physiology and performance. To begin addressing this gap in the study of biophysical properties of human motoneurons, we quantified MU discharge rates and estimates of persistent inward current (PIC) magnitude in both sexes. We decomposed MU spike trains from the tibialis anterior (TA), medial gastrocnemius (MG), and soleus (SOL) using high-density surface electromyography and blind source separation algorithms. Ten participants of each sex performed slow triangular (10 s up and down) isometric contractions to a peak of 30% of their maximum voluntary contraction. We then used linear mixed-effects models to determine if peak discharge rate and estimates of PICs were predicted by the fixed effects of sex, muscle, and their interaction. Despite a lack of sex-differences in peak discharge rates across all muscles, estimates of PICs were larger [x²(1) = 6.26, P = 0.012] in females [4.73 ± 0.242 pulses per second (pps)] than in males (3.81 ± 0.240 pps). These findings suggest that neuromodulatory drive, inhibitory input, and/or biophysical properties of motoneurons differ between the sexes and may contribute to differences in MU discharge patterns. NEW & NOTEWORTHY Sex-related differences in motoneuron analyses have emerged with greater inclusion of female participants, however, mechanisms for these differences remain unclear. Estimates of persistent inward currents (i.e., DF) in motoneurons of the lower limb muscles were larger in females than in males. This suggests neuromodulatory drive, monoaminergic signaling, intrinsic motoneuron properties, and/or descending motor commands may differ between the sexes, which provides a potential mechanism underlying previously reported sex-related differences in motoneuron discharge patterns. [ABSTRACT FROM AUTHOR]