Robert J. Callister

Physiological and performance responses to overtraining in elite judo athletes

To determine the effect of large and sudden increases in training volume on performance characteristics and the feasibility of using overtraining syndrome symptoms to monitor performance changes, 15 elite judo athletes were examined through 10 wk of training. Athletes performed their regular regimens of resistance (3 d.wk-1), interval (2 d.wk-1), and judo (5 d.wk-1) training in weeks 1-4. Interval and resistance training volumes increased by 50% in weeks 4-8 and returned to baseline in weeks 9-10. Judo training volume was unchanged in weeks 1-8 but increased by 100% in weeks 9-10. Assessments were made in weeks 2, 4, 8, and 10. Isokinetic strength of elbow and knee extensors and flexors increased significantly from weeks 2 to 4 (3-13%), was unchanged from weeks 4 to 8, and decreased significantly (6-12%) from weeks 4 to 10. Total time for 3 x 300 m intervals increased (P less than 0.05) between weeks 2 and 4 and between weeks 4 and 8, while total time for 5 x 50 m sprints decreased (P less than 0.05) from weeks 8 to 10 (less than 2%). Body fat percentage decreased (P less than 0.05) from weeks 2 to 10. Body weight, submaximal and maximal aerobic power, resting (sleeping) systolic and diastolic pressures, resting (sleeping) submaximal and maximal heart rates, exercising blood lactate levels, and vertical jump performance did not change significantly with increases in training volume. These results suggest that 6 wk of overtraining may affect some but not all aspects of performance and that performance may be affected before symptoms of the overtraining syndrome appear.

Neural Responses to Visual Food Cues According to Weight Status: A Systematic Review of Functional Magnetic Resonance Imaging Studies

Emerging evidence from recent neuroimaging studies suggests that specific food-related behaviors contribute to the development of obesity. The aim of this review was to report the neural responses to visual food cues, as assessed by functional magnetic resonance imaging (fMRI), in humans of differing weight status. Published studies to 2014 were retrieved and included if they used visual food cues, studied humans >18 years old, reported weight status, and included fMRI outcomes. Sixty studies were identified that investigated the neural responses of healthy weight participants (n = 26), healthy weight compared to obese participants (n = 17), and weight-loss interventions (n = 12). High-calorie food images were used in the majority of studies (n = 36), however, image selection justification was only provided in 19 studies. Obese individuals had increased activation of reward-related brain areas including the insula and orbitofrontal cortex in response to visual food cues compared to healthy weight individuals, and this was particularly evident in response to energy dense cues. Additionally, obese individuals were more responsive to food images when satiated. Meta-analysis of changes in neural activation post-weight loss revealed small areas of convergence across studies in brain areas related to emotion, memory, and learning, including the cingulate gyrus, lentiform nucleus, and precuneus. Differential activation patterns to visual food cues were observed between obese, healthy weight, and weight-loss populations. Future studies require standardization of nutrition variables and fMRI outcomes to enable more direct comparisons between studies.

In vivo responses of mouse superficial dorsal horn neurones to both current injection and peripheral cutaneous stimulation.

In the superficial dorsal horn (SDH) processing of noxious and innocuous stimuli is critically dependent on the input–output relationship of its component neurones. Such relationships are routinely examined by assessing neuronal responses to somatic current injection or activation of synaptic inputs. A more complete understanding of input–output relationships would be achieved by comparing, in the same neurone, how the two forms of activation contribute to neuronal output. Therefore, we examined how SDH neurones transform depolarizing current injections and synaptic excitation via peripheral cutaneous stimuli (brush and pinch of the hindpaw) into trains of action potentials, in an in vivo preparation of the adult mouse spinal cord. Under whole‐cell current clamp recording conditions four action potential discharge patterns were observed during depolarizing current injection: tonic firing neurones (21/93) discharged spikes throughout the step; initial bursting neurones (35/93) discharged several spikes at step onset; single spiking neurones (16/93) discharged one or two spikes at step onset; and delayed firing neurones (21/93) discharged spikes delayed from the step onset. Four characteristic profiles were observed in response to application of noxious (pinch) and innocuous (brush) cutaneous stimuli: nociceptive neurones (20/37) responded maximally to pinch stimulation; light touch neurones (9/37) responded maximally to brush stimulation; subthreshold neurones (4/37) exhibited depolarizing responses without firing action potentials; and hyperpolarizing neurones (4/37) exhibited a sustained pinch‐induced hyperpolarization. Comparisons of current‐evoked discharge patterns with peripherally evoked responses indicate SDH neurones expressing each of the four discharge patterns could receive, and therefore participate in the processing of information concerning, either noxious or innocuous stimuli. These data suggest that a neurones response to current injection does not necessarily help identify or predict how the same neurone will respond to physiologically or functionally relevant stimuli.

Morphological, neurochemical and electrophysiological features of parvalbumin‐expressing cells: a likely source of axo‐axonic inputs in the mouse spinal dorsal horn

•  Perception of normal bodily sensations relies on the precise regulation of sensory information entering the dorsal horn of the spinal cord. •  Inhibitory, axoaxonic, synapses provide a mechanism for this regulation, but the source of these important inhibitory connections remains to be elucidated. •  This study shows that a subpopulation of spinal interneurons that expresses parvalbumin and have specific morphological, connectivity and functional characteristics are a likely source of the inhibitory inputs that selectivity regulate non‐noxious tactile input in the spinal cord. •  Our findings suggest that a loss of normal function in parvalbumin positive dorsal horn neurons may result in the development of tactile allodynia, where non‐painful stimuli gain the capacity to evoke the sensation of pain.

The expression and localization of the human placental prorenin/renin-angiotensin system throughout pregnancy: Roles in trophoblast invasion and angiogenesis?

The renin-angiotensin system (RAS) is thought to regulate placentation, however, the expression and localization of RAS pathways in early gestation human placenta is not known. Here we describe the expression of prorenin (REN), (pro)renin receptor (ATP6AP2), angiotensinogen (AGT), angiotensin-converting enzyme 1 and 2 (ACE; ACE2), angiotensin II type 1 and 2 receptors (AGTR1; AGTR2) and angiotensin 1-7 receptor (MAS1), as well as the angiogenic factor, vascular endothelial growth factor (VEGF), and transforming growth factor-β1 (TGF-β1), in early gestation (6-16 weeks) and term (>37 weeks) human placentae. We also describe the location of all of the key RAS proteins in the early gestation placentae. The highest levels of REN, ATP6AP2, AGT, AGTR1 and ACE2 mRNAs were found in early gestation, whereas ACE1 mRNA was highest at term. AGTR2 and MAS1 mRNA expression were low to undetectable in all samples. REN, ATP6AP2 and AGTR1 mRNA levels were correlated with VEGF expression, but not with TGF-β1 mRNA. In early gestation placentae, prorenin, (pro)renin receptor and the angiotensin II type 1 receptor (AT(1)R) were localized to extravillous trophoblast cells, suggesting they play a key role in trophoblast migration. ACE2 in syncytiotrophoblasts could regulate release of Ang 1-7 into the maternal circulation contributing to the vasodilation of the maternal vasculature. ACE was only found in fetal vascular endothelium and may specifically target the growing fetal placental vessels. Because REN, ATP6AP2 and AGTR1 show strong correlations with expression of VEGF this pathway is likely to be important in placental angiogenesis.

Distinct Physiological Mechanisms Underlie Altered Glycinergic Synaptic Transmission in the Murine Mutants spastic, spasmodic, and oscillator

Spastic (spa), spasmodic (spd), and oscillator (ot) mice have naturally occurring glycine receptor (GlyR) mutations, which manifest as motor deficits and an exaggerated “startle response.” Using whole-cell recording in hypoglossal motoneurons, we compared the physiological mechanisms by which each mutation alters GlyR function. Mean glycinergic miniature IPSC (mIPSC) amplitude and frequency were dramatically reduced (>50%) compared with controls for each mutant. mIPSC decay times were unchanged in spa/spa (4.5 ± 0.3 vs 4.7 ± 0.2 ms), reduced in spd/spd (2.7 ± 0.2 vs 4.7 ± 0.2 ms), and increased in ot/ot (12.3 ± 1.2 vs 4.8 ± 0.2 ms). Thus, in spastic, GlyRs are functionally normal but reduced in number, whereas in spasmodic, GlyR kinetics is faster. The oscillator mutation results in complete absence of α1-containing GlyRs; however, some non-α1-containing GlyRs persist at synapses. Fluctuation analysis of membrane current, induced by glycine application to outside-out patches, showed that mean single-channel conductance was increased in spa/spa (64.2 ± 4.9 vs 36.1 ± 1.4 pS), but unchanged in spd/spd (32.4 ± 2.1 vs 35.3 ± 2.1 pS). GlyR-mediated whole-cell currents in spa/spa exhibited increased picrotoxin sensitivity (27 vs 71% block for 100 μm), indicating α1 homomeric GlyR expression. The picrotoxin sensitivity of evoked glycinergic IPSCs and conductance of synaptic GlyRs, as determined by nonstationary variance analysis, were identical for spa/spa and controls. Together, these findings show the three mutations disrupt GlyR-mediated inhibition via different physiological mechanisms, and the spastic mutation results in “compensatory” α1 homomeric GlyRs at extrasynaptic loci.

A Systematic Review of Exercise Training To Promote Locomotor Recovery in Animal Models of Spinal Cord Injury

In the early 1980s experiments on spinalized cats showed that exercise training on the treadmill could enhance locomotor recovery after spinal cord injury (SCI). In this review, we summarize the evidence for the effectiveness of exercise training aimed at promoting locomotor recovery in animal models of SCI. We performed a systematic search of the literature using Medline, Web of Science, and Embase. Of the 362 studies screened, 41 were included. The adult female rat was the most widely used animal model. The majority of studies (73%) reported that exercise training had a positive effect on some aspect of locomotor recovery. Studies employing a complete SCI were less likely to have positive outcomes. For incomplete SCI models, contusion was the most frequently employed method of lesion induction, and the degree of recovery depended on injury severity. Positive outcomes were associated with training regimens that involved partial weight-bearing activity, commenced within a critical period of 1-2 weeks after SCI, and maintained training for at least 8 weeks. Considerable heterogeneity in training paradigms and methods used to assess or quantify recovery was observed. A 13-item checklist was developed and employed to assess the quality of reporting and study design; only 15% of the studies had high methodological quality. We recommend that future studies include control groups, randomize animals to groups, conduct blinded assessments, report the extent of the SCI lesion, and report sample size calculations. A small battery of objective assessment methods including assessment of over-ground stepping should also be developed and routinely employed. This would allow future meta-analyses of the effectiveness of exercise interventions on locomotor recovery.

Evidence for a Critical Period in the Development of Excitability and Potassium Currents in Mouse Lumbar Superficial Dorsal Horn Neurons

The output of superficial dorsal horn (SDH; laminae I-II) neurons is critical for processing nociceptive, thermal, and tactile information. Like other neurons, the combined effects of synaptic inputs and intrinsic membrane properties determine their output. It is well established that peripheral synaptic inputs to SDH neurons undergo extensive reorganization during pre- and postnatal development. It is unclear, however, how membrane properties or the subthreshold whole cell currents that shape SDH neuron output change during this period. Here we assess the intrinsic membrane properties and whole cell currents in mouse SDH neurons during late embryonic and early postnatal development (E15-P25). Transverse slices were prepared from lumbar spinal cord and whole cell recordings were obtained at 32 degrees C. During this developmental period resting membrane potential (RMP) became more hyperpolarized (by approximately 10 mV, E15-E17 vs. P21-P25) and input resistance decreased (1,074 +/- 78 vs. 420 +/- 27 MOmega). In addition, action potential (AP) amplitude and AP afterhyperpolarization increased, whereas AP half-width decreased. Before and after birth (E15-P10), AP discharge evoked by intracellular current injection was limited to a single AP at depolarization onset in many neurons (>41%). In older animals (P11-P25) this changed, with AP discharge consisting of brief bursts at current onset ( approximately 46% of neurons). Investigation of major subthreshold whole cell currents showed the rapid A-type potassium current (I(Ar)) dominated at all ages examined (90% of neurons at E15-E17, decreasing to >50% after P10). I(Ar) expression levels, based on peak current amplitude, increased during development. Steady-state inactivation and activation for I(Ar) were slightly less potent in E15-E17 versus P21-P25 neurons at potentials near RMP (-55 mV). Together, our data indicate that intrinsic properties and I(Ar) expression change dramatically in SDH neurons during development, with the greatest alterations occurring on either side of a critical period, P6-P10.

Recording Temperature Affects the Excitability of Mouse Superficial Dorsal Horn Neurons, In Vitro

Superficial dorsal horn (SDH) neurons in laminae I-II of the spinal cord play an important role in processing noxious stimuli. These neurons represent a heterogeneous population and are divided into various categories according to their action potential (AP) discharge during depolarizing current injection. We recently developed an in vivo mouse preparation to examine functional aspects of nociceptive processing and AP discharge in SDH neurons and to extend investigation of pain mechanisms to the genetic level of analysis. Not surprisingly, some in vivo data obtained at body temperature (37 degrees C) differed from those generated at room temperature (22 degrees C) in spinal cord slices. In the current study we examine how temperature influences SDH neuron properties by making recordings at 22 and 32 degrees C in transverse spinal cord slices prepared from L3-L5 segments of adult mice (C57Bl/6). Patch-clamp recordings (KCH(3)SO(4) internal) were made from visualized SDH neurons. At elevated temperature all SDH neurons had reduced input resistance and smaller, briefer APs. Resting membrane potential and AP afterhyperpolarization amplitude were temperature sensitive only in subsets of the SDH population. Notably, elevated temperature increased the prevalence of neurons that did not discharge APs during current injection. These reluctant firing neurons expressed a rapid A-type potassium current, which is enhanced at higher temperatures and thus restrains AP discharge. When compared with previously published whole cell recordings obtained in vivo (37 degrees C) our results suggest that, on balance, in vitro data collected at elevated temperature more closely resemble data collected under in vivo conditions.

Pinch-current injection defines two discharge profiles in mouse superficial dorsal horn neurones, in vitro

Neurones in the superficial dorsal horn (SDH) are a major target for nociceptive afferents and play an important role in pain processing. One approach to understanding the role of SDH neurones has been to study their action potential (AP) discharge in spinal cord slices during injection of depolarizing step‐currents. Four or five neurone subpopulations are typically identified based on AP discharge, with various roles proposed for each in pain processing. During noxious peripheral stimulation in vivo, however, SDH neurones are activated via synaptic inputs. This produces a conductance change with different somato‐dendritic distributions and temporal characteristics to that provided by a somatic step‐current injection. Here we introduce an alternative approach to studying SDH neurone discharge under in vitro conditions. We recorded voltage‐clamp responses in SDH neurones, in vivo, during noxious mechanical stimulation of the hindpaw (1 s pinch, ∼100 g mm−2). From these recordings a representative ‘pinch‐current’ was selected and subsequently injected into SDH neurones in spinal cord slices (recording temperature 32°C). Pinch‐current‐evoked discharge was compared to that evoked by rectangular step‐current injections. Pinch‐ and step‐current‐evoked AP discharge frequency was highly correlated (r2= 0.61). This was also true for rheobase current comparisons (r2= 0.61). Conversely, latency to discharge and discharge duration were not correlated when step‐ and pinch‐current responses were compared. When neurones were grouped according to step‐current‐evoked discharge, five distinct patterns were apparent (tonic firing, initial bursting, delayed firing, single spiking, and reluctant firing). In contrast, pinch‐current responses separated into two clear patterns of activity (robust and resistant firing). During pinch‐current injection, tonic‐firing and initial‐bursting neurones exhibited robust AP discharge with similar characteristics. In contrast, single‐spiking and reluctant‐firing neurones were resistant to AP discharge. Delayed‐firing neurones exhibited pinch‐current responses that were transitional between those of tonic‐firing/initial‐bursting and single‐spiking/reluctant‐firing neurones. Injection of digitally filtered pinch‐currents indicated that transient current fluctuations are necessary for robust repetitive discharge in initial‐bursting neurones. These data suggest the functional significance of the diverse step‐current‐evoked firing patterns, previously reported in SDH neurones remains to be fully understood. When a ‘facsimile’ current profile or pinch‐current is used in place of step‐currents, AP discharge diversity is much reduced.