Comparison of physical therapy utilization, timing of return-to-sport test completion, and hop test performance by age and between sexes in youth athletes after anterior cruciate ligament reconstruction.

OBJECTIVE: To compare physical therapy (PT) utilization, timing of return-to-sport (RTS) test and hop test performance by age and between sexes in youth after anterior cruciate ligament reconstruction (ACLR). DESIGN: Multicenter retrospective cohort. METHODS: A retrospective review of adolescents after primary ACLR was conducted. Participants completed return-to-sport (RTS) tests including single-legged hop testing. PT frequency, average weekly visits, and timing of RTS test were calculated. T-tests assessed the effect of age and sex on average weekly PT visits and multivariable logistic regressions assessed odds of passing hop tests. RESULTS: 289 participants were included (15.7 ± 1.9 years). There was no difference in average weekly PT visits (p = 0.321) or time to RTS test (p = 0.162) by age. There were significant differences in average weekly PT visits (p = 0.047) and mean time from surgery to RTS test (p = 0.048) between sexes with small effect sizes (d = 0.24 and d = 0.21, respectively). Age and sex had no effect on odds of passing hop tests (OR, 1.29; 95% CI, 0.71-2.35 and OR, 0.79; 95%CI, 0.43-1.45, respectively). CONCLUSION: In a youth cohort, age and sex may have no clinically important effect on PT visit utilization, timing of RTS test or hop test performance.

Which Tests Predict 6-Month Isokinetic Quadriceps Strength After ACL Reconstruction? An Examination of Isometric Quadriceps Strength and Functional Tests at 3 Months.

Background: Restoration of quadriceps strength after anterior ligament reconstruction (ACLR) is a persistent challenge for patients and clinicians. Inadequate recovery of quadriceps strength has been linked to increase risk of re-injury. Developing methods of early identification of strength deficits is essential to allow clinicians to provide more individualized interventions early in the rehabilitation process. Purpose: To determine whether 3-month isometric quadriceps strength, the Y-Balance Test (YBT), and the anterior step-down test are predictive of isokinetic quadriceps strength at six months in adolescents after ACLR. Design: Retrospective cohort. Methods: Thirty-six adolescent patients with primary ACLR (58% female, 36% with concomitant meniscal repair, age: 15.7 ± 1.6 years). At three months post-operative, isometric quadriceps strength via isokinetic dynamometer, YBT-Lower Quarter, and anterior step-down tests were completed. At six months post-operative, an isokinetic knee strength assessment was completed. Regression analysis was used to evaluate the predictive relationship between 3-month isometric tests and 6-month isokinetic knee extension tests. Results: Three-month post operative isometric quadriceps peak torque predicted isokinetic quadriceps peak torque at 6 months, F(1,34) = 19.61, p <0.001. Three-month isometric quadriceps peak torque accounted for 36.6% of the variance in normalized isokinetic quadriceps peak torque at 6 months with adjusted R2 = 34.7%. Including YBT anterior reach (ß = 0.157, p = 0.318) in regression added 1.9% of variance when predicting 6-month isokinetic quadriceps peak torque, F (2,33) = 10.32, p <0.001, R2 = 0.385, ΔR2 = 0.019. Conclusion: At three months post-ACLR, isometric strength testing appears more optimal than other functional tests in predicting isokinetic quadriceps peak torque in later stages of rehabilitation for adolescents. Clinicians should use tests at three months that measure quadriceps strength if aiming to predict isokinetic quadriceps peak torque at six months post-ACLR, rather than using functional tests such as the YBT-LQ or anterior step-down. Level of Evidence: Level 3.

Early- and Late-Stage Benefits of Blood Flow Restriction Training on Knee Strength in Adolescents After Anterior Cruciate Ligament Reconstruction.

Background: Blood flow restriction training (BFRT) after anterior cruciate ligament reconstruction (ACLR) is rising in popularity because of its benefits in reducing muscle atrophy and mitigating knee strength deficits. Purpose: To investigate the impact BFRT has on adolescent knee strength after ACLR at 2 postoperative time points: at 3 months and the time of return to sport (RTS). Study Design: Cohort study; Level of evidence, 3. Methods: A prospective intervention (BFRT) group was compared to an age-, sex-, and body mass index-matched retrospective control group. Patients aged 12 to 18 years who underwent primary ACLR with a quadriceps tendon autograft were included. Along with a traditional rehabilitation protocol, the BFRT group completed a standardized BFRT protocol (3 BFRT exercises performed twice weekly for the initial 12 weeks postoperatively). Peak torque values for isometric knee extension and flexion strength (at 3 months and RTS) and isokinetic strength at 180 deg/s (at RTS) as well as Pediatric International Knee Documentation Committee (Pedi-IKDC) scores were collected. Differences between the BFRT and control groups were compared with 2-way mixed analysis of variance and 1-way analysis of variance. Results: The BFRT group consisted of 16 patients (10 female; mean age, 14.84 ± 1.6 years) who were matched to 16 patients in the control group (10 female; mean age, 15.35 ± 1.3 years). Regardless of the time point, the BFRT group demonstrated significantly higher isometric knee extension torque compared to the control group (2.15 ± 0.12 N·m/kg [95% CI, 1.90-2.39] vs 1.74 ± 0.12 N·m/kg [95% CI, 1.49-1.98], respectively; mean difference, 0.403 N·m/kg; P = .024). The BFRT group also reported significantly better Pedi-IKDC scores compared to the control group at both 3 months (68.91 ± 9.68 vs 66.39 ± 12.18, respectively) and RTS (89.42 ± 7.94 vs 72.79 ± 22.81, respectively) (P = .047). Conclusion: In adolescents, the addition of a standardized BFRT protocol to a traditional rehabilitation protocol after ACLR significantly improved knee strength and patient-reported function compared to a traditional rehabilitation program alone.

The Impact of Meniscal Tear Type and Surgical Treatment on Quadriceps Strength: A Study of Adolescent Patients Post Anterior Cruciate Ligament Reconstruction.

BACKGROUND: Treatment of meniscal injuries at the time of anterior cruciate ligament reconstruction (ACLR) can result in restrictions on weightbearing and range of motion in the early rehabilitative phases. What is unknown is the effect of (1) meniscal tear type and location at the time of anterior cruciate ligament injury and (2) meniscal treatment at the time of ACLR on quadriceps strength in adolescents during the late rehabilitative phase. HYPOTHESIS: Meniscal tears involving the root and requiring repair would adversely affect quadriceps strength at 6 to 9 months postoperatively. STUDY DESIGN: Cohort study; Level of evidence, 3. METHODS: Patients who underwent ACLR at 1 of 2 research sites between 2013 and 2021 were identified. Adolescent participants were included if they were between the ages of 12 and 20 years at the time of assessment and had undergone primary unilateral ACLR in the previous 6 to 9 months. Participants were subgrouped by meniscal tear type (no tear, nonroot tear, root tear) and meniscal treatment at the time of ACLR (no treatment, meniscectomy, meniscal repair), which were confirmed via chart review. Isokinetic strength testing occurred at 60 deg/s, and quadriceps strength and quadriceps strength limb symmetry index were compared between the meniscal tear type and meniscal procedure subgroups using analysis of covariance while controlling for the effects of age, sex, and ACLR graft source. RESULTS: An overall 236 patients were included in this analysis (109 male, 127 female; mean ± SD age, 16.0 ± 1.9 years). There were no significant differences in ACLR limb quadriceps strength based on meniscal tear type (P = .61) or meniscal procedure at the time of ACLR (P = .61), after controlling for age, biological sex, and ACLR graft source. Similarly, quadriceps strength limb symmetry index did not differ by meniscal tear type (P = .38) or meniscal procedure at the time of ACLR (P = .40). CONCLUSION: Meniscal tear type and treatment at the time of ACLR did not affect quadriceps strength or quadriceps strength symmetry in adolescents 6 to 9 months after ACLR.

Neurodegeneration in a novel invertebrate model system: Failed microtubule-mediated cell adhesion and unraveling of macroglia.

Neurodegenerative diseases are among the main causes of death in the United States, leading to irreversible disintegration of neurons. Despite intense international research efforts, cellular mechanisms that initiate neurodegeneration remain elusive, thus inhibiting the development of effective preventative and early onset medical treatment. To identify underlying cellular mechanisms that initiate neuron degeneration, it is critical to identify histological and cellular hallmarks that can be linked to underlying biochemical processes. Due to the poor tissue preservation of degenerating mammalian brain tissue, our knowledge regarding histopathological hallmarks of early to late degenerative stages is only fragmentary. Here, we introduce a novel model organism to study histological hallmarks of neurodegeneration, the spider Cupiennius salei. We utilized toluidine blue-stained 0.9-µm serial semithin and 50-nm ultrathin sections of young and old spider nervous tissue. Our findings suggest that the initial stages of neurodegeneration in spiders may be triggered by (1) dissociation of neuron- and glia-derived microtubules, and (2) the weakening of microtubule-associated desmosomal junctions that lead to the unraveling of neuron-insulating macroglia, compromising the structural integrity of affected neurons. The involvement of macroglia in the disposal of neuronal debris described here-although different in the proposed transport mechanisms-shows resemblance to the mammalian glymphatic system. We propose that this model system is highly suitable to investigate invertebrate neurodegenerative processes from early onset to scar formation and that this knowledge may be useful for the study of neurodegeneration in mammalian tissue.

Age-, Sex-, and Graft-Specific Reference Values From 783 Adolescent Patients at 5 to 7 Months After ACL Reconstruction: IKDC, Pedi-IKDC, KOOS, ACL-RSI, Single-Leg Hop, and Thigh Strength.

OBJECTIVE: To describe age-, sex-, and graft source-specific reference values for patient-reported, physical function, and strength outcome measures in adolescents at 5 to 7 months after anterior cruciate ligament reconstruction. DESIGN: Cross-sectional study. METHODS: Data were collected at 3 universities and 2 children's hospitals. The participants completed at least one of the International Knee Documentation Committee (IKDC) Subjective Evaluation Form, Pediatric IKDC (Pedi-IKDC), Knee Injury and Osteoarthritis Outcomes Score (KOOS), and Anterior Cruciate Ligament Return to Sport After Injury (ACL-RSI) Scale. Participants also completed single-leg hop tests and/or isokinetic quadriceps and hamstrings strength assessments (at 60°/s). Reference values were summarized using descriptive statistics and stratified for age, sex, and graft source. RESULTS: Reference values were reported for common patient-reported outcomes and measures of physical function and strength from 783 participants (56% females, age = 16. 4 ± 2.0 years) who were in early adolescence (12-14 years, N = 183, 52% females), middle adolescence (15-17 years, N = 456, 58% females), or late adolescence (18-20 years, N = 144, 55% females). Three hundred seventy-nine participants (48.4%) received a bone-patellar tendon-bone autograft, 292 participants (37.3%) received hamstring tendon autograft, and 112 participants (14.3%) received autograft or allograft from an alternative source. CONCLUSION: Reference values for common patient-reported outcomes and measures of physical function and strength differed depending on a patient's age, sex, and graft source. Using patient-specific reference values, in addition to previously described age-appropriate cutoff values, may help clinicians monitor and progress patients through rehabilitation and return to physical activity after anterior cruciate ligament reconstruction. J Orthop Sports Phys Ther 2023;53(4):1-8. Epub: 23 January 2023. doi:10.2519/jospt.2023.11389.

Rehabilitation After Pediatric and Adolescent Knee Injuries.

According to epidemiology studies, the majority of youth sports injuries presenting to primary care, athletic trainers, and emergency departments impact the musculoskeletal system. Both acute and overuse knee injuries can contribute to sports attrition before high school. Effective rehabilitation of knee injuries ensures a timely return to sports participation and minimizes the negative physical, psychological, and social consequences of becoming injured. The following article provides rehabilitation and returns to play strategies for postsurgical and nonsurgical injuries of the young athlete's knee.

Differences in the course of rehabilitation and outcomes for publicly insured pediatric patients after anterior cruciate ligament reconstruction.

OBJECTIVE: Examine the effect of insurance type on physical therapy (PT) utilization and outcomes within pediatric and adolescent patients after anterior cruciate ligament reconstruction. DESIGN: Multicenter retrospective cohort study. METHODS: PT visits and functional hop test performance were extracted into a shared database. The average number of PT visits per week was assessed overall and by time period. Independent samples t-test examined the effect of insurance on PT utilization and the effect of insurance status on the odds of passing single-legged hop tests was assessed using multivariable logistic regression. RESULTS: A total of 281 patients (15.7 ± 1.9, 42% female) were included in this analysis. Of these, 128 (45%) had public insurance. Publicly insured patients experienced a longer delay from surgery to hop test (8.3vs7.7 months, p = 0.009), attended overall fewer PT visits per week (0.92vs1.04, p = 0.005), with most of the decreased frequency occurring between weeks 7-24. Insurance status had a significant effect on the odds of passing the single leg hop test (2.72; 95%CI, 1.27-5.81). CONCLUSION: Publicly insured patients average a lower number of weekly PT visits, experienced a longer delay from surgery to hop testing and were 2.7 times less likely to pass the single leg hop for distance test.

Short-Term Clinical Outcomes After Anterior Cruciate Ligament Reconstruction In Adolescents During The COVID-19 Pandemic.

Background/Purpose: The COVID-19 pandemic has impacted adolescents across multiple areas of health. While many factors influence outcomes following anterior cruciate ligament reconstruction (ACLR), the impact of the COVID-19 pandemic on early patient outcomes after ACLR is currently unknown in an adolescent population. The purpose of this study was to determine if short-term clinical outcomes were different in adolescents after ACLR for those who underwent surgery pre-COVID versus during the COVID-19 pandemic timeframe. Design: Retrospective cohort. Methods: A retrospective review of records occurred for patients who underwent ACLR with a quadriceps tendon autograft. Two separate review timeframes were defined according to date of surgery (control: September 2017 - October 2019; COVID: March 2020 - May 2021). Patients were classified into pre-COVID (control) and COVID groups by surgical date and were then age- and sex-matched. Three-month postoperative outcomes were included for analysis, including normalized isometric quadriceps and hamstring peak torque, Anterior Cruciate Ligament - Return to Sport after Injury (ACL-RSI), and the Pedi International Knee Documentation Committee Form (Pedi-IKDC) scores. Results: Sixty patients met the inclusion criteria (34 females, 56.7%). Follow-up testing occurred at 3.2 months (98.13 ± 14.91 days) postoperative. A significant difference was found between groups for normalized quadriceps peak torque on the uninvolved limb, with the control group (2.03 ± 0.47 Nm/kg) demonstrating decreased peak torque compared to the COVID group (2.49 ± 0.61 Nm/kg) (p =0.002, effect size (d) = 0.84). For the involved limb, no difference in normalized quadriceps peak torque was observed between the control group (1.25 ± 0.33 Nm/kg) and those who underwent surgery during the COVID-19 pandemic (1.49 ± 0.70 Nm/kg) (p = 0.09). No differences were identified between groups for any of the other strength outcomes (p = 0.31 - 0.87). Similarly, no differences in patient reported outcomes were found for Pedi-IKDC or ACL-RSI between groups (p = 0.12 - 0.43). Conclusion: At roughly three months after ACLR, normalized quadriceps peak torque on the uninvolved limb was reduced by 18.5% for adolescents who underwent surgery pre-COVID versus during the COVID-19 pandemic timeframe. No group differences were observed for other isometric strength outcomes, Pedi-IKDC, or ACL-RSI scores.

Side Effects and Patient Tolerance with the Use of Blood Flow Restriction Training after ACL Reconstruction in Adolescents: A Pilot Study.

Background: Blood flow restriction training (BFRT) has gained popularity in rehabilitation due to its benefits in reducing muscle atrophy and mitigating strength deficits following anterior cruciate ligament reconstruction (ACLR). While the effectiveness and safety of BFRT has been well studied in healthy adult subjects, there is limited information about the use of BFRT in the adolescent population, specifically related to patient tolerance and reported side effects post ACLR. Purpose: To investigate and record reported side effects and patient tolerance to BFRT during ACLR rehabilitation in adolescents. Study Design: Prospective Cohort Study. Methods: Patients between 12 and 18 years of age who underwent ACLR at Connecticut Children's were included. Patients utilized an automatic personalized tourniquet system and followed a standardized BFRT exercise protocol over 12 weeks starting 8.72 ± 3.32 days post-op. Upon completion of exercise while using BFRT, patients reported side effects and any adverse events were logged. Descriptive statistics were used to describe the reported side effects and adverse events associated with BFRT and calculate the frequencies of those events over a 12-week period. Results: Five hundred and thirty-five total BFRT sessions were completed between 29 patients (15.39 ± 1.61 years of age). There were zero reports of subcutaneous hemorrhage (SubQ hemorrhage) and deep vein thrombosis (DVT). Reported minor side effects to BFRT included itchiness of the occluded limb (7.85%), lower extremity paresthesia (2.81%), and dizziness (0.75%). A total of 10.47% of BFR treatment sessions were unable to be completed due to tolerance, and 3.5% of sessions required a reduction in limb occlusion pressure (LOP). Conclusion: These preliminary data suggest that BFRT is safe with only minor side effects noted in the adolescent population after ACLR. Further investigations are warranted to continue to evaluate patient tolerance and safety with BFRT, because while these preliminary results suggest a positive safety profile and good tolerance in the adolescent population after ACLR, they represent the experiences of only a small sample. Level of Evidence: Level 3.

Short-term isokinetic and isometric strength outcomes after anterior cruciate ligament reconstruction in adolescents.

OBJECTIVES: To examine differences in knee strength outcomes after ACL reconstruction according to quadriceps tendon (QT) or hamstring tendon (HT) autograft in adolescents. DESIGN: Retrospective cohort. METHODS: Surgical and clinical outcome data were collected. Analyses were conducted separately for female and male cohorts and grouped by graft type (HT or QT). A Mann-Whitney U test of independent samples was used to examine group differences according to graft type. RESULTS: 107 females (age = 15.6 ± 1.5 years) and 94 males (age = 15.7 ± 1.5 years) were included. Mean time since surgery ranged from 7.2 to 7.9 months. Those with a QT autograft had decreased normalized isokinetic quadriceps peak torque on the involved limb compared to the HT group (p < 0.01, ES = 0.71-0.89). Normalized isometric hamstring peak torque was decreased for those with HT autograft in the female cohort (p = 0.02, ES = 0.57). CONCLUSION: Normalized isokinetic quadriceps peak torque was reduced by 18-20% on the involved limb in those with a QT autograft. Normalized isometric hamstring peak torque was decreased by 13% for those with HT autograft in the female cohort. Method of strength testing may be an important consideration to fully appreciate strength deficits after ACL reconstruction according to graft type.

Knee strength outcomes in adolescents by age and sex during late-stage rehabilitation after anterior cruciate ligament reconstruction.

OBJECTIVE: To determine if knee strength differences exist according to age group and sex among adolescents during late-stage anterior cruciate ligament reconstruction (ACLR) rehabilitation. DESIGN: Retrospective cohort study. METHODS: Consecutive patients who had undergone ACLR with a hamstring autograft completed isokinetic knee strength assessment. Patients were categorized into early (ages 11-14 years) and middle (ages 15-17 years) adolescence. A two-way MANOVA was used to examine strength differences according to age group and sex. RESULTS: 144 patients were included in the analysis (56.9% females, age = 15.3 ± 1.5 years; days since surgery = 228.2 ± 41.2). Differences in quadriceps peak torque were identified between age groups on the involved (p = 0.001) and uninvolved limbs (p < 0.001), however, no differences in quadriceps peak torque were found between age groups when normalized to body mass (p = 0.16-0.49). Differences between groups according to sex were identified for each strength outcome (p < 0.01), with decreased normalized quadriceps (12-13%) and hamstring (13-16%) peak torque for females. No interactions between age group and sex were noted, F(8, 133) = 1.48, p = 0.17. CONCLUSION: Early adolescents produced less quadriceps and hamstring peak torque compared to middle adolescents after ACLR. No differences were found between age groups when normalized to body mass.

Deletion of Calcineurin in Schwann Cells Does Not Affect Developmental Myelination, But Reduces Autophagy and Delays Myelin Clearance after Peripheral Nerve Injury.

In the PNS, myelination occurs postnatally when Schwann cells (SCs) contact axons. Axonal factors, such as Neuregulin-1 Type III, trigger promyelinating signals that upregulate myelin genes. Neuregulin-1 Type III has been proposed to activate calcineurin signaling in immature SCs to initiate differentiation and myelination. However, little is known about the role of calcineurin in promyelinating SCs after birth. By creating a SC conditional KO of calcineurin B (CnBscko), we assessed the effects of CnB ablation on peripheral myelination after birth in both male and female mice. Surprisingly, CnBscko mice have minimal myelination defects, no alteration of myelin thickness, and normal KROX20 expression. In contrast, we did find a unique role for calcineurin in SCs after nerve injury. Following nerve crush, CnBscko mice have slower degeneration of myelin compared with WT mice. Furthermore, absence of CnB in primary SCs delays clearance of myelin debris. SCs clear myelin via autophagy and recent literature has demonstrated that calcineurin can regulate autophagy via dephosphorylation of transcription factor EB (TFEB), a master regulator of lysosomal biogenesis and autophagy. We demonstrate that loss of CnB reduces autophagic flux in primary SCs, indicating a possible mechanism for impaired myelin clearance. In addition, ablation of CnB impairs TFEB translocation to the nucleus 3 d after crush, suggesting that calcineurin may regulate autophagy in SCs via TFEB activation. Together, our data indicate that calcineurin is not essential for myelination but has a novel role in myelin clearance after injury.SIGNIFICANCE STATEMENT Our data offer a novel mechanism for activation of autophagy after peripheral nerve injury. Efficient clearance of myelin after injury by Schwann cells is important for axonal regrowth and remyelination, which is one reason why the PNS is significantly better at recovery compared with the CNS. Improved understanding of myelin clearance allows for the identification of pathways that are potentially accessible to increase myelin clearance and improve remyelination and recovery. Finally, this paper clarifies the role of calcineurin in Schwann cells and myelination.

Melanocortin 1 Receptor-Targeted α-Particle Therapy for Metastatic Uveal Melanoma.

New effective therapies are greatly needed for metastatic uveal melanoma, which has a very poor prognosis with a median survival of less than 1 y. The melanocortin 1 receptor (MC1R) is expressed in 94% of uveal melanoma metastases, and a MC1R-specific ligand (MC1RL) with high affinity and selectivity for MC1R was previously developed. Methods: The 225Ac-DOTA-MC1RL conjugate was synthesized in high radiochemical yield and purity and was tested in vitro for biostability and for MC1R-specific cytotoxicity in uveal melanoma cells, and the lanthanum-DOTA-MC1RL analog was tested for binding affinity. Non-tumor-bearing BALB/c mice were tested for maximum tolerated dose and biodistribution. Severe combined immunodeficient mice bearing uveal melanoma tumors or engineered MC1R-positive and -negative tumors were studied for biodistribution and efficacy. Radiation dosimetry was calculated using mouse biodistribution data and blood clearance kinetics from Sprague-Dawley rat data. Results: High biostability, MC1R-specific cytotoxicity, and high binding affinity were observed. Limiting toxicities were not observed at even the highest administered activities. Pharmacokinetics and biodistribution studies revealed rapid blood clearance (<15 min), renal and hepatobillary excretion, MC1R-specific tumor uptake, and minimal retention in other normal tissues. Radiation dosimetry calculations determined pharmacokinetics parameters and absorbed α-emission dosages from 225Ac and its daughters. Efficacy studies demonstrated significantly prolonged survival and decreased metastasis burden after a single administration of 225Ac-DOTA-MC1RL in treated mice relative to controls. Conclusion: These results suggest significant potential for the clinical translation of 225Ac-DOTA-MC1RL as a novel therapy for metastatic uveal melanoma.

A novel set of structures within the elasmobranch, ovarian follicle.

Elasmobranch fishes produce some of the largest oocytes known, exceeding 10 cm in diameter. Using various microscopy techniques we investigated the structural adaptations which facilitate the production of these large egg cells in three species of shark: the Atlantic sharpnose shark, Rhizoprionodon terraenovae, dusky smoothound, Mustelus canis and the little gulper shark, Centrophorus uyato. The ovarian follicle of elasmobranchs follows the typical vertebrate pattern, with one notable exception; the zona pellucida reaches extreme widths, over 70 µm, during early oogenesis. Contact between the follicle cells and the oocyte across the zona pellucida is necessary for oogenesis. We describe here a novel set of large, tube-like structures, which we named follicle cell processes that bridge this gap. The follicle cell processes are more robust than the microvilli associated with the follicle cells and the oocyte plasma membrane and much longer. During early oogenesis the follicle increases in size relatively quickly resulting in a wide zona pellucida. At this stage the follicle cell processes appear taut, uniform and radially oriented. As oogenesis continues the zona pellucida narrows and the follicle cell processes change their orientation, appearing to wrap around the oocyte. The presence of the contractile protein actin within the follicle cell processes and their change in orientation may well be an adaptation for maintaining the integrity of these large oocytes. The follicle cell processes also contain electron dense material, identical to material found within the follicle cells, suggesting a role in the transport of metabolites to the developing oocyte.

A role for compromise: synaptic inhibition and electrical coupling interact to control phasing in the leech heartbeat CpG.

How can flexible phasing be generated by a central pattern generator (CPG)? To address this question, we have extended an existing model of the leech heartbeat CPG's timing network to construct a model of the CPG core and explore how appropriate phasing is set up by parameter variation. Within the CPG, the phasing among premotor interneurons switches regularly between two well defined states - synchronous and peristaltic. To reproduce experimentally observed phasing, we varied the strength of inhibitory synaptic and excitatory electrical input from the timing network to follower premotor interneurons. Neither inhibitory nor electrical input alone was sufficient to produce proper phasing on both sides, but instead a balance was required. Our model suggests that the different phasing of the two sides arises because the inhibitory synapses and electrical coupling oppose one another on one side (peristaltic) and reinforce one another on the other (synchronous). Our search of parameter space defined by the strength of inhibitory synaptic and excitatory electrical input strength led to a CPG model that well approximates the experimentally observed phase relations. The strength values derived from this analysis constitute model predictions that we tested by measurements made in the living system. Further, variation of the intrinsic properties of follower interneurons showed that they too systematically influence phasing. We conclude that a combination of inhibitory synaptic and excitatory electrical input interacting with neuronal intrinsic properties can flexibly generate a variety of phase relations so that almost any phasing is possible.

Plastic and stable electrophysiological properties of adult avian forebrain song-control neurons across changing breeding conditions.

Steroid sex hormones drive changes in the nervous system and behavior in many animal taxa, but integrating the former with the latter remains challenging. One useful model system for meeting this challenge is seasonally breeding songbirds. In these species, plasma testosterone levels rise and fall across the seasons, altering song behavior and causing dramatic growth and regression of the song-control system, a discrete set of nuclei that control song behavior. Whereas the cellular mechanisms underlying changes in nucleus volume have been studied as a model for neural growth and degeneration, it is unknown whether these changes in neural structure are accompanied by changes in electrophysiological properties other than spontaneous firing rate. Here we test the hypothesis that passive and active neuronal properties in the forebrain song-control nuclei HVC and RA change across breeding conditions. We exposed adult male Gambel's white-crowned sparrows to either short-day photoperiod or long-day photoperiod and systemic testosterone to simulate nonbreeding and breeding conditions, respectively. We made whole-cell recordings from RA and HVC neurons in acute brain slices. We found that RA projection neuron membrane time constant, capacitance, and evoked and spontaneous firing rates were all increased in the breeding condition; the measured electrophysiological properties of HVC interneurons and projection neurons were stable across breeding conditions. This combination of plastic and stable intrinsic properties could directly impact the song-control system's motor control across seasons, underlying changes in song stereotypy. These results provide a valuable framework for integrating how steroid hormones modulate cellular physiology to change behavior.

Slow conductances could underlie intrinsic phase-maintaining properties of isolated lobster (Panulirus interruptus) pyloric neurons.

The rhythmic pyloric network of the lobster stomatogastric system approximately maintains phase (that is, the burst durations and durations between the bursts of its neurons change proportionally) when network cycle period is altered by current injection into the network pacemaker (Hooper, 1997a,b). When isolated from the network and driven by rhythmic hyperpolarizing current pulses, the delay to firing after each pulse of at least one network neuron type [pyloric (PY)] varies in a phase-maintaining manner when cycle period is varied (Hooper, 1998). These variations require PY neurons to have intrinsic mechanisms that respond to changes in neuron activity on time scales at least as long as 2 s. Slowly activating and deactivating conductances could provide such a mechanism. We tested this possibility by building models containing various slow conductances. This work showed that such conductances could indeed support intrinsic phase maintenance, and we show here results for one such conductance, a slow potassium conductance. These conductances supported phase maintenance because their mean activation level changed, hence altering neuron postinhibition firing delay, when the rhythmic input to the neuron changed. Switching the sign of the dependence of slow-conductance activation and deactivation on membrane potential resulted in neuron delays switching to change in an anti-phase-maintaining manner. These data suggest that slow conductances or similar slow processes such as changes in intracellular Ca(2+) concentration could underlie phase maintenance in pyloric network neurons.

A central pattern generator producing alternative outputs: pattern, strength, and dynamics of premotor synaptic input to leech heart motor neurons.

The central pattern generator (CPG) for heartbeat in medicinal leeches consists of seven identified pairs of segmental heart interneurons and one unidentified pair. Four of the identified pairs and the unidentified pair of interneurons make inhibitory synaptic connections with segmental heart motor neurons. The CPG produces a side-to-side asymmetric pattern of intersegmental coordination among ipsilateral premotor interneurons corresponding to a similarly asymmetric fictive motor pattern in heart motor neurons, and asymmetric constriction pattern of the two tubular hearts, synchronous and peristaltic. Using extracellular recordings from premotor interneurons and voltage-clamp recordings of ipsilateral segmental motor neurons in 69 isolated nerve cords, we assessed the strength and dynamics of premotor inhibitory synaptic output onto the entire ensemble of heart motor neurons and the associated conduction delays in both coordination modes. We conclude that premotor interneurons establish a stereotypical pattern of intersegmental synaptic connectivity, strengths, and dynamics that is invariant across coordination modes, despite wide variations among preparations. These data coupled with a previous description of the temporal pattern of premotor interneuron activity and relative phasing of motor neuron activity in the two coordination modes enable a direct assessment of how premotor interneurons through their temporal pattern of activity and their spatial pattern of synaptic connectivity, strengths, and dynamics coordinate segmental motor neurons into a functional pattern of activity.

A central pattern generator producing alternative outputs: phase relations of leech heart motor neurons with respect to premotor synaptic input.

The central pattern generator (CPG) for heartbeat in leeches consists of seven identified pairs of segmental heart interneurons and one unidentified pair. Four of the identified pairs and the unidentified pair of interneurons make inhibitory synaptic connections with segmental heart motor neurons. The CPG produces a side-to-side asymmetric pattern of intersegmental coordination among ipsilateral premotor interneurons corresponding to a similarly asymmetric fictive motor pattern in heart motor neurons, and asymmetric constriction pattern of the two tubular hearts: synchronous and peristaltic. Using extracellular techniques, we recorded, in 61 isolated nerve cords, the activity of motor neurons in conjunction with the phase reference premotor heart interneuron, HN(4), and another premotor interneuron that allowed us to assess the coordination mode. These data were then coupled with a previous description of the temporal pattern of premotor interneuron activity in the two coordination modes to synthesize a global phase diagram for the known elements of the CPG and the entire motor neuron ensemble. These average data reveal the stereotypical side-to-side asymmetric patterns of intersegmental coordination among the motor neurons and show how this pattern meshes with the activity pattern of premotor interneurons. Analysis of animal-to-animal variability in this coordination indicates that the intersegmental phase progression of motor neuron activity in the midbody in the peristaltic coordination mode is the most stereotypical feature of the fictive motor pattern. Bilateral recordings from motor neurons corroborate the main features of the asymmetric motor pattern.