Studies in adults have shown that the role of the postural system during most motor behaviors is more complex than just merely minimizing positional deviations away from a stable equilibrium point. Rather, the postural system appears to be highly coordinated and integrated with other suprapostural behaviors. How the integration and coordination between the postural system and other suprapostural behaviors develops has not been extensively examined. In this project the developmental integration and coordination between posture and manual control was studied in children (7- and 10-years of age) and compared with healthy college aged adults. All subjects were required to fit a block through an opening as precision, postural and visual constraints were manipulated. Trunk and arm kinematics and center of pressure data were obtained. Compared to adults children adopt different postural strategies during the fitting task (Chapter 4), appear less able to modulate postural stability as precision demands increase (Chapter 5), and exhibit less ability to use functionally exploit postural fluctuations (Chapter 6). Taken together, results suggest that even by 10-years of age, the postural system is not integrated with the manual control system at adult like levels.

Mice with a deletion of the hypothalamic basic helix-loop-helix transcription factor Nhlh2 (N2KO) display adult onset obesity, implicating Nhlh2 in the neuronal circuits regulating energy availability. Nhlh2 co-localizes with the hypothalamic thyrotropin-releasing hormone (TRH) neurons in the paraventricular nucleus (PVN) and proopiomelanocortin (POMC) neurons in the arcuate nucleus. N2KO mice become obese due to reduced physical activity in the absence of hyperphagia making them a unique mouse model for the study weight gain, obesity and energy expenditure. Signals that regulate Nhlh2 and the effects of Nhlh2 on peripheral tissues remain largely unknown. The research presented here utilized numerous techniques to investigate the effects of changes in energy availability on Nhlh2 expression. We show that Nhlh2 expression decreases significantly with food deprivation and cold exposure. Nhlh2 expression is stimulated with food return or leptin injection following food deprivation or return to room temperature following cold exposure. These data suggest that Nhlh2 gene expression responds positively to increased energy availability and negatively to reduced energy availability. These findings combined with the phenotype of N2KO mice led us to propose that Nhlh2 integrates energy availability inputs in various hypothalamic nuclei to drive expression of genes required for body weight maintenance. Investigation into peripheral tissues in N2KO mice revealed that responses of genes in the hypothalamus-pituitary-thyroid axis, muscle, and brown and white adipose tissue to changes in energy availability require Nhlh2 expression. The responses of serum total T4 levels and UCP1 mRNA and UCP3 mRNA to energy availability signals are altered in N2KO mice. In addition, N2KO mice maintain body temperature with cold exposure but are unable to maintain body weight. In summary, my work provides new insight into the role of Nhlh2 in coordinating energy availability signals to downstream genes required for body weight maintenance and thermoregulation.

One the most serious health hazards of aging and of long term space flight is the loss of bone. The most important determinant of the debilitation due to bone loss is the peak bone mass achieved during late adolescence, which itself may be influenced by gender and environmental factors such as mineral balance. Sodium intake is considered a risk factor for both hypertension and osteoporosis. It is estimated that 30-60% of the population is hypertensive and 30-40% of the population is salt sensitive. The primary purpose of the present studies was to both delineate and combine the effects between salt intake and salt sensitive hypertensive genotype on bone. Our hypothesis was that hypertensive rats would have more severely affected bone than normotensive rats due to salt supplementation and/or genotype. In addition, how these effects might be altered by immobilization/overloading stress was examined as this further burdens NASA space pioneers. This study investigated the possible effects of an ad libidum 1% or 2% saline instead of water on the normotensive (W) and salt sensitive hypertensive (SS) young female rats. A total of 46 weight-matched female rats (7 weeks old) were used. Treated rats in the 1% study drank 1% saline ad libitum for a 42 day salt supplementation period, beginning at day 7 (after arrival) to day 49. Treated rats in the 2% study drank 2% saline ad libitum for a 42 day salt supplementation period, beginning at day 7 (after arrival) to day 49. The right hindlimb of each animal was immobilized by binding to the abdomen with 4 layers of elastic bandage tape, the hip joint in flexion and the knee and ankle joint in extension for the 42 day salt experimental period. Body weight and urine volume was measured biweekly. Food and fluid intake was monitored daily. After sacrifice, three sites (both the underloaded and the overloaded tibiae, as well as the L-2 vertebrae) were processed for histomorphometric analysis. The wet weight (g) and length (mm) of the excised right immobilized and left overloaded femur and the ulna were measured. A 3-point bending test was applied to femurs only. Immediately after the femur breaking strength measurements, bone was cut transversely, one mm from breaking point (fracture location), and a 1.0 mm cross-section was cut for morphological measurement. In addition, a 5 mm high cylinder section from each femur was cut and used for bone composition measurements along with the right ulna bone. A number of elements were analyzed at one time with Induced Coupled Plasma (ICP) spectrometry. The systolic blood pressure and heart rate were measured in the 6th week of study by the tail-cuff sphygmomanometer method. A more robust result was seen with increased concentration of saline treatment from a 1% saline threshold level, to the 2% saline level. Using two-way ANOVA, both hypertensive genotype and 2% saline treatment significantly increased blood pressure and heart rate, and decreased femur magnesium. The SS rat had significant reductions in bone mass, femur cross-sectional area and zinc concentrations with simultaneous elevations in femur stiffness, strength and calcium concentrations. Two percent saline treatment markedly increased both blood pressure and heart rate and decreased both femurs magnesium and cancellous bone in the weight-bearing tibia bone. After 6 weeks of immobilization (to simulate space weightlessness), reductions in cancellous tibia bone volume, with elevations in femur bone stiffness, mineral concentration (calcium and phosphorus) and in trace elements (zinc and manganese) were found in the underloaded femur. Our findings suggest genotype, and saline treatment, and immobilization adversely affect bone in adolescent female rats. In addition, the deleterious bone effects are site specific, affecting each site differently.

The morphology and physiology of crustacean cardiovascular systems has long been regarded as poorly organized and loosely controlled, systems serving only as a conduit to carry hemolymph. Current investigations of cardiovascular systems of decapod Crustacea have revealed an organization that is more complex than previously thought. The purpose of this research is to extend the study of crustacean cardiovascular physiology by investigating the hemodynamics of the freshwater crayfish, Procambarus clarkii, and the lobster, Homarus americanus. Crayfish and lobster were exposed to a P$\sb{\rm O\sb2}$ of 150 mmHg (control) followed by P$\sb{\rm O\sb2}$s of 25, 40, 75 and 115 mmHg O$\sb2$. Arterial hemolymph velocities were measured (Pulsed Doppler system) in the major arteries of crayfish and lobster. Hemolymph pressures were measured throughout the circulatory system of the crayfish. The cardiovascular response of hypoxic crayfish to injection of hyperoxic water into the branchial chamber was monitored to determine the location of O$\sb2$ receptors. Heart frequency in both species decreased as water P$\sb{\rm O\sb2}$ was lowered. Cardiac output was maintained in the crayfish due to an increase in stroke volume. Hemolymph flow increased to the anterior aorta only. Hemolymph pressures and ventilatory frequency increased down to a P$\sb{\rm O\sb2}$ of 50 mmHg O$\sb2$; below this all parameters declined. Cardiac output and stroke volume in the lobster were maintained down to a P$\sb{\rm O\sb2}$ of 75 mmHg O$\sb2$; at lower P$\sb{\rm O\sb2}$s cardiac output declined as a result of the hypoxia induced bradycardia. Hemolymph flow increased in the lateral arteries and ventral thoracic artery. Hypoxic crayfish showed a rapid increase in cardiovascular parameters (2.5 second) with a long lag in the respiratory response (75 seconds) to injection of hyperoxic water into their branchial chamber. Injection of hyperoxic water into animals that had defined gill sets removed indicates the presence of O$\sb2$-sensitive chemoreceptors in the posterior region of the branchial chamber. The redistribution of cardiac output in crayfish and lobster results in a maintenance of hemolymph flow to the anterior regions of the animals. The maintenance of cardiac output with hypoxia may not be solely related to maintaining M$\sb{\rm O\sb2}$, but may play a role in maintaining oxygen delivery to nervous tissue. The response to a declining water P$\sb{\rm O\sb2}$ is mediated by O$\sb2$ receptors associated with the posterior gills.

Reduced heart rate variability (HRV) is related to an increased risk of mortality. The primary aim of this dissertation was to determine the independent effects of regular exercise and maturation on HRV. It was hypothesized that (1) regular exercise increases HRV in adults and (2) HRV declines as a result of maturation. Resting HRV was measured using the (1) average change in HR (ΔHR) during each breathing cycle; (2) standard deviation of HR (HRSD); (3) root of mean squared differences of successive interbeat intervals (rMSSD); and (4) proportion of adjacent intervals that differed by more than 50 ms (pNN50). Spectral analysis was used to determine the power of oscillations in HR occurring at low (LF, 0.04–0.12 Hz), and high (HF, 0.12–0.40 Hz) frequencies, which are believed to represent cardiac sympathetic and parasympathetic influences, respectively. In Study I, HRV was compared in 40 adult males grouped according to their physical activity level (LOW, MOD, and HIGH). HRV appeared to be greater in the active groups (LOW < MOD = HIGH), but only pNN50 achieved statistical significance. Study II examined the effects of a 16 week moderate intensity endurance training program on HRV. Twelve adult males that exercised three times weekly, thirty minutes per session (EXP) were compared to a non-exercising control group (CON, N = 5). Aerobic capacity, pNN50, and rMSSD increased significantly in EXP (∼14%, 75%, and 37%, respectively) but not controls. There were no changes in ΔHR or LF power, but HF power increased in both EXP and CON. In Study III, HRV was compared between the adults from Study I and twelve boys. HRSD and ΔHR were greater in boys. All other measures of HRV appeared to be greater in boys, but none of these comparisons achieved statistical significance. It is concluded that (1) participation in regular aerobic exercise training appears to augment HRV; and (2) HRV declines as a result of maturation. When the data from studies I and II are considered in light of the existing literature, it appears that significant increases in HRV occur only after many weeks or months of endurance training.

A rat model was used to determine whether prenatal cocaine exposure results in long-term changes in hippocampal-dependent contextual fear conditioning. Pregnant dams received either 40 mg/kg cocaine HCl SC (COC), an equal volume of 0.9% saline (SAL), or received no injections (UT) from gestational day 8 through 20. SAL animals were also pair-fed to COC subjects. Experiment 1 tested one-trial contextual fear conditioning in adult male offspring. Freezing and defecation were measures of fear. Prenatal cocaine exposure did not affect context conditioning, but there was an overall increase in SAL and COC defecation, indicating an increased generalized fear in these subjects. To better mimic binge cocaine use, COC dams in Experiment 2 and 3 received 20 mg/kg cocaine HCl SC, b.i.d. A preliminary open field task revealed that SAL offspring were more exploratory than UT controls and that females were more active than males. In Experiment 2, adult male and female offspring received 4 days of context conditioning and 3 days of no-shock extinction. During extinction, access to an adjacent chamber enabled the observation of four additional measures of fear: side crossing, latency, nose crossing, and side-differential. Experiment 2 repeated previous reports of gender-specific contextual fear. Males showed a greater level of freezing and defecation, higher latencies and side-differentials, and a lower level of side crossings and nose crossings than females. Prenatal cocaine exposure resulted in exaggerated gender-specific fear conditioning as measured by nose-crossing and side differential during extinction. Experiment 3 tested the effects of prenatal cocaine exposure on latent inhibition (LI) of contextual fear in year-old females. Vertical nose crossing (VNC), freezing, and defecation were measures of fear. LI was evidenced as an attenuation of freezing and VNC in pre-exposed (PE) animals compared to non-pre-exposed subjects. Prenatal cocaine exposure resulted in an enhanced LI effect. COC females showed a low level of baseline VNC, but COC-PE subjects showed a greater level of VNC than controls following the first shock during conditioning. The results of these experiments suggest that the effects of prenatal cocaine exposure on hippocampal-dependent learning are subtle, selective, and gender specific.

These studies examined the pharmacokinetics of cocaine following its chronic subcutaneous (s.c.) administration to pregnant rats and the effects of this treatment on neurotensin/neuromedin (NT/N) mRNA expression in the brains of their offspring. First, I examined the distribution of cocaine and its metabolites benzoylecgonine (BE) and norcocaine in pregnant rats following twice-daily s.c. injections of 20 mg/kg cocaine from gestational day (GD) 8–GD 21. Following a single injection on GD 21, maternal and fetal trunk blood, fetal brains, and amniotic fluid (AF) were collected at 8 separate time points from 5 min to 12 h. Cocaine peaked in maternal plasma at 1 h and at 2 h in fetal plasma, fetal brain and AF. Peak BE levels were detected at 4 h in maternal plasma, fetal plasma, and fetal brain, and at 8 h in the AF. An additional group of dams given both injections on GD 21 and sacrificed 2 h later showed increased concentrations of BE in both fetal compartments and in the AF. Previously undetectable, norcocaine was now measurable in the AF. Chronic cocaine administration increases NT/N mRNA in the nucleus accumbens. To further understand the mechanisms involved, I conducted a dose response study evaluating the role of the D3 receptor on the expression of NT/N mRNA in the nucleus accumbens shell using in situ hybridization. Animals were sacrificed 3 h following an acute challenge with either the D3 agonist PD 128904 or the antagonist nafadotride. As neither compound significantly altered NT/N mRNA levels, no further work was performed with these drugs. To examine the effects of prenatal cocaine exposure on neurotensin expression, adult male offspring from either cocaine (40 mg/kg daily, GD 8–21) or saline-injected dams were treated with a single daily i.p. injection of cocaine or saline for 10 days and sacrificed 1 h after the last injection. This treatment resulted in increased NT/N mRNA in the nucleus accumbens, fundus, striati, and dorsomedial striatum regardless of prenatal treatment, and significantly greater NT/N mRNA expression within the medial preoptic nucleus (MPN) of offspring from pair-fed saline dams. Thus, prenatal cocaine exposure alters the NT/N response in the MPN to postnatal cocaine challenge.

Human performance will be altered by changes in movement speed. The inertial properties of human limbs may play an important role in these alterations. The effects of these changes may be observed with the measurement of joint and segmental mechanics, as well as muscular kinematics, kinetics and muscular activity patterns. In this study, the cycling motion was used to investigate these inertial effects, following the development of a new mechanical model that provided the theoretical basis of coordination changes with movement speed. The alteration of cycling performance with different pedaling speed was examined using: (1) Surface EMG as an indication of the changes in muscular coordination as a function of cadence; (2) Inverse dynamics and decomposition of mechanical parameters to identify the influence of gravitational, inertial, and external factors; and (3) Simulations via a musculoskeletal modeling approach to assess the contributions of individual muscles. As predicted by the theoretical model, an increase in pedaling speed produced greater changes at the hip joint compared to knee and ankle joint in both muscular activities and mechanical measures. The changes in muscular activity were evident in both the activity of the single joint hip extensor and the coordination among the synergistic muscles. The altered muscular activities with increased cadence were accompanied by changes in joint moments, in the order of hip, knee and ankle joint from greatest to smallest. Further, the responses in movement organization were not linearly related to the increased inertial influence as the pedaling speed increased. Finally, the simulation analysis demonstrated a compensatory relation between gastrocnemius and soleus muscular activities with different pedaling speeds, although the combined patterns of the two were consistent.

The primary aim of this dissertation was to examine the effects of creatine (Cr) supplementation on exercise performance, body mass, muscle phosphocreatine (PCr), and blood Cr in older men. The effect of acute (20 g of Cr d −1 for 5 d, preliminary study) and longer term (20 g of Cr d −1 for 10 d followed by 4 g of Cr d−1 for 20 d, Study I) Cr supplementation on isokinetic leg fatigue, maximal isometric force (MIF), and body mass was examined in healthy older men (60–82 yr) over two studies. In both the preliminary study and Study I there was a small improvement on the isokinetic leg fatigue test, but this did not achieve statistical significance. There was no effect of the Cr supplement on MIF. In the preliminary study there was a small (0.5 kg) increase in body mass in the Cr group after supplementation, but in Study I this difference was not statistically significant between groups. In Study II, the effects of Cr supplementation on muscle PCr, blood Cr, urine Cr, and urine creatinine (Cn) were assessed in eight young (20–32 yrs) and seven old (63–83 yrs) male subjects who ingested Cr (20 g d −1) for 5 days. Plasma Cr, following a 5 gram oral Cr bolus, increased, with no difference in the response between groups. Urine Cr, assessed pre and on five days of supplementation, increased, with no difference between groups. Urine Cn did not change as a result of Cr supplementation. Muscle PCr, assessed pre- and post-supplementation increased significantly more in the young subjects. Data from the preliminary study and Study I suggest that acute and longer term oral Cr supplementation does not affect MIF and only produces small increases in body mass and performance on an isokinetic leg fatigue test in men over the age of 60. The smaller increase in muscle PCr in the older subjects in Study II may explain the lack of a significant ergogenic effect of Cr in this population.

The primary aim of this dissertation was to examine the role of short-term immobilization on muscle function recovery, excitability of the muscle, evoked contractile properties of the muscle, and muscle proteins in the blood after contraction-induced muscle injury. In Studies I and II, the effects of four days of immobilization on recovery of muscle function and serum creatine kinase (CK) activity after eccentric exercise was examined in 26 males, who were placed into one of three groups: immobilization, control, or light exercise. When the damaged elbow flexor muscles were immobilized or exercised for four consecutive days, force recovery over eight days was significantly enhanced compared to a control. In Study II, during the four-day treatment period after eccentric exercise, immobilization resulted in a significant blunting of the CK response compared to the light exercise or control groups. However, increasing activity with light exercise did not have any effect on the CK response compared to control. The data from Study II suggested that reduced lymphatic transport with decreased muscular activity may have contributed to the lower CK response in the immobilized muscle. In Study III, mechanisms to explain the observations in Studies I and II with immobilization were undertaken. Muscle excitability and evoked contractile properties of the muscle were examined to determine whether immobilization altered the mechanical properties of the muscle to favor an enhanced force response. After eccentric exercise, there were immediate and prolonged reductions in the evoked contractile properties of the muscle. Immobilization, however, had no effect on these measures. CK and myoglobin were assessed during the four-day treatment period as well as during the five-day recovery period. There was a significant difference in the CK response between groups, with the immobilization demonstrating significant blunting of the CK response during the treatment period. Upon remobilization of the arm, CK activity increased but not as high as was anticipated. The myoglobin response, however, was not different between groups. Because their routes of entry into the blood differ, taken together, the myoglobin and CK response suggest that lymph transport likely contributed to the blunting of the CK response observed with immobilization.