Thesis (Ph. D.)--University of Hong Kong, 1989.

No description available.

The primary goal of this work was to examine the role of voltage-dependent Ca2+ channels in regulating the output of larval Drosophila motoneurons functioning within an intact network. To accomplish this goal, two major aims were addressed: 1. To determine whether larval Drosophila motoneurons express voltage-dependent Ca2+ channels in their central processes, and further, to determine the genes responsible. 2. To determine the role of centrally expressed voltage-dependent Ca2+ channels in the regulation of motoneuron output as motoneurons receive behaviorally relevant input from the locomotor network. To address these goals, genetic tools available in Drosophila were used along side in situ patch clamp techniques from larval motoneurons.Using whole cell voltage-clamp techniques in situ, we have shown that two identified motoneurons, aCC and RP-2, carry voltage-dependent currents recorded from the soma. Dmca1D, the L-type like channel in Drosophila, is primarily responsible for this current. Expressing Dmca1D RNAi in aCC and RP-2, as the preparation displayed fictive bouts of locomotion, caused an increase in burst duration in both RP-2 and aCC as well as an increase in the number of action potentials fired per burst. Additionally, the afterhyperpolarization between spikes was greatly reduced and spiking became less regular. This work indicates a role for Dmca1D in the processing of synaptic information in Drosophila motoneurons aCC and RP-2.

Cognitive demands for postural control in younger and older adults were examined under conditions of postural threat. Age-related differences emerged in the distribution of attention for postural control in conditions of postural threat. Specifically, porutral compensations were implented to reduce cognitive demands for postural control. In addition, it was determined that the effect of performing a secondary cognitive task on postural control was altered when the potential consequences of instability were increased. Younger adults were found to maintain postural control and improve secondary task performance in conditions of increased threat whereas postural control in older adults improved at the expense of secondary task performance. In older adults, postural control may be prioritized under conditions that increase arousal and the consequences of imbalance. These findings have implications for reducing falls in elderly populations, as they reveal that the ability to adequately perform concurrent tasks is compromised when environmental factors threaten balance in elderly populations. / xi, 113 leaves ; 28 cm.

The effects of postural threat and the potential consequences of obstacle contact on the obstacle contact on the obstacle negotiation kinematics among younger and older adults were examined. Seventeen older (OA;7males, 10 females; mean age, 68.94 + 4.85) and fifteen younger adults (YA; 5males, 10 females; mean age, 22.53 + 2.77) negotiated virtual and real obstacles while walking at a self-determined velocity along a 7.2m walkway under 4 different conditions of postural threat. Postural threat was manipulated by varying the width (0.60m)) of the walkway. Postural threat altered crossing kinematics for all subjects. Specifically, age-related differences emerged with increasing postural threat, however the changes observed among older adults were considerably different from those of younger adults. Additionally, there was no effect for the potential consequences of obstacle contact, however, no age-related differences emerged. These results revealed an effect for postural threat and obstacle characteristics on the negotiation strategies of younger and older adults. Both postural threat and obstacle characteristics elicit conservative crossing kinematics in younger and older adults. Specifically, these findings illustrate age-dependent differences in obstacle negotiation strategies and that postural threat affects older adults differently than younger adults whereas the potential consequences of obstacle contact affects younger and older adults equally. / xii, 79 leaves ; 28 cm.

Caenorhabditis elegans" locomotion consists of long forward crawling interrupted by short spontaneous reversals. We identified several intrinsic and extrinsic variables that influence the reversal frequency. In particular, reversal frequency can be transiently suppressed by touch. The genes glr-1 and nmr-1, which encode subunits of AMPA- and NMDA-type glutamate receptors, play a central role in touch-induced reversal suppression. Thus, reversal behavior is a motor output reflecting the integration of sensory inputs that display a form of memory. Food has a dramatic effect on reversal frequency that depends on chemosensation. Wild-type worms dramatically reduce reversal frequency on food but chemosensory mutants do not. A null allele of eat-2, a gene necessary for the proper response to food, confers a hyperreversal phenotype. eat-2 also enhances dauer formation in a serotonin deficient genetic background. These phenotypes do not appear to result from the effect of eat-2 on eating efficiency.

Bone is a 3D dynamic and unique tissue that structurally adapts in response to mechanical stimuli. Comparative skeletal morphology is commonly utilized to infer ancient hominins' modes of locomotion; however, instances of remarkable gross similarity despite different modes of locomotion do occur. A common cited example is the similarity between the skeletal elements of bipedal human (Homo sapiens) hands/feet and quadrupedal black bear (Ursus americanus) front/hind paws. Through novel 3D Micro-CT and 2D histomorphology analysis, this thesis tests the hypothesis that a 3D microscopic analysis of biomechanically regulated cortical bone structures provides a more representative and accurate means to infer a species' mode of locomotion. Micro-CT data were collected at the mid-diaphysis of human (n=5) and bear (n=5) third metacarpal/metatarsal pairs and compared with independent and paired t-tests, Pearson correlation coefficients and Bland-Altman plots. Bone microarchitecture is quantifiable in 3D and accessible through non-destructive Micro-CT. Interspecies variation was present, however no significant cortical differences between elements of humans and bears was found. Histological inspection revealed further variation between and within species and element. A key limitation was sample size and further investigation of the relationship between mechanical loading and mode of locomotion is warranted.

The backwards swimming behavior exhibited by American weakly electric fishes (Gymnotiformes) is thought to be an important component of foraging, particularly in the electrolocation of prey items. Previous studies of Eigenmannia virescens and Apteronotus albifrons have shown that backwards swimming appears to allow a fish to scan a potential prey item across its cutaneous electroreceptor array, then put itself in position for a short, forward lunge preceding ingestion. Adult gymnotiforms exhibit considerable variation in size, shape, and electric organ characteristics. For example, gymnotiforms produce either a wave or a pulse electric organ discharge (EOD). Given this variation, we ask whether the results reported previously can be completely generalized to all gymnotiforms. To address this question we observed the foraging patterns of phylogenetically and ecologically distinct gymnotiforms: three wave species, E. virescens, A. albifrons and Sternopygus macrurus; and three pulse species, Gymnotus carapo, Brachyhypopomus cf. brevirostris, and Rhamphichthys rostratus. Electric organ placement and body shape were also noted in these species to determine if morphological differences correlate with variations in foraging behaviors. Results demonstrate that following prey detection the wave species examined primarily swim backwards during prey approach, prior to lunging forward and ingesting prey. This result is similar to previous findings. In contrast, the pulse species examined detect, approach, and ingest prey primarily in the forward direction, swimming backwards only to reposition themselves. / Department of Biology

Bone is a 3D dynamic and unique tissue that structurally adapts in response to mechanical stimuli. Comparative skeletal morphology is commonly utilized to infer ancient hominins' modes of locomotion; however, instances of remarkable gross similarity despite different modes of locomotion do occur. A common cited example is the similarity between the skeletal elements of bipedal human (Homo sapiens) hands/feet and quadrupedal black bear (Ursus americanus) front/hind paws. Through novel 3D Micro-CT and 2D histomorphology analysis, this thesis tests the hypothesis that a 3D microscopic analysis of biomechanically regulated cortical bone structures provides a more representative and accurate means to infer a species' mode of locomotion. Micro-CT data were collected at the mid-diaphysis of human (n=5) and bear (n=5) third metacarpal/metatarsal pairs and compared with independent and paired t-tests, Pearson correlation coefficients and Bland-Altman plots. Bone microarchitecture is quantifiable in 3D and accessible through non-destructive Micro-CT. Interspecies variation was present, however no significant cortical differences between elements of humans and bears was found. Histological inspection revealed further variation between and within species and element. A key limitation was sample size and further investigation of the relationship between mechanical loading and mode of locomotion is warranted.

We studied the expression of c-fos in medullary serotonergic neurons after a locomotor task on a treadmill in adult mice. We used a transgenically modified line in which serotonergic cells expressed enhanced yellow fluorescent protein (eYFP). We counted and plotted cells using Micro Bright Field Co. software. We determined the location of the serotonergic cells in this mouse line in the adult. We found an increase in the number of eYFP-positive cells expressing c-fos after a locomotor task in the raphe and PPR between bregma -6.8 and bregma -6.48 in the mouse (flanked rostrally by the seventh cranial nerve and caudally by the inferior olive). The percentage of eYFP-positive cells that expressed c-fos after the locomotor task in the raphe was 4%, whereas in the PPR the percentage was13.3%. Our results corroborate the observation that a specific group of serotonergic neurons located in the PPR are involved in locomotion.