Hsp22 has been implicated in stress tolerance and longevity in various organisms though its role in Drosophila melanogaster larval thermal tolerance has not yet been investigated. I undertook this project to determine if over-expression of hsp22 in either muscle or motor neurons could alter locomotor ability at high temperature in third instar larvae of D. melanogaster. A combination of the UAS-gal4 and tet-On promoter systems was used to over-express transgenic hsp22 in the larvae. A β-galactosidase assay was used to determine the level of gene expression following administration of different amounts of tetracycline. A concentration of 100 μg/ml of tetracycline was found to elicit appreciably higher expression of the reporter gene than 0 and 0.1 μg/ml of tetracycline. Locomotor ability of larvae was assessed at a temperature of approximately 400C by measuring the time to movement failure (TMF). Larvae that were fed 100 μg/ml of tetracycline showed a significant decline in the TMF, which could be attributed to the presence of tetracycline at a concentration of 100 μg/ml. Possible reasons behind the lack of a noticeable effect of hsp22 over-expression on the TMF are discussed. The detrimental effect of tetracycline could be attributed to the decline in mitochondrial translation or a decline in the population of endogenous bacteria, which are known to exert positive effects on the development and function of Drosophila larvae. / Thesis (Master, Biology) -- Queen's University, 2007-10-01 14:24:15.801

No description available.

The ability to move is essential to an animal’s ability to interact with and respond to its changing environment. The nematode Caenorhabditis elegans is a commonly used organism in the study of the genetic and neural bases of behaviours, yet the mechanistic explanation for its ability to move in a smooth sinusoidal wave remains elusive. Here, I present studies of an uncharacterized gene, sto-6, encoding a stomatin protein that regulates C. elegans motor behaviour. I show that this gene plays a role in two unexplained and fundamental processes to C. elegans locomotion: wave initiation and wave propagation. Furthermore, I examine the genetic interaction between sto-6 and an innexin gene unc-7, providing support for the hypothesis that stomatins regulate gap junction proteins in C. elegans. Together, these studies push forward our understanding of the mechanistic basis of C. elegans locomotion, and open up avenues of further inquiry.

The ability to move is essential to an animal’s ability to interact with and respond to its changing environment. The nematode Caenorhabditis elegans is a commonly used organism in the study of the genetic and neural bases of behaviours, yet the mechanistic explanation for its ability to move in a smooth sinusoidal wave remains elusive. Here, I present studies of an uncharacterized gene, sto-6, encoding a stomatin protein that regulates C. elegans motor behaviour. I show that this gene plays a role in two unexplained and fundamental processes to C. elegans locomotion: wave initiation and wave propagation. Furthermore, I examine the genetic interaction between sto-6 and an innexin gene unc-7, providing support for the hypothesis that stomatins regulate gap junction proteins in C. elegans. Together, these studies push forward our understanding of the mechanistic basis of C. elegans locomotion, and open up avenues of further inquiry.

No description available.

No description available.

Nerve cells are organized into complex networks that comprise the building blocks of our nervous system. Neurons communicate by transmitting messenger molecules released from synaptic vesicles. Alterations in neuronal circuitry and synaptic signaling contribute to a wide range of neurological conditions, often with consequences for movement. Intrinsic neuronal networks in the spinal cord serve to coordinate vital rhythmic motor functions. In spite of extensive efforts to address the organization of these neural circuits, much remains to be revealed regarding the identity and function of specific interneuron cell types and how neuromodulation tune network activity. In this thesis, two novel genes initially identified as markers for spinal neuronal populations were investigated: Slc10a4 and Dmrt3. The orphan transporter SLC10A4 was found to be expressed on synaptic vesicles of the cholinergic system, including motor neurons, as well as in the monoaminergic system, including dopaminergic, serotonergic and noradrenergic nuclei. Thus, it constitutes a novel molecular denominator shared by these classic neuromodulatory systems. SLC10A4 was found to influence vesicular transport of dopamine and affect neuronal release and reuptake efficiency in the striatum. Mice lacking Slc10a4 displayed impaired monoamine homeostasis and were hypersensitive to the drugs amphetamine and tranylcypromine. These findings demonstrate that SLC10A4 is capable of modulating the modulatory systems of the brain with potential clinical relevance for neurological and mental disorders. The transcription factor encoded by Dmrt3 was found to be expressed in a population of inhibitory commissural interneurons originating from the dorsal interneuron 6 (dI6) domain in the spinal cord. In parallel, a genome-wide association study revealed that a non-sense mutation in horse DMRT3 is permissive for the ability to perform pace among other alternate gaits. Further analysis of Dmrt3 null mutant mice showed that Dmrt3 has a central role for spinal neuronal network development with consequences for locomotor behavior. The dI6 class has been suggested to take part in motor circuits but remains one of the least studied classes due to lack of molecular markers. To further investigate the Dmrt3-derived neurons, and the dI6 population in general, a Dmrt3Cre mouse line was generated which allowed for characterization on the molecular, cellular and  behavioral level. It was found that Dmrt3 neurons synapse onto motor neurons, receive extensive synaptic inputs from various neuronal sources and are rhythmically active during fictive locomotion. Furthermore, silencing of Dmrt3 neurons in Dmrt3Cre;Viaatlx/lx mice led to impaired motor coordination and alterations in gait, together demonstrating the importance of this neuronal population in the control of movement.

Evidence suggests that a flexible, task-dependent neuronal coupling of the upper and lower limbs exists, and this allows for coordinated rhythmic movement (e.g., locomotion). To further understand this coupling, muscle activity and reflex patterns can be examined by stimulating peripheral nerves during various tasks. In particular, cutaneous reflexes demonstrate task- and phase-dependent modulation, making them highly sensitive probes into neural activity during rhythmic movement. The purpose of this research was to use reflex modulation to probe the neuronal coupling between the arms and legs. This was done using a cycling paradigm that allowed for the separation of arm and leg movement, which is difficult to do in most forms of locomotion (i.e., walking). Participants (N=14) performed three cycling tasks: 1)arm cycling with stationary legs (ARM); 2)leg cycling with stationary arms (LEG); and 3)combined arm and leg cycling (ARM&LEG). The relative contributions from the arms and legs to reflex modulation in the legs were then determined throughout the movement cycle. It was hypothesized that the individual contributions from arm and leg movement to reflex amplitudes in the legs would summate during the combined arm and leg task. This hypothesis was tested explicitly by comparing the reflex amplitudes expressed during the combined arm and leg task to the algebraic summation of the reflex amplitudes expressed during the arm cycling and leg cycling tasks alone. Static trials were also collected at 4 positions within each task. Tasks were performed under two different cycling conditions: 1) Focused tibialis anterior (TA) contraction (FCC) (N=14); and 2) normal cycling (NC) (n=8). During all trials, stimulation was delivered pseudorandomly throughout the movement cycle to the superficial peroneal nerve at the ankle. EMG was recorded bilaterally from muscles in the arms and legs, and kinematic data were obtained from the elbow and knee joints. Results focused on the middle latency reflex amplitudes in TA (ipsilateral to the site of stimulation) during the FCC condition because the focused contraction did not significantly alter EMG or reflex activity in the other leg muscles studied. This also allowed for comparisons among tasks at comparable EMG levels. The main finding from this study was that reflex amplitudes expressed during the ARM&LEG task agreed with the predicted algebraic summation of reflex amplitudes expressed during the ARM and LEG tasks separately. Examination of the relative contributions from the arms and legs to the reflexes expressed during the combined task revealed that across all movement phases the legs accounted for 33% (p < .05) of the variance observed during the ARM&LEG task, while the arms accounted for an additional 5% (p < .05). The relative contributions from the arms and legs were also found to be phase dependent. That is, the relative contribution from the arms was dominant during the power phase of leg cycling while the leg contribution was dominant during the recovery phase. More specifically, the greatest contribution from the arms accounted for 57% of the variance in the ARM&LEG task when the leg was at 11 o'clock (p < .05) and the greatest contribution from the legs was 71% of the variance accounted for when the legs were at 9 o'clock (p < .05). Additionally, characteristic patterns of reflex amplitude modulation (i.e., phase- and task-dependent modulation) were observed during most of the cycling tasks. In conclusion, these findings suggest evidence for a neuronal coupling between the rhythm generators responsible for arm and leg movement which is functionally gated throughout the movement cycle of a combined arm and leg task.

Rhythmic locomotor activity involving the arms or the legs results in task and phase specific Hoffmann (H)-reflex modulation between the two arms or between the two legs. As well, specific ipsilateral and contralateral movement effects are observed. Recently it has been found that there is also interlimb (between arms and legs) task modulation of the H-reflex, using a rhythmic arm cycling paradigm. That is, the stationary Soleus H-reflex amplitude during arm cycling was attenuated when compared to a static condition (Frigon et al. 2004). The specific parameters of the arm cycling movement which may contribute to this attenuation however are unknown. The purpose of this research was to examine whether the interlimb Soleus H-reflex suppression is specific to: the phase of the arm movement; the movement of both arms; arm excursion; and, rate of arm cycling. Participants sat in a custom designed chair to prevent leg and trunk movement and performed bilateral arm cycling at frequencies of 1 and 2 Hz and with short and long crank lengths (to alter arm range of motion; ROM). As well. ipsilateral (relative to leg stimulated) and contralateral single arm cycling were performed at 1Hz with a long crank length. The Tibial nerve at the popliteal fossa was stimulated psuedorandomly at four phases of the arm cycle and changes in the Soleus H-reflex were recorded while maintaining a small, but stable motor (M)-wave for all trials. EMG was recorded from the Soleus, Tibialis Anterior. Vastus Lateralis and the Anterior Deltoid muscles. Peak to peak amplitudes of the H-reflex from each participant were determined off line and normalized to the M-max determined from individual M-H recruitment curves. Results indicate comparable suppressive effects in all phases of the arm movement, and with bilateral or unilateral cycling. The large ROM and the 2 Hz frequency of movement resulted in a stronger inhibition than with the small ROM and the 1 Hz arm cycling. This suggests that neural processes associated with generating both the rhythmic arm cycling pattern and the peripheral feedback from the arms, have an effect on the H-reflex modulation in the legs. We conclude that a general, rather than a specific, signal related to rhythmic arm muscle activity mediates the suppression of Soleus H-reflex during arm cycling.

In common with animal species, evidence in humans suggests that similar neural mechanisms (e.g. locomotor central pattern generator (CPG)) regulate rhythmic movements in both arm and leg and that interlimb neural connections coordinate movement between upper and lower limbs ; however, by comparison the evidence in humans is limited. This thesis focused upon exploring the neural control of rhythmic arm cycling and the influence of the neural control of arm cycling on the neural circuits controlling the legs. Specifically, the effect of five different arm cycling paradigms on EMG and reflex responses in arm and leg muscles were explored. First, the pattern of muscle activity and cutaneous reflex modulation evoked with electrical stimulation to the superficial radial (SR) nerve were evaluated during forward and backward arm cycling. Irrespective of the cycling direction, background electromyographic (bEMG) and cutaneous reflex patterns were similarly modulated suggesting similar neural control mechanisms for both forward and backward cycling. These bEMG and reflex findings provide further evidence of contributions from CPG activity to the neural regulation of rhythmic arm movement. Second, bEMG and cutaneous reflex (SR nerve) modulation were evaluated during three dissimilar bilateral rhythmic arm cycling tasks created by unilaterally manipulating crank length (CL). The neural regulation of arm cycling was shown to be insensitive to asymmetrical changes in arm crank length suggesting that the neural control was equivalent across the three dissimilar rhythmic arm cycling tasks and that differences in peripherally generated inputs between the dissimilar rhythmic tasks had limited effect on the neural control. Third, the neural control of arm movements was evaluated between those with unstable shoulders and control participants. The alterations of bEMG and the cutaneous reflex patterns suggest that the neural control is compromised in those with shoulder instabilities during rhythmic arm movement. Fourth, inhibition of the soleus H-reflex in stationary legs induced by rhythmic arm cycling was shown to be graded with arm cycling frequency. A minimum threshold arm cycling frequency of .8Hz was required to produce a significant interlimb effect. Fifth, the degree of the soleus H-reflex suppression induced by arm cycling was independent of afferent feedback associated with arm cycling at different crank loads. In combination the latter two studies suggest that central motor commands related to the frequency of arm cycling is the major signal responsible for the soleus H-reflex suppression in stationary legs, while afferent feedback related to upper limb loading during arm cycling is not. Collectively, the data contained in this thesis contribute to the evidence suggesting that CPG activity contributes to neural regulation of rhythmic arm movement, alterations in sensory feedback associated with arm cycling have limited influence on the observed reflex modulation and that the neural control can be disrupted in the presence of prolonged orthopaedic injury. Taken together with our previous findings, the current results also suggests that central motor command (e.g. CPGs) for rhythm generation of the rhythmic arm movement is the primary source of the signal responsible for the observed interlimb neural communication.