Organization of the command system in the lamprey brain that initiates locomotor behavior

Abstract only availableIn vertebrate animals, the muscle activity pattern for locomotor behavior is produced by central pattern generators (CPGs) in the spinal cord. In the brain, “command” systems, which have several levels, process information and, if appropriate, initiate locomotor behavior. The output neural elements of the command system, which are reticulospinal (RS) neurons, send neural processes to the spinal cord to activate the CPGs and initiate locomotor behavior. The lamprey, a lower vertebrate, has many advantages for studying the organization of command systems. Neurophysiological experiments indicate that several brain areas are part of the command system: rostrolateral rhombencephalon (RLR); ventromedial diencephalons (VMD); dorsolateral mesencephalon (DLM); and RS neurons (Paggett et al. 2004). Other experiments suggest the following organization for the command system: RLR VMD & DLM RS neurons à spinal CPGs In the present study, various lesions were made in the brain to interrupt some of the above pathways, and muscle activity (EMGs) was recorded soon after the lesions to test the behavioral capabilities of the animals. Also, for lesions that initially abolished locomotor behavior, EMG recordings were made at various recovery times to determine if axonal regeneration within the brain restored the lesioned pathways in the command system. First, lesions at the mesencephalon-rhombencephalon border, which disrupt the RLR VMD & DLM pathways, usually abolished locomotor activity that normally would be initiated by stimulation of the head. Two weeks after the above lesion, locomotor activity could once again be initiated by stimulation of the head. Second, lesions in the middle of the mesencephalon or at the diencephalons-mesenencephalon border, both of which disrupt the RLR VMD but not the RLR DLM pathways, did not abolish locomotor behavior. Results from the present study support the above model of the locomotor command system in the lamprey brain. Furthermore, the results demonstrate that axons severed by brain lesions could regenerate and restore the function of the command system.NSF-REU Biology & Biochemistr

Imaging reticulospinal neurons in the lamprey brainstem using calcium indicator

Abstract only availableImaging reticulospinal neurons in the lamprey brainstem using calcium indicator In the lamprey, a lower vertebrate, reticulospinal (RS) neurons in the brain are the output elements of the command system that activate spinal pattern generators and initiate swimming. In order to better understand the locomotor command system in the lamprey, it is necessary to determine the locations of neurons in the network, as well as their connectivity and patterns of activity. Calcium indicator dyes are an important technique for labeling and monitoring neuron activity. During impulse, calcium enters neurons and binds to the dye, increasing the fluorescence of the dye and creating an optical image that can be recorded and analyzed. In the present study, Calcium Green dextran amine was applied to the transected spinal cord at 20% body length (BL). After retrograde transport of the dye and labeling of RS neurons, the brain and spinal cord were removed and placed on a slide for viewing under a microscope equipped for fluorescence. Electrical stimulation of the spinal cord activated labeled RS neurons in the brain, resulting in a fluorescence increase that was recorded by an S-VHS video camera. The next step will be to image RS neuron activity during actual swimming movements. For this purpose, RS neurons will be labeled in a semi-intact preparation in which the brain and upper spinal cord are exposed and the lower half of the body is free to produce swimming movements. As a control experiment, the spinal cord was transected and Calcium Green applied at 60% BL. Semi-intact preparations were observed to produce swimming movements. Imaging of the isolated brain and rostral spinal cord showed RS neuron labeling and fluorescent changes similar to when tracer was applied at 20% BL. These results lay the groundwork for imaging brain neuron activity during actual swimming behavior.Life Sciences Undergraduate Research Opportunity Progra

Effects of axotomy on calcium influx in reticulospinal neurons of larval lamprey [abstract]

Abstract only availableThe lamprey is a prime example of the remarkable axonal regeneration that can occur in lower vertebrates. Previous studies showed that spinal cord transected lamprey recover normal locomotor behavior in about 8 weeks (McClellan, 1998). With increasing recovery time, increasing numbers of axons from injured reticulospinal (RS) neurons in the brain regenerate across the lesion site and for greater distances below the lesion. One factor that might affect axonal regeneration is the individual properties of the RS neurons. During electrical activity (action potentials) in these neurons, calcium influx occurs through voltage-gated and chemical-gated calcium channels. First, previous research demonstrated that in injured RS neurons from lamprey, action potentials are missing a component that is due to calcium influx and that is present in uninjured RS neurons (McClellan, 2003). Furthermore, it has been shown that when calcium channels and calcium influx are blocked in uninjured (normal) RS neurons, firing patterns are similar to these observed in injured RS neurons. Second, lamprey RS neurons in cell culture retract as a result of calcium influx (Ryan et al., 2004). Thus, preliminary results suggest that injured RS neurons may down regulate calcium channels to lower intracellular calcium and to allow axonal regeneration. The purpose of the project was to determine the factors that influence axonal regeneration and obtain evidence for the possible down regulation of calcium channels in injured RS neurons. A calcium indicator dye was loaded into RS neurons and the neurons were stimulated to produce electrical activity (action potentials) during which fluorescence images were captured. The calcium indicator dye allowed imaging of the levels of intracellular calcium and changes in fluorescence. However, a higher signal-to-noise ratio is needed before calcium levels can be compared in injured and uninjured larval lamprey RS neurons.Life Sciences Undergraduate Research Opportunity Progra

Axonal regeneration following spinal cord hemi-transection in larval lamprey

Abstract only availableIn higher vertebrates, including humans, axonal regeneration following spinal cord injury (SCI) is very limited and there is little behavioral recovery. In contrast, lower vertebrates, such as lamprey, fish, and certain amphibians, display robust axonal regeneration and dramatic behavioral recovery after a complete spinal cord transection. In the lamprey, we have examined the properties of left and right descending brain neurons at various recovery times following spinal cord hemi-transection (HT). However, it is not known if axonal regeneration following spinal HTs is similar to that following a complete spinal cord transection. For example, uninjured axons on one side of the cord might influence regeneration of injured axons on the opposite side. In the present project, animals received a HT of the right side of the upper spinal cord and were allowed to recovery for 1, 2, 4, 8, 12 and 16 weeks. After recovery, an anatomical tracer (HRP) was applied 10 mm below the HTs to retrogradely label descending brain neurons. For all cell groups containing descending brain neurons, there was a gradual increase in the numbers of injured neurons that regenerated their axons for at least 10 mm below the lesion with increasing recovery time. At the longer recovery times, the numbers of labeled descending brain neurons in certain cell groups were not significantly different than those in control animals, indicative of significant axonal regeneration. In other cell groups, regeneration had not restored the normal numbers of projections to the spinal cord. These results appear to be similar to those following complete spinal cord transections, in which descending neurons in different cell groups in the brain display different capacities for axonal regeneration. Therefore, the results of the present study suggest that the rate and extent of axonal regeneration is similar following spinal HTs and complete spinal transections.Missouri Academy at Northwest Missouri State Universit

Factors that affect the degree of axonal regeneration following spinal cord transection in larval lamprey

Abstract only availableIn all vertebrate animals, reticulospinal (RS) neurons in a locomotor “command” systems in the brain send neural processes to the spinal cord to activate “central pattern generators” (CPGs) and initiate locomotor behavior. Unlike higher vertebrates, such as birds and mammals, lower vertebrates such as lamprey can behaviorally recover following spinal cord injury because axons from brain neurons regenerate and reconnect with neurons in the spinal CPGs. Although the lamprey can behaviorally recover following spinal cord transections, most injured axons regenerate for relatively short distances below the lesion. Thus, axonal regeneration is incomplete, possibly because regenerating axons make synapses just below the lesion, and these synapses might provide factors that suppress further regeneration. We hypothesize that following spinal cord transection, the degree to which axons of RS neurons are stimulated to regenerate is determined, in part, by the numbers of synapses these neurons have made, either above or below the lesion. Preliminary results indicate that rostral spinal cord transections are a “strong” stimulus for regeneration, while caudal spinal cord transections are a relatively “weak” stimulus. The purpose of the present study was to determine the degree to which the above “strong” or “weak” axonal regeneration could initiate locomotor activity below the lesion. Spinal cord transections were made at 10% body length (BL, normalized distance from the head; “rostral” lesion) or 50% BL (“caudal” lesion) in larval lamprey. After various recovery times, muscle activity (EMGs) was recorded below each of the two types of lesions to determine the degree of recovery of locomotor activity. First, 2 weeks after rostral spinal cord transections, animals could produce weak swimming movements, and muscle activity was present just below the lesion. With increasing recovery times muscle activity could be recorded at progressively lower levels of the body. Second, 2 weeks after caudal spinal cord transections, muscle activity was present above the lesion, but did not appear just below the lesion until ~8 weeks after the lesion. The results indicate that following rostral (caudal) spinal cord lesions, axonal regeneration from RS neurons is robust (weak), and locomotor behavior recovers relatively quickly (slowly). These results support our hypothesis and suggest that factors associated with the number of synapses are involved in controlling regeneration. Identification of these factors might be used to modulate axonal regeneration following spinal cord injury, especially in animals where regeneration is limited, such as humans.NSF-REU Biology & Biochemistr

Organization and repair of the trigeminal system in the lamprey using fluorescent double labeling [abstract]

Abstract only availableFaculty Mentor: Andrew McClellan, Biological ScienceIn the CNS, many sensory and motor systems are topologically organized relative to various body structures.  For example, in humans, sensory inputs from the lower, middle, and upper parts of the body are received by the anterior, middle, and posterior somatosensory cortex, respectively.  Following injury in the CNS of higher vertebrates, such as birds and mammals, there is very little regeneration and recovery of function.  In contrast, in lower vertebrates, including lamprey, fish, and certain amphibians, substantial axonal regeneration occurs following CNS injuries, and there is virtually complete recovery of functions.  However, it is not known whether axonal regeneration restores the topological organization that may have existed prior to injury.  The trigeminal system is responsible for transmitting sensory and motor information from the head via axons in the trigeminal cranial nerve.  In the lamprey following injury of the trigeminal nerve, sensory and motor axons regenerate.  The purpose of the present study was to determine whether the trigeminal system of normal lamprey is topologically organized and whether regeneration of axons in injured trigeminal nerve restores this organization.  In normal larval lamprey, Alexa 488 dextran amine (Alexa) and Texas red dextran amine (TRDA), two different anatomical fluorescent tracers, were applied to the medial and lateral parts of the head, respectively.  This resulted in clear labeling of the medial and lateral parts of the trigeminal system in the brain with Alexa and TRDA, respectively.  Thus, in normal lamprey, the trigeminal system appears to be topologically organized.  If following injury of the trigeminal nerve, axonal regeneration restores this topological organization, this will indicate that regeneration in the lamprey is relatively precise and possibly controlled by specific guidance factors.  Identification of these guidance factors would greatly improve our understanding of the mechanisms that regulate axonal regeneration following CNS injury in vertebrate animals, including humans.

Test of the half-center model for locomotor activity in adult lamprey spinal cord [abstract]

Abstract only availableRhythmic motor behaviors, such as locomotion, chewing, scratching, copulation, and communication, are critical for survival. In all animals, rhythmic motor activity is produced by central patterns generators (CPGs) which consist of neuronal modules that are coupled by a coordinating system. For example, in a cat separate spinal modules control the movements of each limb, and the coordinating system can couple the modules in different ways to produce different gaits (walk, trot, gallop). Each module can be divided into oscillators that usually are connected by reciprocal inhibition (i.e. "half-center" model) to produce alternating motor patterns (e.g. flexion « extension). These oscillators generally are assumed to be autonomous and able to function without the reciprocal connections. In the lamprey, locomotion (swimming) is produced by pairs of oscillators that are distributed along the spinal cord and connected by left-right reciprocal inhibition (Hagevik and McClellan, 1994). In adult lamprey, we tested the half-center model by investigating whether the phasing of left-right burst activity could be correctly maintained in the absence of left-right reciprocal coupling. Adult lamprey received a longitudinal midline lesion in the rostral spinal cord (10% à 35% body length). After the midline lesion, the animals were able to swim, and the appropriate phasing of left and right muscle burst activity was present in both caudal and rostral parts of the body. After a spinal transection was made at 35% body length to isolated the rostral left and right halves of the spinal cord from intact cord, locomotor-like burst activity was no longer present in the rostral spinal cord. We obtained similar results in larval lamprey (Jackson et al., 2005). Thus, in lamprey, the data do not support the "half-center" model because left and right spinal cord oscillators are not autonomous but appear to require left-right reciprocal coupling to function properly

Recovery of locomotor function following spinal cord hemi-transections in larval lamprey [abstract]

Abstract only availableIn vertebrates, reticulospinal (RS) neurons in the brain activate spinal motor networks to initiate locomotor behavior. Following spinal cord injury (SCI), RS neurons no longer communicate with the spinal cord, and animals are paralyzed below the lesion. In higher vertebrates, such as birds and mammals, the axons of RS neurons do not regenerate, and paralysis usually is permanent. In contrast, spinal cord transected lower vertebrates such as the lamprey display robust axonal regeneration and recovery of function within a few weeks. In our previous studies we showed that following spinal cord hemi-transections (HTs) in larval lamprey, injured RS neurons undergo a number of substantial changes in electrical properties and expression of ion channels which recover within several weeks. The purpose of the present study is to determine the rate of behavioral recovery following HTs and ultimately to correlate axonal regeneration of injured RS neurons with recovery of normal properties of these neurons. In the present study, animals received HTs on the right side of the rostral spinal cord and recovered for 1d - 6 wks. At early recovery times (1 day), animals swam with a spiraling movement and turned toward the intact side of the spinal cord, but the pattern of muscle activity was relatively normal. Swimming movements began to recover within the first week, and by the fourth week animals swam normally with little or no spiraling. In the future, anatomical experiments will be conducted to determine if recovery of swimming following HTs is due to regeneration of injured axons through the HT or to functional compensation of intact pathways on the opposite side of the spinal cord. This information will be important in determining what factors alter the properties of RS neurons following SCI and if these altered properties are important for successful axonal regeneration

Linear Reduced Order Model Predictive Control

Model predictive controllers leverage system dynamics models to solve constrained optimal control problems. However, computational requirements for real-time control have limited their use to systems with low-dimensional models. Nevertheless many systems naturally produce high-dimensional models, such as those modeled by partial differential equations that when discretized can result in models with thousands to millions of dimensions. In such cases the use of reduced order models (ROMs) can significantly reduce computational requirements, but model approximation error must be considered to guarantee controller performance. In this work a reduced order model predictive control (ROMPC) scheme is proposed to solve robust, output feedback, constrained optimal control problems for high-dimensional linear systems. Computational efficiency is obtained by leveraging ROMs obtained via projection-based techniques, and guarantees on robust constraint satisfaction and stability are provided. Performance of the approach is demonstrated in simulation for several examples, including an aircraft control problem leveraging an inviscid computational fluid dynamics model with dimension 998,930.Comment: This work has been submitted to the IEEE Transactions on Automatic Control for possible publication. Copyright may be transferred without notice, after which this version may no longer be accessibl