Development of a Device for Neurochemical Sample Collection from Freely Moving Monkeys

1. Development of a Device for Neurochemical Sample Collection from Freely Moving Monkeys Cole Drifka, Lauren Eichaker, Ben Fleming, Adam Pala & Sarah Springborn Client: Dr. Ei Terasawa, Dept. of Pediatrics Advisor: Professor Brenda Ogle, Dept. of Biomedical Engineering Design Criteria Testing Abstract • To construct a device that: • Protects the microdrive unit to free the monkey from chairing • Allows for easy researcher implementation • Is safe for and protected from the monkey • Weighs less than 0.5 kg • Is detachable for gas sterilization • Is made of a material able to withstand at least 100 N of force before failure • Complies with USDA regulations and NIH guidelines • Following the completion of the prototype, quantitative testing was carried out to ensure stability of the prototype on a monkey mannequin prior to eventual installment on a live candidate. Using a manual spring scale, the following results were obtained: • Over 20 N of force was applied vertically to a force scale attached to the interior of the helmet, simulating a monkey’s attempt to pry the helmet off (the head of the monkey was held down by a team member).  • The helmet sustained forces of up to 12 N in the side-to-side and front-to-back directions before the interior of the polystyrene shell contacted the microdrive unit. • The prototype consistently stayed on the mannequin, and the amount of force the team applied was limited by the signs of decapitation of the mannequin from the base. The team last semester developed and constructed a device to provide protection for a microdrive unit, an apparatus which is used in microdialysis experiments conducted on non-human primates. This would allow the experiments to be conducted without restraining the monkeys in a chair, providing them with a more comfortable and realistic experimental setting. The goal of the project this semester was to improve on a previous design. With a new design, our team has significantly reduced the overall weight of the device. Quantitative testing has shown that the prototype is capable of withstanding forces that could be generated by an experimental monkey. In the near future, live animal testing will be performed to identify any areas of improvement. Final Design • Our final design improves upon two previous semesters of development. Last semester, a prototype composed of three interlocking aluminum pieces and a silicone rubber interior was constructed. However, observations during live testing made it obvious that the device needed to be made lighter, designed to more evenly distribute weight, minimized in regards to height, and designed to be better secured on the monkey’s head. Our current design consists of four main components: a helmet shell, a silicone rubber interior, an air bladder, and a chin strap. • The Helmet • The helmet provides protection for the microdrive unit; its conical shape provides for even weight distribution on top of the monkey’s head. • It is made of high-impact polystyrene and was molded using a process known as thermoforming. • The helmet is one piece made of two halves bonded together and slides down over the monkey’s head. • The Silicone Rubber Interior • The silicone rubber protects the microdrive unit, insures that the helmet positions correctly on top of the monkey’s head, and provides stability to the design. • It is composed of two halves and is molded precisely to form an interface between the helmet shell and the microdrive unit. • The Air Bladder • An air bladder cushions the monkey’s head, prevents the helmet from being pulled off due to its position beneath the occipital lobe and gives the design a limited amount of adjustability through inflation and deflation. • Custom made from the inner tube of a bicycle tire, the air bladder is recessed into the helmet to deter tampering by the monkey. • The Chin Strap • The chin strap provides additional security to the helmet while at the same time providing comfort to the monkey. • It is comprised of a watch strap and zip ties attached to the base of the helmet via two metal loops. Background Future Work • Client’s Research • Our client is interested in understanding how growth and development are controlled in humans. One particular focus is on the role of the brain in triggering puberty. Currently, this research is being carried out on Rhesus monkeys, due to their anatomical and physiological closeness to humans. • Microdialysis & Experimental Procedure • Microdialysis is used to study release of substances from the hypothalamus of Rhesus monkeys • Cranial pedestal (head cap) is first implanted into their skulls and secured using dental cement • Microdrive unit is attached and monkey is transferred to a primate chair that restricts its movement • A pump is used to perfuse cerebrospinal fluid through the microdialysis probe and exchange of substances occurs at the semi-permeable membrane • The substances are collected by a fraction collector and immediately frozen for storage • Monkey is confined to the chair throughout the 12-hour experiment • Following the results of live testing in the future, areas of improvement may become apparent. As of now, work still needs to be done so the device performs optimally. • The current plastic prototype lacks any attention to the metal tether that attaches to the top of the helmet.  • One possibility to alleviate a majority of the weight felt by the monkey by this component is to incorporate a dual swivel system into the design. • Also, implementing a swivel joint system to attach the tether to a pulley system would provide greater freedom for the monkey to turn its head and body. • A custom air bladder that allows uniform inflation could be constructed. • Once the initial prototype has been completed and tested, the client would like to consider the possibility of producing more helmets of variable sizes.  • This involves making molds of various sizes as determined by a biometric analysis but utilizing our instated concept. • After implementing the changes, further testing will be carried out to ensure that the prototype satisfies all design requirements. Figure 3: Silicone rubber interface on monkey mannequin. Figure 4: Complete prototype implemented on monkey mannequin. Figure 7: Quantitative testing for helmet displacement due to lateral forces. Figure 8: Counter weight system and cage. Figure 1: Experimental setup for microdialysis. Figure 2: Rhesus monkey in a primate chair. Motivation References • In our client’s research, the current procedure requires restraining the monkeys in chairs for up to 12 hours while samples are collected. This situation is less than ideal since the monkeys are subjected to discomfort due to the restricted movement and long period of chairing. The data collected might also not be representative of a monkey in its natural environment, since it is confined to a chair. Our client wants to allow the monkeys to be free from chairing to: • Alleviate the discomfort experienced by the monkeys • Better simulate the monkey’s natural environment • Allow the experiments to be conducted without the 12-hour time limit • There are currently no products in the market that specifically address this issue, so a suitable device must be developed and constructed. Frost, S. I., Keen, K. L., Levine, J. E., and Terasawa, E. 2008. Microdialysis methods for in vivo neuropeptide measurement in the Stalk-median eminence in the Rhesus monkey. J Neurosci Methods. 168 (1): 26-34. Müller, M. 2002. Science, medicine, and the future: Microdialysis. BMJ. 324: 588-91. Terasawa, E. 2006. Postnatal remodeling of gonadotropin-releasing hormone I neurons: toward understanding the mechanism of the onset of puberty. Endocrinology. 147 (8): 3650-51. Terasawa, E. 2005. Role of GABA in the mechanism of the onset of puberty in non-human primates. Int Rev Neurobiol. 71: 113-29 Ekstrøm, P. O. 2006. Microdialysis [Online] www.radium.no/srg/?k=srg/Microdialysis&aid=5401&submenu=5/ The EAP/Human Armwrestling Match. 2008. [Online] ndeaa.jpl.nasa.gov/nasa-nde/lommas/eap/EAP-armwerestling.htm The Mary T. and Frank L. Hoffman Family Foundation. 2008. S. A. E. N. [Online] all-creatures.org/saen/res-fr.html Wikipedia. 2007. Microdialysis [Online] en.wikipedia.org/wiki/Microdialysis Figure 5: Components of the previous design. Inclusive total mass: 456.5 g. Figure 6: One-piece final design. Inclusive total mass: 265.9 g.