Therapeutic hypothermia (TH) protocols consist of mild lowering of core body temperature (32-34?C) and have proven effective in increasing survival and functional outcome following multiple injuries including stroke. Current TH protocols involve actively cooling patients by a variety of methods including cold blankets and ice baths which is slow, uncomfortable, and triggers a shiver response. This shiver response must be counteracted (such as by muscle paralysis) to allow body cooling and also to avoid clinical complications that accompany prolonged shivering such as increased oxygen consumption and hyperglycemia. The agents currently used to prevent the shiver response produce respiratory depression and typically require patient ventilation. The combination of difficult implementation, slow achievement of target temperature, and clinical complications associated with forced cooling limits the applicability and potential effectiveness of traditional TH. In the current proposal, we will investigate pharmacological hypothermia (PH) through targeting the body's warm and cold receptors (thermoreceptors). These thermoreceptors are believed to include temperature sensitive ion channels of the transient receptor potential (TRP) channel family. By activating warm receptors (TRPV1 channels) alone or in combination with inhibiting cold receptors (TRPM8 channels), we will lower the body's temperature set point and employ the body's existing thermoregulatory pathways to promote cooling.
Aim 1 is a """"""""proof of principle"""""""" experiment in which we will demonstrate that PH is neuroprotective in a mouse model of focal cerebral ischemia/reperfusion. Multiple physiologic variables (such as core temperature, blood pressure, and heart rate) will be collected by chronic catheterization or telemetry. Neuroprotection will be measured by histological means and behavioral testing out to 28 days recovery.
Aim 2 will determine the role of TRPV1 and TRPM8 channels in setting the threshold of the shiver response during hypothermia. Physiologic variables will be collected as above in addition to measurements of shiver threshold by electromyography (EMG). Hypothermia shows great promise for a number of brain and nerve injuries. However, new methods for producing hypothermia are needed that can 1) increase the availability of the technique, 2) speed the achievement of therapeutic temperature, and 3) produce less stress on the body. If successful, our proposed method of lowering core temperature by targeting thermoreceptors could significantly increase the availability of TH to non-ventilated conscious patients and patients in environments where traditional cooling is not possible (in the field, small medical clinics, military combat setting, etc.). In addition, we expect that this method of cooling will produce less physiologic stress compared with traditional cooling protocols.
Mild hypothermia (lowering of body temperature by 3 to 4?C) shows great promise for a number of brain and nerve injuries. However, new methods for producing hypothermia are needed that can 1) increase the availability of this technique, 2) speed the achievement of therapeutic temperature, and 3) produce less stress on the body. We propose new methods for lowering core body temperature by targeting the temperature- sensing nerves of the body which could significantly increase the availability of mild hypothermia to conscious patients and patients in environments where traditional cooling is not possible.
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