The ability of humans and animals to localize the source of a sound in a complex acoustic environment facilitates communication and survival. Two cues are used for sound localization at horizontal planes, interaural time and level differences (ITD and ILD), which are analyzed by distinct neural circuits in the brainstem. Here, we review the studies on metabotropic glutamate receptor (mGluR)-mediated neuromodulation of both intrinsic and synaptic properties of brainstem neurons in these circuits. Both mammalian and avian animal models have been used, with each having their advantages that are not present in the other. For the mammalian model, we discuss mGluR neuromodulation in the ILD circuit, with an emphasis on the recent discovery of differential modulation of synaptic transmission of different transmitter release modes. For the avian model, we focus on reviewing mGluR neuromodulation in the ITD pathway, with an emphasis on tonotopic distribution and synaptic plasticity of mGluR modulation in coincidence detector neurons. Future works are proposed to further investigate the functions and mechanisms of mGluRs in the sound localization circuits.

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PURPOSE: The purpose of this study was to evaluate the effectiveness of intrathecal morphine following selective dorsal rhizotomy in pediatric patients previously diagnosed with cerebral palsy. METHODS: This was a retrospective, cohort analysis over the course of four years. The analysis consisted of a treatment group which received intrathecal morphine (5 mcg/kg) injection and a control group that did not receive the injection prior to dural closure. All patients underwent multilevel laminectomies for selective dorsal rhizotomy at Akron Children’s Hospital. The effectiveness of the treatment was measured by total dose of hydromorphone administered on patient-controlled analgesia (PCA), number of days on oral narcotics, and cumulative dose of oral narcotic. RESULTS: Of the analyzed 15 pediatric patients, seven patients received intrathecal morphine injection while the other eight did not receive the treatment prior to dural closure. There was a difference of 1135 mcg in total PCA dose between the study group (3243 mcg) and the control group (4378 mcg). The total PCA dose based on weight was lower in the study group (163 mcg/kg) than in the control group (171 mcg/kg). CONCLUSION: Based on these findings, the administration of intrathecal morphine clinically reduces the opiate need in the first 96 hours post-operatively.