Neuromodulatory Effects of Delta Opioid Receptors on Accessory Olfactory Bulb Processing

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The opioids are a diverse set of neurotransmitters that potently modulate synaptic processing as a function of behavioral state. While most studies of opioids have investigated their synaptic actions in the context of analgesia and addiction, few have examined their role in sensory processing. This potential role is especially compelling in the olfactory system, where it was recently identified that there is a robust and unexpected expression of opioid receptors. This suggests that even the earliest steps of sensory olfactory processing may be powerfully modulated by opioidergic inputs. To investigate the synaptic actions of opioids in olfactory processing, I obtained whole cell recordings from mitral cells of the accessory olfactory bulb (AOB) – a brain region critical for detecting and discriminating non-volatile ligands derived from conspecifics. Previous research suggested that opioidergic agonists would decrease recurrent inhibitory activity. Contrary to these findings, I observed a marked effect of DADLE (a delta-opioid receptor agonist) on recurrent excitatory activity when inhibitory input was blocked. Analysis of the intrinsic and passive properties of the mitral cells demonstrated that this increase in recurrent excitation was the result of a synaptic change and not due to a global alteration in cellular excitability or passive properties. Furthermore, examination of spontaneous activity demonstrated a dramatic increase in the frequency of excitatory postsynaptic potentials with DADLE application. Taken together, these results demonstrate that opioids powerfully modulate recurrent excitation in the AOB through a presynaptic mechanism. These findings represent, to the best of my knowledge, a novel mechanism for opioidergic modulation.

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Restricted: Archival Copy [No Access]

First Advisor

Castro, Jason

Date of Graduation


Degree Name

Bachelor of Science

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