Odor preference learning and memory modify GluA1 phosphorylation and GluA1 distribution in the neonate rat olfactory bulb: Testing the AMPA receptor hypothesis in an appetitive learning model

Abstract

An increase in synaptic AMPA receptors is hypothesized to mediate learning and memory. AMPA receptor increases have been reported in aversive learning models, although it is not clear if they are seen with memory maintenance. Here we examine AMPA receptor changes in a cAMP/PKA/CREB-dependent appetitive learning model: odor preference learning in the neonate rat. Rat pups were given a single pairing of peppermint and 2 mg/kg isoproterenol, which produces a 24-h, but not a 48-h, peppermint preference in the 7-d-old rat pup. GluA1 PKA-dependent phosphorylation peaked 10 min after the 10-min training trial and returned to baseline within 90 min. At 24 h, GluA1 subunits did not change overall but were significantly increased in synaptoneurosomes, consistent with increased membrane insertion. Immunohistochemistry revealed a significant increase in GluA1 subunits in olfactory bulb glomeruli, the targets of olfactory nerve axons. Glomerular increases were seen at 3 and 24 h after odor exposure in trained pups, but not in control pups. GluA1 increases were not seen as early as 10 min after training and were no longer observed 48 h after training when odor preference is no longer expressed behaviorally. Thus, the pattern of increased GluA1 membrane expression closely follows the memory timeline. Further, blocking GluA1 insertion using an interference peptide derived from the carboxyl tail of the GluA1 subunit inhibited 24 h odor preference memory providing causative support for our hypothesis. PKA-mediated GluA1 phosphorylation and later GluA1 insertion could, conjointly, provide increased AMPA function to support both short-term and long-term appetitive memory.

What a nostril knows: Olfactory nerve-evoked AMPA responses increase while NMDA responses decrease at 24-h post-training for lateralized odor preference memory in neonate rat

“…This result is consistent with the earlier biochemical demonstration of an increase in membraneassociated AMPA receptors in trained olfactory bulbs 24 h posttraining and with immunohistochemical evidence of increased staining density for AMPA receptor antibodies 24 h post-training in the glomerular layer, where these olfactory nerve-mitral connections occur (Cui et al 2011). While the physiological patterns are evaluated statistically on grouped data, it is of interest that each pair tested showed a difference in the same direction.…”

“…With the present training protocol, an odor preference for the trained odor is seen at 24 h, but not at 48 h. In the immunohistochemical data, the increase in glomerular AMPA receptor staining is not seen 48 h after the training, consistent with behavioral "forgetting" (Cui et al 2011). It will be of interest to examine AMPA responses electrophysiologically at a 48-h time point in a future study.…”

“…While the physiological patterns are evaluated statistically on grouped data, it is of interest that each pair tested showed a difference in the same direction. In contrast to the generalized increase in glomerular AMPA immunohistochemistry seen in the Cui et al (2011) study, the present electrophysiological data suggest the functional increase in AMPA current and concomitant decrease in NMDA current is restricted to the midlateral bulbar region implicated in early peppermint odor preference learning (Johnson and Leon 1996). Further investigation of the specificity of receptor insertion using combined immunohistochemical and electrophysiological approaches would be helpful in clarifying the localization of bulbar memory circuit changes.…”

“…This hypothesis has been supported by an increase in membrane AMPA receptors 24 h after training, as revealed in synaptoneurosome preparations from trained pups compared with controls and in increases in AMPA immunohistochemical staining densities at the same time point in the glomerular layer, where the olfactory nerve contacts mitral cell dendrites, in trained versus untrained olfactory bulbs (Cui et al 2011). AMPA receptor insertion in the membrane appears causally linked to odor-preference memory, since infusion of an interference peptide that prevents AMPA insertion also prevents memory expression at 24 h (Cui et al 2011). Others have reported that NMDA receptor contributions decrease developmentally in sensory systems, including the olfactory system, as measured at lateral olfactory tract synapses in the piriform cortex (Franks and Isaacson 2005).…”

Epac activation initiates associative odor preference memories in the rat pup

“…The olfactory bulbs were removed and frozen on dry ice and stored at 280˚C until used. Western Cold Spring Harbor Laboratory Press on May 9, 2018 -Published by learnmem.cshlp.org Downloaded from blots were examined to measure the phosphorylation of ERK (phosphorylated at Thr202/Tyr204 or ERK1/2, and total ERK1/ 2, Cell Signaling Technology) and followed protocols previously described (Cui et al 2011). …”