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

Abstract

Increased AMPA signaling is proposed to mediate long-term memory. Rat neonates acquire odor preferences in a single olfactory bulb if one nostril is occluded at training. Memory testing here confirmed that only trained bulbs support increased odor preference at 24 h. Olfactory nerve field potentials were tested at 24 h in slices from trained and untrained bulbs. A larger AMPA component and a smaller NMDA component characterized responses in the bulb receiving odor preference training. Field potential changes were not seen in a bulbar region separate from the lateral odor-encoding area. These results support models in which memory is mediated by increased olfactory nerve-mitral cell AMPA signaling, and memory stability is promoted by decreased NMDA-mediated signaling.

Lateralized Odor Preference Training in Rat Pups Reveals an Enhanced Network Response in Anterior Piriform Cortex to Olfactory Input That Parallels Extended Memory

“…A single naris occlusion protocol was used to test whether lateralized learning that is confined to the spared hemisphere (Yuan and Harley, 2012) can be induced by multitrial training. O/S ϩ and O/S Ϫ multiday behavioral training was performed in pups from PD3-PD6 as described above.…”

“…Pups were anesthetized using halothane and decapitated. Sagittal PC slices (400 m) were cut on a vibratome into a cutting solution (in mM: 83 NaCl, 2.5 KCl, 3.3 MgSO 4 , 1 NaH 2 PO 4 , 26.2 NaHCO 3 , 22 glucose, 72 sucrose, 0.5 CaCl 2 ) equilibrated with 95% O 2 /5% CO 2 (Apicella et al, 2010;Morrison et al, 2013), then incubated in the same solution at 34°C for 30 min before being left at room temperature. Slices were transferred to an open bath recording chamber continuously perfused with artificial CSF (aCSF; in mM: 110 NaCl, 2.5 KCl, 1.3 MgSO 4 , 1 NaH 2 PO 4 , 26.2 NaHCO 3 , 22 glucose, 2.5 CaCl 2 ) heated to 30.0 -32.0°C.…”

“…Action potentials in dye-loaded cells generate somatic calcium transients that identify cells recruited by LOT stimulation (Apicella et al, 2010). Activity maps of recruited cells were created by averaging the peak ⌬F/F images collected from several consecutive stimulus trials (see Fig.…”

“…Efforts to assess sustained increases in the AMPA receptor (AMPAR)-mediated excitation predicted to support cortical memory are typically not successful, although initial increases have been documented (Whitlock et al, 2006;Matsuo et al, 2008). It is widely assumed that increases in AMPAR strength are fundamental underpinnings of memory (Malenka and Bear, 2004).…”

“…The preference memory duration is readily varied in this model. A single 10 min trial pairing odor and maternal care stimuli in the first week of life produces an odor preference at 24 h that is not seen at 48 h. Manipulations that extend learning-associated intracellular signaling in the olfactory bulb (Christie-Fougere et al, 2009;McLean et al, 2009) or that increase the frequency of odor and reward pairings (Woo and Leon, 1987) produce memories of varying durations, including robust life-long memory (Fillion and Blass, 1986). We therefore ask whether the previously observed increase in AMPAR responses in the aPC following a single training trial would disappear at 48 h and whether extending memory using multiple training trials would prolong the AMPAR-mediated enhanced fEPSP to 48 h.…”