pCREB in the Neonate Rat Olfactory Bulb Is Selectively and Transiently Increased by Odor Preference–Conditioned Training

Abstract

Early olfactory preference learning in rat pups occurs when novel odors are paired with tactile stimulation, for example stroking. cAMP-triggered phosphorylation of cAMP response element binding protein (pCREB) has been implicated as a mediator of learning and memory changes in various animals (Frank and Greenberg 1994). In the present study we investigate whether CREB is phosphorylated in response to conditioned olfactory training as might be predicted given the proposed role of the phosphorylated protein in learning.On postnatal day 6, pups were trained for 10 min using a standard conditioned olfactory learning paradigm in which a conditioned stimulus, Odor, was either used alone or paired with an unconditioned stimulus, Stroking (using a fine brush to stroke the pup). In some instances stroking only was used. The pups were sacrificed at 0, 10, 30, or 60 min after the training. Using Western blot analysis, we observed that the majority of olfactory bulbs in conditioned pups (Odor + Stroking) had a greater increase in pCREB activation at 10 min after training than pups given nonlearning training (Odor only or Stroking only). The phosphorylated protein levels were low at 0 min and at 60 min after training. This is in keeping with the slightly delayed and short-lived activation period for this protein.The localization of pCREB increases within the olfactory bulb as seen by immunocytochemistry. Naive pups were not exposed to odor or training. There was a significantly higher level of label in mitral cell nuclei within the dorsolateral quadrant of the bulb of pups undergoing odor-stroke pairing. No significant differences were observed among nonlearning groups (Naive, Odor only, or Stroking only) or among any training groups in the granule or periglomerular cells of the dorsolateral region. The localized changes in the nuclear protein are consistent with studies showing localized changes in the bulb in response to a learned familiar odor. The present study demonstrates that selective increases in pCREB occur as an early step following pairing procedures that normally lead to the development of long-term olfactory memories in rat pups. These results support the hypothesized link between pCREB and memory formation.

Dual Circuitry for Odor-Shock Conditioning during Infancy: Corticosterone Switches between Fear and Attraction via Amygdala

“…The failure of the postsensitive-period ADX CORT replacement group to show amygdala activation, yet learn an odor aversion, suggests nonamygdala pathways for odor aversion exist. Although the olfactory bulb has been shown previously to code odor aversions and preferences in pups, this area is not coding for the learned odor aversion in the postsensitive period ADX CORT pups (McLean et al, 1999;Zhang et al, 2003;Moriceau and Sullivan, 2004). These pups may be using the nonamygdala odor-aversion pathway, although this needs to be more carefully assessed in pups (Poulos and Fanselow, 2005).…”

Ontogeny of odor-LiCl vs. odor-shock learning: Similar behaviors but divergent ages of functional amygdala emergence

“…Previous data on infant odor learning indicate that the olfactory bulb exhibits robust learning-associated changes in early life, regardless of pups learning an odor preference or odor aversion (Sullivan and Leon 1986;Wilson et al 1987;Sullivan et al 1990;Woo et al 1996;McLean et al 1999;Yuan et al 2003;Roth et al 2006). The role of the olfactory bulb changes with development since older pups and adults do not usually show odor learning-induced changes in this brain area (Hamrick et al 1993;Woo et al 1996;Sevelinges et al 2007).…”

Molecular Biology Of Early Olfactory Memory: Figure 1.

“…Elevation in cAMP can contribute to enhanced phosphorylation of CREB, also known to occur in early olfactory learning (McLean et al 1999), and thus to a variety of reported changes in mitral-cell and olfactory-bulb circuit physiology (Fig. 1).…”

“…The molecular mechanisms involved in producing these changes in olfactory circuit function have only recently begun to be addressed (e.g., McLean et al 1999;Zhang et al in press), but a significant step forward in this regard is taken with the work of Yuan et al (2003).…”