Defining age limits of the sensitive period for attachment learning in rat pups

Abstract

Enhanced odor preference learning and attenuated fear learning characterizes rat pups’ attachment learning Sensitive Period for learning the maternal odor. This period terminates at 10 days old (PN10) with increasing endogenous levels of the stress hormone, corticosterone. Increasing Sensitive Period pups’ corticosterone prematurely terminates the Sensitive Period, while decreasing corticosterone in older pups delays Sensitive Period termination. Here we extend these findings and define the age range corticosterone alters learning and question whether corticosterone permanently terminates the Sensitive Period. Pups were odor-0.5mA shock conditioned with either corticosterone increased (PN5–6; 4 mg/kg vs. saline) or decreased (PN15–16; naturally by maternal presence or corticosterone synthesis blocker, Metyrapone). Finally, PN7–8 pups were conditioned with corticosterone and reconditioned without corticosterone to assess whether the Sensitive Period was permanently terminated. Results indicate developmental limits for corticosterone regulation of pup learning are PN6 through PN15. Furthermore, inducing precocious corticosterone induced fear learning was not permanent, since reconditioning without corticosterone enabled odor preference learning. Results suggest pups are protected from learning aversions to maternal odor until approaching weaning.

Central amygdala nucleus (Ce) gene expression linked to increased trait-like Ce metabolism and anxious temperament in young primates

“…Rather, these findings provide an initial rationale for exploring behavioral or pharmacological interventions aimed at up-regulating regional NTRK3 expression early in the lives of individuals likely to develop anxiety and depressive disorders. Recent studies in rodents demonstrate the feasibility of performing early targeted interventions that have long-term impacts on anxiety and adaptive responses to stress (54)(55)(56). For example, neonatal injections of the neuroplasticity-related growth factor fibroblast growth factor 2 (FGF2) altered the developmental trajectory of highanxious rodents, resulting in decreased adult anxiety (55).…”

The Importance of Early Experiences for Neuro-Affective Development

“…One reason we cannot make this claim in humans is because the youngest age tested (i.e., 6 years old)(Gee, et al, in press) is probably too late to identify a developmental switch from a quiescent amygdala state to a functional one. The normative switch probably predates the ages tested; to begin to answer this question, preschool age children or younger would need to be scanned to identify the age at which the amygdala becomes functionally active as has been done in rodents (Upton & Sullivan, 2010; Wiedenmayer & Barr, 2001). …”

Rodent model of infant attachment learning and stress

“…As depicted in Table 1, our results indicate that maternal presence in PN10–15 pups reengages the attachment circuitry during learning, effectively preventing them from acquiring an odor aversion or fear. The ability of maternal presence to reengage the attachment circuitry appears to end at PN15, as PN16 pups still learn an odor aversion even in the presence of the mother (Upton & Sullivan, 2010). Based upon these data, we now define PN10–15 as a “conditional sensitive period,” in which odor preference learning and attenuated fear learning can be reestablished if the mother is present.…”