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Updated: Jun 11, 2026
Neurodevelopmental Reflex Testing in Neonatal Rat Pups
Published on: April 24, 2017
Defining age limits of the sensitive period for attachment learning in rat pups
Karen J Upton1, Regina M Sullivan
1Department of Zoology, University of Oklahoma, 730 Van Vleet Oval, Norman, OK 73019, USA. kupton@ou.edu
Insights
Stress hormone corticosterone levels regulate a sensitive period for maternal odor learning in rat pups. This period, crucial for attachment, is influenced by corticosterone, but fear learning is not permanent.
Area of Science:
- Neuroscience
- Developmental Biology
- Behavioral Science
Background:
- Rat pups exhibit a sensitive period for learning maternal odor, crucial for attachment.
- This sensitive period normally terminates around postnatal day 10 (PN10) due to rising corticosterone levels.
- Corticosterone influences the timing of this sensitive period, with increased levels prematurely terminating it and decreased levels delaying termination.
Purpose of the Study:
- To define the specific age range during which corticosterone affects rat pup learning.
- To investigate whether corticosterone permanently terminates the sensitive period for maternal odor learning.
- To understand the developmental limits of corticosterone's role in olfactory learning and attachment.
Main Methods:
- Rat pups (PN5-16) were conditioned with odors paired with mild shock, with manipulated corticosterone levels (increased or decreased).
- Specific interventions included corticosterone administration or Metyrapone (a synthesis blocker) and maternal presence.
- Pups conditioned under elevated corticosterone were subsequently reconditioned without it to assess permanence of learned fear.
Main Results:
- Corticosterone significantly alters rat pup learning between postnatal days 6 (PN6) and PN15.
- Precocious corticosterone-induced fear learning was reversible; pups could re-learn odor preference without corticosterone.
- These findings indicate that corticosterone's effects on fear learning within this period are not permanent.
Conclusions:
- The sensitive period for maternal odor learning is developmentally regulated by corticosterone within a defined window (PN6-PN15).
- Rat pups are protected from forming lasting aversions to maternal odors until closer to weaning.
- This suggests a biological mechanism to ensure attachment and prevent negative associations with the primary caregiver during early development.
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-0.5 mA 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.
