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Published on: January 30, 2014
Isolation alters striatal met-enkephalin immunoreactivity in rat pups
S E Carden1, A Tempel, N Hernandez
1Department of Developmental Psychobiology, New York State Psychiatric Institute, New York, USA.
Physiology & Behavior
|July 1, 1996
Summary
Social contact with littermates reduces ultrasonic vocalizations in rat pups by increasing methionine enkephalin (Met-ENK) levels. This opioid peptide may mediate the quieting effect of companionship.
Area of Science:
- Neuroscience
- Behavioral Biology
- Endocrinology
Background:
- Preweanling rats emit ultrasonic vocalizations (USVs) when isolated.
- Opioid agonists and social companionship effectively reduce these USVs.
- Naltrexone, an opioid receptor blocker, inhibits both opioid-induced and companion-induced quieting.
Purpose of the Study:
- To quantify methionine enkephalin (Met-ENK) immunoreactivity in rat pups under different social and isolation conditions.
- To investigate the role of Met-ENK in mediating the effects of social interaction and isolation on USVs.
Main Methods:
- Quantification of Met-ENK immunoreactivity in specific brain regions (striatum, hypothalamus, hippocampus, frontal cortex) of 10-day-old Wistar rat pups.
- Comparison of Met-ENK levels in pups housed in home cages, isolated briefly (5 min), isolated for a prolonged period (60 min), or housed with a companion.
Main Results:
- Striatal Met-ENK levels were significantly higher in pups housed with a companion compared to isolated pups.
- Met-ENK levels were higher after brief isolation (5 min) than after prolonged isolation (60 min).
- No significant changes in Met-ENK levels were observed in the hypothalamus, hippocampus, or frontal cortex based on social condition or isolation duration.
Conclusions:
- Social companionship in rat pups is associated with increased striatal Met-ENK levels, potentially mediating the reduction in ultrasonic vocalizations.
- Brief isolation may lead to an initial release and subsequent reduction in Met-ENK levels, while prolonged isolation might cause depletion.
- These findings suggest a role for the endogenous opioid system, specifically Met-ENK, in the regulation of social behavior and distress vocalizations in young mammals.
