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Neonatal Isolation Increases the Susceptibility to Learned Helplessness through the Aberrant Neuronal Activity in the
Hironori Kobayashi1, Manabu Fuchikami1, Kenichi Oga1
1Division of Graduate School of Biomedical and Health Sciences, Department of Psychiatry and Neuroscience, Hiroshima University, Hiroshima, Japan.
Insights
Neonatal isolation in rats increased learned helplessness and decreased ventral pallidum (VP) vesicular glutamate transporter 2 (VGLUT2) cells. These findings link early environmental deprivation to depression-like behaviors and VP alterations.
Area of Science:
- Neuroscience
- Developmental Psychology
- Behavioral Science
Background:
- Childhood environmental deprivation can impair cognitive development.
- Pessimism, a key feature of depression, is linked to ventral pallidum (VP) changes.
- Learned helplessness (LH) in rats models depression-like behavior.
Purpose of the Study:
- To investigate if neonatal isolation (NI) affects learned helplessness (LH) incidence in rats.
- To examine the impact of NI on VP vesicular glutamate transporter 2 (VGLUT2) and Penk-expressing cells.
Main Methods:
- Rats underwent neonatal isolation (NI) or sham procedures.
- Learned helplessness (LH) was assessed via escape failures in a foot-shock test.
- VP cell counts for VGLUT2 and Penk were determined using immunohistochemistry.
Main Results:
- NI rats exhibited increased LH incidence compared to controls.
- VGLUT2-expressing VP cells were reduced in NI rats, but Penk-expressing cells were not.
- Reduced VGLUT2 cells in NI rats correlated with longer escape latencies in the LH test.
Conclusions:
- Early life environmental deprivation (NI) may cause aberrant VP neuronal activity.
- This VP dysfunction is linked to pessimistic learning and depression-like behaviors.
- Targeting VP neuronal activity offers potential therapeutic strategies for related disorders.
Objective:
: Environmental deprivation, a type of childhood maltreatment, has been reported to constrain the cognitive developmental processes such as associative learning and implicit learning, which may lead to functional and morphological changes in the ventral pallidum (VP) and pessimism, a well-known cognitive feature of major depression. We examined whether neonatal isolation (NI) could influence the incidence of learned helplessness (LH) in a rat model mimicking the pessimism, and the number of vesicular glutamate transporter 2 (VGLUT2)-expressing VP cells and Penk-expressing VP cells.
Methods:
: The number of escape failures from foot-shocks in the LH test was measured to examine stress-induced depression-like behavior in rats. The number of VGLUT2-expressing VP cells and Penk-expressing VP cells was measured by immunohistochemistry.
Results:
: In NI rats compared with Sham rats, the incidence of LH in adulthood was increased and VGLUT2-expressing VP cells but not Penk-expressing VP cells in adulthood were decreased. VGLUT2-expressing VP cells were decreased only in the LH group of NI rats and significantly correlated with the escape latency in the LH test.
Conclusion:
: These findings suggest that the aberrant VP neuronal activity due to environmental deprivation early in life leads to pessimistic associative and implicit learning. Modulating VP neuronal activity could be a novel therapeutic and preventive strategy for the patients with this specific pathophysiology.
