Rearing in enriched environment increases parvalbumin-positive small neurons in the amygdala and decreases anxiety-like behavior of male rats.
BACKGROUND
Early life experiences including physical exercise, sensory stimulation, and social interaction can modulate development of the inhibitory neuronal network and modify various behaviors. In particular, alteration of parvalbumin-expressing neurons, a gamma-aminobutyric acid (GABA)ergic neuronal subpopulation, has been suggested to be associated with psychiatric disorders. Here we investigated whether rearing in enriched environment could modify the expression of parvalbumin-positive neurons in the basolateral amygdala and anxiety-like behavior.


RESULTS
Three-week-old male rats were divided into two groups: those reared in an enriched environment (EE rats) and those reared in standard cages (SE rats). After 5 weeks of rearing, the EE rats showed decreased anxiety-like behavior in an open field than the SE rats. Under another anxiogenic situation, in a beam walking test, the EE rats more quickly traversed an elevated narrow beam. Anxiety-like behavior in the open field was significantly and negatively correlated with walking time in the beam-walking test. Immunohistochemical tests revealed that the number of parvalbumin-positive neurons significantly increased in the basolateral amygdala of the EE rats than that of the SE rats, while the number of calbindin-D28k-positive neurons did not change. These parvalbumin-positive neurons had small, rounded soma and co-expressed the glutamate decarboxylase (GAD67). Furthermore, the number of parvalbumin-positive small cells in the basolateral amygdala tended to positively correlate with emergence in the center arena of the open field and negatively correlated with walking time in the beam walking test.


CONCLUSIONS
Rearing in the enriched environment augmented the number of parvalbumin-containing specific inhibitory neuron in the basolateral amygdala, but not that of calbindin-containing neuronal phenotype. Furthermore, the number of parvalbumin-positive small neurons in the basolateral amygdala was negatively correlated with walking time in the beam walking test and tended to be positively correlated with activity in the center arena in the open field test. The results suggest that rearing in the enriched environment augmented parvalbumin-positive specific neurons in the basolateral amygdala, which induced behavioral plasticity that was reflected by a decrease in anxiety-like behavior in anxiogenic situations.
Susumu
S
Urakawa
Kouich
K
Takamoto
Etsuro
E
Hori
Natsuko
N
Sakai
Taketoshi
T
Ono
Hisao
H
Nishijo
D000679:Amygdala / Q000166:cytology*; D000704:Analysis of Variance; D000818:Animals; D001007:Anxiety / Q000473:pathology / Q000517:prevention & control*; D064092:Calbindin 1; D064026:Calbindins; D002452:Cell Count; D048429:Cell Size; D004195:Disease Models, Animal; D004777:Environment; D005106:Exploratory Behavior / Q000502:physiology; D005786:Gene Expression Regulation / Q000502:physiology; D005968:Glutamate Decarboxylase / Q000378:metabolism; D008124:Locomotion / Q000502:physiology; D008297:Male; D009474:Neurons / Q000378:metabolism*; D010320:Parvalbumins / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D012044:Regression Analysis; D064030:S100 Calcium Binding Protein G / Q000378:metabolism
C576500:Calb1 protein, rat; D064092:Calbindin 1; D064026:Calbindins; D010320:Parvalbumins; D064030:S100 Calcium Binding Protein G; D005968:Glutamate Decarboxylase; C402565:glutamate decarboxylase 1