Abstract
BackgroundEarly 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.ResultsThree-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.ConclusionRearing 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.
Highlights
Life experiences including physical exercise, sensory stimulation, and social interaction can modulate development of the inhibitory neuronal network and modify various behaviors
Number of PV and CalB-positive cells in basolateral amygdala (BLA) To determine whether rearing in EE leads to an altered organization of inhibitory circuits in BLA, we analyzed the number of cells expressing the calcium-binding proteins PV or CalB
BLA contained the highest density of PV-positive neurons (Figure 1A-D), whereas only a few PV-positive neurons were observed in other areas of the amygdala
Summary
Life experiences including physical exercise, sensory stimulation, and social interaction can modulate development of the inhibitory neuronal network and modify various behaviors. The basolateral amygdala (BLA) plays a critical role in emotional responsiveness and anxiety [8,9] and approximately 10%–15% BLA neurons are GABAergic interneurons [10,11]. PV-positive neurons constitute approximately 50% of the interneuronal population and extensively colocalize with calbindin-D28k (CalB, a kind of calcium-binding protein) [12]. These PV-positive interneurons are potent inhibitors of both the perisomatic and distal dendritic domains of principal glutamatergic neurons [13]. PVpositive neurons are critical for the expression of anxietylike behavior since activation of PV-positive neurons and pharmacological stimulation of the GABAergic neuronal system in BLA can decrease emotional arousal and anxietylike behavior [7,19,20]
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