Postnatal development of the amygdala: A stereological study in rats

Abstract

The amygdala is the central component of a functional brain system regulating fear and emotional behaviors. Studies of the ontogeny of fear behaviors reveal the emergence of distinct fear responses at different postnatal ages. Here, we performed a stereological analysis of the rat amygdala to characterize the cellular changes underlying its normal structural development. Distinct amygdala nuclei exhibited different patterns of postnatal development, which were largely similar to those we have previously shown in monkeys. The combined volume of the lateral, basal, and accessory basal nuclei increased by 113% from 1 to 3 weeks of age and by an additional 33% by 7 months of age. The volume of the central nucleus increased only 37% from 1 to 2 weeks of age and 38% from 2 weeks to 7 months. At 1 week of age, the medial nucleus was 77% of the 7-monthold's volume and exhibited a constant, marginal increase until 7 months. Neuron number did not differ in the amygdala from 1 week to 7 months of age. In contrast, astrocyte number decreased from 3 weeks to 2 months of age in the whole amygdala. Oligodendrocyte number increased in all amygdala nuclei from 3 weeks to 7 months of age. Our findings revealed that distinct amygdala nuclei exhibit different developmental profiles and that the rat amygdala is not fully mature for an extended period postnatally. We identified different periods of postnatal development of distinct amygdala nuclei and cellular components, which are concomitant with the ontogeny of different fear and emotional behaviors.

Ontogeny of contextual fear memory formation, specificity, and persistence in mice

“…Considering that eye opening occurred only 1-2 d prior to the onset of contextual fear learning in mice (i.e., at 12 d of age), the ongoing development of the visual system (Bourne 2010) may also underlie the onset of this type of learning. Furthermore, our observation that spontaneous freezing declined steadily across infancy suggests that the emergence of conditioned fear (as opposed to unconditioned fear) may rely on the maturation of brain regions involved in emotion, such as the amygdala (Gogolla et al 2009;Chareyron et al 2012) and prefrontal cortex (van Eden et al 1990).…”

Social Isolation During Postweaning Development Causes Hypoactivity of Neurons in the Medial Nucleus of the Male Rat Amygdala

“…The MeA undergoes prepubertal maturation and peripubertal refinement in response to gonadal hormones that parallels the refinement of these social behaviors (Cooke, 2006). There is enlargement of the MeApd during puberty (Romeo and Sisk, 2001;Chareyron et al, 2012;De Lorme et al, 2012) that is coupled with increased synaptophysin (Zehr et al, 2006), PSD-95, and vesicular glutamate transporter 2, consistent with increased number of excitatory synaptic inputs (Cooke, 2011). Disruption of synaptic refinement in MeApd may contribute to the effects of social isolation on social behaviors.…”

Effects of Repeated Stress on Age-Dependent GABAergic Regulation of the Lateral Nucleus of the Amygdala

“…Repeated stress increased the number of active neurons encountered in adolescent rats, but not in adult rats (Figures 1d and e; main effect of stress, F(1,153) = 5.676, p = 0.0184; po0.05, Holm-Sidak's multiple comparisons test in adults but not in adolescents; adolescent control n = 40 tracks, adolescent stress n = 39 tracks, adult control n = 40 tracks, adult stress n = 39 tracks). The size of the LAT is slightly smaller in adolescent rats (Chareyron et al, 2012). Therefore, we normalized neurons/track by the track distance, and compared neurons per mm.…”