Sex-Specific Divergent Maturational Trajectories in the Post-Natal Rat Basolateral Amygdala

The basolateral amygdala (BLA), the part of the amygdala complex involved in the transduction of perceptual stimuli into emotion, undergoes profound reorganization at adolescence in rodents and humans. How cellular and synaptic plasticity evolve throughout postnatal development in both sexes is only partially understood. We used a cross-sectional approach to compare the morphology, neuronal, and synaptic properties of BLA neurons in rats of both sexes at adolescence and adulthood. While BLA pyramidal neurons from rats of both sexes displayed similar current-voltage relationships, rheobases, and resting potentials during pubescence, differences in these parameters emerged between sexes at adulthood: BLA neurons were more excitable in males than females. During pubescence, BLA neuron excitability was highest in females and unchanged in males; male action potentials were smaller and shorter than females and fast afterhyperpolarizations were larger in males. During post-natal maturation, no difference in spine density was observed between groups or sexes but spine length increased and decreased in females and males, respectively. A reduction in spine head diameter and volume was observed exclusively in females. Basic synaptic properties also displayed sex-specific maturational differences. Stimulus-response relationships and maximal fEPSP amplitudes where higher in male adolescents compared with adults but were similar in females of both ages. Spontaneous excitatory postsynaptic currents mediated by AMPA receptors were smaller in BLA neurons from adolescent female compared with their adult counterparts but were unchanged in males. These differences did not directly convert into changes in overall synaptic strength estimated from the AMPA/NMDA ratio, which was smaller in adolescent females. Finally, the developmental courses of long-term potentiation and depression (LTP, LTD) were sexually dimorphic. LTP was similarly present during the adolescent period in males and females but was not apparent at adulthood in females. In contrast, LTD followed an opposite development: present in adolescent females and expressed in both sexes at adulthood. These data reveal divergent maturational trajectories in the BLA of male and female rats and suggest cellular substrates to the BLA linked sex-specific behaviors at adolescence and adulthood.