Pubertal exposure to anabolic androgenic steroids increases spine densities on neurons in the limbic system of male rats

Abstract

Human studies show that the number of teenagers abusing anabolic androgenic steroids (AAS) is increasing. During adolescence, brain development is altered by androgen exposure, which suggests that AAS may potentially alter central nervous system (CNS) development. The goal of the present study was to determine whether pubertal AAS exposure increased dendritic spine densities on neurons within the medial amygdala and the dorsal hippocampus. Pubertal gonadally intact male rats received the AAS testosterone propionate (5 mg/kg) or vehicle for 5 days/week for 4 weeks. To determine the long-term implications of pubertal AAS use, another set of males received the same AAS treatment and was then withdrawn from AAS exposure for 4 weeks. Results showed that pubertal AAS exposure significantly increased spine densities on neurons in the anterior medial amygdala, posterodorsal medial amygdala, and the cornu ammonis region 1 (CA1) of the hippocampus compared with gonadally intact control males. Spine densities returned to control levels within the anterior medial amygdala and the posterodorsal medial amygdala 4 weeks after withdrawal. However, spine densities remained significantly elevated after AAS withdrawal in the CA1 region of the hippocampus, suggesting that pubertal AAS exposure may have a long-lasting impact on CA1 hippocampal neuroanatomy. Since pubertal AAS exposure increased spine densities and most excitatory synapses in the CNS occur on dendritic spines, AAS may increase neuronal excitation. It is proposed that this increase in excitation may underlie the behavioral responses seen in pubertal AAS-treated male rats.

Figure 1

Shaded regions indicate the placement of DiI crystals within the anterior medial amygdala (A), posterodorsal medial amygdala (B), and CA1 region of the dorsal hippocampus (B).

Figure 2

Spine density (mean ± SEM) resulting from three treatment conditions: vehicle control (n = 8), AAS testosterone (n = 6), and AAS withdrawal (n = 3). Secondary dendritic segments originating from three nuclei were analyzed: anterior medial amygdala, posterodorsal medial amygdala, and the CA1 region of the dorsal hippocampus. Spine densities within the anterior medial amygdala and the posterodorsal medial amygdala were significantly higher after AAS testosterone treatment compared to control (Tukey/Kramer, * = p<0.05). Spine densities returned to control levels within both regions of the medial amygdala following AAS withdrawal. AAS testosterone significantly increased spine densities in the CA1 region compared to control, and spine densities remained elevated after 4 weeks of AAS withdrawal (* = p<0.05).

Figure 3

Representative photomicrographs of DiI-labeled dendrite segments of neurons in the anterior medial amygdala in the 3 treatment conditions: vehicle control (A), AAS testosterone (B), and AAS withdrawal (C). Example of a dendritic spine is indicated by arrow. Scale bar = 10 μm.

Figure 4

Representative photomicrographs of DiI-labeled dendrite segments of neurons in the posterodorsal medial amygdala in the 3 treatment conditions: vehicle control (A), AAS testosterone (B), and AAS withdrawal (C). Example of a dendritic spine is indicated by arrow. Scale bar = 10 μm

Figure 5

Representative photomicrographs of DiI-labeled dendrite segments of neurons in the CA1 region of the dorsal hippocampus in the 3 treatment conditions: vehicle control (A), AAS testosterone (B), and AAS withdrawal (C). Example of a dendritic spine is indicated by arrow. Scale bar = 10 μm