Visualizing traumatic stress-induced structural plasticity in a medial amygdala pathway using mGRASP

Abstract

Traumatic stress has been shown to contribute to persistent behavioral changes, yet the underlying neural pathways are not fully explored. Structural plasticity, a form of long-lasting neural adaptability, offers a plausible mechanism. To scrutinize this, we used the mGRASP imaging technique to visualize synaptic modifications in a pathway formed between neurons of the posterior ventral segment of the medial amygdala and ventrolateral segment of the ventromedial hypothalamus (MeApv-VmHvl), areas we previously showed to be involved in stress-induced excessive aggression. We subjected mice (7–8 weeks of age) to acute stress through foot shocks, a reliable and reproducible form of traumatic stress, and compared synaptic changes to control animals. Our data revealed an increase in synapse formation within the MeApv-VmHvl pathway post-stress as evidenced by an increase in mGRASP puncta and area. Chemogenetic inhibition of CaMKIIα-expressing neurons in the MeApv during the stressor led to reduced synapse formation, suggesting that the structural changes were driven by excitatory activity. To elucidate the molecular mechanisms, we administered the NMDAR antagonist MK-801, which effectively blocked the stress-induced synaptic changes. These findings suggest a strong link between traumatic stress and enduring structural changes in an MeApv-VmHvl neural pathway. Furthermore, our data point to NMDAR-dependent mechanisms as key contributors to these synaptic changes. This structural plasticity could offer insights into persistent behavioral consequences of traumatic stress, such as symptoms of PTSD and social deficits.

Acute social defeat during adolescence promotes long-lasting aggression through activation of the medial amygdala

“…We began by assessing the impact of SD during adolescence on long-lasting aggression in C57 mice. We previously showed that traumatic stress during adolescence in the form of non-contingent foot shock could promote long-lasting aggression ( Nordman J. et al, 2020 ; Nordman J. C. et al, 2020 ; Bartsch et al, 2023a , b ). However, given the comorbidity of childhood physical abuse and violent aggression later in life ( Widom, 1989 ; Caspi et al, 2002 ; Widom and Brzustowicz, 2006 ), and to simulate a more ethologically realistic stressful encounter to humans, for this study we elected to use SD as our traumatic stressor.…”

“…We chose foot shock as it is a more reliable stressor than SD due to the variability of CD1 attacks and because we have consistently shown that foot shock activates MeApv neurons in vivo . We began by administering intraperitoneal (IP) injections of 1 mg/kg CNO, the effective dose in our previous study ( Bartsch et al, 2023b ), or vehicle 30 min before non-contingent foot shock ( Figures 4A , B ). The mice were then euthanized 30 min later for c-Fos immunolabeling.…”

“…The activation of the MeApv and VmHvl immediately after SD and foot shock and the efficacy of MeApv inhibition in suppressing the ensuing long-lasting aggression underscores the importance of these regions in stress-induced aggression. While activation of these regions after traumatic stress is transient, our previous research has demonstrated that foot shock promotes long-lasting aggression by strengthening synaptic connections in an excitatory MeApv-VmHvl pathway ( Nordman J. et al, 2020 ; Nordman J. C. et al, 2020 ; Bartsch et al, 2023b ). These alterations were shown to persist for a week at testing, and likely longer.…”

“…3 weeks after viral injection, surgical animals were transferred from their housing room to a darkened behavior room and left alone to acclimate for 1 h prior to stress induction. Mice were injected with 0.9% saline (vehicle) or 1 mg/kg clozapine N-oxide (CNO, Sigma) ( Chang and Gean, 2019 ; Bartsch et al, 2023b ) 30 min before SD or foot shock.…”

“…It has been successfully targeted in neurosurgical interventions aimed at treating intractable, escalated aggression ( Mpakopoulou et al, 2008 ). Building on this foundation, our recent research demonstrated that traumatic stress, induced by non-contingent foot shock, significantly enhances aggression through the strengthening of synaptic connections between the posterior ventral segment of the MeA (MeApv) and the ventrolateral segment of the ventromedial hypothalamus (VmHvl) ( Nordman J. et al, 2020 ; Nordman J. C. et al, 2020 ; Nordman et al, 2022 ; Bartsch et al, 2023b ). Potentiation of these MeApv-VmHvl synapses results in excessive and recurrent attack behavior that persists into adulthood.…”