Rapid cold hardening modifies mechanisms of ion regulation to delay anoxia-induced spreading depolarization in the CNS of Locusta migratoria

Insects live in varied habitats and experience different kinds of environmental stresses. These stresses can impair neural performance, leading to spreading depolarization (SD) of nerve cells and neural shutdown underlying coma. The sensitivity of an insects nervous system to stress (e.g., anoxia) can be modulated by acute pre-treatment. Rapid cold hardening (RCH) is a form of preconditioning, in which a brief exposure to low temperature can enhance the stress tolerance of insects. SD is associated with a sudden loss of ion, notably K+, homeostasis. We used a pharmacological approach to investigate whether RCH affects anoxia-induced SD in the locust, L. migratoria, via one or more of the following homeostatic mechanisms: (1) Na+/K+-ATPase (NKA), (2) Na+/K+/2Cl- co-transporter (NKCC), and (3) voltage-gated K+ (Kv) channels. We also assessed abundance and phosphorylation of NKCC using immunoblotting. We found that inhibition of NKA or Kv channels delayed the onset of anoxia-induced SD in both control and RCH preparations. However, NKCC inhibition preferentially abrogated the effect of RCH. Additionally, we observed a higher abundance of NKCC in RCH preps but no statistical difference in its phosphorylation level, indicating the involvement of NKCC expression or degradation as part of the RCH mechanism.