Efflux of neurotransmitter from brain slices during O2 deprivation – comparing diving and non-diving species

Abstract

During hypoxic insult, neuronal tissue undergoes an excitotoxic cascade of events leading to cell death. This response involves loss of membrane potential and uncontrolled release of primarily excitatory neurotransmitters. I propose that this fatal cascade is significantly delayed or attenuated in diving species, which are adapted to repeated exposures to hypoxic conditions as a consequence of breath-hold diving. Here I have compared the in vitro overflow/efflux of neurotransmitters from cerebellar slices of a diving bird, the common eider duck (Somateria mollissima) and of the non-diving chicken (Gallus gallus domesticus), using a microperfusion technique as described by Kirschner et al. (2009). Slices were cut in ice cold oxygenated aCSF and stored at room temperature before transfer to custom-made microperfusion chambers. After 20 min equilibration at 37°C, the superfusate was collected while exposing the slices to 20 min hypoxic or normoxic (control) perfusions, before reoxygenation. I used Waters UPLC AAA application solution for physiological amino acids to detect changes in the concentration of the excitatory neurotransmitters Glutamate and Serine and the inhibitory Glycine, in the superfusate. I found that neurotransmitter release, for both eider duck and chicken, tended to increase in hypoxia. In addition, higher levels of neurotrasmitter efflux during the hypoxia, and normoxia exposure were present in the chicken.