Predation cues induce predator specific changes in olfactory neurons encoding defensive responses in agile frog tadpoles

Although behavioural defensive responses have been recorded several times in both laboratory
and natural habitats, their neural mechanisms have seldom been investigated. To
explore how chemical, water-borne cues are conveyed to the forebrain and instruct behavioural
responses in anuran larvae, we conditioned newly hatched agile frog tadpoles using
predator olfactory cues, specifically either native odonate larvae or alien crayfish kairomones.
We expected chronic treatments to influence the basal neuronal activity of the tadpoles’
mitral cells and alter their sensory neuronal connections, thereby impacting
information processing. Subsequently, these neurons were acutely perfused, and their
responses were compared with the defensive behaviour of tadpoles previously conditioned
and exposed to the same cues. Tadpoles conditioned with odonate cues differed in both
passive and active cell properties compared to those exposed to water (controls) or crayfish
cues. The observed upregulation of membrane conductance and increase in both the number
of active synapses and receptor density at the postsynaptic site are believed to have
enhanced their responsiveness to external stimuli. Odonate cues also affected the resting
membrane potential and firing rate of mitral cells during electrophysiological patch-clamp
recordings, suggesting a rearrangement of the repertoire of voltage-dependent conductances
expressed in cell membranes. These recorded neural changes may modulate the
induction of an action potential and transmission of information. Furthermore, the recording
of neural activity indicated that the lack of defensive responses towards non-native predators
is due to the non-recognition of their olfactory cues.