Figure 1
Complex olfactory learning-induced hyperpolarization of the fast IPSP. (A) Schematic description of the olfactory maze. An electronic ‘start’ command opens randomly two out of eight valves (V), releasing a positive-cue odor (P) into one of the arms and a negative-cue odor (N) into another. Eight seconds later, the two corresponding guillotine doors (D) are lifted to allow the rat to enter the selected arms. Upon choosing the arm containing the positive-cue odor, reaching the far end of an arm (90 cm long), the rat body interrupts an infrared beam (I, arrow) and a drop of drinking water is released from a water hose (W) into a small drinking well. A trial ends when the rat interrupts a beam, or in 10 seconds, if no beam is interrupted. A fan is operated for 15 seconds between trials, to remove odors. (B) Schematic illustration of the piriform cortex in a coronal brain slice and the experimental procedure. Intracellular recordings were performed from cell bodies in layer II. Feed forward inhibition (FF) inputs are terminated on the distal apical dendrites, while feedback inhibition (FB) is terminated on cell bodies and proximal dendrites of the cell41,42. For activation of inhibitory synaptic inputs, electrical stimuli were applied at the border between layers II and III, in the presence of the glutamatergic AMPA and NMDA receptors blockers. (C) Learning-induced hyperpolarization of the fast IPSP’s reversal potential. Averaged values of the IPSP’s reversal potential in the three experimental groups. This value is significantly hyperpolarized for the neurons taken from trained rats (***p < 0.001). (D) A cumulative frequency graph comparing the reversal potentials of the fast IPSP in neurons from controls versus trained rats. Each point represents VCl, the reversal potential of the fast IPSP for a neuron. Notably, the curve for the trained group is shifted smoothly leftwards, indicating that learning-induced reduction in the fIPSP reversal potential is apparent throughout the recorded pyramidal neurons population. Data was taken from 50 naive rats, 54 trained rats, and 45 pseudo-trained rats. Values represent mean ± SE.
