Comparison of the number of spikes and number active cells in P5–P8 and P14–P17 aPC pyramidal cells evoked by conditioned maternal odor. After the conditioning of CS (maternal odor) and UCS (maternal care) in an artificial olfactory circuit with aPC pyramidal cells with passive and active electrophysiological characteristics of P5–P8 rats, the evoked response of pyramidal cells to CS alone was tested in the same age circuit (first CS in A,B). In order to compare the evoked pyramidal cells to conditioned maternal odor at P5–P8 and P14–P17, the CS alone was presented again (second CS in A,B) 1 sec after the first CS was finished and 2 sec after the second CS was finished (third CS in A,B). (A) The number of spikes with characteristics of P5–P8 was higher in response to CS alone (black points). On the other hand, the evoked response of pyramidal cells characteristic of P14–P17 was reduced progressively throughout the CS presentation (red points). The same evoked response was observed for the two age group cells during the third CS presentation. (B) The reduced spike activity at P14–P17 in response to CS was due to the reduction in the number of active pyramidal cells compared with P5–P8. Excitatory mitral inputs fire at the respiratory rhythm (2 Hz). Bin 0.5 msec.
