Neonatal basal forebrain cholinergic hypofunction affects ultrasonic vocalizations and fear conditioning responses in preweaning rats

The present study investigated the effects of intracebroventricular injections of 192 IgG-saporin in 7-day-old rats on (i) ultrasound vocalizations (USVs) on postnatal day (pnd) 13 following isolation and reunion with the mother and (ii) fear conditioning on pnd 18-19 recording both freezing and other behavioural responses as well as USVs. On pnd 13 lesioned and control pups showed comparable USV baseline values; a brief reunion with the mother induced a significant increase in USVs in all rats (maternal potentiation). On pnd 18, during the fear conditioning training, 192 IgG-saporin rats emitted a lower number of USVs. On pnd 19 all rats showed a stronger conditioned response (with full inhibition of locomotion) to auditory than to contextual cues. Surprisingly, lesioned rats showed a stronger fear-conditioned response to contextual cues than controls. These results suggest that early selective removal of the cholinergic basal forebrain paradoxically enhances hippocampally dependent fear-conditioned responses on pnd 19.