Intraseptal injection of the cholinergic immunotoxin 192-IgG saporin fails to disrupt latent inhibition in a conditioned taste aversion paradigm

Male Sprague-Dawley rats received injections of 100 or 375 ng 192-IgG saporin (SAP) or artificial CSF (C) into the medial septum/diagonal band complex (MSDB). SAP treated rats exhibited brief increases in daily water consumption which recovered to control levels by twenty one days following surgical treatment. Half of all subjects were preexposed to a 0.2% saccharin solution (CS) for 4 consecutive days prior to the establishment of a conditioned taste aversion (CTA) to saccharin. SAP was not found to alter acquisition of a normal CTA nor CS preexposure effects. All subjects which experienced CS/US pairing displayed aversions to saccharin when given a two bottle choice test. However, those subjects which were preexposed to saccharin prior to CS/US pairing displayed significantly weaker aversions than non-preexposed subjects. These subjects consumed a higher percent saccharin on test day and their CTAs extinguished more rapidly relative to non-preexposed subjects. While these behavioral measures remained undisrupted, intraseptal SAP treatment dose-dependently decreased hippocampal levels of high affinity choline transport as well as significantly decreasing HAChT in cingulate and frontal cortices. No such changes in HAChT were observed in striatum or entorhinal cortex. These data suggest that the MSDB cholinergic cell population is not critical to selective attentional processes believed to underlie latent inhibition.