FLINDERS RESISTANT HYPOCHOLINERGIC RATS EXHIBIT STARTLE SENSITIZATIONAND REDUCED STARTLE THRESHOLDS

Based on the hypothesis that depression involves a cholinergic-adrener gic neurotransmitter imbalance, a putative genetic animal model of dep ression has been developed by selectively breeding rats to exhibit hyp ocholinergia (Flinders Resistant Line - FRL), or hypercholinergia (Fli nders Sensitive Line - FSL). The present experiments were designed to test the behavioral reactivity of these rats to external stimuli by me asuring acoustic startle responses. The FRL rats exhibited lower start le thresholds compared to both FSL and control rats, while the FSL rat s' startle thresholds were between those of controls and FRL rats. Des pite the differences in thresholds, the three groups demonstrated simi lar levels of maximal startle reactivity to a high-intensity acoustic stimulus. With repeated stimulus presentations, FRL rats developed sta rtle sensitization, a rarely observed phenomenon, while FSL and contro l rats exhibited habituation. There were no differences between the th ree groups in prepulse inhibition of startle. These results indicated that FRL rats exhibited interesting startle phenomena that are charact eristic of certain psychiatric disorders, such as schizophrenia: post- traumatic stress disorder, and, potentially, depression.