Effects of shock controllability on rat brain noradrenaline turnover under FR-1 and FR-3 Sidman avoidance schedules.

ABSTRACT

We examined changes in brain noradrenaline (NA) turnover as a function of shock controllability and the task complexity (fixed ratio, FR-1 and FR-3) under a 21-hr continuous discriminated Sidman avoidance schedule with shock intensity of 0.7-1.0 mA, shock duration of 1.0 sec, shock-shock interval of 1.5 sec, response-shock interval of 100 sec and signal-shock interval of 10 sec, by measuring levels of a principal metabolite of NA, 3-methoxy-4-hydroxyphenylethyleneglycol sulfate (MHPG-SO4), in discrete brain regions of male Wistar rats. In an FR-1 operant schedule, experimental rats which could avoid or escape shock by pulling a disk manipulandum only once showed significantly lower levels of MHPG-SO4 in the hypothalamus, amygdala, thalamus, locus coeruleus (LC) region and cerebral cortex than did yoked rats which received the same amount of shock but could not perform any effective avoidance and/or escape responses. The MHPG-SO4 levels for the experimental rats did not differ significantly from "non-shock" control rats in most regions. In an FR-3 operant schedule, however, the experimental rats which could control shock by emitting three disk-pulling responses showed significantly higher levels of MHPG-SO4 in most brain regions, as compared to FR-1 experimental rats. The FR-3-experimental rats exhibited levels of MHPG-SO4 similar to those seen in the FR-3 yoked rats in all brain regions. These two groups of shocked rats showed significantly higher levels of MHPG-SO4 in all brain regions with the exception of the basal ganglia, as compared to the FR-3 control rats.(ABSTRACT TRUNCATED AT 250 WORDS)