Shows the mean ± s.e.m change in mean arterial pressure in response to the CS (end-stimulus minus pre-stimulus mean arterial pressure; crosshatched bars) and the US (post-stimulus minus end-stimulus mean arterial pressure; dark bars).

<p>Statistical differences in mean arterial pressure across time for either the CS or US were determined by one-way ANOVA with repeated measures using a Dunnett’s post-hoc comparison to the initial exposure period at 9 am (left hand crosshatched and gray bar in each of the four panels. (A) The initial mtHC alone series produced a small but significant hypertensive response as did exposure to the three US periods of footshock. (B) A small but significant CS hypertensive response across all exposure sets for animals exposed to CO₂ without footshock. (C) Arterial blood pressure responses to the tone paired with footshock produced a small, but significant increase in mean arterial blood pressure in two of the first three paired exposures. (D) Responses to tone alone were small, inconsistent and had no effect on mean arterial blood pressure. *p<0.05.