Effects of pentagastrin and the cold presser test on the acoustic startle response and pupillary function in man

Pentagastrin, a cholecystokinin(2) (CCK2) receptor agonist, evokes autonomic and subjective features of anxiety in healthy volunteers. The present experiments examined the effects of pentagastrin on two responses with known sensitivity to another anxiogenic procedure (threat of electric shock): the acoustic startle response and the pupillary light reflex. The effects of pentagastrin were compared with those of the cold presser test, a procedure known to elicit sympathetic activation. Twelve healthy males (18-35 years) participated in two experiments each consisting of two sessions in which they received (1) pentagastrin (0.3 mug/kg, i.v.) and a control infusion (saline), and (2) cold presser test (90 s hand immersion at 4 degreesC) and a control immersion (37 degreesC), using a balanced single-blind protocol, Electromyographic responses of the orbicularis oculi to 40 ms, 1 kHz, 115 dB tones ('startle responses') [Experiment 1], and miotic responses to 200 ms, 0.43 mW/cm(2) light pulses [Experiment 2] were recorded before, during and after the infusions and hand immersions. Heart rate, blood pressure and subjective feelings were also recorded. The amplitude of the startle response was not significantly affected by pentagastrin, but was reduced during the cold presser test. Resting pupil diameter increased during both pentagastrin infusion and the cold presser test, but neither procedure altered the amplitude of the light reflex. Tachycardia, increased blood pressure and subjective anxiety were induced by both pentagastrin and the cold presser test, The cardiovascular and mydriatic effects of pentagastrin and the cold presser test are consistent with the known ability of these treatments to induce sympathetic activation. The anxiety induced by these treatments, unlike anxiety induced by threat of electric shock, was not accompanied by potentiation of the startle response or reduction of the miotic response. The results indicate that different anxiogenic procedures do not have equivalent effects on these reflexes.