Time course of cardiac conditioned responses in restrained rats as a function of the trace CS–US interval.

Abstract

Two experiments aimed at understanding the temporal characteristics of trace-conditioned heart-rate responses to a 0.5-s tone (conditioned stimulus [CS]) in restrained rats. A CS paired with a tail-shock (unconditioned stimulus [US]) elicited lasting bradycardiac responses. The magnitude and extinction rate of conditioned responses (CR) were independent of the CS-US interval (interstimulus interval [ISI], 3 s to 20 s). Unreinforced test trials were analyzed for CR topography. Responding was delayed in groups with longer ISIs, but CR latencies, peak and decay times were not proportional to the ISI. Response peaks tended to cluster either about 6 s after CS onset, or about 10 s with a slow decay, depending on the ISI. The authors postulated 2 components of auditory stimulus traces involved in cardiac conditioning, maximally active 6 s and 10 s respectively after CS onset. The topography of the CR could be constrained to combinations of associative strength and instantaneous activity of these 2 components.

Autonomic Changes Associated with Enhanced Anxiety in 5-HT1A Receptor Knockout Mice

“…Thus, the observed tachycardia does not necessarily reflect increased anxiety. Although the majority of animal studies focuses on the effects of aversive situations on autonomic responses, e.g., foot-shock in mice (Gross et al 2000), fear-conditioning in rats and mice (Marchand and Kamper 2000;Nijsen et al 1998b;Stiedl and Spiess 1997;Stiedl et al 1999), novelty in rats (Nijsen et al 1998a), increased tachycardia after appetitive situations has also been reported, e.g., after feeding in pigs (Schouten et al 1991), and reinforcing intracranial brain stimulation in rats (Burgess et al 1993).…”

Integration of cardiac responses to serial stimuli after Pavlovian conditioning in rats

“…The mean period change was measured on the 10th second after sound onset (Marchand & Kamper, 2000). For robustness, all data were collapsed with respect to the physical nature of the stimuli (tone, clicker, or noise, counterbalanced).…”

“…Responses conditioned with distinct CS-US intervals usually show different topographies (Marchand & Kamper, 2000). In particular, the peak of a CR often occurs near the instant of US presentation (Smith, 1968).…”

“…Yet the use of heart rate as a measure of conditioned fear has been somewhat debated, and cardiac CRs have not been extensively investigated within a trace paradigm (Fitzgerald & Martin, 1971;Fitzgerald & Teyler, 1970;Marchand & Kamper, 2000;Meredith & Schneiderman, 1967).…”

“…In a recent study, Marchand and Kamper (2000) studied trace fear conditioning to brief auditory stimuli in restrained rats. They reported that distinct cardiac CR topographies could be observed, depending on the CS-US interval.…”