Classically conditioned heart rate and respiratory-motor activity in newborn and neonatal pygmy goats

Abstract

Classical discrimination conditioning of heart rate (HR) and respiratory-motor (RM) activity was examined in 16 newborn (average age = 1 day) and 8 neonatal (average age = 2 weeks) pygmy goats over 4 days of conditioning involving an electric shock US and auditory CSs. On the 4th day, one-half of the animals in each group received a low to moderate dose of ethanol to test the resistance of the CRs to drug effects. Discriminated conditioning of RM activity but not HR occurred in the newborn group, indicating an absence of close coupling between skeletal-motor activity and HR at this early age. While the newborn group failed to show recognizable HR reactions to the CSs during the 4 days of testing, it did show a long-latency bradycardia UR beginning at 2 days of age that may have been secondary to baroreceptor reflex actions. The neonatal group displayed conditioning of both HR and RM activity.

Inhibition of the expression of conditioned cardiac responses in the developing rat

“…This series of experiments has extended previous findings (Campbell & Ampuero, 1985;Fitzgerald et al, 1984;Richardson et al, 1996;Sebastiani et al, 1994) showing that heart rate as a conditioned response appears to be delayed in its emergence with respect to conditioned motor responses during ontogeny. During a training session animals 14 -16 days of age exhibited conditioned freezing responses to a light CS paired with a footshock US, while conditioned changes in heart rate were absent.…”

“…For some time it has been assumed that the delayed emergence of the cardiac CR, with respect to motor responses, represented a later maturation within the central nervous system structures mediating the cardiovascular response (Campbell & Ampuero, 1985;Fitzgerald et al, 1984;. The present finding that cardiac responses can be observed as early as freezing during ontogeny suggests instead that what is changing during development is the susceptibility of the cardiac response to inhibition by the US.…”

“…Campbell and Ampuero (1985) demonstrated that young rats were capable of acquiring conditioned suppression of appetitively motivated running several days earlier in development than they could express changes in heart rate to the CS (see also Richardson, Wang, & Campbell, 1996). Similarly, Sebastiani, Salamone, Silvestri, Simoni, and Ghelarducci (1994), working with young rabbits, and Fitzgerald, Francisco, Metcalfe, and Lawson (1984), working with young pygmy goats, have reported an analogous developmental sequence of motor and cardiac conditioned responses. Collectively, these findings suggest not only that the autonomic and behavioral response systems are independent, but that their ontogenetic development follows different trajectories of maturation.…”

“…For several years, the dichotomy of these two response systems during development has been generally accepted and confirmed by a number of investigators (e.g., Campbell & Ampuero, 1985;Fitzgerald et al, 1984;Richardson et al, 1996;Sananes, Gaddy, & Campbell, 1988;Sebastiani et al, 1994). Of interest, in the experiments reporting such dissociations between somatomotor and cardiac CRs, heart rate responses were recorded during CS -US pairings, but never after a delay.…”

A further investigation of the developmental emergence of fear-potentiated startle in rats

“…We and others (Campbell & Ampuero, 1985;Fitzgerald, Francisco, Metcalfe, & Lawson, 1984;Hunt et al, 1994;Richardson et al, 1995;Sebastiani, Salamone, Silvestri, Simoni, & Ghelarducci, 1994) have attributed the previously reported sequential emergence of conditioned fear responses during ontogeny to maturation along central pathways involved in the production of these responses. Specifically, the amygdala central nucleus, a structure implicated in defensive responding, has been shown to project to several structures that are each involved in the generation of a specific fear response.…”