Biomedical subjects

Robert C Barnet

Publications and source records attributed to Robert C Barnet.

3 recordsLinked to original sources

PubMed2006

Cholinergic modulation of trace conditioning trained in serial compound: A developmental analysis.

In four experiments the effects of serial compound conditioning on responding to a trace-conditioned CS were evaluated using a fear conditioning paradigm. The subjects were 18- and 25-day-old Sprague-Dawley rats, previously shown to exhibit little or no trace fear conditioning. Here, animals as young as 18 days of age were shown to be capable of trace conditioning between a visual CS1 and a shock US, provided the trace interval was filled with a non-target CS2 during serial conditioning trials (CS1-->CS2-->US). To explore cholinergic mechanisms involved in trace and serial conditioning, additional experiments assessed conditioned responding following pre-training administration of the muscarinic receptor antagonist scopolamine. Scopolamine produced a dose-dependent reduction in responding to the trace CS1, regardless of whether subjects were trained with standard trace (CS1-->trace interval-->US) or serial (CS1-->CS2-->US) trials. Responding to CS2 was unaffected by scopolamine. These data suggest that central cholinergic systems are functional in the young animals, but are not normally sufficiently activated by standard trace conditioning procedures. The results suggest that serial compound conditioning can promote trace conditioning in young rats, as it does in adults, perhaps by enhancing cholinergic activity during training. Implications for the late ontogenetic emergence of trace conditioning as it relates to maturation of neural pathways and their role in the potentiating effects of a gap filler are discussed.

Age Factors↗

PubMed2006

The expression of fear-potentiated startle during development: integration of learning and response systems.

Relative to freezing, fear-potentiated startle (FPS) is developmentally delayed. Rats trained on Postnatal Day (PD) 18 expressed conditioned stimulus learning on PD 19 in freezing but not in FPS, whereas rats trained on PD 24 and tested on PD 25 expressed both freezing and FPS (Experiment 1). According to a neural maturation hypothesis, this delay results from functional immaturity of pathways mediating FPS. When rats were trained on PD 18, neither delaying the FPS test, allowing FPS pathways to develop, nor administrating the "reminder" treatment, the expression of FPS was promoted (Experiments 1, 2, and 2A). PD 18 learning was expressed in FPS on PD 25 when nontarget conditioned stimulus-unconditioned stimulus training occurred prior to the test, and this effect was modality dependent (Experiments 3 and 4). The authors conclude that engaging mechanisms of associative encoding when FPS pathways are functional is a critical condition for integrating learning and FPS response systems in development.

Acoustic Stimulation↗

PubMed2005

Trace and long-delay fear conditioning in the developing rat.

In two experiments with rats, we examined the developmental emergence of conditioned freezing following trace and short-delay conditioning and also included a long-delay comparison group. In the short-delay and trace groups, a 10-sec conditioned stimulus (CS) was paired with shock; for the trace rats, a 10-sec trace interval followed CS termination. The long-delay groups received a 20-sec CS paired with shock, to equate for the longer interstimulus interval (ISI) in the trace group. Trace conditioning emerged later in development than did short-delay conditioning (see Moye & Rudy, 1987). Importantly, long-delay conditioning emerged in parallel with trace conditioning, at a similar time, and with similar strength. These findings suggest a role for the longer ISI, as opposed to the unfilled gap per se, in the late emergence of trace conditioning. The role of the hippocampus in trace conditioning and the possibility that young rats encode the temporal relationship between CSs and unconditioned stimuli are also considered.

Animals↗