Sodium pentobarbital: sensory and associative effects in classical conditioning of the rabbit nictitating membrane response

Abstract

Four experiments were conducted to determine the effects of sodium pentobarbital (0, 3, 9, and 15 mg/kg) on the acquisition of the rabbit's classically conditioned nictitating membrane response (NMR) and to determine the locus of the drug's effects on sensory, motor, associative, and nonassociative processes. In experiment 1, classical conditioning of the NMR was accomplished by pairing tone and light conditioned stimuli (CSs) with paraorbital shock as the unconditioned stimulus (US). The experiment revealed that pentobarbital retarded the acquisition of conditioned responses (CRs) to both tone and light CSs. Experiment 2, employing unpaired CS, UCS presentations, indicated small but significant drug effects on NMR base rate and nonassociative NMRs to the CS. Experiment 3 revealed no significant drug effect on the psychophysical functions relating UCS intensity to UCR frequency or amplitude, nor on the UCS intensity threshold for eliciting UCRs. On the other hand, in experiment 4, the drug significantly impaired CR frequency over an extended range of CS intensities and raised CS intensity threshold. It was concluded that pentobarbital's attenuation of CS intensity also operated to impair CR acquisition.

Cholesterol Modifies Classical Conditioning of the Rabbit (Oryctolagus cuniculus) Nictitating Membrane Response.

“…In designing this experiment, we noted that a large number of substances may affect classical conditioning of the rabbit NMR (Du & Harvey, 1996;Du, Weiss, & Harvey, 2000;Harvey & Romano, 1993;Kronforst-Collins et al, 1997;Moore, Goodall, & Solomon, 1976;Oh, Power, Thompson, Moriearty, & Disterhoft, 1999;Solomon et al, 1995;Weiss et al, 2000;Welsh, Romano, & Harvey, 1998;Woodruff-Pak, 1997;Woodruff-Pak & Santos, 2000). However, not all compounds that affect responding during classical conditioning affect associative processes (P. Chen, Ghoneim, & Gormezano, 1992;Schindler, Gormezano, & Harvey, 1984). Assessing the effects of cholesterol on classical conditioning of the rabbit NMR also requires assessing and controlling for potential sensory, motor, and nonassociative effects of the substance (P. Chen et al, 1992;Gormezano, 1994;Moon, Ghoneim, & Gormezano, 1994;Schindler et al, 1984).…”

“…However, not all compounds that affect responding during classical conditioning affect associative processes (P. Chen, Ghoneim, & Gormezano, 1992;Schindler, Gormezano, & Harvey, 1984). Assessing the effects of cholesterol on classical conditioning of the rabbit NMR also requires assessing and controlling for potential sensory, motor, and nonassociative effects of the substance (P. Chen et al, 1992;Gormezano, 1994;Moon, Ghoneim, & Gormezano, 1994;Schindler et al, 1984). For example, cholesterol may decrease responding to a tone conditioned stimulus (CS) that was paired with an airpuff or periorbital electrical stimulation unconditioned stimulus (US) because it affects sensory perception (e.g., the animal may become hard of hearing) or motor performance (e.g., the animal may develop muscle weakness) rather than associative processes.…”

“…For example, cholesterol may decrease responding to a tone conditioned stimulus (CS) that was paired with an airpuff or periorbital electrical stimulation unconditioned stimulus (US) because it affects sensory perception (e.g., the animal may become hard of hearing) or motor performance (e.g., the animal may develop muscle weakness) rather than associative processes. Explicitly unpaired presentations of the CS and US have been used to assess the various nonassociative contributors to responding, including sensitization and pseudoconditioning, as well as providing a simple assessment of sensory perception and motor performance (P. Chen et al, 1992;Gormezano, 1984;Gormezano & Kehoe, 1981;Gormezano, Kehoe, & Marshall, 1983;Moon et al, 1994;Schindler, Gormezano, & Harvey, 1983;Schindler et al, 1984). Additional CS and US intensity manipulations have been used to provide more thorough and extensive assessments of sensory processing and motor performance (P. Chen et al, 1992;Gormezano, 1984;Gormezano & Kehoe, 1981;Gormezano et al, 1983;Moon et al, 1994;Schindler et al, 1983Schindler et al, , 1984.…”

“…Explicitly unpaired presentations of the CS and US have been used to assess the various nonassociative contributors to responding, including sensitization and pseudoconditioning, as well as providing a simple assessment of sensory perception and motor performance (P. Chen et al, 1992;Gormezano, 1984;Gormezano & Kehoe, 1981;Gormezano, Kehoe, & Marshall, 1983;Moon et al, 1994;Schindler, Gormezano, & Harvey, 1983;Schindler et al, 1984). Additional CS and US intensity manipulations have been used to provide more thorough and extensive assessments of sensory processing and motor performance (P. Chen et al, 1992;Gormezano, 1984;Gormezano & Kehoe, 1981;Gormezano et al, 1983;Moon et al, 1994;Schindler et al, 1983Schindler et al, , 1984. The manipulation of US intensity provides a means of assessing the sensory processing of the US and motor performance of the unconditioned response (UR) system being studied.…”

“…The ability to manipulate US intensity also allows us to assess the effects of classical conditioning on the UR and potential interactions of cholesterol with the UR and its modification by classical conditioning (Gruart & Yeo, 1995;Schreurs, Oh, Hirashima, & Alkon, 1995;Schreurs, Shi, Pineda, & Buck, 2000;Wikgren, Ruusuvirta, & Korhonen, 2002). Manipulating CS intensity after conditioning allows the conditioned response (CR) to act as an objective test of whether the subject can detect the CS (P. Chen et al, 1992;Moon et al, 1994;Schindler et al, 1984). Various associative aspects of classical conditioning can also be tested by the selection of specific behavioral paradigms.…”