Conditioning and reflex modification of the rabbit nictitating membrane response using electrical stimulation in auditory nuclei.

Electrical brain stimulation (EBS) was applied to four nuclei in the auditory system, namely, the cochlear nucleus (CN), superior olive (SO), inferior colliculus, and medial geniculate. EBS was also applied to the pontine nuclei, which are the main relays for transmitting auditory conditioned stimuli (CSs) into the cerebellar pathways for conditioning of the nictitating membrane response (NMR). EBS of the CN, but no other site, yielded reflex modification, which was an increase in the unconditioned NMR to an airpuff unconditioned stimulus (US) when preceded by EBS.

Elicitation, modification, and conditioning of the rabbit nictitating membrane response by electrical stimulation in the spinal trigeminal nucleus, inferior olive, interpositus nucleus, and red nucleus.

Elicitation of responses by electrical brain stimulation (EBS) was related to the synaptic distance of the target nucleus from the accessory abducens. Specifically, responses to EBS in the spinal trigeminal nucleus (TRIG) and red nucleus (RN) increased as a positive function of stimulation parameters. Responding to EBS in the interpositus nucleus (IP) was lower, and responding to EBS in the inferior olive (IO) was negligible.

Effects of subanesthetic concentrations of isoflurane and their interactions with epinephrine on acquisition and retention of the rabbit nictitating membrane response.

Background: Evidence concerning the concentrations of volatile anesthetics that prevent learning and recall is limited. Epinephrine is believed to enable learning during anesthesia. We investigated the effects of isoflurane and its interaction with epinephrine on learning and subsequent retention of the rabbit's classically conditioned nictitating membrane response.

Nitrous oxide: sensory, motor, associative, and behavioral tolerance effects in classical conditioning of the rabbit nictitating membrane response.

Experiment 1, of a series of six experiments with the rabbit nictitating membrane response (NMR) preparation, revealed that nitrous oxide (0%, 33%, 67%) impaired acquisition of conditioned responses (CRs). Subsequent experiments indicated that nitrous oxide (N2O) had no reliable effects upon nonassociative processes (Experiment 2); impaired unconditioned response (UR) amplitude (Experiment 3); attenuated tone-conditioned stimulus (CS) intensity (Experiment 4); decremented tone-induced reflex modification of the unconditioned NMR (Experiment 5); and demonstrated no reliable evidence of behavioral tolerance (Experiment 6). It was concluded that N2O's impairment of CR acquisition was attributable to its attenuation of the intensity of tone CSs and shock USs and/or UR amplitude.

MDA effects on classical appetitive conditioning of the rabbit jaw movement response.

We determined MDA's effects on: (a) conditioning of the rabbit's jaw movement response (JMR) (Experiment 1); and (b) nonassociative JMRs and unconditioned JMRs (Experiment 2). Rabbits were administered 3,4-methylenedioxyamphetamine (MDA; 0, 2, or 4 mg/kg) into the marginal ear vein 20-30 min prior to each of 10 daily sessions. Experiment 1 involved 30 daily training trials of 15 tone- and 15 light-conditioned stimuli (CSs) paired with a 1-ml squirt of water, as the unconditioned stimulus (UCS), injected into the oral cavity.

Effects of MDA upon differential serial compound conditioning and reflex modification of the rabbit's nictitating membrane response.

The present investigations sought to determine the effects of 3,4-methylenedioxyamphetamine (MDA) on: 1) differential conditioning of the rabbit's nictitating membrane response to the serial compounds A-X-US (tone-light-reinforced compound) and B-X (white noise-light-unreinforced compound) by examining differential responding to A and B and their conditional control over responding to X within the compounds (Experiment 1); and 2) the ability of the compound stimuli and their components to modify the amplitude of the unconditioned nictitating membrane response (Experiment 2). Experiment 1 revealed that MDA decremented differential responding to the serial compounds and their A and B components, while enhancing conditioned responding to the X component. In addition, Experiment 2 indicated that MDA attenuated reflex modification to the compounds and their A and B components, but facilitated reflex modification to X alone.

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

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.

Second-order conditioning of the rabbit's nictitating membrane response. Interstimulus interval and frequency of CS-CS pairings.

Second-order conditioning of the rabbit's nictitating membrane response (NMR) was investigated when second-order trials (CS1-CS2) were intermixed with first-order trials (CS2-US) from the outset of training. Experiment 1 showed that CR acquisition to CS1 was inversely related to the CS1-CS2 interval but nevertheless extended to an interval of 8,400 ms. Experiment 2 revealed that CR acquisition of CS1 was an inverted-U function of the number of CS1-CS2 trials relative to a fixed number of CS2-US trials.

Conditioning of the rabbit's nictitating membrane response to a CSA-CSB-US serial compound: manipulations of CSB's associative character.

Response acquisition to a trace conditioned stimulus (CSA) can be facilitated by insertion of a second stimulus (CSB) at the end of the trace interval just before the unconditioned stimulus (US). This effect may arise from serial mediation of trace conditioning, second-order conditioning, or both. Whereas serial mediation relies only on the presence of CSB, associative transfer relies on CSB's associative strength.

Morphine's effects on differential serial compound conditioning and reflex modification of the rabbit's (Oryctolagus cuniculus) nictitating membrane response.

This study sought to determine the effects of morphine (0, 2, and 5 mg/kg) on (a) differential classical conditioning of the rabbit's (Oryctolagus cuniculus) nictitating membrane response (NMR) to the serial compounds A-X-unconditioned stimulus (US) and B-X-US (Experiment 1) and (b) the reflex modification effects of the compounds and their components (Experiment 2). These experiments determined specifically morphine's effects on the distinctiveness and time course of stimulus representations by examining morphine's dose-response effect on (a) differential responding to A and B and their conditional control over responding to X within the compounds and (b) the unconditioned excitatory effects of the compounds and their components as assessed by their ability to modify the amplitude of the unconditioned NMR. The results of these experiments indicate that morphine, in a dose-dependent manner, can operate to profoundly attenuate the distinctiveness and persistence (short-term memory) of stimulus representations.

Effects of cocaine on conditioning of the rabbit nictitating membrane response.

Two experiments were conducted to determine cocaine's (0, 1, 3, and 6 mg/kg) effects on associative, nonassociative, and motor processes in classical conditioning of the rabbit's nictitating membrane response (NMR). In Experiment 1, acquisition training consisted of tone- and light-conditioned stimuli (CSs) each paired on separate trials with a shock unconditioned stimulus (UCS). Cocaine injected prior to each session significantly impaired acquisition of conditioned responses (CRs).

Effects of MDA on classical conditioning of the rabbit nictitating membrane response.

In Experiment 1, classical conditioning of the rabbit's nictitating membrane response (NMR) was accomplished by pairing tone and light conditioned stimuli (CSs) with a shock unconditioned stimulus (UCS). MDA impaired the acquisition of conditioned responses (CR) to a tone-CS, while significantly enhancing CR acquisition to a light-CS. Experiment 2, employing explicitly unpaired CS, UCS training, revealed no reliable effects of MDA upon nonassociative processes.

Electrical stimulation of brainstem nuclei: elicitation, modification, and conditioning of the rabbit nictitating membrane response.

Electrical stimulation of the reticular formation, pars oralis of the spinal trigeminal, abducens, and accessory abducens nuclei was used to assess the role of these sites in the elicitation, reflex modification, and classical conditioning of the rabbit's nictitating membrane response (NMR). Although electrical brain stimulation of the targeted sites revealed comparable levels of unconditioned responses, the spinal trigeminal nucleus was the only site at which reflex modification and conditioned response acquisition occurred reliably. These findings suggest that a locus of conditioned stimulus and unconditioned stimulus interaction, mediating either or both reflex modification and NMR conditioning, is on the sensory side of the reflex arc, at the pars oralis of the spinal trigeminal nucleus.

Effects of LSD on classical conditioning as a function of CS-UCS interval: relationship to reflex facilitation.

Classical conditioning of the rabbit nictitating membrane response was accomplished by presenting a 100-msec tone CS at intervals 0, 100, 200, 400 and 800 msec before the presentation of a 100-msec shock UCS. In addition, tone-alone trials were used to monitor CR acquisition and shock-alone trials to measure facilitation of the nictitating membrane reflex by the tone CS at the various CS-UCS intervals. LSD at a dose of 13 micrograms/kg (30 nmol/kg) increased the excitatory effects of the shock UCS as measured by a greater frequency and amplitude of UCRs elicited across a wide range of UCS intensities and by the ability of a low intensity shock to produce reflex facilitation.

Effects of morphine, ethylketocyclazocine, U-50,488H and naloxone on the acquisition of a classically conditioned response in the rabbit.

A series of five experiments examined the effects of mu and kappa opioid agonists on acquisition of conditioned responses in the rabbit and the antagonism of their effects by naloxone. Extension of the nictitating membrane was classically conditioned to a tone stimulus presented before delivery of an electric shock unconditioned stimulus to the skin over the paraorbital region of the head. Morphine, ethylketocyclazocine and U-50,488H retarded the acquisition of conditioned responses to the tone conditioned stimulus with ethylketocyclazocine being twice as potent as the more specific kappa agonist U-50,488H, and 40 times more potent than the prototypic mu agonist morphine.

Differential conditioning of the rabbit's nictitating membrane response to serial compound stimuli.

Three experiments were conducted to determine the time course and contents of CS representations through an examination of differential conditioning of the rabbit's nictitating membrane response to two serial compounds. One compound (A-X+) was always paired with the unconditioned stimulus, and the other (B-X-) was always presented alone. All three experiments entailed manipulation of the interstimulus interval between the initial distinctive element of each compound (A and B) and the second, shared element (X).

Effects of morphine, ethylketocyclazocine, and N-allylnormetazocine on classical conditioning of the rabbit nictitating membrane response.

The rabbit's nictitating membrane response was classically conditioned to tone and light conditioned stimuli presented for 800 ms before delivery of a 100-ms unconditioned shock stimulus. Both the mu receptor agonist morphine (5 mg/kg) and the kappa receptor agonist ethylketocyclazocine (1 mg/kg) significantly retarded the acquisition of conditioned responses (CRs). The retardant effects of both morphine and ethylketocyclazocine on CR acquisition could still be detected when the rabbits were tested 5 days after cessation of drug injections.

Effect of LSD on acquisition, maintenance, extinction and differentiation of conditioned responses.

Three experiments were conducted to compare the effects of LSD (30 nmol/kg) on the acquisition, maintenance, extinction and differentiation of the rabbit's classically conditioned nictitating membrane response. LSD significantly enhanced the acquisition of conditioned responses to tone and light conditioned stimuli as compared with vehicle injected controls (Experiments 1 and 2), but had no detectable effect on differential conditioning in Experiment 3. The conditioned responses acquired under LSD in Experiments 1 and 2 exhibited some unusual features in that: they were more rapidly extinguished under continued injections of LSD; they demonstrated a significant decrement when animals were switched from LSD to vehicle during maintenance; and they were virtually eliminated when animals were switched from LSD to vehicle during extinction.

Relationship between heterosynaptic reflex facilitation and acquisition of the nictitating membrane response in control and scopolamine-injected rabbits.

Classical conditioning of the rabbit nictitating membrane response was accomplished by presenting a 100-msec tone conditioned stimulus at intervals of 0, 100, 200, 400, and 800 msec before the presentation of a 100-msec shock unconditioned stimulus. In addition, tone-alone and shock-alone trials were interspersed during conditioning. On the first day of conditioning, during which there was no evidence of acquisition of conditioned responses to the tone conditioned stimulus, the amplitudes of the nictitating membrane response evoked on paired tone-shock trials were compared with the amplitudes obtained on shock-alone trials to provide a measure of reflex facilitation.

Appetitive differential conditioning of the rabbit's jaw movement response. Effects of cue similarity and US magnitude.

Two experiments examined appetitive differential conditioning of the rabbit's jaw movement response (JMR) in a two-phase procedure. The first phase entailed reinforced training with one conditioned stimulus (CS+), and the second phase involved intermixed presentations of CS+ and an unreinforced stimulus (CS-). In Experiment 1, CS+ was a 600-Hz tone, and CS- was either a 660-, 1,000-, or 2,100-Hz tone.

Effects of morphine and LSD on the classically conditioned nictitating membrane response.

Two experiments were carried out to determine the effects of LSD and morphine on the unconditioned nictitating membrane response of the rabbit elicited by 5 intensities of a 100 msec puff of air directed at the cornea, and on the acquisition of conditioned responses to a tone and light conditioned stimulus using the air-puff as an unconditioned stimulus. In Experiment 1, LSD tartrate (0.013 mg/kg) had no effect of the frequency, amplitude, magnitude or latency of the unconditioned response.

The role of the accessory abducens nucleus in the rabbit nictitating membrane response.

Electrolytic and knife-cut lesions were employed in the rabbit to examine the role of the VIth cranial nerve, and of the motoneurons in the abducens (ABD) and accessory abducens (ACC) nuclei that supply the VIth nerve, in the reflex extension of the nictitating membrane. The nictitating membrane response (NMR) was elicited by tactual stimulation of the cornea with a puff of air or by electric shock delivered to the skin over the paraorbital region of the head. Total destruction of the VIth nerve or interruption of all ACC inputs to the VIth nerve (while leaving ABD inputs intact) produced a large and comparable reduction in the magnitude of the NMR elicited by air puff, although a small residual NMR of less than 1 mm could still be detected.

Sensory and associative effects of morphine and naloxone in classical conditioning of the rabbit nictitating membrane response.

In Experiment I, classical conditioning of the rabbit's nictitating membrane response was accomplished by the pairing of tone and light conditioned stimuli with a shock unconditioned stimulus applied to the paraorbital region of the head. Morphine (5 mg/kg) significantly retarded the acquisition of conditioned responses to both conditioned stimuli. Moreover, morphine had no effect on nonassociative responding (baseline responding or responding to tone and light stimuli) or on the latency and amplitude of the unconditioned response elicited by shock during the explicitly unpaired presentations of tone, light and shock stimuli.

Effect of morphine on acquisition of the classically conditioned nictitating membrane response of the rabbit.

The nictitating membrane response of the rabbit was classically conditioned to tone and light-conditioned stimuli presented for 800 msec before delivery of the unconditioned stimulus, consisting of a 100-msec electrical shock to the skin over the paraorbital region of the head. Morphine significantly retarded (1 and 5 mg/kg) or completely blocked (10 mg/kg) the acquisition of conditioned responses. The retarded or blocked acquisition of conditioned responses produced by morphine could still be detected when the rabbits were tested 5 days after cessation of drug injections, suggesting that morphine was affecting acquisition and not performance of conditioned responses.

Effects of scopolamine and methylscopolamine on classical conditioning of the rabbit nictitating membrane response.

Classical conditioning of the rabbit nictitating membrane response was accomplished by presenting tone- and light-conditioned stimuli for 800 msec before delivery of a 100-msec shock as the unconditioned stimulus. Scopolamine significantly retarded the rate of acquisition and final asymptotic performance of conditioned responses to the tone- and light-conditioned stimuli. Methylscopolamine was approximately 20 times less potent than scopolamine in retarding the rate of acquisition, and had no effect on the final asymptotic performance of conditioned responses.