Cholinergic modulation of tonic immobility in the rabbit (Oryctolagus cuniculus).

The present study was performed to determine the effects of the anticholinergic agent scopolamine and the cholinergic agent physostigmine on tonic immobility in rabbits. Recordings of the electroencephalographic (EEG) activity from cortex and hippocampus were also made before, during, and after each test session. Scopolamine significantly prolonged the response and produced large amplitude slow wave activity in the EEG of both cortex and hippocampus. Physostigmine significantly shortened the duration of immobility and increased rhythmic slow activity in the frequency range of 5.5-9.1 Hz in the hippocampus while producing a desynchronized cortical rhythm. It is suggested that the cortex and hippocampus play a role in modulating tonic immobility duration by inhibiting the brain-stem structures thought to control this response.     

Unconditional-stimulus locus and interstimulus-interval shift in rabbit(Oryctolagus cuniculus) nictitating membrane conditioning

The nictitating membrane response of rabbits was conditioned at a 200 msec interstimulus interval (ISI) with either circumorbital (C) or paraorbital (P) shock as the unconditional-stimulus locus. After 3 acquisition days half of each group was shifted to a 700 msec interstimulus interval. Results indicated: (1) more rapid acquisition for Group C, (2) postshift response decrements for both groups, (3) more rapid and stable, as well as complete return to preshift performance levels for Group C. Results were discussed in terms of the response-shaping hypothesis and the contiguity-substitution hypothesis in explaining both conditional response emergence and subsequent modifications of CR topography.     

Neuronal unit activity in the abducens nucleus during classical conditioning of the nictitating membrane response in the rabbit (Oryctolagus cuniculus).

Neuronal unit activity was recorded from the abducens (6th nerve) nucleus, the "final common path," during classical conditioning of the nictitating membrane (NM) response in the rabbit, with the use of a tone conditioned stimulus, an air puff unconditioned stimulus (UCS), 250-msec interstimulus interval, and 60-sec intertrial interval. Animals were given 2 days of conditioning training (104 trials in eight blocks per day) and 1 day of extinction. Control animals were given comparable periods of stimulus presentations, explicitly unpaired. Activity of small clusters of units--"multiple unit" recording--was compared with the amplitude-time course of the NM response. Between-blocks comparisons of neural and behavioral responses indicated an essentially perfect correlation during acquisition of the conditioned response (Day 1, r = .99; Day 2, r = .98) and a slightly lower correlation during extinction (r = .93) for the conditioning animals. Within-blocks comparisons indicated a close correspondence between the histograms of unit activity and the amplitude-time course of the NM response for the conditioning animals in all phase of training and for the control animals in the UCS trial blocks.     

The effects of interpolated US alone (USa) presentations on classical nictitating membrane conditioning in rabbit(Oryctolagus cuniculus)

The nictitating membrane (NM) response of 36 rabbits was classically conditioned using a 1,000-Hz tone (CS) paired with circumorbital shock (US) at a 250-msec CS-US interval. Two experimental groups received additional presentations of the US given alone (USa), either 30 seconds (Group E30) or 60 seconds (Group E60) following each CS-US pairing, and their performance was compared to that of control Ss (Group C60) which never experienced USa. Presentations of USa resulted in significant and approximately equal performance decrements in both experimental groups relative to the C60 controls. However, no significant differences among the groups appeared during an extinction phase. The effects of USa presentations were discussed in terms of Papsdorf’s consolidation interpretation and Rescorla’s (1967) contingency theory of conditioning, and appeared to favor the latter view. Additional analyses led to the conclusions that (1) the increased amplitude of the NM UR on paired CS-US trials relative to USa trials can be attributed, at least in part, to the simple laws of the reflex, independent of the conditioning processper se, and (2) the partial reinforcement extinction effects previously reported by Leonard and Theios (1968) cannot be attributed solely to the presence of USa in their continuous reinforcement control Ss.     

Timing in trace conditioning of the nictitating membrane response of the rabbit (Oryctolagus cuniculus): scalar, nonscalar, and adaptive features

Using interstimulus intervals (ISIs) of 125, 250, and 500 msec in trace conditioning of the rabbit nictitating membrane response, the offset times and durations of conditioned responses (CRs) were collected along with onset and peak latencies. All measures were proportional to the ISI, but only onset and peak latencies conformed to the criterion for scalar timing. Regarding the CR's possible protective overlap of the unconditioned stimulus (US), CR duration increased with ISI, while the peak's alignment with the US declined. Implications for models of timing and CR adaptiveness are discussed.     

Consequences of response-contingent change in unconditioned stimulus intensity upon the rabbit (Oryctolagus cuniculus) nictitating membrane response.

In a between-groups design, an instrumental contingency was superimposed on classical conditioning of the rabbit nictitating membrane response. Subjects were exposed to a tonal conditioned stimulus (CS) and, if no conditioned response (CR) occurred, a 5.0-ma. paraorbital electric shock unconditioned stimulus (US). USs of 5.0, 3.3, 1.7, and 0.0 ma., respectively, were contingent on occurrence of a CR in the CS-US interval for subjects in the 4 groups of the experiment. The group exposed to contingent US omission differed from the other 3 groups in percentage CR, onset latency, amplitude, and 2 indices of CR form, and those 3 groups generally did not differ significantly among themselves on these dependent variables. Results were interpreted to be contrary to "law of effect" formulations of classical conditioning.     

Apparatus exposure produces profound declines in conditioned nictitating-membrane responses to discrete conditioned stimuli by the rabbit (Oryctolagus cuniculus)

The present experiments demonstrated that in the rabbit (Oryctolagus cuniculus) nictitacing-membrane (NM) preparation, exposure to the experimental apparatus produces profound declines in conditioned responding to a discrete conditioned stimulus (CS; Experiments 1, 2A, and 3). Moreover, this decremental effect is at most attenuated in only a minor way when the unconditioned stimulus (US) is presented during exposure to the apparatus (Experiment 2B). Controls for retention loss (Experiments 1 and 3) and for handling and placement in a different context (Experiment 3) did not produce significant declines in responding. These findings challenge theories of extinction that rely primarily on context-US associations but are more consistent with theories that assume context-CS-US associations.     

Backward conditioning in Pavlovian type studies

Authors of almost all learning texts have indicated that unconditional/ stimulus-conditional stimulus (UCS-CS) trials (backward conditioning) utilized in classical conditioning experiments will not result in establishing a conditional response (CR) (excitation). Recently, it has been proposed that backward conditioning can take place although whether UCS-CS trials result in excitation or inhibition has been left unspecified. It is proposed that the diversity of findings can be attributed to inadequate methodology and the use of a classical-instrumental transfer paradigm. When only traditional Pavlovian conditioning studies are examined, the experimental findings suggest that UCS-CS trials will result in inhibition.     

Conditioning the unconditioned response: modification of the rabbit's (Oryctolagus cuniculus) unconditioned nictitating membrane response

Conditioning-specific reflex modification (CRM) occurs when classical conditioning modifies responding to an unconditioned stimulus (US) in the absence of a conditioned stimulus (CS). Three experiments monitored rabbit nictitating (Oryctolagus cuniculus) membrane unconditioned responses to 5 intensities and 4 durations of periorbital electrical stimulation before and after CS or US manipulation. CRM occurred after 12 days of CS-US pairings but not following unpaired CS/US presentations or restraint. CRM survived CS-alone and CS/US-unpaired extinction of the conditioned response (CR) but not presentations of the US alone, although CRs remained intact. Thus, CRs could be weakened without eliminating CRM and CRM could be weakened without eliminating CRs. Data indicate CRM is a reliable, associative effect that is more than a generalized CR and may not be explained by habituation, stimulus generalization, contextual conditioning, or bidirectional conditioning.     

Backward conditioning: mediation by the context

The information acquired in backward conditioning (i.e., outcome-->cue) was assessed in 3 Pavlovian lick-suppression experiments with water-deprived rats as subjects. Experiment 1 confirmed previous research that few outcome-->cue pairings made the cue into a conditioned excitor and additionally showed that massive posttraining extinction of the training context attenuated a backward-trained cue's excitatory value. Experiment 2 found that many outcome-->cue pairings made the cue into a conditioned inhibitor and that the same context manipulation attenuated this inhibitory value. Experiment 3 confirmed the observations of Experiments 1 and 2 and demonstrated that these effects of context extinction were specific to backward-trained cues conditioned in the extinguished context. These results are interpreted in terms of cue-->context and context-->outcome associations.     

Intrafemale agonistic interactions in the domestic rabbit (oryctolagus cuniculus L.)

Agonistic interactions between adult domestic rabbit females were observed. Females were housed in groups of four in outdoor enclosures measuring 4 × 4 m. Agonistic patterns included aggression (AG), flight (FL), and submission (SB). Observations focused on 1) initial interactions between unfamiliar females, concomitant with the formation and establishment of a social structure (Phase 1); and 2) interactions between familiar females organized in a stable social structure (Phase 2). AG was frequent between unfamiliar females and appeared related to the acquisition of social dominance. When social organization was settled, there was a dramatic reduction in the number and frequency of aggressive behaviors. Similarly, FL was more frequent when females were unfamiliar, but it did not appear to be merely a response to AG. The decreased frequency of both AG and FL in Phase 2 was paralleled by an increased frequency of SB with respect to FL. Under stable social conditions, subordinate females frequently signalled submission to dominant counterparts. In contrast, the latter did not signal their social status with any consistent behavioral pattern. It follows that SB was not necessarily induced as the appropriate response to aggression given by dominant females. Thus, SB appeared relevant in social communication especially in structured groups, where it conveyed information on the actor's subordination and possibly inhibited the receiver's aggression. A further possibility is that it has an autonomous rather than secondary role in the maintenance of stable dominance/subordination relationships.     

Heart rate changes during conditioning-specific reflex modification of the rabbit's (Oryctolagus cuniculus) nictitating membrane response

Conditioning-specific reflex modification (CRM) of the rabbit's nictitating membrane response (NMR) involves changes in responding to an unconditioned stimulus (US) when the US is tested in the absence of the conditioned stimulus. Previous experiments have shown that CRM is a function of the type and intensity of the aversive US used during classical conditioning. As a result, it has been suggested that CRM may be mediated, at least in part, by the aversiveness of the US. Here, we show that by using a moderately intense electrical pulse to the skin as a US, CRM of the rabbit NMR is accompanied by an increase in heart rate. The largest changes in heart rate occur at US intensities that produce the strongest levels of CRM. The heart rate data show that there may be an increased emotional/arousal component to the US that is correlated with CRM and support the use of CRM as a potential model for posttraumatic stress disorder.     

Backward conditioning as an extinction procedure

In two conditioned suppression experiments, rats received Pavlovian forward defense conditioning in which tonal conditioned stimuli (CSs) terminated with the onset of scrambled grid shock unconditioned stimuli (USs). After this experience, the rats then received a Pavlovian backward conditioning procedure in which the same USs now terminated with the onset of the same CSs. Although the two experiments differed greatly in terms of CS and US parameters, number of forward and backward pairings, and in terms of the general techniques used to establish and measure the Pavlovian conditioned response (CR), the results of both experiments agreed in showing that backward conditioning can indeed weaken a CR based on forward pairings. The results also show that, under some conditions, the backward procedure can be at least as effective in weakening an established CR as the traditional CS-alone extinction procedure; but, under other conditions, the backward procedure is less effective and leads to more spontaneous recovery than the CS-alone procedure.     

Social environment and reproduction in female European rabbits (Oryctolagus cuniculus): benefits of the presence of litter sisters

The authors investigated in an observational study the consequences of the presence of litter sisters on the social interactions and on reproductive performance of young female European rabbits (Oryctolagus cuniculus) from a population living under seminatural conditions. In early winter, when all young females were settled in a social group, they were characterized by the presence or absence of litter sisters in their groups. Females with litter sisters in their groups displayed significantly more positive social interaction with females of their social group compared to females without sisters, whereas this difference was mainly due to the high frequency of positive social interactions among the respective sisters. Such differences between the females of both categories were already apparent during the animals' juvenile phase, before the females integrated into a particular group: females which later had litter sisters in their group showed more positive social behavior than females which later no longer had litter sisters. During their first breeding season, females with litter sisters present generally started to breed earlier by an average of 14 days. A more favorable social environment might have possibly facilitated the earlier onset of breeding in females with present litter sisters by attenuating the negative consequences of stress.