Effects of the intertrial interval on taste-aversion learning in rats

Variations in the intertrial interval (ITI) between two taste-aversion conditioning trials indicated that more saccharin-aversion learning occurs with longer ITIs (Experiments 1, 2 and 4). Two conditioning trials separated by 35 min did not produce stronger taste aversions than a single saccharin-lithium pairing; however, stronger conditioning was evident when the two trials were administered with a 3-day intertrial interval. Independent evaluation of saccharin and lithium exposure as possible sources of proactive and retroactive interference suggested that poor conditioning at short ITIs occurs because lithium treatment during Trial 1 interferes with conditioning during Trial 2 (Experiment 2). Assessments of the unconditioned suppression of activity (Experiments 3) and novel-fluid intake (Experiment 4) indicated that drug treatment was effective during both conditioning trials regardless of the intertrial interval. Furthermore, with a 35-min ITI (but not with a 3-day ITI) drug treatment in Trial 1 persisted long enough to summate with the unconditioned responses to drug treatment in Trial 2. These findings are consistent with the idea that with short ITIs the lingering effects of the US from Trial 1 overshadow or mask the CS flavor in Trial 2, and this interferes with the conditioning that Trial 2 would otherwise produce.     

Skin Conductance Conditioning to Potentially Phobic Stimuli as a Function of Interstimulus Interval and Delay Versus Trace Paradigm

Because prepared learning has been defined in terms of response acquisition in spite of degraded input, it was expected that differences in resistance to extinction between skin conductance responses conditioned to potentially phobic and neutral stimuli would increase with increased interstimulus interval (ISI) and be larger with a trace than with a delay conditioning paradigm. Twelve groups with 10 subjects each were observed in a differential conditioning experiment manipulating ISI (2, 8, or 16 sec), paradigm (delay versus trace), and fear-relevance of the conditioned stimulus (potentially phobic versus neutral). The results showed highly reliable resistance to extinction of first-interval anticipatory responses to phobic stimuli, and no resistance to extinction of the corresponding responses to the neutral stimuli. This difference did not interact either with the ISI or the paradigm factor. Thus, although underscoring the reliability of the difference in conditioning to potentially phobic and neutral stimuli, the results did not support the specific hypothesis of conditioning to phobic stimuli as being less dependent on the ISI parameters than conditioning to neutral stimuli.     

Blood Pressure and Heart Rate Changes Accompanying Classical Eyeblink Conditioning In The Rabbit (Oryctolagus Cuniculus)

In two experiments employing 38 rabbits differential classical conditioning of heart rate, blood pressure, and corneoretinal potential (CRP) response were examined using l-sec and 4-sec interstimulus intervals ISI respectively. The conditioned response consisted of HK decelerations and DP depressor responses early in conditioning. However, many, but not all, animals revealed pressor responses and HR accelerations after the CRP discrimination was acquired. Significant correlations were also obtained between BP pressor responses, HR accelerations, and the frequency of CRP CRs. These results were discussed within the context of the orienting and defense reflexes.     

Branchial ventilation rates of cataleptic goldfish (Carassius auratus) and the effects of light and electric shock

Inverted, cataleptic goldfish showed an increase in ventilation rate over a 20 min period. The time-dependent increase in respiratory movement was initially suppressed when a 10 sec light or a 0.1 sec shock was presented at 1.5 min intervals. Contingent presentation of the light and shock, in a classical conditioning paradigm, resulted in reduced ventilation rates during the session. Physiological changes accompanying conditioning may thus alter the cataleptic state.     

SELECTIVE ATTENTION AND INSTRUMENTAL MODIFICATION OF THE GSR

A series of experiments were conducted on instrumental modification of the Galvanic Skin Response (GSR) in a discrimination procedure where preparatory signals indicated which discriminative stimulus was to occur. When shock avoidance was contingent upon the presence of a response the GSR was enhanced; when shock avoidance was contingent upon the inhibition of a response there was a decrement in reactivity. Heart rate acceleration occurred to Respond stimuli while deceleration occurred to Inhibit stimuli. Various types of cognitive strategies were reported by the subjects from attempts to control attention by attending less to stimuli associated with inhibition to attempts to arouse a response by thinking of exciting events and to inhibit by thinking of calming events. Postexperimental recognition of words tended to be negatively related to magnitude of response. When the verbal stimuli served directly as discriminative stimuli, however, these relationships tended to be reversed.     

Orienting and classical conditioning in the rabbit (Oryctolagus cuniculus): effects of septal area lesions

Rabbits with either sham or septal lesions recieved differential classical conditioning training in which tones of different frequencies served as CSs and paraorbital shock served as the UCS. Eyeblink (EB), EMG, and heart rate (HR) CRs were concommitantly assessed. Free field activity was also studied in selected animals. Animals with septal lesions revealed an impaired EB discrimination which resulted from increased responding to the CS-. These animals showed HR CRs of greater magnitude than sham animals. The HR discrimination was, however, unimpaired by septal lesions. Differential EMG activity also occurred, but was unaffected by septal destruction. Septal lesions resulted in greater free-field activity associated with visual stimulation, but no differences were obtained between septal and sham animals in the dark. It is suggested that these results were due to an enhanced reactivity to environmental stimulation, possibly related to dysfunctions of the orienting reflex.     

Voluntary consumption of NaCl,KCl, CaCl2, and NH4Cl solutions by 28 mouse strains

Male mice from 28 inbred strains (129P3/J, A/J, AKR/J, BALB/cByJ, BUB/BnJ, C3H/HeJ, C57BL/6J, C57L/J, CAST/Ei, CBA/J, CE/J, DBA/2J, FVB/NJ, I/LnJ, KK/H1J, LP/J, NOD/LtJ, NZB/B1NJ, P/J, PL/J, RBF/DnJ, RF/J, RIIIS/J, SEA/GnJ, SJL/J, SM/J, SPRET/Ei, and SWR/J) were tested with NaCl (75–450 mM), KCl (30–300 mM), CaCl₂ (3–100 mM), and NH4Cl (10–300 mM) solutions using two-bottle preference tests with water as the second choice. For each mineral, there was a wide range of strain variation in solution intakes and preferences. This variation had a substantial genetic component as assessed using heritability estimates. In most cases, the strain means were continuously distributed; however, strains with deviating high or low intakes or preferences were also observed. The associations among the responses to different minerals were only modest, suggesting distinct genetic controls of sodium, potassium, calcium, and ammonium consumption. These results provide a valuable resource for investigators who wish to identify genes involved in the regulation of mineral consumption and balance.     

Hormonal control of odor preferences and urine-marking in male and female rats

Gonadectomized male and female rats show no preferences for the odors of conspecifics of the opposite sex and no urine-marking. Castrated males given testosterone propionate (TP) injections showed preferences for female odors over no odor as did males given estradiol benzoate (EB). Males given EB plus progesterone (P), P only, or oil (controls) showed no preferences for female odors. No group of ovariectomized females (TP, EB, EB+P, or oil injected) showed a preference for male odors over no odor. Males given TP, EB, or EB+P injections showed an increase in urine-marking while males given P or oil showed no marking. Females given TP injections showed an increase in marking but those given EB, EB+P or oil showed no marking. These results are discussed in relation to studies on the hormonal control of scent-marking in gerbils and sexual behaviour in rats.     

5-HT mechanisms of median raphe nucleus in the conditioned freezing caused by light/foot-shock association

We have shown that 5-HT mechanisms of the median raphe nucleus (MRN) are involved in contextual fear-conditioning processes as electrolytic or neurotoxic lesions with N-methyl-D-aspartate (NMDA) or injections of 8-hydroxy-2-(di-n-propilamino)-tetralin (8-OH-DPAT) into this structure inhibit freezing behavior in a contextual fear paradigm. In this work, we extend these studies by analyzing the behavioral responses in a classical fear-conditioning paradigm (light or tone/foot-shock association) in rats with either neurochemical lesion with NMDA or injected with 8-OH-DPAT into the MRN. The animals received NMDA or 8-OH-DPAT or saline microinjections into the MRN and were submitted to conditioning trials in an experimental chamber, where they received 10 foot-shocks (0.6 mA, 1 s, variable interval between 10 and 50 s) paired with tone or light (CS). On the next day, they were tested in a different experimental chamber, with or without CS presentation, where the duration of freezing and the number of rearing episodes were recorded. Light or tone alone caused a significant amount of freezing. NMDA lesions or 8-OH-DPAT injections into the MRN clearly inhibited freezing behavior in rats conditioned to light/foot-shock association, but not in the conditioning sessions with tones. Besides the proposed role in contextual fear conditioning, these results clearly show that MRN is involved in the fear conditioning with light as conditioned stimuli. Distinct neural substrates seem to subserve conditioning fear with acoustic stimuli.     

Rewarding properties of social interactions in adolescent and adult male and female rats: impact of social versus isolate housing of subjects and partners

Social interactions have been shown to be rewarding for adolescent and adult rats; however, there has been little emphasis on comparing the strength of the rewarding value of social stimuli across ontogeny. Since age differences in social interactions may vary with sex or housing circumstances, the present study assessed social conditioned place preference (CPP) in adolescent and adult male and female Sprague-Dawley rats housed either socially or in isolation and conditioned with either group-housed or isolate-housed partners. Isolated animals of both sexes and ages demonstrated social CPP, with the strongest preference emerging in adolescent males. Social CPP was not evident in group-housed adults whereas group-housed adolescents developed a preference for the compartment previously paired with similarly housed partners; however, when socially housed adolescents were conditioned with isolated partners, social CPP did not emerge. Age differences in social CPP may reflect age-related neural alterations in brain systems implicated in regulation of social behavior.