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Results for “fear conditioning”

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PubMed1990

Synaptic plasticity in fear conditioning circuits: induction of LTP in the lateral nucleus of the amygdala by stimulation of the medial geniculate body.

Electrical stimulation of the medial geniculate body in the anesthetized rat produces an evoked potential in the lateral nucleus of the amygdala. The potential varies in amplitude with stimulus intensity and reaches peak amplitude in 8.5 msec on the average. High-frequency stimulation of the pathway produces long-lasting increases in the amplitude and slope of the potential. These robust and enduring experience-dependent modifications in neural transmission occur in a pathway known to be involved in the formation of emotional memories and may offer a means for examining the cellular mechanisms of emotional learning, as well as a new approach to questions concerning the relevance of long-term potentiation to normal mnemonic processes.

Amygdala↗
PubMed2006

Environmental enrichment increases responding to contextual cues but decreases overall conditioned fear in the rat.

This study aimed at investigating the effects of environmental enrichment on various aspects of contextual processing in adult female rats. In experiment 1, simple conditioning was studied using either a training procedure allowing overshadowing of the contextual cues by signalling footshock with a discrete tone or a training procedure allowing a reduction of this overshadowing by explicitly unpairing the footshock and the tone. In experiment 2, contextual discrimination and contextual occasion-setting were assessed. Rats were daily exposed to two different contexts. In one context, a footshock was delivered 30s after the offset of a tone, whereas in the other context the same tone was presented alone. Experiment 3 examined familiarization to a new context. Experiment 1 showed that environmental enrichment reduced the overshadowing of contextual cues by the tone and also reduced freezing to the more predictive cue according to the training procedure used. Experiment 2 showed that environmental enrichment increased the ability of rats to discriminate two contexts. Experiment 3 showed that enriched rats familiarized faster to a new context than standard rats. Taken together, these results suggest that environmental enrichment in adult rats enhances learning about contextual cues and reduces overall fear associated with aversive events.

Acoustic Stimulation↗
PubMed2004

Contributions of the anterior cingulate cortex and amygdala to pain- and fear-conditioned place avoidance in rats.

The pain experience includes a sensory-discriminative and an affective-emotional component. The sensory component of pain has been extensively studied, while data about the negative affective component of pain are quite limited. The anterior cingulate cortex (ACC), and amygdala are thought to be key neural substrates underlying emotional responses. Using formalin-induced conditioned place avoidance (F-CPA) and electric foot-shock conditioned place avoidance (S-CPA) models, the present study observed the effects of bilateral excitotoxic (quinolinic acid 200 nmol/microl) lesions of the ACC and amygdala on pain and fear induced negative emotion, as well as on sensory component of pain. In the place-conditioning paradigm, both intraplantar (i.pl.) injection of formalin and electric foot-shock produced conditioned place avoidance. Excitotoxin-induced lesion of either the ACC or amygdala significantly reduced the magnitude of F-CPA. However, the decrease in the magnitude of S-CPA occurred only in the amygdala, but not ACC lesioned animals. Neither ACC nor amygdala lesion significantly changed formalin-induced acute nociceptive behaviors. These results suggest that the amygdala is involved in both pain- and fear-related negative emotion, and the ACC might play a critical role in the expression of pain-related negative emotion.

Amygdala↗
PubMed2001

Effect of chronic administration of flesinoxan and fluvoxamine on freezing behavior induced by conditioned fear.

The present study investigated the acute effects of flesinoxan (a selective 5-HT(1A) receptor agonist), fluvoxamine (a selective serotonin reuptake inhibitor) and their co-administration on the expression of conditioned freezing, and index of anxiety in rats. This study also examined the acute effects of fluvoxamine and flesinoxan following chronic flesinoxan or chronic fluvoxamine on the expression of conditioned freezing. Acute administration of flesinoxan (s.c.; 0.1-3 mg/kg) reduced freezing dose dependently, and fluvoxamine (i.p.) at a high dose (60 mg/kg) reduced freezing significantly. Acute co-administration of fluvoxamine (30 mg/kg) and flesinoxan (0.3 mg/kg) showed an additive inhibitory effect on freezing. Chronic flesinoxan treatment (0.3 mg/kg, for 13 days) did not affect the inhibitory effect of acute flesinoxan treatment, but enhanced that of acute fluvoxamine (30 mg/kg) on conditioned freezing. Chronic fluvoxamine treatment (30 mg/kg, for 13 days) enhanced the inhibitory effect of acute fluvoxamine (30 mg/kg) and the inhibitory effect of acute flesinoxan (0.3 mg/kg) on conditioned freezing. These results suggest that co-administration of a selective serotonin reuptake inhibitor and a 5-HT(1A) receptor agonist is useful for the treatment of anxiety disorders.

Analysis of Variance↗
PubMed2001

Impaired fear conditioning but enhanced seizure sensitivity in rats given repeated experience of withdrawal from alcohol.

Repeated experience of withdrawal from chronic alcohol treatment increases sensitivity to seizures. It has been argued by analogy that negative affective consequences of withdrawal also sensitize, but repeated experience of withdrawal from another sedative-hypnotic drug, diazepam, results in amelioration of withdrawal anxiety and aversiveness. We tested whether giving rats repeated experience of withdrawal from alcohol altered their ability to acquire a conditioned emotional response (CER). Male Hooded Lister rats were fed a nutritionally complete liquid diet as their only food source. Different groups received control diet, or diet containing 7% ethanol. Rats receiving ethanol diet were fed for either 24 days (Single withdrawal, SWD), or 30 days, with two periods of 3 days, starting at day 11, and 21, in which they received control diet (Repeated withdrawal, RWD). All rats were fed lab chow at the end of their liquid diet feeding period. Starting 12 days after the final withdrawal, groups of Control, SWD and RWD rats were given pentylenetetrazole (PTZ; 30 mg/kg, i.p.) three times a week, and scored for seizures. The occurrence of two successive Stage 5 seizures was taken as the criterion for full PTZ kindling. Other groups of control, SWD and RWD rats were trained to operate levers to obtain food, and were then exposed, in a fully counterbalanced design, to light and tone stimuli which predicted unavoidable footshock (CS+), or which had no consequences (CS-). Rats consumed approximately 17.5 g/kg/day of ethanol, resulting in blood alcohol levels of approximately 100 mg/dL. Repeated administration of PTZ resulted in increasing seizure scores. RWD rats achieved kindling criterion faster than either Control or SWD rats. No differences were seen in the groups in flinch threshold to footshock (0.3 mA). At a shock intensity of 0.35 mA, Control, but not RWD or SWD rats showed significant suppression to the CS+ CS- presentation did not affect response rates. The three groups differed in their response to pairing the CS+ with increasing shock levels, the Controls remaining more sensitive to the CS+. SWD rats showed significant suppression of lever pressing during CS+ presentations only at 0.45 and 0.5 mA, and RWD rats only at 0.5 mA. Giving rats repeated experience of withdrawal from chronic ethanol results in increased sensitivity to PTZ kindling, but reduces their ability to acquire a CER. Withdrawal kindling of sensitivity to anxiogenic events does not seem to occur under circumstances which give rise to kindling of seizure sensitivity.

Acoustic Stimulation↗
PubMed1989

Preparedness and electrodermal fear-conditioning: ontogenetic vs phylogenetic explanations.

In a review of existing theories of learning, Seligman (Psychol. Rev. 77, 406-418, 1970) suggested that humans should have an evolutionary derived preparedness to associate fear-relevant (e.g. snakes) events with aversive reinforcers. The preparedness hypothesis has been extensively tested by Ohman and his colleagues. One argument against a non-preparedness explanation for the Ohman findings has been that culturally aversive stimuli, like pictures of guns have not shown the same resistance towards extinction as pictures of snakes. However, the effect of pointing a gun directly towards the S vs pointing it to the side has not been tested. Therefore both slides of guns and snakes, directed both towards and aside from the subject, were used as conditioned stimuli (CSs) in the present study. A second question that has been discussed in the preparedness-literature is the quality of the unconditioned stimulus (UCS), i.e. if only shock can act as UCS for prepared CSs. Thus, both shock and noise UCSs were used in the present study. Skin conductance responses (SCRs) were recorded as dependent measures. The results showed conditioned acquisition, i.e. larger SCRs to CS+ than to CS-, in all groups except for the shock and noise UCS groups with the gun pointing aside as CS+ (where actually larger responses were observed to the CS-, i.e. the gun pointing towards). The extinction data showed significantly larger SCRs to CS+ than to CS- for both snakes and guns directed towards the S. Strongest resistance to extinction was observed for the group with the gun pointed towards as CS+ and with noise as UCS. The gun with noise as UCS pointed towards the S was not different from the snake with shock as UCS. Taken together, the results have shown three things; (a) directing a fear-relevant CS towards the S was a potent manipulation, and especially directing a gun with noise as UCS; (b) shock was overall not superior to noise as UCS, and especially not for snake CSs; (c) a weak form of unique belongingness was demonstrated.

Adult↗
PubMed1978

Conditioned fear and startle magnitude: effects of different footshock or backshock intensities used in training.

In Experiment 1 four groups of rats received 30 light-shock pairings using footshock intensities of either .2, .4, .8, or 1.6 mA. One day later all rats were tested for startle by presenting tones in the presence or absence of the light CS. Potentiated startle (the difference between startle on light-tone vs tone-alone trials) was nonmonotonically related to the shock intensity used in training, with the greatest potentiation at intermediate shock levels. Experiment 3 demonstrated a similar relationship when backshocks instead of footshocks were used. In Experiment 2 rats were trained with either a moderate or high shock and then given an extended extinction-test session 1 day later. The moderate-shock group showed a gradual decline in potentiated startle over extinction. The high-shock group showed a nonmonotonic extinction curve where potentiation progressively increased toward the middle of extinction and dissipated thereafter. The results suggest that acoustic startle bears an inverted U-shaped relationship to fear and are discussed in relation to other studies concerned with this issue.

Acoustic Stimulation↗
PubMed1998

Conditioned fear suppresses light-induced resetting of the circadian clock.

The possibility that circadian rhythms can be modulated by emotional state is suggested by clinical evidence of altered physiological and endocrine rhythms in primary depression and related affective disorders and is supported by experiments in humans and laboratory animals showing that stress disrupts circadian rhythmicity. How emotional state might modulate circadian rhythms is not known. Here we report that induction of the emotional state of fear disrupts a process essential for stable entrainment of circadian rhythms, the resetting of the circadian clock by environmental light. A cellular correlate of light-induced clock resetting, expression of the transcription factor Fos in the suprachiasmatic nucleus of the hypothalamus (the circadian clock), and a behavioral measure of clock resetting, phase shifts in free-running activity rhythms, were found to be suppressed in rats exposed to light in a context made to induce fear by previous pairings with intermittent footshock. These findings show that fear disrupts a physiological process mediating light-induced clock resetting and suggest a mechanism through which emotional state could modulate circadian rhythms.

Animals↗