Introduction Neural circuits which are involved in fear/threat learning and emotional memory have been studied in various ways including human subjects and laboratory animals. We will first discuss the basic circuits involved in fear conditioning and emotional memory learning. After that, two specific systems – norepinephrine (NE) projections from locus coeruleus (LC) and serotonin (5-HT) projections from dorsal raphe nuclei (DR) – and its effects on threat learning and fear conditioning will be discussed. Locus Coeruleus and its projections to other regions involved in threat learning
The locus coeruleus (LC) is the largest nucleus of noradrenergic neurons in the central nervous system and is located in the pons. The excitation of …show more content…
(2013) tested the hypothesis that orexin neurons phasically activate LC neurons during an aversive event to enable threat learning. To test the hypothesis that orexin carries information important for aversive memory formation, they blocked the OrxR1 activity of an auditory threat conditioning paradigm. The OrxR1 antagonist SB 334867 was administrated by intracerebro-ventricular infusion before fear conditioning and conditioned freezing behavior was examined. Here, a freezing behavior is considered to be a general reaction to perceived threat in a long-term memory (LTM) test. The results showed that freezing behavior was impaired during LTM When SB 334867 infusions were made before training. Therefore, it can be said that OrxR1, specifically during the training phase, is required for normal threat memory …show more content…
Behavioral pharmacology experiments revealed no direct role for OrxR1 signaling in the lateral nucleus of the amygdala in the formation of threat memories. Because orexin projections and OrxR1s are dense in the LC, orexin positively modulates the activation of LC neurons. Furthermore, the LC is a major source of the NE, which is greatly implicated in aversive memory formation, it was hypothesized that local blockade of OrxR1 in LC during the learning period would impair threat memory formation. As expected, the experimental results showed that pharmacological blockade of OrxR1 signaling in LC before conditioning reduced threat memory formation. Therefore, it can be said that OrxR1 signaling in LC is important during the learning period of aversive memory
The locus coeruleus (LC) is the largest nucleus of noradrenergic neurons in the central nervous system and is located in the pons. The excitation of …show more content…
(2013) tested the hypothesis that orexin neurons phasically activate LC neurons during an aversive event to enable threat learning. To test the hypothesis that orexin carries information important for aversive memory formation, they blocked the OrxR1 activity of an auditory threat conditioning paradigm. The OrxR1 antagonist SB 334867 was administrated by intracerebro-ventricular infusion before fear conditioning and conditioned freezing behavior was examined. Here, a freezing behavior is considered to be a general reaction to perceived threat in a long-term memory (LTM) test. The results showed that freezing behavior was impaired during LTM When SB 334867 infusions were made before training. Therefore, it can be said that OrxR1, specifically during the training phase, is required for normal threat memory …show more content…
Behavioral pharmacology experiments revealed no direct role for OrxR1 signaling in the lateral nucleus of the amygdala in the formation of threat memories. Because orexin projections and OrxR1s are dense in the LC, orexin positively modulates the activation of LC neurons. Furthermore, the LC is a major source of the NE, which is greatly implicated in aversive memory formation, it was hypothesized that local blockade of OrxR1 in LC during the learning period would impair threat memory formation. As expected, the experimental results showed that pharmacological blockade of OrxR1 signaling in LC before conditioning reduced threat memory formation. Therefore, it can be said that OrxR1 signaling in LC is important during the learning period of aversive memory