Trace and contextual fear conditioning are impaired following unilateral microinjection of muscimol in the ventral hippocampus or amygdala, but not the medial prefrontal cortex

• Published in: Neurobiology of learning and memory Vol. 97; no. 4; pp. 452 - 464
• Main Authors: Gilmartin, Marieke R., Kwapis, Janine L., Helmstetter, Fred J.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier Inc 01.05.2012; Elsevier; Elsevier BV
• Subjects: Amygdala; Amygdala - drug effects; Amygdala - physiology; Animal memory; Animals; Behavioral psychophysiology; Biological and medical sciences; Conditioning, Classical - drug effects; Conditioning, Classical - physiology; Cortex (prefrontal); Disconnection; Fear & phobias; Fear - drug effects; Fear - physiology; Fear conditioning; Fear memory; Freezing Reaction, Cataleptic - drug effects; Freezing Reaction, Cataleptic - physiology; Fundamental and applied biological sciences. Psychology; GABA-A Receptor Agonists - pharmacology; Hippocampus; Hippocampus - drug effects; Hippocampus - physiology; Lidocaine; Long term memory; Male; Memory, Long-Term - drug effects; Memory, Long-Term - physiology; Microinjection; Muscimol; Muscimol - pharmacology; Nervous system; Neurobiology; Prefrontal Cortex - drug effects; Prefrontal Cortex - physiology; Prelimbic; Psychology. Psychoanalysis. Psychiatry; Psychology. Psychophysiology; Psychotropic drugs; Rats; Rats, Long-Evans; Rodents; Temporal discrimination learning; Temporal lobe; Trace fear conditioning; UCS; Temporal lobe; Fear memory; Trace fear conditioning; Prelimbic; Lidocaine; Disconnection; Affect affectivity; Amygdala; Memory; Central nervous system; Anticonvulsant; Encephalon; Learning; Medial prefrontal cortex; Acquisition process; Amygdaloid nucleus; Basal ganglion; Emotion emotionality; Prefrontal cortex; Antiarrhythmic agent; Classical conditioning; Local anesthetic; Fear; Organic amide; Hippocampus
• ISSN: 1074-7427; 1095-9564
• DOI: 10.1016/j.nlm.2012.03.009

► Trace fear conditioning requires bilateral participation of the ventral hippocampus. ► The amygdala is necessary for both trace and delay fear learning. ► Trace conditioning is more sensitive than delay to unilateral amygdala disruption. Trace fear conditioning, in which a brief empty “trace interval” occurs between presentation of the CS and UCS, differs from standard delay conditioning in that contributions from both the hippocampus and prelimbic medial prefrontal cortex (PL mPFC) are required to form a normal long term memory. Little is currently known about how the PL interacts with various temporal lobe structures to support learning across this temporal gap between stimuli. We temporarily inactivated PL along with either ventral hippocampus or amygdala in a disconnection design to determine if these structures functionally interact to acquire trace fear conditioning. Disconnection (contralateral injections) of the PL with either the ventral hippocampus or amygdala impaired trace fear conditioning; however, ipsilateral control rats were also impaired. Follow-up experiments examined the effects of unilateral inactivation of the PL, ventral hippocampus, or amygdala during conditioning. The results of this study demonstrate that unilateral inactivation of the ventral hippocampus or amygdala impairs memory, while bilateral inactivation of the PL is required to produce a deficit. Memory deficits after unilateral inactivation of the ventral hippocampus or amygdala prevent us from determining whether the mPFC functionally interacts with the medial temporal lobe using a disconnection approach. Nonetheless, our findings suggest that the trace fear network is more integrated than previously thought.