Differential impairment of auditory and contextual fear conditioning by protein synthesis inhibition in C57BL/6N mice.

A 1-trial fear conditioning was used to investigate the temporal development of fear responses expressed as increase of freezing or heart rate and its impairment by the protein synthesis inhibitor cycloheximide (CHX) in male C57BL/6N mice. Heart rate was measured with an implanted transmitter. In the memory tests, mice were exposed to tone and context provided either as foreground or background stimulus during training. The fear responses developed differently from 0 to 24 hr after training under these 3 conditions. A single pretraining CHX injection impaired both memory forms, whereas a single posttraining CHX injection impaired tone- but not context-dependent memory, with the context provided as background stimulus. It was concluded that consolidation of tone-, foreground context-, and background context-dependent fear conditioning may be mediated by partly different neuronal or partly different biochemical pathways, or both. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Pharmacology and biology of corticotropin-releasing factor (CRF) receptors

The biology of corticotropin-releasing factor (CRF) finds increasing interest in the scientific community because of the neuromodulatory actions of CRF on brain functions such as learning, anxiety, feeding, and locomotion. Additional actions on immunumodulation and apoptosis have recently been discovered. All actions of CRF are mediated by G protein-coupled receptors, which trigger different, sometimes opposite actions in different regions of the central nervous system. The CRF system exhibits considerable plasticity by the involvement of numerous different ligands, splice variants, and transductional couplings. The generation of multiple splice variants is facilitated by the intron exon structure of the CRF receptor genes.     

Effect of tone-dependent fear conditioning on heart rate and behavior of C57BL/6N mice.

The effects of the temporal sequence of tone (conditioned stimulus [CS]) and footshock (unconditioned stimulus [US]) during training (acquisition) on tone-dependent retention were studied in mice. Freezing increased significantly as an associative behavioral response in mice subjected to CS paired with US or after unpaired by 30 s in the memory test performed 24 hr after training. In the home cage of freely moving mice implanted with an electrocardiogram transmitter, CS triggered a strong tachycardiac response in the memory test. Heart rate (HR) increased from about 580 bpm to more than 750 bpm, and HR variability decreased significantly. The inhibition of the HR increase by the nonspecific β-adrenergic antagonist sotalol indicated the strong sympathetic contribution to the tachycardiac response. CS evoked a significant but minor HR increase in mice subjected to either CS or US only or CS and US unpaired by 60 s. Thus, HR and HR variability reflected associative learning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Dissociation of Temporal Dynamics of Heart Rate and Blood Pressure Responses Elicited by Conditioned Fear but Not Acoustic Startle.

Fear-inducing stimuli were hypothesized to elicit fast heart rate (HR) responses but slow mean arterial blood pressure (MAP) responses and thus were studied in auditory fear conditioning and acoustic startle at high temporal resolution in freely moving mice and rats. Fear-induced instantaneous acceleration of HR reaching maximum physiological values and subsequent recovery to baseline were observed. The MAP response consisted of an immediate, mild, and transient increase followed by a sluggish, profound elevation and slow recovery. HR and MAP responses served as reliable indicators of conditioned fear in mice with dissociated temporal dynamics. Unconditioned auditory stimuli, including acoustic startle stimuli, elicited only fast, mild, and transient MAP and HR elevations in mice and rats, reflecting arousal and attention under these experimental conditions. (PsycINFO Database Record (c) 2010 APA, all rights reserved)