Opposite effects of lateral septal LTP and lateral septal lesions on contextual fear conditioning in mice.

The effect of fimbrial high-frequency stimulation (HFS)-induced long-term potentiation (LTP) in the lateral septum (LS) on contextual fear conditioning was studied in mice. Mice were conditioned for fear toward a novel context through the use of footshocks. The 1st experiment showed that pretraining HFS reduced significantly conditional freezing to contextual stimuli. The 2nd experiment was designed to determine whether the reduction of freezing produced by fimbrial HFS resulted from LTP in the LS rather than from LTP in other brain structures. Accordingly, mice with lesions of the LS were used and submitted to the same protocol as in the 1st experiment. Results showed that LS lesions completely abolished the impairing effect of fimbrial HFS and, as a whole, potentiated the freezing response. These data suggest that contextual fear conditioning is strongly modulated by the level of hippocampal–LS synaptic neurotransmission. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Long-term potentiation and long-term depression in the lateral septum in spatial working and reference memory

We report two experiments conducted on a radial arm maze in the mouse showing that training could either enhance or reduce the efficacy of the fimbria-lateral septal synapses. It is suggested that the direction of change is determined by the kind of situation the animal is faced with (ie trial-dependent, respectively).     

Potentiation of conditioned freezing following dorsomedial prefrontal cortex lesions does not interfere with fear reduction in mice.

In Experiment 1, an auditory conditioned stimulus (CS) was paired with footshock, except when it was preceded by another stimulus (a visual conditioned inhibitor [CI]). After conditioning, all mice displayed less CS-evoked freezing when the CI-CS compound was presented than when the CS was presented alone. However, lesions of the dorsomedial prefrontal cortex (dmPFC) potentiated CS-evoked freezing on each of the 2 sessions (i.e., CI-CS and CS alone). In Experiment 2, mice were submitted to fear extinction (CS-alone presentation for 3 days). Lesioned mice exhibited a higher level of freezing behavior than controls on each of the 3 sessions. However, lesioned mice and controls displayed the same rate of reduction of freezing over the 3 days of extinction. These data in mice support previous studies in rats, which suggests that the dmPFC is not critical for either conditioned inhibition or extinction of acquired freezing behavior. (PsycINFO Database Record (c) 2010 APA, all rights reserved)