Biology Reference
In-Depth Information
induced, LTP at one synapse is usually not arbitrarily propagated to adjacent synapses; rather
LTP is input specific. In most cases LA-LTP is only propagated to those synapses according
to the rules of associativity and cooperativity.
Figure 1. Horizontal and coronal sections of the rodent brain. Recording (1;3) and stimulation
electrodes (2;4;5) are schematically shown. A. Bielshowsky-impregnated horizontal section of a rat
brain. B. Coronal section of a mouse brain (DAPI-staining).
LA - lateral nucleus of the amygdala; BLA - basolateral nucleus of the amygdala; EC - external
capsule.
In brain slices LA-LTP can be rapidly induced by applying brief tetanic stimuli (high
frequency stimulation - HFS) to a presynaptic input
in both, horizontal (Chapman and
Bellavance 1992b; Schubert et al. 2005) and coronal brain slices (Gean et al. 1993). It can be
supposed that inhibitory mechanisms in horizontal slices are weaker than those in coronal
slices (Samson et al. 2003). Therefore, we could establish stable HFS-induced LA-LTP
without bath application of GABA receptor antagonists by stimulating either EC or
intranuclear afferences. Tetanic stimulation applied within the LA could represent a stronger
stimulus than tetanic EC stimulation because of the involvement of intraamydaloid
glutamatergic afferences from the basolateral and medial amygdala to the LA. This leads to a
greater depolarization of the postsynaptic neurons, greater postsynaptic calcium entry and
thus enhanced LTP.
Studies done in coronal brain slices showed that the use of high frequency stimulation
needed an additional depolarization of cells (Weisskopf et al. 1999) or was only effective by
perfusing the slices with GABA receptor antagonists (Rammes et al. 2000; Watanabe et al.
1995a). Although the intrinsic connectivities within the amygdala are poorly understood, it
has been shown that stimulation of the LA effectively induces LTP in the basolateral
amygdala in coronal slices (Azad et al. 2004; DeBock et al. 2003).
TBS can be considered as a weak tetanic stimulus and considering the different
architecture of LA in comparison to the layered architecture of the
hippocampus this
stimulation paradigm is not always strong enough to activate pre- and postsynaptic sites. TBS
is sufficient to induce LA-LTP at least in horizontal slices in young rats and mice when
