Table 1.

Comparison of synaptic plasticity in the direct and the indirect hippocampal afferents to anterior thalamus

		Response to
Stimulated pathway	BDNF dependence	Paired-pulse stimulation	1-Hz stimulation	HFS	LFS
Dfx	No	Facilitation	Suppression of the FP slope and amplitude	LTP of the FP slope No effect on the FP amplitude	LTD of the FP slope and amplitude
MTT	Yes	Facilitation	Suppression of the FP slope No effect on the FP amplitude	LTP of the FP slope and amplitude	LTP of the FP slope and amplitude

The opposing synaptic properties of the hippocampothalamic (dorsal fornix; Dfx) and mammillothalamic tract (MTT) pathways are represented in their basal synaptic transmission, as well as short- and long-term plasticity modifications. A use-dependent baseline augmentation is observed only at mammillothalamic synapses. Paired-pulse facilitation was present for 20-, 30- and 40-ms interstimulus intervals for the field potential (FP) amplitude of the MTT-evoked responses; Dfx paired pulses induced facilitation for 20- and 30-ms intervals. 1-Hz frequency stimulation of MTT stimulation did not affect FP amplitude, while Dfx stimuli induced a gradually developing decrease in the anterior thalamic nuclei (ATN) response. FP amplitude of the thalamic response underwent long-term potentiation (LTP) after high-frequency stimulation (HFS) application to MTT, but not to Dfx. Low-frequency stimulation (LFS) of Dfx induced stable long-term depression (LTD) of the FP parameters; however, the same stimulation protocol applied to MTT evoked mild LTP (Tsanov et al., 2010).