Hippocampal synaptic transmission and LTP in vivo are intact following bilateral vestibular deafferentation in the rat

Abstract

Numerous studies in animals and humans have shown that damage to the vestibular system in the inner ear results in spatial memory deficits, presumably because areas of the brain such as the hippocampus require vestibular input to accurately represent the spatial environment. Consistent with this hypothesis, studies in animals have demonstrated that complete bilateral vestibular deafferentation (BVD) causes a disruption of place cell firing as well as theta activity. The aim of this study was to investigate whether BVD in rats affects baseline field potentials (field excitatory postsynaptic potentials and population spikes) and long-term potentiation (LTP) in CA1 and the dentate gyrus (DG) of awake freely moving rats up to 43 days post-BVD and of anesthetized rats at 7 months post-BVD. Compared to sham controls, BVD had no significant effect on either baseline field potentials or LTP in either condition. These results suggest that although BVD interferes with the encoding, consolidation, and/or retrieval of spatial memories and the function of place cells, these changes are not related to detectable in vivo decrements in basal synaptic transmission or LTP, at least in the investigated pathways.

Reduction of long-term potentiation at Schaffer collateral-CA1 synapses in the rat hippocampus at the acute stage of vestibular compensation

“…A previous experimental study observed no significant changes in LTP induction in the CA1 area and dentate gyrus of awake and anesthetized rats 1~7 months following bilateral labyrinthectomy [15]. Transient activation of the peripheral vestibular system by passive whole-body rotation enhances LTP via activation of cholinergic septohippocampal cells in the CA1 area in freely behaving rats [16].…”

“…Bilateral labyrinthectomy did not affect the induction and maintenance of LTP in the hippocampal CA1 area in rats 6 weeks after surgery [15]. The induction rate of LTP in the CA1 area by passive whole-body rotation was higher than by immobility in the CA1 area of behaving rats [16].…”

Vestibular stimulation enhances hippocampal long-term potentiation via activation of cholinergic septohippocampal cells

“…This is consistent with our results in which facilitation of LTP was observed when the rat was tetanized during whole-body passive rotation compared to during awake-immobility. A recent study showed that bilateral ablation of the vestibular apparatus had no effect on hippocampal LTP in behaving rats [52]. However, the latter study did not investigate LTP induced during different behaviors such as walking and rotation.…”

The Effects of Bilateral Vestibular Loss on Hippocampal Volume, Neuronal Number, and Cell Proliferation in Rats

“…This spatial memory impairment is likely to be related to hippocampal dysfunction, since both place cell responses (Stackman et al, 2002; Russell et al, 2003b) and theta rhythm have been reported to be abnormal (Russell et al, 2006; Neo et al, 2012; Tai et al, 2012; but see Stackman et al, 2002 for conflicting evidence regarding theta rhythm). On the other hand, CA1 and dentate gyrus (DG) field potentials and long-term potentiation (LTP) in vivo were not significantly affected by bilateral vestibular loss (Zheng et al, 2010a). …”