Effect of tooth loss on spatial memory and trkB‐mRNA levels in rats

Abstract

The mechanism by which tooth loss accelerates spatial memory impairment is unknown. The purpose of this study was to test the hypothesis that tooth loss affects trkB-mRNA levels and leads to an accelerated decrease in the hippocampal cell density in rats. A radial maze was used to evaluate the spatial memory of male Wistar rats that were categorized based on the number of extracted molar teeth. Number of hippocampal pyramidal cells and the trkB-mRNA expressions in the amygdala, perirhinal cortex, thalamus, and the hippocampal CA1, CA3, and CA4 areas, were evaluated using molecular biological techniques. Seven weeks after tooth extraction, maze performance was significantly lower in each tooth loss group than in the control group, and the number of extracted teeth was inversely proportional to the induction of the trkB-mRNA and the hippocampal cell density. The average weight of rats increased by controlled feeding throughout the experiment without showing a significant difference between the control and experimental groups. The results indicated that, in rats, the spatial memory-linked trkB-mRNA was reduced in association with the tooth loss; this supports the hypothesis and suggests that teeth have a role in the prevention of spatial memory impairment.

Decision-making deficits associated with disrupted synchronization between basolateral amygdala and anterior cingulate cortex in rats after tooth loss

“…Rodent models of decision-making, such as rat gambling task (RGT), are particularly valuable as experimental conditions can be controlled. In the current study we performed RGT eight weeks after tooth extraction, consistent with the time point showing spatial memory deficits in rats after tooth loss in another study (Yamazaki et al, 2008). We determined that tooth extraction surgery and long-term unilateral molarless had no general effect on the motivation to actively retrieve food reward (duration of the last training session before reaching the criterion).…”

“…Both human and animal studies consistently suggest that tooth loss interferes with cognitive function (Kato et al, 1997;Kim et al, 2007;Yamazaki et al, 2008;Zhu et al, 2014). In patients with multiple teeth loss, the emotional and cognitive changes are usually self-reported, which are subjective, and could be multifactorial, which include personality, appearance changing, economic status, etc.…”

“…It has been shown that reduced hippocampus cell growth and development (Onozuka et al, 1999), and the impaired cholinergic neurotransmitter system in the parietal cortex (Kato et al, 1997), or trkB-mRNA expression in multiple brain areas (Yamazaki et al, 2008) occurred in animals after tooth loss. These are compelling evidences indicating the afferent inputs play an essential role in neuronal development and plasticity.…”

“…These are compelling evidences indicating the afferent inputs play an essential role in neuronal development and plasticity. It is conceivable and strongly suggested that the loss of the periodontium following tooth extraction was a critical factor for the diminished sensory input to the central nervous system (Yamazaki et al, 2008). A retrograde tracing study has shown that the peripheral signals from orofacial afferents relay via the trigeminal ganglion, and ascend through multi-synaptic pathways from spinal trigeminal nucleus, and medial thalamus to the ACC bilaterally (Iwata et al, 2011).…”

Chewing Maintains Hippocampus-Dependent Cognitive Function

“…Masticatory stimulation may prevent degradation of senile brain function and stress-related disorders without medication. The decrease of masticatory function, by either extraction of or reduction in molars and associated long-term soft-diet feeding, can inhibit learning and memory 12, 13, 16, 18, 19, 22, 33, 34. Learning ability was shown to decrease in adult rats from 2 to 30 months after the extraction of molars 13, 28, 29.…”