Malocclusion is often encountered in clinical, especially young individuals. Among older
patients, poor mastication due to tooth loss results in functional deficiency, and being suggested
as risk factor of Alzheimer. However, little research has been done in developing animals. This
study aimed to explore the effects of BTXA-induced masticatory hypofunction on cognitive
function of learning and spatial memory as a result of neuropathological change in the
hippocampus in developing rats.
「Materials and Methods」
4-week-old male Wistar rats (N = 20) were randomly divided into control and BTXA-injected
groups. Total dose of 1U BTXA was prepared for each rat in experimental group, being injected
in bilateral masseter muscle on day 1. Conversely, the same amount of sterile, nonpreserved
0.9% normal saline was injected in control group. In the 4th week, the rats were tested in Morris
water maze for five consecutive days. After concluding the maze, rats were sacrificed on day 28,
and their brains were collected for evaluation of neuropathological changes in the hippocampus
through Nissl staining and phosphorylated cyclic adenosine 3',5'-monophosphate (cAMP)
response element binding protein (CREB) immunohistochemistry.
「Results and Discussion」
In Behavior test, the rats from BTXA-injected group required a longer time to escape from maze
compared with control. Nissl staining revealed a significant reduction in the neuron density in
the BTXA-injected rats. Further, experimental rats exhibited a decreased level of CREB
The BTXA-injected rats required longer escape latency than did control, signifying the
decreased spatial learning ability. The BTXA-injected rats also exhibited a reduction in neuron
density and phosphorylated CREB, indicating that mastication might influence learning and
memory ability during growth period.