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Abstract
The sensory system is developed and optimized by experiences given in the early phase of life in association with other regions of the nervous system. To date, many studies have revealed that deprivation of specific sensory experiences can modify the structure and function of the central nervous system; however, the effects of sensory overload remains unclear. Here we studied the effect of overloading the taste sense in the early period of life on the synaptic plasticity of rat hippocampus and somatosensory cortex. We prepared male and female Sprague Dawley rats with ad libitum access to a 0.1% saccharin solution for 2 hrs per day for three weeks after weaning on postnatal day 22. Saccharin consumption was slightly increased in males compared with females; however, saccharin intake did not affect chow intake or weight gain either in male or in female rats. We examined the effect of saccharin-intake on long term potentiation (LTP) formation in hippocampal Schaffer collateral pathway and somatosensory cortex layer IV – II/III pathways in the 6-week old saccharin-fed rats. There was no significant difference in LTP formation in the hippocampus between the control group and saccharin-treated group in both male and female rats. Also in the somatosensory cortex, we did not see a significant difference in LTP among the groups. Therefore, we conclude that saccharin-intake during 3∼6 weeks may not affect the development of physiological function of the cortical and hippocampal synapses in rats.
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Fig. 1.
Daily saccharin intake and body weight of male and female rats. (A) Amount of saccharin solution consumed during daily drinking sessions. Male (circle) and female (triangle) Sprague-Dawley pups had ad libitum access to 0.1% saccharin solution for 2 hr daily for 3 weeks following weaning on postnatal day 22. (B) Total saccharin consumption during each drinking session. (C, D) Body weight gain and food intake of male rat by saccharin intake. Food intake and body weight gain were monitored with (filled circle) or without (open circle) the exposure to 0.1% saccharin for 2 hr daily for 3 weeks during the indicated experimental period. (E, F) Body weight gain and food intake of female rat by saccharin intake. Food intake and body weight gain were monitored with (filled triangle) or without (open triangle) the exposure to 0.1% saccharin for 2 hr daily for 3 weeks during the indicated experimental period. All results are presented as mean±SEM from more than five individual rats.
Fig. 2.
Effect of saccharin intake on LTP induction in hippocampal Schaffer collateral pathway in male rat. (A) Hippocampal slices were prepared from 6∼7 weeks old male Sprague-Dawley rat with (filled circle) and without (open circle) ad libitum access to 0.1% saccharin solution for 2 hr daily for 3 weeks, and recorded fEPSP in Schaffer collateral-CA1 synapses. Average changes in the fEPSP slope induced by theta burst stimulation are depicted. (B) Typical field potential traces from experiments performed in saccharine-treated group (right) and chow only group (left) are shown. The superimposed traces are averages of four consecutive responses recorded 1 min before (black traces) and 1 hr after (gray traces) theta burst stimulation. (C) The magnitude of LTP formation of baseline responses is shown depicted. All results are presented as mean±SEM from more than four independent trials. n.s., not significant statistical difference (p>0.05).
Fig. 3.
Effect of saccharin intake on LTP induction in hippocampal Schaffer collateral pathway in female rat. (A) Hippocampal slices were prepared from 6∼7 weeks old female rat with (filled circle) and without (open circle) 0.1% saccharin intake, and recorded fEPSP in Schaffer collateral-CA1 synapses. Average changes in the fEPSP slope induced by theta burst stimulation are depicted. (B) Typical field potential traces from experiments performed in saccharine-treated group (right) and chow only group (left) are shown. The superimposed traces are averages of four consecutive responses recorded 1 min before (black traces) and 1 hr after (gray traces) theta burst stimulation. (C) The magnitude of LTP formation of baseline responses is shown depicted. All results are presented as mean±SEM from more than five independent trials. n.s., not significant statistical difference (p>0.05).
Fig. 4.
Effect of saccharin intake on LTP induction in somatosensory cortex layer IV-II/III pathway in male rat. (A) Somatosensory cortical slices were prepared from 6∼7 weeks old male rat with (filled circle) and without (open circle) 0.1% saccharin intake, and recorded fEPSP in layer IV-II/III synapses. Average changes in the fEPSP amplitude induced by theta burst stimulation are depicted. (B) Typical field potential traces from experiments performed in saccharine-treated group (right) and chow only group (left) are shown. The superimposed traces are averages of four consecutive responses recorded 1 min before (black traces) and 1 hr after (gray traces) theta burst stimulation. (C) The magnitude of LTP formation of baseline responses is shown depicted. All results are presented as mean±SEM from more than three independent trials. n.s., not significant statistical difference (p>0.05).
Fig. 5.
Effect of saccharin intake on LTP induction in somatosensory cortex layer IV-II/III pathway in female rat. (A) Somatosensory cortical slices were prepared from 6∼7 weeks old female rat with (filled circle) and without (open circle) 0.1% saccharin intake, and recorded fEPSP in layer IV-II/III synapses. Average changes in the fEPSP amplitude induced by theta burst stimulation are depicted. (B) Typical field potential traces from experiments performed in saccharine-treated group (right) and chow only group (left) are shown. The superimposed traces are averages of four consecutive responses recorded 1 min before (black traces) and 1 hr after (gray traces) theta burst stimulation. (C) The magnitude of LTP formation of baseline responses is shown depicted. All results are presented as mean±SEM from more than three independent trials. n.s., not significant statistical difference (p>0.05).
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