The effect of endurance training on regional serotonin metabolism in the brain during early stage of detraining period in the female rat

Abstract

1. The effect was examined of a single bout of nonexhaustive endurance exercise on tryptophan (Try), serotonin (5-HT), 5-hydroxyindolacetic acid (5-HIAA), and tryptophan hydroxylase (TpH) levels in different parts of rat brain (brain cortex, cerebellum, hypothalamus, midbrain striatum, medulla) on the last day of endurance training and 48 h later (detraining period). 2. Female rats were subjected to a 6-week endurance training programme. The effectiveness of the training was evaluated by measuring anaerobic threshold (AT). High performance liquid chromatography (HPLC) was used to determine regional Try, 5-HT, and 5-HIAA contents in the brain, and thin layer chromatography followed by gas-liquid chromatography was used to determine blood levels of free fatty acids. Regional TpH levels were measured by Western blot analysis. 3. In the two rat groups subjected to endurance training, in all brain regions studied but cerebellum, 5-HT content was significantly lower after the last bout of nonexhaustive endurance exercise than in resting control rats that were not subjected to the training. Similarly, the cortical and striatal, but not cerebellar, 5-HT/Try ratios were significantly lower in the trained rats at the end of the last training session and at the end of a single bout of nonexhaustive exercise administered after a 48-h detraining period than in the controls. TpH protein level was decreased by 15-25% after the last bout of exercise either during the training process or after the and 1 h bout of endurance exercise performed 48 h after cessation of endurance training in brain cortex and striatum but not cerebellar.4. These results indicate that the reduction in 5-HT level was the adaptive response to endurance training. The lowered 5-HT/Try ratio and lowered TpH protein level attained after the training process suggests and that this change may be, at least partially, attributed to downregulation of TpH activity.

Fig. 1.

Effect of detraining period on free tryptophan concentration in different parts of brain. Rats to be exercise-trained were running on treadmill 5 days a week for 6 weeks. Endurance-trained animals were divided into two groups: (1) trained animals killed immediately after last bout of exercise in training process, (2) trained rats performed the same bout of exercise like the last bout of exercise in training process 48 h after cessation of endurance training. f-Tryptophan concentration determined in different parts of brain using HPLC methods as described in Material and Methods section. Results are expressed as the mean ± SEM of data from 8 separate experiments. Two-way ANOVA was followed by a Newman–Keuls post hoc test (main effect of groups F(2, 126)=97.27, ^* p < 0.0001 versus the control value, # versus training value).

Fig. 2.

Effect of detraining period on serotonin concentration in different parts of brain. Rats to be exercise-trained were running on treadmill 5 days a week for 6 weeks. Endurance-trained animals were divided into two groups: (1) trained animals killed immediately after last bout of exercise in training process, (2) trained rats performed the same bout of exercise like the last bout of exercise in training process 48 h after cessation of endurance training. Serotonin concentration determined in different parts of brain using HPLC methods as described in Material and Methods section. Results are expressed as the mean ± SEM of data from eight separate experiments. experiments. Two-way ANOVA was followed by a Newman–Keuls post hoc test, (main effect of groups F(2, 126)=33.84, ^* p < 0.0005 versus the control value).

Fig. 3.

Effect of detraining period on 5HIAA concentration in different parts of brain. Rats to be exercise-trained were running on treadmill 5 days a week for 6 weeks. Endurance-trained animals were divided into two groups: (1) trained animals killed immediately after last bout of exercise in training process, (2) trained rats performed the same bout of exercise like the last bout of exercise in training process 48 h after cessation of endurance training. 5-HIAA concentration determined in different parts of brain using HPLC methods as described in Material and Methods section. Results are expressed as the mean ± SEM of data from eight separate experiments Two-way ANOVA was followed by a Newman–Keuls post hoc test (main effect of groups F(2, 126)=10.46, ^* p < 0.0034 versus the control value).

Fig. 4.

Effect of detraning period on TPH protein level in different part of brain. Results are expressed as the means ± SEM of data from four separate experiments. One-way ANOVA was followed by a Newman–Keuls post hoc test (main effect of groups F(2, 27)=189.40, ^* p < 0.05 versus the control value.

Fig. 5.

Effect of detraining period on free tryptophan concentration in plasma. Rats to be exercise-trained were running on treadmill 5 days a week for 6 weeks. Endurance trained animals were divided into two groups: (1) trained animals killed immediately after last bout of exercise in training process, (2) trained rats performed the same bout of exercise like the last bout of exercise in training process 48 h after cessation of endurance training. f-Tryptophan concentration determined in plasma using HPLC methods as described in Material and Methods section. Results are expressed as the means ± SEM of data from eight separate experiments. Two-way ANOVA was followed by a Newman–Keuls post hoc test (main effect of groups F(2, 21)=36.17, ^* p < 0.0001 versus the control value, # p < 0,01 versus training value.

Fig. 6.

Effect of detraining period on free fatty acid concentration in plasma. Rats to be exercise-trained were running on treadmill 5 days a week for 6 weeks. Endurance trained animals were divided into two groups: (1) trained animals killed immediately after last bout of exercise in training process, (2) trained rats performed the same bout of exercise like the last bout of exercise in training process 48 h after cessation of endurance training. FFA concentration determined in plasma using HPLC methods as described in Material and Methods section. Results are expressed as the means ± SEM of data from eight separate experiments. One-way ANOVA was followed by a Newman–Keuls post hoc test (F(2, 21)=7.08, ^* p < 0.005 versus the control value).

Fig. 7.

Anaerobic threshold (AT), expressed as the running speed at which lactate (LA) starts to accumulate in blood. Results are expressed as the mean ± SEM of data from six separate experiments. One-way ANOVA was followed by a Newman–Keuls post hoc test (F(2, 15)=47.73, ^* p < 0.005 versus the control value.