Objective:To investigate the role of serotonergic (5-HT) neurons activation in the dorsal raphe nucleus (DRN) in heat-induced seizures and its influence on breathing patterns in Scn1a + /- mice. Methods:24-day-old male Scn1a + /- mice were used for experiments, and sudden unexpected death in epilepsy(SUDEP) model was established through heat induction for 5 consecutive days. (1) Fluoxetine intervention experiment: 20 male mice were randomly divided into model group( n=10) and fluoxetine group ( n=10) according the weight-matched method. The fluoxetine group received intraperitoneal injection of fluoxetine (10 mg/kg) 45 min before heat induction each day for 5 consecutive days, while the model group received equal volume of 0.9% NaCl solution. (2) Chemogenetic activation experiment: 20 male mice were randomly divided into vector control group( n=10) and chemogenetic activation group ( n=10) according the weight-matched method. Empty vector or rAAV-TPH2-hM3d(Gq)-EGFP-WPREs was stereotaxically injected into DRN 14 d prior to seizure induction, and deschloroclozapine (5 mg/kg) was intraperitoneally injected 30 min before heat induction. Seizure characteristics and survival were assessed through video monitoring, and respiratory parameters were monitored. Immunofluorescence was used to detect colocalization of tryptophan hydroxylase 2(TPH2) and c-Fos in DRN. Statistical analysis was performed using SPSS 24.0 and GraphPad Prism 9.0. The independent sample t-test or Mann-Whitney test was used for inter-group comparison. Results:(1) In the fluoxetine intervention experiment: the survival rates between the model group and fluoxetine group showed no statistically significant difference ( χ2=2.23, P>0.05). As for the frequency of grade Ⅳ seizures, the model group (1.50(1.25, 2.35)min) demonstrated higher frequency than the fluoxetine group (0.43(0.20, 0.67)min) ( t=-3.40, P<0.05).With respect to respiratory parameters, the model group demonstrated shorter expiratory time ((0.10±0.02) s) and inspiratory time ((0.15±0.02) s) compared to the fluoxetine group ((0.16±0.05) s, (0.19±0.04) s) ( t=-3.47, -3.73, both P<0.01). The respiratory rate in the model group ((269.96±44.84) times/min) was significantly higher compared to the fluoxetine group ((195.04±52.37) times/min) ( t=3.44, P<0.01). The tidal volume in the model group ((0.10±0.02) mL) was significantly lower than the fluoxetine group ((0.13±0.04) mL) ( t=-2.19, P<0.05).The number of TPH2+ /c-Fos+ co-expressing cells in the model group (11.00±4.00) was lower than that in the fluoxetine group (33.00±8.39)( t=-4.16, P<0.05). (2) In the chemogenetic activation experiment: compared to the vehicle group, the chemogenetic activation group demonstrated significantly enhanced survival rates ( χ2=5.83, P<0.05). As for the frequency of grade Ⅴ seizures, the vehicle group (2.11(1.62, 3.44) times/min) showed higher frequency compared to the chemogenetic activation group (0.81(0.00, 1.62) times/min) ( t=18.00, P<0.05). In terms of respiratory parameters, the vehicle group showed shorter expiratory time ((0.10±0.01) s) and inspiratory time ((0.14±0.01) s) compared to the chemogenetic activation group ((0.12±0.01) s, (0.15±0.01) s) ( t=-2.78, -2.50, both P<0.05). The respiratory rate in the vehicle group ((208.37±9.73) times/min) was significantly higher than the chemogenetic activation group ((191.85±8.83) times/min) ( t=3.98, P<0.01). The tidal volume in the vehicle group ((0.09±0.01) mL) was significantly lower than the chemogenetic activation group ((0.12±0.02) mL) ( t=-4.77, P<0.001).The number of TPH2+ /c-Fos+ co-expressing cells in the vehicle group (9.00±3.46) was lower than that in the chemogenetic activation group (43.00±11.02)( t=-5.20, P<0.01). Conclusion:Specific activation of serotonergic neurons in the DRN can ameliorate heat-induced epileptic symptoms, improve respiratory function, and prolong survival time in Scn1a + /- mice.

Objective:To investigate the role of serotonergic (5-HT) neurons activation in the dorsal raphe nucleus (DRN) in heat-induced seizures and its influence on breathing patterns in Scn1a + /- mice. Methods:24-day-old male Scn1a + /- mice were used for experiments, and sudden unexpected death in epilepsy(SUDEP) model was established through heat induction for 5 consecutive days. (1) Fluoxetine intervention experiment: 20 male mice were randomly divided into model group( n=10) and fluoxetine group ( n=10) according the weight-matched method. The fluoxetine group received intraperitoneal injection of fluoxetine (10 mg/kg) 45 min before heat induction each day for 5 consecutive days, while the model group received equal volume of 0.9% NaCl solution. (2) Chemogenetic activation experiment: 20 male mice were randomly divided into vector control group( n=10) and chemogenetic activation group ( n=10) according the weight-matched method. Empty vector or rAAV-TPH2-hM3d(Gq)-EGFP-WPREs was stereotaxically injected into DRN 14 d prior to seizure induction, and deschloroclozapine (5 mg/kg) was intraperitoneally injected 30 min before heat induction. Seizure characteristics and survival were assessed through video monitoring, and respiratory parameters were monitored. Immunofluorescence was used to detect colocalization of tryptophan hydroxylase 2(TPH2) and c-Fos in DRN. Statistical analysis was performed using SPSS 24.0 and GraphPad Prism 9.0. The independent sample t-test or Mann-Whitney test was used for inter-group comparison. Results:(1) In the fluoxetine intervention experiment: the survival rates between the model group and fluoxetine group showed no statistically significant difference ( χ2=2.23, P>0.05). As for the frequency of grade Ⅳ seizures, the model group (1.50(1.25, 2.35)min) demonstrated higher frequency than the fluoxetine group (0.43(0.20, 0.67)min) ( t=-3.40, P<0.05).With respect to respiratory parameters, the model group demonstrated shorter expiratory time ((0.10±0.02) s) and inspiratory time ((0.15±0.02) s) compared to the fluoxetine group ((0.16±0.05) s, (0.19±0.04) s) ( t=-3.47, -3.73, both P<0.01). The respiratory rate in the model group ((269.96±44.84) times/min) was significantly higher compared to the fluoxetine group ((195.04±52.37) times/min) ( t=3.44, P<0.01). The tidal volume in the model group ((0.10±0.02) mL) was significantly lower than the fluoxetine group ((0.13±0.04) mL) ( t=-2.19, P<0.05).The number of TPH2+ /c-Fos+ co-expressing cells in the model group (11.00±4.00) was lower than that in the fluoxetine group (33.00±8.39)( t=-4.16, P<0.05). (2) In the chemogenetic activation experiment: compared to the vehicle group, the chemogenetic activation group demonstrated significantly enhanced survival rates ( χ2=5.83, P<0.05). As for the frequency of grade Ⅴ seizures, the vehicle group (2.11(1.62, 3.44) times/min) showed higher frequency compared to the chemogenetic activation group (0.81(0.00, 1.62) times/min) ( t=18.00, P<0.05). In terms of respiratory parameters, the vehicle group showed shorter expiratory time ((0.10±0.01) s) and inspiratory time ((0.14±0.01) s) compared to the chemogenetic activation group ((0.12±0.01) s, (0.15±0.01) s) ( t=-2.78, -2.50, both P<0.05). The respiratory rate in the vehicle group ((208.37±9.73) times/min) was significantly higher than the chemogenetic activation group ((191.85±8.83) times/min) ( t=3.98, P<0.01). The tidal volume in the vehicle group ((0.09±0.01) mL) was significantly lower than the chemogenetic activation group ((0.12±0.02) mL) ( t=-4.77, P<0.001).The number of TPH2+ /c-Fos+ co-expressing cells in the vehicle group (9.00±3.46) was lower than that in the chemogenetic activation group (43.00±11.02)( t=-5.20, P<0.01). Conclusion:Specific activation of serotonergic neurons in the DRN can ameliorate heat-induced epileptic symptoms, improve respiratory function, and prolong survival time in Scn1a + /- mice.