Figure 3. Alteration of 5-HT neurotransmission affects the inhibitory effect of photostimulation on S-IRA.

A, photostimulation of 5-HT neurons in the DR at 9 mW for 10 min had no effect on S-IRA evoked by acoustic stimulation in transgenic DBA/1 mice pre-treated with vehicle once daily for two days (n = 6). However, pre-treatment with 5-hydroxytryptophan (5-HTP, 50 mg/kg, i.p.), once daily for two days, significantly reduced S-IRA by photostimulation at 9 mW for 10 min (n = 6). B, photostimulation following pre-treatment with vehicle in the DR at 9 mW for 15 min blocked S-IRA evoked by acoustic stimulation in transgenic DBA/1 mice (n = 6), which exhibited 100% of S-IRA 24 hr prior to vehicle treatment without photostimulation. However, pre-treatment with ondansetron (OND, 2 mg/kg, i.p.) significantly reversed the blockade effect of photostimulation on S-IRA (n = 6). C, D, box plots show that as compared with corresponding photostimulation following vehicle treatment, pre-treatment with 5-HTP followed by photostimulation at 9 mW for 10 min did not result in a significant change in the latency to AGSz, nor did pre-treatment with OND followed by photostimulation at 9 mW for 15 min. E, F, box plots show that as compared with corresponding vehicle control, pre-treatment with 5-HTP followed by photostimulation did not significantly alter the duration of wild running and clonic seizures, however, pre-treatment with OND followed by photostimulation significantly reduced the duration of wild running and clonic seizures. Blue bars, photostimulation at 9 mW for 10 min; red bars, photostimulation at 9 mW for 15 min. PS, photostimulation; 5-HTP, 5-hydroxytryptophan; OND, ondansetron; W/C, wild running and clonic seizures. See figure 2 for photostimulation parameters.

* p < 0.05: Significantly different from vehicle control (PS at 9 mW for 10 min) in A or vehicle control (PS at 9 mW for 15 min) in B and F.