Discussion

The integration of non-pharmacological interventions with established pharmacotherapies represented a promising frontier in the holistic management of neurological disorders. This study provided compelling preclinical evidence that moderate-intensity treadmill exercise synergistically enhanced the therapeutic profile of topiramate in a chronic model of PTZ-kindling. This synergy manifested not only as a potentiation of antiseizure efficacy but, more notably, as an attenuation of the drug's adverse depressive-like effects. These behavioral outcomes were associated with a concomitant upregulation of 5-HT1A receptor expression level in key brain regions, offering a plausible neurobiological substrate for the observed benefits.

Combination therapy of topiramate and exercise improved the dose-efficacy profile

Our findings delineate a clear superiority of the combination regimen over monotherapy in controlling convulsive activity. While topiramate alone produced the expected dose-dependent reduction in seizure scores and prolongation of seizure latency, the temporal kinetics and magnitude of these effects were markedly amplified by concurrent exercise. Notably, the high-dose combination group (EX+TPM (70 mg)) exhibited a significant reduction in seizure scores from day 6. In contrast, the corresponding monotherapy group (TPM (70 mg)) achieved a comparable effect only from day 9 onward. Moreover, direct comparisons revealed that seizure scores in the EX + TPM (70 mg) group were significantly lower than those in the TPM (70 mg) group at the experiment's endpoint. These findings suggest that exercise fundamentally altered the brain's responsiveness to topiramate.

We posit that this pharmacodynamic synergy arises from complementary mechanisms. Voltage-gated sodium channel blockade (Zona et al., 1997), enhancement of GABAergic neurotransmission, and reduction of AMPA/kainate glutamate receptor activation (Skradski and White, 2000) are involved in the antiseizure effects of topiramate. Exercise induces broad-spectrum neuroplastic and homeostatic adaptations, including upregulation of neurotrophic factors such as BDNF (Mozhgan Abdullahzadeh Nobejari et al., 2024), enhancement of neuronal survival, and synaptic resilience (Mandolesi et al., 2018). It bolsters endogenous antioxidant defenses, reduces oxidative stress, and improves cerebral hemodynamics (Ebrahimnezhad et al., 2023). Critically, the present study identified upregulation of 5-HT1A receptor expression level in the hippocampal and cerebral cortex following combination therapy. The 5-HT1A receptor, an inhibitory G-protein-coupled receptor, induced neuronal hyperpolarization via GIRK channels (Ambrogini et al., 2023). This effect is mediated not only through direct postsynaptic inhibition but also through broader serotonergic modulation of network excitability. For instance, serotonin can indirectly control neuronal firing by facilitating GABAergic inhibition through mechanisms such as increased GABA release through interneuron activation (Bennett, 2026) and by dampening glutamatergic excitation through presynaptic inhibition of glutamate release (Nishijo et al., 2022). Its enhanced expression, likely driven by exercise, therefore provided a pervasive inhibitory and stabilizing tone across neural circuits through these multifaceted mechanisms, effectively raising the seizure threshold. Thus, when topiramate was administered, it acted upon a brain already primed for stability by exercise, resulting in a supra-additive antiseizure effect. This mechanistic overlap provided a rational basis for the observed dose-efficacy enhancement, implying that lower doses of topiramate may achieve therapeutic control when paired with exercise, thereby minimizing dose-dependent side effects.

Combination therapy of topiramate and exercise ameliorated drug-induced depressive-like behaviors

The behavioral findings of the current study demonstrate a clear mitigation of depressive-like phenotypes by combination therapy, in contrast to literature reports that high-dose topiramate monotherapy can exacerbate such behaviors (Lin et al., 2023, Phabphal and Udomratn, 2010). This study has shown that the PTZ-kindling process downregulated 5-HT1A receptor expression level, a pathophysiological deficit strongly associated with the emergence of depression in epilepsy. Critically, the combined intervention of exercise and topiramate was associated with the prevention of this receptor downregulation. This finding aligned with strong pharmacological evidence demonstrating that selective agonists of this receptor exert potent anticonvulsant effects across diverse animal models (López-Meraz et al., 2005).

The observed upregulation of 5-HT1A receptor expression level following combination therapy may have contributed to the improvement in depressive-like behaviors, consistent with the established role of this receptor in mood regulation. However, the precise intracellular signaling pathways underlying this effect were not examined in the present study and warrant further investigation.

Furthermore, the functional significance of 5-HT1A receptor upregulation in the hippocampus, as observed in the current study, is strongly supported by circuit-level evidence. Specifically, the integrity of the serotonergic projection from the dorsal raphe nucleus (DRN) to the hippocampus is fundamental for regulating mood and cognition. The compromised function of this specific DRN–hippocampal circuit has been directly and causally linked to the manifestation of both depressive and cognitive impairments in preclinical models (Chen et al., 2024). Therefore, the current finding that combination therapy was associated with increased hippocampal 5-HT1A receptor expression level suggests a potential restoration of signaling within this critical mood-regulating pathway, which may serve as a neurobiological correlate of the observed antidepressant effect.

The present study revealed a biphasic, dose-dependent effect of topiramate on anxiety-like behavior in the elevated plus maze (EPM). While the lowest dose (25 mg) reduced closed-arm time, suggesting an anxiolytic-like effect, higher doses (50 and 70 mg) significantly increased this parameter, indicating an anxiogenic response. This pattern was consistent with the complex pharmacological profile of topiramate. At lower doses, topiramate has been reported to exert anxiolytic-like effects in rodent models, an effect attributed to its modulatory actions on GABAergic and glutamatergic systems (Junqueira-Ayres et al., 2017). Mechanistically, this might be explained by the selective antagonism of GluR5 kainate receptors at low concentrations (Gryder and Rogawski, 2003), which reduced excitatory drive in the amygdala, a key region for anxiety regulation. In contrast, the emergence of anxiety at higher doses aligned with the well-documented, dose-dependent psychiatric side effects of topiramate, including anxiety and mood disturbances, as reported in preclinical and clinical trials and summarized in the FDA prescribing information (Physicians' Desk Reference, 2009, Kanner et al., 2003). This shift from an anxiolytic to an anxiogenic response likely reflected a change in the predominant mechanism of action as dosage increases, potentially involving broader modulation of AMPA receptors at higher concentrations (Gryder and Rogawski, 2003).These findings highlighted that the behavioral effects of topiramate were critically dose dependent.

Taken together, these findings suggested that the combination of exercise and topiramate exerts beneficial effects on mood-related behaviors, potentially through modulation of 5-HT1A receptor expression. However, further studies are needed to elucidate the precise mechanisms underlying these effects.

Assessment of emotional behaviors

In the present study, the elevated plus maze (EPM) and the tail suspension test (TST) were used to evaluate anxiety- and depressive-like behaviors, which frequently occur together in epilepsy patients and animal models.

The finding that exercise improved both anxiety-like (EPM) and depressive-like (TST) behaviors suggested a broad beneficial effect on mood, which is clinically relevant given the high comorbidity of anxiety and depression in epilepsy. However, we observed a significant association between exercise-induced 5-HT1A receptor upregulation and behavioral improvements, this was not establish causation. Future studies using 5-HT1A antagonists or genetic knockdown approaches wouhl be needed to determine causlity. We also recommend that future studies use additional validated tests, such as the forced swim test or sucrose preference test, to specifically assess depressive-like behavior.