Low-Dose Glyphosate Exposure Alters the Enteric Tachykinin System in the Porcine Small Intestine

Glyphosate is a widely used herbicide, yet its effects on the enteric nervous system (ENS) remain poorly understood. This study investigated the effects of low-dose glyphosate exposure on substance P (SP)-immunoreactive neurons and tachykinin receptor gene expression in the porcine small intestine. Fifteen juvenile pigs were assigned to three groups (n = 5 per group): a control group and two groups receiving oral glyphosate for 28 days at doses corresponding to the estimated maximum daily intake in Europe (0.05 mg/kg BW/day) and the acceptable daily intake (0.5 mg/kg BW/day). Double immunofluorescence was used to determine the percentage of SP-immunoreactive neurons in the myenteric (MP), outer submucosal (OSP), and inner submucosal (ISP) plexuses of the duodenum, jejunum, and ileum. The expression of TACR1, TACR2, and TACR3 was analysed by RT-qPCR. Glyphosate exposure increased the percentage of SP-immunoreactive neurons in all analysed intestinal segments and plexuses, with a clear dose-related pattern. TACR2 mRNA expression was significantly increased in the duodenum in both glyphosate-exposed groups but decreased in the ileum at the higher glyphosate dose. TACR3 mRNA expression was significantly decreased in the duodenum in both exposed groups and in the jejunum at the higher dose, whereas TACR1 expression remained unchanged. SOD activity was significantly increased in the duodenum and ileum of pigs exposed to the higher glyphosate dose, whereas no significant changes were observed in the jejunum. These findings demonstrate that low-dose glyphosate exposure is associated with region-specific alterations in selected components of the enteric tachykinin system, indicating a complex neurochemical response of the ENS to glyphosate.