New models of experimental parotitis and parotid gland distension in rats

A significant reduction of the escape threshold to mechanical stimulation of the lateral facial skin was observed bilaterally at days 2 and 3 after unilateral complete Freund's adjuvant (CFA) administration into parotid gland. A slight reduction of mechanical escape threshold was also observed in rats with saline administration. The parotid gland inflammation was verified and quantified by measuring the tissue Evans' blue dye extravasation. The Evans' blue concentration in the parotid gland tissues was significantly greater in the CFA-injected rats than that of the saline-injected rats at 72 h after treatment. On day 10 after CFA administration into the parotid gland, the Evans' blue concentration was recovered to the control level. The administration of capsaicin into the parotid gland did not alter neuronal activities in the transition zone between the trigeminal spinal subnucleus interpolaris and caudalis (Vi/Vc). In contrast, capsaicin administration induced significant increases in the receptive field size and mechanical and cold responses of neurons located in superficial laminae of the C1/C2. The subgroup of C1/C2 neurons responded to mechanical distension of the parotid gland, whereas no Vi/Vc neurons responded to parotid distension.