c-Fos expression in the parabrachial nucleus following intraoral bitter stimulation in the rat with dietary-induced zinc deficiency

Zinc deficiency causes various symptoms including taste disorders. In the present study, changes in expression of c-Fos immunoreactivity in neurons of the parabrachial nucleus (PBN), one of the relay nuclei for transmission of gustatory information, after bitter stimulation to the dorsal surface of the tongue were examined in zinc-deficient rats. Experimental zinc-deficient animals were created by feeding a low-zinc diet for 4 weeks, and showed the following symptoms of zinc deficiency: low body weight, low serum zinc content and behavioral changes to avoid bitter stimulation. In normal control animals, intraoral application of 1 mM quinine caused increased numbers of c-Fos-immunoreactive (c-Fos-IR) neurons in the external lateral subnucleus and external medial subnucleus of the PBN (elPBN and emPBN, respectively) compared with application of distilled water. However, in the zinc-deficient animals, the numbers of c-Fos-IR neurons in the elPBN and emPBN did not differ significantly between application of quinine and distilled water. After feeding the zinc-deficient animals a normal diet for 4 weeks, the symptoms of zinc deficiency recovered, and the expression of c-Fos-IR neurons following intraoral bitter stimulation became identical to that in the normal control animals. The present results indicate that dietary zinc deficiency causes alterations to neuronal activities in the gustatory neural circuit, and that these neuronal alterations can be reversed by changing to a normal diet.