Dopamine receptor immunohistochemistry in the rat choroid plexus

1 Earlier studies have demonstrated a high density of dopamine D1-like rece ptor binding in the choroid plexus by light microscope autoradiography, but the dopaminergic specificity of this binding was questioned. 2 In this study the localization of dopamine receptor subtypes was investig ated in the rat choroid plexus by Western blot analysis and immunohistochem istry using antibodies raised against dopamine D1-D5 receptor protein. 3 Western blot analysis revealed reactivity with immune bands of approximat ely 50 and 51 KDa corresponding to dopamine D1 and D5 receptors, respective ly. Dopamine D1-like (D1 and D5) receptor protein immunoreactivity insensit ive to superior cervical ganglionectomy was located in smooth muscle of cho roid arteries and to a larger extent within choroid plexus epithelium. 4 Western blot analysis revealed reactivity with immune bands of approximat ely 53 KDa and 40-42 KDa corresponding to dopamine D2 and D4 receptors, res pectively, and no dopamine D3 receptor reactivity. Dopamine D2-like recepto r protein immunoreactivity displayed a distribution similar to that of tyro sine-hydroxylase (TH)-immunoreactive sympathetic fibres and disappeared aft er superior cervical ganglionectomy. It consisted in the expression of dopa mine D2 and to a lesser extent of D4 receptor protein immunoreactivity peri vascularly and associated with choroid epithelium. No D3 receptor protein i mmunoreactivity was found in rat choroid plexus. 5 The above results indicate that rat choroid plexus expresses dopamine rec eptor protein, being dopamine D1-like receptors predominant in epithelium a nd arterial smooth muscle and D2-like receptors in sympathetic nerve fibres supplying choroid plexus epithelium and vasculature. 6 These findings suggests that dopamine receptors with a different anatomic al localization may modulate production of cerebrospinal fluid.