DOES HISTAMINE STIMULATE TRIGEMINAL NASAL AFFERENTS

The response to histamine of nasal afferents has been studied in guine a pigs by recording the electrical activity of the whole ethmoidal ner ve (EN) or that of single units. Guinea pigs were anaesthetized with u rethane and breathed through a tracheostomy. Prior to intranasal insti llation of histamine (1 x 10(-4)-10(-1) M), the nasal mucosa was treat ed with 20 mu l of saline (0.9% NaCl) or HCl (pH = 2), and in some cas es, H2SO4 (pH = 2). In other experiments, following HCl instillation a nimals were pretreated by tripelennamine (1 x 10(-2) M) and/or cimetid ine (1 x 10(-2) M) in order to determine the histamine receptor type o f sensory nerve endings. Whole EN activity was not stimulated even by the highest dose (1 x 10(-1) M) of histamine when the nose was pretrea ted with saline, but was substantially stimulated by histamine in a do se-response fashion (1 x 10(-2) M) after pretreatment with HCl or H2SO 4. Pretreatment with tripelennamine and HCl prevented the effect of hi stamine on the afferent EN activity; but after cimetidine and HCl pret reatment histamine still had a marked stimulant effect. In the case of single unit activities, histamine with HCl pretreatment had a long-la sting stimulatory effect (110.2 +/- 26.6 sec). It is concluded that th e EN in guinea pigs include histamine-sensitive fibers whose sensitivi ty is mediated by H-1 receptors and can respond to histamine only unde r abnormal conditions of the nasal mucosa. (C) 1998 Elsevier Science B .V. All rights reserved.