“…Low histamine concentrations elicit facilitatory effects, and higher concentrations produce depressant effects in both the cat (Brezenoff & Gertner, 1972) and the bullfrog (Yamada, Tokimasa & Koketsu, 1982) SCG. These opposing effects of histamine have been attributed to activation of different histamine receptor subtypes (Marshall, 1981). Histamine-induced facilitation of synaptic transmission in sympathetic ganglia of several species has been demonstrated to be mediated via histamine Hi receptors (Trendelenberg, 1957;Brimble & Wallis, 1973;Yamada et al 1982;Lindl, 1983;Snow & Weinreich, 1987), and histamine-induced synaptic depression has been linked to H2 histamine receptor activation (Brimble & Wallis, 1973;Yamada et al 1982; Snow & Weinreich, 1987).…”