The activation of sexual behaviour in cats by the subcutaneous administration of oestrogen

Abstract

The female cat possesses a characteristic and highly stereotyped pattern of sexual behaviour, which is remarkably constant in individual animals (Stricht, 1911; Greulich, 1934;Bard, 1939;Dawson, 1950;Michael, 1958). The pattern of oestrous behaviour depends upon the secretory activity of the ovaries and is never observed in immature, anoestrous or ovariectomized animals (Bard, 1939;Michael, 1961). It can therefore be regarded as a pattern of behaviour that is hormone-dependent. This study deals mainly with the activation of oestrous behaviour in ovariectomized cats stimulated by treatment with oestrogens, with particular reference to the time taken for mating to occur and the relations between the vaginal and behavioural changes.In order to interpret the results of experiments in which oestrogens were introduced directly into the substance of the brain (Harris & Michael, 1964), it was necessary first to know the effects upon both behaviour and genital tract when oestrogens were administered systemically. In the mouse (Brouha & Simonnet, 1927;Marrian & Parkes, 1930;Mirskaia & Crew, 1930; Wiesner & Mirsakia, 1930), the rat (Allen, Francis, Robertson, Colgate, Johnston, Doisy, Kountz & Gibson, 1924), the guinea-pig (Boling, Young & Dempsey, 1938), and the ewe (Cole & Miller, 1935;Robinson, 1955) it has been found that the dosage of oestrogen required to induce cornification of the vagina is less than that required to evoke mating behaviour, and hence it was important to determine whether this relation also holds true in the feline species. Further, observations upon the natural oestrous cycles of normal cats (Michael, 1961) suggested that the total pattern of sexual behaviour was organized from simpler component reflexes upon a hierarchical basis by increasing levels of ovarian hormone. In the present study oestrogens have been administered to ovariectomized cats under conditions which permit this hypothesis to be tested. The preliminary results obtained were briefly reported by Michael & Scott (1957).

The activation of sexual behaviour by hypothalamic implants of oestrogen

“…The latent period to mating was found to be 5-6 days in all four animals (see Michael & Scott, 1964). These animals were therefore shown to have a similar order of sensitivity to systemic oestrogen.…”

“…Most animals in this group had small implants (< 0-2 mg). Since it has been shown that prolonged, daily systemic administration of small doses of stilboestrol ester and oestradiol results in full development of the genital tracts in ovariectomized cats, without producing mating (Michael & Scott, 1964), it is improbable that the response seen in this group of animals (sustained mating without genital-tract development) is due to an effect exerted by absorption of the stilboestrol ester into the general systemic circulation. It is therefore likely that the ester implants were acting by a local and direct effect on the surrounding neural tissue.…”

“…Routine vaginal smears were made throughout the experiments and the degree of cornification expressed as a cornification index as previously described (Michael & Scott, 1964 In assessing the responses of the uterus during the course of an experiment attention was paid to the cross-sectional area of the endometrium as observed in biopsy material. The condition of the genital tract at death was assessed in terms of weight, endometrial cross-sectional area, the number oflayers in the vaginal epithelium, and general histological picture.…”

“…The anaesthetic used was pentobarbitone sodium ('Nembutal', Abbott Laboratories), 36 mg/kg body weight injected intraperitoneally. Ovariectomy was performed by the technique previously described (Michael & Scott, 1964) . Vaginal smears were taken by means of a cotton-wool-covered probe three times weekly from each cat, stained by the method of Papanicolaou (1933), and any cornification response to the hormone treatment was assessed.…”

“…Since there is at present no reliable method for the biochemical estimation of very small amounts of oestrogen in blood, the state of the uterus and vagina was used throughout to indicate the extent to which oestrogen was released from the implant into the general circulation. It has been found (Michael & Scott, 1964) that the dose of oestrogen required to evoke vaginal development in the spayed cat is lower than that required for mating behaviour (genital tract threshold below mating threshold). Thus, the presence of behavioural oestrus in the absence of reproductive-tract development, in animals with a brain implant, can be taken to indicate a local and direct stimulation of central nervous tissue rather than a stimulation mediated via the systemic circulation.…”