Daniel G. Webster

Tonic immobility and the dorsal immobility response in twelve species of muroid rodents

Two behavioral inhibitory responses, tonic immobility and the dorsal immobility response, were studied in 12 species of rodents. The duration and number of positive trials of tonic immobility were found to be correlated with the duration of the dorsal immobility response across species. These observations, along with the behavioral similarity of these two responses (e.g., rigid immobile posture, tremor) support the suggestion that tonic immobility and the dorsal immobility response be considered as members of a general class of complex behavioral inhibitory responses that are mediated by a common neural substrate. Although there is no reason to suspect gross differences in cortical development or function across the species in this study, large differences were apparent in various measures of the immobility responses studied. These results do not appear to support the hypothesis of an inverse relation between “phylogenetic rank” and susceptibility to immobility. Peromyscus species were found to exhibit longer durations of immobility than Microtus species. In light of earlier observations on predators, and the failure of Onychomys leucogaster (a predatory mouse) to exhibit tonic immobility in the present study, it was suggested that predatory species may be less susceptible to immobility responses than other species.

Muroid Copulatory Plugs and Female Reproductive Tracts: A Comparative Investigation

Structural variations in copulatory plugs and female reproductive tracts are described for 23 species of muroid rodents. Females were killed and examined 15 min after receiving one ejaculation from a conspecific male. Measurements of the copulatory plug and the females reproductive tract were then recorded. The data suggest that: 1) vaginal length may be a significant determinant of plug length, the coagulant essentially occupying the entire vaginal lumen; 2) vaginal length significantly covaries with penile length; 3) lengths of the upper reproductive tract of the female are significantly related to her body mass and do not appear to be influenced by insemination; and 4) tract lengths do not appear to vary appreciably with the estrous cycle, at least in Peromyscus maniculatus bairdi .

Open-field behavior in eight taxa of muroid rodents

Open-field behavior was observed in 10-min tests of 10 males of each of eight taxa of muroid rodents. Results parallel those of an earlier study of muroid rodents by Wilson, Vacek, Lanier, and Dewsbury (1976). Considerable variation among species was found for measures of locomotion, boli deposited, and most other behavioral patterns recorded. As in the Wilson et al. (1976) study, animals displayed a strong tendency to seek walls. Correlation coefficients between measures of locomotor-exploratory behavior and number of boli are presented for 20 taxa of muroid rodents; no support is found for a negative correlation between these measures for these taxa.

Pregnancy initiation in postpartum estrus in three species of muroid rodents

Abstract Pregnancy initiation in postpartum estrus was studied in 14 male-female pairs of white-footed mice, Peromyscus leucopus ; 12 pairs of prairie voles, Microtus ochrogaster ; and 14 pairs of montane voles, M. montanus . When mated for one ejaculatory series, the percentages of females pregnant were 25, 43, and 71% for M. ochrogaster , M. montanus , and P. leucopus , respectively. Whereas mating to satiety produced a significant increase in the probability of pregnancy relative to mating for one ejaculatory series in M. montanus , there was no significant difference in P. leucopus . M. ochrogaster did not differ significantly when mated for one ejaculation versus two. P. leucopus resemble P. maniculatus in having a lower stimulus requirement for pregnancy initiation in postpartum than in cycling estrus. M. ochrogaster resemble laboratory rats in having a higher stimulus requirement for pregnancy initiation in postpartum estrus. M. montanus show no significant difference.

Effects of estrus, estrogen-progesterone priming, and vaginal stimulation on tonic immobility, dorsal immobility, and lordosis in the female rat

Three complex inhibitory responses, tonic immobility, the dorsal immobility response, and lordosis, were studied in the intact female rat during estrus and diestrus and in ovariectomized rats with estrogen-progesterone treatment or controls. In each condition, the effects of vaginal-cervical stimulation were also studied. The results of two experiments indicate that estrus and estrogen-progesterone treatment significantly potentiate lordosis and the dorsal immobility response with or without vaginal-cervical stimulation. Tonic immobility was also potentiated by estrus and estrogen-progesterone treatment, but only if vaginal-cervical stimulation was applied. Vaginal-cervical stimulation potentiated both tonic immobility and the dorsal immobility response, but not lordosis, which was already at a high level.

Baroreceptor involvement in the immobility reflex.

Denervation of the carotid sinus in rabbits resulted in a significant reduction in the incidence of the immobility reflex. When the immobility reflex was obtained, it was not different in duration from that of controls. The results suggest that the initiation of the immobility reflex may be related to an increase in blood pressure in the sinoaortic area and that the response may function as a homeostatic mechanism.

Immobility responses in Anolis carolinensis

A “retrieval-like” response, similar to that exhibited by the young of many mammalian species when carried by adults, was found to be exhibited by Anolis carolinensis. These animals were found to be more susceptible to induction of this inhibitory response than to tonic immobility. The results are discussed in terms of possible common neural mechanisms mediating these complex behavioral inhibitory states.

Evidence for baroreceptor involvement in the immobility reflex in the rabbit: blood pressure changes during induction and termination.

It has been hypothesized [ B. Lofving, 1961, Acta Physiologica Scandinavica (Suppl) 53, 184 ; W. R. Klemm, 1971, In S. Ehrenpreis & O. C. Solnitzky, Eds., Neurosciences Research, Vol. 4, New York: Academic Press ; D. C. Hatton, T. Lanthorn, D. Webster, & M. E. Meyer, 1975, Behavioral Biology, 22, 122–127 ] that baroreceptor activity, as a consequence of postural inversion and restraint, plays a major role in the induction of the immobility reflex in rabbits. To investigate that hypothesis, blood pressure and heart rate were recorded from normal rabbits and rabbits with their carotid sinus denervated during induction and termination of the immobility reflex. The results indicated that a baroreceptor reflex occurred with postural inversion as measured by amount of bradycardia and the relative fall in blood pressure. There were significant differences in the pattern of the heart rate and blood pressure response between induction and termination for all animals. There were also significant differences between normal and denervated animals in their blood pressure response to inversion and termination. The results support the hypothesis that reflexive baroreceptor activity occurs as a consequence of the induction procedure for immobility.

Stimulus control of ovulation in red-backed voles (Clethrionomys gapperi)

Reproductive function is under the control of stimuli mediated by the central nervous system in many species. In species classified as’ induced ovulators,’ ovulation is generally contingent on external stimuli, particularly the vaginal stimulation derived from males during copulation. However, although they are classified as induced ovulators, 7 of 17 female red- backed voles (Clethrionomys gapperi) ovulated when housed either across a mesh barrier from a male or in isolated cages in a room containing males. There was no appreciable difference as a function of housing condition. Thus, red-backed voles ovulate in response to a variety of stimuli and do not require copulatory stimulation. Unmated Clethrionomys appear to ovulate more readily than do Microtus. The category of “induced ovulation” requires refinement.

An automated apparatus for the assessment of social preferences in rodents

Preference apparatuses offer a straightforward method for the assessment of social preference in a controlled manner. The present paper provides the information necessary for the construction of an automated preference apparatus for rodents and a demonstration of the operation of this apparatus. In a representative study,Peromyscus polionotus females demonstrated preference for intact over castrated males.