An inexpensive meter to measure differences in electrical resistance in the rat vagina during the ovarian cycle

Abstract

The inherent electrical resistance of the rat vaginal wall rises markedly near the beginning of estrus and then falls again to low levels for the remainder of the ovarian cycle. Accordingly, special instruments have been developed to measure such resistances (within seconds) on simply inserting a small probe fitted with a pair of recording electrodes into the vagina (i.e., the MK-10A impedance checker and the EC40 estrus cycle monitor). As described herein, these two instruments are far more convenient for monitoring individual cycles than more laborious methods in which vaginal smears are inspected for changes in numbers of cornified (C), nucleated (N), and leukocytic (L) cells. However, they are also expensive and their use has essentially remained uncited in the literature. Thus we sought to determine whether a simple, inexpensive electrical meter (with resistance-measuring capacity), as commonly used by professional electricians, would serve the same purpose. We chose a standard multifunctional meter (model 22-178, RadioShack) and attached leads to it fabricated from the internal wiring of a shielded audio cable (model 42-2387A, RadioShack), one male terminal of which was used as a vaginal probe. In rats from which vagina smears revealed cell numbers in the order of C > N > L (typical of early estrus) electrical resistances were high, 488 +/- 130 k Omega (18 rats). In rats from which vagina smears revealed all other possible cell distributions, electrical resistances (combined) were much lower (P < 0.05), 124 +/- 23 k Omega (32 rats). Thus readily accessible, inexpensive electrical meters may be useful in assessing the status of estrus in female rats, either to improve reproductive efficiencies and/or for other purposes involving experiments in which such information is desirable.

Cloning, Distribution, and Colocalization of MNAR/PELP1 with Glucocorticoid Receptors in Primate and Nonprimate Brain

“…Cycle stages were determined by recording daily electrical impedance readings of the vaginal wall using a commercially available EC40 estrous cycle monitor (Fine Science Tools, Foster City, Calif., USA). The EC40 estrous cycle monitor measures the inherent electrical resistance of the vaginal wall which fluctuates markedly across different phases of the estrous cycle [13]. Vaginal lavage and microscopic determination of vaginal cytology was also used to confirm estrous cycle stage determinations.…”

Fluoxetine administration to pregnant rats increases anxiety-related behavior in the offspring

“…To assess the estrous stage, the cycle of female Wistar rats (Harlan laboratories, Horst, The Netherlands) was measured daily in the late afternoon with an impedance checker (Impedance Checker MK-10B, Muromachi; see also Ramos et al 2001). When a female reached the estrous stage it was placed together with a Wistar male (Harlan laboratories, Horst, The Netherlands) in Macrolon type 3 cage (42× 26×20 cm) with a wire gauze bottom.…”

Differential impact of cocaine on meal patterns in female and male rats

“…Each rat was lightly restrained, and a probe inserted into the vagina for about 5 s. The probe provides a measure of the resistance of the vaginal mucosa, which is known to increase on the morning of estrus to a value greater than 6000 Ω, relative to a basal value of 2000-3000 Ω on other days of the estrous cycle (Koto et al, 1987a,b;Ramos et al, 2001). Prior studies have confirmed that increased vaginal resistance occurs when the vaginal cell type obtained from swabs is predominantly of the cornified type (Ramos et al, 2001). After each use, the probe was cleaned using distilled water, dried, and then wetted with distilled water prior to the next resistance determination.…”