Follicle-stimulating hormone is secreted more irregularly than luteinizing hormone in both humans and sheep

Recently introduced statistical tools capable of discerning differences between the pattern of luteinizing hormone (LH) secretion and that of follicle-stimulating hormone (FSH) could be valuable in understanding ovulation and menopause, and ultimately in making diagnostic decisions and treating infertility and polycystic ovary syndrome. We assessed the validity and scope of the hypothesis that FSH is secreted more irregularly than LH in ewes and fertile women. We compared secretory irregularity of LH to that of FSH in both ovariectomized ewes (n = 7) and women of proven fertility (n = 5) during the follicular and luteal phases of their reproductive cycles. In each sheep, time series from both hypophyseal portal blood (HPB) and peripheral blood were evaluated in 72 samples obtained every 5 min; in each human, both luteal and follicular periods were studied in 192 samples obtained every 7.5 min. To quantify serial irregularity, we used approximate entropy (ApEn), a scale- and model-independent statistic. FSH secretion was consistently more irregular than that of LH in each subject. For sheep HPB, ApEn(FSH) = 1.415+/-0.097 was larger than ApEn(LH) = 0. 822+/-0.213, P < 0.0001 (mean+/-SD, paired t test). This difference persisted peripherally: ApEn(FSHper) = 1.431+/-0.101 > ApEn(LHper) = 1.252+/-0.086, P = 0.024. In women, ApEn(FSH) = 1.467+/-0.217 > ApEn(LH) = 0.923+/- 0.305, P < 0.0001. ApEn(FSH) > ApEn(LH) in 100% of women (peripheral) and sheep HPB. Secretion during the follicular phase was more irregular than during the luteal phase for both FSH and LH (P < 0.01). LH mean level secretion showed a wake/sleep difference in women, P < 0.005, with higher values awake. The consistency and statistical significance of these findings suggest that this LH/FSH difference may be broadly based within higher mammals. Ranges of normative and abnormal regularity values of LH, FSH, and their difference can be used in a number of settings, both (currently) research and (potentially ultimately) clinical milieus.

Temporal resolution of general odor pulses by olfactory sensory neurons in American cockroaches

Behavioral and physiological evidence indicates that insect pheromone sensory neurons are able to resolve pulses of pheromone concentration as they occur downwind from a point source, but the abilities of insect sensory neurons that are sensitive to general odors to respond to pulsatile stimuli are unknown. The temporal response characteristics of olfactory sensory neurons of female American cockroaches Periplaneta americana in response to general odors were measured using a series of short odor pulses (20&shy;400 ms). Odor pulses were delivered to olfactory sensilla in a moving airstream controlled by electromagnetic valves. The responses of sensory neurons were recorded using a tungsten electrode placed at the base of the sensillum. The temporal responses of sensory neurons followed the temporal changes in stimulus concentration, which were estimated by replacing the odorant with oil smoke and measuring the concentration of smoke passing through a light beam. Spike frequency varied with odorant concentration with surprisingly fine temporal resolution. Cockroach olfactory sensory neurons were able reliably to follow 25 ms pulses of the pure odorant 1-hexanol and 50 ms pulses of the complex odor blend coconut oil. Lower concentrations of odorants elicited responses with lower peak spike frequencies that still retained the temporal resolution of the stimulus pulses. Thus, responses of olfactory sensory neurons can reflect the fine structures of non-uniform distributions of general odorants in a turbulent odor plume as well as the average odorant concentration.