Normal Light Cycle Research Articles

Patterns of hibernation in the arctic ground squirrel.

Cyclic patterns were defined in subspecies of arctic ground squirrels (Citellus undulatus) from the Brooks and Alaskan Ranges. In the annual cycle a heterothermal (hibernation) season with entry, maintenance, and emergence stages was distinguished from a homeothermal (active) season with reproductive, recovery/growth, maintenance, and fattening stages. The heterothermal season consisted of a series of short hibernation cycles in which heterothermal (hibernation) periods with reentry, refractory, and irritable phases were distinguished from homeothermal (active) periods with arousal, maintenance, and preparation phases. Squirrels in which exposure to darkness at 5 °C was delayed (Nov. vs. Sept.) showed a lesser response but emerged synchronously with the normal group. Entry was attenuated with a normal light cycle at 5 °C (8 vs. 3 weeks). Juveniles showed a 2- to 4-week delay in entry as compared to adults.

Inhibition effects of “neo-natal” estrogenization on the sexual behavior of the male rat and modifications of the genital tract

Publisher Summary This chapter focuses on the complimentary effect on pituitary gonadal function. Testicular hypertrophy response was used as a measurement for relative effect of light and social effect on neurosecretory activity in hypothalamo-hypophysial complex. Right testes (larger of the two) were removed from male doves and were weighed. Birds were then assigned to various combinations of (1) short vs . normal light cycle, and (2) isolation vs. social stimulation. At the end of 4 weeks all birds were laporatomized. The left testis was removed, weighed and expressed in percentage weight of right testis for each bird. This effect is not attributable to added light exposure associated with female-exposure period. The results were discussed in terms of existing hypothalamic neurosecretory system. In addition, the chapter also deals with the inhibition effects of “neo-natal” estrogenization on the sexual behavior of the male rat and modifications of the genital tract.

Light and social exposure: complimentary effect on pituitary gonActal function

This chapter mentions the complimentary effect on pituitary gonadal function. Testicular hypertrophy response was used as a measurement for relative effect of light and social effect on neurosecretory activity in hypothalamo-hypophysial complex. Right testis (larger of the two) was removed from male doves and was weighed. Birds were then assigned to various combinations of (1) short vs . normal light cycle, and (2) isolation vs. social stimulation. At the end of 4 weeks, all birds were laporatomized. The left testis was removed, weighed and expressed in percentage weight of right testis for each bird. The main results are (1) testicular hypertrophy is complete in 4 weeks in 14 h light cycle. In addition, the chapter also highlights the inhibition effects of “neo-natal” estrogenization on the sexual behavior of the male rat and modifications of the genital tract.

Circulating LH and FSH levels and testicular function in hamsters during light deprivation and subsequent photoperiodic stimulation.

The relationship between testicular function and peripheral gonadotropin levels was investigated in adult hamsters throughout a 60-day period of light deprivation and then again after a return to normal light cycles (L:D, 14:10). Hypophyseal LH and plasma LH and FSH concentrations declined slowly and progressively (at least 5-fold) during the 60-day period of constant darkness. Thedecline in gonadotropin release was associated with a 73% decrease in plasma testosterone concentrations and a 4-fold reduction in the capacity of testicular tissue to convert [7-3H]progesterone to [3H]testosterone in vitro (p < 0.05). Testis atrophy accompanied the collapse of the hypophysealgonadonal endocrine system as evidenced by a 98% reduction in the relative number of step 7 spermatids and the absence of step 17 spermatids from the seminiferous epithelium. Once previously light-deprived hamsters (i.e., 60 days) were exposed o L:D, 14:10 cycles, hypophyseal LH and plasma LH and FSH levels returned to near control levels w...

Effect of varying light and temperature cycles on the ovipositional response of malathion-treated indian meal moth adults.

Light was a primary stimulus in the ovipositional cycle of Plodia interpunctella (Hübner) when the insects were exposed to normal light and temperature phasing. Temperature exhibited a secondary stimulus when it was out of phase with the normal light cycle. Under a normal 14:10-hour light:dark cycle and temperatures varying from 27 to 32°C with the high occurring at 5 PM, the peaks of oviposition occurred at 9 PM. Peaks also occurred at 9 PM with the same light cycle and reverse temperature conditions (high temperature at 7 AM). when light and temperature conditions were out of phase, the peaks assumed a bimodal tendency. Constant light conditions caused lessened egg production and accordingly less distinct peaks. Malathion caused the peak period of oviposition to occur on the 1st day with decreased production on all succeeding days. Egg viability was not affected by any change in light or temperature conditions.

Host Effects on the Migration of Nippostrongylus brasiliensis in a Thermal Gradient

Nippostrongylus brasiliensis of a 17-day-old infection migrated more slowly than those of a 7-day infection in a thermal gradient. Worms, 17 days old, which were transplanted into an unexposed rat on day 7 migrated at the same rate as those of a 7-day infection. The migration rate of Nippostrongylus was faster during the night than the day. Reversal of the day-night light cycle for the host rats caused their worms to migrate faster during the day than those of rats on a normal day-night light cycle. McCue and Thorson (1964) and Thorson, Mueller, and McCue (1964) reported that parasitic stages of several phyla of helminths migrated toward higher temperatures in a thermal gradient until thermal damage and death occurred. With Nippostrongylus brasiliensis worms of older infections (18 days) migrated slower than those of a 7-day infection. It was suggested that this may be due to a host effect, presumably an immune response, or to senescence of the worms of the older infection. Preliminary observations also indicated that the response of the worms varied throughout a 24hr period with more rapid migrations occurring at night. This could also be interpreted as a host effect since the physiological and behavioral activity of rats is greatest during the night (Hemmingsen and Krarup, 1937; Browman, 1937). The experiments reported herein were designed to determine if in fact there was a host effect in older infections which caused slower migration in a thermal gradient and if the daily activity cycle of the host also influenced the migration rate of worms in a thermal gradient. MATERIALS AND METHODS The basic apparatus and methods described in McCue and Thorson (1964) were used. Male Wistar rats, 4 to 8 weeks old, were obtained from the Lobund Laboratory Conventional Animal ColReceived for publication 11 August 1964. * These studies were supported in part by a research grant (AI-03049) from NIAID, NIH, Public Health Service. t From work done by the senior author at the University of Notre Dame in partial fulfillment of the requirements for the Ph.D. degree. t Present address (R. E. T.): Department of Tropical Health, American University of Beirut, Beirut, Lebanon. ony, University of Notre Dame. Special experimental manipulations will be discussed in the following section.