Circadian Rhythms in Locomotor Activity of the Hagfish, Eptatretus burgeri VI. The Effects of Cutting the Spinal Cord.

The present study is designed to clarify the mechanism by which the circadian pacemaker controls the locomotor activity of the hagfish and also to estimate the role of brain and spinal cord in the swimming behavior of the animal. We examined the effect of cutting the spinal cord at the 6 different positions on the circadian rhythm and the locomotor behavior of the animal. The most frontal cut was located between the brain and spinal cord, and the other 5 cuts were given to every 1/6 the length of the spinal cord.

A possible retinal information route to the circadian pacemaker through pretectal areas in the hagfish, Eptatretus burgeri.

By recording the locomotor activity rhythm of hagfish, Eptatretus burgeri, in which surgical lesions of the pretectal areas were made, we searched for the route of light information from the eyes to the circadian pacemaker, which is considered to be located in the preoptic nucleus. The entrainment of circadian activity rhythm to the light dark cycle, under 12 h light/12 h dark (12L:12D) was lost in animals whose pretectum was ablated with a pair of scissors and the animals then showed a free-running rhythm. Destruction of the pretectal areas with a high-frequency lesion generator also caused a free-running rhythm under 12L:12D.

The preoptic nucleus: the probable location of the circadian pacemaker of the hagfish, Eptatretus burgeri.

By recording the locomotor activity rhythm of hagfish, Eptatretus burgeri, in which surgical lesions of the preoptic nucleus (PON) were made, we searched for the location of the circadian pacemaker in the hypothalamus. The characteristic rhythms were lost in animals lacking the anterior part of the hypothalamus, which includes the PON. Cuts in front of the PON did not affect the rhythm, but cuts behind the PON caused the animals to loose their rhythms.

Changes in certain diurnal hormonal rhythms in developing male rats exposed to adiurnal environmental cues.

It has traditionally been thought that diurnal rhythmicities cannot be entrained to follow adiurnal environmental cues that deviate greatly from a 24-hour periodicity. In this study, exposure of male rats pre- and postnatally to an adiurnal lighting schedule of 9 hours light: 9 hours dark resulted in the entertainment of certain hormonal rhythms (such as plasma corticosterone and plasma TSH) but not of others (such as pituitary TSH and plasma T3). Even though thyroid rhythms were influenced only partially by the shorter, 18-hour day, absolute levels of pituitary TSH and plasma T3 were significantly higher in experimental rats (9 hours light:9 hours dark) than controls (12 hours light:12 hours dark).

Diurnal rhythm of pituitary-thyroid axis in male rats and the effect of adrenalectomy.

Levels of TSH, thyroxine (T4) and triiodothyronine (T3) were measured by radioimmunoassay in plasma (TSH, T4, T3) and pituitary (TSH) of 60-day old male Long-Evans rats. Definite diurnal rhythms were demonstrated in pituitary TSH, plasma TSH and T3 in intact rats, evidenced by the statistically significant differences between zenith and nadir for pituitary TSH, plasma TSH and T3. The zenith value of pituitary TSH and the nadir values of plasma TSH, T4 and T3 were observed at the same time (2400 h) as were the nadir value of pituitary TSH and the zenith values of plasma TSH, T4, and T3 (at 1200 h).

Developmental patterns of plasma TSH, T4 and T3 in rats deprived of light from birth.

Plasma levels of TSH, T4 and T3 in the rat show characteristic developmental patterns within the first postnatal month, with TSH reaching a peak on day 13, T4 on day 16 and T3 on day 20. In dark-reared rats, a significant reduction in plasma T3 associated with low plasma T4 as well as high plasma TSH suggest that light-deprivation from birth impairs and/or delays maturation of pituitary-thyroid axis.

The effect of neonatal treatment of male mice with antiandrogens and of females with androgens on the development of the os penis and os clitoridis.

The os penis in mice and rats is composed of a proximal intramembranous and endochondral osseous element and a distal cartilaginous, ossifying element. Female mice, but not rats, have a small os clitoridis which corresponds to the intramembranous part of the proximal element of the os penis. In mice of either sex a dense mesenchymatous formation ventral to the urethra is the anlage for the bones of the external genitalia.