2112 Dexamethasone increase the Arg-vasopressin release in suprchiasmatic nucleus explant-slice culture of rats

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2112 Department

Dexamethasone increase the Arg-vasopressin release in suprchiasmatic nucleus explantslice culture of rats. of Physiology, Nagoya City University, Medical School, Mizuho-ku, Nagoya 467, Japan

Yoshiaki Isobe Circadian rhythm of locomotor activity is controlled by suprachiasmatic nucleus (SCN), a center of a biological clock. Arg-vasopressin (AVP) containing neuron is a output neuron from the SCN. In this study, effects of dexamethasone (Dx) on the AVP release are analyzed using a slice culture on SCN of rats. Twenty min after adding the Dx (0.2 pg/ml), AVP release was increased. Dose dependency was observed from 0.02 to 0.2 pg/ml of Dx. AVP release from the SCN was different by the time of day. Beside,the relationship of the AVP contents in SCN with the serum corticosterone levels are analyzed in vivo. AVP rhythms in SCN synchronized with locomotor activity rhythm;the peak developed about 180 degree out of phase of that of the locomotor activity rhythm. Under a light-dark cycle, the serum corticosterone levels are reciprocally correlated with the AVP content in SCN. These results suggest that corticosterone may relate with the AVP rhythm in SCN.

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RESPONSES OF RAT SUPRACHIASMATIC

Faculty of Information Sciences, Hiroshima roshima 731-31, Japan

NEURONS

TO MAGNETIC

City University, 3-4-1, Ozuka-Higashi,

FIELDS

Asa-Minami-Ku,

Hi-

OSAMU HIWAKI The responses of neurons in the rat suprachiasmatic nucleus (SCN) to magnetic fields were investigated. Urethane anesthetized rats l&d with ear bars were exposed to 40 micro tesla magnetic fields in the magnetically and electromagnetically shielded room. It was verified that the electrical activity of the neurons in the SCN responded to the change of the direction of the magnetic field.

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INHIBITORY EFFECT OF FOOT SHOCK STRESS ON LIGHT-INDUCED PHASE SHIFTS OF HAMSTER WHEEL-RUNNING RHYTHM Department of Pharmacology, School of Human Science, Waseda University, Mikazima, Tokorozawa, Saitama359, Japan SHIGENOBU

SHIBATA,

AYAKO TANIAI,

AKIHIKO

NUMATA,

TAKAHIRO

MORIYA

It is well known that circadian rhythms are entrained by light exposure (photic entrainment) and forced awake (non-photic entrainment) such as stress and motor activation. In this paper we studied whether non-photic treatment can affect the photic entrainment in the circadian systems. An effect of foot shock stress on lightinduced phase shifts was examined using hamster wheel-running rhythm. Foot shock treated 5 min before and during light exposure (5 min) significantly attenuated the light-induced phase advance at CT21 and phase delay at CT13. However, foot shock stress treatment itself caused the phase advance nor phase delay. In addition, foot shock attenuated the induction of FOS-like immunoreactivity in the hamster suprachiasmatic nucleus by light exposure at CT 13. These results suggest that stress may produce an inhibitory influence on light-induced phase shifts of circadian rhythms.