Pergamon 0031-9384(93)E0057-W Physiology& Behavior, Vol.55, No. 6, pp. 1015-1019,1994 Copyright© 1994Elsevier Science Ltd Printedin the USA.All rightsreserved 0031-9384/94$6.00 + .00 Hypothalamic Injection of Prolactin or its Antibody Alters the Rat Sleep-Wake Cycle RACHIDA ROKY, 1 JEAN LOUIS VALATX, LUCE PAUT-PAGANO AND MICHEL JOUVET Laboratoire de M~decine Exp~rimentale, INSERM U 52,CNRS UA 1195, UniversiM Claude Bernard, 8, Avenue Rockefeller, 69373 Lyon Cedex 08, France Received 8 June 1993 ROKY, R., J. L. VALATX, L. PAUT-PAGANO AND M. JOUVET. Hypothalamic injectionofprolactin or its antibody alters the rat sleep-wake cycle. PHYSIOL BEHAV 55(6) 1015-1019, 1994.--Several studies have suggested an interaction between prolactin and the sleep-wake cycle. In this study ovine prolactin (oPRL) and anti-prolactinantibody were microinjectedinto the rat dorsolateralhypothalamus, which contains prolactin-likeimmunoreactive neurons. Results indicate that during the light period, prolactin injection induced an increase in paradoxical sleep duration, whereas it caused a decrease when injected during the dark period. Anti-prolactinantibody injection during the dark period also decreased paradoxical sleep duration. There was no effect of oPRL or antibody on slow wave sleep duration irrespective of injection time. These results suggest that prolactin injection may have an inhibitory effect on hypothalamicprolactin neurons. Prolactin Paradoxical sleep Dorsolateral hypothalamus Circadian rhythm Rat brain SEVERAL studies demonstrate that prolactin (PRL) can induce behavioral effects such as lordosis (12), grooming, yawning (18), active avoidance behavior (7), and reduction of the responsive- ness to electrical foot shock (7). These effects may be mediated by an action on brain neurotransmissionthrough central prolactin receptors (21,38). Indeed, recent studies indicate that PRL alters brain level of catecholamine (11,17), GABA (19), acetylcholine (40), opioid (23), VIP (27,30), and pro-opiomelanocortin (32). Moreover, several studies demonstrate that cerebral administra- tion of PRL can influence the activity of hypothalamic neurons (4,11,14,41). The involvement of PRL in sleep regulation was suggested by the observation that injections of PRL in the pontine cat increase paradoxical sleep (PS) (16). In hypoprolactinemic mu- tant rats, on the other hand, the circadian rhythm of PS was reversed, whereas slow wave sleep (SWS) remained unchanged (36). Moreover, Obal et al. have found that SC injections of ovine prolactin (oPRL) enhance PS duration in rabbits (22). We recently have observed the same sleep alteration in the rat after SC or ICV administration of oPRL during the light period. However, nocturnal injection produced a decrease in PS dura- tion, suggesting that PRL may play a role in the regulation of the PS rhythm. Recently, the existence of a central neuronal population containing (24,31,33) and synthesizing (8,35) a PRL-like substance has been demonstrated. In our laboratory, we have found that PRL-like perikarya are exlusively located in the dorsolateral hypothalamus (24). The present study was undertaken to try to directly influence these neurons by in situ injection of oPRL or anti-oPRL antibody and observe the ef- fects on sleep regulation. METHOD Twenty male OFA Sprague-Dawley rats weighing 250 g (IFFA-CREDO, France) were anesthetized with ketamine (150 mg/kg, IP) and implanted with four EEG electrodes over the parietal and occipital cortex and two EMG electrodes in the dor- sal neck muscles. A permanent stainless steel guide cannula (o.d. = 0.64 mm, i.d. = 0.34 mm) was placed in the dorsolat44eral hypothalamus 2 mm above the PRL perikarya (Fig. 1) (1.3 mm to the midline, 3.3 mm posterior to bregma, and 8 mm ventral to the dural surface) according to the Paxinos and Watson atlas (25). A removable mandrel was used to close the cannula. The elec- trodes and cannula were fixed to the skull with dental cement. After surgery, animals were individually housed in a Plexiglas cage at a constant ambient temperature (23 _ I°C) and a 12 h- 12 h light-dark schedule (lights on at 0700 h, lights off at 1900 h) with water and food ad lib. A cable, through a swivel coupler, was routed to an eight-channel polygraph. After 10 days of post- operative recovery, rats were continuously recorded (24 h/24 h) for 2 days as a baseline control recording. In situ injections were performed with a very small diameter glass needle (o.d. = 145/zm, i.d. = 75/~m) linked by a catheter to a Hamilton syringe. Rats received 0.2 #1 of either the vehicle or active substance over a l-rain period. The needle was removed after an additional 1 rain following the end of the injection. An- 1To whom requests for reprints should be addressed. 1015