Male Rats 52 Pineal Gland 50 pineal body 48 rat 46 Animal 44 animal experiment 38 Rats, Inbred Strains 36 Support, Non-U.S. Gov't 36 endocrine system 36 central nervous system 34 radioisotope 32 Melatonin 26 melatonin 24 nonhuman 22 Norepinephrine 20 autonomic nervous system 20 Ganglia, Sympathetic 18 superior cervical ganglion 18 Pineal gland 16 noradrenalin 16 pineal gland 16 Female 14 in vitro study 12 nervous system 12 Animals 10 Circadian Rhythm 10 Hypothalamus 10 Kinetics 10 animal cell 10