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THE amino acids L-glutamic and L-aspartic acids form the most widespread excitatory transmitter network in mammalian brain1,2. The excitation produced by L-glutamic acid is important in the early development of the nervous system3,4, synaptic plasticity and memory formation5,6, seizures7,8 and neuronal degeneration9,10. The receptors activated by L-glutamic acid are a target for therapeutic intervention in neurodegenerative diseases, brain ischaemia and epilepsy. There are two types of receptors for the excitatory amino acids, those that lead to the opening of cation-selective channels and those that activate phospholipase C (ref. 11). The receptors activating ion channels are NMDA (N-methyl-D-aspartate) and kainate/AMPA (α-amino-3-hydroxy-5-methyl-4-isoxazole propionate)-sensitive receptors. The complementary DNAs for the kainate/AMPA receptor12,13 and for the meta-botropic receptor14 have been cloned. We report here on the isolation and characterization of a protein complex of four major proteins that represents an intact complex of the NMDA receptor ion channel and on the cloning of the cDNA for one of the subunits of this receptor complex, the glutamate-binding protein.

Direct (via the skull) and indirect (via the eyes) light on the rate of adaptation of circadian rhythms of pineal, retina and serum indoleamines and of locomotor activity was examined by observing photoperiod reversal in eye covered and normally sighted chickens. Eye covering did not affect indoleamine levels nor locomotor activity on the regular light:dark (L:D) cycle. However, following photoperiod reversal, the eye covered chickens showed slower rates of adaptation of retinal melatonin and locomotor activity to the new L:D cycle than did the normal sighted chickens. Pineal and serum indole levels were unaffected by eye covering. Our results in birds indicate that 1) light to the eye has a role in governing retinal melatonin and locomotor activity, 2) the pineal is directly photosensitive, and 3) the endogenous rhythm of pineal melatonin may play a role in the entrainment of the locomotor rhythm in the chicken.