1. Whole-cell recordings were made from 390 neurons of the suprachiasmatic nucleus (SCN) in horizontal brain slices during different portions of the circadian day. The locomotor activity of the rats was measured prior to the preparation of brain slices to insure that each rat was entrained to a 12 h-12 h light-dark cycle. 2. The mean input conductance was 42% higher (1 fi58 nS) in neurons recorded near the subjective dawn than those (1 11 nS) recorded near the subjective dusk. The current required to hold the neurons at -60 mV also showed a circadian variation with a peak in the middle of the subjective day and a nadir in the middle of the subjective night. Analysis of the variations in the input conductance and the holding current at -60 mV suggested that at least two ion conductances are involved in the pacemaking of the circadian rhythms.3. Voltage-clamped SCN neurons often had both outward and inward spontaneous postsynaptic currents. The outward currents were blocked by bicuculline but not by strychnine, and were identified as IPSCs mediated by GABAA receptors. The inward currents were blocked by 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) and were identified as EPSCs mediated by glutamate. Most spontaneous synaptic currents were miniature currents but action potentialdependent large events were seen more often in IPSCs than in EPSCs. 4. Stimulation of the optic nerve or chiasm usually evoked a monosynaptic EPSC which was mediated by both NMDA and non-NMDA receptors. In 13% of cells, optic nerve stimulation evoked an outward current or an inward current followed by an outward current; all the evoked currents were blocked by 4-aminophosphonovaleric acid (APV) and CNQX whereas the outward current only was blocked by bicuculline, suggesting involvement of an inhibitory interneuron. 5. SCN neurons sum the excitatory inputs from both optic nerves; on average each SCN cell receives innervation from at least 4 8 retinohypothalamic tract (RHT) axons. 6. Focal stimulation in the vicinity of the recorded neuron revealed that nearly all SCN neurons receive local or extranuclear GABAergic inputs operating via GABAA receptors. The EPSCs activated by such stimulation were not significantly different in amplitude and pharmacological properties from those induced by RHT stimulation. 7. One hundred and one neurons were labelled with neurobiotin during whole-cell recording.Based on the dendritic structures, four types of SCN neurons (monopolar, radial, simple bipolar and curly bipolar) were identified. The curly bipolar cells had a higher membrane conductance, holding current and hyperpolarization-activated current (Ih) amplitude than the other neuronal types. Radial neurons did not respond to optic nerve stimulation, which activated EPSCs in the other cell types.Behavioural and physiological functions of mammals show (SCN), a paired hypothalamic structure lying dorsal to the daily patterns, called circadian rhythms.

The human norepinephrine transporter (NET) gene was cloned and structurally analyzed. The far 5' fragment containing exon 1 (a non-coding exon) and exon 2 was sequenced. The transcription start site of the gene in human brain stem tissue was determined by primer extension analysis. It was found that the gene could be transcribed from multiple starting points. The 5' flanking sequence contains a proximal G-C rich region, one possible GSG element and several SP1 sites. However it does not contain TATA box and CAAT box motifs. Gel shift analysis with nuclear extracts from different tissues of mouse shows that the G-C rich region may be involved in tissue specific expression of the gene.