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正

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Extracellular discharges of neurons in the dorsomedial nucleus（DMN）were recordedwith glass microelectrode from rat hypothalamic slices.The firing frequency decreased in 77 andincreased in 48 units during the addition of norepinephrine into the bath(NE

2×10

-5

mol/L)of160 units when the slices were perfused with artificial cerebrospinal fluid （ACSF）.Most of theseresponses could be antagonized by Yohimbine(YOH

2×10

-5

～4×10

-5

mol/L).Nevertheless

when the perfusion fluid was changed

i.e.

with low Ca

2+

-high Mg

2+

ACSF（CM-ACSF）whichcould block the chemical synaptic transmission

26 out of 35 units were inhibited by NE and only1 unit excited.The inhibition could he blocked by YOH. A very significant difference（P

<

0.01）was seen between the data obtained in ACSF and those in CM-ACSF.Furthermore

all NE-inhibited units in ACSF were also NE-inhibited in CM-ACSF

but the majority of NE-excited u-nits in ACSF changed into NE-inhibited or NE-unresponsive in CM-ACSF.The results suggestedthat NE produced a direct inhibitory effect on neurons in DMN which was mediated by the post-synaptic alpha 2 adrenergic receptors.