20 Neuroendocrinology

$111

20 Neuroendocrinology THE RAPID EFFECT OF ESTROGEN ON MEDIAL AMYGDALA NEURONS:

AN I N VITRO STUDY

JUNICHI NABEKURA*, TAKETSUGU MINAMI*, ATSUO FUKUDA* and YUTAKA OOMURA. Department of Physiology, Faculty of Medicine, Kyushu University 60, Fukuoka 812, Japan The rapid effects of estrogen on neural excitability that are very difficult to interpret in terms of protein synthesis have recently been reported. The mechanism of the rapid action, however, remains unclear. Medial amygdala neurons (MedrAMG) are well known to have a high affinity to estradiol and to be one of the estrogen target sites in the central nervous system. We used intracellular recording from Med-AMG of male and female rats to investigate the mechanism of this rapid effect, in vitro. All female rats were ovariectomized bilaterally and estradiol benzoate des-injected two weeks after the operation. Two days after estradiol injection, fame Administration of 17B-estradiol (i0" ~ eM) rats were used for experimentation. produced brief hyperpolarization (6-11 mV) in association with increased membrane conductance The reversal potential of this hyperpolarization was sifted for changes in the K 4 concentration of the perfusion m~@ium. This~ffect persist~ during the elimination of synaptic inputs by 0 mM C a , 12 mM Mg'' and 2 mM Cd-containing medium and suppression of RNA dependent protein synthesis using actlnomycin D. These results indicate that the K conductance of the postsynaptic membrane of Med-AMG neurons is changed by the direct effect of 17B-estradiol rather than via a protein synthesis mechanism. Significant differences (P<0.05, X 2 test) of estradiol responding rates between males (3/37) and females (14/58) were also observed. We believe that the rapid effect of estradiol is a feedback mechanism of this sexual steroid.

RESPONSES OF THE MIDBRAIN CENTRAL LHRH APPLICATION IN FEMALE RATS

GREY

NEURONS

TO

HYPOTHALAMIC

YOSHIMASA KOYAMA* and YU~AKA OOMURA. Department of Physiology, Medicine, Kyushu University 60, Fukuoka 812, Japan

STIMULATION

AND

Faculty of

Midbrain central grey ( C G } and dorsal raphe ( D R ) have important roles on lordosis behavior. They receive neural inputs from the hypothalamus. LHRH applied to the CG has facilitatory effects on this behavior. In this study, to elucidate the neural mechanisms on lordosis, the effects of electrical hypothalamic stimulations on the CG and DR neurons were examined, and LHRH were applied to these electrically identified neurons. Ovariectomized-estrogen primed female rats (200-300 g) were used. Under light urethane anesthesia, the medial preoptic area (MPO) and ventromedial hypothalamic nucleus (VMH) were stimulated by bipolar concentric electodes (less than 0.3 mA, 0.-5 - 1.0Hz). Extracellular units were recorded from the CG and DR. LHRH (I mM in sali 7) was applied ....................... h . . . . . . . . . . . . . . . . . . . . . . I n ~ ; c~~ neurons, 3. . . . (48/154) were excited and 16.2 % (25/154) were inhibited by the SPO stimulations. The VMH stimulations had nearly the same effects on the CG neurons: 33.3 % (51/153) were excited and 10.5 % (16/153) were inhibited. In the DR neurons, the ratio of excitation by VMH stimulation (16.7 %; 10/60) smaller than that in the CG neurons, and the ratio of inhibition (16.7 %; 10/60) was larger than that in the CG neurons (p<0.05 by x2-test). The ratio of inhibition by MPO stimulation ~as also larger than that in the CG neurons (25.6 %;29/78). In the CG neurons, 23.9 % (ii/46) were excited and 10.9 % (5/46) were inhibited by LHRH applications. the LHRH-excited neurons in the CG receive excitatory inputs mainly from the MPO (p<0.05 by Fisher exact probability test). These results suggest that (i) the CG (lordosis facilitatoty area) receive facilitatory inputs from the MPO and VMH, 4hich have facilitatory effects on lordosis, while on the DR (lordosis inhibitory ............ ~ V~ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . lordosis. (2) H s one of the important bio-active agents inv61ved in the Lordosis-facilitating systems from MPO to CG.

POSITIVE AND NEGATIVE FEEDBACK REGULATION OF PLASMA LH BY SEX STEROIDS AND HYPOTHALAMIC UIRH CONTENT IN NEONATALLY ESTROGENIZED FEMALE RATS ~MSAHIRO AIHARA(I,~), SHINJI HAYASHI(2), KATSUMI WAKABAYASHI(3,~), and HIDESHI KOBAYASHI(I,*) (1)Dept.Biol.Fac.Sei.,Toh0 Univ.,Funabashi,Chiba 274, (2)Dept.Anat/Fabryol.,Tokyo Metropol.lnst.Neurosci.,Fuchu,Tokyo 183, and (3)Inst. Endocr.,Gunma Univ.,Maebashi,Gunma 371,Japan Female rats of the Sprague-Dawley strain received 5 daily injections of lO~g estradlol benzoate (EB) d i s s o l v e d i n 0 . 0 2 ml sesame e l l from t h e day o f b i r t h , D a i l y v a g i n a l s m e a r s were e x a mined in adults (41-50 and 91-100 days of age). They failed to show any regular sexual cycles but showed either persistent estrous (incidence of proestrous (P) and/or estrous (E) vaginal smear was 70-I00%: PE-type) or persistent diestrous (0-30Z of smears were P and/or E: PD-type). At either 50or lO0-days of age, the animals were decapitated and hypothalamic blocks were isolated. Serial frontal sections of ~00 ~m thickness were made by a cryostat. The LHRH content in the acid extract of each slice was assessed by radlolmmunoassay. The LHRH content of similar samples from intact P and E rats was also assayed for control values. There were clearly two peaks of LHRH distribution in the rostro-caudal direction, being divided by a low content at the suprachiasmatic nucleus (SCN) region. At both 50 and I00 days of age, no clear difference in the distribution patterns of hypothalamic I~RH was detected among the groups, The total LHRH content ei~her anterior or posterior ~o the SCN was calculated in each animal. No difference was detected between PE- and PD-types at both ages. At 50 days of age, the total LHRH contents in the rostral and mediobasal hypothalami in the sterile rats (PE- and PD-types) were significantly higher than that of normal E rats. At 100 days of age, however, no significant difference was detected. On the other hand, the gonadotropic ability of these rats was examined by the positive and negative feedback effects of sex steroids. The neonatally estrogenlzed female rats were ovariectomized prepuberally and plasma LHwas measured at 50 and I00 days of age after the administration of EB and progesterone. A decrease in plasma LH after ~B and an increase following progesterone was evident in control rats. In contrast, the plasma [/4 of neonatally estrogenized female rats was as low as around 1/10 of control rats and no suppressive influence of EB was detected. Progesterone could induce a slight, but significant increase in plasma LH at 100 days of age but not at 50 days. These results indicate that sterility in neonatally estrogenlzed rats, characterized by a loss of sexual cyclicity and gonadotropln surges, was net due to the reduction of the LHRH content in the hypothalamus, but was due to the changes in hypothalamic LHRH production and releasing systems. ELECTROPHYSIOLOGICAL IDENTIFICATION H Y P O T H A L A M I C P A R A V E N T R I C U L A R NUCLEUS

OF

PUTATIVE

M I T S U K O H A M A M U R A , T A T S U S H I ONAKA* and KINJI YAGI Medical School, T o c h i g i - k e n 329-04, Japan.

CRF

NEURONES

IN

THE

D e p a r t m e n t of Physiology,

RAT

Jichi

In a previous study we developed a t e c h n i q u e to identify a n t i d r o m i c a l l y parvocellular n e u r o s e c r e t o r y (PCNS) cells in the rat p a r a v e n t r i c u l a r nucleus (PVN) (Hamamura et al., 1984). PCNS cells containing i m m u n o r e a c t i v e c o r t i c o t r o p h i n - r e l e a s i n g factor (CRF), p r o l a c t i n - r e l e a s i n g factor and t h y r o t r o p h i n - r e l e a s i n g h o r m o n e have been d e m o n s t r a t e d h i s t o l o g i c a l l y to exist in the PVN. Our previous r a d i o i m m u n o a s s a y s t u d y has d i s c l o s e d t h a t s a p h e n o u s n e r v e s t i m u l a t i o n e l e v a t e s p l a s m a A C T H and prolactln but not t h y r o t r o p h i n levels; w h e r e a s h e m o r r h a g e potentiates s e c r e t i o n of all t h e s e t h r e e h o r m o n e s ( H a m a m u r a et al., 1985). T h e s e d a t a s u g g e s t t h a t if c e r t a i n PCNS c e l l s in the P V N r e c e i v e c o n v e r g i n g e x c i t a t o r y i n p u t s b o t h a f t e r saphenous n e r v e s t i m u l a t i o n and h e m o r r h a g e , t h e s e c e l l s m a y be i d e n t i f i e d as putative CRF neurones since i m m u n o r e a c t i v e CRF and PRF have been d e m o n s t r a t e d in the same PCNS cells. The present e x p e r i m e n t s a i m e d to show e l e c t r o p h y s i o l o g i c a l l y the e x i s t e n c e of s u c h p u t a t i v e C R F n e u r o n e s in the PVN of a n a e s t h e t i z e d rats. S a p h e n o u s n e r v e s t i m u l a t i o n at 4 Hz i n c r e a s e d the d i s c h a r g e r a t e in 14 of the 60 P C N S c e l l s i d e n t i f i e d in the PVN and t e s t e d . The n e r v e s t i m u l a t i o n at I Hz w a s found to p r o d u c e e x c i t a t o r y s y n a p t i c i n p u t s to t h e s e r e s p o n s i v e c e l l s on p e r l s t i m u l u s histograms. Of the 14 cells 10 were tested for h e m o r r h a g e (0.4 % b.w.) and the d i s c h a r g e rate w a s e l e v a t e d in 7 of the 10 t e s t e d cells. T h e s e d a t a c l e a r l y s h o w that c e r t a i n P C N S c e l l s in the P V N r e c e i v e c o n v e r g i n g excitatory s y n a p t i c inputs after noxious and hypovolaemlc s t i m u l i and thus t h e s e P C N S c e l l s a r e identified as p u t a t i v e C~F neurones. References: H a m a m u r a M. et el. (1984) J Phvsiol 3oc Japan 46: 545. ~ a m a m u r a M. et el. (1985) ~ Physlol 47: 594.

T.E

EFFZCT OF ~ Z

TUMOR PROMOTER 12-0-TZTP~ZC~O~LPHORSOL-13-ACETATE

(TPA)

ON m E

~J~SE

OF

LUTEINIZING HORMONE (LH) IN DISPERSED RAT ANTERIOR PITUITARY CELLS TAKASHI SEKI*,

TSUNEHISA MAKINO and RIHACHI

Department of Obstetrics and Gynecology,

IIZUKA*,

Kelo University ~ h o o l of Medicine, 35 Shinano-machl, ShinJuku-Ku 160, Tokyo, Japan The effect of

TPA,

the most potent phorbol ester, on

dispersed rat anterior pituitary cells.

the release of LH was studied

Anterior pituitaries were obtained from mature

Sprague-Dewley rats and then dispersed enzymatically with 0.5% of trypsin.

In

male

The dlnpersed cells

were cultured on Cytodex beads 2 in Medium 199 containing 10t of horse serum for 2-3 days.

The

cultured cells attached to Cytodex beads were packed In a small column and were superfused wlth Medium 199 containing 25 mM of Hepes.

Samples were collected every five minute.

results were obtained, 1) A f i v e minute stlmulatlon with lO - l o L~ release in a dose-dependent manner.

The maximal ~

release by TPA was 6O% of that by LH~, 2) Desensitization, which was

by TPA was observed. markedly

observed

with

LHRH, was n o t

antagonist

(N-acetyl-D-P-chloro-Phe 1,2,

stimulated

LH

release.

4)

significant

with

continuous

D-Try 3, D-Lys 6,

Nlfedipine,

a

Ca 2§

The following

to 10-6M TPA caused s i g n i f i c a n t

D-AIR I0

channel

release, whereas Ca-ionophore remarkably reinforced it.

TPA s t i m u l a t i o n .

LHRM) partially

blocker,

reduced

3)

blocked

LHRH TPA-

TPA-stimulated

LH

Additionally, the removal of Ca 2+ from

the auperfuslon medium completely supressed LH release by TPA.

These results are compatible

with the idea that Ca 2+ may be involved in the process of TPA-stimulated LH release.

As TPA has

been reported to activate protein kinase C, the data may suggest that TPA stimulates LH release mainly by activating the enzyme and partially by activating LHRH receptors. THE TIME COURSE AND IONIC HECHANISH OF PITUITARY CELLS

hpGRF-INDUCED GRONTH HORMONE (GH) RELEASE IN DISPERSED RAT

MASAKATSU KATO* and HITSUO SUZUKI. Department of Physiology) Institute of Endocrinology) Gunma University) Maebashi 371. Japan Rat anterior pituitary was removed under pentobarbital anesthesia and was dispersed with 0.5Z trypsin.

Dispersed pituitary cells were mixed with Blogel-P-2 and packed in

connected to a peristaltic pump, for the perlfuslon experiment (flow race, 1.2 ml/min).

G H release ~nduced by hpGRFczr~ eztrczceZZu~zl, Ca 2+

The threshold concentration of hpGRF was

10 -12 M and the response showed dose-dependency up t o 10 -8 M.

A one mln application of hpGRF

produced a gradual increase In GH release which reached maximum response at two mln after the decreased to the basal value by 15 mln after the application. response pattern differed greatly from that of 30 mH KCI.

This

Excess K+ stimulation produced a prompt

rise and fall of GH release which is p a r a U e l co the change of K+ concentration in the column. Both responses were dependent on extracellular Ca 2+.

Decreasing extracellular Ca 2+ concentration

partially suppressed the responses, and the removal of extracellular Ca 2+ completely suppressed both hpORF-induced and high K-stlmulated responses. with Ba 2+ greatly increased GH release

Effec~ of other d~vaZent

but the replacement by Sr 2+ caused a small increment of GH release.

GH release induced by hpGRF

was biggest with Ba 2+ and the response with Sr 2+ was slightly greater than that with Ca 2+. Thus.

extracellular

Ca 2 + , w h i c h m e a n s a n i n f l u x

high K+-stlmulated GH release. although

Ba 2+ c o u l d n o t s u b s t i t u t e

o f Ca 2 + , w a s e s s e n t i a l

for hpGRF-induced and

Ba 2+ and Sr 2+ could substitute for Ca 2+ in hpGRF-Induced responses, f o r Ca 2+ i n e x c e s s

K+-stlmulated

CH r e l e a s e .

$114

THE EFFECT OF SOMATOSTATIN ON TRH-STIHULATED TSH AND VIP-STIMULATED PROLACTIN PENTOBARBITAL ANAESTHETIZED P,ATS Z'~AS

SECRETIONSIN

*

o f E n d o c r i n o l o g y , Gunma U n i v e r s i t y , Maebashl S o m a t o s t a t i n (SRIF) has been known co be a p o t e n t hypothaZamic p e p t i d e f o r i n h i b i t i ~ B the release of OH. In recent years, the physiological role of the peptlde has been disclosed In relation to the pulsatile GH secretion of the rat. On the other hand, SRIF has been also found to inhibit both TRH-stimulated TSH and VIP-stlmulated prolactln release when applied in in vitro dispersed rat pituitary cells or pituitary tumor cells. Moreover, specific binding sites for SRIF have been identified on rac lactotrophs." In contrast, there are conflicting reports from in vivo study, and the physiological role of SRIF in the regulation of TSH and FRL secretion still remains unclear. S h i i dl h 1 I i i ti of the .......... CRF-stimulated . . . . . . . . . . . .GH ... t b h he i f . . . .or . .PRL . . . .release. . . . . . . . . In . . .another . . . . . ~;~al~ ; h e Y ~ e c ~ :f~ bolusW . . . . .injection . . . . . . . .or . . :fOcontinuous ................. Infusion TSH of high doses of SRIF-I~ on TRY-stimulated TSH a~d VIP-stlmulated PKL releases was also observed. Pen~obarbltal anaesthetized by concentric, e r l O K B wa bipolar electrodes with i00 ~A blphaslc current. About 3 n~oles of RH and V I inJ . . . . . . . . . . . . . . . . . . . . J . . . . . . . . . . . . . . . . . . . . . . d.......... Telther asPaPbolus0intoWthe s Jugular vein (7.6 nmoles/lO0 g BW) or infused continuously through the femoral vein (i0 nmoles/lO0 g BW/10 min). The plasma level of TSH in response to TRH was not changed after the Pe stimulation, while it was slightly lowered after the bolus injection (-34.5%, n:8, p<0.Ol), and was strongly

~n~:s~l~elnSae~r~;~;;ei~el:::~n~ftS~Fes~[c;:~tS:om~n~tb;~

of the Pe did not diminish VtP-elevated PRL secretion but even raised it ( 7 Basal prolactln secretion was not affected by this treatment. Similarly, the bolus injection and ti i f i of SRIF-14 "paradoxically" enhanced VIP-induced PRL release (+109.9%, n:7, n:ll, p<0.05, respectively). Thus, we conclude that SRIF can not be involved in the control of TSH and PRL release as a physiologically important factor.

;:;.0;YL ;J~l~?

C O N D I T I O N E D F E A R STRESS S U P P R E S S E S F O O T S H O C K - I N D U C E D V A S O P R E S S I N S E C R E T I O N IN R A T S T A T S U S H I ONAKA*, M I T S U K O H A M A M U R A and KINJI YAGI M e d i c a l School, T o c h i g i - k e n 329-04, Japan.

D e p a r t m e n t of Physiology,

Jichi

Our p r e v i o u s study has s h o w n that v a s o p r e s s i n (VP) s e c r e t i o n is p o t e n t i a t e d by c o n t i n u o u s l y a p p l i e d 5 0 - H I f o o t s h o c k s (FS) but not by i n t e r m i t t e n t l y a p p l i e d FS; a n d in the l a t t e r case, r a t s e x h i b i t 'freeze' b e h a v i o u r d u r i n g i n t e r - F S p e r i o d (Yagl e t a l . J P h y s i o l .8oc J a p a n 47: 599, 1985). A p p a r e n t d i s c r e p a n c i e s in t h e s e data m i g h t have been due to 1} e x h a u s t i o n of VP stores in the p o s t e r i o r pituitary, 2) p o s s i b l e a c t i v a t i o n of i n t r i n s i c a n a l g e s i a s y s t e m i n v o l v i n g b l o c k a g e of p r i m a r y a f f e r e n t t r a n s m i s s i o n and 3) s u p p r e s s i o n by fear stress of FS-induced p o t e n t i a t i o n of VP s e c r e t i o n . An I.D. i n j e c t e d h y p e r t o n i c s a l i n e or u r e t h a n e s i g n i f i c a n t l y e l e v a t e d p l a s m a VP l e v e l s in the r a t s w h i c h had r e c e i v e d i n t e r m i t t e n t FS for 10 min. T h e s e d a t a e x c l u d e the f i r s t p o s s i b i l i t y of VP s t o r e e x h a u s t i o n . To t e s t the third p o s s i b i l i t y we h a v e c l a s s i c a l l y c o n d i t i o n e d r a t s w i t h f l a s h and s o u n d as c o n d i t i o n e d s t i m u l i (CS) a c c o m p a n i e d by 50 Hz FS for I s as u n c o n d i t i o n e d s t i m u l u s (UCS) a n d t r a i n i n g w a s r e p e a t e d e v e r y 6 s for 10 min. The r a t s w e r e t e s t e d by FS (60-s d u r a t i o n ) p r e c e d e d by CS (60-s d u r a t i o n ) at 0, 0.5, I, 2 a n d 4 h a f t e r the training. P l a s m a VP levels w e r e s i g n i f i c a n t l y lower and ACTH levels w e r e higher in the c o n d i t i o n e d t h a n in the c o n t r o l rats. T h e m a x i m u m e f f e c t s on b o t h h o r m o n e levels o c c u r r e d at I h after the training. ~.,ese effects of c o n d i t i o n i n g d e p e n d e d on i n t e n s i t i e s of t r a i n i n g UCS. Scores of 'freeze' behavlour i n c r e a s e d c o n s i s t e n t l y as the s u p p r e s s i o n of VP s e c r e t i o n occurred. D i f f e r e n t i a l r e s p o n s e s b e t w e e n VP and ACTH e x c l u d e the second p o s s i b i l i t y that the s u p p r e s s i o n of p r i m a r y a f f e r e n t s by i n t r i n s i c a n a l g e s i a m i g h t have played a crucial role for the o b s e r v e d s u p p r e s s i o n of VP s e c r e t i o n . T h e s e d a t a s t r o n g l y s u g g e s t t h a t p h y s i c a l s t r e s s p o t e n t i a t e s VP s e c r e t i o n and p s y c h o l o g i c a l stress of fear suppresses the p o t e n t i a t e d VP s e c r e t i o n and thus i n d i c a t e that 'stress' is no longer an a d e q u a t e p h y s i o l o g i c a l concept.

HIROMICHI HASHIMOTO*, TERUO N A K A J I M A Dept. N e u r o p s y c h i a t . ,

TADASHI NOTO*, JUNJI NAKAO*, Kyoto Pref.

Univ. Med.

HIROSHI K A M I M U R A * and

Kamikyo-ku,

Kyoto,

Japan

In order to c l a r i f y the release m e c h a n i s m of v a s o p f e s s i n and o x y t o c i n in the p o s t e r i o r pituitary, the effects of h y p e r t o n i c saline, b i o a c t i v e amines, carbachol, a n g i o t e n s i n II and p r o s t a g l a n d i n E 9 on the release of these h o r m o n e s w e r e studied using the i n t r a v e n t r i c u l a r i n j e c t i o n t e c h n i q u e and p e r f u s i o n t e c h n i q u e for the isolated pituitary. The i n t r a v e n t r i c u l a r a d m i n i s t r a t i o n of h y p e r t o n i c saline, carbachol (5~g), a n g i o t e n s i n II (5~g), p r o s t a g l a n d i n E 9 (5pg} or h i s t a m i n e (20pg) to a r a b b i t increased the c o n c e n t r a t i o n s of p i a s m a v a s ~ p r e s s i n and oxytocin,. whereas s e r o t o n i n (20~g) d e c r e a s e d them. N o r a d r e n a l i n e (20~g) i n c r e a s e d the c o n c e n t r a t i o n of oxytocin, but not that of v a s o p r e s s i n . D o p a m i n e (20~g) had no s i g n i f i c a n t effect on the plasma level of both hormones. The release of v a s o pressin and o x y t o c i n from p o s t e r i o r p i t u i t a r y f r a g m e n t s of a rat was s i g n i f i c a n t l y stimulated by the change in o s m o l a l i t y of the p e r f u s i o n medium, s u g g e s t i n g that the p o s t e r i o r p i t u i t a r y i t s e l f 5 c o u l d possess a kind of osmoreceptor. Perfusion with the m e d i u m c o n t a i n i n g i0- M d o p a m i n e s u p p r e s s e d the r e l e a s e of both h o r m o n e s to 70-80% of the control levels. However, the o t h e r b i o a c t i v e amines and the agents e x a m i n e d did not affect the release of these hormones under e x p e r i m e n t a l conditions. F r o m the above f i n d i n g s the r e l e a s e m e c h a n i s m of v a s o p r e s s i n and oxytocin was discussed.

DEPOLARIZING EFFECT OF NORADRENALINE ON NEURONS OF THE RAT SUPRAOPTIC NUCLEUS IN yITRO HIROSHI YAMASHITA, KIYOTOSHI INENAGA* and HIROSHI KANNAN, Department of PhysioloF~v, University of

It

is

well known that the hypothalamic nuclei, especially the supraoptic nucleus (SON) and

paraventrlcular brainstem

(AI

nucleus area).

(PVN), receive Electrical

oxytocin c e l l s o f the SON and PVN.

on vasopressin are

(I0-6-10-4

potential

neurons

both

in

the

vasopressin

and

recordings.

still some inconsistencies in the evidence obtained from rats by

application.

characteristics

increase

catecholaminergic

of the AI area excites

the mouse slice preparation using extracellular

However, there iontophoretic

dense inputs from

stimulation

We have shown the ~1 e x c i t a t o r y e f f e c t of noradrenaline (NA)

The

present

study

was

attempted

to

analyse

cells in the rat slice preparation by intracellular

means

the

M) excited t h i r t y four (83 %) neurons tested showing depolarization of the

in

a dose-dependent manner accompanied by a decrease of membrane

of the firing rate.

resistance

NA

membrane

and

the ~-agonist isoproterenol did not cause any change in membrane characteristics in 6

of

SON

7

neurons.

an

The~l-agonist phenylephrine excited i0 out of 11 neurons tested,

while

(putative

of

membrane

recordin E.

We found no difference of response to NA

between

neurons

vasopressinerEic) and non-phasic (putative oxytocinerEic) patterns

having

phasic

of firing.

These

results suggest that HA elicits depolarizing effects resulting in an increase of excitability both v a s o p r e s s t n and o x y t o c i n neurons o f the r a t SON through ~ l - a d r e n e r g l c

out

receptors.

on

$116 DIRECT EFFECTS OF 2-DTA, 3-DPA AND ESTROGEN GUINEA-PIG VENTROMEDIAL HYPOTHALAMIC NEURONS

ON

THE

MEMBRANE

EXCITABILITY

OF

TAKETSUGU MINAMI*, JUNICHI NABEKURA*, ATSUO FUKUDA* and YUTAKA OOMURA. Department of Physiology, Faculty of Medicine, Kyushu University 60, Fukuoka 812, Japan Ventromedial hypothalamic neurons control feeding and sexual behaviors. In the present study, we have used the intracellular recording from guinea-pig hypothalamic neruons in vitro to examine the direct effects of 2-deoxytetronic acid (2-DTA), satiety organic acfd, 3-deoxypentonic acid (3-DPA), hunger organic acid, and estrogen(E 9) on these neruons. Six neurons tested with 2-DTA (n=23) were depolarized with associated increased membrane resistance. Five neurons tested with 3-DPA (n=21) were hyperpolarized with associated decreased membrane resistance. The reversal potentials of both effects were about -90 mV. In the E experiment, female guinea-pig, ovariectomized bilaterally and Ep-p~imed, were used~ The administration of E.~ produced depolarization (7/29) an~ (14/29) 9 Both effects ~ersisted during the elimination of synaptic inputs by 0 mM Ca "+, and 12 mM Mg 2 containing medium. Depolarization was accompanied with increased membrane resistance and hyperpolarization was associated with decreased resistance. The reversal potentials of both effects were almost -90 mV. r the reversalfpotentials of hyperpolarization were shifted for changes in concentration o the perfusion medium. These results suggest that ventromedial hypothalamic neurons influenced by organic acids and E 2 may be involved in the feeding and sexual behaviors.

hyperpolarization

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