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Electrical stimulation of the median eminence in rats, changes in catecholamine content and in plasma prolactin and growth hormone concentrations
Life Sciences, Vol. 27, pp. 929-933 Printed in the U.S.A.
Pergamon Press
ELECTRICAL STI3/ULATION OF THE MEDIAN EMINENCE IN RATS, CHANGES IN CATECHOLAMINE CONTENT AND IN PLASMA PROLACTIN AND GROWTH HORMONE CONCENTRATIONS M.I.K. Pekete, J.P. Herman, B. Kanyicska I and G.B. Nakara Institute of Experimental Medicine, ~ungarian Academy of Sciences, P.O.B. 67, Budapest, 1450, and ~Institute for Animal Husbandry, Herceghalom, Hungary (Received in final form July i, 1980) SUMMARY Effects of field stimulation of the medial basal hypcthalamus (MBH) and coaxial stimulation of the median eminence was studied on the catecholamine and DOPAC levels of the median eminence and on the prolactin and growth hormone release. The field stimulation induced an increased prolactin and growth hormone secretion without altering the catecholamine and DOPAC level. The direct electrical stimulation of the median eminence reduced the noradrenaline and dopamine content without significant changes in DOPAC concentration and in hormone secretions. It is concluded that (1) variations of DOPAC content are inadequate indicators of neuronal activity in the median eminence; (2) the multiple interaction of the stimulated neurons in the median eminence may mask the expected biochemical and hormonal responses to electrical stimulation. The biochemical reactions of the dopaminergic neurons in the median eminence (~E) are different from those in the striatum, as it has been shown by several studies examining the effects on the dopamine metabolism and on DOPAC (dihydroxyphenylacetic acid) level ~1-6). Moreover, it was found that the relative importance of reuptake of dopamine (7) and that of the presynaptic dopaminergic inhibition is smaller in the ME than in other areas of the brain (see 8). Evidences derived from drug action may be misleadLug, however, as any of these compounds may act directly, and/or via an extrahypothalamic site of action, indirectly on the dopa~'~ergic activity of the ME, as most recently direct noradrenergic, dopaminergic and adrenergic connections were demonstrated between brain stem mesencephalic amine containing cell groups (Fekete et al., to be published). The stimulation of noradrenergic neurons arising from the locus coeruleus or that of the nigrostriatal dopaminergic neurons in the terminal areas resulted in a decrease of the endogenous amine content or an increase of amine metabolite concentrations (9,10). We decided to investigate the same problem in the ME using direct electrical stimulation. Measurements of oatecholaminee and DOPAC were done, and as a second indicator of the stimulation the changes of plasma prolactin and growth hormone levels were determined. 0024-3205/80/370929-05502.00/0 Copyright (c) 1980 Pergamon Press Ltd
930
ElectricalStimulation of Median Eminence
Vol. 27, No. ii, 1980
METHODS Male CFY rats weighing 200-260 g were anaesthetized with l-l,2 g/kg urethane i.p. The rats were placed in a stereotaxic frame with the tooth bar i0 ° nose down. The top of the skull was exposed, a bone flap removed and the stimulating electrodes were introduced into the hypothalamus. Two series of experiments were done. In Series 1. we intended to stimulate a wide area of the hypothalamic tuberal region (in^cluding the ME) vi_i_~aan electrode a r r ~ consisting of 3 pairs of N ~ O0 steel insect plus to within 0,5mm of the tip with Insulx. Each electrode tip was 1 mm from its neighbours, with the pairs in the same coronal plane of the brain, and 1 mm distance between planes. The array was placed in the hypcthalamus, so that the first pair was 1,8 mm behind the bregma, and 0,5 mm above the floor of the skull. The tips were in the region of arcuate and ventromedial nuclei on both sides of the ME. Stimulation current between the pairs of electrodes flowed across the midline. Stimulation was given first through the anterior pair of electrodes for lO sec, then after 10 sec rest the next electrode pair was connected. After stimulation through the caudal pair sequence started again with the first pair. In Series 2. a commercial coaxial semimicroelectrode (SNEX200, Rhodes Instruments), was lowered in the midline 3,0 mm behind the bregma until it touched the sphenoid bone, then it was withdrawn O,1 mm. In this position the electrode usually pierced the ME near to its Junction with the pituitary stalk. We inferred that most of the current had to flow through the ME and pituitar~ stalk between the tip (below the ME) and barrel (above the ~ ) of the coaxial electrode. The stimulation was given for lO sec periods with 10 sec silent periods in between.
CATECHOLAMINE AND DOPAC CONCENTRATIONS OF THE MEDIAN EMINENCE AS APFECTED BY FIELD STIMULATION, GEOMETRICAL MEANS (ln S.E.), n~20 Noradrenaline ng Control Stimulated
16.4 . (0.085) 14.5
(0.106)
Do, amine /mg pr 74.1 (0.082) 74.8
(0.084)
DOPAC o t e in 10.4 (0. I18) 9.99
(0.088)
DOPAC/Dopamine 0.141 (0.120) O. 133
(0.074)
The stimulation parameters were as follows: rectangular biphasic pulses of 1 msec, 2OO/uA, lO0 Hz, gsnerated by a Digitimeter programmer and IsolateG Stimulators (Devices, UK) and monitored with a cathode ray oscilloscope. The overall stimulation time was 30 min in both series. To the end of the stimulation period the brains were quickly removed after decapitation, and the stalk-ME was dissected under microscopic control. Tissue pieces were quickly frozen and stored on dry ice; they were homogenized 20 to 24 h later in O,1 N perchloric acid (40tul/M~). Catecholamines and DOPAC were measured radioenzymatical~y (3).
Vol. 27, No. ii, 1 9 8 0
ElectricalStimulation of Median Eminence
931
TABLE 2 INDUCED CHANGES OF PLASMA HORMONE LEVELS BY FIELD STIMULATION OF THE MEDIAL BASAL HYPOTHALAMUS Prolactin Growth hormone Cortioosterone na/ml ng/ml ng/ml Control 7.20 24.2 502 +2.95 + 2.32 +ii Stimulated 28.2 xx 36.2 xx 520 +9.28 + 3. I +20 ,
Xx
,
p
Trunk blood was collected for the hormone determinations. Plasma corticosterone was measured fluorimetrically (ii) while growth hormone and prolactin were determined by radioimmunoassay using NIAMDD materials sent by Dr. A. Parlow (Torrance, Calif.). Logarithmically transformed data of radioenzymatic analysis, and the original values of hormone measurements were treated with analysis of variance for statistical evaluation. Results and Discussion Both types of ~stimulation of the ME region (field and coaxia~ resulted changes showing release of neurotransmitters or neurohumoral messenger substance from the ME. The field stimulation (Series I.). induced an increase of prolactin and growth hormone secretion (Table 2). The coaxial stimulation caused a decrease of dopamine and noradrenaline content of the ME (Table 3), charecteristic signs of prolonged and forced activation of other catecholaminergic neurons (9). After a 30 min period of field stimulation no changes in catecholamine and DOPAC level of the ME could be demonstrated (Table i). In the same time the plasma prolactin and growth hormone concentrations were significantly increased (Table 2). The urethane-induced elevated plasma corticosterone level was not influenced. TABLE CHANGES OF CA CH0 AND DOPAC CO TE T 07 THE IAN m l NENCE INDUCED BY DIRECT ELECTRICAL STIMULATION VIA A COAXIAL BIPOLAR ELECTRODE (n=lO-12, GEOMETRICAL MEANS /~--S.E./) Noradrenaline Dopamine DOPAC DOPAC/Dopamine n~/mg pr ot e in Control Stimulated ,
x p
14.2 (0°066) 8.72 xx (0.109) ,
82.9 (0.058) 63.7 x (0.096)
I0.5 . (0.094) II. 5 . (0.104)
0.132 (0.088) O. 174 x (0.O91) ,
,
xx p < O . O l
When stimulating the ME region the r e s u l t ~ changes of pituitary hormone release and neurotransmitter release probably depend on the ratio of stimulated inhibitory/excitatory neurons. It may be suggested that by field stimulation releasing hormone
932
ElectricalStimulation of Median Eminence
Vol. 27, No. ii, 1980
containing elements were preferably excited (neurons containing the hypothetical prolactin and growth hormone releasing factors). A marked increase of adrenocortical activity in dexamethasone treated rats was also demonstrated by this same way of stimulation of the medial basal hypothalamus (12). An other possibility to explain our results is that the stimulated neurons inhibit the inhibitor factor containing elements, resulting an increased release of the measured pituitary hormones. TABLE 4 PLASMA PROLACTIN, GROWTH HORMONE AND CORTICOSTERONE LEVELS AS AFFECTED BY DIRECT ELECTRICAL STINfULATION OF THE MEDIAN E~INENCE (MEANS + S.E., n = lO-12) Prolactin Growth hormone Corticosterone ng/ml ng/ml ng/ml m
Control Stimulated
20.0 ~1.88 21.2 ~1.45
14.9 ~1.34 23.8 ~4.75
389 !17 390 ~22
As we could not observe any signs of stimulation of dopaminergic or noradrenergic neurons during field stimulation, it may be suggested that in this case fibers inhibiting the catecholaminergic neurons of the ME were excited, too. In a recent study (Fekete et al., to be published) we could demonstrate possible inhibitory adrenergic neurons arising the ~E from the A1-C1 area (13). These neurons were probably stimulated during field stimulation, as well as opiate peptide containing neural elements which also inhibit the dopaminergic neurons of the ~ (14). Electrical stimulation of the ~E through a coaxial electrode placed in the middle of this region decreased catecholamine levels without significantly altering the hormone levels (Tables 3 and 4). The decrease of noradrenaline and dopamine concentration is similar to that described (9) after stimulating the locus coeruleus and measuring the catecholamine level in the cortex. Stimulation of the medial forebrain bundle caused an increase of striatal DOPAC content (lO, 16) in our study, however, the DOPAC level in the ME remained unchanged (Table 3). Electrical stimulation with the coaxial electrode induced maximal compound action potential of fibers in the ME (17), suggesting that most if not all the neurons around the electrode were activated, the dopaminergic neurons included. This phenomenon may be a further argument for the relatively little importance of the reuptake system in the ~E presuming that dopamine newly taken up is preferentially deaminated as it has been proved in case of noradrenaline in the periphery (15), and dopamine in the striatum (16). The question arises why the hormone secretion - at least the plasma prolactin level - did not change under the effect of electrical stimulation of the tuberoinfundibular dopaminergic tract during coaxial stimulation. A possible explanation is that the stimulation caused possible decrease of prolactin secretion could not take place because of the simultaneous stimulation of releasing factor-containing fibres. The changes of prolactin secretion throughout these experiments may be influenced by elevated corticosterone level caused by urethane, as glucocorticoid feedback may affect prolactin secretion (18,19).
Vol. 27, No. II, 1 9 8 0
1. 2. 3. 4. 5. 6. 7. 8° 9. I0. ii. 12. 13. 14. 15. 16. 17. 18. 19.
ElectricalStimulation of Median Eminence
933
References G°Ao GUDELSKY and K.E. MOORE, J.Pharmacol.exp. Ther. 202, 149-156 (1977) • A. ARGIOLAS, E° PARGLETTI, F. FADDA, E. STEFANINI and G.L. GESSA, Life Sci. 22, 461-466 (1978). M.I.K. FEKETE, B.-~ANYICSKA and J.P. HERMAN, Life Sci. 23, 1549-1556 (1978) • M.I.K. FEKETE, J.P. HERMAN, B. KANYICSKA and M. PALKOVITS, J.Neural Transmission 45, 207-218 (1979). M.I°K° FEKETE, T. SZENTENDREI, J°P. E E R ~ and B. KANYICSKA, Eur. JoPharmacol. in press (1980). M.I.K. FEKETE, J.P. HERMAN, B. KANYICSKA and M. PALKOVITS, Proc. ?_ud Int°Cong.Hun~.Pharmacol. (Ed. J.Knoll), Akad~miai Kiad6, Budapest, 1980 ~in press). K.I° DE, ARES and K.E. MOORE, Brain Res° 171o 545-551 (1979). L. ANUNZIATO, Neuroendocrinology 29, 66-7E-(1979). J° KORF, R.H° ROTH and G°K. AGHAJ-~IAN, Eur°J.Pharmacol. 23, 276-282 (1973). J. KOR9, ~. ZIELE~tAN and H.C. WESTERINK, Brain Res. 120, 184-187 (1977). R. GUILLF~IN, G.W. CLAYTON, H.S. LIPSCOMB and J.G. S ~ T H , J.Lab.Clin.Med. 53, 830-832 (1959). G.B. MAKARA, E. STARK and M. PALKOVITS, Neuroendocrinology 27, 109-118 (1978). ~. HOKgELT, K. FUXE, M. GOLDSTEIN and O. JOHANSSON, Brain Res. 66, 235-252 (1974). . . G.A. ~ b E L S K Y and J.C. PORTER, Life Sci. 25, 1697-1702 (1979) S.Z° LANGER, M.B. FARAH, M.A. LUCHELLI-DO~IS, E. ADLER-GRASCHINSKY and E.J. FILINGER, Proc.VI.Cong.Pharmacol., Vol.2 (Ed. L. Ahtee), p. 17-31, Finnish Pharmacol.Soc. (1975)° R.H. ROTH, L.C. MURRIN and J.R. WALTERS, Eur. J.Pharmacol. 36, 163-171 (1976). G.B. MAKARA, M.C. HARRIS and K.M. SPYER, Brain Res. 40, 283290 (1972). M. JOBIN, L. PERLAND and P. LABRIE, Endocrinology 99, 146151 (1976). M.I.K. FEKETE, E. STARK, J.P. HERMAN, B. KANYICSKA and M. PALKOVITS, Proc. II. Inst.Symp. on Catecholamines and Stress (Eds R. Kvet~ansk# and E. Usdin), Elsevier/North Holland, 1980 (in press).
Pergamon Press
ELECTRICAL STI3/ULATION OF THE MEDIAN EMINENCE IN RATS, CHANGES IN CATECHOLAMINE CONTENT AND IN PLASMA PROLACTIN AND GROWTH HORMONE CONCENTRATIONS M.I.K. Pekete, J.P. Herman, B. Kanyicska I and G.B. Nakara Institute of Experimental Medicine, ~ungarian Academy of Sciences, P.O.B. 67, Budapest, 1450, and ~Institute for Animal Husbandry, Herceghalom, Hungary (Received in final form July i, 1980) SUMMARY Effects of field stimulation of the medial basal hypcthalamus (MBH) and coaxial stimulation of the median eminence was studied on the catecholamine and DOPAC levels of the median eminence and on the prolactin and growth hormone release. The field stimulation induced an increased prolactin and growth hormone secretion without altering the catecholamine and DOPAC level. The direct electrical stimulation of the median eminence reduced the noradrenaline and dopamine content without significant changes in DOPAC concentration and in hormone secretions. It is concluded that (1) variations of DOPAC content are inadequate indicators of neuronal activity in the median eminence; (2) the multiple interaction of the stimulated neurons in the median eminence may mask the expected biochemical and hormonal responses to electrical stimulation. The biochemical reactions of the dopaminergic neurons in the median eminence (~E) are different from those in the striatum, as it has been shown by several studies examining the effects on the dopamine metabolism and on DOPAC (dihydroxyphenylacetic acid) level ~1-6). Moreover, it was found that the relative importance of reuptake of dopamine (7) and that of the presynaptic dopaminergic inhibition is smaller in the ME than in other areas of the brain (see 8). Evidences derived from drug action may be misleadLug, however, as any of these compounds may act directly, and/or via an extrahypothalamic site of action, indirectly on the dopa~'~ergic activity of the ME, as most recently direct noradrenergic, dopaminergic and adrenergic connections were demonstrated between brain stem mesencephalic amine containing cell groups (Fekete et al., to be published). The stimulation of noradrenergic neurons arising from the locus coeruleus or that of the nigrostriatal dopaminergic neurons in the terminal areas resulted in a decrease of the endogenous amine content or an increase of amine metabolite concentrations (9,10). We decided to investigate the same problem in the ME using direct electrical stimulation. Measurements of oatecholaminee and DOPAC were done, and as a second indicator of the stimulation the changes of plasma prolactin and growth hormone levels were determined. 0024-3205/80/370929-05502.00/0 Copyright (c) 1980 Pergamon Press Ltd
930
ElectricalStimulation of Median Eminence
Vol. 27, No. ii, 1980
METHODS Male CFY rats weighing 200-260 g were anaesthetized with l-l,2 g/kg urethane i.p. The rats were placed in a stereotaxic frame with the tooth bar i0 ° nose down. The top of the skull was exposed, a bone flap removed and the stimulating electrodes were introduced into the hypothalamus. Two series of experiments were done. In Series 1. we intended to stimulate a wide area of the hypothalamic tuberal region (in^cluding the ME) vi_i_~aan electrode a r r ~ consisting of 3 pairs of N ~ O0 steel insect plus to within 0,5mm of the tip with Insulx. Each electrode tip was 1 mm from its neighbours, with the pairs in the same coronal plane of the brain, and 1 mm distance between planes. The array was placed in the hypcthalamus, so that the first pair was 1,8 mm behind the bregma, and 0,5 mm above the floor of the skull. The tips were in the region of arcuate and ventromedial nuclei on both sides of the ME. Stimulation current between the pairs of electrodes flowed across the midline. Stimulation was given first through the anterior pair of electrodes for lO sec, then after 10 sec rest the next electrode pair was connected. After stimulation through the caudal pair sequence started again with the first pair. In Series 2. a commercial coaxial semimicroelectrode (SNEX200, Rhodes Instruments), was lowered in the midline 3,0 mm behind the bregma until it touched the sphenoid bone, then it was withdrawn O,1 mm. In this position the electrode usually pierced the ME near to its Junction with the pituitary stalk. We inferred that most of the current had to flow through the ME and pituitar~ stalk between the tip (below the ME) and barrel (above the ~ ) of the coaxial electrode. The stimulation was given for lO sec periods with 10 sec silent periods in between.
CATECHOLAMINE AND DOPAC CONCENTRATIONS OF THE MEDIAN EMINENCE AS APFECTED BY FIELD STIMULATION, GEOMETRICAL MEANS (ln S.E.), n~20 Noradrenaline ng Control Stimulated
16.4 . (0.085) 14.5
(0.106)
Do, amine /mg pr 74.1 (0.082) 74.8
(0.084)
DOPAC o t e in 10.4 (0. I18) 9.99
(0.088)
DOPAC/Dopamine 0.141 (0.120) O. 133
(0.074)
The stimulation parameters were as follows: rectangular biphasic pulses of 1 msec, 2OO/uA, lO0 Hz, gsnerated by a Digitimeter programmer and IsolateG Stimulators (Devices, UK) and monitored with a cathode ray oscilloscope. The overall stimulation time was 30 min in both series. To the end of the stimulation period the brains were quickly removed after decapitation, and the stalk-ME was dissected under microscopic control. Tissue pieces were quickly frozen and stored on dry ice; they were homogenized 20 to 24 h later in O,1 N perchloric acid (40tul/M~). Catecholamines and DOPAC were measured radioenzymatical~y (3).
Vol. 27, No. ii, 1 9 8 0
ElectricalStimulation of Median Eminence
931
TABLE 2 INDUCED CHANGES OF PLASMA HORMONE LEVELS BY FIELD STIMULATION OF THE MEDIAL BASAL HYPOTHALAMUS Prolactin Growth hormone Cortioosterone na/ml ng/ml ng/ml Control 7.20 24.2 502 +2.95 + 2.32 +ii Stimulated 28.2 xx 36.2 xx 520 +9.28 + 3. I +20 ,
Xx
,
p
Trunk blood was collected for the hormone determinations. Plasma corticosterone was measured fluorimetrically (ii) while growth hormone and prolactin were determined by radioimmunoassay using NIAMDD materials sent by Dr. A. Parlow (Torrance, Calif.). Logarithmically transformed data of radioenzymatic analysis, and the original values of hormone measurements were treated with analysis of variance for statistical evaluation. Results and Discussion Both types of ~stimulation of the ME region (field and coaxia~ resulted changes showing release of neurotransmitters or neurohumoral messenger substance from the ME. The field stimulation (Series I.). induced an increase of prolactin and growth hormone secretion (Table 2). The coaxial stimulation caused a decrease of dopamine and noradrenaline content of the ME (Table 3), charecteristic signs of prolonged and forced activation of other catecholaminergic neurons (9). After a 30 min period of field stimulation no changes in catecholamine and DOPAC level of the ME could be demonstrated (Table i). In the same time the plasma prolactin and growth hormone concentrations were significantly increased (Table 2). The urethane-induced elevated plasma corticosterone level was not influenced. TABLE CHANGES OF CA CH0 AND DOPAC CO TE T 07 THE IAN m l NENCE INDUCED BY DIRECT ELECTRICAL STIMULATION VIA A COAXIAL BIPOLAR ELECTRODE (n=lO-12, GEOMETRICAL MEANS /~--S.E./) Noradrenaline Dopamine DOPAC DOPAC/Dopamine n~/mg pr ot e in Control Stimulated ,
x p
14.2 (0°066) 8.72 xx (0.109) ,
82.9 (0.058) 63.7 x (0.096)
I0.5 . (0.094) II. 5 . (0.104)
0.132 (0.088) O. 174 x (0.O91) ,
,
xx p < O . O l
When stimulating the ME region the r e s u l t ~ changes of pituitary hormone release and neurotransmitter release probably depend on the ratio of stimulated inhibitory/excitatory neurons. It may be suggested that by field stimulation releasing hormone
932
ElectricalStimulation of Median Eminence
Vol. 27, No. ii, 1980
containing elements were preferably excited (neurons containing the hypothetical prolactin and growth hormone releasing factors). A marked increase of adrenocortical activity in dexamethasone treated rats was also demonstrated by this same way of stimulation of the medial basal hypothalamus (12). An other possibility to explain our results is that the stimulated neurons inhibit the inhibitor factor containing elements, resulting an increased release of the measured pituitary hormones. TABLE 4 PLASMA PROLACTIN, GROWTH HORMONE AND CORTICOSTERONE LEVELS AS AFFECTED BY DIRECT ELECTRICAL STINfULATION OF THE MEDIAN E~INENCE (MEANS + S.E., n = lO-12) Prolactin Growth hormone Corticosterone ng/ml ng/ml ng/ml m
Control Stimulated
20.0 ~1.88 21.2 ~1.45
14.9 ~1.34 23.8 ~4.75
389 !17 390 ~22
As we could not observe any signs of stimulation of dopaminergic or noradrenergic neurons during field stimulation, it may be suggested that in this case fibers inhibiting the catecholaminergic neurons of the ME were excited, too. In a recent study (Fekete et al., to be published) we could demonstrate possible inhibitory adrenergic neurons arising the ~E from the A1-C1 area (13). These neurons were probably stimulated during field stimulation, as well as opiate peptide containing neural elements which also inhibit the dopaminergic neurons of the ~ (14). Electrical stimulation of the ~E through a coaxial electrode placed in the middle of this region decreased catecholamine levels without significantly altering the hormone levels (Tables 3 and 4). The decrease of noradrenaline and dopamine concentration is similar to that described (9) after stimulating the locus coeruleus and measuring the catecholamine level in the cortex. Stimulation of the medial forebrain bundle caused an increase of striatal DOPAC content (lO, 16) in our study, however, the DOPAC level in the ME remained unchanged (Table 3). Electrical stimulation with the coaxial electrode induced maximal compound action potential of fibers in the ME (17), suggesting that most if not all the neurons around the electrode were activated, the dopaminergic neurons included. This phenomenon may be a further argument for the relatively little importance of the reuptake system in the ~E presuming that dopamine newly taken up is preferentially deaminated as it has been proved in case of noradrenaline in the periphery (15), and dopamine in the striatum (16). The question arises why the hormone secretion - at least the plasma prolactin level - did not change under the effect of electrical stimulation of the tuberoinfundibular dopaminergic tract during coaxial stimulation. A possible explanation is that the stimulation caused possible decrease of prolactin secretion could not take place because of the simultaneous stimulation of releasing factor-containing fibres. The changes of prolactin secretion throughout these experiments may be influenced by elevated corticosterone level caused by urethane, as glucocorticoid feedback may affect prolactin secretion (18,19).
Vol. 27, No. II, 1 9 8 0
1. 2. 3. 4. 5. 6. 7. 8° 9. I0. ii. 12. 13. 14. 15. 16. 17. 18. 19.
ElectricalStimulation of Median Eminence
933
References G°Ao GUDELSKY and K.E. MOORE, J.Pharmacol.exp. Ther. 202, 149-156 (1977) • A. ARGIOLAS, E° PARGLETTI, F. FADDA, E. STEFANINI and G.L. GESSA, Life Sci. 22, 461-466 (1978). M.I.K. FEKETE, B.-~ANYICSKA and J.P. HERMAN, Life Sci. 23, 1549-1556 (1978) • M.I.K. FEKETE, J.P. HERMAN, B. KANYICSKA and M. PALKOVITS, J.Neural Transmission 45, 207-218 (1979). M.I°K° FEKETE, T. SZENTENDREI, J°P. E E R ~ and B. KANYICSKA, Eur. JoPharmacol. in press (1980). M.I.K. FEKETE, J.P. HERMAN, B. KANYICSKA and M. PALKOVITS, Proc. ?_ud Int°Cong.Hun~.Pharmacol. (Ed. J.Knoll), Akad~miai Kiad6, Budapest, 1980 ~in press). K.I° DE, ARES and K.E. MOORE, Brain Res° 171o 545-551 (1979). L. ANUNZIATO, Neuroendocrinology 29, 66-7E-(1979). J° KORF, R.H° ROTH and G°K. AGHAJ-~IAN, Eur°J.Pharmacol. 23, 276-282 (1973). J. KOR9, ~. ZIELE~tAN and H.C. WESTERINK, Brain Res. 120, 184-187 (1977). R. GUILLF~IN, G.W. CLAYTON, H.S. LIPSCOMB and J.G. S ~ T H , J.Lab.Clin.Med. 53, 830-832 (1959). G.B. MAKARA, E. STARK and M. PALKOVITS, Neuroendocrinology 27, 109-118 (1978). ~. HOKgELT, K. FUXE, M. GOLDSTEIN and O. JOHANSSON, Brain Res. 66, 235-252 (1974). . . G.A. ~ b E L S K Y and J.C. PORTER, Life Sci. 25, 1697-1702 (1979) S.Z° LANGER, M.B. FARAH, M.A. LUCHELLI-DO~IS, E. ADLER-GRASCHINSKY and E.J. FILINGER, Proc.VI.Cong.Pharmacol., Vol.2 (Ed. L. Ahtee), p. 17-31, Finnish Pharmacol.Soc. (1975)° R.H. ROTH, L.C. MURRIN and J.R. WALTERS, Eur. J.Pharmacol. 36, 163-171 (1976). G.B. MAKARA, M.C. HARRIS and K.M. SPYER, Brain Res. 40, 283290 (1972). M. JOBIN, L. PERLAND and P. LABRIE, Endocrinology 99, 146151 (1976). M.I.K. FEKETE, E. STARK, J.P. HERMAN, B. KANYICSKA and M. PALKOVITS, Proc. II. Inst.Symp. on Catecholamines and Stress (Eds R. Kvet~ansk# and E. Usdin), Elsevier/North Holland, 1980 (in press).