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Adrenal steroid-induced changes in serotonin receptors in rat hippocampus and hypothalamus
PharmacologicalResearchCommunications,Vol. 20, No. 5, 1988 ADRENAL ~TERDID-INDUCEDCHANGESIN SEROTONINRECEPTORSIN RAT HIPPOCAMPUS AHD HYPOTHALAHUS. ~ARTIRE M.,.NAVARRA ~., PISTRITTO G.and PREZ!O$I P. Dept. of Pharmacology, Catholic University, L.go F. Vtto 1, 00168 Rome. Key words: Adrenalectomy, serotontn receptors, htoDocamvus, hypotha]amus.
Increasing evidence has shown that neurotransm|tters and hormones may tn teract on each other leading to a change in their biochemical dynamics and functions. Among the hormonal systems, steroid hormones of the p i t u i t a r y adrenal axis may play an important role in the regulation of neurotransmtttar systems in the brain (McEwen, 1987), Thus, mu]ttple interplay between glucocorttcotds and serotonergJc system may take place in two crucial a~eas of the brain lilnbJc system, the htppocampus and the hypo~halamua (De Kloet et e l . , lgB3; Wether et e l , , 1978). In the present study we evaluate the characbertst~cs of sero~on~n pre ~ and postsynapttc receptors in ~he htppocampus and hypothalamus of adrenalecto = mized male PaLs {180~220 g) with or w|thout B-day corttcosterone replacement (at a dose, 1 mg/Rg twice daily, able to restore normal hormonal levels). Two methodological approaches were employed: the ability of presynaptic r£ ceptvrs to regulate serotonin release and the binding capacity of 5-HT1 and 5-HT2 receptor subtypes. Neurotransmttter release was studied in synaptosomes prelabelled with 3H-5-HT (0.04 pM; 10 m{n), and exposed in superfuston to vartous concentrations of exogenous 5-HT. After 8 mtn of superfuston with 5-HT, the synaptosomes were depolarized with lS mM KCl. Fractional release curves were obtained for different concentrations of 5-HT in control and CreaCed rats. Binding experiments, were performed using as rad|oligands 3H-5-HT for 5-HT1 subtypes and 3H-Ketanserin for 5-HT2. The d i s t i n c t i v e features of serotonin receptors in the two brain regions were d i f f e r e n t l y affected after adrenalectomy: the presynaptic receptors showed subsensittvity in both (the Figure 1 shows the i n i b i t o r y effect of 0.1 pM 5-HT; this concentration resu]ted ha]f-effective in tnhibitind the release in adrena]-ablated anima]s); whereas the nutnber of 5-HT1 and 5-HT2 receptor sites in the hippocampus increased by near]y 30% (the Figure 1shows the B values in sham-operated and adrena]ectomtzed rats for 3H-5-HT and 3 max • H-Ketansertn binding). No KD changes were observed. None of these changes were present in adrenal-ablated corttcosterone-treatedantmals~ N o s t g n i f t cant changes in 5-HT) and 5-HT2 receptor binding Were observed t n t h e h y p o thalamus. The dov/n-regulation qf presynapttc receptors observed In the two brain regions examined may be explained by the reduced ]evelS of seroton|n resulting in the whole brain stem of adrena]ectomtzed r a t s Cortlcosterone
0031-6989/88/050415-21503,0010
© 1988 The Italian Pharmacological Society
416
Pharrnacological Research Communications, Vo],20, IVo. 5, 1988 HIPPOCAMPUS
n
15ram K C l
HYPOTHALAMUS
15ntM*O. 11JM 5-HT
1-
@
lOG
100
60
80
60
60
40
40
°O I
• 20
Adx
Cot!
.....
Adx. . . . . . HIPPOCAMPUS ~] ItYPOTHALAMU$
|'~
3H.5.HT --
tort
3H-Ketansefin
40Q
v :o
200 100
Adx
Cot!
Adx
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dx Coct
is involved in the regulation of enzimatic activities and at central level, i t s permissive role in the induction of tryptophan hydroxylase activity has been shown in a number of studies (Sze, 1976). I t may therefore be assumed that presynaptic 5-HT receptors become subsensitive when glucocorticoids are lacking in order to increase the 5-HT release, thus maintaining the con stancy of serotonergic synaptic transmission. The increased density of sero tonin receptors at hippocampal level may be also secondary to the corticosterone-induced alterations in serotonin synthesis and/or turnover; however, because of the lack of a similar effect at hypothalamic level, a unique hippocampal cell membrane change may be postulated. The corticosterone-shorta ge may selectively induce a compensatory increase of serotonln unmask ~ece~ tor sites in the hippocampus, where a dependent correlation between cortico steroid receptors and the activity of the raphe-hippocampal 5-HT system has been r~vealed on the control of adaptive behavioral responses (De Kloet et
zgs3). De Kloet E.R., Angelucci L., Kov~cs G.L.,Versteeg D.H.G.,Bohus B.(1983). In: EndrBczi E., De Wied D., Angelucci L., Scapagnini U. (eds). Integrative neurohumoral mechanisms. Developments in Neuroscience, vol. i~6:157-164. McEwen B.S. (1987), Biochem. Pharmacol. 36: 1755-1763. Sze P.Y (1976). Advances in Biochemical'-Psychopharmacology 15: 251-265. Weiner R,J., Ganong W.F. (1978) Physiological Rew|evs 58: 9,05-973. • h l s work was s u p p o r t e d by a HPI g r a n t ( 6 0 ~ - 8 5 ) .
Increasing evidence has shown that neurotransm|tters and hormones may tn teract on each other leading to a change in their biochemical dynamics and functions. Among the hormonal systems, steroid hormones of the p i t u i t a r y adrenal axis may play an important role in the regulation of neurotransmtttar systems in the brain (McEwen, 1987), Thus, mu]ttple interplay between glucocorttcotds and serotonergJc system may take place in two crucial a~eas of the brain lilnbJc system, the htppocampus and the hypo~halamua (De Kloet et e l . , lgB3; Wether et e l , , 1978). In the present study we evaluate the characbertst~cs of sero~on~n pre ~ and postsynapttc receptors in ~he htppocampus and hypothalamus of adrenalecto = mized male PaLs {180~220 g) with or w|thout B-day corttcosterone replacement (at a dose, 1 mg/Rg twice daily, able to restore normal hormonal levels). Two methodological approaches were employed: the ability of presynaptic r£ ceptvrs to regulate serotonin release and the binding capacity of 5-HT1 and 5-HT2 receptor subtypes. Neurotransmttter release was studied in synaptosomes prelabelled with 3H-5-HT (0.04 pM; 10 m{n), and exposed in superfuston to vartous concentrations of exogenous 5-HT. After 8 mtn of superfuston with 5-HT, the synaptosomes were depolarized with lS mM KCl. Fractional release curves were obtained for different concentrations of 5-HT in control and CreaCed rats. Binding experiments, were performed using as rad|oligands 3H-5-HT for 5-HT1 subtypes and 3H-Ketanserin for 5-HT2. The d i s t i n c t i v e features of serotonin receptors in the two brain regions were d i f f e r e n t l y affected after adrenalectomy: the presynaptic receptors showed subsensittvity in both (the Figure 1 shows the i n i b i t o r y effect of 0.1 pM 5-HT; this concentration resu]ted ha]f-effective in tnhibitind the release in adrena]-ablated anima]s); whereas the nutnber of 5-HT1 and 5-HT2 receptor sites in the hippocampus increased by near]y 30% (the Figure 1shows the B values in sham-operated and adrena]ectomtzed rats for 3H-5-HT and 3 max • H-Ketansertn binding). No KD changes were observed. None of these changes were present in adrenal-ablated corttcosterone-treatedantmals~ N o s t g n i f t cant changes in 5-HT) and 5-HT2 receptor binding Were observed t n t h e h y p o thalamus. The dov/n-regulation qf presynapttc receptors observed In the two brain regions examined may be explained by the reduced ]evelS of seroton|n resulting in the whole brain stem of adrena]ectomtzed r a t s Cortlcosterone
0031-6989/88/050415-21503,0010
© 1988 The Italian Pharmacological Society
416
Pharrnacological Research Communications, Vo],20, IVo. 5, 1988 HIPPOCAMPUS
n
15ram K C l
HYPOTHALAMUS
15ntM*O. 11JM 5-HT
1-
@
lOG
100
60
80
60
60
40
40
°O I
• 20
Adx
Cot!
.....
Adx. . . . . . HIPPOCAMPUS ~] ItYPOTHALAMU$
|'~
3H.5.HT --
tort
3H-Ketansefin
40Q
v :o
200 100
Adx
Cot!
Adx
d~ C o r t
~d~
A~
dx Coct
is involved in the regulation of enzimatic activities and at central level, i t s permissive role in the induction of tryptophan hydroxylase activity has been shown in a number of studies (Sze, 1976). I t may therefore be assumed that presynaptic 5-HT receptors become subsensitive when glucocorticoids are lacking in order to increase the 5-HT release, thus maintaining the con stancy of serotonergic synaptic transmission. The increased density of sero tonin receptors at hippocampal level may be also secondary to the corticosterone-induced alterations in serotonin synthesis and/or turnover; however, because of the lack of a similar effect at hypothalamic level, a unique hippocampal cell membrane change may be postulated. The corticosterone-shorta ge may selectively induce a compensatory increase of serotonln unmask ~ece~ tor sites in the hippocampus, where a dependent correlation between cortico steroid receptors and the activity of the raphe-hippocampal 5-HT system has been r~vealed on the control of adaptive behavioral responses (De Kloet et
zgs3). De Kloet E.R., Angelucci L., Kov~cs G.L.,Versteeg D.H.G.,Bohus B.(1983). In: EndrBczi E., De Wied D., Angelucci L., Scapagnini U. (eds). Integrative neurohumoral mechanisms. Developments in Neuroscience, vol. i~6:157-164. McEwen B.S. (1987), Biochem. Pharmacol. 36: 1755-1763. Sze P.Y (1976). Advances in Biochemical'-Psychopharmacology 15: 251-265. Weiner R,J., Ganong W.F. (1978) Physiological Rew|evs 58: 9,05-973. • h l s work was s u p p o r t e d by a HPI g r a n t ( 6 0 ~ - 8 5 ) .