Peptides, Vol. 12, pp. 1113-1117. ©Pergamon Press plc, 1991. Printed in the U.S.A.
0196-9781191 $3.00 + .00
Regulation of Histamine Release in Rat Hypothalamus and Hippocampus by Presynaptic Galanin Receptors J. M. A R R A N G , C. G U L A T - M A R N A Y ,
N. D E F O N T A I N E A N D J. C. S C H W A R T Z
Unitg de Neurobiologie et Pharmacologie (U. 109) de I'INSERM, Centre Paul Broca 2ter rue d'Algsia, 75014 Paris, France R e c e i v e d 27 February 1991 ARRANG, J. M., C. GULAT-MARNAY, N. DEFONTAINE AND J. C. SCHWARTZ, Regulation of histamine release in rat hypothalamus and hippocampus by presynaptic galanin receptors. PEPTIDES 12(5) 1113-1117, 1991.--The effect of galanin, a peptide present in a subpopulation of histaminergic neurons emanating from the rat posterior hypothalamus, was investigated on K+-evoked [3H]histamine release in slices and synaptosomes from rat cerebral cortex, striatum, hippocampus and hypothalamus, Porcine galanin (0.3 ~M) significantly inhibited histamine release induced by 25 mM K ÷ in slices from hypothalamus and hippocampus, but not from cerebral cortex and striatum, i.e., only in regions in which a colocalization of histamine and galanin has been described. The inhibitory effect of galanin was concentration dependent, with an ECso value of 5.8--- 1.9 nM. The maximal inhibition was of 30--40% in hypothalamic and hippocampal slices depolarized with 25 mM K + . The galanin-induced inhibition observed in hypothalamic slices was not prevented in the presence of 0.6 p,M tetrodotoxin and also occurred in hippocampal and hypothalamic synaptosomes, strongly suggesting the activation by galanin of presynaptic receptors located upon histaminergic nerve endings. The maximal inhibitory effect of galanin in slices or synaptosomes was lower than that previously reported for histamine acting at H3-autoreceptors, possibly suggesting that not all histaminergic axon terminals, even in the hypothalamus and hippocampus, are endowed with galanin receptors. It increased progressively in hypothalamic and hippocampal synaptosomes as the strength of the depolarizing stimulus was reduced. It is concluded that galanin modulates histamine release via presynaptic receptors, presumably autoreceptors located upon nerve terminals of a subpopulation of cerebral histaminergic neurons. Galanin
Histamine release
Hippocampus
Hypothalamus
METHOD
GALANIN, a 29 amino acid peptide, is widely distributed in the central nervous system (26). Among other biological effects, galanin has a potent inhibitory effect on the release of acetylcholine in the ventral hippocampus of the rat (8). Potent inhibitory effects of galanin on serotonergic neurons in the rat brain (34) and on dopamine release from the rat median eminence (24) have also been reported. In all the previous studies, galanin presumably acts at a presynaptic level. Radioimmunological and immunohistochemical studies have shown that galanin-like immunoreactivity coexists with acetylcholine in the septum-basal forebrain (19), with serotonin in the dorsal raphe nucleus, with dopamine in the hypothalamic arcuate nucleus and with noradrenaline in the locus coeruleus (20). Galanin has also been shown to be colocalized with histamine in some tuberomammillary neurons of the posterior hypothalamus (16,33), suggesting its involvement in histaminergic neurotransmission. Presynaptic histamine H3-autoreceptors (1-4, 12, 35), M 1muscarinic heteroreceptors (9), ot2-adrenergic heteroreceptors (10,12) and K-opioid heteroreceptors (11) modulate histamine release from rat brain slices in which the endogenous pool of the amine was labeled using [3H]histidine. The same model is used here to examine whether galanin receptors regulate histamine release in various regions of the rat brain.
[3H]Histamine Release From Slices The procedure was essentially that described by Arrang et al. (1,2). Slices from rat cerebral cortex (total), striatum (total), hippocampus (total), or hypothalamus (total or dissected rostrocaudally about 2/3, 1/3 in anterior and posterior part) were preincubated for 45 min with L-[3H]histidine (1 txM). After several washing steps, aliquots of the slice suspension (1-2 mg of protein) were incubated for 2 min with 25 mM potassium (final concentration). In each experiment, burimamide, a histamine H 2and H3-receptor antagonist (1), was added 10 min before the depolarizing stimulus. When required, galanin was added together with burimamide. Incubations were stopped by rapid centrifugation, and [3H]histamine levels in tissue and medium were quantiffed after isolation by ion-exchange chromatography (27). In each set of experiments, the recovery of [3H]histamine (88 --- 3%) and the contamination by L-[3H]histidine (
0196-9781191 $3.00 + .00
Regulation of Histamine Release in Rat Hypothalamus and Hippocampus by Presynaptic Galanin Receptors J. M. A R R A N G , C. G U L A T - M A R N A Y ,
N. D E F O N T A I N E A N D J. C. S C H W A R T Z
Unitg de Neurobiologie et Pharmacologie (U. 109) de I'INSERM, Centre Paul Broca 2ter rue d'Algsia, 75014 Paris, France R e c e i v e d 27 February 1991 ARRANG, J. M., C. GULAT-MARNAY, N. DEFONTAINE AND J. C. SCHWARTZ, Regulation of histamine release in rat hypothalamus and hippocampus by presynaptic galanin receptors. PEPTIDES 12(5) 1113-1117, 1991.--The effect of galanin, a peptide present in a subpopulation of histaminergic neurons emanating from the rat posterior hypothalamus, was investigated on K+-evoked [3H]histamine release in slices and synaptosomes from rat cerebral cortex, striatum, hippocampus and hypothalamus, Porcine galanin (0.3 ~M) significantly inhibited histamine release induced by 25 mM K ÷ in slices from hypothalamus and hippocampus, but not from cerebral cortex and striatum, i.e., only in regions in which a colocalization of histamine and galanin has been described. The inhibitory effect of galanin was concentration dependent, with an ECso value of 5.8--- 1.9 nM. The maximal inhibition was of 30--40% in hypothalamic and hippocampal slices depolarized with 25 mM K + . The galanin-induced inhibition observed in hypothalamic slices was not prevented in the presence of 0.6 p,M tetrodotoxin and also occurred in hippocampal and hypothalamic synaptosomes, strongly suggesting the activation by galanin of presynaptic receptors located upon histaminergic nerve endings. The maximal inhibitory effect of galanin in slices or synaptosomes was lower than that previously reported for histamine acting at H3-autoreceptors, possibly suggesting that not all histaminergic axon terminals, even in the hypothalamus and hippocampus, are endowed with galanin receptors. It increased progressively in hypothalamic and hippocampal synaptosomes as the strength of the depolarizing stimulus was reduced. It is concluded that galanin modulates histamine release via presynaptic receptors, presumably autoreceptors located upon nerve terminals of a subpopulation of cerebral histaminergic neurons. Galanin
Histamine release
Hippocampus
Hypothalamus
METHOD
GALANIN, a 29 amino acid peptide, is widely distributed in the central nervous system (26). Among other biological effects, galanin has a potent inhibitory effect on the release of acetylcholine in the ventral hippocampus of the rat (8). Potent inhibitory effects of galanin on serotonergic neurons in the rat brain (34) and on dopamine release from the rat median eminence (24) have also been reported. In all the previous studies, galanin presumably acts at a presynaptic level. Radioimmunological and immunohistochemical studies have shown that galanin-like immunoreactivity coexists with acetylcholine in the septum-basal forebrain (19), with serotonin in the dorsal raphe nucleus, with dopamine in the hypothalamic arcuate nucleus and with noradrenaline in the locus coeruleus (20). Galanin has also been shown to be colocalized with histamine in some tuberomammillary neurons of the posterior hypothalamus (16,33), suggesting its involvement in histaminergic neurotransmission. Presynaptic histamine H3-autoreceptors (1-4, 12, 35), M 1muscarinic heteroreceptors (9), ot2-adrenergic heteroreceptors (10,12) and K-opioid heteroreceptors (11) modulate histamine release from rat brain slices in which the endogenous pool of the amine was labeled using [3H]histidine. The same model is used here to examine whether galanin receptors regulate histamine release in various regions of the rat brain.
[3H]Histamine Release From Slices The procedure was essentially that described by Arrang et al. (1,2). Slices from rat cerebral cortex (total), striatum (total), hippocampus (total), or hypothalamus (total or dissected rostrocaudally about 2/3, 1/3 in anterior and posterior part) were preincubated for 45 min with L-[3H]histidine (1 txM). After several washing steps, aliquots of the slice suspension (1-2 mg of protein) were incubated for 2 min with 25 mM potassium (final concentration). In each experiment, burimamide, a histamine H 2and H3-receptor antagonist (1), was added 10 min before the depolarizing stimulus. When required, galanin was added together with burimamide. Incubations were stopped by rapid centrifugation, and [3H]histamine levels in tissue and medium were quantiffed after isolation by ion-exchange chromatography (27). In each set of experiments, the recovery of [3H]histamine (88 --- 3%) and the contamination by L-[3H]histidine (
