Opening of brain potassium-channels inhibits the ACTH-induced behavioral syndrome in the male rat

Opening of brain potassium-channels inhibits the ACTH-induced behavioral syndrome in the male rat

ELSEVIER Neuroscience Letters 188 (1995) 29-32 NEUBUSCI[NC[ LETTERS Opening of brain potassium-channels inhibits the ACTH-induced behavioral syndro...

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ELSEVIER

Neuroscience Letters 188 (1995) 29-32

NEUBUSCI[NC[ LETTERS

Opening of brain potassium-channels inhibits the ACTH-induced behavioral syndrome in the male rat A n n a V a l e r i a V e r g o n i * , M a u r i z i o S a n d r i n i , M o n i c a F i l a f e r r o , A. B e r t o l i n i Department of Biomedical Sciences, Section of Pharmacology, University of Modena, Via G. Campi 287, 1-41100 Modena MO, Italy Received 15 September 1994; revised version received 18 January 1995; accepted 8 February 1995

Abstract

In adult male rats, the intracerebroventricular (i.c.v.) injection of pinacidil, a potassium channel opener, at the doses of 100, 200 or 300/zg/rat, dose-dependently reduced the display of the most typical behavioral symptoms (excessive grooming, stretching, yawning, penile erections) induced by the i.c.v, administration of ACTH-(1-24) (4#g/rat). These data indicate that the complex mechanism of the melanocortin-induced behavioral syndrome involves closure of potassium channels in target neurons, and provide further experimental support to the idea that melanocortins are functional antagonists of opioids.

Keywords: K÷ channels; Pinacidil; Melanocortins; Behavior; Grooming; Stretching; Yawning; Penile erection

Melanocortins (MSH-ACTH neuropeptides) induce in mammals a peculiar collection of behavioral effects (for reviews see Refs. [4,5,16]): intense grooming and scratching [22,25]; recurrent bouts of stretching and yawning [21,22]; and, in males, repeated episodes of penile erection usually terminating with ejaculation [8]; furthermore, melanocortins potently inhibit food intake [42,44]. All these effects are observed only after injection into the cerebrospinal fluid or into selected brain areas, while other typical behavioral effects of melanocortins (increased motivation and attention, and improved shortterm memory) are observed after either intracranial or peripheral administration [13-16]. Structure-activity studies have shown that these behavioral effects of melanocortins are produced by the melanocyte-stimulating core of the molecule [4,16,17,20]. An impressive amount of experimental data suggests that melanocortins may play the role of physiological antagonists of endogenous opioids (for reviews see Refs. [3,6,7,16,27,35,43]). Activation of ~ and 6 opioid receptors opens ATPsensitive potassium channels (KATp) in several areas of the CNS and this in turn causes the closure of N-type calcium channels, with decreased neuronal calcium influx * Corresponding author, Tel.: +39 59 360247; Fax: +39 59 372653.

and calcium-dependent action potentials [12,33,34,45]. Accordingly, Kar P channel openers increase and prolong the analgesic effect of morphine [41] and inhibit morphine withdrawal [39], while KATP channel blockers antagonize morphine antinociception [36,47]. Conversely, Ca 2÷ channel openers antagonize opiate-induced antinociception [19,29], while Ca z÷ channel blockers increase it [18,29] and inhibit morphine withdrawal [2]. On the other hand, the influx of Ca 2+ into target neurons is a step of key importance for the display of the melanocortin-induced behavioral syndrome, that is in fact antagonized by the blockade of L- and N-type Ca 2÷ channels [38]. Here we present experimental evidence that opening of potassium channels by means of a drug (pinacidil) typically active at KATp channels (for a review see Ref. [1]), as well as at high-conductance Ca 2÷activated K+ channels (Kca) [28], can similarly antagonize the melanocortin-induced behavioral syndrome. A total of 78 adult male rats of Wistar strain (Charles River, Calco, CO, Italy), weighing 200-220 g, were used. They were housed 4-5 per cage (25 x 40 x 15 cm makrolon cages) in climatized colony rooms (21 + I°C; 60% humidity) with food and water continuously available. Stainless-steel guide cannulae (23 gauge) (Plastic Products Co., Roanoke, VA, USA) were stereotaxically implanted into both lateral ventricles, to a depth of 0.5 mm

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above the ventricles (measured in millimeters from the bregma: A P = - 0 . 8 ; L = 1.4; V= 3.25) [37], under ketamine plus xylazine anesthesia (115 + 2 mg/kg i.p.; Farmaceutici Gellini, Aprilia, Italy and Bayer, Milano, Italy, respectively), and fixed to the skull with screws and dental acrylic. A removable plug, which extended 0.5 mm below the tip of the guide cannula was kept in place except during the drug injections. Correct placement was verified at the end of the experiment by injecting 2/.tl of toluidine blue dye through an internal cannula used for drug (or solvent) injection (which extended 0.5 mm below the tip of the implanted guide cannula), followed by decapitation under ethyl ether anesthesia and dissection of the brain. Data obtained from improperly implanted animals (6 out of 78) were discarded. ACTH-(1-24) (Ciba-Geigy, Basel, Switzerland), which fully retains all the behavioral effects of melanocortin peptides and is maximally active [5,16,17], was used throughout. It was freshly dissolved in saline and injected into a brain lateral ventricle (i.c.v.) at the dose of 4/ag in a volume of 5#1 at the rate of 1/tl/20 s, via the i.c.v, internal cannula connected by polyethylene tubing

to a 10/~1 Hamilton syringe driven by a micrometric screw. This dose of ACTH-(1-24) had proved to be the maximally behaviorally effective in the rat in previous dose-response experiments performed in this laboratory [5]. Pinacidil (kindly supplied by Dr. W.O. Godtfredsen, Leo Pharmaceutical Products, Ballerup, DK) was dissolved in dimethylsulfoxide (DMSO) and injected into the other brain lateral ventricle 5 min after ACTH, in the same way. Control rats received the same volumes of solvents by the same routes. All the experiments were performed between 0900 and 1300 h, and rats were placed in individual cages. For grooming, animals were scored every 15 s for a period of 50 min according to the procedure of Gispen et al. [25], starting 10 rain after ACTH-(1-24) (or saline) administration. The observer noted whether or not one of the behavioral components of the grooming act was displayed. If so, a positive score was given for the time interval, so that a maximum of 200 positive grooming scores could be obtained [25]. For stretching, yawning and penile erections, animals were observed continuously for 60 min, again starting 10 min after treatment. Each

PENILE E R E C T I O N S

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Fig. 1. Influenceof pinacidil on the behavioral syndromeinduced by ACTH-(1-24). Pinacidil (PIN,gg/rat, at the doses indicated) or dimethylsulfoxide (DMSO, 5/.d/rat, as solvent) were injected 5 min after ACTH-(I-24) (ACTH, 4#g/rat) or saline (SAL, 5/~l/rat). Substances and solvents were i.c.v, administered. N = 11-13 per group. Values reported are means :t SEM. *P < 0.05 versus ACTH+ DMSO (Kruskal-Wallisanalysis of variance followed by Mann-Whitney U-test).

A. V. Vergoni et al. / Neuroscience Letters 188 (1995) 29-32

stretch, yawn and penile erection (spontaneously occurring, not elicited by genital grooming) was scored [5]. Grooming, stretchings, yawnings and penile erections were scored in the same animals and in the same test by two observers unaware of the treatment. Experiments were performed with non-paired groups, each rat being tested only once, and the behavioral experiment was performed 5-7 days after implantation of the i.c.v, cannulae. For each behavioral element, data were submitted to an overall Kruskall-Wallis analysis of variance followed by the Mann-Whitney U.-test for individual comparisons between groups when F values indicated a significant difference among treatments. Even at the highest dose used (300/.tg/rat i.c.v.) pinacidil caused no acute toxicity, behavioral modifications, or locomotor impairment. On the other hand, pinacidil dose-dependently antagonized the behavioral syndrome induced in the adult male rat by the i.c.v, injection of ACTH-(1-24). The grooming score and the number of stretchings were significantly reduced by the lowest dose of pinacidil (100/~g/rat i.c.v.), while the number of yawnings and penile erections was significantly reduced by the highest doses (200 and 300big/rat i.c.v.) (Fig. 1). The present results show that an opener of KATP and Kca channels significantly reduces the behavioral effects induced by the i.c.v, injection of A C T H (excessive grooming, stretching, yawning, penile erections). The melanocortin receptors [40], like most hormones and neurotransmitters receptors [9] are G-protein coupled [31]. The complex regulation of the KATP channel involves Gproteins besides ATP, ADP, Mg 2÷, and channel phosphorylation [10]. Opening of KATp channels in several areas of the CNS plays an important role in # and t~ receptor-mediated effects of opioids. A reciprocal functional antagonism between melanocortin and opioid peptides has been repeatedly suggested (for reviews see Refs. [3,5,7,16,27,35]). According to this hypothesis, target cells of proopiomelanocortinergic (POMC) terminals are continuously subjected to the simultaneous, opposite influence of the two main families of POMC-derived neuropeptides: endorphins and melanocortin,;. This hypothesis is strongly supported by a long list of experimental data (for a review see Ref. [6]). The most impressive, and relevant to the discussion of our present results, are: (a) melanocortins and opioids have an opposite influence on transmembrane Ca 2÷ fluxes [26,35] and on adenylate cyclase activity [11,46] in target neurons; (b) firing of target neurons is stimulated by melanocortins, and depressed by opioids [30,32]; (c) the simultaneous i.c.v, injection of a melanocortin (ACTH) and of fl-endorphin reciprocally suppress their respective effects on behavior and nociception [23]; (d) the chronic administration of opioids is associated with increased hypothalamic levels of melanocortins, and, conversely, the chronic i.c.v, infusion of melanocortins is

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associated with increased hypothalamic levels of opioids [24,43]. Our present data, showing that opening of brain K ÷ channels (a condition that potentiates opioid activity) inhibits the behavioral activity of melanocortins, indicate that the complex mechanism of the melanocortin-induced behavioral syndrome involves closure of K ÷ channels in target neurons and provide additional evidence to the hypothesis that melanocortins are physiological antagonists of opioids. This work was supported by grants from CNR (94.02554.CT04) and from MURST (40 and 60%), Rome, Italy. [1] Atwal, K.S., Modulation of potassium channels by organic molecules, Med. Res. Rev., 12 (1992) 569-591. [2] Baeyens, J.M., Esposito, E., Ossowska, G. and Samanin, R., Effects of peripheral and central administration of calcium channel blockers in the naloxone-precipitated abstinence syndrome in morphine-dependent rats, Eur. J. Pharmacol., 137 (1987) 9-13. [3] Bertolini, A. and Ferrari, W., Evidence and implication of a melanocortins-endorphins homeostatic system. In E. Endrtczi (Ed.), Neuropeptides and Psychosomatic Processes, Akadtmiai Kiadt, Budapest, 1981, pp. 245-261. [4] Bertolini, A. and Gessa, G.L., Behavioral effects of ACTH and MSH peptides, J. Endocrinol. Invest., 4 (1981) 241-251. [5] Bertolini, A., Poggioli, R. and Vergoni, A.V., Cross-species comparison of the ACTH-inducedbehavioral syndrome, Ann. N. Y. Acad. Sci., 525 (1988) 114-129. [6] Bertolini, A., Poggioli, R., Arletti, R., Benelli, A., Marrama, D., Bazzani, C., Tagliavini, S., Bemardi, M., Rasori, E., Sandrini, M., Guarini, S., Genedani, S. and Vergoni, A.V., Anatomia Chimica e Funzionale dei Sistemi Peptidergici. In E. Gori and E.E. Miiller (Eds.), Basi biologiche e Farmacologiche delle Tossicodipendenze, Pythagora Press, Milano, 1992, pp. 25-76. [7] Bertolini, A., Poggioli, R., Vergoni, A.V., Castelli, M. and Guarini, S., Evidence that melanotropins are physiological antagonists of opioids. In D. De Wied and W. Ferrari (Eds.), Central Actions of ACTH and Related Peptides, Liviana Press-Springer Verlag, Padova-Berlin, 1986, pp. 207-222. [8] Bertolini, A., Vergoni, W., Gessa, G.L. and Ferrari, W., Induction of sexual excitement by the action of adrenocorticotrophic hormone in brain, Nature. 221 (1969) 667-669. [9] Birnbaumer, L., G proteins in signal transduction, Annu. Rev. Pharmacol. Toxicol., 30 (1990) 675-705. [10] Bimbaumer, L., G proteins and the modulation of potassium channels. In A.H. Weston and T.C. Hamilton (Eds.), Potassium Channel Modulators, Blackwell Scientific, Oxford, 1992, pp. 4475. [11] Collier, H.O.J. and Roy, A.C., Morphine-like drugs inhibit the stimulation by E prostaglandins of cyclic AMP formation in rat brain homogenate, Nature, 248 (1974) 24-27. [12] Crain, S.M. and Shen, K.-F., Opioids can evoke direct receptormediated excitatory effect on sensory neurons, Trends Pharmacol. Sci., 11 (1990)77-81. [13] De Wied, D., Influenceof anterior pituitary on avoidance learning and escape behavior, Am. J. Physiol., 207 (1964) 255-259. [14] De Wied, D., Inhibitory effect of ACTH and related peptides on extinction of conditioned avoidance behavior in rats, Proc. Soc. Exp. Biol. Med., 122 (1966) 28-32. [15] De Wied, D. and Bohus, B., Long term and short term effects on retention of a conditioned avoidance response in rats by treatment with long acting pitressin and a-MSH, Nature, 212 (1966) 14841486.

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[16] De Wied, D. and Jolles, J., Neuropeptides derived from proopiomelanocortin: behavioral, physiological and neurochemical effects, Physiol. Rev., 62 (1982) 976-1059. [17] De Wied, D. and Wolterink, G., Structure-activity studies on the neuroactive and neurotrophic effects of neuropeptides related to ACTH, Ann. N. Y. Acad. Sci., 525 (1988) 130-140. [18] Del Pozo, E., Caro, G. and Baeyens, J.M., Analgesic effects of several calcium channel blockers in mice, Eur. J. Pharmacol., 137 (1987) 155-160. [19] Dierssen, M., Fl6rez, J. and Hurl6, M.A., Calcium channel modulation by dihydropiridines modifies sufentanil-induced antinociception in acute and tolerant conditions, NannynSchmiedeberg's Arch. Pharmacol., 342 (1990) 559-565. [20] Eberle, A.N., The Melanotropins, Karger, Basel, 1988, 556 pp. [21] Ferrari, W., Behavioural changes in animals after intracistemal injection with adrenocorticotrophic hormone and melanocytestimulating hormone, Nature, 181 (1958) 925-926. [22] Ferrari, W., Gessa, G.L. and Vargiu, L., Behavioral effects induced by intracisternally injected ACTH and MSH, Ann. N. Y. Acad. Sci., 14 (1963) 330-345. [23] Fratta, W., Rossetti, Z.L., Poggioli, R. and Gessa, G.L., Reciprocal antagonism between ACTH 1-24 and fl-endorphin in rats, Neurosci. Lett., 24 (1981) 71-74. [24] Gessa, G.L., Fratta, W., Melis, M., Bertolini, A. and Ferrari, W., Hypothalamic ACTH and MSH levels increase in morphine tolerance and decrease after morphine withdrawal, Eur. J. Pharmacol. 95 (1983) 143-144. [25] Gispen, W.H., Wiegant, V.M., Greven, H.M. and De Wied, D., The induction of excessive grooming in the rat by intraventricular application of peptides derived from ACTH: structure-activity study, Life Sci., 17 (1975) 645-652. [26] Guerrero-Munoz, F., Guerrero, M.L., Way, E.L. and Li, C.H., Effect of fl-endorphin on Ca 2+ uptake in the brain, Science, 206 (1979) 89-91. [27] Hendrie, C.A., Opiate dependence and withdrawal - a new synthesis, Pharmacol. Bioehem. Behav., 23 (1985) 863-868. [28] Hermsmeyer, K., Ion channel effects of pinacidil in vascular muscle, Drugs, 36 (Suppl. 7) (1988) 29-32. [29] Hoffmeister, F. and Tettenborn, D., Calcium agonists and antagonists of the dihydropiridine type: Antinociceptive effects, interference with opiate-#-receptor agonists and neuropharmacological actions in rodents, Psychopharmacology, 90 (1986) 299-307. [30] Krivoy, W.A. and Zimmermann, E., An effect of fl-melanocyte stimulating hormone (fl-MSH) and a-motoneurons of cat spinal cord, Eur. J. Pharmacol., 46 (1977) 315-322. [31] Mountjoy, K.G., Robbins, L.S., Mortrud, M.T. and Cone, R.D., The cloning of a family of genes that encode the melanocortin receptors, Science, 257 (1992) 1248-1251.

[32] Nicoll, R.A., Siggins, G.R., Ling, N., Bloom, F.E. and Guillemin, R., Neuronal action of the endorphins and enkephalins among brain regions: a comparative microiontophoretic study, Proc. Natl. Acad. Sci. USA, 74 (1977) 2584-2588. [33] North, R.A., Drug receptors and the inhibition of nerve cells, Br. J. Pharmacol., 98 (1989) 13-28. [34] North, R.A., Williams, J.T., Surprenant, A. and Christie, M.J.,/.t and 6 receptors belong to a family of receptors that are coupled to potassium channels, Proc. Natl. Acad. Sci. USA, 84 (1987) 54875491. [35] O'Donohue, T.L. and Dorsa, D.M., The opiomelanotropinergic neuronal and endocrine systems, Peptides, 3 (1982) 353-395. [36] Ocafia, M., Del Pozo, E., Barrios, M., Robles, L.I. and Baeyens J.M., An ATP-dependent potassium channel blocker antagonizes morphine analgesia, Eur. J. Pharmacol., 186 (1990) 377-378. [37] Paxinos, G. and Watson, C., The Rat Brain in Stereotaxic Coordinates, Academic Press, Sidney, 1982. [38] Poggioli, R., Rasori, E. and Bertolini, A., The behavioral syndrome induced by adrenocorticotropic hormone in rats is prevented by Ca 2÷ channel blockade, J. Endocrinol. Invest., 16 (1993) 83-86. [39] Robles, L.I., Barrios, M. and Baeyens J,M., ATP-sensitive K+ channel openers inhibit morphine withdrawal, Eur. J. Pharmacol., 251 (1994) 113-115. [40] Tatro, J.B., Melanotropin receptors in the brain are differentially distributed and recognized both corticotropin and a-melanocyte stimulating hormone, Brain Res., 536 (1990) 124-132. [41] Vergoni, A.V., Scarano, A. and Bertolini, A., Pinaeidil potentiates morphine analgesia, Life Sci., 50 (1992) PL135-PL138. [42] Vergoni, A.V., Poggioli, R. and Bertolini, A., Corticotropin inhibits food intake in rats, Neuropeptides, 7 (1986) 153-158. [43] Vergoni, A.V., Poggioli, R., Facchinetti, F., Bazzani, C., Marrama, D. and Bertolini, A., Tolerance develops to the behavioural effects of ACTH-(1-24) during continuous I.C.V. infusion in rats, and is associated with increased hypothalamic levels of betaendorphin, Neuropeptides, 14 (1989) 93-98. [44] Vergoni, A.V., Poggioli, R., Marrama, D. and Bertolini, A., Inhibition of feeding by ACTH-(1-24): behavioral and pharmacological aspects, Eur. J. Pharmacol., 179 (1990) 347-355. [45] Werz, M.A. and MacDonald, R.L., Dynorphin and neoendorphin peptides decrease dorsal root ganglion neuron calcium-dependent action potential duration, J. Pharmacol. Exp. Ther., 234 (1985) 49-56. [46] Wiegant, V.M., Dunn, A.J., Schotman, P. and Gispen, W.H., ACTH-Iike neurotropic peptides: possible regulators of rat brain cyclic AMP, Brain Res., 168 (1979) 565-584. [47] Wild, K.D., Vanderah, T., Mosberg, H.I. and Porreca, F., Opioid 6 receptor subtypes are associated with different potassium channels, Eur. J. Pharmacol., 193 (1991) 135-136.