- Email: [email protected]
6 mice
Brain Research, 479 (1989) 1-5 Elsevier BRE 14126
Research Reports
Blocking of morphine-induced locomotor hyperactivity by amygdaloid lesions in C57BL/6 mice Vincenzo Libri, Martine Ammassari-Teule and Claudio Castellano lstituto di Psicobioiogia e Psicofarmacologia del C.N.R., Rome (Italy)
(Accepted 21 June 1988) Key words: Morphine; Amygdala; Caudate nucleus; Hippocampus; Lesion; Locomotor activity; C57BL/6 mouse
Bilateral lesions of the amygdaloid complex in C57BL/6 mice prevented the occurrence of morphine-induced hypermotility (running fit). This effect, that was different from that observed after hippocampal lesions but similar to that observed after caudate lesions, confirms the role of the basal ganglia catecholaminergic system in the development of the motor stimulation consecutive to the administration of this opiate receptor agonist. INTRODUCTION A number of researches have shown that morphine administration results in locomotor hyperactivity (running fit) in C57BL/6 mice 6'11'21. ! n v c ~ t ~ , i o n s on neurochemical mechanisms responsible for this effect have outlined the role of catecholaminergic ]'5'8, serotonergic 2 and histaminergic 1° systems in mediating the running fit response to opiates while the cholinergic system appears involved in a lesser extent 14. More recent investigations using lesion techniques have then been devoted to the identification of subcortical sites at which morphine should exert its stimulating effect. The results have shown that, within .'.l=e iimbic system, septal lesions do not affect morphi.~e-i~uced hyperactivity ], --'~':'w.,.e,,,~r,u,.,~mr,,.t': ....... ' lesions enhance it 19. However, lesion,~ localized in the basal forebrain (nucleus accumbens, striatum) always result in attenuating or blocking the running fit syndrome 19,2°. Since it is known that the amygdaloid complex, which contains among the highest concentrations of opioid receptors in rodents brain ~s, belongs to the' limbic system but p~'esents anatomical connections with forebrain nucle, (striatum) since at least some of
its portions are better identified with basal ganglia 15, we have studied in the present research the role of this structure in modulating morphine-induced hyperactivity in C57BL/6 mice. Moreover, since among the above reported data, lesions of hippocampus and caudate nucleus were made by in situ injections of kainic acid, we also decided to assess the effect of electrolytic lesions in these two areas on the development of morphine-induced running fit. MATERIALS AND METHODS Subjects The subjects were 80 male C57BL/6 mice (Charles River, Como, Italy) 11-12 weeks old and weighing about 22-25 g at the beginning of the experiments. They were housed in opaque plastic cages (27 x 21 x 13.5 cm) with 4 animals per cage and fed with standard diet ad libitum. The animals were maintained on 12 h light/12 h dark cycle (07.00-19.00 h) and at a constant temperature (21 °C). Surgery Mice were anesthetized with chloral hydrate (400
Correspondence: C. Castellano, Istituto di Psicobiologia e Psicofarmacologia, Via Reno 1, 00198 Rome, Italy.
0006-8993/89/$03.50© 1989Elsevier Science Publishers B.V. (Biomedical Division)
mg/kg) and placed in a Narishige stereotaxic apparatus with mouse adaptor. A stainless steel electrode (0.2 mm diameter), insulated except at the tip, was inserted bilaterally in the following areas with lambda and bregma in the same horizontal plane: amygdaloid complex (A -1.8 mm posterior to bregma; L +_3.1 mm lateral to the midline; H 4.3 mm ventral from the dura), caudate nucleus (A +0.5 anterior to bregma; L +2.2 mm lateral to the midline; H 4.3 mm ventral to the dura and hippocampus). (In order to make a wide lesion of the hippocampal structure, the electrode was inserted twice at the same anterior plane but at two different lateral and ventral coordinates: A -2.2 posterior to bregma; L _+1.8 and 2.8 lateral to the midline; H 1.5 and 2.5 ventral from the dura.) A 2.5-mA anodal direct current was passed for 5 s through the electrode, the circuit being completed by taping the cathode to the tail. Sham operations were performed by inserting the electrode at the coordinates used for lesioning the amygdaloid complex but without making electrocoagulation. It must be noted that a single group of sham-operated animals was considered since at those coordinates the electrode crosses hippocampus, caudate nucleus and amygdala. The subjects were then left in their home cage for a recovery period of one week.
meres n. Injections were made intraperitoneally, 30 min before the beginning of a 30-min long locomotor activity test.
Statistics For each studied area, the data concernil~g locomotor activity scores of lesioned, sham-operated and
Apparatus Locomotor activity was measured in Plexiglas toggle-floor boxes (24.5 x 9.0 cm) n. The number of crossings from one side to the other of the box was recorded automatically by means of a microswitch connected to the tilting floor. Circuitry was arranged so that whenever the mouse crossed the cage, a cumulative counter was advanced: this count constituted the score of each mouse.
Procedure The animals were divided into 5 groups of 16 animals each. The first 3 groups received bilateral lesions of the amygdaloid complex, the caudate nucleus and the hippocampus respectively. The fourth group received sham operations as described above. The fifth group was an unoperated control group. Each group was subdivided im¢, two subgroups of 8 animals each injected with saline (0.9% NaCl) and morphine-hydrochloride (20 mg/kg) respectively. This dose was chosen on the basis of previous experi-
C Fig. 1. Typicalexample showingsite and extent of (A) the caudate lesion, (B) the amygdaloidlesionand (C) the hippocampal lesion. The whitened areas correspond to the maximumextent of the lesions.
control animals were statistically evaluated by a twofactor analysis of variance, the factors being lesion (3 levels) and treatment (2 levels). Eventual differences among the reactivity to morphine of animals beating lesions in distinct areas were then assessed by a twofactor analysis of variance, the factors being lesion (3 levels) and treatment (2 levels). Subsequent between-group comparisons were carried out with a Duncan multiple-range test. RESULTS
Histology At the completion of the experiment, lesioned and sham-operated mice were sacrificed. The brains were fixed in a Formalin solution (10%) sectioned coronally at 60 ~m and stained with Toluidine blue according to the Nissl method. Examination of the tissue revealed bilateral lesions of (1) the amygdaloid central nucleus, extended in some cases to the basolateral nucleus, (2) the dorsal and central part of the caudate nucleus, (3) the dorsal and ventrolateral hippocampus, extended in some cases to corpus callosum and parietal cortex (Fig. 1).
Behavior The activity scores recorded in each group are shown in Fig. 2. Amygdaloid lesion. The results show a significant effect of the lesion factor (F2.42 = 14.33, P < 0.001) indicating that, independently of the treatment, the activity rate of lesioned animals is significantly lower than that recorded in non-lesioned animals. Moreover, a significant effect of the treatment factor (F],42 400
g ~oo
I"-I Sa
c =. o
200
I00 e,
-r-
F
Co
Sh
Am
Ca
Hi
Fig. 2. Effects of amygdaloid (Am), caudate (Ca) and hippocampal (Hi) lesions on morphine-induced hyperactivity (20 mg/kg) in C57BL/6 mice. Co, unoperated mice; Sh, sham-lesioned mice. The vertical lines represent S.E.M. values.
= 75.12, P < 0.001) reveals that, independently of the iesion, the activity rate of morphine-injected animals is significantly higher than that recorded in saline-injected animals. However, a significant effect of the lesion x treatment interaction (F2.42 = 12.03, P < 0.001) outlines that the scores recorded in lesioned animals injected with morphine are si~ificantly lower than those recorded in non-lesioned animals injected with morphine. In fact, subsequent between-group comparisons show no significant difference between the number of crossings recorded in control + saline, sham-operated + saline, lesioned + saline and lesioned + morphine groups. However, the scores recorded in these 4 groups are significantly lower (P < 0.01) than those recorded in control + morphine and sham-operated + morphine groups among which no difference is found. Caudate lesion. A significant effect of the lesion factor (F2,42 = 15.28, P < 0.001) also indicates that, independently of the treatment, lesioned animals made less crossings than non-lesioned animals while a significant effect of the treatment factor (F1,42 = 85.30, P < 0.001) reveals that, independently of the lesion, animals injected with morphine were more active than animals injected with saline. Moreover, as for amygdaloid lesions, a significant effect of the lesion x treatment interaction (F2.42 = 10.90, P < 0.001) outlines that the scores recorded in lesioned animals injected with morphine are significantly lower than those recorded in non-lesioned animals injected with morphine. Subsequent between-group comparisons also show (1) no significant difference in locomotor activity between control and sham-operated mice injected with morphine but (2) significant differences (P < 0.01) between the scores of these two groups and those recorded in the other 4 groups (lesioned + saline, lesioned + morphine, control + saline, sham-operated + saline) among which no significant difference is found. Hippocampal lesion. A significant effect of the treatment factor (F1.42 - 85.46, P < 0.001) but no effect of the lesion factor nor of the treatment x lesion interaction indicate that morphine injections increase locomotor activity in all the treated mice. Reactivity of lesioned animals to morphine. A significant effect of the lesion factor (F2,42 = 6.48, P < 0.003) indicates that, independently of the treatment, hippocampai lesioned animals make more
crossings than animals beating lesions of the caudate nucleus or the amygdaloid complex, while a significant effect of the treatment factor (FL42 = 24.73, P < 0.001) shows that locomotor activity is higher in animals receiving morphine injections. However, a significant lesion x treatment interaction (F2.42 = 5.89, P < 0.005) confirms that morphine injections do n o t affect locomotor activity of animals lesioned in the 3 different structures in the same fashion. In fact, as revealed by the subsequent between-group comparisons, hippocampal lesioned animals injected with morphine display locomotor activity scores significantly higher (P < 0.01) than those recorded in the other 5 groups among which no difference is found. DISCUSSION The present results show that electrolytic lesions of amygdala and caudate nucleus antagonize morphineinduced running fit while electrolytic lesions of hippocampus do not interfere with this syndrome. On the one hand, this observation indicates differences in the control exerted by the amygdaloid complex and other limbic structures such as septum and hippocampus on morphine-induced hyperactivity. Concerning hippocampus, previous data have indicated an enhancement of morphine-induced running fit following kainic acid lesions ]9 while the present results show no interference of electrolytic lesions with this syndrome. This discrepancy can be explained either by assuming that the passing fibers left intact by the kainic acid lesion play a role in the development of the running fit or, more likely, on the basis of previous data from the literature showing that kainic acid injections within hippocampus produce a drastic increase in the content of hippocampal Met-enkephalin 9 which is known to enhance locomotor activity in rodents ]2. On the other hand, from these results, similarities among the effects of lesions localized i~ the amygdala and in forebrain basal nuclei (striatum or nucleus accumbens) are evident since all those le-
REFERENCES 1.~Castel~ano, C., Llovera, B.E. and Oliverio, A., Morphineinduc.~ running and analgesia in two strains of mice following septal lesions or modification of brain amines, Naunyn-
sions produce a blocking or an attenuation of morphine-induced hyperactivity 19,2°. Interestingly, anatomical and electrophysiological data indicate important connections between limbic and striatal sectors of the basal forebrain. In particular, since the basolateral amygdaloid nucleus projects onto the caudate nucleus, it has been suggested that this pathway may constitute a route over which the limbic system can influence motor functions 16. Moreover, analogies have been observed at the neurochemical level between amygdala and striatum (caudate, putamen). First, the existence of a heavy dopaminergic innervation of particular relevance for the development of stereotypic behaviors 1~ has been demonstrated in both structures 3,4. Second, these two structures also show an analogous distribution of enkephalin cell bodies and terminals. Therefore, the antagonism of morphine-induced running fit following lesions of the amygdaloid complex which reproduces the effect obtained after caudate lesions (1) can be interpreted in the light of the connections as well as the neurochemical similarities existing between caudate nucleus and amygdaloid complex and (2) seems to restrict to the basal ganglia and its related systems the mediation of morphine-induced hyperactivity evident in C57BL/6 mice. Moreover, on the basis of the large amount of data from the literature showing the involvement of the limbic system in the regulation of emotional states, it could be hypothesized that the amygdaloidstriatal pathway could represent a crucial route for the transcription of emotionality into stereotypic behaviors.
ACKNOWLEDGEMENTS V.L. is a postdoctoral fellow from the Institute of Pharmacology, Faculty of Medicine, University of Reggio Calabria, Catanzaro (Italy). Partial support from Fidia Research Laboratory is gratefully acknowledged.
Schmiedeberg's Arch. Pharmacol., 288 (1975) 355-370. 2 Chang, K.J., Hazum, E. and Cuatrecasas, P., Multiple opiate receptors, TINS, 3 (1980) 162-162. 3 Fallon, J.H. and Moore, R.Y., Catecholamine innervation of the basal forebrain. IV. Topography of the dopamine
projection to the basal forebrain and neostriatum, J. Comp. Neurol., 180 (1978) 545-580. 4 Failon, J., Koziell, D.A. and Moore, R.Y., Catecholamine innervation of the basal forebrain. II. Amygdala, suprarhinai cortex and entorhinal cortex, J. Comp. Neurol., 180 (1978a) 509-532. 5 Filibeck, U., Castellano, C. and Oliverio, A., Inhibition by clonidine of morphine-induced running fit but not analgesia in C57BL/6 mice, Pol. J. Pharmacol. Pharm., 32 (1980) 140-154. 6 Frigeni, V., Bruno, I., Carenzi, A., Racagni, G. and Santini, V., Analgesia and motor activity elicited by morphine and enkephalins in two inbred strains of mice, J. Pharm. Pharmacol., 30 (1978) 310-311. 7 Fuxe, K., Evidence for the exsitence of monoamine new rons in the central nervous system: IV. Distribution of monoamine nerve terminals in the central nervous system, Acta Physiol. Scand., 64 (suppl. 247) (1965) 36-85. 8 Hollinger, M., Effects of reserpine, a-methyl-p-tyrosine,pchlorophenylalanineand pargyline on levorphanol-induced running activity in mice, Arch. Int. Pharmacodyn., 179 (1969) 419-424. 9 Hong, J.S., Wood, P.L., Gillin, J.C., Yong, Y.T. and Costa, E., Changes of hippocampal Met-enkephalin content after recurrent motor seizures, Neture (Lond.), 285 (1980) 230-231. 10 Lee, J.R. and Fennessey, M.R., Effects of morphine on brain histamine, antinociception and activity in mice, Clin. Exp. Pharmacol. Physiol., 3 (1976) 179-189. 11 Oliverio, A. and Castellano, C., Genotype-dependent sensitivity and tolerance to morphine and heroin: dissociation between opiate-induced running and analgesia in the mouse, Psychopharmacology, 39 (1974) 13-22. 12 Oliverio, A., Castellano, C. and Pugiisi-Allegra, S., Psychobiology of opioids, Int. Rev. Neurobiol., 25 (1984) 277-337. 13 Pycock, C.J. and Phillipson, O.T., A neuroanatomical and
neuropharmacological analysis of basal ganglia output. In L.L. Iversen, S.D. Iversen and S.M. Snyder (Eds.), Handbook of Psychopharmacology, Plenum, New York, 1984, pp. 191-278. 14 Racagni, G., Bruno, F., luliani, E. and Paoletti, R., Differential sensitivity to morphine-induced analgesia and motor activity in two inbred strains of mice: behavioral and biochemical correlations, J. Pharmacol. Exp. Ther., 209 (1979) 111-116. 15 Rodgers, R.J., Influence of intra-amygdaloid opiate injections on shock thresholds, tail flick latencies and open field behavior in rats, Brain Research, 153 (1978) 211-216. 16 Royce, G.S., Cells of origin of subcortical afferents to the caudate nucleus: a horseradish peroxidase study in the cat, Brain Research, 153 (1978) 465-475. 17 Sansone, M., Ammassari-Teule, M., Renzi, P. and Oliverio, A., Different effects of apomorphine on locomotor activity in C57BL/6 and DBAJ2 mice, Pharmac. Biochem. Behav., 14 (1981) 741-743. 18 Sar, M., Stumpf, W.E., Miller, R.J., Chang, K.J. and Cuatrecasas, P., Immunohistochemical localization of enkephalin in rat brain and spinal cord, J. Comp. Neurol., 182 (1978) 17-38. 19 Siegfried, B., Filibeck, U., Gozzo, S. and Castellano, C., Lack of morphine-induced hyperactivity in C57BL/6 mice following striatal kainic lesions, Behm,. Brain Res., 4 (1982) 389-399. 20 Teitelbaum, H., Giamatteao, P. and Michley, G.A., Differential effects of localized lesions of n. accumbens on morphine- and amphetamine-induced locomotor activity in the C57BL/6 mouse, Y. Comp. Physiol. Psychol., 93 (1979) 745-751. 21 Trabucchi, M., Spano, P.F., Racagni, G. and Ofiverio, A., Genotype-dependent sensitivity to morphine: dopamine involvement in morphine-induced running fit in the mouse, Brai,~ Research, 114(1976) 1-48.
Research Reports
Blocking of morphine-induced locomotor hyperactivity by amygdaloid lesions in C57BL/6 mice Vincenzo Libri, Martine Ammassari-Teule and Claudio Castellano lstituto di Psicobioiogia e Psicofarmacologia del C.N.R., Rome (Italy)
(Accepted 21 June 1988) Key words: Morphine; Amygdala; Caudate nucleus; Hippocampus; Lesion; Locomotor activity; C57BL/6 mouse
Bilateral lesions of the amygdaloid complex in C57BL/6 mice prevented the occurrence of morphine-induced hypermotility (running fit). This effect, that was different from that observed after hippocampal lesions but similar to that observed after caudate lesions, confirms the role of the basal ganglia catecholaminergic system in the development of the motor stimulation consecutive to the administration of this opiate receptor agonist. INTRODUCTION A number of researches have shown that morphine administration results in locomotor hyperactivity (running fit) in C57BL/6 mice 6'11'21. ! n v c ~ t ~ , i o n s on neurochemical mechanisms responsible for this effect have outlined the role of catecholaminergic ]'5'8, serotonergic 2 and histaminergic 1° systems in mediating the running fit response to opiates while the cholinergic system appears involved in a lesser extent 14. More recent investigations using lesion techniques have then been devoted to the identification of subcortical sites at which morphine should exert its stimulating effect. The results have shown that, within .'.l=e iimbic system, septal lesions do not affect morphi.~e-i~uced hyperactivity ], --'~':'w.,.e,,,~r,u,.,~mr,,.t': ....... ' lesions enhance it 19. However, lesion,~ localized in the basal forebrain (nucleus accumbens, striatum) always result in attenuating or blocking the running fit syndrome 19,2°. Since it is known that the amygdaloid complex, which contains among the highest concentrations of opioid receptors in rodents brain ~s, belongs to the' limbic system but p~'esents anatomical connections with forebrain nucle, (striatum) since at least some of
its portions are better identified with basal ganglia 15, we have studied in the present research the role of this structure in modulating morphine-induced hyperactivity in C57BL/6 mice. Moreover, since among the above reported data, lesions of hippocampus and caudate nucleus were made by in situ injections of kainic acid, we also decided to assess the effect of electrolytic lesions in these two areas on the development of morphine-induced running fit. MATERIALS AND METHODS Subjects The subjects were 80 male C57BL/6 mice (Charles River, Como, Italy) 11-12 weeks old and weighing about 22-25 g at the beginning of the experiments. They were housed in opaque plastic cages (27 x 21 x 13.5 cm) with 4 animals per cage and fed with standard diet ad libitum. The animals were maintained on 12 h light/12 h dark cycle (07.00-19.00 h) and at a constant temperature (21 °C). Surgery Mice were anesthetized with chloral hydrate (400
Correspondence: C. Castellano, Istituto di Psicobiologia e Psicofarmacologia, Via Reno 1, 00198 Rome, Italy.
0006-8993/89/$03.50© 1989Elsevier Science Publishers B.V. (Biomedical Division)
mg/kg) and placed in a Narishige stereotaxic apparatus with mouse adaptor. A stainless steel electrode (0.2 mm diameter), insulated except at the tip, was inserted bilaterally in the following areas with lambda and bregma in the same horizontal plane: amygdaloid complex (A -1.8 mm posterior to bregma; L +_3.1 mm lateral to the midline; H 4.3 mm ventral from the dura), caudate nucleus (A +0.5 anterior to bregma; L +2.2 mm lateral to the midline; H 4.3 mm ventral to the dura and hippocampus). (In order to make a wide lesion of the hippocampal structure, the electrode was inserted twice at the same anterior plane but at two different lateral and ventral coordinates: A -2.2 posterior to bregma; L _+1.8 and 2.8 lateral to the midline; H 1.5 and 2.5 ventral from the dura.) A 2.5-mA anodal direct current was passed for 5 s through the electrode, the circuit being completed by taping the cathode to the tail. Sham operations were performed by inserting the electrode at the coordinates used for lesioning the amygdaloid complex but without making electrocoagulation. It must be noted that a single group of sham-operated animals was considered since at those coordinates the electrode crosses hippocampus, caudate nucleus and amygdala. The subjects were then left in their home cage for a recovery period of one week.
meres n. Injections were made intraperitoneally, 30 min before the beginning of a 30-min long locomotor activity test.
Statistics For each studied area, the data concernil~g locomotor activity scores of lesioned, sham-operated and
Apparatus Locomotor activity was measured in Plexiglas toggle-floor boxes (24.5 x 9.0 cm) n. The number of crossings from one side to the other of the box was recorded automatically by means of a microswitch connected to the tilting floor. Circuitry was arranged so that whenever the mouse crossed the cage, a cumulative counter was advanced: this count constituted the score of each mouse.
Procedure The animals were divided into 5 groups of 16 animals each. The first 3 groups received bilateral lesions of the amygdaloid complex, the caudate nucleus and the hippocampus respectively. The fourth group received sham operations as described above. The fifth group was an unoperated control group. Each group was subdivided im¢, two subgroups of 8 animals each injected with saline (0.9% NaCl) and morphine-hydrochloride (20 mg/kg) respectively. This dose was chosen on the basis of previous experi-
C Fig. 1. Typicalexample showingsite and extent of (A) the caudate lesion, (B) the amygdaloidlesionand (C) the hippocampal lesion. The whitened areas correspond to the maximumextent of the lesions.
control animals were statistically evaluated by a twofactor analysis of variance, the factors being lesion (3 levels) and treatment (2 levels). Eventual differences among the reactivity to morphine of animals beating lesions in distinct areas were then assessed by a twofactor analysis of variance, the factors being lesion (3 levels) and treatment (2 levels). Subsequent between-group comparisons were carried out with a Duncan multiple-range test. RESULTS
Histology At the completion of the experiment, lesioned and sham-operated mice were sacrificed. The brains were fixed in a Formalin solution (10%) sectioned coronally at 60 ~m and stained with Toluidine blue according to the Nissl method. Examination of the tissue revealed bilateral lesions of (1) the amygdaloid central nucleus, extended in some cases to the basolateral nucleus, (2) the dorsal and central part of the caudate nucleus, (3) the dorsal and ventrolateral hippocampus, extended in some cases to corpus callosum and parietal cortex (Fig. 1).
Behavior The activity scores recorded in each group are shown in Fig. 2. Amygdaloid lesion. The results show a significant effect of the lesion factor (F2.42 = 14.33, P < 0.001) indicating that, independently of the treatment, the activity rate of lesioned animals is significantly lower than that recorded in non-lesioned animals. Moreover, a significant effect of the treatment factor (F],42 400
g ~oo
I"-I Sa
c =. o
200
I00 e,
-r-
F
Co
Sh
Am
Ca
Hi
Fig. 2. Effects of amygdaloid (Am), caudate (Ca) and hippocampal (Hi) lesions on morphine-induced hyperactivity (20 mg/kg) in C57BL/6 mice. Co, unoperated mice; Sh, sham-lesioned mice. The vertical lines represent S.E.M. values.
= 75.12, P < 0.001) reveals that, independently of the iesion, the activity rate of morphine-injected animals is significantly higher than that recorded in saline-injected animals. However, a significant effect of the lesion x treatment interaction (F2.42 = 12.03, P < 0.001) outlines that the scores recorded in lesioned animals injected with morphine are si~ificantly lower than those recorded in non-lesioned animals injected with morphine. In fact, subsequent between-group comparisons show no significant difference between the number of crossings recorded in control + saline, sham-operated + saline, lesioned + saline and lesioned + morphine groups. However, the scores recorded in these 4 groups are significantly lower (P < 0.01) than those recorded in control + morphine and sham-operated + morphine groups among which no difference is found. Caudate lesion. A significant effect of the lesion factor (F2,42 = 15.28, P < 0.001) also indicates that, independently of the treatment, lesioned animals made less crossings than non-lesioned animals while a significant effect of the treatment factor (F1,42 = 85.30, P < 0.001) reveals that, independently of the lesion, animals injected with morphine were more active than animals injected with saline. Moreover, as for amygdaloid lesions, a significant effect of the lesion x treatment interaction (F2.42 = 10.90, P < 0.001) outlines that the scores recorded in lesioned animals injected with morphine are significantly lower than those recorded in non-lesioned animals injected with morphine. Subsequent between-group comparisons also show (1) no significant difference in locomotor activity between control and sham-operated mice injected with morphine but (2) significant differences (P < 0.01) between the scores of these two groups and those recorded in the other 4 groups (lesioned + saline, lesioned + morphine, control + saline, sham-operated + saline) among which no significant difference is found. Hippocampal lesion. A significant effect of the treatment factor (F1.42 - 85.46, P < 0.001) but no effect of the lesion factor nor of the treatment x lesion interaction indicate that morphine injections increase locomotor activity in all the treated mice. Reactivity of lesioned animals to morphine. A significant effect of the lesion factor (F2,42 = 6.48, P < 0.003) indicates that, independently of the treatment, hippocampai lesioned animals make more
crossings than animals beating lesions of the caudate nucleus or the amygdaloid complex, while a significant effect of the treatment factor (FL42 = 24.73, P < 0.001) shows that locomotor activity is higher in animals receiving morphine injections. However, a significant lesion x treatment interaction (F2.42 = 5.89, P < 0.005) confirms that morphine injections do n o t affect locomotor activity of animals lesioned in the 3 different structures in the same fashion. In fact, as revealed by the subsequent between-group comparisons, hippocampal lesioned animals injected with morphine display locomotor activity scores significantly higher (P < 0.01) than those recorded in the other 5 groups among which no difference is found. DISCUSSION The present results show that electrolytic lesions of amygdala and caudate nucleus antagonize morphineinduced running fit while electrolytic lesions of hippocampus do not interfere with this syndrome. On the one hand, this observation indicates differences in the control exerted by the amygdaloid complex and other limbic structures such as septum and hippocampus on morphine-induced hyperactivity. Concerning hippocampus, previous data have indicated an enhancement of morphine-induced running fit following kainic acid lesions ]9 while the present results show no interference of electrolytic lesions with this syndrome. This discrepancy can be explained either by assuming that the passing fibers left intact by the kainic acid lesion play a role in the development of the running fit or, more likely, on the basis of previous data from the literature showing that kainic acid injections within hippocampus produce a drastic increase in the content of hippocampal Met-enkephalin 9 which is known to enhance locomotor activity in rodents ]2. On the other hand, from these results, similarities among the effects of lesions localized i~ the amygdala and in forebrain basal nuclei (striatum or nucleus accumbens) are evident since all those le-
REFERENCES 1.~Castel~ano, C., Llovera, B.E. and Oliverio, A., Morphineinduc.~ running and analgesia in two strains of mice following septal lesions or modification of brain amines, Naunyn-
sions produce a blocking or an attenuation of morphine-induced hyperactivity 19,2°. Interestingly, anatomical and electrophysiological data indicate important connections between limbic and striatal sectors of the basal forebrain. In particular, since the basolateral amygdaloid nucleus projects onto the caudate nucleus, it has been suggested that this pathway may constitute a route over which the limbic system can influence motor functions 16. Moreover, analogies have been observed at the neurochemical level between amygdala and striatum (caudate, putamen). First, the existence of a heavy dopaminergic innervation of particular relevance for the development of stereotypic behaviors 1~ has been demonstrated in both structures 3,4. Second, these two structures also show an analogous distribution of enkephalin cell bodies and terminals. Therefore, the antagonism of morphine-induced running fit following lesions of the amygdaloid complex which reproduces the effect obtained after caudate lesions (1) can be interpreted in the light of the connections as well as the neurochemical similarities existing between caudate nucleus and amygdaloid complex and (2) seems to restrict to the basal ganglia and its related systems the mediation of morphine-induced hyperactivity evident in C57BL/6 mice. Moreover, on the basis of the large amount of data from the literature showing the involvement of the limbic system in the regulation of emotional states, it could be hypothesized that the amygdaloidstriatal pathway could represent a crucial route for the transcription of emotionality into stereotypic behaviors.
ACKNOWLEDGEMENTS V.L. is a postdoctoral fellow from the Institute of Pharmacology, Faculty of Medicine, University of Reggio Calabria, Catanzaro (Italy). Partial support from Fidia Research Laboratory is gratefully acknowledged.
Schmiedeberg's Arch. Pharmacol., 288 (1975) 355-370. 2 Chang, K.J., Hazum, E. and Cuatrecasas, P., Multiple opiate receptors, TINS, 3 (1980) 162-162. 3 Fallon, J.H. and Moore, R.Y., Catecholamine innervation of the basal forebrain. IV. Topography of the dopamine
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