- Email: [email protected]
S.20.03 Effects of NOS inhibitors on ethanol intoxication and withdrawal
5'.20, New molecular i~sights i~to addiction serotonin receptor agonists phase shift the circadian clock through an increase in cAMP production (Sprouse e t a l . , 2004) but the drug Ecstasy (3,4-methylenedioxymetharrphetamine) alters this response (t3iello etal., 2001). Metarnphetamine treatment of rats alters the circadian expression rhythms of clock genes in the caudate putamen and the parietal cortex and desynchronizes them from the SCN rhythms (Masubuchi et al., 2000). The signaling pathways mentioned above can be stimulated by doparnine and glutamate. Hence, the levels of these neurotransmitters are critical for cellular responses and they are removed from their site of action by specific cell membrane transporters to avoid overstimulation of receptors. Cocaine and metarrphetamines interfere with the %nction of cell membrane transporters that normally remove neurotransmitters from the synaptic deft. This interference produces an elevation of neurotransmitter levels, which results in a psychomotor stimulation. Altered neurotransmitter levels in the brains of Per mutant mice are indicated by the finding that these mice display altered sensitization to cocaine (Abarca e t a h , 2002). Gone expression analysis in these animals revealed abnormal expression of glutamate receptors and transporters suggesting that Per genes influence directly or indirectly the responsiveness of the nervous system to neurotransmitters and drugs of abuse such as cocaine and ethanoh
References Abates C., Albrecht U., Spanagel R. 2002. Cocaine sensitization and reward are under the influence of okeadian genes and rhythm. Pro¢ Natl. Aead. Soi. 99, 9026-9030. Albrecht U., Zheng I3., Larldn D., Sun Z.S., Lee C.C. 2001. mPerl and roper2 are essential components for normal resetting of the okoadian olo&. J. 13iol. Rhythms, 16, 100-104. 13iello S., Darters R.I. 2001. MDMA and fenflurarnine alter the response of the circadian dock to a serotonin agonist t~ t,~t,'o. Brain Res., 920, 202-209. Masubuc_xhi S., Honrna S., Abe H., Ishizaki K., Narnihira M., Ikeda M., Honma K. 2000. Clo& genes outside the supra&iasmatio nucleus involved in manifestation of locomotor activity rhythm in rats. Eur. J. Nenrosd., 12, 4206-4214. Sprouse J., Reynolds L., Li X., 13raselton J., S&midt A. 2004. 8-OHDPAT as a 5-fiT7 agonist: phase shifts of the circadian biological clock throu@ increase of cAMP production. Nenropharmacology,46, 52-62.
•
Effects of NOS inhibitors on ethanol intoxication and w i ~ d r a w a l
R Pokk. Tartu U~iver##y, Department ofPJ~arrnacology Tartu,
Estouia Inla~duelion-" There are numerous data in the literature showing the interaction of ethanol with L-arginine - nitric oxide synthase (NOS) - NO pathways. Thus, NO-related agents, i.e. NO donors and NOS inhibitom, influence the acute effects of ethanol and ethanol withdrawal syndrome. It has been repeatedly demonstrated that NOS inhibitors strengthen and NO donom attenuate the anesthetic effects of ethanol after its acute administration (Adams and Cicero, 1994). However, different authors have reported contradictory results concerning the effects of NOS inhibitors on ethanol withdrawal syndrome (Uzbay and Oglesby, 2001). Thus, depending on the NOS inhibitor administered, its dose and route of administration, attenuation (Adams e t a l . 1995), worsening (Uzbay 2001) or no changes (Ikeda etal. 1999) in the severity of ethanol withdrawal signs have been reported. Aim: The aim of our work was to further study the interaction of ethanol and NOergic pathways. For this purpose we observed
$151
the effects of NOS inhibitors 7-nitroindazole (7-NI), NG-nitroL-arginine methyl ester (-L-NANfE) and NG-nitro-L-arginine (LNEAR@) on the effects of ethanol after acute and chronic ethanol administration and withdrawal. Methods: Acute ethanol administration was carried out intraperitoneally (i.p.) .30 minutes before behavioural tests (openfield test, plus-maze test) or immediately before the measurement of sleeping time. NOS inhibitors were injected i.p. 30 minutes before ethanol. For chronic ethanol administration mice were placed into inhalation chamber and exposed to increasing ethanol concentrations for 18 days. In separate groups physical signs of ethanol withdrawal and the anxiogenic effect of ethanol withdrawal in the plus-maze test were measured 7.5 h after the end of ethanol administration. NOS inhibitors were administered immediately after the end of chronic ethanol administration or 6.5 h later. Results: N e E inhibitors 7-NI (20-120 me/ks), L-NA/ME (20, 40 mg/kg) and L-NOARQ (20, 40 mg/kg) significantly increased the duration of ethanol (2, 3, 4 g/kg) induced sleep in mice and rats. L-NAME (20, 40 me/ks) and L-NOARG (20, 40 mg/kg) also significantly increased the sedative effect of ethanol (2 g a g ) in the open-field of reduced size as evidenced by a significant decrease in the number of rearings made and squares crossed. L-NAME and L-NOARG had no effect on ethanol pharmacokinetics. 7-NI at lower doses (20, 40 rag/ks) had no effect and at higher doses (80, 120 mg/kg) dose-dependently inhibited ethanol clearance after acute ethanol administration. After the removal of mice from the inhalation chamber the behavioural signs of ethanol withdrawal severe tremor and convulsions - developed in vehicle-treated mice. 7-NI at a dose of 20 me/ks blocked the development of the behavioural signs of ethanol withdrawal when administered immediately after the end of ethanol exposure, but had no effect when administered 6.5 hours later. L-NAIVIE and L-NeAR@ administered at a dose of 20 mg/kg had no effect on ethanol withdrawal syndrome, irrespective of time of administration. In mice treated with 7-NI immediately after the end of ethanol exposure the fall in ethanol concentrations was slower, significant concentrations were measured in blood 7.5 hours after the end of ethanol exposure. 7-NI and L-NOARG induced an anxiolytic effect in the plus-maze test as evidenced by an increase in the percentage of entries made onto and in the percentage of time spent on the open arms of the plus-maze. In accordance with numerous data in the literature chronic ethanol administration caused an anxiolytie and ethanol withdrawal- an anxiogenic effect in the plus-maze test as evidenced by changes in the percentage of entries made onto and in the percentage of time spent on the open arms. Neither 7-NI nor L-NeAR@ had significant effect on the behaviour of ethanol-intoxicated mice. 7-NI did not have effect and L-NOARG attenuated the anxiogenic effect of ethanol withdrawal in the plus-maze test. Concl~ioes-" 1. NOS inhibitors 7-1',]1,L-NAME and L-NOA.RG increased the sedative and anesthetic effects of ethanol as evidenced by an increase of the ethanol-induced sleep and sedative effect in the open-field test. These results suggest a role of L-arginine - NOS - NO pathways in the acute effects of ethanol. 2. 7-NI inhibited the elimination of ethanol. This effect is not probably due to 7-NIs effect on NO synthesis but is caused by the presence of 1,2-diazole ring in 7-NIs chemical structure. This effect was more pronounced after chronic ethanol administration. 3. NOS inhibitors L-NAME and L-NOARG did not have effect on the physical signs of ethanol withdrawal. 7-NI had attenuated the physical signs of ethanol withdrawal only due to pharmacokinetic interaction. 4.7-NI did not have effect and L-N©ARG attenuated
S.20. New mdecular ~s~ts *~to add*or*on
$152
the anxiogenic effect of ethanol withdrawal in the plus-maze teat. 7-NI and L-NOARG inhibit different NOS subtypes, while L-NOARG and L-NAME inhibit both endothelial NOS (eNOS) and neuronal NOS (nNOS), 7-NI is a selective nNOS inhibitor. These resulb suggest that different NOS subtypes might be involved in the development of physical signs of ethanol withdrawal and anxiogenic effect of ethanol withdrawal in the plus-maze test.
References [1] Adams ML, Cicero TJ (1998) Alcohol intoxication and withdrawal: the role of nitric oxide. Alcoholism: Clinical and Experimental Reseat& 16, 153-158. [2] Adams, ML, Sewing, BN, Chert,J, Mey% ER, Cicero, TJ (1995) Nitric oxide-related agents alter alo&ol withdrawal in male rats. Alcoholism: Clinical and Experimental Reseat& 19, 195-199. [3] Ikeda, M, Komiyama, ,i_;Sato, I, Himi, T, Murota, S (1999) Neuronalnitrio oxide s3mthaseis resistant to ethanol. Life Sciences 64, 1623-1630. [4] Uzbay, IT (2001) L-NAME precipitates catatonia &ring ethanol withdrawal in rats. Behavioural Brain Research 119, 71-76. [5] Uzbay IT, Oglesby MW (2001) Nitric oxide and substance dependence. Neurosoienee and Biobehavioral Reviews 25: 43-52.
•
Glut~matergic mechanisms underlying nicotine addiction
A. Markou, RI Kenny, N.E. Paterson, S. Semenova. Scripps iResearo~ I~t~t~e, Department of Ne~rop~arrnaco~og,T, £a Jo~a, CA, USA. Two factors that maintain habitual tobacco smoking are the rewarding effects of nicotine, and the motivation to alleviate the negative affective aspects of nicotine withdrawal. Cholineegicglutamatergic-dopaminergic interactions in the ventral tegmental area (VTA) and other brain sites may be critically involved in mediating the rewarding effects of nicotine, and exhibit adaptations with the development of nicotine dependence. Glutamate, the main excitatory nenrotransmitter, acts through ionotropic and metabotropic glutamate receptors. Ionotropic glutamate receptors are glutamate-gated ion channels that regulate fast glutamatemediated transmission, and comprise NMDA, AMPA and kainate receptors. Metabotropic glutamate (mGlu) receptors, classified into three groups, are coupled to intracellular signaling pathways and regulate slow glutamate-mediated transmission. Group I mGlu receptors (mGlul, mGlu5) are located postsynaptically and couple to Gq proteins. Group II mGlu receptors (mGlu2, mGlu3) are located pre- and post-synaptioally and couple to Gi/Go proteins to negatively regulate the activity of adenylyl cyclase. Finally, Group III mGlu receptors are autoreceptors coupled to Gi/Go proteins to decrease adenylyl cyclase activity (for review, Kenny and Markou 2004). Using intravenous self-administration, we investigated the effects of agents that block glutamate transmission on nicotine intake. Systemic administration of the mGlu5 receptor antagonist MPEP dose-dependently decreased intravenous nicotine selfadministration in rats and mice (Paterson et ai. 2003). MPEP also decreased breaking points for nicotine in a progressive ratio procedure that assesses both the incentive-motivational and the reinforcing effects of nicotine in rate. Further, the competitive NNDA receptor antagonist LY235959 injected systemically or intra-VTA decreased nicotine self-administration in rats. Thus, the reinforcing effects of nicotine may be partly mediated by nicotineinduced increase in glutamate action at mGla5 and NMDA receptors in the VTA. These effects are unlikely to be due to nonspecific effects, because MPEP and LY235959 had no effect on locomotor activity (Henry et ah 2002), and/or responding for food. Interestingly, however, administration of MPEP (I-larrison et ah
2002) or L¥235959 did not block nicotine-induced facilitationof brain reward function, as measured by lowering of brain reward thresholds. Thus, different mechanisms may mediate nicotine consumption, as measured by self-administration,versus the euphorigeni¢ effects of nicotine reflected in facilitationof brain stimulation reward. Nevertheless, IVII°EP elevated reward thresholds under baseline conditions indicatingthat tonic activationof mGlu5 receptors regulates baseline brain reward function (Harrison et al. 2002). The systems involved in mediating the reinforcing effects of nicotine may undergo adaptations with the development of nicotine dependence that may lead to the affective aspects of nicotine withdrawal. In rats,spontaneous and nicotinic-antagonistprecipitated nicotine withdrawal is characterized by elevations of brain reward thresholds, a sensitive measure of reward function, reflecting an anhedonic state. By investigating differential effects of pharrnacological manipulations on reward thresholds in nicotine-dependent versus control rats, one can reveal the transmitter systems showing adaptations with the development of nicotine dependence. Thus, we investigated the effects of glutamateegic agents on reward thresholds in nicotine-dependent and control rats. Nicotine dependence was induced by administering nicotine through subcutaneous osmotic minipumps. The Group II mGlu receptor agonist LY314582 precipitated withdrawal-like elevations of thresholds in nicotine-dependent but not control rats. L¥314582 did not affect response latencies, a measure of performance in this procedure. Bilateral infusion of LY314582 intra-VTA likewiseprecipitated threshold elevations in nicotine-dependent, bat not control, rata (Kenny et al. 2003). Thus, activity of mGluII receptors increased with the development of nicotine dependence. Considering that mGluII are autoreceptors throughout the mesocorticolimbic system, increased activity of these receptors probably results in decreased glutamate transmission possibly to compensate for the stimulatory effects of nicotine on glutamate transmission. Thus, it wa~ predicted that blockade of mGlurr receptom would reverse the threshold elevations associated with spontaneous nicotine withdrawal. Indeed, the mGluII receptor antagonist LY341495 attenuated the threshold elevations observed in rats undergoing spontaneous nicotine withdrawal (Kenny et ah 2003). To investigate whether mGlulI receptors contributed to nicotine withdrawal by decreasing glutamate transmission, we examined if blockade of postsynaptic glutamate receptors precipitated reward deficits in nicotine-dependent rats. The AMPA/Kainate receptor antagonist Nt)QX precipitated threshold elevations in nicotine-dependent but not control rats, whereas MPEP and dizocilpine, antagonists at mGlu5 and NMDA receptors respectively, did not. In conclusion, mGlulI receptors play an important role in generating the reward deficits associated with nicotine withdrawal, possibly by decreasing glutamate transmission at AMPA/Kainate receptors. In summary, these data indicate that glutamate transmission through mGln5 and NMDA receptors, in areas such as the VTA, is critically involved in mediating the reinforcing effects of nicotine as reflected in intravenous nicotine self-administration. Further, there appear to be adaptations in mGluIZ and AMPA/kainate receptors with the development of nicotine dependence that probably lead to decreased glutamate transmission upon discontinuation of nicotine administration, that in turn may mediate the negative affective aspects of nicotine withdrawN. References
Harrison AA, Gasparini F, Markou, A. (2002) Nicotine potentiationof brain stimulationreward reversed by DHf~E and SCH 23390, but not by etioloprid~ LY 314582 or M P E P in rats, Psyohopharmaeoloay, 160:56-66.
References Abates C., Albrecht U., Spanagel R. 2002. Cocaine sensitization and reward are under the influence of okeadian genes and rhythm. Pro¢ Natl. Aead. Soi. 99, 9026-9030. Albrecht U., Zheng I3., Larldn D., Sun Z.S., Lee C.C. 2001. mPerl and roper2 are essential components for normal resetting of the okoadian olo&. J. 13iol. Rhythms, 16, 100-104. 13iello S., Darters R.I. 2001. MDMA and fenflurarnine alter the response of the circadian dock to a serotonin agonist t~ t,~t,'o. Brain Res., 920, 202-209. Masubuc_xhi S., Honrna S., Abe H., Ishizaki K., Narnihira M., Ikeda M., Honma K. 2000. Clo& genes outside the supra&iasmatio nucleus involved in manifestation of locomotor activity rhythm in rats. Eur. J. Nenrosd., 12, 4206-4214. Sprouse J., Reynolds L., Li X., 13raselton J., S&midt A. 2004. 8-OHDPAT as a 5-fiT7 agonist: phase shifts of the circadian biological clock throu@ increase of cAMP production. Nenropharmacology,46, 52-62.
•
Effects of NOS inhibitors on ethanol intoxication and w i ~ d r a w a l
R Pokk. Tartu U~iver##y, Department ofPJ~arrnacology Tartu,
Estouia Inla~duelion-" There are numerous data in the literature showing the interaction of ethanol with L-arginine - nitric oxide synthase (NOS) - NO pathways. Thus, NO-related agents, i.e. NO donors and NOS inhibitom, influence the acute effects of ethanol and ethanol withdrawal syndrome. It has been repeatedly demonstrated that NOS inhibitors strengthen and NO donom attenuate the anesthetic effects of ethanol after its acute administration (Adams and Cicero, 1994). However, different authors have reported contradictory results concerning the effects of NOS inhibitors on ethanol withdrawal syndrome (Uzbay and Oglesby, 2001). Thus, depending on the NOS inhibitor administered, its dose and route of administration, attenuation (Adams e t a l . 1995), worsening (Uzbay 2001) or no changes (Ikeda etal. 1999) in the severity of ethanol withdrawal signs have been reported. Aim: The aim of our work was to further study the interaction of ethanol and NOergic pathways. For this purpose we observed
$151
the effects of NOS inhibitors 7-nitroindazole (7-NI), NG-nitroL-arginine methyl ester (-L-NANfE) and NG-nitro-L-arginine (LNEAR@) on the effects of ethanol after acute and chronic ethanol administration and withdrawal. Methods: Acute ethanol administration was carried out intraperitoneally (i.p.) .30 minutes before behavioural tests (openfield test, plus-maze test) or immediately before the measurement of sleeping time. NOS inhibitors were injected i.p. 30 minutes before ethanol. For chronic ethanol administration mice were placed into inhalation chamber and exposed to increasing ethanol concentrations for 18 days. In separate groups physical signs of ethanol withdrawal and the anxiogenic effect of ethanol withdrawal in the plus-maze test were measured 7.5 h after the end of ethanol administration. NOS inhibitors were administered immediately after the end of chronic ethanol administration or 6.5 h later. Results: N e E inhibitors 7-NI (20-120 me/ks), L-NA/ME (20, 40 mg/kg) and L-NOARQ (20, 40 mg/kg) significantly increased the duration of ethanol (2, 3, 4 g/kg) induced sleep in mice and rats. L-NAME (20, 40 me/ks) and L-NOARG (20, 40 mg/kg) also significantly increased the sedative effect of ethanol (2 g a g ) in the open-field of reduced size as evidenced by a significant decrease in the number of rearings made and squares crossed. L-NAME and L-NOARG had no effect on ethanol pharmacokinetics. 7-NI at lower doses (20, 40 rag/ks) had no effect and at higher doses (80, 120 mg/kg) dose-dependently inhibited ethanol clearance after acute ethanol administration. After the removal of mice from the inhalation chamber the behavioural signs of ethanol withdrawal severe tremor and convulsions - developed in vehicle-treated mice. 7-NI at a dose of 20 me/ks blocked the development of the behavioural signs of ethanol withdrawal when administered immediately after the end of ethanol exposure, but had no effect when administered 6.5 hours later. L-NAIVIE and L-NeAR@ administered at a dose of 20 mg/kg had no effect on ethanol withdrawal syndrome, irrespective of time of administration. In mice treated with 7-NI immediately after the end of ethanol exposure the fall in ethanol concentrations was slower, significant concentrations were measured in blood 7.5 hours after the end of ethanol exposure. 7-NI and L-NOARG induced an anxiolytic effect in the plus-maze test as evidenced by an increase in the percentage of entries made onto and in the percentage of time spent on the open arms of the plus-maze. In accordance with numerous data in the literature chronic ethanol administration caused an anxiolytie and ethanol withdrawal- an anxiogenic effect in the plus-maze test as evidenced by changes in the percentage of entries made onto and in the percentage of time spent on the open arms. Neither 7-NI nor L-NeAR@ had significant effect on the behaviour of ethanol-intoxicated mice. 7-NI did not have effect and L-NOARG attenuated the anxiogenic effect of ethanol withdrawal in the plus-maze test. Concl~ioes-" 1. NOS inhibitors 7-1',]1,L-NAME and L-NOA.RG increased the sedative and anesthetic effects of ethanol as evidenced by an increase of the ethanol-induced sleep and sedative effect in the open-field test. These results suggest a role of L-arginine - NOS - NO pathways in the acute effects of ethanol. 2. 7-NI inhibited the elimination of ethanol. This effect is not probably due to 7-NIs effect on NO synthesis but is caused by the presence of 1,2-diazole ring in 7-NIs chemical structure. This effect was more pronounced after chronic ethanol administration. 3. NOS inhibitors L-NAME and L-NOARG did not have effect on the physical signs of ethanol withdrawal. 7-NI had attenuated the physical signs of ethanol withdrawal only due to pharmacokinetic interaction. 4.7-NI did not have effect and L-N©ARG attenuated
S.20. New mdecular ~s~ts *~to add*or*on
$152
the anxiogenic effect of ethanol withdrawal in the plus-maze teat. 7-NI and L-NOARG inhibit different NOS subtypes, while L-NOARG and L-NAME inhibit both endothelial NOS (eNOS) and neuronal NOS (nNOS), 7-NI is a selective nNOS inhibitor. These resulb suggest that different NOS subtypes might be involved in the development of physical signs of ethanol withdrawal and anxiogenic effect of ethanol withdrawal in the plus-maze test.
References [1] Adams ML, Cicero TJ (1998) Alcohol intoxication and withdrawal: the role of nitric oxide. Alcoholism: Clinical and Experimental Reseat& 16, 153-158. [2] Adams, ML, Sewing, BN, Chert,J, Mey% ER, Cicero, TJ (1995) Nitric oxide-related agents alter alo&ol withdrawal in male rats. Alcoholism: Clinical and Experimental Reseat& 19, 195-199. [3] Ikeda, M, Komiyama, ,i_;Sato, I, Himi, T, Murota, S (1999) Neuronalnitrio oxide s3mthaseis resistant to ethanol. Life Sciences 64, 1623-1630. [4] Uzbay, IT (2001) L-NAME precipitates catatonia &ring ethanol withdrawal in rats. Behavioural Brain Research 119, 71-76. [5] Uzbay IT, Oglesby MW (2001) Nitric oxide and substance dependence. Neurosoienee and Biobehavioral Reviews 25: 43-52.
•
Glut~matergic mechanisms underlying nicotine addiction
A. Markou, RI Kenny, N.E. Paterson, S. Semenova. Scripps iResearo~ I~t~t~e, Department of Ne~rop~arrnaco~og,T, £a Jo~a, CA, USA. Two factors that maintain habitual tobacco smoking are the rewarding effects of nicotine, and the motivation to alleviate the negative affective aspects of nicotine withdrawal. Cholineegicglutamatergic-dopaminergic interactions in the ventral tegmental area (VTA) and other brain sites may be critically involved in mediating the rewarding effects of nicotine, and exhibit adaptations with the development of nicotine dependence. Glutamate, the main excitatory nenrotransmitter, acts through ionotropic and metabotropic glutamate receptors. Ionotropic glutamate receptors are glutamate-gated ion channels that regulate fast glutamatemediated transmission, and comprise NMDA, AMPA and kainate receptors. Metabotropic glutamate (mGlu) receptors, classified into three groups, are coupled to intracellular signaling pathways and regulate slow glutamate-mediated transmission. Group I mGlu receptors (mGlul, mGlu5) are located postsynaptically and couple to Gq proteins. Group II mGlu receptors (mGlu2, mGlu3) are located pre- and post-synaptioally and couple to Gi/Go proteins to negatively regulate the activity of adenylyl cyclase. Finally, Group III mGlu receptors are autoreceptors coupled to Gi/Go proteins to decrease adenylyl cyclase activity (for review, Kenny and Markou 2004). Using intravenous self-administration, we investigated the effects of agents that block glutamate transmission on nicotine intake. Systemic administration of the mGlu5 receptor antagonist MPEP dose-dependently decreased intravenous nicotine selfadministration in rats and mice (Paterson et ai. 2003). MPEP also decreased breaking points for nicotine in a progressive ratio procedure that assesses both the incentive-motivational and the reinforcing effects of nicotine in rate. Further, the competitive NNDA receptor antagonist LY235959 injected systemically or intra-VTA decreased nicotine self-administration in rats. Thus, the reinforcing effects of nicotine may be partly mediated by nicotineinduced increase in glutamate action at mGla5 and NMDA receptors in the VTA. These effects are unlikely to be due to nonspecific effects, because MPEP and LY235959 had no effect on locomotor activity (Henry et ah 2002), and/or responding for food. Interestingly, however, administration of MPEP (I-larrison et ah
2002) or L¥235959 did not block nicotine-induced facilitationof brain reward function, as measured by lowering of brain reward thresholds. Thus, different mechanisms may mediate nicotine consumption, as measured by self-administration,versus the euphorigeni¢ effects of nicotine reflected in facilitationof brain stimulation reward. Nevertheless, IVII°EP elevated reward thresholds under baseline conditions indicatingthat tonic activationof mGlu5 receptors regulates baseline brain reward function (Harrison et al. 2002). The systems involved in mediating the reinforcing effects of nicotine may undergo adaptations with the development of nicotine dependence that may lead to the affective aspects of nicotine withdrawal. In rats,spontaneous and nicotinic-antagonistprecipitated nicotine withdrawal is characterized by elevations of brain reward thresholds, a sensitive measure of reward function, reflecting an anhedonic state. By investigating differential effects of pharrnacological manipulations on reward thresholds in nicotine-dependent versus control rats, one can reveal the transmitter systems showing adaptations with the development of nicotine dependence. Thus, we investigated the effects of glutamateegic agents on reward thresholds in nicotine-dependent and control rats. Nicotine dependence was induced by administering nicotine through subcutaneous osmotic minipumps. The Group II mGlu receptor agonist LY314582 precipitated withdrawal-like elevations of thresholds in nicotine-dependent but not control rats. L¥314582 did not affect response latencies, a measure of performance in this procedure. Bilateral infusion of LY314582 intra-VTA likewiseprecipitated threshold elevations in nicotine-dependent, bat not control, rata (Kenny et al. 2003). Thus, activity of mGluII receptors increased with the development of nicotine dependence. Considering that mGluII are autoreceptors throughout the mesocorticolimbic system, increased activity of these receptors probably results in decreased glutamate transmission possibly to compensate for the stimulatory effects of nicotine on glutamate transmission. Thus, it wa~ predicted that blockade of mGlurr receptom would reverse the threshold elevations associated with spontaneous nicotine withdrawal. Indeed, the mGluII receptor antagonist LY341495 attenuated the threshold elevations observed in rats undergoing spontaneous nicotine withdrawal (Kenny et ah 2003). To investigate whether mGlulI receptors contributed to nicotine withdrawal by decreasing glutamate transmission, we examined if blockade of postsynaptic glutamate receptors precipitated reward deficits in nicotine-dependent rats. The AMPA/Kainate receptor antagonist Nt)QX precipitated threshold elevations in nicotine-dependent but not control rats, whereas MPEP and dizocilpine, antagonists at mGlu5 and NMDA receptors respectively, did not. In conclusion, mGlulI receptors play an important role in generating the reward deficits associated with nicotine withdrawal, possibly by decreasing glutamate transmission at AMPA/Kainate receptors. In summary, these data indicate that glutamate transmission through mGln5 and NMDA receptors, in areas such as the VTA, is critically involved in mediating the reinforcing effects of nicotine as reflected in intravenous nicotine self-administration. Further, there appear to be adaptations in mGluIZ and AMPA/kainate receptors with the development of nicotine dependence that probably lead to decreased glutamate transmission upon discontinuation of nicotine administration, that in turn may mediate the negative affective aspects of nicotine withdrawN. References
Harrison AA, Gasparini F, Markou, A. (2002) Nicotine potentiationof brain stimulationreward reversed by DHf~E and SCH 23390, but not by etioloprid~ LY 314582 or M P E P in rats, Psyohopharmaeoloay, 160:56-66.