**4.2 KOP-R activation and ethanol consumption**

Systemic administration of the KOP-R agonist, U50488, reduces intake of 10% ethanol using two-bottle choice paradigms (Lindholm et al., 2001; Nestby et al., 1999) (Table 1). Furthermore, administration of the KOP-R agonists, dynorphin1-17 or MR-2266-BS, prior to the first free-choice session following a period of forced ethanol exposure reduced preference for ethanol (Sandi et al., 1988; Sandi et al., 1990). The long-acting benzomorphan opioid compound, bremazocine, which acts as an antagonist at MOP-R and DOP-R and an agonist at KOP-R, was shown to more potently reduce 10% ethanol intake than the nonselective opioid antagonist, naltrexone (Nestby et al., 1999). However, as KOP-R agonists

The Role of Delta Opioid Receptors in Ethanol Consumption

reviewed (Ciccocioppo et al., 2000; Ciccocioppo et al., 2003).

**6. Sigma Receptors and ethanol consumption** 

**seeking** 

and Seeking: Implications for New Treatments for Alcohol Use Disorders 215

Reinscheid et al., 1998) and appears to possess anti-opioid functional activity (Mogil et al., 1996a; Mogil et al., 1996b; Mogil & Pasternak, 2001). Opioid antagonists, such as naloxone and naltrexone, are not reported to have activity at the NOP-R (Ciccocioppo et al., 2007; Darland et al., 1998; Henderson & McKnight, 1997), although indirect interactions between NOP-R and the classical opioid receptors have been suggested (Yu et al., 2002). In mice with a genetic deletion of the NOP-R ethanol consumption was reduced and ethanol-induced CPP was increased compared to wild-type mice (Koster et al., 1999; Sakoori & Murphy, 2008). However, activation of the NOP-R, using NOP-R agonists including nociceptin and R0-64-6198, have consistently shown reductions in ethanol intake and ethanol CPP (Ciccocioppo et al., 2003; Ciccocioppo et al., 2007; Ciccocioppo et al., 1999; Ciccocioppo et al., 2002b; Economidou et al., 2006; Kuzmin et al., 2007) . In addition, NOP-R agonists have been shown to increase food intake (Cifani et al., 2006). In contrast, the effects of NOP-R antagonists administered alone to rats have not resulted in altered ethanol consumption and seeking. The results of these studies are summarized in Table 1 and have been previously

Sigma receptors (SIG-R) were originally categorized as members of the opioid receptor family (Quirion et al., 1992) although more recent studies suggested SIG-Rs are unique binding sites including phencyclidine binding sites (Gundlach et al., 1985; Gundlach et al., 1986; Martin et al., 1976; Walker et al., 1990). Furthermore, the opioid antagonist, naltrexone,

The SIG-Rs antagonist, BD1047, reduces ethanol-induced locomotion, ethanol-induced place preference and taste conditioning in Swiss mice (Maurice et al., 2003). Conversely, the SIG-R agonist, PRE-084, increased ethanol CPP without effects on ethanol-induced locomotion (Maurice et al., 2003). A series of studies have shown the SIG-R to play a role in ethanol consumption and seeking in Sardinian alcohol-preferring (sP) rats (Sabino et al., 2011; Sabino et al., 2009a; Sabino et al., 2009b) (Table 1). Administration of the SIG-R antagonists, BD1063 NE-100, selectively reduces ethanol consumption, responding for ethanol and also prevents the increase in ethanol intake after an ethanol-deprivation period in rats (Sabino et al., 2009b). Chronic administration of the SIG-R agonist, DTG, increased responding for ethanol in rats, an effect that was blocked with BD-1063 pretreatment (Sabino et al., 2011). However, DTG treatment also increased responding for saccharin and sucrose (Sabino et al., 2011). Chronic administration of DTG to naive rats resulted in increased mRNA expression of MOP-R and DOP-R, but not KOP-R, in the VTA (Sabino et al., 2011). This increased opioid mRNA expression was suggested to be responsible for the excessive alcohol intake following DTG treatment, in agreement with previous studies reporting the importance of DOP-R activity in maintaining high ethanol intake in alcohol-preferring rats (Froehlich et al., 1991) and the roles of MOP-R and DOP-R activation on VTA-mediated dopamine release (Devine et al., 1993b).

**7. Brain-region specific roles of opioid receptors in ethanol consumption and** 

The mesolimbic dopamine system plays a key role in mediating the reinforcing properties of ethanol and other drugs of abuse (Herz, 1997). Moreover, ethanol reinforcement and high

is not reported to have activity at the SIG-R (Holtzman, 1989; Vaupel, 1983).

produce aversion, this may lead to reductions in ethanol consumption but this remains to be studied. The KOP-R agonist, U69593, produces conditioned place aversion (CPA) in animals (Shippenberg & Herz, 1986) and KOP-R agonists induce dysphoria in humans (Kumor et al., 1986; Pfeiffer et al., 1986; Rimoy et al., 1994). In contrast, the KOP-R agonist, enadoline (or CI-977), when delivered via mini-osmotic subcutaneous pumps increased 10 and 20% ethanol consumption (Holter et al., 2000). However, in rats responding for ethanol for long periods, the lever pressing for ethanol was either decreased or increased following acute systemic administration of higher or lower doses of enadoline, respectively (Holter et al., 2000). As lever pressing for water was also reduced with enadoline treatment, these reductions in responding for ethanol may have been due to sedative effects of this treatment at higher doses.

#### **4.3 KOP-R antagonists and ethanol consumption and seeking**

A number of studies have shown mixed results for the selective KOP-R antagonist, nor-BNI using a variety of models of ethanol consumption and seeking (Table 1). In rats given continuous access to 10% ethanol using the two-bottle choice paradigm, a single systemic injection of nor-BNI induced a long-lasting increase in ethanol consumption, particularly in higher drinking rats without inducing CPP (Mitchell et al., 2005). However, nor-BNI has been shown to increase ethanol-induced place preference in rats (Matsuzawa et al., 1999a). In rhesus monkeys responding for solutions of 1-2% ethanol, nor-BNI reduced responding for ethanol on the day of the systemic injection (Williams & Woods, 1998). nor-BNI has low affinity for the MOP-R at 2 h post-injection time point and high affinity for the KOP-R up to 24 h post-injection (Broadbear et al., 1994; Endoh et al., 1992; Horan et al., 1992) suggesting the reductions in ethanol responding on the day of nor-BNI dosing may be MOP-R mediated. In Wistar rats responding for 10% ethanol, nor-BNI has been shown to be more effective in a rat model of ethanol-dependence, using a 4-week intermittent vapor exposure paradigm, compared to non-ethanol dependent rats (Walker & Koob, 2008). Although i.c.v. administration of nor-BNI given immediately before the testing session reduced responding for ethanol in dependent rats (Walker & Koob, 2008), further studies performed with systemically administered nor-BNI given 24 h before the test session similarly reduced responding in ethanol-dependent rats but not in non-dependent rats (Walker et al., 2011). These studies suggest that the dynorphin/KOP-R systems are dysregulated in dependence and contribute to the increased consumption observed during acute withdrawal in dependent rats. Systemic administration of nalmefene, which has similar affinity for MOP-R but higher affinity for KOP-R and DOP-R, compared to naltrexone (Michel et al., 1985), was found to more effectively reduce responding for ethanol in dependent rats than naltrexone (Walker and Koob, 2008). As nalmefene and naltrexone had similar effects on reducing responding in non-dependent rats, this further supports a specific role of the KOP-R in ethanol-dependence (Walker & Koob, 2008).

#### **5. Nociceptin/Orphanin FQ Receptors (NOP-R) and ethanol consumption and seeking**

A number of studies have investigated the role of the nociceptin receptor (NOP-R), also known as the opioid receptor-like 1 receptor (ORL1), using the endogenous ligand for the NOP-R, nociceptin/orphanin FQ. Although nociceptin has structural homology with opioid peptides, it does not bind to MOP-R, DOP-R or KOP-R (Reinscheid et al., 1996;

produce aversion, this may lead to reductions in ethanol consumption but this remains to be studied. The KOP-R agonist, U69593, produces conditioned place aversion (CPA) in animals (Shippenberg & Herz, 1986) and KOP-R agonists induce dysphoria in humans (Kumor et al., 1986; Pfeiffer et al., 1986; Rimoy et al., 1994). In contrast, the KOP-R agonist, enadoline (or CI-977), when delivered via mini-osmotic subcutaneous pumps increased 10 and 20% ethanol consumption (Holter et al., 2000). However, in rats responding for ethanol for long periods, the lever pressing for ethanol was either decreased or increased following acute systemic administration of higher or lower doses of enadoline, respectively (Holter et al., 2000). As lever pressing for water was also reduced with enadoline treatment, these reductions in responding

A number of studies have shown mixed results for the selective KOP-R antagonist, nor-BNI using a variety of models of ethanol consumption and seeking (Table 1). In rats given continuous access to 10% ethanol using the two-bottle choice paradigm, a single systemic injection of nor-BNI induced a long-lasting increase in ethanol consumption, particularly in higher drinking rats without inducing CPP (Mitchell et al., 2005). However, nor-BNI has been shown to increase ethanol-induced place preference in rats (Matsuzawa et al., 1999a). In rhesus monkeys responding for solutions of 1-2% ethanol, nor-BNI reduced responding for ethanol on the day of the systemic injection (Williams & Woods, 1998). nor-BNI has low affinity for the MOP-R at 2 h post-injection time point and high affinity for the KOP-R up to 24 h post-injection (Broadbear et al., 1994; Endoh et al., 1992; Horan et al., 1992) suggesting the reductions in ethanol responding on the day of nor-BNI dosing may be MOP-R mediated. In Wistar rats responding for 10% ethanol, nor-BNI has been shown to be more effective in a rat model of ethanol-dependence, using a 4-week intermittent vapor exposure paradigm, compared to non-ethanol dependent rats (Walker & Koob, 2008). Although i.c.v. administration of nor-BNI given immediately before the testing session reduced responding for ethanol in dependent rats (Walker & Koob, 2008), further studies performed with systemically administered nor-BNI given 24 h before the test session similarly reduced responding in ethanol-dependent rats but not in non-dependent rats (Walker et al., 2011). These studies suggest that the dynorphin/KOP-R systems are dysregulated in dependence and contribute to the increased consumption observed during acute withdrawal in dependent rats. Systemic administration of nalmefene, which has similar affinity for MOP-R but higher affinity for KOP-R and DOP-R, compared to naltrexone (Michel et al., 1985), was found to more effectively reduce responding for ethanol in dependent rats than naltrexone (Walker and Koob, 2008). As nalmefene and naltrexone had similar effects on reducing responding in non-dependent rats, this further supports a specific role of the KOP-R in

**5. Nociceptin/Orphanin FQ Receptors (NOP-R) and ethanol consumption and** 

A number of studies have investigated the role of the nociceptin receptor (NOP-R), also known as the opioid receptor-like 1 receptor (ORL1), using the endogenous ligand for the NOP-R, nociceptin/orphanin FQ. Although nociceptin has structural homology with opioid peptides, it does not bind to MOP-R, DOP-R or KOP-R (Reinscheid et al., 1996;

for ethanol may have been due to sedative effects of this treatment at higher doses.

**4.3 KOP-R antagonists and ethanol consumption and seeking** 

ethanol-dependence (Walker & Koob, 2008).

**seeking** 

Reinscheid et al., 1998) and appears to possess anti-opioid functional activity (Mogil et al., 1996a; Mogil et al., 1996b; Mogil & Pasternak, 2001). Opioid antagonists, such as naloxone and naltrexone, are not reported to have activity at the NOP-R (Ciccocioppo et al., 2007; Darland et al., 1998; Henderson & McKnight, 1997), although indirect interactions between NOP-R and the classical opioid receptors have been suggested (Yu et al., 2002). In mice with a genetic deletion of the NOP-R ethanol consumption was reduced and ethanol-induced CPP was increased compared to wild-type mice (Koster et al., 1999; Sakoori & Murphy, 2008). However, activation of the NOP-R, using NOP-R agonists including nociceptin and R0-64-6198, have consistently shown reductions in ethanol intake and ethanol CPP (Ciccocioppo et al., 2003; Ciccocioppo et al., 2007; Ciccocioppo et al., 1999; Ciccocioppo et al., 2002b; Economidou et al., 2006; Kuzmin et al., 2007) . In addition, NOP-R agonists have been shown to increase food intake (Cifani et al., 2006). In contrast, the effects of NOP-R antagonists administered alone to rats have not resulted in altered ethanol consumption and seeking. The results of these studies are summarized in Table 1 and have been previously reviewed (Ciccocioppo et al., 2000; Ciccocioppo et al., 2003).
