**3. Sociality deficits in animal models of schizophrenia; Effect of neuropeptides**

Social behaviors comprise various domains, such as social (learning) memory and social bonding [20; 21]. The intracerebroventricular administration of AVP has been shown to facilitate social memory, as measured by the social discrimination test (SDT), in rats [22; 23].

The neural substrates governing the ability of AVP to enhance sociality include the lateral septum (LS), bed nucleus of the stria terminalis, and medial amygdala [24]. Specifically, overexpression of the V1A receptors in the LS enhanced SDT performance, an effect blocked

Role for Pituitary Neuropeptides in Social Behavior Disturbances of Schizophrenia 87

by application of a V1A antagonist, but not oxytocin receptor antagonist [2]. By contrast, administration of oxytocin into the medial amygdala restored impaired social recognition in oxytocin knockout mice, while vasopressin was ineffective [25]. Overall, these observations are consistent with the contribution of V1 receptors in the LS to the maintenance of long-

Experimental data from our laboratory also suggest a role for altered AVP transmissions in social interaction deficits. Thus, chronic administration of phencyclidine, an antagonist at Nmethyl-D-aspartate (NMDA) receptors, impaired social interaction behavior, and reduced the density of V1A receptors in several brain regions, including the LS in rats [18] (Figure 3). In a subsequent study, Matsuoka et al. (2008) [27] found decreased levels of mRNA encoding AVP in the amygdala, as measured by a microarray system and real-time quantitative PCR assay, in rats chronically treated with MK-801, a non-competitive antagonist at the NMDA receptor. These findings provide a basis for the ability of AVP or its analogues to ameliorate social interaction deficits in animal models of schizophrenia.

Accordingly, we reported that NC-1900, an AVP analogue and agonist at V1a receptors, ameliorates social interaction deficits in rats chronically treated with MK-801 [17] (Figure 4).

**Figure 4.** Measurement of social interaction behavior. A pair of rats (one dye-marked) are placed in an open arena, whose behavior, including "contact" (between-subject distance < 20 cm) is video-taped for manual viewing and/or automatically analyzed by a computer. (Inset )Total duration of contact (TDC) of rats during a 10-min observation period. Each bar represents mean ± SD of the time spent in social interaction (in seconds). \**P* < 0.05, chronic (MK-801, vehicle) × acute (NC-1900, vehicle) treatment interaction. Matsuoka et al. Brain Res 1053 (2005) 131-136. (Permission obtained from Elsevier).

term potentiation [26], which is crucial for learning and memory.

**Figure 3.** Autoradiographic localization of V1a receptor binding sites in coronal sections of the brain of the vehicle group (A–D) and PCP group (E–H) of rats with [125I]-Linear AVP antagonist. Abbreviations: Acb, nucleus accumbens; FStr, fundus striati; LS, lateral septum; BST, bed nucleus of the stria terminalis; Ce, central amygdaloid nucleus; DG, dentate gyrus; VM, ventromedial thalamic nucleus; LH, lateral hypothalamic area; Rli, rostral linear raphe nucleus; SN, substantia nigra; IP, interpeduncular nucleus; SC, superior colliculus. Tanaka et al ., *Brain Res* 992; 239–245, 2003 (Permission obtained from Elsevier)

by application of a V1A antagonist, but not oxytocin receptor antagonist [2]. By contrast, administration of oxytocin into the medial amygdala restored impaired social recognition in oxytocin knockout mice, while vasopressin was ineffective [25]. Overall, these observations are consistent with the contribution of V1 receptors in the LS to the maintenance of longterm potentiation [26], which is crucial for learning and memory.

86 Neuroendocrinology and Behavior

**Figure 3.** Autoradiographic localization of V1a receptor binding sites in coronal sections of the brain of the vehicle group (A–D) and PCP group (E–H) of rats with [125I]-Linear AVP antagonist. Abbreviations: Acb, nucleus accumbens; FStr, fundus striati; LS, lateral septum; BST, bed nucleus of the stria terminalis; Ce, central amygdaloid nucleus; DG, dentate gyrus; VM, ventromedial thalamic nucleus; LH, lateral

hypothalamic area; Rli, rostral linear raphe nucleus; SN, substantia nigra; IP, interpeduncular nucleus; SC, superior colliculus. Tanaka et al ., *Brain Res* 992; 239–245, 2003 (Permission obtained from Elsevier)

Experimental data from our laboratory also suggest a role for altered AVP transmissions in social interaction deficits. Thus, chronic administration of phencyclidine, an antagonist at Nmethyl-D-aspartate (NMDA) receptors, impaired social interaction behavior, and reduced the density of V1A receptors in several brain regions, including the LS in rats [18] (Figure 3). In a subsequent study, Matsuoka et al. (2008) [27] found decreased levels of mRNA encoding AVP in the amygdala, as measured by a microarray system and real-time quantitative PCR assay, in rats chronically treated with MK-801, a non-competitive antagonist at the NMDA receptor. These findings provide a basis for the ability of AVP or its analogues to ameliorate social interaction deficits in animal models of schizophrenia.

Accordingly, we reported that NC-1900, an AVP analogue and agonist at V1a receptors, ameliorates social interaction deficits in rats chronically treated with MK-801 [17] (Figure 4).

**Figure 4.** Measurement of social interaction behavior. A pair of rats (one dye-marked) are placed in an open arena, whose behavior, including "contact" (between-subject distance < 20 cm) is video-taped for manual viewing and/or automatically analyzed by a computer. (Inset )Total duration of contact (TDC) of rats during a 10-min observation period. Each bar represents mean ± SD of the time spent in social interaction (in seconds). \**P* < 0.05, chronic (MK-801, vehicle) × acute (NC-1900, vehicle) treatment interaction. Matsuoka et al. Brain Res 1053 (2005) 131-136. (Permission obtained from Elsevier).

This result from an animal model of schizophrenia is consistent with the observation, discussed above [18], that chronic administration of the NMDA antagonist phencyclidine reduces the density of V1a receptor binding sites in several brain regions, including the LS, in rats showing social interaction deficits. These findings from our laboratory are consistent with Bielsky et al [16] who reported that re-expressing of V1a receptors in the lateral septum of V1a receptor knockout mice exhibits complete recovery from impaired social recognition. Down-regulation of the AVP gene in the amygdala of MK-801-treated rats may provide a basis for the ability of AVP-analogues to ameliorate the behavioral disturbances by blockade of NMDA receptor [17]. Similar benefits regarding social behavior have been reported for oxytocin [3; 13; 28; 29; 30].

Role for Pituitary Neuropeptides in Social Behavior Disturbances of Schizophrenia 89

**Table 1.** Nucleotide sequences of RT-qPCR primers for target genes

Efforts to enhance social ability are important from the perspective of adjusting patients to the community, thus improving functional outcome. Social ability disturbances in schizophrenia are thought to be partly attributable to negative symptoms and disturbances of cognitive function [4; 31; 32]. Although treatment with the first generation antipsychotic drugs, e.g. haloperidol, has been shown to ameliorate positive symptoms, only a limited number of agents, such as the second generation antipsychotics, or so-called "atypical antipsychotic drugs (AAPDs)", e.g. clozapine, melperone, risperidone, olanzapine, quetiapine, ziprasidone, and perospirone, with variable affinities for serotonin (5-HT) receptor subtypes, have been shown to be partially effective to treat negative symptoms and cognitive disturbances of schizophrenia [32; 33; 34; 35; 36] (see [4; 37] for review). Thus, more effective strategy to treat neurocognition, in addition to social abilities, is needed to enhance quality of life for patients. In this context, the results from a recent study of the effect of augmentation therapy with oxytocin on cognitive function in patients with schizophrenia are noteworthy [38]. The investigators report a significant enhancement of verbal learning memory, a cognitive domain thought to largely influence the outcome, in subjects receiving daily intranasal oxytocin (twice daily) for 3 weeks. Further controlled study is warranted to confirm the

cognition-boosting effect of neuropeptides in the treatment of schizophrenia.

As has been discussed, neuropeptides, e.g., vasopressin and oxytocin, have been suggested to be associated with the pathophysiology of schizophrenia. Accordingly, a whole-genome scan for schizophrenia in a large inbred Arab-Israeli pedigree has found a possible linkage on chromosome 20p13 [39] (Fig. 6). Importantly, this locus harbors four strong candidate genes for the illness, two of which are for oxytocin (*OXT*) and AVP (*AVP*) [39]. Further, examination of the association with gene expression in the brain identified genetic variants in the *OXT-AVP* cluster, and three of these variants were associated with schizophrenia [12]. These findings provide a strong proof for the contribution of these neuropeptides to the

**Figure 6.** A scheme of the genes oxytocin and vasopressin on the chromosomal region 20p13 and the positions of the seven examined SNPs. Teltsh et al., *Int J Neuropsychopharmacol* 15;309-19, 2012

**4. Clinical implications** 

etiology of the illness.

(Permission obtained from CINP).

We conducted a further analysis of the change in the expression of RNAs encoding AVP and its receptor subtypes (V1A, V1B) in the amygdala of the model rat by means of qPCR (Table 1). As shown in Fig 5, expression of the AVP gene was significantly reduced by treatment with MK-801 (0.13 mg/day) for 14 days, while the same treatment did not affect the expressions of V1A, and V1B receptors. These results may help understand a mechanism by which impaired NMDA receptor-mediated transmissions, a putative pathophysiology of schizophrenia, disturbs social behaviors.

**Figure 5.** RNA quantification by means of real-time qPCR. Expression ratios for MK-801-treated rats vs. vehicle-treated animals are shown (n=5-6 for each group). Expression of the arginine-vasopressin (AVP) gene was significantly reduced by treatment with MK-801 (0.13 mg/day) for 14 days, (\*p<0.05 by one-way ANOVA), while the same treatment did not affect the expressions of V1a and V1b receptors.Mx3000P (StrataGene) was used for pPCR with SYBER Premix Ex Taq (Takara Co. Ltd.). GAPDH was used as internal standard.

