To develop and validate a vasopressin (AVP) receptor knockdown strategy, we infused an antisense oligodeoxynucleotide to the V1 subtype mRNA into the septum of male rats with osmotic minipumps and measured behavioral, cellular and molecular parameters. Compared to vehicle and scrambled-sequence oligo controls, chronic antisense administration for up to 4 d diminished the ability of the animals to distinguish a previously exposed juvenile from a novel one and to respond to exogenous AVP (1 ng/5 microliters, intracerebroventricular) with an improved social memory. Furthermore, anxiety-related behavior was reduced. As measured in the behaviorally tested rats, antisense treatment resulted in a reduced binding of radiolabeled AVP in the septum, but not in other limbic brain areas (receptor autoradiography), and an increased amount of V1 receptor mRNA (reverse transcriptase PCR), indicating translational arrest and ongoing transcriptional activity. In sense oligo-treated rats, on the other hand, both the social and the anxiety-related behavior scores lay between levels obtained in control and antisense-treated animals. These sense-treated rats showed a slightly reduced V1 receptor density in the septum and reduced receptor mRNA levels, indicating hybridization of the sense oligo to the DNA. The data show the potential of antisense targeting to further reveal relationships between local gene expression, neuropeptide-receptor interactions in distinct brain areas, and behavioral performance.

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The neuropeptide orphanin FQ (also known as nociceptin; OFQ͞N) has been implicated in modulating stress-related behavior. OFQ͞N was demonstrated to reverse stress-induced analgesia and possess anxiolytic-like activity after central administration. To further study physiological functions of OFQ͞N, we have generated OFQ͞N-deficient mice by targeted disruption of the OFQ͞N gene. Homozygous mice display increased anxiety-like behavior when exposed to a novel and threatening environment. OFQ͞N-null mice show elevated basal pain threshold but develop normal stressinduced analgesia. Interestingly, these mice show impaired adaptation to repeated stress when compared with wild-type mice, whereas their performance in spatial learning remained unaffected. Basal and poststress plasma corticosterone levels were found to be elevated in OFQ͞N-deficient animals. Thus, OFQ͞N appears to be crucially involved in the neurobiological regulation of stress-coping behavior and fear.Physiological responses to stress include changes in behavior, sensory processing, and endocrine and metabolic homeostasis that are positively or negatively regulated by a multitude of neuronal pathways (1-7). An increased vulnerability to stress is discussed as a major contributing factor in human psychiatric disorders, such as anxiety and depression (8). At the hormonal level, these diseases often are accompanied by an overactivity of the hypothalamic-pituitary-adrenal (HPA) system (9, 10). However, the physiological basis for this dysregulation remains unclear. The recently discovered neuropeptide OFQ͞N (11, 12) appears to alleviate behavioral and sensory responses to stress, such as fear responses (13) or analgesia (14). Further studies on the functions of OFQ͞N in the neuronal processing of stress are hampered by the unavailability of a selective and high-affinity antagonist. Therefore, we took a genetic approach and generated OFQ͞N-deficient mice that were analyzed for phenotypical differences in stress-related responses. The absence of OFQ͞N increases stress-related variables of behavior and sensory processing, such as anxiety and nociceptive threshold, in genetically engineered mice. Mice lacking OFQ͞N show elevated glucocorticoid levels, indicating a chronic activation of the HPA system that might contribute to the observed phenotypic changes. In addition, an important function of OFQ͞N for stress adaptation was discovered, because OFQ͞N-deficient mice failed to habituate after repeated exposure to stressful stimuli. These results suggest that the OFQ͞N system may have important functions in the neural circuitry of stress processing.

Anxiolytic effects of ethanol have been proposed to be important factors in the initiation of ethanol consumption. To examine this hypothesis, drug-naive Wistar rats were tested in the elevated plus-maze to determine their initial level of anxiety. Based on their response, we separated the animals into anxious and non-anxious groups. After that, animals went through an oral ethanol self-administration procedure. Rats that were initially classified as anxious showed a significantly (P < 0.01) higher intake and preference for ethanol during the initiation phase of the voluntary drinking procedure than non-anxious animals. In another experiment, intraperitoneal (IP) injections of ethanol (0.5-1.5 g/kg) produced dose-dependent anxiolytic effects in rats when tested in the elevated plus-maze procedure. Blood ethanol levels following IP injections during the plus-maze test were similar to those reached during the oral ethanol self-administration procedure, which shows that the rats indeed drank sufficient amounts of ethanol to experience its anxiolytic effects. These findings indicate that the basal level of anxiety plays an important role in vulnerability to alcohol drinking.

The effects of emotional stressors on the release of arginine vasopressin (AVP) and oxytocin (OXT) within the rat hypothalamus and the origin and physiological significance of AVP released within the hypothalamic paraventricular nucleus (PVN) were investigated. First, adult male Wistar rats with a microdialysis probe aimed at the PVN or the supraoptic nucleus were exposed to either a dominant male rat (social defeat) or a novel cage. Release of AVP within the PVN was significantly increased in response to social defeat but not to novelty. In contrast to an activation of the hypothalamic-pituitary-adrenal (HPA) system, neither stressor stimulated the hypothalamic-neurohypophysial system (unchanged plasma AVP and OXT and unchanged release within the supraoptic nucleus [AVP] and the PVN [OXT]). Next, we demonstrated by simultaneous microdialysis of the suprachiasmatic nucleus and the PVN that AVP measured in PVN dialysates during social defeat was probably of intranuclear origin. Finally, a mixture of a V1 AVP and the alpha-helical corticotropin-releasing hormone (CRH) receptor antagonists administered via inverse microdialysis into the PVN caused a significant increase in the plasma adrenocorticotropic hormone (ACTH) concentration compared with vehicle-treated controls both under basal conditions and during social defeat, indicating inhibitory effects of intra-PVN-released AVP and/or CRH on HPA system activity. The antagonists failed to affect anxiety-related behavior of the animals as assessed with the elevated plus-maze. Taken together, our results show for the first time that AVP is released within the PVN in response to an emotional stressor. We hypothesize that this intranuclear release provides a negative tonus on ACTH secretion.