Resilience to mental and physical stress is a key determinant for the survival and functioning of mammals. Although the importance of stress resilience has been recognized, the underlying neural mediators have not yet been identified. Neuropeptide Y (NPY) is a peptide known for its anti-anxiety-like effects mediated via the amygdala. The results of our current study demonstrate, for the first time that repeated administration of NPY directly into the basolateral nucleus of the amygdala (BLA) produces selective stress-resilient behavioral responses to an acute restraint challenge as measured in the social interaction test, but has no effect on hypothalamic-adrenal-pituitary axis activity or stress-induced hyperthermia. More importantly, the resilient behaviors observed in the NPY-treated animals were present for up to 8 weeks. Antagonizing the activity of calcineurin, a protein phosphatase involved in neuronal remodeling and present in NPY receptor containing neurons within the BLA, blocked the development of long-term, but not the acute increases in social interaction responses induced by NPY administration. This suggests that the NPY-induced long-term behavioral resilience to restraint stress may occur via mechanisms involving neuronal plasticity. These studies suggest one putative physiologic mechanism underlying stress resilience and could identify novel targets for development of therapies that can augment the ability to cope with stress.

Intrathecal (i.t.) pretreatment with a low dose (0.3 nmol) of morphine causes an attenuation of i.t. morphine-produced analgesia; the phenomenon has been defined as morphine-induced antianalgesia. The opioid-produced analgesia was measured with the tail-flick (TF) test in male CD-1 mice. Intrathecal pretreatment with low dose (0.3 nmol) of morphine time dependently attenuated i.t. morphine-produced (3.0 nmol) TF inhibition and reached a maximal effect at 45 min. Intrathecal pretreatment with morphine (0.009 -0.3 nmol) for 45 min also dose dependently attenuated morphine-produced TF inhibition. We have previously reported that intrathecal (i.t.) pretreatment with an endogenous -opioid peptide, endomorphin-2 (0.05-1.75 nmol), attenuates the antinociception produced by opioid agonists. The antianalgesic effect is caused by the release of dynorphin A(1-17) through the stimulation of a subtype of -opioid receptors. The unique features of this endomorphin-2-induced antianalgesic action are that there is a lag period before dynorphin A(1-17) is released, and the antianalgesic action of endomorphin-2 corresponds with the time course of dynorphin release Wu et al., 2003). Furthermore, i.t. administered endomorphin-2 at larger doses (5.25-35 nmol) produces analgesia by itself through activation of spinal -opioid receptors (Ohsawa et al., 2001), whereas its delayed antianalgesic action is manifested more easily at small doses of endomorphin-2 by its ability to attenuate the analgesic action of other opioids administered after endomorphin-2 pretreatment.There are indications from the literature that morphine may have an antianalgesic action. Pretreatment with a low dose of naloxone (0.00028 fmol) or dynorphin A antiserum given i.t. enhances the analgesic effect of intracerebroventricularly and i.t.-administered morphine (Fujimoto and Rady, 1989;Holmes and Fujimoto, 1993). Studies performed by Crain and Shen (1990, 2000 indicate that even though generally morphine has a depressant effect on action potential duration in mouse dorsal root ganglion preparations, very low doses (1 fmol-1 pmol) of morphine produce the opposite effect by prolonging the duration of the action potential, an excitatory action. Recent studies also have shown that morphine and opioid compounds not only simply elicit

Neuropeptide Y (NPY) expression is tightly linked with the development of stress resilience in rodents and humans. Local NPY injections targeting the basolateral amygdala (BLA) produce long-term behavioral stress resilience in male rats via an unknown mechanism. Previously, we showed that activation of NPY Y receptors hyperpolarizes BLA principal neurons (PNs) through inhibition of the hyperpolarization-activated, depolarizing H-current, The present studies tested whether NPY treatment induces stress resilience by modulating NPY (10 pmol) was delivered daily for 5 d bilaterally into the BLA to induce resilience; thereafter, the electrophysiological properties of PNs and the expression of in the BLA were characterized. As reported previously, increases in social interaction (SI) times persisted weeks after completion of NPY administration. intracellular recordings showed that repeated intra-BLA NPY injections resulted in hyperpolarization of BLA PNs at 2 weeks (2W) and 4 weeks (4W) after NPY treatment. At 2W, spontaneous IPSC frequencies were increased, whereas at 4W, resting was markedly reduced and accompanied by decreased levels of HCN1 mRNA and protein expression in BLA. Knock-down of HCN1 channels in the BLA with targeted delivery of lentivirus containing HCN1-shRNA increased SI beginning 2W after injection and induced stress resilience. NPY treatment induced sequential, complementary changes in the inputs to BLA PNs and their postsynaptic properties that reduce excitability, a mechanism that contributes to less anxious behavior. Furthermore, HCN1 knock-down mimicked the increases in SI and stress resilience observed with NPY, indicating the importance of in stress-related behavior. Resilience improves mental health outcomes in response to adverse situations. Neuropeptide Y (NPY) is associated with decreased stress responses and the expression of resilience in rodents and humans. Single or repeated injections of NPY into the basolateral amygdala (BLA) buffer negative behavioral effects of stress and induce resilience in rats, respectively. Here, we demonstrate that repeated administration of NPY into the BLA unfolds several cellular mechanisms that decrease the activity of pyramidal output neurons. One key mechanism is a reduction in levels of the excitatory ion channel HCN1. Moreover, shRNA knock-down of HCN1 expression in BLA recapitulates some of the actions of NPY and causes potent resilience to stress, indicating that this channel may be a possible target for therapy.

We have previously demonstrated that both endomorphin-1 (EM-1) and endomorphin-2 (EM-2) at high doses (1.75-35 nmol) given intrathecally (i.t.) or intracerebroventricularly produce antinociception by stimulation of -opioid receptors. Now, we report that EM-2 at small doses (0.05-1.75 nmol), which injected alone did not produce antinociception, produces antianalgesia against opioid agonist-induced antinociception. The tail-flick (TF) response was used to test the antinociception in male CD-1 mice. Intrathecal pretreatment with EM-2 (0.02-1.75 nmol) 45 min before i.t. morphine (3.0 nmol) injection dose dependently attenuated morphine-induced TF inhibition. On the other hand, a similar dose of EM-1 (1.64 nmol) failed to produce any antianalgesic effect. The EM-2 (1.75 nmol)-produced anti-analgesia against morphine-induced TF inhibition was blocked by i.t. pretreatment with the -opioid antagonist naloxone or 3-methoxynaltrexone, but not ␦-opioid receptor antagonist naltrindole, -opioid receptor antagonist nor-binal- Endogenous opioid tetrapeptides endomorphin-1 (EM-1) and endomorphin-2 (EM-2) have been found to be highly selective for -opioid receptors (Zadina et al., 1997). Both EM-1 and EM-2 potently compete with -opioid receptor binding with no appreciable affinity with ␦-and -opioid receptors and selectively activate -opioid receptor-mediated G-proteins with [35 S]guanosine 5Ј-O-(3-thio)triphosphate binding (Goldberg et al., 1998;Narita et al., 1998Narita et al., , 2000Monory et al., 2000). The increases of the [ 35 S]guanosine 5Ј-O-(3-thio)triphosphate binding and antinociceptive effects induced by both EM-1 and EM-2 are selectively blocked by the pretreatment with selective -opioid receptor antagonist ␤-funaltrexamine or D-Phe-Cys-Tyr-D-Trp-Orn-Thr-Pen-Thr-NH 2 , indicating that the effects are mediated by the stimulation of -opioid receptors.However, recent studies indicate that the antinociceptive effects induced by EM-1 and EM-2 are mediated by the stimulation of different subtypes of -opioid receptors. Pretreatment with -opioid receptor antagonist 3-methoxynaltrexone selectively attenuated EM-2-but not EM-1-induced antinociception, whereas ␤-funaltrexamine inhibits both (Sakurada et al., 2000). There is an asymmetric cross-tolerance between EM-1 and EM-2, where mice made acutely tolerant to EM-1 are not cross-tolerant to EM-2, but mice made acutely tolerant to EM-2 cause partial cross-tolerance to EM-1 (Wu et al., 2001). Intrathecal pretreatment with antisense oligodeoxynucleotides against exon-8 of -opioid receptor clone inhibits the antinociception induced by EM-1

An unbiased conditioned place preference (CPP) paradigm was used to evaluate the reward effects of endogenous -opioid receptor ligands endomorphin-1 (EM-1) and endomorphin-2 (EM-2) from the mesolimbic posterior nucleus accumbens (Acb) shell and the ventral tegmental area (VTA) in CD rats. EM-1 (1.6 -8.1 nmol) microinjected into posterior Acb shell produced CPP, whereas EM-2 (8.7-17.5 nmol) given into the same Acb shell produced conditioned place aversion (CPA). EM-1 (1.6 -16.3 nmol) microinjected into the VTA produced CPP, whereas EM-2 (8.7 and 17.5 nmol) given into the same VTA site did not produce any effect, but at a high dose (35 nmol) produced CPP. EM-1 (3.3 nmol) or EM-2 (17.5 nmol) microinjected into the nigrostriatal substantia nigra was not significantly different from vehicle-injected groups. D-Phe-Cys-Tyr-D-Trp-Orn-Thr-PenThr-NH 2 (CTOP) at 94.13 pmol or 3-methoxynaltrexone at 0.64 pmol microinjected into the posterior Acb shell blocked EM-1-induced CPP and EM-2-induced CPA. At a higher dose, CTOP (941.3 pmol) and 3-methoxynaltrexone (6.4 pmol) produced CPA and CPP, respectively. Coadministration with antiserum against dynorphin A(1-17) (Dyn) (10 g) microinjected into the posterior Acb shell blocked EM-2-induced CPA. However, it did not affect EM-1-induced CPP. It is concluded that EM-1 and EM-2 produce site-dependent CPP and CPA, respectively, by stimulation of different subtypes of -opioid-receptors; stimulation of one subtype of -opioid-receptor at the posterior Acb shell and VTA by EM-1 induces CPP, whereas stimulation of another subtype of -opioid receptor at the posterior Acb shell, but not the VTA, by EM-2 induces the release of Dyn to produce CPA.