Further Characterization of a Novel Tetrapeptide with an Analgesic Action in the Central and Peripheral Nervous System in Rats

The novel tetrapeptide FLPS has been previously shown to induce antinociception in a model of post-incisional pain in the rat. It has been demonstrated in membrane preparations of rat brain that 10 μM tetrapeptide did not compete with [³H]naloxone for its binding site on the opioid receptors which differentiates it from typical opioids. In the first set of experiments, the stimulation of [³⁵S]GTPγS binding by the tetrapeptide to membrane preparations of recombinant cell lines expressing human μ, δ, and κ receptors has been investigated. The specific [³⁵S]GTPγS binding did not change in the presence of 100 μM tetrapeptide and DAMGO, DPDPE, or U-69593 at submaximal and maximal concentrations, indicating that the tetrapeptide was not an agonist or antagonist of the opioid receptors and it did not stimulate or blocked the stimulation of G-proteins coupled to these receptors. Studies with naloxone and naloxone methiodide pretreatment suggested that the tetrapeptide was either directly or indirectly affected by a naloxone-binding site located primarily within the central nervous system and to a lesser extent in the periphery. Naloxone pretreatment had a dual effect on morphine antinociception based on the concentration used. At 2 mg/kg, naloxone competed reversibly with 25 mg/kg morphine on its binding site on the opioid receptors, while at 5.4 mg/kg it blocked antinociception induced by 10 mg/kg morphine, 2.7 mg/kg aspirin, or 75 mg/kg tetrapeptide. These data suggest that a new naloxone-binding site is involved in alleviation of pain by at least three classes of analsegics (opioids, cycloogenase 2 inhibitors, and the tetrapeptide). The biological activity of the peptide was discovered first and the mechanism of action is now being studied. In an attempt to identify the therapeutic target of the tetrapeptide, a total of 23 radioligand binding assays to targets within the CNS were conducted. The results of these assays were negative and they reinforce the notion that the tetrapeptide activates an unknown mechanism involved in pain perception after surgery.     

Involvement of opioid receptors in the oxytocin-induced antinociception in the central nervous system of rats

Recent studies showed that oxytocin and opioid peptides play important roles in pain modulation at different levels in the central nervous system. The present study was performed to explore whether opioid system is involved in the oxytocin-induced antinociception in the brain of rats. The results showed that: (1) intracerebroventricular injection of oxytocin induced dose-dependent increases in hindpaw withdrawal latencies (HWL) to noxious thermal and mechanical stimulation in rats. (2) The antinociceptive effect of oxytocin was attenuated dose-dependently by intracerebroventricular injection of naloxone, indicating an involvement of opioid system in the oxytocin-induced antinociception. (3) It is interesting that the antinociceptive effect of oxytocin was attenuated by subsequent intracerebroventricular injection of the μ-opioid antagonist β-funaltrexamine (β-FNA) and the κ-opioid antagonist nor-binaltorphimine (nor-BNI), but not the δ-opioid antagonist naltrindole. The results indicate that oxytocin plays an antinociceptive role in the brain of rats; μ- and κ-opioid receptors, not δ-receptors, are involved in the oxytocin-induced antinociception in the central nervous system of rats.     

免疫复合物致疼痛与甲醛致炎性痛的大鼠模型比较及巨噬细胞游走抑制因子在两组模型中的表达

目的 比较免疫复合物所致疼痛模型与甲醛致炎性疼痛模型的大鼠疼痛行为、局部炎症反应及巨噬细胞游走抑制因子在不同模型不同部位的表达,探讨免疫复合物所致疼痛的病理机制.方法 成年SD清洁级大鼠15只,随机分为正常对照组,甲醛组及免疫复合物组,每组5只.分别在大鼠右后足底注入20 μL PBS、甲醛及免疫复合物.于30 min、1h、2h、4h、8h、12 h测定疼痛行为.并于12 h后采血、取大鼠局部皮肤及脊髓测定巨噬细胞游走抑制因子(MIF)表达.结果 疼痛行为变化:在甲醛致炎后大鼠立刻出现明显的自发痛,疼痛阈值明显下降,注射足高度肿胀并于1h达高峰后逐渐缓解.免疫复合物组的疼痛阈值低峰在4h后,并持续至8h后逐渐缓解,注射足肿胀不明显.皮肤及脊髓的MIF表达在甲醛组明显增加(P＜0.05),在免疫复合物组中无明显改变.结论 MIF参与炎症性疼痛病理过程,但无证据参与免疫复合物所致疼痛.抗原抗体复合物所致疼痛与甲醛炎性痛病理机制有一定区别.     

Long-term changes in self-stimulation threshold by repeated morphine and naloxone treatment

To analyse the interaction between endogenous opioid systems and brain reward, the influence of repeated treatment for 3 weeks with morphine and the opioid antagonist naloxone was investigated in rats with self-stimulation electrodes in the ventral tegmental area. Changes in threshold of self-stimulation determined by a response rate insensitive two lever method were considered as changes in reward. Morphine induced a temporary decrease of the response rate which lasted 3 days, and decreased the threshold for self-stimulation. The effect on threshold remained present till morphine treatment was discontinued, indicating that tolerance does not develop to this effect of morphine. Repeated naloxone treatment gradually increased the threshold for self-stimulation. This effect persisted after discontinuation of naloxone treatment. It is concluded that blockade of opioid receptors induces long term changes in the setpoint of self-stimulation reward.     

DDD-028: A potent potential non-opioid,non-cannabinoid analgesic for neuropathic and inflammatory pain

DDD-028 (4), a novel pentacyclic pyridoindolobenzazepine derivative was evaluated in vitro for receptor binding affinity and in vivo for analgesic activity using rodent models of neuropathic and inflammatory pain. DDD-028 does not bind to opioid, cannabinoid, dopamine, or histamine receptors. DDD-028 is very active even at the low oral dose of 1–5 mg/kg in both neuropathic, (spinal nerve ligation and chronic constriction injury) and inflammatory (Complete Freund’s Adjuvant Induced) models of pain. DDD-028 appears to be about 6-fold more potent than pregabalin and indomethacin. Visual observation of all the animals used in these studies indicated that DDD-028 is well tolerated without any sedation. Thus, DDD-028 seems to be a promising candidate for the treatment of neuropathic and inflammatory pain without the possible side effects or abuse potential associated with opioid or cannabinoid activities.     

Peptide fragments derived from the beta-chain of hemoglobin (hemorphins) are centrally active in vivo

A novel tetrapeptide (hemorphin-4) and pentapeptide (hemorphin-5), derived from the beta-chain of hemoglobin, were synthesized by solid-phase methodology, purified and the amino acid sequences confirmed. The central (ICV) effects of hemorphin-4 and -5 were studied in two models of phasic and tonic nociception, the mouse warm water tail-flick assay and hindpaw formalin assay, respectively. Additionally, two physiological endpoints, central modulation of bladder motility and central effects on intestinal propulsion, were studied in rats and mice, respectively. In the tail-flick assay, both peptides (40-100 nmoles) produced a dose-related naloxone-reversible antinociceptive effect when tested 10 min after peptide administration, with the tetrapeptide being slightly more potent than the pentapeptide. No effect was noted for either peptide using the tonic nociception assay, except at a dose of 150 nmoles for hemorphin-5. Inhibition of gastrointestinal propulsion was also not affected by either peptide. However, both peptides (10-40 nmoles) inhibited micturition contractions in a dose-related and naloxone-reversible fashion, with the tetrapeptide being twice as potent as the pentapeptide. These findings provide evidence that hemorphin-4 and -5 exert naloxone-reversible opioid actions in vivo and, therefore, may be physiologically important blood-borne peptides.     

Serum IL-10 involved in morphine tolerance development during adjuvant-induced arthritis

Opioid receptors play an important role in modulation of hyperalgesia in inflamed tissues, but chronic morphine application induces such side effects as tolerance. There is near communications between cytokines and mu opioid receptor expression. This study was aimed to assess the role of serum IL-10 in morphine tolerance development during adjuvant-induced arthritis. Adjuvant arthritis (AA) was induced on day 0 by single injection of Complete Freund’s Adjuvant (CFA) into the rats’ hindpaw. Hyperalgesia, edema, and spinal mu opioid receptor (mOR) variations were assessed on 0, 7, 14, and 21 days of the study. For assessment of the morphine tolerance development, morphine effective dose (4 mg/kg) was administered from the 14th day after CFA injection and continued until the morphine post-dose paw withdrawal latency (PWL); it did not significantly differ from the baseline. For assessment of the effects of IL-10 on tolerance induction, a neutralizing dose (ND50) of anti-IL-10 was administered daily during different stages of the study. AA induction in the right hindpaw of rats resulted in unilateral inflammation and hyperalgesia within 21 days of the study. Anti-IL-10 antibody administration in the AA rats induced marked elevation of hyperalgesia compared to the AA control group. Our data also indicated that morphine effective anti-hyperalgesic dose significantly decreased in the AA rats compared to the control group, which this symptom was aligned with spinal mu opioid receptor (mOR) expression increase during AA. Moreover, there was a significant difference in morphine tolerance induction between the AA and control rats, and our results also demonstrated that IL-10 played an important role in tolerance-induction process. It can be concluded that morphine tolerance slowly progressed when administered morphine effective dose was reduced during AA chronic inflammation. On the other hand, it seems that increased level of serum IL-10 may affect morphine tolerance development during inflammation.     

N‐terminal guanidinylation of the cyclic 1,4‐ureido‐deltorphin analogues: the synthesis,receptor binding studies,and resistance to proteolytic digestion

The synthesis of a series of N‐guanidinylated cyclic ureidopeptides, analogues of 1,4‐ureido‐deltorphin/dermorphine tetrapeptide is described. The δ‐ and μ‐opioid receptor affinity of new guanidinylated analogues and their non‐guanidinylated precursors was determined by the displacement radioligand binding experiments. Our results indicate that the guanidinylation of cyclic 1,4‐ureidodeltorphin peptide analogues does not exhibit a uniform influence on the opioid receptor binding properties, similarly as reported earlier for some linear peptides. All analogues were also tested for their in vitro resistance to proteolysis during incubation with large excess of chymotrypsin, pepsin, and papain by means of mass spectroscopy. Guanidinylated ureidopeptides 1G–4G showed mixed μ agonist/δ agonist properties and high enzymatic stability indicating their potential as therapeutic agents for treatment of pain. Copyright © 2015 European Peptide Society and John Wiley & Sons, Ltd.     

Antinociceptive role of oxytocin in the nucleus raphe magnus of rats, an involvement of mu-opioid receptor

Recent studies showed that oxytocin plays an important role in nociceptive modulation in the central nervous system. The present study was undertaken to investigate the role of oxytocin in antinociception in the nucleus raphe magnus (NRM) of rats and the possible interaction between oxytocin and the opioid systems. Intra-NRM injection of oxytocin induced dose-dependent increases in hindpaw withdrawal latencies (HWLs) to noxious thermal and mechanical stimulation in rats. The antinociceptive effect of oxytocin was significantly attenuated by subsequent intra-NRM injection of the oxytocin antagonist 1-deamino-2-D-Tyr-(Oet)-4-Thr-8-Orn-oxytocin. Intra-NRM injection of naloxone dose-dependently antagonized the increased HWLs induced by preceding intra-NRM injection of oxytocin, indicating an involvement of opioid receptors in oxytocin-induced antinociception in the NRM of rats. Furthermore, the antinociceptive effect of oxytocin was dose-dependently attenuated by subsequent intra-NRM injection of the mu-opioid antagonist beta-funaltrexamine (beta-FNA), but not by the kappa-opioid antagonist nor-binaltorphimine (nor-BNI) or the delta-opioid antagonist naltrindole. The results demonstrated that oxytocin plays an antinociceptive role in the NRM of rats through activating the oxytocin receptor. Moreover, mu-opioid receptors, not kappa and delta receptors, are involved in the oxytocin-induced antinociception in the NRM of rats.     

Alpha-lactorphin lowers blood pressure measured by radiotelemetry in normotensive and spontaneously hypertensive rats

Cardiovascular effects of subcutaneous administration of synthetic alpha-lactorphin, a tetrapeptide (Tyr-Gly-Leu-Phe) originally derived from milk alpha-lactalbumin, were studied in conscious spontaneously hypertensive rats (SHR) and in normotensive Wistar Kyoto rats (WKY) with continuous radiotelemetric monitoring. Alpha-lactorphin dose-dependently lowered blood pressure (BP) without affecting heart rate in SHR and WKY. The lowest dose which reduced BP was 10 microg/kg, and the maximal reductions in systolic and diastolic BP (by 23+/-4 and 17+/-4 mm Hg, respectively) were observed at 100 microg/kg dose in SHR. No further reductions were obtained at a higher dose of 1 mg/kg. There were no significant differences in the BP responses to alpha-lactorphin between SHR and WKY. Naloxone (1 and 3 mg/kg s.c.), a specific opioid receptor antagonist, abolished the alpha-lactorphin-induced reduction in BP and reversed it into a pressor response, which provides evidence for an involvement of opioid receptors in the depressor action of the tetrapeptide.     

Acupuncture Alleviates the Affective Dimension of Pain in a Rat Model of Inflammatory Hyperalgesia

Although studies demonstrate that electroacupuncture (EA) alleviates the sensory dimension of pain, they have not addressed EA’s effect on the affective dimension. An inflammatory pain rat model, produced by a complete Freund adjuvant (CFA) injection into the hind paw, was combined with a conditioned place avoidance test to determine EA’s effects and its underpinning mechanism on the affective dimension of pain. CFA-injected rats showed place aversion, i.e. the affective dimension of pain, by spending less time in a pain-paired compartment after conditioning than before, while saline-injected rats did not. CFA rats given EA treatment at GB30 before a post-conditioning test showed no aversion to the pain-paired compartment, indicating that EA inhibited the affective response. Intra-rostral anterior cingulate cortex (rACC) administration of a κ-, but not μ-opioid receptor antagonist, blocked EA action. These data demonstrate that EA activates opioid receptors in the rACC to inhibit the affective dimension of pain.     

Characteristics of the course of the wound process in spontaneously hypertensive rats and the effect of morphine, substance P and its fragment SP1-4

The paper demonstrates that in spontaneously hypertensive rats (SHR) as compared with normotensive controls exudative processes at the sites of lesions are much more prominent. Such exudative processes include edema, fibrinous exudation as well as permeability of capillaries and venular walls for leukocytes. These effects prolong the phase of its inflammation and retard the regeneration phase in wound healing. Morphine and SP1-11 stimulate in a similar fashion repair during wound healing in the both rat strains. Their effect is similar to the effect of opioid peptides. SP1-4 does not affect vessel reactivity and wound healing in SHR, which is related to disturbed expression of receptors to SP fragments. Synergism in the effect of two functional antagonists i.e. opioids and SP on wound healing confirms our hypothesis about the role of pain as an inducer of a variety of mechanisms underlying repair regeneration.     

Combined antiallodynic effect of Neurotropin® and pregabalin in rats with L5-spinal nerve ligation

AimsIn this study, we investigated the combined effect of Neurotropin® and pregabalin for L5-spinal nerve ligation (L5-SNL) model in rats and thiopental-induced sleep in mice.Main methodsThe left fifth lumbar nerve of rats was tightly ligated with silk sutures under pentobarbital anesthesia. The hindpaw withdrawal threshold was measured by application of von Frey filaments. Thiopental sodium was intravenously administered in mice and sleeping time was measured. In L5-SNL rats, an isobolographic analysis was performed to clarify the combined antiallodynic effect of Neurotropin and pregabalin 14 days after ligation in rats. In isobolographic analysis and thiopental-induced sleep test, Neurotropin and pregabalin were orally administered to coincide with the timing of the peak effect of each drug.Key findingsNeurotropin (50–200 NU/kg) and pregabalin (2.5–10 mg/kg) showed a dose-dependent antiallodynic action in L5-SNL rats. The antiallodynic effect of pregabalin was reversed by intrathecal injection of yohimbine or ondansetron. Isobolographic analysis suggested that the combined antiallodynic effect of Neurotropin and pregabalin in L5-SNL rats may have been more than a mere additive effect. Neurotropin (50–400 NU/kg) had no effect on thiopental-induced sleeping time whereas pregabalin (30–100 mg/kg) significantly prolonged it. When the dose of pregabalin was 30 mg/kg, Neurotropin (50–400 NU/kg) did not further exacerbate the prolongation effect of pregabalin on thiopental-induced sleep.SignificanceIt was suggested that when Neurotropin was administered in combination with pregabalin, it might provide more effective pain relief than that obtained with each agent alone in neuropathic pain without aggravating adverse effects of pregabalin.     

Nociceptin/orphanin FQ in spinal nociceptive mechanisms under normal and pathological conditions

Nociceptin and its receptor are present in dorsal spinal cord, indicating a possible role for this peptide in pain transmission. The majority of functional studies using behavioral and electrophysiological studies have shown that nociceptin applied at spinal level produces antinociception through pre- and post-synaptic mechanisms. The spinal inhibitory effect of nociceptin is not sensitive to antagonists of opioid receptors such as naloxone. Thus, nociceptin-induced antinociception is mediated by a novel mechanism independent of activation of classic opioid receptors. This has raised the possibility that agonists of the nociceptin receptor may represent a novel class of analgesics. Supporting this hypothesis, several groups have shown that intrathecal nociceptin alleviated hyperalgesic and allodynic responses in rats after inflammation or partial peripheral nerve injury. Electrophysiological studies have also indicated that the antinociceptive potency of spinal nociceptin is maintained or enhanced after nerve injury. It is concluded that the predominant action of nociceptin in the spinal cord appears to be inhibitory. The physiological role of nociceptin in spinal nociceptive mechanisms remains to be defined. Moreover, further evaluation of nociceptin as a new analgesic calls the development of non-peptide brain penetrating agents.     

Delta-Opioid Receptor Analgesia Is Independent of Microglial Activation in a Rat Model of Neuropathic Pain

The analgesic effect of delta-opioid receptor (DOR) ligands in neuropathic pain is not diminished in contrast to other opioid receptor ligands, which lose their effectiveness as analgesics. In this study, we examine whether this effect is related to nerve injury-induced microglial activation. We therefore investigated the influence of minocycline-induced inhibition of microglial activation on the analgesic effects of opioid receptor agonists: morphine, DAMGO, U50,488H, DPDPE, Deltorphin II and SNC80 after chronic constriction injury (CCI) to the sciatic nerve in rats. Pre-emptive and repeated administration of minocycline (30 mg/kg, i.p.) over 7 days significantly reduced allodynia and hyperalgesia as measured on day 7 after CCI. The antiallodynic and antihyperalgesic effects of intrathecally (i.t.) administered morphine (10–20 µg), DAMGO (1–2 µg) and U50,488H (25–50 µg) were significantly potentiated in rats after minocycline, but no such changes were observed after DPDPE (10–20 µg), deltorphin II (1.5–15 µg) and SNC80 (10–20 µg) administration. Additionally, nerve injury-induced down-regulation of all types of opioid receptors in the spinal cord and dorsal root ganglia was not influenced by minocycline, which indicates that the effects of opioid ligands are dependent on other changes, presumably neuroimmune interactions. Our study of rat primary microglial cell culture using qRT-PCR, Western blotting and immunocytochemistry confirmed the presence of mu-opioid receptors (MOR) and kappa-opioid receptors (KOR), further we provide the first evidence for the lack of DOR on microglial cells. In summary, DOR analgesia is different from analgesia induced by MOR and KOR receptors because it does not dependent on injury-induced microglial activation. DOR agonists appear to be the best candidates for new drugs to treat neuropathic pain.     

The role of the angiotensin AT2 receptor on the diurnal variations of nociception and motor coordination in rats

Phasic pain demonstrates significant diurnal variation in rats. Angiotensin II modulates pain transmission and the diurnal variation in nociception in several rodent pain models. The participation of AT2 receptors in the diurnal regulation of nociception is not yet elucidated. In the present study we investigated the effects of selective peptide AT2 agonist CGP 42112A and the nonpeptide AT2 receptor antagonist PD 123319 on the nociception, motor coordination and arterial blood pressure. Male Wistar 12 weeks old rats were used. CGP 42112A was injected at single doses of 1 and 5 μg/rat intracerebroventricularly (ICV) and infused chronically ICV at a dose of 12 μg/rat/day during 14 days by osmotic minipumps. PD123319 was injected at single doses of 1 and 5 μg/rat, ICV and chronically subcutaneously at a dose of 10 mg/kg/day/14 days. Nociception was assessed by an analgesimeter, arterial blood pressure (ABP) was measured by tail cuff method, and motor coordination by Rota-rod method. Single doses of CGP 42112A (1 and 5 μg/rat) provoked a short lasting antinociception. Unlike acute injection, chronic CGP 42112A infusion increased nociception at the beginning and the end of light phase thus attenuating the diurnal variations observed in the controls. Moreover, it produced an increase of ABP and improved motor coordination. Both acute (1 μg/rat) and chronic PD 123319 treatment resulted in a decrease of pain threshold and chronic treatment attenuated its diurnal fluctuation. Our data support a role for Ang II type 2 receptors in the control of diurnal variations of nociception in rats.     

Role of nerve growth factor-tyrosine kinase receptor A signaling in paclitaxel-induced peripheral neuropathy in rats

The mechanisms underlying paclitaxel-induced peripheral neuropathy remain unknown. Nerve growth factor (NGF) is a representative neurotrophic factor that maintains neuronal function, promotes survival, and mediates neuropathic pain. We investigated expression levels of NGF and its receptors in the dorsal root ganglia (DRG) and spinal dorsal horn (DH) following paclitaxel treatment. Intraperitoneal (I.P.) administration of paclitaxel induced significant mechanical hypersensitivity and cold allodynia in rats, significantly increased the expression of NGF and its receptor tyrosine kinase receptor A (trkA) in the DRG, and increased NGF expression in the DH. In contrast, paclitaxel treatment did not alter the mRNA levels of NGF or its receptors in the DRG, DH, sciatic nerve, or hindpaw skin. Moreover, expression of NEDD4-2, a negative regulator of trkA, was significantly increased in the DRG of paclitaxel-treated rats. Intrathecal (I.T.) administration of the tyrosine kinase receptor inhibitor k252a significantly alleviated mechanical hypersensitivity in paclitaxel-treated rats. Our results suggest that NGF–trkA signaling is involved in mechanical allodynia in paclitaxel-induced neuropathy.     

Stress-induced hypokinesia is facilitated by ACTH-(7-10)

Subcutaneous treatment with the neuropeptide ACTH-(4-10) induced hypokinesia in rats subjected to a mild stress induced by placing the animals on a non-functional "hot" plate (21 degrees C) for 30 sec, but not in control animals not exposed to this stress-inducing environment. The lowest effective dose of ACTH-(4-10) was 5 micrograms/kg, administered 50 min before testing. The combination of peptide treatment and the mild stress-inducing procedure mimicked the effect of a short intense stress induced by placing the rats on a hot plate (57 degrees C) for 30 sec, suggesting that this stress-induced hypokinesia is mediated by ACTH neuropeptides. Structure-activity relationship studies revealed that the active core for the ACTH-(4-10)-induced hypokinesia is located in the C-terminal tetrapeptide Phe-Arg-Try-Gly (ACTH-(7-10)). Pretreatment with the opioid antagonist naltrexone did not influence the effect of ACTH-(4-10) indicating that activation of opioid systems is not implicated in this behavioral effect of the peptide.     

Intradermal pregnenolone sulfate attenuates capsaicin-induced nociception in rats

We have previously shown that the neurosteroid pregnenolone sulfate (PS) inhibits the capsaicin receptor-mediated current in rat dorsal root ganglion neurons. Here, we examined the effect of intradermal injection of PS into the rat hindpaw on capsaicin-induced nociception. Results revealed that PS co-injected with capsaicin dose-dependently inhibited the capsaicin-induced nocifensive response. In contrast, injections of PS into one hindpaw and capsaicin into the contralateral hindpaw had no effect on the capsaicin-induced nocifensive response, suggesting that PS produced its effect locally but not systemically. Moreover, PS inhibition of the capsaicin-induced nocifensive response was not significantly reduced by a nonselective opioid receptor antagonist or by cannabinoid receptor antagonists, indicating that neither an opioid- nor a cannabinoid-dependent mechanism mediated the effect of PS. These data demonstrate that PS acts peripherally to attenuate capsaicin-induced nociception through an opioid- and cannabinoid-independent mechanism and suggest a new therapeutic potential for PS in pain management.     

Prenatal Morphine Exposure Differentially Alters Addictive and Emotional Behavior in Adolescent and Adult Rats in a Sex-Specific Manner

The effects of prenatal opioid exposure in adult animals has been widely studied, but little is known about the effects of prenatal opioid on adolescents. Most of the risk behaviors associated with drug abuse are initiated during adolescence. The developmental state of the adolescent brain makes it vulnerable to initiate drug use and susceptible to drug-induced brain changes. In this study, pregnant rats were subcutaneously injected with an increasing dose of morphine (5 mg/kg, 7 mg/kg, 10 mg/kg) for 9 days since the gestation day 11. The effects of prenatal morphine (PNM) on learning and memory, anxiety- and depressive- like behavior, morphine induced conditioned place preference (CPP) as well as locomotor sensitization were tested in both adolescent and adult rats. The results showed that: (1) PNM decreased anxiety-like behavior in both adolescent and adult female rats, but not males; (2) PNM decreased depressive-like behavior in adolescent but increased depressive -like behavior in adult females; (3) PNM increased low dose morphine induced locomotor sensitization in females; (4) PNM decreased tyrosine hydroxylase (TH) expression in the prefrontal cortex but decreased dopamine D1 receptor expression in the nucleus-accumbens (NAc) in female rats. These results suggested that PNM altered the emotional and addictive behavior mainly in female rats, with female rats being less anxiety and depressive during adolescence, but more depressive in adult, and more sensitive to low dose morphine induced locomotor activity sensitization, which might be mediated in part by the differential expression of the TH, dopamine D1 receptors in the female brain.