Injection Of norBNI Research Articles

The Antidepressant Effect of Magnolol on Depression-Like Behavior of CORT-Treated Mice.

Although the antidepressant-like effect of magnolol has been revealed in previous reports, the mechanism remains unclear. In this study, the antidepressant-like effect of magnolol on corticosterone-induced (CORT-induced) mice was investigated in vivo. After 21 days of CORT induction, the mice showed marked depressive-like behaviors, with a decrease in sucrose preference score and an increase in immobility time in the tail suspension test (TST) and forced swimming test (FST). Pretreatment with either magnolol (50 mg/kg, i.p.) or the kappa opioid receptor (KOR) antagonist nor-BNI (10 mg/kg, i.p.) prevented CORT-induced depression-like behavior and reduced CORT-induced dynorphin (DYN A) elevation in the hippocampal ventral DG. However, no depression-like behavior was observed in mice with KOR downregulation in the ventral DG. We further found that upregulation of DYN A in the DG caused depression-like behavior, which was blocked by intraperitoneal injection of nor-BNI and modulated by magnolol. The present study demonstrated that magnolol could ameliorate CORT-induced depression-like behaviors, by modulating the DYN A/KOR system in the ventral DG of the hippocampus.

Amygdala dynorphin/κ opioid receptor system modulates depressive-like behavior in mice following chronic social defeat stress.

Major depression disorder is a severe and recurrent neuropsychological disorder characterized by lowered mood and social activity and cognitive impairment. Owing to unclear molecular mechanisms of depression, limited interventions are available in clinic. In this study we investigated the role of dynorphin/κ opioid receptor system in the development of depression. Mice were subjected to chronic social defeat stress for 14 days. Chronic social defeat stress induced significant social avoidance in mice characterized by decreased time duration in the interaction zone and increased time duration in the corner zone. Pre-administration of a κ opioid receptor antagonist norBNI (10 mg/kg, i.p.) could prevent the development of social avoidance induced by chronic social defeat stress. Social avoidance was not observed in κ opioid receptor knockout mice subjected to chronic social defeat stress. We further revealed that social defeat stress activated c-fos and ERK signaling in the amygdala without affecting the NAc, hippocampus and hypothalamus, and ERK activation was blocked by systemic injection of norBNI. Finally, the expression of dynorphin A, the endogenous ligand of κ opioid receptor, was significantly increased in the amygdala following social defeat stress; microinjection of norBNI into the amygdala prevented the development of depressive-like behaviors caused by social defeat stress. The present study demonstrates that upregulated dynorphin/κ opioid receptor system in the amygdala leads to the emergence of depression following chronic social defeat stress, and sheds light on κ opioid receptor antagonists as potential therapeutic agents for the prevention and treatment of depression following chronic stress.

Brain site-specific regulation of hedonic intake by orexin and DYN peptides: role of the PVN and obesity

ABSTRACT The orexin peptides promote hedonic intake and other reward behaviors through different brain sites. The opioid dynorphin peptides are co-released with orexin peptides but block their effects on reward in the ventral tegmental area (VTA). We previously showed that in the paraventricular hypothalamic nucleus (PVN), dynorphin and not orexin peptides enhance hedonic intake, suggesting they have brain-site-specific effects. Obesity alters the expression of orexin and dynorphin receptors, but whether their expression across different brain sites is important to hedonic intake is unclear. We hypothesized that hedonic intake is regulated by orexin and dynorphin peptides in PVN and that hedonic intake in obesity correlates with expression of their receptors. Here we show that in mice, injection of DYN-A1–13 (an opioid dynorphin peptide) in the PVN enhanced hedonic intake, whereas in the VTA, injection of OXA (orexin-A, an orexin peptide) enhanced hedonic intake. In PVN, OXA blunted the increase in hedonic intake caused by DYN-A1–13. In PVN, injection of norBNI (opioid receptor antagonist) reduced hedonic intake but a subsequent OXA injection failed to increase hedonic intake, suggesting that OXA activity in PVN is not influenced by endogenous opioid activity. In the PVN, DYN-A1–13 increased the intake of the less-preferred food in a two-food choice task. In obese mice fed a cafeteria diet, orexin 1 receptor mRNA across brain sites involved in hedonic intake correlated with fat preference but not caloric intake. Together, these data support that orexin and dynorphin peptides regulate hedonic intake in an opposing manner with brain-site-specific effects.

Kappa opioid receptor activation in the Preoptic Area (POA) contributes to the impairment of brown adipose tissue activation in rats on a high fat diet (HFD)

We have recently demonstrated that cold‐evoked activation of brown adipose tissue is inhibited in rats maintained on a high fat diet for at least eight weeks. Activation of neurons in the external lateral parabrachial nucleus is a necessary relay in the afferent pathway for cold‐evoked increases in BAT thermogenesis and BAT sympathetic nerve activity. In order to assess whether there was an impaired activation of the cold afferent pathway, the present study examined the expression of the immediate early gene, fos, in the external lateral parabrachial nucleus of cold exposed rats maintained on either a control diet or a HFD. Contrary to the hypothesis, there was no difference in HFD rats compared to control diet rats, in the number of neurons in the external lateral parabrachial nucleus which expressed fos in response to cold‐exposure. However, there was an increase in the number of neurons expressing fos in the dorsal lateral parabrachial nucleus (LPBd) of HFD rats compared to control diet rats. This is interesting since the LPBd is an area that has been shown to inhibit cold‐evoked activation of BAT SNA. Furthermore, many of the dorsal lateral parabrachial neurons that were activated in the HFD rats during cold exposure contained preprodynorphin. Preprodynorphin cells in the LPBd project to the preoptic area and can produce the kappa opioid receptor agonist dynorphin. These observations led to my hypothesis that activation of kappa opioid receptor (KOR) in the POA contributes to the inhibition of BAT thermogenesis during HFD. Therefore, the present study tested the hypothesis that selective blockade of KOR, in the POA would reverse the impairment of cooling‐evoked BAT SNA in HFD rats, but fail to increase BAT SNA in control diet rats. Nanoinjection of the KOR antagonist, norBNI, in the POA reversed the HFD‐induced impairment of cold evoked BAT SNA and thermogenesis. In contrast, injection of norBNI in rats on a control diet did not increase BAT SNA or BAT thermogenesis. These data suggest that there is an aberrant activation of a dynorphin input from the LPBd to the POA in rats on a high fat diet. Activation of this pathway in HFD‐induced obesity may help to explain the weight reducing effects of KOR antagonists such as naltrexone.Support or Funding Information1 R01 DK112198‐01A1This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Effects of ICI204,448, naloxone methiodide and levocetirizine on the scratching behavior induced by a κ-opioid antagonist, nor-BNI, in ICR mice

Objective: In this study, we aimed to study the effects of ICI204,448, naloxone methiodide and levocetirizine on the scratching behavior induced by intradermal injection of a ?-opioid antagonist, nor-binaltorphimine (nor-BNI), into the rostral back of ICR mice were investigated.Materials and methods: Male ICR mice weighing 30?35 g were used. The number of scratching episodes were counted for 60 min after i.d. injection of nor-BNI.Results: nor-BNI dose dependently increased in the number of scratching episodes in ICR mice. nor-BNI-induced scratching behavior was inhibited by not only nalfurafine but also ICI204,448, a peripherally selective ?-opioid agonist. Naloxone and naloxone methiodide, a peripherally restricted ?-opioid antagonist, also inhibited nor-BNI-induced scratching behavior. Scratching behavior induced by nor-BNI was inhibited by chlorpheniramine as well as levocetirizine, a third-generation H1 antagonist that does not cross into the CNS.Conclusion: These results suggest that scratching behavior induced by this ?-opioid antagonist, nor-BNI, is related to not only central but also peripheral opioid and H1 receptors.

Long-Term Reduction of Kappa Opioid Receptor Function by the Biased Ligand, Norbinaltorphimine, Requires c-Jun N-Terminal Kinase Activity and New Protein Synthesis in Peripheral Sensory Neurons.

A single administration of the κ opioid receptor (KOR) antagonist, norbinaltorphimine (norBNI), produces long-term reduction in KOR function in heterologous expression systems and brain that is mediated by activation of c-Jun N-terminal kinase (JNK). In this study, we examined the long-term effects of norBNI on adult rat peripheral sensory neurons in vivo and ex vivo. Following a single intraplantar (i.pl.) injection of norBNI into the hind paw, peripheral KOR-mediated antinociception in the ipsilateral, but not the contralateral, hindpaw was abolished for at least 9 days. By contrast, the antinociceptive response to mu and delta opioid receptor agonists was unaltered. The long-term inhibitory effect on antinociception produced by pretreatment with norBNI required occupancy of peripheral KOR and was completely blocked by i.pl. injection of the JNK inhibitor, SP600125. In cultures of peripheral sensory neurons, norBNI activated JNK for at least 30 minutes. Furthermore, norBNI blocked KOR-mediated inhibition of adenylyl cyclase activity measured 24 hours later in a JNK-dependent manner, but did not block activation of extracellular signal-regulated kinase (ERK). The long-term inhibitory effect of norBNI on KOR function in vivo and ex vivo was blocked by inhibitors of mRNA translation, cycloheximide and rapamycin. These data suggest that in peripheral sensory neurons norBNI is a KOR-biased ligand for activation of JNK signaling, resulting in long-term blockade of some (antinociception, inhibition of adenylyl cyclase activity), but not all (ERK), KOR signaling. Importantly, norBNI elicits de novo protein synthesis in sensory neuron terminals that produces selective long-term regulation of KOR.

Inhibition of opioid systems in the hypothalamus as well as the mesolimbic area suppresses feeding behavior of mice

Opioid receptors, especially μ-opioid receptors, in the ventral tegmental area (VTA) and nucleus accumbens (NAcc) are reported to regulate food motivation. However, the roles of μ-, δ- and κ-opioid receptors are not fully understood. Moreover, since μ-, δ- and κ-opioid receptors are reported to distribute in the hypothalamus, these receptors in the hypothalamus might regulate feeding behavior. Thus, the present study investigated the role of μ-, δ- and κ-opioid receptors in the VTA, the NAcc and the hypothalamus in the regulation of feeding behavior. Male ICR mice were subjected to a feeding test after food deprivation for 16h. The mRNA levels of proopiomelanocortin (POMC), preproenkephalin (PENK) and prodynorphin (PDYN), the precursors of endogenous opioid peptides, were measured by reverse transcription-polymerase chain reaction (RT-PCR). The systemic injection of non-selective (naloxone) and selective μ (β-funaltrexamine; β-FNA), δ (naltrindole) and κ (norbinaltorphimine; norBNI) opioid receptor antagonists markedly reduced food intake. In contrast, the systemic injection of preferential μ (morphine), selective δ (KNT-127) and κ (U-50,488) opioid receptor agonists did not change food intake. The mRNA levels of POMC, PENK and PDYN were decreased in the hypothalamus and the midbrain after food deprivation, whereas the mRNA levels of PENK and PDYN, but not POMC, were decreased in the ventral striatum. The injection of naloxone into the NAcc, VTA and lateral hypothalamus (LH), but not the ventromedial nucleus of the hypothalamus, significantly decreased food intake. The injection of β-FNA and naltrindole into the LH, but not the VTA or NAcc, decreased food intake. The injection of norBNI into the LH and VTA, but not the NAcc, decreased food intake. These results indicate that μ-, δ- and κ-opioid receptors in the LH play a more important role in the regulation of feeding behavior than those receptors in the VTA and the NAcc.

The kappa-opioid receptor antagonist, nor-binaltorphimine (nor-BNI), decreases morphine withdrawal and the consequent conditioned place aversion in rats

Much data suggest that the binding of dynorphin-like peptides to kappa-opioid receptors (KORs) during the administration of and withdrawal from a variety of addictive drugs is aversive and serves to limit the reinforcing properties of those drugs and to enhance tolerance, withdrawal, and the probability of stress-induced relapse. In this study, we examined the role of KORs in mediating opioid withdrawal and its aversive consequences in rats. We found that selective blockade of KORs by i.p. administration of 20mg/kg nor-binaltorphimine (nor-BNI) 5h prior to naltrexone-precipitated withdrawal in morphine-dependent rats decreased feces excreted during a 30-min withdrawal session. More critically, this injection of nor-BNI decreased the subsequent conditioned place aversion (CPA) for the withdrawal chamber 2 days later. The subsequent finding that administration of nor-BNI 2h following withdrawal did not affect the CPA 2 days later suggested that nor-BNI reduced the CPA in the prior experiment because it reduced the aversive effects of withdrawal, not because it reduced the aversive/anxiogenic effects of the withdrawal chamber at the time of CPA testing. These data indicate that the binding of dynorphin-like peptides to KORs during opioid withdrawal serves to enhance withdrawal and its aversive consequences and suggest that selective KOR antagonists may be useful in reducing these aversive effects and consequent relapse.

How Does Stress-Induced Activation of the Kappa Opioid System Increase Addiction Risk?

How Does Stress-Induced Activation of the Kappa Opioid System Increase Addiction Risk?

Stress-Induced Activation of the Dynorphin/κ-Opioid Receptor System in the Amygdala Potentiates Nicotine Conditioned Place Preference

Many smokers describe the anxiolytic and stress-reducing effects of nicotine, the primary addictive component of tobacco, as a principal motivation for continued drug use. Recent evidence suggests that activation of the stress circuits, including the dynorphin/κ-opioid receptor system, modulates the rewarding effects of addictive drugs. In the present study, we find that nicotine produced dose-dependent conditioned place preference (CPP) in mice. κ-receptor activation, either by repeated forced swim stress or U50,488 (5 or 10 mg/kg, i.p.) administration, significantly potentiated the magnitude of nicotine CPP. The increase in nicotine CPP was blocked by the κ-receptor antagonist norbinaltorphimine (norBNI) either systemically (10 mg/kg, i.p.) or by local injection in the amygdala (2.5 μg) without affecting nicotine reward in the absence of stress. U50,488 (5 mg/kg, i.p.) produced anxiety-like behaviors in the elevated-plus maze and novel object exploration assays, and the anxiety-like behaviors were attenuated both by systemic nicotine (0.5 mg/kg, s.c.) and local injection of norBNI into the amygdala. Local norBNI injection in the ventral posterior thalamic nucleus (an adjacent brain region) did not block the potentiation of nicotine CPP or the anxiogenic-like effects of κ-receptor activation. These results suggest that the rewarding effects of nicotine may include a reduction in the stress-induced anxiety responses caused by activation of the dynorphin/κ-opioid system. Together, these data implicate the amygdala as a key region modulating the appetitive properties of nicotine, and suggest that κ-opioid antagonists may be useful therapeutic tools to reduce stress-induced nicotine craving.

CRF1-R Activation of the Dynorphin/Kappa Opioid System in the Mouse Basolateral Amygdala Mediates Anxiety-Like Behavior

Stress is a complex human experience and having both rewarding and aversive motivational properties. The adverse effects of stress are well documented, yet many of underlying mechanisms remain unclear and controversial. Here we report that the anxiogenic properties of stress are encoded by the endogenous opioid peptide dynorphin acting in the basolateral amygdala. Using pharmacological and genetic approaches, we found that the anxiogenic-like effects of Corticotropin Releasing Factor (CRF) were triggered by CRF1-R activation of the dynorphin/kappa opioid receptor (KOR) system. Central CRF administration significantly reduced the percent open-arm time in the elevated plus maze (EPM). The reduction in open-arm time was blocked by pretreatment with the KOR antagonist norbinaltorphimine (norBNI), and was not evident in mice lacking the endogenous KOR ligand dynorphin. The CRF1-R agonist stressin 1 also significantly reduced open-arm time in the EPM, and this decrease was blocked by norBNI. In contrast, the selective CRF2-R agonist urocortin III did not affect open arm time, and mice lacking CRF2-R still showed an increase in anxiety-like behavior in response to CRF injection. However, CRF2-R knockout animals did not develop CRF conditioned place aversion, suggesting that CRF1-R activation may mediate anxiety and CRF2-R may encode aversion. Using a phosphoselective antibody (KORp) to identify sites of dynorphin action, we found that CRF increased KORp-immunoreactivity in the basolateral amygdala (BLA) of wildtype, but not in mice pretreated with the selective CRF1-R antagonist, antalarmin. Consistent with the concept that acute stress or CRF injection-induced anxiety was mediated by dynorphin release in the BLA, local injection of norBNI blocked the stress or CRF-induced increase in anxiety-like behavior; whereas norBNI injection in a nearby thalamic nucleus did not. The intersection of stress-induced CRF and the dynorphin/KOR system in the BLA was surprising, and these results suggest that CRF and dynorphin/KOR systems may coordinate stress-induced anxiety behaviors and aversive behaviors via different mechanisms.

Anxiolytic-Like Effects of κ-Opioid Receptor Antagonists in Models of Unlearned and Learned Fear in Rats

Endogenous opioid systems regulate neurobiological responses to threatening stimuli. Stimulation of kappa-opioid receptors (KORs) produces analgesia but induces prodepressive-like effects in a variety of animal models. In contrast, KOR antagonists have antidepressant-like effects. KORs and their endogenous ligand dynorphin are expressed throughout brain areas involved in fear and anxiety, including the extended amygdala. Here, we examined whether KOR antagonists would affect unlearned fear (anxiety) in the elevated plus maze (EPM) and open field (OF) paradigms and learned fear in the fear-potentiated startle (FPS) paradigm. These studies were designed to accommodate the slow onset (approximately 24 h) and extended time course (>3 weeks) of the prototypical KOR antagonists nor-binaltorphimine hydrochloride (norBNI) and JDTic [(3R)-7-hydroxy-N-[(1S)-1-[[(3R, 4R)-4-(3-hydroxyphenyl)-3,4-dimethyl-1-piperidinyl]methyl]-2-methylpropyl]-1,2,3,4-tetrahydro-3-isoquinoline-carboxamide hydrochloride]. Rats received an i.p. injection of norBNI (3.0-30 mg/kg) or JDTic (1.0-10 mg/kg) 48 h before EPM testing. One day later, they were tested in the OF, and 5 and 7 days later, they were trained and tested in the FPS paradigm. Both KOR antagonists dose-dependently increased open arm exploration in the EPM without affecting OF behavior. They also decreased conditioned fear in the FPS paradigm. The anxiolytic-like effects of KOR antagonists were qualitatively similar to those of the benzodiazepine chlordiazepoxide in the EPM. The selective serotonin reuptake inhibitor fluoxetine had no effect in the EPM and anxiogenic-like effects in the OF. Our results indicate that KOR antagonists produce a unique combination of antidepressant- and anxiolytic-like effects and suggest that this class of drugs may be particularly effective for the treatment of comorbid depressive and anxiety disorders.

Transient activation of the CA3 Kappa opioid system in the dorsal hippocampus modulates complex memory processing in mice

The hippocampus plays a central role in various forms of complex learning and memory. Opioid peptides and receptors are abundant in the hippocampus. These peptides are co-released with glutamate from mossy fiber- and lateral perforant path-synapses. In this study, we evaluated the functional relevance of the CA3 Kappa opioid receptors (KOR) by transient pharmacological activation or inactivation using single bilateral intrahippocampal microinjections of a selective agonist (U50,488H, 1 or 2.5 nmol), a selective antagonist (nor-binaltorphimine, norBNI 5 nmol) or a mixture of both. C57Bl/6J mice were tested in a fear conditioning paradigm (FC) or in a modified version of the water maze task thought to reveal how flexibly animals can learn and manipulate spatial information (WM). In FC, the agonist (2.5 nmol) decreased context-induced (but not tone-induced) freezing whereas norBNI had no effect. The impairment caused by the agonist U50,488H was blocked by the injection of norBNI, suggesting that overstimulation of CA3-KOR impairs the acquisition and consolidation of contextual fear-related memory. In the WM task, mice were trained repeatedly each day to find a hidden platform. After having reached this goal, the platform position was changed the next day for a new task. U50,488H injection before the last task abolished the previously acquired ability to find rapidly a new platform location, whereas adding norBNI reversed this impairment. Thus, in the mouse, even partial and topographically restricted activation of CA3-KOR entails impairments in two different hippocampus-dependent tasks, indicating functional relevance of the kappa opioid system.

The dynamic relationship between mu and kappa opioid receptors in body temperature regulation

Previous studies demonstrated that intracerebroventricular (icv) injection of a kappa opioid receptor agonist decreased, and a mu agonist increased, body temperature ( T b) in rats. A dose–response study with the selective kappa antagonist nor-binaltorphimine (nor-BNI) showed that a low dose (1.25 nmol, icv) alone had no effect, although a high dose (25 nmol, icv) increased T b. It was hypothesized that the hyperthermia induced by nor-BNI was the result of the antagonist blocking the kappa opioid receptor and releasing its inhibition of mu opioid receptor activity. To determine whether the T b increase caused by nor-BNI was a mu receptor-mediated effect, we administered the selective mu antagonist CTAP (1.25 nmol, icv) 15 min after nor-BNI (25 nmol, icv) and measured rectal T b in unrestrained rats. CTAP significantly antagonized the T b increase induced by icv injection of nor-BNI. Injection of 5 or 10 nmol of CTAP alone significantly decreased the T b, and 1.25 nmol of nor-BNI blocked that effect, indicating that the CTAP-induced hypothermia was kappa-mediated. The findings strongly suggest that mu antagonists, in blocking the basal hyperthermia mediated by mu receptors, can unmask the endogenous kappa receptor-mediated hypothermia, and that there is a tonic balance between mu and kappa opioid receptors that serves as a homeostatic mechanism for maintaining T b.

A single injection of the kappa opioid antagonist norbinaltorphimine increases ethanol consumption in rats

Kappa opioid receptor (KOR) agonists interfere with the reinforcing effects of drugs of abuse. KOR agonists decrease heroin, cocaine, and ethanol self-administration, and block heroin and cocaine conditioned place preference (CPP) in rats. However, KOR agonists also produce emesis and dysphoria, making it difficult to determine if their effects on self-administration are due to an action on reward mechanisms or are secondary to the drug's direct aversive effects. Assuming that endogenous KOR ligands modulate circuits involved in drug and alcohol reward, selective KOR antagonists can be used to clarify these issues. If KOR antagonists increase drug self-administration then it is likely that endogenous KOR agonists directly modulate drug intake. To determine the effects of nor-BNI, the highly selective KOR antagonist, on ethanol consumption and CPP. Thirty-eight male Lewis rats were given free access to ethanol until stable self-administration was achieved. Animals were then administered a single injection of nor-BNI (10 mg kg(-1)) while ethanol intake was monitored. A single injection of nor-BNI induces a long-lasting increase in ethanol consumption, but does not induce a CPP. A high/low split revealed that this effect was primarily due to an increase in drinking in nor-BNI-treated high drinkers, which drank significantly more than saline-treated high drinkers and also drank significantly more when compared to their own pretreatment baseline. Blocking the KOR system increases ethanol self-administration, suggesting that the decrease in self-administration seen with KOR agonists is due to a direct modulation of reward circuitry.

222 Effects of sigma ligands on the nociceptin/orphanin FQ receptor

Much data suggest that the binding of dynorphin-like peptides to kappa-opioid receptors (KORs) during the administration of and withdrawal from a variety of addictive drugs is aversive and serves to limit the reinforcing properties of those drugs and to enhance tolerance, withdrawal, and the probability of stress-induced relapse. In this study, we examined the role of KORs in mediating opioid withdrawal and its aversive consequences in rats. We found that selective blockade of KORs by i.p. administration of 20 mg/kg nor-binaltorphimine (nor-BNI) 5 h prior to naltrexone-precipitated withdrawal in morphine-dependent rats decreased feces excreted during a 30-min withdrawal session. More critically, this injection of nor-BNI decreased the subsequent conditioned place aversion (CPA) for the withdrawal chamber 2 days later. The subsequent finding that administration of nor-BNI 2 h following withdrawal did not affect the CPA 2 days later suggested that nor-BNI reduced the CPA in the prior experiment because it reduced the aversive effects of withdrawal, not because it reduced the aversive/anxiogenic effects of the withdrawal chamber at the time of CPA testing. These data indicate that the binding of dynorphin-like peptides to KORs during opioid withdrawal serves to enhance withdrawal and its aversive consequences and suggest that selective KOR antagonists may be useful in reducing these aversive effects and consequent relapse.

Dynorphin A-induced rat hindlimb paralysis and spinal cord injury are not altered by the κ opioid antagonist nor-binaltorphimine

The selective κ opioid receptor antagonist nor-binaltorphimine (nor-BNI) was used to distinguish a κ opioid component in the mechanisms underlying the hindlimb paralysis, ischemia, and neuronal injury induced in the rat by the κ opioid agonist dynorphin A. Spinal intrathecal (i.t.) injection of nor-BNI (20 nmol) either 15 min or immediately before i.t. injections of 5 or 20 nmol of dynorphin A failed to alter the dynorphin A-induced disruption of hindlimb motor function and nociceptive responsiveness. Nor-BNI also did not change the 3-fold increases in cerebrospinal fluid lactate concentrations produced by 20 nmol of dynorphin A. Neuroanatomical evaluations revealed that the cell loss, fiber degeneration, and central gray necrosis in lumbosacral spinal cords of rats treated with 20 nmol of dynorphin A were not altered by nor-BNI (20 nmol, i.t.). Thus, the spinal cord injury and associated neurological deficits resulting from i.t. injection of dynorphin A appear to be primarily, if not totally, attributable to its non-κ opioid action(s).