Complex plastic changes in the neuropeptide Y system during ethanol intoxication and withdrawal in the rat brain

Investigation of allyphenyline efficacy in the treatment of alcohol withdrawal symptoms

We have recently demonstrated that allyphenyline, behaving as α2C-adrenoceptor/serotonin 5-HT1A receptor agonist and α2A-adrenoceptor antagonist, in mice enhanced morphine analgesia, attenuated morphine withdrawal symptoms, showed significant antidepressant-like activity and was devoid of sedative side effects. Opioid and alcohol withdrawal shares several common neurobiological and molecular mechanisms. Therefore, in this study we expanded our analysis of the pharmacological properties of allyphenyline by investigating its ability to prevent the expression of somatic withdrawal signs, anxiety-like behavior and hyperlocomotion associated with chronic ethanol intoxication. Rats were subjected to induction of ethanol dependence via repeated daily intragastric ethanol (20%) administration for 4 consecutive days. Twelve hours after the last alcohol administration, somatic alcohol withdrawal signs were scored. Results revealed a significant expression of physical withdrawal signs that were not affected by intraperitoneal (i.p.) administration of allyphenyline at the doses of 0.05, 0.275 and 0.5 mg/kg. In contrast, allyphenyline (0.05 and 0.275 mg/kg i.p.) significantly reduced hyperanxiety-like behavior observed 6 days after alcohol intoxication as measured using the defensive burying test. Allyphenyline also reduced open field hyperlocomotor activity associated with alcohol withdrawal. Notably, the anxiolytic effect of the compound, as well as the already reported antidepressant action, was observed at very low doses, suggesting the involvement of its α2C-adrenoceptor/serotonin 5-HT1A receptor agonism. Therefore, the present investigation suggests that allyphenyline might represent an interesting pharmacological tool to investigate the potential of compounds exhibiting α2C-adrenoceptor/serotonin 5-HT1A receptor agonism and α2A-adrenoceptor antagonism in the treatment of hyperanxiety and hyperlocomotion occurring during alcohol withdrawal in dependent subjects.

Neuropeptide Y-stimulated [(35) S]GTPγs functional binding is reduced in the hippocampus after kainate-induced seizures in mice

Kainate-induced seizures constitute a model of temporal lobe epilepsy where prominent changes are observed in the hippocampal neuropeptide Y (NPY) system. However, little is known about the functional state and signal transduction of the NPY receptor population resulting from kainate exposure. Thus, in this study, we explored functional NPY receptor activity in the mouse hippocampus and neocortex after kainate-induced seizures using NPY-stimulated [(35) S]GTPγS binding. Moreover, we also studied levels of [(125) I]-peptide YY (PYY) binding and NPY, Y1, Y2, and Y5 receptor mRNA in these kainate-treated mice. Functional NPY binding was unchanged up to 12 h post-kainate, but decreased significantly in all hippocampal regions after 24 h and 1 week. Similarly, a decrease in [(125) I]-PYY binding was found in the dentate gyrus (DG) 1 week post-kainate. However, at 2 h, 6 h, and 12 h, [(125) I]-PYY binding was increased in all regions, and in the CA1 also at 24 h post-kainate. NPY mRNA levels were prominently increased in hippocampal regions, reaching maximum at 12 and 24 h. Y1 and Y5 mRNA levels were lowered in the DG at 24 and 2 h, respectively, while Y2 mRNA levels were elevated at 24 h in the DG and CA3. This study confirms rat kainate studies by showing pronounced adaptive changes in the mouse hippocampus both with regard to NPY synthesis and NPY receptor synthesis and binding, which may contribute to regulating neuronal seizure susceptibility after kainate. However, the potential seizure-suppressant effects of increased NPY gene expression at late time points post-kainate could be attenuated by the novel finding of reduced NPY-receptor G-protein activation.

Differential patterns of expression of neuropeptide Y throughout abstinence in outbred Swiss mice classified as susceptible or resistant to ethanol-induced locomotor sensitization

Several studies have focused on the negative emotional state associated with drug abstinence. The peptide NPY plays an important role given its involvement in drug addiction, anxiety, and mood disorders. Interestingly, it is well established that outbred Swiss mice exhibit a prominent behavioral variability to ethanol-induced locomotor sensitization. Here, we investigated whether mice that were either susceptible or resistant to ethanol sensitization differed in their NPY expression during abstinence. The mice were treated daily with ethanol (2 g/kg, i.p.) or saline for 21 days. According to the locomotor activity after the last injection, the ethanol group was classified as sensitized (EtOH_High) or non-sensitized (EtOH_Low). To evaluate NPY expression, some of the mice were sacrificed at 18 h or 5 days of abstinence, and others were challenged at the 5th day of abstinence with ethanol (1.4 g/kg) and sacrificed after 1.5 h. At 5 days of abstinence, NPY expression increased in the orbital cortex, dorsomedial striatum, and dentate gyrus in the EtOH_High mice. These changes were counteracted by the ethanol challenge. In the EtOH_Low mice, NPY expression increased in the dentate gyrus only after 18 h of abstinence. Lastly, a decreased level of NPY was found in the prelimbic cortex of the EtOH_Low mice at 5 days of abstinence, and this was reversed by ethanol challenge. Therefore, behavioral variability in ethanol sensitization confers differential neurochemical features during the subsequent abstinence, including distinct patterns of NPY expression.

Effect of Acetaldehyde Intoxication and Withdrawal on NPY Expression: Focus on Endocannabinoidergic System Involvement

Acetaldehyde (ACD), the first alcohol metabolite, plays a pivotal role in the rewarding, motivational, and addictive properties of the parental compound. Many studies have investigated the role of ACD in mediating neurochemical and behavioral effects induced by alcohol administration, but very little is known about the modulation of neuropeptide systems following ACD intoxication and withdrawal. Indeed, the neuropeptide Y (NPY) system is altered during alcohol withdrawal in key regions for cerebrocortical excitability and neuroplasticity. The primary goal of this research was to investigate the effects of ACD intoxication and withdrawal by recording rat behavior and by measuring NPY immunoreactivity in hippocampus and NAcc, two brain regions mainly involved in processes which encompass neuroplasticity in alcohol dependence. Furthermore, on the basis of the involvement of endocannabinoidergic system in alcohol and ACD reinforcing effects, the role of the selective CB1 receptor antagonist AM281 in modulating NPY expression during withdrawal was assessed. Our results indicate that (i) ACD intoxication induced a reduction in NPY expression in hippocampus and NAcc; (ii) symptoms of physical dependence, similar to alcohol's, were scored at 12 h from the last administration of ACD; and (iii) NPY levels increased in early and prolonged acute withdrawal in both brain regions examined. The administration of AM281 was able to blunt signs of ACD-induced physical dependence, to modulate NPY levels, and to further increase NPY expression during ACD withdrawal both in hippocampus and NAcc. In conclusion, the present study shows that complex plastic changes take place in NPY system during ACD intoxication and subsequent withdrawal in rat hippocampal formation and NAcc. The pharmacological inhibition of CB1 signaling could counteract the neurochemical imbalance associated with ACD, and alcohol withdrawal, likely boosting the setting up of homeostatic functional recovery.

Methamphetamine-induced changes in the mice hippocampal neuropeptide Y system: implications for memory impairment

Methamphetamine (METH) is a psychostimulant drug that causes irreversible brain damage leading to several neurological and psychiatric abnormalities, including cognitive deficits. Neuropeptide Y (NPY) is abundant in the mammalian central nervous system (CNS) and has several important functions, being involved in learning and memory processing. It has been demonstrated that METH induces significant alteration in mice striatal NPY, Y(1) and Y(2) receptor mRNA levels. However, the impact of this drug on the hippocampal NPY system and its consequences remain unknown. Thus, in this study, we investigated the effect of METH intoxication on mouse hippocampal NPY levels, NPY receptors function, and memory performance. Results show that METH increased NPY, Y(2) and Y(5) receptor mRNA levels, as well as total NPY binding accounted by opposite up- and down-regulation of Y(2) and Y(1) functional binding, respectively. Moreover, METH-induced impairment in memory performance and AKT/mammalian target of rapamycin pathway were both prevented by the Y(2) receptor antagonist, BIIE0246. These findings demonstrate that METH interferes with the hippocampal NPY system, which seems to be associated with memory failure. Overall, we concluded that Y(2) receptors are involved in memory deficits induced by METH intoxication.

Family of CNP neuropeptides: common morphology in various invertebrates

Neuropeptides expressed in the command neurons for withdrawal behavior were originally detected in the the central nervous system (CNS) of the terrestrial snail Helix (command neurons peptides, CNP). The family of CNP-like neuropeptides bears a C-terminal signature sequence Tyr-Pro-Arg-X. Using antisera against two of them, we have studied the CNS of various invertebrates belonging to the phyla of mollusks, annelids and insects. The immunoreactive neurons were detected in all studied species. Stained neurons were either interneurons projecting along the CNS ganglia chain, or sensory neurons, or neurohormonal cells. Beyond common morphological features, the immunoreactive cells had another similarity: the level of CNP expression depended on the functional state of the animal. Thus, the homologous neuropeptides in evolutionary distant invertebrate species possess some common morphological and functional features.

Gene expression in the neuropeptide Y system during ethanol withdrawal kindling in rats

BACKGROUND

Multiple episodes of ethanol intoxication and withdrawal result in progressive, irreversible intensification of the withdrawal reaction, a process termed "ethanol withdrawal kindling." Previous studies show that a single episode of chronic ethanol intoxication and withdrawal causes prominent changes in neuropeptide Y (NPY) and its receptors that have been implicated in regulating withdrawal hyperexcitability. This study for the first time examined the NPY system during ethanol withdrawal kindling.

METHODS

Ethanol withdrawal kindling was studied in rats receiving 16 episodes of 2 days of chronic ethanol intoxication by intragastric intubations followed by 5 days withdrawal. The study included 6 groups: 4 multiple withdrawal episode (MW) groups [peak withdrawal plus (MW+)/minus (MW-) seizures, 3-day (MW3d), and 1-month (MW1mth) withdrawal], a single withdrawal episode group (SW), and an isocalorically fed control group. Gene expression of NPY and its receptors Y1, Y2, and Y5 was studied in the hippocampal dentate gyrus (DG) and CA3/CA1, as well as piriform cortex (PirCx), and neocortex (NeoCx).

RESULTS

MW+/- as well as SW groups showed decreased NPY gene expression in all hippocampal areas compared with controls, but, in the DG and CA3, decreases were significantly smaller in the MW- group compared with the SW group. In the MW+/- and SW groups, Y1, Y2, and Y5 mRNA levels were decreased in most brain areas compared with controls; however, decreases in Y1 and Y5 mRNA were augmented in the MW+/- groups compared with the SW group. The MW+ group differed from the MW- group in the PirCx, where Y2 gene expression was significantly higher.

CONCLUSION

Multiple withdrawal episodes reversibly decreased NPY and NPY receptor mRNA levels at peak withdrawal, with smaller decreases in NPY mRNA levels and augmented decreases in Y1/Y5 mRNA levels compared with a SW episode. Multiple withdrawal-induced seizures increased the Y2 mRNA levels in PirCx. These complex changes in NPY system gene expression could play a role in the ethanol withdrawal kindling process.

Neuropeptide S receptor gene expression in alcohol withdrawal and protracted abstinence in postdependent rats

BACKGROUND

Alcoholism is a chronic disease characterized by frequent intoxications followed by withdrawal episodes and relapse to alcohol use. Neuroplastic changes associated with these intoxication and withdrawal cycles are thought to play a key role in disease progression. Recently, it has been shown that neuropeptide S (NPS), a newly deorphanized neuropeptide receptor system, facilitates relapse to alcohol seeking in laboratory animals. Given that a history of ethanol intoxication may increase vulnerability to alcohol addiction, we sought to determine whether NPS receptor (NPSR) gene expression is altered during withdrawal.

METHODS

Rats were subjected to 1 week of intoxication by oral alcohol administration. NPSR gene expression was analyzed by in situ hybridization in rats 12 hours and 7 days after the last alcohol administration. To investigate the functional significance of NPSR system adaptation following protracted withdrawal 7 days after intoxication, we tested the anxiolytic-like properties of NPS in nondependent and postdependent rats using the shock probe defensive burying test (DB).

RESULTS

At both time points, increased NPSR gene expression was observed in several brain areas, including the endopiriform nucleus, the motor cortex, and the medial amygdaloid nucleus. Moderate increases in gene expression were also found in the lateral hypothalamus, paraventricular nucleus, basolateral and central amygdala. Differences from control animals were more pronounced after 7 days of abstinence. The upregulation of the NPSR system at this time point was confirmed by functional data indicating that intracerebroventricular (ICV) NPS administration (0.0, 0.3, and 0.1 nmol/rat) elicits more pronounced anxiolytic effects in postdependent animals than in controls subjected to the electric shock probe DB test.

CONCLUSIONS

Neuropeptide S receptor mRNA expression is increased in different brain areas of postdependent rats; as shown in the DB test, this expression change is functionally relevant.