Inhibitory effect of intrahippocampal NPY injection on amphetamine-induced behavioural activity

Effects of drugs of abuse on the central neuropeptide Y system

Neuropeptide Y (NPY), which is widely expressed in the central nervous system is involved in several neuropathologies including addiction. Here we comprehensively and systematically review alterations on the central NPY system induced by several drugs. We report on the effects of psychostimulants [cocaine, amphetamine, methamphetamine, 3,4-methylenedioxymethamphetamine (MDMA) and nicotine], ethanol, and opioids on NPY protein levels and expression of different NPY receptors. Overall, expression and function of NPY and its receptors are changed under conditions of drug exposure, thus affecting several physiologic behaviors, such as feeding, stress and anxiety. Drugs of abuse differentially affect the components of the NPY system. For example methamphetamine and nicotine lead to a consistent increase in NPY mRNA and protein levels in different brain sites whereas ethanol and opioids decrease NPY mRNA and protein expression. Drug-induced alterations on the different NPY receptors show more complex regulation pattern. Manipulation of the NPY system can have opposing effects on reinforcing and addictive properties of drugs of abuse. NPY can produce pro-addictive effects (nicotine and heroin), but can also exert inhibitory effects on addictive behavior (AMPH, ethanol). Furthermore, NPY can act as a neuroprotective agent in chronically methamphetamine and MDMA-treated rodents. In conclusion, manipulation of the NPY system seems to be a potential target to counteract neural alterations, addiction-related behaviors and cognitive deficits induced by these drugs.

The effect of intrahippocampal injection of group II and III metobotropic glutamate receptor agonists on anxiety; the role of neuropeptide Y

Earlier studies conducted by our group and by other authors indicated that metabotropic glutamatergic receptor (mGluR) ligands might have anxiolytic activity and that amygdalar neuropeptide Y (NPY) neurons were engaged in that effect. Apart from the amygdala, the hippocampus, another limbic structure, also seems to be engaged in regulation of anxiety. It is rich in mGluRs and contains numerous NPY interneurons. In the present study, we investigated the anxiolytic activity of group II and III mGluR agonists after injection into the hippocampus, and attempted to establish whether hippocampal NPY neurons and receptors were engaged in the observed effects. Male Wistar rats were bilaterally microinjected with the group II mGluR agonist (2S,1'S,2'S)-2-(carboxycyclopropyl)glycine (L-CCG-I), group III mGluR agonist O-Phospho-L-serine (L-SOP), NPY, the Y1 receptor antagonist BIBO 3304, and the Y2 receptor antagonist BIIE 0246 into the CA1 or dentate area (DG). The effect of those compounds on anxiety was tested in the elevated plus-maze. Moreover, the effects of L-CCG-I and L-SOP on the expression of NPYmRNA in the hippocampus were studied using in situ hybridization method. It was found that a significant anxiolytic effect was induced by L-SOP injection into the CA1 region or by L-CCG-I injection into the DG. The former effect was inhibited by BIBO 3304, the latter by BIIE 0246. NPY itself showed antianxiety action after injection into both structures. In the CA1 area, the effect of NPY was prevented by BIBO 3304, whereas in the DG by BIIE 0246. Both the mGluR agonists L-CCG-I and L-SOP induced a potent increase in NPYmRNA expression in the DG region of the hippocampal formation. The obtained results indicate that group II and III mGluR agonists, L-CCG-I and L-SOP, as well as NPY display anxiolytic activity in the hippocampus, but act differently in the CA1 and DG. It was observed that group III mGluRs and Y1 receptors were engaged in the response in the CA1 area, whereas group II mGluRs and Y2 receptors played a pivotal role in the DG region.

Differential roles for neuropeptide Y Y1 and Y5 receptors in anxiety and sedation

Central administration of neuropeptide Y (NPY) causes both anxiolysis and sedation. Previous studies suggest that both effects are mediated via NPY Y1 receptors. However, most of these studies were carried out before the advent of specific NPY receptor ligands. Therefore, a potential role for other NPY receptors in anxiety and sedation remains a possibility. In the present study, we addressed this issue by testing the effects of intracerebroventricular (i.c.v.) injection of NPY as well as specific receptor agonists for the Y1 receptor ([D-His(26)]NPY), Y2 receptor (C2-NPY), and Y5 receptor ([cPP(1-7),NPY(19-23),Ala(31),Aib(32),Gln(34)]hPP) in the elevated plus maze and open field tests. As with NPY, the Y1 agonist had a dose-dependent anxiolytic-like effect in both behavioral tests. In contrast to NPY, which caused significant sedation in the open field test, the Y1 agonist was without sedative effect. The Y2 agonist showed neither anxiolytic-like nor sedative effects. The Y5 agonist showed anxiolytic-like activity in both behavioral tests and caused sedation in the same dose range as NPY in the open field test. These results indicate that anxiolytic-like effects of i.c.v.-administered NPY in rats are mediated via both Y1 and Y5 receptors, whereas sedation is mediated via Y5 receptors.

Anticonvulsant and antiepileptogenic effects mediated by adeno-associated virus vector neuropeptide Y expression in the rat hippocampus

Neuropeptide Y (NPY) inhibits seizures in experimental models and reduces excitability in human epileptic tissue. We studied the effect of long-lasting NPY overexpression in the rat hippocampus with local application of recombinant adeno-associated viral (AAV) vectors on acute kainate seizures and kindling epileptogenesis. Transgene expression was significantly increased by 7 d, reached maximal expression by 2 weeks, and persisted for at least 3 months. Serotype 2 AAV vector increased NPY expression in hilar interneurons, whereas the chimeric serotype 1/2 vector caused far more widespread expression, also including mossy fibers, pyramidal cells, and the subiculum. EEG seizures induced by intrahippocampal kainate were reduced by 50-75%, depending on the vector serotype, and seizure onset was markedly delayed. In rats injected with the chimeric serotype 1/2 vector, status epilepticus was abolished, and kindling acquisition was significantly delayed. Thus, targeted NPY gene transfer provides a potential therapeutic principle for the treatment of drug-resistant partial epilepsies.

The “Yoking” of glutamatergic brain mechanisms involved in controlling brain neuronal excitability and psychosis to brain mechanisms involved in appetite regulation: a new hypothesis on the origin of psychosis

The authors speculate that the human primate evolved psychosis generating brain mechanisms in the service of certain feeding behaviors (i.e., appetite, foraging) during the course of evolution. Furthermore, these "psychosis generating brain mechanisms" may have grown directly out of brain mechanisms servicing appetite, of which neuropeptide Y (NPY) played an important role. A case is made for an NPY contribution to the pathophysiology of psychosis. We hypothesize that the psychomimetic effects of NPY extend to supporting certain "psychomotor" functions that might have been useful for obtaining food resources in "stressful environments" (potentially food resource rich/predator-competitor dangerous). The "psychomotor" functions proposed include helping the evolving ancestral human primate overcome behavioral inhibitions and fears related to venturing into "stressful environments" (potentially food resource rich/predator-competitor dangerous) after their home ranges had been stripped of resources, by providing feelings of decreased anxiety (anxiolysis), infatigability, and, perhaps, even grandiose delusions of physical ability and supernatural supports. We further speculate that it is this NPY mechanism that in part becomes dysregulated in idiopathic psychotic disorders such as schizophrenia. The NPY connection with psychosis could theoretically account for the possible associations between weight changes and antipsychotic response (e.g. [Acta Psychiatr. Scand. 100 (1999) 3] reported by others and body mass index and cocaine-induced psychosis by our group (i.e. [Israel J. Psychiatr. (2004), in submission]).

Neuropeptide Y administration into the amygdala does not affect ethanol consumption

Evidence seems to indicate that the anxiolytic effects of centrally administered neuropeptide Y (NPY) are mediated by the central nucleus of the amygdala. Because findings seem to indicate that ethanol may be self-administered partially for its anxiolytic effects, it was hypothesized that NPY, microinjected into the central nucleus of the amygdala, would decrease ethanol intake. In this study, we examined the effects of NPY, administered into the central nucleus of the amygdala, on ethanol, sucrose, and food consumption, as well as the concomitant effects of NPY on cortical electroencephalographic activity. Wistar rats were implanted with cortical recording electrodes and cannulae above the central amygdaloid nuclei, after use of a sucrose-substitution procedure, to establish ethanol self-administration. Neuropeptide Y (0-250 pmol/0.5 micro l) was infused into the amygdala before drinking sessions, when 10% ethanol (10 E), 2% sucrose (2S), or food was available. Consumption, locomotor activity, and cortical electroencephalographic activity were then monitored concurrently. Neuropeptide Y had no effect on the intake of 10 E, 2S, or food, nor on the cortical electroencephalographic or locomotor activity. However, as reported previously, distinct changes in the electroencephalogram were associated with consumption of ethanol and sucrose. Cortical power in the 6-8 Hz frequency range was significantly increased during the beginning of the sucrose and ethanol sessions, with greater increases observed during the sucrose session. Overall, these findings support the suggestion that NPY administration into the central nucleus of the amygdala does not alter consumption of 10 E, 2S, or food, nor the cortical electroencephalographic or locomotor activity.