Response of nitrergic system in the brain of rat conditioned to intracranial self-stimulation.

The role of nitrergic system in modulating the action of psychostimulants on reward processing is well established. However, the relevant anatomical underpinnings and scope of the involved interactions with mesolimbic dopaminergic system have not been clarified. Using immunohistochemistry, we track the changes in neuronal nitric oxide synthase (nNOS) containing cell groups in the animals conditioned to intracranial self-stimulation (ICSS) via an electrode implanted in the lateral hypothalamus-medial forebrain bundle (LH-MFB) area. An increase in the nNOS immunoreactivity was noticed in the cells and fibers in the ventral tegmental area (VTA) and nucleus accumbens shell (AcbSh), the primary loci of the reward system. In addition, nNOS was up-regulated in the nucleus accumbens core (AcbC), vertical limb of diagonal band (VDB), locus coeruleus (LC), lateral hypothalamus (LH), superficial gray layer (SuG) of the superior colliculus, and periaqueductal gray (PAG). The brain tissue fragments drawn from these areas showed a change in nNOS mRNA expression, but in opposite direction. Intracerebroventricular (icv) administration of nNOS inhibitor, 7-nitroindazole (7-NI) showed decreased lever press activity in a dose-dependent manner in ICSS task. While an increase in the dopamine (DA) and 3, 4-dihydroxyphenylacetic acid (DOPAC) efflux was noted in the microdialysates collected from the AcbSh of ICSS rats, pre-administration of 7-NI (icv route) attenuated the response. The study identifies nitrergic centers that probably mediate sensory, cognitive, and motor components of the goal-directed behavior.

Neuropeptide Y system in accumbens shell mediates ethanol self-administration in posterior ventral tegmental area.

Although modulatory effects of neuropeptide Y (NPY) on ethanol consumption are well established, its role in ethanol reward, in the framework of mesolimbic dopaminergic system, has not been studied. We investigated the influence of nucleus accumbens shell (AcbSh) NPYergic system on ethanol self-administration in posterior ventral tegmental area (p-VTA) using intracranial self-administration paradigm. Rats were stereotaxically implanted with cannulae targeted unilaterally at the right p-VTA and trained to self-administer ethanol (200 mg%) in standard two-lever (active/inactive) operant chamber, an animal model with high predictive validity to test the rewarding mechanisms. Over a period of 7 days, these rats showed a significant increase in the number of lever presses for ethanol self-administration suggesting reinforcement. While intra-AcbSh NPY (1 or 2 ng/rat) or [Leu(31) , Pro(34) ]-NPY (0.5 or 1 ng/rat) dose-dependently increased ethanol self-administration, BIBP3226 (0.4 or 0.8 ng/rat) produced opposite effect. The rats conditioned to self-administer ethanol showed significant increase in the population of NPY-immunoreactive cells and fibres in the AcbSh, central nucleus of amygdala (CeA), hypothalamic arcuate nucleus (ARC) and lateral part of bed nucleus of stria terminalis as compared with that in the naïve rats. Neuronal tracing studies showed that NPY innervations in the AcbSh may derive from the neurons of ARC and CeA. As NPY and dopamine systems in reward areas are known to interact, we suggest that NPY inputs from ARC and CeA may play an important role in modulation of the dopaminergic system in the AcbSh and consequently influence the ethanol induced reward and addiction.

Chronic agmatine treatment prevents olanzapine-induced obesity and metabolic dysregulation in female rats.

Antipsychotic-induced obesity affects millions of people and is a serious health condition worldwide. Olanzapine is the most widely prescribed antipsychotic agent with high obesogenic potential. However, the exact mechanism by which it causes its metabolic dysregulation remains poorly understood. In this study, we investigated the effect of agmatine in olanzapine-induced metabolic derangements in Female Sprague-Dawley rats. Repeated olanzapine administration for 28 days increased body weight while treatment with agmatine from days 15 to 28 prevented the body weight gain induced by olanzapine without any alteration in food intake. Repeated agmatine treatment decreased the elevated feeding efficiency and adiposity index, as well as improved dysregulated lipid metabolism induced by olanzapine. Increased activity of fatty acid synthase (FAS) and decreased expression of carnitine palmitoyl transferase-1 (CPT-1) were detected in chronic olanzapine-treated rats. Although agmatine treatment did not alter FAS activity, it increased CPT-1 activity. It is possible that the inhibitory effect of agmatine on weight gain and adiposity might be associated with increased mitochondrial fatty acid oxidation and energy expenditure in olanzapine-treated rats. We suggest that agmatine can be explored for the prevention of obesity complications associated with chronic antipsychotic treatment.

Multimodal electrophysiological analyses reveal that reduced synaptic excitatory neurotransmission underlies seizures in a model of NMDAR antibody-mediated encephalitis.

Seizures are a prominent feature in N-Methyl-D-Aspartate receptor antibody (NMDAR antibody) encephalitis, a distinct neuro-immunological disorder in which specific human autoantibodies bind and crosslink the surface of NMDAR proteins thereby causing internalization and a state of NMDAR hypofunction. To further understand ictogenesis in this disorder, and to test a potential treatment compound, we developed an NMDAR antibody mediated rat seizure model that displays spontaneous epileptiform activity in vivo and in vitro. Using a combination of electrophysiological and dynamic causal modelling techniques we show that, contrary to expectation, reduction of synaptic excitatory, but not inhibitory, neurotransmission underlies the ictal events through alterations in the dynamical behaviour of microcircuits in brain tissue. Moreover, in vitro application of a neurosteroid, pregnenolone sulphate, that upregulates NMDARs, reduced established ictal activity. This proof-of-concept study highlights the complexity of circuit disturbances that may lead to seizures and the potential use of receptor-specific treatments in antibody-mediated seizures and epilepsy.

Encephalitis patient-derived monoclonal GABAA receptor antibodies cause epileptic seizures.

Autoantibodies targeting the GABAA receptor (GABAAR) hallmark an autoimmune encephalitis presenting with frequent seizures and psychomotor abnormalities. Their pathogenic role is still not well-defined, given the common overlap with further autoantibodies and the lack of patient-derived mAbs. Five GABAAR mAbs from cerebrospinal fluid cells bound to various epitopes involving the α1 and γ2 receptor subunits, with variable binding strength and partial competition. mAbs selectively reduced GABAergic currents in neuronal cultures without causing receptor internalization. Cerebroventricular infusion of GABAAR mAbs and Fab fragments into rodents induced a severe phenotype with seizures and increased mortality, reminiscent of encephalitis patients' symptoms. Our results demonstrate direct pathogenicity of autoantibodies on GABAARs independent of Fc-mediated effector functions and provide an animal model for GABAAR encephalitis. They further provide the scientific rationale for clinical treatments using antibody depletion and can serve as tools for the development of antibody-selective immunotherapies.

Nicotine-induced Brain Stimulation Reward is Modulated by Melanocortin-4 Receptors in Ovariectomized Rats.

Apart from reproduction, estrogen influences a multitude of processes. Increase in estrogen levels in women is known to promote reward probably mediated via the melanocortin and dopamine systems. Reduced estrogen in post-menopausal women attenuates reward, evoking the need for stimulation with greater rewarding salience. This is reflected in the well-recognized phenomena of difficulty in quitting and increased craving for nicotine in women following the onset of menopause. The present study aims at understanding the role of melanocortin receptors (MC-R) in nicotine-induced reward behavior following ovariectomy in rats. The MC4-R mRNA level was increased in ipsilateral nucleus accumbens (Acb) of the intact rats implanted with electrode in medial forebrain bundle and trained in intracranial self-stimulation (ICSS) paradigm. Additional groups of ICSS trained rats were ovariectomized (OVX) and subjected to reward evaluation. Trained OVX rats revealed a significant increase in threshold frequency and rightward shift in rate frequency curve, suggesting reward deficit behavior. However, pre-administration with nicotine, alpha-melanocyte stimulating hormone (α-MSH) or NDP-MSH (MC4-R agonist) to OVX animals restored the rewarding activity in ICSS protocol; HS014 (MC4-R antagonist) suppressed the lever press activity. Prior treatment with sub-effective doses of α-MSH or NDP-MSH potentiated the reward effect of nicotine, but was attenuated by HS014. Alpha-MSH-immunoreactivity was decreased in the Acb shell, arcuate and paraventricular nucleus of hypothalamus, and ventral bed nucleus of stria terminalis in the OVX rats, while nicotine treatment restored the same. We suggest a role for the endogenous MC system, perhaps acting via MC4-R, in the nicotine-induced reward in OVX rats.

Central administration of selective melanocortin 4 receptor antagonist HS014 prevents morphine tolerance and withdrawal hyperalgesia.

Major problem involved in treatment of chronic pain with morphine is the development of tolerance and dependence. Previous studies have demonstrated the participation of melanocortin (MC) system in the development of tolerance to antinociceptive effect of morphine. However, the impact of supraspinal MC4 receptors (MC4 R) modulation on this phenomenon and morphine withdrawal hyperalgesia remained unexplored. We investigated the role of central MC4 R in acute, chronic effects and withdrawal reactions of morphine using tail flick test. Acute intracerebroventricular (icv) administration of morphine (2-20 microg/rat) exhibited antinociceptive activity, which was antagonized by subeffective dose of nonselective MC R agonist NDP-MSH (0.04 ng/rat, icv), and potentiated by subeffective dose of MC4 R antagonist HS014 (0.008 ng/rat, icv). Isobolographic analysis revealed antagonistic interaction between NDP-MSH and morphine, and additive interaction between HS014 and morphine combinations. While chronic icv infusion of morphine (20 ng/microl/h) via osmotic pump for 7 days developed tolerance to its antinociceptive effect, its discontinuation produced hyperalgesia. Co-administration of HS014 (0.008 ng/rat, icv) with chronic morphine not only delayed the development of tolerance but also prevented withdrawal hyperalgesia. Furthermore, acute treatment with HS014 (0.008 and 0.04 ng/rat, icv) dose dependently attenuated the withdrawal hyperalgesia. This suggests the involvement of central MC4 R in the mechanism of development of tolerance and dependence following chronic morphine administration. We speculate that targeting this receptor may be a novel strategy to improve the effectiveness of morphine in the treatment of chronic pain.

CART modulates the effects of levodopa in rat model of Parkinson's disease.

Parkinson's disease (PD) is an age-related disorder characterized by a progressive degeneration of dopaminergic neurons of substantia nigra (SN). The neuropeptide cocaine- and amphetamine-regulated transcript (CART) is known to closely interact with the dopamine system and regulate psychomotor activity. We screened the effectiveness of CART in reversing the symptoms of PD in a rat model. PD like condition was induced by administering 6-hydroxydopamine (6-OHDA) directly in the SN of the right side. Fifteen days later, intraperitoneal (IP) treatment with apomorphine hydrochloride to these rats, resulted in contralateral rotations in the rotation test chamber suggesting induction of PD-like symptoms. This action of apomorphine was significantly attenuated by intracerebroventricular (ICV) treatment with CART and potentiated by CART antibody. IP treatment with levodopa also produced contralateral rotation in PD induced rats, and showed anti-Parkinson-like action. Prior treatment with CART via ICV route potentiated the anti-Parkinsonian effects of levodopa, while CART antibody produced opposite effects. CART treatment per se, to PD induced rats produced ipsilateral rotations, suggesting that the peptide may promote the endogenous release of dopamine from intact neurons. While CART-immunoreactivity in arcuate nucleus, paraventricular nucleus, striatum, substantia nigra, ventral tegmental area and locus coeruleus was reduced in the PD induced rats, levodopa treatment restored the expression of CART-immunoreactivity in these nuclei. These results suggest that endogenous CART might closely interact with the dopamine containing SN-striatal pathway which is known to profoundly influence the motor system. The study underscores the importance of CART as a potential therapeutic agent in the treatment of PD.

CART in the brain of vertebrates: circuits, functions and evolution.

Cocaine- and amphetamine-regulated transcript peptide (CART) with its wide distribution in the brain of mammals has been the focus of considerable research in recent years. Last two decades have witnessed a steady rise in the information on the genes that encode this neuropeptide and regulation of its transcription and translation. CART is highly enriched in the hypothalamic nuclei and its relevance to energy homeostasis and neuroendocrine control has been understood in great details. However, the occurrence of this peptide in a range of diverse circuitries for sensory, motor, vegetative, limbic and higher cortical areas has been confounding. Evidence that CART peptide may have role in addiction, pain, reward, learning and memory, cognition, sleep, reproduction and development, modulation of behavior and regulation of autonomic nervous system are accumulating, but an integration has been missing. A steady stream of papers has been pointing at the therapeutic potentials of CART. The current review is an attempt at piecing together the fragments of available information, and seeks meaning out of the CART elements in their anatomical niche. We try to put together the CART containing neuronal circuitries that have been conclusively demonstrated as well as those which have been proposed, but need confirmation. With a view to finding out the evolutionary antecedents, we visit the CART systems in sub-mammalian vertebrates and seek the answer why the system is shaped the way it is. We enquire into the conservation of the CART system and appreciate its functional diversity across the phyla.

A simple and economical method of electrode fabrication for brain self-stimulation in rats.

INTRODUCTION: Intracranial self-stimulation (ICSS) is an operant paradigm in which rodents self-administer rewarding electrical stimulation through electrodes implanted into the brain. We describe a simple, inexpensive and reliable method to fabricate monopolar and bipolar electrodes, along with the swivel system, for delivery of electric pulses at the targeted sites in the brain of rat. METHODS: The system consists of an insulated stainless steel wire(s) (diameter: 0.25 mm), plastic base, pedestal and connector attached to a swivel via a stimulating cable, which is connected to the stimulator. We provide the specifications, source of each component, and the method of fabrication in details. RESULTS: In-house fabricated monopolar or bipolar electrodes were subjected to rigorous tests. We implanted the electrode into the medial forebrain bundle (MFB) and rat was trained to press the lever for electrical self-stimulation in operant chamber for 60 min each day. In about 3-4 days, the animal gave a consistent response (~40 presses/min) and was considered as conditioned. For evaluation of reinforcement behavior, the number of lever pressings of conditioned rat with or without electrical stimulation was assessed for a period of 30 min each day for 10 weeks. The rewarding frequency sustained for the entire duration. In addition, we compared the lever pressing data of the groups of rats implanted with in-house fabricated versus with those with commercial electrodes; no significant differences were encountered. DISCUSSION: The required components for the electrode fabrication are easily available. With some practice, the system can be easily assembled in the laboratory and costs less than a dollar. We suggest that the electrodes, fabricated using this method, may serve as an economical and reliable tool in neuropharmacological and neurobehavioral studies.

Cocaine- and amphetamine-regulated transcript peptide (CART) in the central nucleus of amygdala potentiates behavioral and hormonal responses of the rat exposed to its predator.

Since cocaine- and amphetamine-regulated transcript peptide (CART) regulates anxiety and stress in amygdala, we hypothesized that the peptide may also process negative psychological experience like fear. During acute exposure to a cat, the rat showed freezing behavior and subsequently, profound signs of anxiety in social interaction test, and elevated serum cortisol concentration. While these behavioral effects were potentiated by the intracerebroventricular (icv) and intra-central nucleus of amygdala (intra-CeA) administration of CART peptide, they were blocked by CART antibody. On the other hand, chronic exposure for 7 days resulted in a steady reduction in freezing, increase in social interaction index and restored cortisol levels. In these rats, the behavior resembled with that of the time matched control rats suggesting habituation. However, CART peptide treatment, via the icv or intra-CeA route, chronically for 7 days, prevented habituation; significant freezing behavior and anxiety were noticed in these rats. The results suggest that CART peptide, in the framework of CeA, may process predator triggered innate fear in acute time scale, while chronic exposure might down-regulate the system and produce habituation.

NPY mediates reward activity of morphine, via NPY Y1 receptors, in the nucleus accumbens shell.

Although the interaction between endogenous neuropeptide Y (NPY) and opioidergic systems in processing of reward has been speculated, experimental evidence is lacking. We investigated the role of NPY, and its Y1 receptors, in the nucleus accumbens shell (AcbSh) in morphine induced reward and reinforcement behavior. Rats were implanted with cannulae targeted at AcbSh for drug administration, and with stimulating electrode in the medial forebrain bundle (MFB). The rats were then conditioned in an operant conditioning chamber for electrical self-stimulation of the MFB. Increased rate of lever pressings was evaluated against the frequency of the stimulating current. Increase in rate of lever presses was considered as a measure of reward and reinforcement. About 30-70% increase in self-stimulation was observed following bilateral intra-AcbSh treatment with morphine, NPY or [Leu(31), Pro(34)]-NPY (NPY Y1/Y5 receptors agonist), however, BIBP3226 (selective NPY Y1 receptors antagonist) produced opposite effect. The reward effect of morphine was significantly potentiated by NPY or [Leu(31), Pro(34)]-NPY, but antagonized by BIBP3226. NPY-immunoreactivity in the AcbSh, arcuate nucleus (ARC) and lateral part of bed nucleus of stria terminalis (BNSTl) was significantly more in the operant conditioned rats than in naïve control. However, morphine administration to the conditioned rats resulted in significant decrease in the NPY-immunoreactivity in all these anatomical regions. Since the role of morphine in modulation of mesolimbic-dopaminergic pathway is well established, we suggest that NPY system in AcbSh, ARC and BNSTl, perhaps acting via Y1-receptor system, may be an important component of the mesolimbic-AcbSh reward circuitry triggered by endogenous opioids.

Neuroprotective effect of cocaine- and amphetamine-regulated transcript peptide in spinal cord injury in mice.

We explored the effect of cocaine- and amphetamine-regulated transcript peptide (CART), alone and in combination with methylprednisolone (MP), on the cellular pathology and locomotor recovery of mice following spinal cord injury (SCI). While cellular pathology was evaluated in terms of spinal cord histology and profile of astrocytes following immunolabeling with antibodies against glial fibrillary acidic protein (GFAP), locomotor recovery was monitored using hindlimb motor function scoring system. At 24 h post-SCI, there was a massive loss of motor function and cysts formation in the spinal cord. The SCI mice, following 3 days and onwards, showed a significant (P < 0.001) increase in the population and hypertrophy of GFAP + astrocytes, suggesting the occurrence of reactive astrogliosis. Intra-fourth ventricular administration of CART (54-102) or intravenous treatment with MP, dose dependently improved motor function score, while CART-antibody (intra-fourth ventricular) was ineffective. This neuroprotective effect of MP was potentiated by the subeffective dose of CART and antagonized by CART-antibody. CART or MP treatment not only prevented the cysts formation, but also significantly attenuated the population of GFAP + astrocytes at days 3, 7, 14, 21 and 28 post-SCI and the hypertrophy of astrocytes at day 14 and 28. The histological consequence of SCI, like cysts formation in the spinal cord, was rapidly improved by CART and/or MP. Taken together, the data suggest that CART may exert its neuroprotective effect via inhibition of post-SCI astrogliosis and participate in the MP mediated neuroprotection.

Nicotine evoked improvement in learning and memory is mediated through NPY Y1 receptors in rat model of Alzheimer's disease.

We investigated the role of endogenous neuropeptide Y (NPY) system in nicotine-mediated improvement of learning and memory in rat model of Alzheimer's disease (AD). Intracerebroventricular (icv) colchicine treatment induced AD-like condition in rats and showed increased escape latency (decreased learning), and amnesic condition in probe test in Morris water maze. In these rats, nicotine (0.5mg/kg, intraperitoneal), NPY (100 ng/rat, icv) or NPY Y1 receptor agonist [Leu(31), Pro(34)]-NPY (0.04 ng/rat, icv) decreased escape latency by 54.76%, 55.81% and 44.18%, respectively, on day 4 of the acquisition. On the other hand, selective NPY Y1 receptor antagonist, BIBP3226 (icv) produced opposite effect (44.18%). In the probe test conducted at 24h time point, nicotine, NPY or [Leu(31), Pro(34)]-NPY increased the time spent by 72.72%, 44.11% and 26.47%, respectively; while BIBP3226 caused reduction (8.82%). It seems that while NPY or [Leu(31), Pro(34)]-NPY potentiated, BIBP3226 attenuated the learning and memory enhancing effects of nicotine. Brains of colchicine treated rats showed significant reduction in NPY-immunoreactivity in the nucleus accumbens shell (cells 62.23% and fibers 50%), bed nucleus of stria terminalis (fibers 71.58%), central nucleus of amygdala (cells 74.33%), arcuate nucleus (cells 70.97% and fibers 69.65%) and dentate gyrus (cells 58.54%). However, in these rats nicotine treatment for 4 days restored NPY-immunoreactivity to the control level. We suggest that NPY, perhaps acting via NPY Y1 receptors, might interact with the endogenous cholinergic system and play a role in improving the learning and memory processes in the rats with AD-like condition.

CART peptide in the nucleus accumbens shell acts downstream to dopamine and mediates the reward and reinforcement actions of morphine.

The opioid-mesolimbic-dopamine circuitry operates between ventral tegmental area (VTA) and nucleus accumbens (Acb) and serves as a major reward pathway. We hypothesized that the neuropeptide cocaine- and amphetamine-regulated transcript (CART) is involved in the natural reward action mediated by the circuitry. Therefore, the modulation of opioid-mesolimbic-dopamine reward circuitry by CART was investigated using pellet self-administration paradigm in operant chamber. Morphine administered bilaterally in shell region of Acb (AcbSh) significantly increased active lever pressings and pellet self-administration. While CART given bilaterally in the AcbSh significantly increased pellet self-administration, CART antibody produced no effect. Morphine induced pellet self-administration was potentiated by CART, and antagonized by CART antibody administered in AcbSh. A close interaction between dopamine and CART systems was observed. Several tyrosine hydroxylase (marker for dopamine) immunoreactive fibers were seen contacting CART neurons in the AcbSh. Intraperitoneal administration of pramipexole, a dopamine agonist, increased pellet self-administration. The effect was blocked by prior treatment with CART antibody targeted at AcbSh. CART-immunoreactive cells and fibers in the AcbSh, and cells but not fibers in hypothalamic paraventricular nucleus (PVN), were significantly increased in the animals trained in operant chamber. However, CART-immunoreactive profile in the medial forebrain bundle, VTA and arcuate nucleus of hypothalamus did not respond. We suggest that CART, released from the axonal terminals in the framework of AcbSh, may serve as the final output of the endogenous opioid-mesolimbic-dopamine circuitry that processes natural reward.

Effect of alpha-melanocyte stimulating hormone on locomotor recovery following spinal cord injury in mice: Role of serotonergic system.

The present study underscores the effect of serotonergic antagonist on alpha-melanocyte stimulating hormone (α-MSH) induced neuronal regeneration. Swiss-albino mice were subjected to experimental spinal cord injury (ESCI) and treated with serotonergic antagonist, ritanserin, alone or in combination with α-MSH, and the locomotor recovery was investigated. ESCI was induced at thoracic T(10-12) level by compression method. Motor function score (0-10) of each mouse was monitored prior to, and on days 1, 4, 7, 10 and 14 following ESCI. Untreated ESCI animals showed almost normal hind limb motor function by 14days. Similar degree of recovery was observed on day 10 in animals given α-MSH or ritanserin. However, in animals treated with both agents, comparable recovery was observed on day 4. While histological examination of the spinal cord following ESCI showed demyelination, necrosis and cyst formation, treatment with ritanserin, alone and in combination with α-MSH, significantly prevented the tissue damage. We suggest that early antagonism of serotonergic 5-HT(2a/2c) receptors may potentiate the neurotropic and locomotor recovery activity of α-MSH.

Cocaine- and amphetamine-regulated transcript peptide increases spatial learning and memory in rats.

AIM: We investigated the involvement of cocaine- and amphetamine-regulated transcript peptide (CART) in spatial learning and memory. MAIN METHODS: Rats were intracerebroventricularly injected with CART or CART-antibody, with or without intraperitoneal scopolamine, for a period of 4 days, during which they were subjected to the acquisition protocol in Morris water maze (MWM). In retrieval protocols, at 24 h and 15 days post-acquisition time points similar treatments were given to trained rats and subjected to MWM. The response of endogenous CART system to the training as well as retrieval sessions in MWM was evaluated with immunohistochemistry. KEY FINDINGS: CART-administered rats showed a significant reduction in escape latency from day 1 through 4 days of acquisition; the rats spent more time in the platform quadrant in MWM during the retrieval protocol. CART-antibody or scopolamine produced an opposite effect. The effects of scopolamine were attenuated by CART, and potentiated by CART-antibody. CART-immunoreactivity in the arcuate and paraventricular nuclei, central nucleus of amygdala, bed nucleus of stria terminalis, accumbens shell, dentate gyrus (DG), and thalamic paraventricular nucleus (PVT), but not in the cornu ammonis 1-3 of hippocampus, was significantly increased following 4 days of training, and at 24 h retrieval time point in MWM. The changes were blocked by scopolamine. At 15 days retrieval time point, the immunoreactivity profiles resembled those in naïve control. SIGNIFICANCE: While CART seems to promote spatial learning and memory, navigational experiences in MWM up regulates the endogenous CART systems in extended amygdala, hypothalamus, DG and PVT.

Evidence for the participation of cocaine- and amphetamine-regulated transcript peptide (CART) in the fluoxetine-induced anti-hyperalgesia in neuropathic rats.

Cocaine- and amphetamine-regulated transcript peptide (CART) has a role in chronic pain, and also in the actions of selective serotonin reuptake inhibitors (SSRIs) employed in the treatment of neuropathic pain. Herein, we test the hypothesis that CART may mediate the anti-hyperalgesic effect of the SSRI, fluoxetine, in neuropathic rats. Sciatic nerve in the right hind paw of rat was ligated to induce neuropathic pain, and the paw withdrawal latency was evaluated using Hargreaves apparatus. Fluoxetine [5-25mg/kg, intraperitoneal (ip)] or CART (54-102) [0.1-1.5µg/rat, intracerebroventricular (icv)] dose-dependently attenuated the hyperalgesic response observed in neuropathic rats, indicating anti-nociceptive properties of each agent. The anti-hyperalgesic effect of fluoxetine was potentiated by the subeffective dose of CART, and attenuated by CART-antibody (1:500 dilution; 5µl/rat, icv); CART-antibody had no effect per se. Isobolographic analysis showed a significant synergism between fluoxetine and CART, and antagonism between fluoxetine and CART-antibody. Immunocytochemical labeling with monoclonal antibodies against CART showed drastic increase in CART-immunoreactive fibers in the ventrolateral periaqueductal gray (VLPAG; 116%), dorsal subdivision of dorsal raphe nucleus (DRD; 176%), and locus coeruleus (LC; 733%) of neuropathic animals. Fluoxetine treatment significantly reduced the immunoreactivity in these areas. However, CART-immunoreactive cells and fibers in the arcuate nucleus did not respond to neuropathy or fluoxetine treatments. We suggest that the CART innervation of DRD, LC and VLPAG may be involved in the (i) central processing of neuropathic pain and (ii) fluoxetine-induced anti-hyperalgesic effect in neuropathic pain.

Neuropeptide Y Y1 receptors in the central nucleus of amygdala mediate the anxiolytic-like effect of allopregnanolone in mice: Behavioral and immunocytochemical evidences.

Since allopregnanolone (ALLO) elicits anxiolytic-like action and increases neuropeptide Y Y1 (NPY Y1) receptors gene expression in the amygdala, we were interested in studying the involvement of NPY Y1 receptors in the anxiolytic-like actions of ALLO. The anxiety-like behavior was evaluated in mice using Vogel's conflict test (VCT), in which number of shocks were measured. ALLO and NPYergic agents, alone or in combinations, were administered bilaterally into the central nucleus of amygdala (CeA). The intra-CeA administration of ALLO, NPY or NPY Y1/Y5 receptors agonist [Leu(31), Pro(34)]-NPY resulted in dose-dependent increase in the number of shocks in VCT, indicating anxiolytic-like effect. However, opposite effect was observed following administration of selective NPY Y1 receptors antagonist BIBP3226. While prior administration with NPY or [Leu(31), Pro(34)]-NPY, at the subeffective dose, potentiated the ALLO-induced anxiolytic-like effect, the same was antagonized by BIBP3226. Further, the effect of acute ALLO (30 mg/kg, intraperitoneal) on the endogenous NPY system in the CeA, ventral part of lateral division of bed nucleus of the stria terminalis (BSTLV), nucleus accumbens core (AcbC) and arcuate nucleus (ARC) was studied with immunocytochemistry. Acute ALLO treatment significantly decreased the population of NPY-immunoreactive cells in the CeA and also in the ARC. While NPY-immunoreactive fibers were slightly increased in the AcbC and BSTLV, the cells in AcbC and fibers in ARC did not respond. We suggest that NPY may mediate ALLO induced anxiolytic-like behavior in the neuroanatomical framework of the CeA, possibly via NPY Y1 receptors.

Neuropeptide Y modulates the antidepressant activity of imipramine in olfactory bulbectomized rats: involvement of NPY Y1 receptors.

Since long-term treatment with imipramine increases the neuropeptide Y (NPY) levels in the frontal cortex and hypothalamus, the possibility exists that the antidepressant action of imipramine may be mediated via the NPY Y1 receptors. Bilateral olfactory bulbectomy (OBX) resulted in hyperactivity (increased number of ambulation, rearing and grooming episodes) in open field test (OFT) suggesting a depression-like condition. Chronic (14 days) administration of NPY, NPY Y1/Y5 receptor agonist [Leu(31), Pro(34)]-NPY (intracerebroventricular, i.c.v.) or tricyclic antidepressant imipramine (intraperitoneal) to OBX rats dose-dependently resulted in decreased hyperactivity in OFT, while selective NPY Y1 receptor antagonist BIBP3226 (i.c.v.) produced opposite effects. The antidepressant actions of imipramine were enhanced by co-administration of NPY or [Leu(31), Pro(34)]-NPY, and antagonized by BIBP3226 given at sub-effective doses. The data suggest that NPY, acting via NPY Y1 receptors, may be involved in antidepressant action of imipramine in OBX rats.