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.

AMPA and NMDA receptors in dentate gyrus mediate memory for sucrose in two port discrimination task.

Although the phenomenon of memory formation and recall associated with the use of psychotropic drugs has been extensively studied, mechanisms underlying memories for natural reward have not been clarified. Herein, we test the hypothesis that glutamatergic receptors in the dentate gyrus play a role in memories associated with sucrose. We used pellet self-administration protocol to generate memories in two-port nose-poke discrimination task using male Wistar rats. During non-rewarded probe trial, the conditioned animals readily discriminated the active port versus inactive port and showed massive increase in mRNA expression of AMPA receptor subunit genes (gria2, gria3) as well as c-Fos protein in the DG. Access to sweet pellet further enhanced c-Fos expression in the DG. However, animals pre-treated with AMPA receptor antagonist CNQX (intra-DG), on exposure to operant chamber (no pellet), showed decreased discrimination as well as c-Fos expression. We suggest that AMPA receptors in DG mediate recall and consolidation of memories associated with sucrose consumption. CNQX pre-treated animals, if presented with sweet pellet on nose poke, exhibited high discrimination index coupled with increased c-Fos expression. In these CNQX treated rats, the DI was again decreased following administration of NMDA receptor antagonist AP5. We suggest that, although AMPA receptors are blocked, the access to sweet pellet may induce surge of glutamate in the DG, which in turn may reinstate memories via activation of erstwhile silent synapses in NMDA dependant manner.

Neuropeptide CART modulates dopamine turnover in the nucleus accumbens: Insights into the anatomy of rewarding circuits.

Neuropeptide cocaine- and amphetamine-regulated transcript (CART) is known to influence the activity of the canonical mesolimbic dopaminergic pathway and modulate reward seeking behaviour. CART neurons of the lateral hypothalamus (LH) send afferents to the ventral tegmental area (VTA) and paraventricular thalamic nucleus (PVT) and these nuclei, in turn, send secondary projections to nucleus accumbens. We try to dissect the precise sites of CART's action in these circuits in promoting reward. Rats were implanted with bipolar electrode targeted at the lateral hypothalamus-medial forebrain bundle (LH-MFB) and trained to press the lever through intracranial self-stimulation (ICSS) protocol. CART (55-102) administered directly into posterior VTA (pVTA) or PVT of the conditioned rats significantly increased the number of lever presses, indicating reward-promoting activity of the peptide. Concomitant increase in dopamine (DA) and 3, 4-dihydroxyphenylacetic acid (DOPAC) efflux was noted in the microdialysate collected from the nucleus accumbens shell (AcbSh). On the other hand, immunoneutralization of endogenous CART with CART antibodies injected directly in the pVTA or PVT reduced the lever press activity as well as DA and DOPAC efflux in the AcbSh. Injection of CART (1-39) in pVTA or PVT was ineffective. We suggest that CART cells in the LH-MFB area send afferents to (a) pVTA and influence dopaminergic neurons projecting to AcbSh and (b) PVT, from where the secondary neurons may feed into the AcbSh. Excitation of the CARTergic pathway to the pVTA as well as the PVT seems to promote DA release in the AcbSh and contribute to the generation of reward.

Neuropeptide CART prevents memory loss attributed to withdrawal of nicotine following chronic treatment in mice.

Although chronic nicotine administration does not affect memory, its withdrawal causes massive cognitive deficits. The underlying mechanisms, however, have not been understood. We test the role of cocaine- and amphetamine-regulated transcript peptide (CART), a neuropeptide known for its procognitive properties, in this process. The mice on chronic nicotine treatment/withdrawal were subjected to novel object recognition task. The capability of the animal to discriminate between the novel and familiar objects was tested and represented as discrimination index (DI); reduction in the index suggested amnesia. Nicotine for 49 days had no effect on DI, but 8-hour withdrawal caused a significant reduction, followed by full recovery at 24-hour withdrawal timepoint. Bilateral CART infusion in dorsal hippocampus rescued deficits in DI at 8-hours, whereas CART-antibody infusion into the dorsal hippocampus attenuated the recovery at 24-hours. Commensurate changes were observed in the CART as well as CART mRNA profiles in the hippocampus. CART mRNA expression and the peptide immunoreactivity did not change significantly following chronic nicotine treatment. However, there was a significant reduction at 8-hour withdrawal, followed by a drastic increase in CART immunoreactivity as well as CART mRNA at 24-hour withdrawal, compared with 8-hour withdrawal. Distinct α7-nicotinic receptor immunoreactivity was detected on the hippocampal CART neurons, suggesting cholinergic inputs. An increase in the synaptophysin immunoreactive elements around CART cells in the dentate gyrus, cornu ammonis 3 and subiculum at 24-hour post-withdrawal timepoint suggested neuronal plasticity. CART circuit dynamics in the hippocampus seems to modulate short-term memory associated with nicotine withdrawal.

Noradrenergic inputs from locus coeruleus to posterior ventral tegmental area are essential to support ethanol reinforcement.

Although dysregulation of the dopaminergic mesolimbic system is generally considered central to addiction, the involvement of other circuits is increasingly being appreciated. An interaction between locus coeruleus (LC) noradrenergic neurons and the posterior ventral tegmental area (pVTA) dopaminergic system, in the processing of drug-triggered reward, has been suggested, but not demonstrated in behaving animals. Herein, we try to tease out the precise role of noradrenergic neurons in the LC-VTA circuit in mediating reward and reinforcement behavior associated with ethanol. In the standard two-lever (active/inactive) operant paradigm, the rats were trained to self-administer ethanol in pVTA and subjected to pharmacological intervention. Intra-pVTA administration of phenylephrine (alpha-1 adrenoceptor agonist) increased ethanol self-administration, while prazosin and disulfiram (agents that reduce noradrenergic tone) produced opposite effects. While degeneration [N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine hydrochloride, DSP-4, intraperitoneal route] or silencing (lidocaine or muscimol, both via intra-LC route) of the LC noradrenergic neurons decreased, phenylephrine via the intra-LC route reinstated ethanol self-administration. Furthermore, lidocaine reduced ethanol self-administration, but the effect was fully attenuated by noradrenaline given directly in the pVTA. This suggests that the feedback signals from LC to pVTA are necessary to sustain the ethanol self-infusion activity. Ethanol self-administration significantly increased tyrosine hydroxylase immunoreactivity in pVTA and LC; the response was blocked by DSP-4 pre-treatment. While dopamine D1 , but not D2 , receptors were localized on noradrenergic LC neurons, pre-treatment with SCH-23390 (intra-LC) dampened the lever press activity. We suggest that two-way communications between VTA and LC regions is essential for ethanol-triggered reinforcement behavior.

Pro-cognitive action of CART is mediated via ERK in the hippocampus.

Although cocaine- and amphetamine-regulated transcript peptide (CART) is detected in several cortical and subcortical areas, its role in higher functions has been largely ignored. We examined the significance of CART in memory formation and tested if the downstream actions of CART involve N-methyl-d-aspartate (NMDA) activated extra-cellular signal-regulated kinase (ERK). Newly formed memory was evaluated using novel object recognition test consisting of familiarization (T1) and choice trials (T2). The choice trials were performed at two time points: 30-min (T230-min ) and 24-h (T224-h ) postacquisition. In choice trial (T230-min ), vehicle control rats explored the novel object for significantly longer duration than the familiar object indicating intact memory formation. However, CART-antibody, U0126 [ERK antagonist, both via intracerebroventricular (icv) or intrahippocampal (ih) route] or MK-801 (NMDA antagonist; intraperitoneal) treated rats spent less time exploring novel objects; CART peptide (icv or ih) was ineffective. During choice trial at T224-h , a significant decrease in novel object exploration time was noticed in vehicle control rats suggesting amnesia. However, treatment with CART, prior to familiarization trial (T1), promoted exploration of the novel object even at T224-h . Pretreatment with U0126 or MK-801 blocked pro-cognitive-like effect of CART suggesting involvement of NMDA-ERK pathway in CART's action. Animals subjected to the object familiarization trial showed a drastic increase in the CART-immunoreactivity in the cells of cornu ammonis 3 and polymorph layer of dentate gyrus, and fibers within ento- (ENT) and peri-rhinal (PRH) cortices. Western blot analysis revealed that CART treatment significantly up-regulated the expression of phospo-ERK1/2 in hippocampus, ENT and PRH. This effect was attenuated following pretreatment with U0126 or MK-801, suggesting the activation of ERK signaling cascade through NMDA receptors. Thus, CART system seems to play an important role in recognition memory and that these effects may be mediated by NMDA receptors-ERK signaling in the ENT/PRH-hippocampal circuit. © 2016 Wiley Periodicals, Inc.

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.

Alpha-melanocyte stimulating hormone modulates ethanol self-administration in posterior ventral tegmental area through melanocortin-4 receptors.

Although the role of alpha-melanocyte stimulating hormone (α-MSH) in alcohol seeking behaviour in rats has been demonstrated, the underlying mechanisms are not understood. Herein, we test the hypothesis that α-MSH might have a permissive effect in promoting the reward action of ethanol. Rats were implanted with cannulae targeted at the posterior ventral tegmental area (pVTA), because the site is sensitive to reinforcing effects of ethanol. These rats were trained to self-administer ethanol in standard two-lever (active/inactive) operant chamber test. Each active lever press resulted in self-administration of 100 nl of ethanol (100-300 mg%) containing solution. Over a period of 7 days, ethanol significantly increased the number of lever presses, which was considered as a measure of reward. Because ethanol at 200 mg% resulted in maximum number of lever presses (∼18-20 lever presses/30-minute session), the dose was employed in further studies. While prior administration of melanocortin (MC) agonists, α-MSH or [Nle4,D-Phe7]-alpha-MSH into pVTA, resulted in an 89% increase in lever presses, the response was attenuated following pre-treatment with MC4 receptors (MC4R) antagonist, HS014. In an immunohistochemical study, the brains of rats that were trained to self-infuse ethanol showed significantly increased α-MSH immunoreactivity in the nucleus accumbens shell, bed nucleus of stria terminalis and arcuate nucleus of the hypothalamus. In the pVTA, α-MSH fibres were found to run close to the dopamine cells, labelled with tyrosine hydroxylase antibodies. We suggest that α-MSH-MC4R system in the pVTA might be a part of the neuroadaptive mechanism underlying ethanol addiction.

Deep brain stimulation targeted at lateral hypothalamus-medial forebrain bundle reverses depressive-like symptoms and related cognitive deficits in rat: Role of serotoninergic system.

The aim of the study is to understand the rationale behind the application of deep brain stimulation (DBS) in the treatment of depression. Male Wistar rats, rendered depressive with chronic unpredictable mild stress (CUMS) were implanted with electrode in the lateral hypothalamus-medial forebrain bundle (LH-MFB) and subjected to deep brain stimulation (DBS) for 4 h each day for 14 days. DBS rats, as well as controls, were screened for a range of parameters indicative of depressive state. Symptomatic features noticed in CUMS rats like the memory deficit, anhedonia, reduction in body weight and 5-hydroxytryptamine (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) levels in mPFC and elevated plasma corticosterone were reversed in rats subjected to DBS. DBS arrested CUMS induced degeneration of 5-HT cells in interfascicular region of dorsal raphe nucleus (DRif) and fibers in LH-MFB and induced dendritic proliferation in mPFC neurons. MFB is known to serve as a major conduit for the DRif-mPFC serotoninergic pathway. While the density of serotonin fibers in the LH-MFB circuit was reduced in CUMS, it was upregulated in DBS-treated rats. Furthermore, microinjection of 5-HT1A receptor antagonist, WAY100635 into mPFC countered the positive effects of DBS like the antidepressant and memory-enhancing action. In this background, we suggest that DBS at LH-MFB may exercise positive effect in depressive rats via upregulation of the serotoninergic system. While these data drawn from the experiments on rat provide meaningful clues, we suggest that further studies aimed at understanding the usefulness of DBS at LH-MFB in humans may be rewarding.

CREB-Binding Protein Regulates Cocaine- and Amphetamine-Regulated Transcript Peptide Expression in the Lateral Hypothalamus: Implication in Reward and Reinforcement.

Neuropeptide cocaine- and amphetamine-regulated transcript peptide (CARTp) is known to play an important role in reward processing. The rats conditioned to intra-cranial self-stimulation (ICSS) showed massive upregulation of CART protein and mRNA in the vicinity of the electrode implanted to deliver the electric current directly at the lateral hypothalamus (LH)-medial forebrain bundle (MFB) area. However, the underlying mechanisms leading to the upregulation of CART in ICSS animals remain elusive. We tested the putative role of CREB-binding protein (CBP), an epigenetic enzyme with intrinsic histone acetyltransferase (HAT) activity, in regulating CART expression during ICSS. An electrode was implanted in LH-MFB and the rats were conditioned to self-stimulation in an operant chamber. CBP siRNA was delivered ipsilaterally in the LH-MFB to knock-down CBP and the effects on lever press activity were monitored. While ICSS-conditioned rats showed distinct increase in CART, CBP and pCREB levels, enhanced CBP binding and histone acetylation (H3K9ac) were noticed on the CART promoter in chromatin immunoprecipitation assay. Direct infusion of CBP siRNA in the LH-MFB lowered lever press activity, CBP levels, histone acetylation at the CART promoter, and CART mRNA and peptide expression. Co-infusion of CARTp in LH-MFB rescued the waning effects of CBP siRNA on self-stimulation. We suggest that CBP-mediated histone acetylation may play a causal role in CART expression in LH, which in turn may drive the positive reinforcement of lever press activity.

In-house fabrication of bipolar electrode-cannula assembly for electrical stimulation and drug delivery at the same site in rat brain.

Strategies drawn at understanding the functional attributes of specific neural circuits often necessitate electrical stimulation and pharmacological manipulation at the same anatomical site. We describe a simple, inexpensive and reliable method to fabricate a bipolar electrode-cannula assembly for delivery of electric pulses and administration of neuroactive agents at the same site in the rat brain. The assembly consisting of a guide cannula, dummy cannula, internal cannula and bipolar electrode was fabricated using syringe needles, wires and simple electronic components. To test the usefulness of the device, it was implanted on the skull of a rat specifically targeting the posterior ventral tegmental area (pVTA). The rat was conditioned to press the lever in intracranial self-stimulation (ICSS) protocol in an operant chamber. The number of lever presses in a 30 min task was monitored. Intra-pVTA administration with bicuculline (GABAA receptor antagonist) increased the lever press activity, while muscimol (GABAA receptor agonist) had opposite effect. The results confirm that the group of neurons responding to the electrical stimulation probably receive GABAergic inputs. The device is light in weight, costs less than a dollar and can be fabricated from readily available components. It can serve a useful purpose in electrically stimulating any given target in the brain - before, during or after pharmacological manipulation at the same locus and may find application in neuropharmacological and neurobehavioral studies.

Neuropeptide S facilitates extinction of fear via modulation of mesolimbic dopaminergic circuitry.

The inability to extinguish learned fear is a hallmark of trauma- and stress-related disorders. A form of inhibitory learning called fear extinction is an effective way to treat these disorders. However, the neurobiology of fear extinction has not been clarified. The involvement of a dopaminergic pathway from the ventral tegmental area (VTA) to the nucleus accumbens shell (AcbSh) in fear extinction has been suggested. Several neuropeptide systems, including neuropeptide S (NPS), modulate the activity of VTA dopaminergic neurons. Herein, we investigated the role of NPS in modulating the VTA-AcbSh circuit in fear extinction. While the NPS-containing neurons of the pericoerulear (periLC) area project to the VTA, the recipient cells are equipped with NPS receptors. Using a Pavlovian fear conditioning procedure, we tested the effect of NPS on fear extinction in male Wistar rats. Intra-VTA administration of NPS prior to fear extinction training facilitated the fear extinction learning and memory, however, NPS receptors antagonist had the opposite effect. Fear extinction training increased the dopamine efflux and cFOS immunoreactivity in the AcbSh area of NPS-treated rats compared with the vehicle-injected controls. We suggest that the NPS neurons of the periLC project to the VTA and might facilitate fear extinction by enhancing the activity of mesolimbic dopaminergic circuit.

TET1-induced DNA demethylation in dentate gyrus is important for reward conditioning and reinforcement.

Neuroadaptations in neurocircuitry of reward memories govern the persistent and compulsive behaviors. The study of the role of hippocampus in processing of reward memory and its retrieval is critical to our understanding of addiction and relapse. The aim of this study is to probe the epigenetic mechanisms underlying reward memory in the frame of dentate gyrus (DG). To that end, the rats conditioned to the food baited arm of a Y-maze and subjected to memory probe trial. The hippocampus of conditioned rats displayed higher mRNA levels of Ten-eleven translocase 1 (Tet1) and brain-derived neurotrophic factor (Bdnf) after memory probe trial. The DNA hydroxymethylation and TET1 occupancy at the Bdnf promoters showed concomitant increase. Stereotactic administration of Tet1 siRNA in the DG before and after conditioning inhibited reward memory formation and recall, respectively. Administration of Tet1 siRNA impaired the reward memory recall that was reinstated following administration of exogenous BDNF peptide or after wash-off period of 8 days. Infusion of a MEK/ERK inhibitor, U0126 in the DG inhibited reward memory retrieval. The TET1-induced DNA demethylation at the Bdnf promoters raised BDNF levels in the hippocampus, thereby setting the stage for reward memory retrieval. The study underscores the causative role of TET1 in the DG for reward memory formation and recall.

Neuroplastic Changes in the Superior Colliculus and Hippocampus in Self-rewarding Paradigm: Importance of Visual Cues.

Coincident excitation via different sensory modalities encoding objects of positive salience is known to facilitate learning and memory. With a view to dissect the contribution of visual cues in inducing adaptive neural changes, we monitored the lever press activity of a rat conditioned to self-administer sweet food pellets in the presence/absence of light cues. Application of light cues facilitated learning and consolidation of long-term memory. The superior colliculus (SC) of rats trained on light cue showed increased neuronal activity, dendritic branching, and brain-derived neurotrophic factor (BDNF) protein and mRNA expression. Concomitantly, the hippocampus showed augmented neurogenesis as well as BDNF protein and mRNA expression. While intra-SC administration of U0126 (inhibitor of ERK 1/2 and long-term memory) impaired memory formation, lidocaine (local anaesthetic) hindered memory recall. The light cue-dependent sweet food pellet self-administration was coupled with increased efflux of dopamine (DA) and 3,4-dihydroxyphenylacetic acid (DOPAC) in the nucleus accumbens shell (AcbSh). In conditioned rats, pharmacological inhibition of glutamatergic signalling in dentate gyrus (DG) reduced lever press activity, as well as DA and DOPAC secretion in the AcbSh. We suggest that the neuroplastic changes in the SC and hippocampus might represent memory engrams sculpted by visual cues encoding reward information.

LSD1-BDNF activity in lateral hypothalamus-medial forebrain bundle area is essential for reward seeking behavior.

Reward induces activity-dependant gene expression and synaptic plasticity-related changes. Lysine-specific histone demethylase 1 (LSD1), a key enzyme driving histone modifications, regulates transcription in neural circuits of memory and emotional behavior. Herein, we focus on the role of LSD1 in modulating the expression of brain derived neurotrophic factor (BDNF), the master regulator of synaptic plasticity, in the lateral hypothalamus-medial forebrain bundle (LH-MFB) circuit during positive reinforcement. Rats, trained for intracranial self-stimulation (ICSS) via an electrode-cannula assembly in the LH-MFB area, were assayed for lever press activity, epigenetic parameters and dendritic sprouting. LSD1 expression and markers of synaptic plasticity like BDNF and dendritic arborization in the LH, showed distinct increase in conditioned animals. H3K4me2 levels at Bdnf IV and Bdnf IX promoters were increased in ICSS-conditioned rats, but H3K9me2 was decreased. While intra LH-MFB treatment with pan Lsd1 siRNA inhibited lever press activity, analyses of LH tissue showed reduction in BDNF expression and levels of H3K4me2 and H3K9me2. However, co-administration of BDNF peptide restored lever press activity mitigated by Lsd1 siRNA. BDNF expression in LH, driven by LSD1 via histone demethylation, may play an important role in reshaping the reward pathway and hold the key to decode the molecular basis of addiction.

Intracellular mechanisms and behavioral changes in mouse model of attention deficit hyperactivity disorder: Importance of age-specific NMDA receptor blockade.

Exposure of NMDA receptor antagonists during developmental stages leads to behavioral consequences like attention deficit hyperactivity disorder (ADHD). However, the underlying molecular mechanisms have remained poorly understood. Herein, we studied the phosphorylated Akt (pAkt) and caspase-3, the key regulators of neuronal cell survival/death, as the probable downstream targets of MK-801 often used to engender ADHD-like condition. Swiss albino mice at postnatal days (PND) 7, 14 or 21 were injected with a single dose of MK-801 and evaluated for hyperactivity (open field test) and memory deficit at adolescence (PND 30) and adult stages (PND 60). PND 7 or 14 treatment groups (but not PND 21) consistently showed hyperactivity at the adolescence stage. A significant increase in working and reference memory errors in radial arm maze was noted at the adolescence age. PND 7 group continued to display the symptoms even in adulthood. All the treatment groups showed a significant decrease in the percent alterations (Y-maze) and discrimination index (novel object recognition test) at adolescence age. A significant increase in caspase-3 expression was noted in the prefrontal cortex (PFC) and hippocampus, whereas increased pAkt was noticed only in the hippocampus, following a single injection of MK-801 at PND 7. Concurrently, PND 7 treatment group showed significantly decreased neuronal nuclei (NeuN) expression (a marker for mature neurons) in the dentate gyrus, cornu ammonis-3 and PFC, but not in cornu ammonis-1, at adolescence age. We suggest that the observed symptoms of ADHD at adolescence and adulthood stages may be linked to alteration in pAkt and caspase-3 followed MK-801 treatment at PND 7.

Cocaine- and amphetamine-regulated transcript peptide promotes reward seeking behavior in socially isolated rats.

Reward deficit, expressed as anhedonia, is one of the major symptoms associated with neuropsychiatric disorders, but the underlying maladaptations have not been understood. Herein, we test the hypothesis that the neuropeptide cocaine- and amphetamine-regulated transcript (CART) may participate in the process. The study is justified since the peptide is a major player in inducing satiety and also processing of reward. The rats were socially isolated to induce reward deficit and conditioned to self-stimulate via an electrode in lateral hypothalamus (LH)-medial forebrain bundle (MFB) region. Compared to group-housed control rats, the socially isolated animals showed decreased lever press activity and elevated ICSS threshold indicating anhedonia-like condition. However, the effects of social isolation were alleviated by CART administered via intracerebroventricular route. The changes in the expression of CART protein and mRNA were screened using immunofluorescence and qRT-PCR methods, respectively. Socially isolated rats showed reduction in the expression of CART in the LH, nucleus accumbens shell (AcbSh) and posterior ventral tegmental area (pVTA) and CART mRNA in the Acb and LH. Double immunostaining with antibodies against CART and synaptophysin revealed significant loss of colabeled elements in LH, AcbSh and pVTA. We suggest that down-regulation of endogenous CARTergic system in the LH-pVTA-AcbSh reward circuitry may be causal to motivational anhedonia like phenotype seen in neuropsychiatric conditions.

Denial of food to the hungry rat: A novel paradigm for induction and evaluation of anger-like emotion.

BACKGROUND: Anger is one of the primary emotions that profoundly impacts our daily life. Although the neural basis of anger needs to be explored on high priority, the field has not sufficiently advanced, perhaps due to the lack of a suitable animal model. NEW METHOD: We fabricated arenas in which the hungry rat can see and smell food but can not consume it. These animals seemed hyperactive and we monitored the (a) motor activity to access food, (b) biting behaviour, (c) blood pressure, heart rate and nor-epinephrine (NE) in plasma, (d) 5-HT and its metabolite in CSF, (e) effect of diazepam, 5-HT agonist, and antagonist on the behaviour, and (f) expression of immediate early gene in discrete areas of the brain. RESULTS: The fasted animal frantically tries to acquire food. It engages in intense biting of the separator plate; the behaviour was considered as an expression of anger-like emotion. These behaviours were attenuated following pre-treatment with diazepam, fluoxetine (both ip) or 5-HT1A receptor agonist (icv), but potentiated by 5-HT1A antagonist (icv). Concomitantly, an increase in the blood pressure, heart rate and NE in plasma, but a decrease in 5-HT and 5-HIAA in the CSF was noted. The animals showed activation of neuronal c-Fos in different brain areas compared to fasted or refed controls. COMPARISON WITH EXISTING METHODS: A novel animal paradigm for assessment of anger. CONCLUSIONS: The protocol enables us to generate and evaluate anger-like responses in rat and permits insights into the neurological basis of anger.

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.

GABAA receptors in nucleus accumbens shell mediate the hyperphagia and weight gain following haloperidol treatment in rats.

AIMS: Weight gain is a common outcome of antipsychotics therapy in schizophrenic patients. However, the underlying neuronal mechanisms are unclear. The present study was undertaken to investigate the role of GABA(A) receptors within the framework of nucleus accumbens shell (AcbSh) in haloperidol-induced hyperphagia and body weight gain in sated rats. MAIN METHODS: In acute studies, GABA(A) receptor agonists muscimol, diazepam or antagonist bicuculline were administered by AcbSh route, alone or in combination with haloperidol (intraperitoneal/ip). Immediately after these treatments, preweighed food was offered to the animals at commencement of dark phase. Cumulative food intake was measured at 2 and 6 h post-injection time-points. Furthermore, effects of subacute haloperidol treatment, alone or in combination with muscimol, diazepam or bicuculline, on food intake and body weight were investigated. KEY FINDINGS: While acute treatment with haloperidol, muscimol or diazepam dose dependently stimulated the food intake, bicuculline suppressed the same. Prior administration of muscimol (20 ng/rat, intra-AcbSh) and diazepam (5 microg/rat, intra-AcbSh) significantly potentiated, whereas bicuculline (40 ng/rat, intra-AcbSh) negated the hyperphagic effect of acute haloperidol (0.005 or 0.01 mg/kg/rat, ip). Subacute administration of haloperidol (0.01 mg/kg/rat/day, ip) for 15 days produced increase in food intake and body weight. Although, concomitant administration of muscimol (20 ng/rat/day, intra-AcbSh) or diazepam (5 microg/rat/day, intra-AcbSh) markedly enhanced, bicuculline (40 ng/rat/day, intra-AcbSh) prevented the subacute haloperidol-induced hyperphagia and weight gain. SIGNIFICANCE: The results of present study suggest that increased food intake and body weight following haloperidol treatment in rats, may be mediated via AcbSh GABA(A) receptors.