A brainstem-hypothalamus neuronal circuit reduces feeding upon heat exposure.

Empirical evidence suggests that heat exposure reduces food intake. However, the neurocircuit architecture and the signalling mechanisms that form an associative interface between sensory and metabolic modalities remain unknown, despite primary thermoceptive neurons in the pontine parabrachial nucleus becoming well characterized1. Tanycytes are a specialized cell type along the wall of the third ventricle2 that bidirectionally transport hormones and signalling molecules between the brain's parenchyma and ventricular system3-8. Here we show that tanycytes are activated upon acute thermal challenge and are necessary to reduce food intake afterwards. Virus-mediated gene manipulation and circuit mapping showed that thermosensing glutamatergic neurons of the parabrachial nucleus innervate tanycytes either directly or through second-order hypothalamic neurons. Heat-dependent Fos expression in tanycytes suggested their ability to produce signalling molecules, including vascular endothelial growth factor A (VEGFA). Instead of discharging VEGFA into the cerebrospinal fluid for a systemic effect, VEGFA was released along the parenchymal processes of tanycytes in the arcuate nucleus. VEGFA then increased the spike threshold of Flt1-expressing dopamine and agouti-related peptide (Agrp)-containing neurons, thus priming net anorexigenic output. Indeed, both acute heat and the chemogenetic activation of glutamatergic parabrachial neurons at thermoneutrality reduced food intake for hours, in a manner that is sensitive to both Vegfa loss-of-function and blockage of vesicle-associated membrane protein 2 (VAMP2)-dependent exocytosis from tanycytes. Overall, we define a multimodal neurocircuit in which tanycytes link parabrachial sensory relay to the long-term enforcement of a metabolic code.

A neural pathway for social modulation of spontaneous locomotor activity (SoMo-SLA) in Drosophila.

Social enrichment or social isolation affects a range of innate behaviors, such as sex, aggression, and sleep, but whether there is a shared mechanism is not clear. Here, we report a neural mechanism underlying social modulation of spontaneous locomotor activity (SoMo-SLA), an internal-driven behavior indicative of internal states. We find that social enrichment specifically reduces spontaneous locomotor activity in male flies. We identify neuropeptides Diuretic hormone 44 (DH44) and Tachykinin (TK) to be up- and down-regulated by social enrichment and necessary for SoMo-SLA. We further demonstrate a sexually dimorphic neural circuit, in which the male-specific P1 neurons encoding internal states form positive feedback with interneurons coexpressing doublesex (dsx) and Tk to promote locomotion, while P1 neurons also form negative feedback with interneurons coexpressing dsx and DH44 to inhibit locomotion. These two opposing neuromodulatory recurrent circuits represent a potentially common mechanism that underlies the social regulation of multiple innate behaviors.

Release of Lipids Stored in the Intestine by Glucagon-Like Peptide-2 Involves a Gut-Brain Neural Pathway.

BACKGROUND: The gut hormone GLP-2 (glucagon-like peptide-2) plays important roles in lipid handling in the intestine. During postabsorptive stage, it releases preformed chylomicrons stored in the intestine, the underlying mechanisms of which are not well understood. Previous studies implicate the involvement of neural pathways in GLP-2's actions on lipid absorption in the intestine, but the role of such mechanisms in releasing postabsorptive lipid storage has not been established. METHODS: Here, in mesenteric lymph duct cannulated rats, we directly tested whether gut-brain neural communication mediates GLP-2's effects on postabsorptive lipid mobilization in the intestine. We performed total subdiaphragmatic vagotomy to disrupt the gut-brain neural communication and analyzed lipid output 5 hours after a lipid load in response to intraperitoneal GLP-2 or saline. RESULTS: Peripheral GLP-2 administration led to increased lymph lipid output and activation of proopiomelanocortin neurons in the arcuate nucleus of hypothalamus. Disruption of gut-brain neural communication via vagotomy blunted GLP-2's effects on promoting lipid release in the intestine. CONCLUSIONS: These results, for the first time, demonstrate a novel mechanism in which postabsorptive mobilization of intestinal lipid storage by GLP-2 enlists a gut-brain neural pathway.

Arkypallidal neurons in basal ganglia circuits: Unveiling novel pallidostriatal loops?

Just over a decade ago, a novel GABAergic input originating from a subpopulation of external globus pallidus neurons known as Arkypallidal and projecting exclusively to the striatum was unveiled. At the single-cell level, these pallidostriatal Arkypallidal projections represent one of the largest extrinsic sources of GABA known to innervate the dorsal striatum. This discovery has sparked new questions regarding their role in striatal information processing, the circuit that recruit these neurons, and their influence on behaviour, especially in the context of action selection vs. inhibition. In this review, we will present the different anatomo-functional organization of Arkypallidal neurons as compared to classic Prototypic neurons, including their unique molecular properties and what is known about their specific input/output synaptic organization. We will further describe recent findings that demonstrate one mode of action of Arkypallidal neurons, which is to convey feedback inhibition to the striatum, and how this mechanism is differentially modulated by both striatal projection pathways. Lastly, we will delve into speculations on their mechanistic contribution to striatal action execution or inhibition.

From single cells to neural circuits.

Neural circuits are mapped in high throughput with single-cell genomics.

A neural pathway underlying hunger modulation of sexual receptivity in Drosophila females.

Accepting or rejecting a mate is one of the most crucial decisions a female will make, especially when faced with food shortage. Previous studies have identified the core neural circuity from sensing male courtship or mating status to decision-making for sexual receptivity in Drosophila females, but how hunger and satiety states modulate female receptivity is poorly understood. Here, we identify the neural circuit and its neuromodulation underlying the hunger modulation of female receptivity. We find that adipokinetic hormone receptor (AkhR)-expressing neurons inhibit sexual receptivity in a starvation-dependent manner. AkhR neurons are octopaminergic and act on a subset of Octß1R-expressing LH421 neurons. Knocking down Octß1R expression in LH421 neurons eliminates starvation-induced suppression of female receptivity. We further find that LH421 neurons inhibit the sex-promoting pC1 neurons via GABA-resistant to dieldrin (Rdl) signaling. pC1 neurons also integrate courtship stimulation and mating status and thus serve as a common integrator of multiple internal and external cues for decision-making.

Neural pathway connectivity and discharge changes between M1 and STN in hemiparkinsonian rats.

Alterations of electrophysiological activities, such as changed spike firing rates, reshaping the firing patterns, and aberrant frequency oscillations between the subthalamic nucleus (STN) and the primary motor cortex (M1), are thought to contribute to motor impairment in Parkinson's disease (PD). However, the alterations of electrophysiological characteristics of STN and M1 in PD are still unclear, especially under specific treadmill movement. To examine the relationship between electrophysiological activity in the STN-M1 pathway, extracellular spike trains and local field potential (LFPs) of STN and M1 were simultaneously recorded during resting and movement in unilateral 6-hydroxydopamine (6-OHDA) lesioned rats. The results showed that the identified STN neurons and M1 neurons exhibited abnormal neuronal activity after dopamine loss. The dopamine depletion altered the LFP power in STN and M1 whatever in rest or movement states. Furthermore, the enhanced synchronization of LFP oscillations after dopamine loss was found in 12-35 Hz (beta frequencies) between the STN and M1 during rest and movement. In addition, STN neurons were phase-locked firing to M1 oscillations at 12-35 Hz during rest epochs in 6-OHDA lesioned rats. The dopamine depletion also impaired the anatomical connectivity between the M1 and STN by injecting anterograde neuroanatomical tracing virus into M1 in control and PD rats. Collectively, impairment of' electrophysiological activity and anatomical connectivity in the M1-STN pathway may be the basis for dysfunction of the cortico-basal ganglia circuit, correlating with motor symptoms of PD.

Multimodal mapping of cell types and projections in the central nucleus of the amygdala.

The central nucleus of the amygdala (CEA) is a brain region that integrates external and internal sensory information and executes innate and adaptive behaviors through distinct output pathways. Despite its complex functions, the diversity of molecularly defined neuronal types in the CEA and their contributions to major axonal projection targets have not been examined systematically. Here, we performed single-cell RNA-sequencing (scRNA-seq) to classify molecularly defined cell types in the CEA and identified marker genes to map the location of these neuronal types using expansion-assisted iterative fluorescence in situ hybridization (EASI-FISH). We developed new methods to integrate EASI-FISH with 5-plex retrograde axonal labeling to determine the spatial, morphological, and connectivity properties of ~30,000 molecularly defined CEA neurons. Our study revealed spatiomolecular organization of the CEA, with medial and lateral CEA associated with distinct molecularly defined cell families. We also found a long-range axon projection network from the CEA, where target regions receive inputs from multiple molecularly defined cell types. Axon collateralization was found primarily among projections to hindbrain targets, which are distinct from forebrain projections. This resource reports marker gene combinations for molecularly defined cell types and axon-projection types, which will be useful for selective interrogation of these neuronal populations to study their contributions to the diverse functions of the CEA.

Neural pathways from the central nucleus of the amygdala to the paraventricular nucleus of the hypothalamus are involved in induction of yawning behavior due to emotional stress in rats.

As yawning is often observed in stressful or emotional situations such as tension and anxiety, this suggests that yawning can be considered to be an emotional behavior. However, the neural mechanisms underlying emotion-induced yawning remain unclear. It is well known that the hypothalamic paraventricular nucleus (PVN) is the most important brain structure for induction of yawning behavior. We previously showed that induction of yawning involves the central nucleus of the amygdala (CeA), as well as the PVN. Therefore, emotion-induced yawning could potentially be induced through activation of the direct/indirect neural pathways from the CeA to the PVN. Our present study used a combination of retrograde tracing (injection of Fluoro-Gold (FG) into the PVN) and c-Fos immunohistochemistry to examine the neural pathways that evoke emotion-induced yawning. We additionally performed lesion experiments on the CeA using ibotenic acid, a neurotoxin, to determine whether the CeA is involved in the induction of emotion-induced yawning. Emotional stress by fear conditioning induced yawning behavior, and induced expression of double-labeled cells for c-Fos and FG in the bed nucleus of the stria terminalis (BNST), but not in the CeA. Furthermore, the CeA lesions caused by ibotenic acid abolished the induction of emotion-induced yawning. These results suggest that a neural pathway from the CeA to the PVN via the BNST may be primarily involved in the induction of emotion-induced yawning behavior.

Molecular characteristics and laminar distribution of prefrontal neurons projecting to the mesolimbic system.

Prefrontal cortical influence over the mesolimbic system - including the nucleus accumbens (NAc) and the ventral tegmental area (VTA) - is implicated in various cognitive processes and behavioral malfunctions. The functional versatility of this system could be explained by an underlying anatomical complexity; however, the detailed characterization of the medial prefrontal cortical (mPFC) innervation of the NAc and VTA is still lacking. Therefore, combining classical retrograde and conditional viral tracing techniques with multiple fluorescent immunohistochemistry, we sought to deliver a precise, cell- and layer-specific anatomical description of the cortico-mesolimbic pathways in mice. We demonstrated that NAc- (mPFCNAc) and VTA-projecting mPFC (mPFCVTA) populations show different laminar distribution (layers 2/3-5a and 5b-6, respectively) and express different molecular markers. Specifically, calbindin and Ntsr1 are specific to mPFCNAc neurons, while mPFCVTA neurons express high levels of Ctip2 and FoxP2, indicating that these populations are mostly separated at the cellular level. We directly tested this with double retrograde tracing and Canine adenovirus type 2-mediated viral labeling and found that there is indeed minimal overlap between the two populations. Furthermore, whole-brain analysis revealed that the projection pattern of these populations is also different throughout the brain. Taken together, we demonstrated that the NAc and the VTA are innervated by two, mostly nonoverlapping mPFC populations with different laminar distribution and molecular profile. These results can contribute to the advancement in our understanding of mesocorticolimbic functions and its disorders in future studies.

An oxytocinergic neural pathway that stimulates thermogenic and cardiac sympathetic outflow.

Oxytocin alters autonomic functions besides social behaviors. However, the central neuronal links between hypothalamic oxytocinergic neurons and the autonomic nervous system remain unclear. Here we show that oxytocinergic neurons in the rat paraventricular hypothalamic nucleus (PVH), a pivotal site for energy homeostasis, innervate sympathetic premotor neurons in the rostral medullary raphe region (rMR) to stimulate brown adipose tissue (BAT) thermogenesis and cardiovascular functions. Oxytocin receptor stimulation in the rMR evokes BAT thermogenesis and tachycardia. In vivo optogenetic stimulation of the PVH→rMR long-range oxytocinergic pathway, using a virus-mediated system for amplified gene expression in oxytocinergic neurons, not only elicits BAT thermogenic and cardiac responses but also potentiates sympathetic responses evoked by glutamatergic transmission in the rMR. The PVH→rMR oxytocinergic pathway connects the hypothalamic circuit for energy homeostasis to thermogenic and cardiac sympathetic outflow, and, therefore, its defects may cause obesity and impaired thermoregulation, as seen in Prader-Willi syndrome.

Electroacupuncture preconditioning alleviates myocardial ischemia-reperfusion injury through the hypothalamic paraventricular nucleus- interposed nucleus nerve pathway.

OBJECTIVE: To explore whether the paraventricular nucleus (PVN) participates in regulation of the anti-myocardial ischemia-reperfusion injury (MIRI) effect of electroacupuncture (EA) and whether this is achieved through the PVN-interposed nucleus (IN) neural pathway. METHODS: The modeling method of myocardial ischemia reperfusion injury was achieved by ligating the left anterior descending coronary artery in Sprague-Dawley rats. We used the Powerlab multi-channel physiological recorder system to record electro-cardiograms and analyze the changes in ST segment displacement; 2,3,5-Triphenyltetrazolium chloride staining was used to observe the percentage of myocardial infarction areas. Detecting cardiac troponin I (cTnI), lactate dehydrogenase (LDH) in serum was done with an enzyme-linked immunosorbent assay kit. Morphological changes in the myocardium were detected in each group with hematoxylin-eosin staining of paraffin sections. Detection of c-fos protein expression in the PVN of the hypothalamus was done with the immune-ofluorescence method. The Plexon multi-channel acquisition system recorded PVN neuron discharges and local field potentials in each group of rats. Offline Sorter software was used for cluster analysis. Neuro Explorer software was used to perform autocorrelation, raster and frequency characteristics and spectral energy analysis of neuron signals in each group. RESULTS: Compared with the MIRI model group, the areas of myocardial infarction in the EA group were significantly reduced; the expression of cTnI, LDH in serum was decreased significantly. The firing frequency of pyramidal cells in the PVN was significantly increased and the spectrum energy map showed energy was reduced, c-fos expression in PVN was reduced, this indicated that neuronal activity in the PVN participates in the effect of EA improving myocardial injury. In addition, we used the kainic acid method to lesion the IN and observed that the effect of EA was weakened. For example, the area of myocardial infarction of lesion IN + EA group in rats was significantly increased compared with that resulting from EA group, the expression of cTnI, LDH in serum was significantly increased, the firing frequency of pyramidal cells in the PVN was significantly reduced. A spectral energy diagram shows that the energy after damage was higher than that of EA group. At the same time, the expression of c-fos in the PVN increased again. CONCLUSION: Our results indicated that the PVN-IN nerve pathway may participate as an effective pathway of EA to improve the effect of myocardial injury.

The Spino-Parabrachial Pathway for Itch.

Itch-induced scratching is an evolutionarily conserved behavioral response that protects organisms from potential parasites/irritants in their immediate vicinity. How the exposure to a pruritogen is translated to the perception of itch and how that perception drives scratching directed towards the site of exposure remains poorly understood. In this review, we focus on the recent findings that shed light on the neural pathways in the brain that underlie itch-induced scratching. We compare the molecularly defined itch pathways with the known pain circuits as they have anatomical and functional overlap. We review the roles played by the neurons in the spinoparabrachial pathway-comprising of the neurons in the spinal cord and the parabrachial nucleus (PBN), which acts as a hub for transmitting itch information across the brain. Lastly, we deliberate on scratching as a behavioral measure of the intensity of itch and its implication in unraveling the underlying supraspinal mechanisms. In summary, we provide a resource on the recent advances and discuss a path forward on our understanding of the neural circuits for itch.

BRAIN 2.0: Transforming neuroscience.

The NIH BRAIN Initiative is entering a new phase. Three large new projects-a comprehensive human brain cell atlas, a whole mammalian brain microconnectivity map, and tools for precision access to brain cell types-promise to transform neuroscience research and the treatment of human brain disorders.

Interplay between nitric oxide and gonadotrophin-releasing hormone in the neuromodulation of the corpus luteum during late pregnancy in the rat.

BACKGROUND: Nitric oxide and GnRH are biological factors that participate in the regulation of reproductive functions. To our knowledge, there are no studies that link NO and GnRH in the sympathetic ganglia. Thus, the aim of the present work was to investigate the influence of NO on GnRH release from the coeliac ganglion and its effect on luteal regression at the end of pregnancy in the rat. METHODS: The ex vivo system composed by the coeliac ganglion, the superior ovarian nerve, and the ovary of rats on day 21 of pregnancy was incubated for 180 min with the addition, into the ganglionic compartment, of L-NG-nitro arginine methyl ester (L-NAME), a non-selective NO synthase inhibitor. The control group consisted in untreated organ systems. RESULTS: The addition of L-NAME in the coeliac ganglion compartment decreased NO as well as GnRH release from the coeliac ganglion. In the ovarian compartment, and with respect to the control group, we observed a reduced release of GnRH, NO, and noradrenaline, but an increased production of progesterone, estradiol, and expression of their limiting biosynthetic enzymes, 3ß-HSD and P450 aromatase, respectively. The inhibition of NO production by L-NAME in the coeliac ganglion compartment also reduced luteal apoptosis, lipid peroxidation, and nitrotyrosine, whereas it increased the total antioxidant capacity within the corpora lutea. CONCLUSION: Collectively, the results indicate that NO production by the coeliac ganglion modulates the physiology of the ovary and luteal regression during late pregnancy in rats.

Dissecting a disynaptic central amygdala-parasubthalamic nucleus neural circuit that mediates cholecystokinin-induced eating suppression.

OBJECTIVE: Cholecystokinin (CCK) plays a critical role in regulating eating and metabolism. Previous studies have mapped a multi-synapse neural pathway from the vagus nerve to the central nucleus of the amygdala (CEA) that mediates the anorexigenic effect of CCK. However, the neural circuit downstream of the CEA is still unknown due to the complexity of the neurons in the CEA. Here we sought to determine this circuit using a novel approach. METHODS: It has been established that a specific population of CEA neurons, marked by protein kinase C-delta (PKC-δ), mediates the anorexigenic effect of CCK by inhibiting other CEA inhibitory neurons. Taking advantage of this circuit, we dissected the neural circuit using a unique approach based on the idea that neurons downstream of the CEA should be disinhibited by CEAPKC-δ+ neurons while being activated by CCK. We also used optogenetic assisted electrophysiology circuit mapping and in vivo chemogenetic manipulation methods to determine the circuit structure and function. RESULTS: We found that neurons in the parasubthalamic nucleus (PSTh) are activated by the activation of CEAPKC-δ+ neurons and by the peripheral administration of CCK. We demonstrated that CEAPKC-δ+ neurons inhibit the PSTh-projecting CEA neurons; accordingly, the PSTh neurons can be disynaptically disinhibited or "activated" by CEAPKC-δ+ neurons. Finally, we showed that chemogenetic silencing of the PSTh neurons effectively attenuates the eating suppression induced by CCK. CONCLUSIONS: Our results identified a disynaptic CEA-PSTh neural circuit that mediates the anorexigenic effect of CCK and thus provide an important neural mechanism of how CCK suppresses eating.

Involvement of Denervated Midbrain-Derived Factors in the Formation of Ectopic Cortico-Mesencephalic Projection after Hemispherectomy.

Neuronal remodeling after brain injury is essential for functional recovery. After unilateral cortical lesion, axons from the intact cortex ectopically project to the denervated midbrain, but the molecular mechanisms remain largely unknown. To address this issue, we examined gene expression profiles in denervated and intact mouse midbrains after hemispherectomy at early developmental stages using mice of either sex, when ectopic contralateral projection occurs robustly. The analysis showed that various axon growth-related genes were upregulated in the denervated midbrain, and most of these genes are reportedly expressed by glial cells. To identify the underlying molecules, the receptors for candidate upregulated molecules were knocked out in layer 5 projection neurons in the intact cortex, using the CRISPR/Cas9-mediated method, and axonal projection from the knocked-out cortical neurons was examined after hemispherectomy. We found that the ectopic projection was significantly reduced when integrin subunit ß three or neurotrophic receptor tyrosine kinase 2 (also known as TrkB) was knocked out. Overall, the present study suggests that denervated midbrain-derived glial factors contribute to lesion-induced remodeling of the cortico-mesencephalic projection via these receptors.SIGNIFICANCE STATEMENT After brain injury, compensatory neural circuits are established that contribute to functional recovery. However, little is known about the intrinsic mechanism that underlies the injury-induced remodeling. We found that after unilateral cortical ablation expression of axon-growth promoting factors is elevated in the denervated midbrain and is involved in the formation of ectopic axonal projection from the intact cortex. Evidence further demonstrated that these factors are expressed by astrocytes and microglia, which are activated in the denervated midbrain. Thus, our present study provides a new insight into the mechanism of lesion-induced axonal remodeling and further therapeutic strategies after brain injury.

Separation from a bonded partner alters neural response to inflammatory pain in monogamous rodents.

Pain experience is known to be modified by social factors, but the brain mechanisms remain unspecified. We recently established an animal model of social stress-induced hyperalgesia (SSIH) using a socially monogamous rodent, the prairie vole, in which males separated from their female partners (loss males) became anxious and displayed exacerbated inflammatory pain behaviors compared to males with partners (paired males). In the present study, to explore the neural pathways involved in SSIH, a difference in neuronal activation in pain-related brain regions, or "pain matrix", during inflammatory pain between paired and loss males was detected using Fos immunoreactivity (Fos-ir). Males were paired with a female and pair bonding was confirmed in all subjects using a partner preference test. During formalin-induced inflammatory pain, both paired and loss males showed a significant induction of Fos-ir throughout the analyzed pain matrix components compared to basal condition (without injection), and no group differences in immunoreactivity were found among the injected males in many brain regions. However, the loss males had significantly lower Fos-ir following inflammatory pain in the medial prefrontal cortex and nucleus accumbens shell than the paired males, even though base Fos-ir levels were comparable between groups. Notably, both regions with different Fos-ir are major components of the dopamine and oxytocin systems, which play critical roles in both pair bonding and pain regulation. The present results suggest the possibility that pain exacerbation by social stress emerges through alteration of signaling in social brain circuitry.

Neuropeptide Y interaction with dopaminergic and serotonergic pathways: interlinked neurocircuits modulating hedonic eating behaviours.

Independent from homeostatic needs, the consumption of foods originating from hyperpalatable diets is defined as hedonic eating. Hedonic eating can be observed in many forms of eating phenotypes, such as compulsive eating and stress-eating, heightening the risk of obesity development. For instance, stress can trigger the consumption of palatable foods as a type of coping strategy, which can become compulsive, particularly when developed as a habit. Although eating for pleasure is observed in multiple maladaptive eating behaviours, the current understanding of the neurobiology underlying hedonic eating remains deficient. Intriguingly, the combined orexigenic, anxiolytic and reward-seeking properties of Neuropeptide Y (NPY) ignited great interest and has positioned NPY as one of the core neuromodulators operating hedonic eating behaviours. While extensive literature exists exploring the homeostatic orexigenic and anxiolytic properties of NPY, the rewarding effects of NPY continue to be investigated. As deduced from a series of behavioural and molecular-based studies, NPY appears to motivate the consumption and enhancement of food-rewards. As a possible mechanism, NPY may modulate reward-associated monoaminergic pathways, such as the dopaminergic and serotoninergic neural networks, to modulate hedonic eating behaviours. Furthermore, potential direct and indirect NPYergic neurocircuitries connecting classical homeostatic and hedonic neuropathways may also exist involving the anti-reward centre the lateral habenula. Therefore, this review investigates the participation of NPY in orchestrating hedonic eating behaviours through the modulation of monoaminergic pathways.

Oxytocin-conjugated saporin injected into the substantia nigra of male rats alters the activity of the nigrostriatal dopaminergic system: A behavioral and neurochemical study.

Saporin conjugated to oxytocin (OXY-SAP) destroys neurons expressing oxytocinergic receptors. When injected unilaterally in the substantia nigra of male rats, OXY-SAP causes a dose-dependent decrease up to 55 % in nigral Tyrosine Hydroxylase (TH)-immunoreactivity compared to control mock peptide BLANK-SAP- and PBS-treated rats or the contralateral substantia nigra. TH decrease was parallel to a dopamine content decrease in the ipsilateral striatum compared to BLANK-SAP- or PBS-treated rats or the contralateral striatum. OXY-SAP-treated rats showed a small but significant increase of locomotor activity 28 days after intranigral injection in the Open field test compared to BLANK-SAP- or PBS-treated rats, in line with an inhibitory role of nigral oxytocin on locomotor activity. OXY-SAP-, but not BLANK-SAP- or PBS-treated rats, also showed marked dose-dependent rotational turning ipsilateral to the injected substantia nigra when challenged with d-amphetamine, but not with apomorphine. Under isoflurane anesthesia OXY-SAP-treated rats showed levels of extracellular dopamine in the dialysate from the ipsilateral striatum only half those of BLANK-SAP- or PBS-treated rats or the contralateral striatum. When treated with d-amphetamine, OXY-SAP_60/120 rats showed increased extracellular dopamine levels in the dialysate from the ipsilateral striatum two third/one third only of those found in BLANK-SAP- or PBS-treated rats or the contralateral striatum, respectively. These results show that OXY-SAP destroys nigrostriatal dopaminergic neurons expressing oxytocin receptors leading to a reduced striatal dopamine function.