Dose dependent effects of oxytocin on cognitive defects and anxiety disorders in adult rats following acute infantile maternal deprivation stress

ABSTRACT

Maternal deprivation at an early age is a powerful stressor that causes permanent alterations in cognitive and behavioral functions during the later stages of life. We investigated the effects of oxytocin on cognitive defects and anxiety disorders caused by acute infantile maternal deprivation in adult rats. We used 18-day-old Wistar albino rats of both sexes. The experimental groups included control (C), maternally deprived (MD), maternally deprived and treated with 0.02 μg/kg oxytocin (MD-0.02 µg/kg oxy), maternally deprived and treated with 2 μg/kg oxytocin (MD-2 µg/kg oxy). When the rats were 60 days old, the open field (OF) and elevated plus maze (EPM) behavioral tests, and the Morris water maze (MWM) test for spatial learning and memory were performed. In addition, the number of neurons in the hippocampus, prefrontal cortex (PFC) and amygdala were determined using quantitative histology. We also measured vascular endothelial growth factor (VEGF) and brain-derived neurotrophic factor (BDNF) levels in the PFC. In both sexes, the MD group failed the learning test and the MD-2 μg/kg oxy group failed in the memory test. The MD-0.02 μg/kg oxy group spent more time in the open arm of the EPM device and their locomotor activities were greater in the OF test. The VEGF and BDNF levels in the PFC were higher in the MD-0.02 μg/kg oxy groups than the other maternally deprived groups (oxytocin ±). The number of PFC neurons was low in all male maternally deprived (oxytocin ±) groups, while the number of amygdala neurons was low in both female and male maternally deprived (oxytocin ±) groups. Male rats were more affected by maternal deprivation; administration of oxytocin had dose-dependent biphasic effects on learning, memory and anxiety.     

Differential Regulation of Hippocampal Neurotrophins During Aging in Rats

Abstract: Neurotrophins are a family of neurotrophic factors with considerable structural homology. We used sensitive and specific two-site enzyme immunoassays to assess age-associated changes in levels of three neurotrophins—nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), and neurotrophin-3 (NT-3)—in the hippocampus of Fischer 344 rats. Expressions of these proteins and their mRNAs were compared in the same animals. More than 200 ng of BDNF per gram of tissue was detected in the hippocampus of 2-month-old rats. This amount was two and 100 times greater than that of NT-3 and NGF, respectively. The levels of BDNF and NT-3 increased further 2–6 months after birth, whereas NGF content declined during this period, and the altered protein levels of all three neurotrophins were maintained 6–18 months postnatally. In contrast to the patterns of protein expression, BDNF mRNA levels increased during both of these periods, and the NT-3 mRNA levels appeared to decline. Changes in the expression of BDNF mRNA and NGF protein were opposite to those reported to occur in Alzheimer's disease. These results suggest that, during normal aging in rats, neurotrophin expression is regulated independently at both the mRNA and posttranslational levels. Any deficiency in their regulation might contribute to neurodegenerative disorders.     

NT-3, BDNF, and NGF in the developing rat nervous system: parallel as well as reciprocal patterns of expression.

To obtain insight into the site and stage specificity of nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), and neurotrophin-3 (NT-3) action in vivo, we compared the expression patterns of the genes for these three related neurotrophic factors as well as for the NGF receptor in developing and adult rats. Initial embryonic expression of these related neurotrophic factors approximately coincides with the onset of neurogenesis. However, the levels at which the three factors are expressed at this time and throughout the developing nervous system are dramatically different. NT-3 is by far the most highly expressed in immature regions of the CNS in which proliferation, migration, and differentiation of neuronal precursors is ongoing. NT-3 expression dramatically decreases with maturation of these regions. By contrast, BDNF expression is low in developing regions of the CNS and increases as these regions mature. NGF expression varies during the development of discrete CNS regions, but not in any consistent manner compared with NT-3 and BDNF. Despite the dramatic variations, NT-3, BDNF, and NGF do share one striking similarity--high level expression in the adult hippocampus. Our observations are consistent with the idea that NT-3, BDNF, and NGF have paralleled as well as reciprocal roles in vivo.     

Immunohistochemical distribution of NGF, BDNF, NT-3, and NT-4 in adult rhesus monkey brains.

Immunohistochemical distribution and cellular localization of neurotrophins was investigated in adult monkey brains using antisera against nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), neurotrophin-3 (NT-3), and neurotrophin-4 (NT-4). Western blot analysis showed that each antibody specifically recognized appropriate bands of approximately 14.7 kDa, 14.2 kDa, 13.6 kDa, and 14.5 kDa, for NGF, BDNF, NT-3, and NT-4, respectively. These positions coincided with the molecular masses of the neurotrophins studied. Furthermore, sections exposed to primary antiserum preadsorbed with full-length NGF, BDNF, NT-3, and NT-4 exhibited no detectable immunoreactivity, demonstrating specificities of the antibodies against the tissues prepared from rhesus monkeys. The study provided a systematic report on the distribution of NGF, BDNF, NT-3, and NT-4 in the monkey brain. Varying intensity of immunostaining was observed in the somata and processes of a wide variety of neurons and glial cells in the cerebrum, cerebellum, hippocampus, and other regions of the brain. Neurons in some regions such as the cerebral cortex and the hippocampus, which stained for neurotrophins, also expressed neurotrophic factor mRNA. In some other brain regions, there was discrepancy of protein distribution and mRNA expression reported previously, indicating a retrograde or anterograde action mode of neurotrophins. Results of this study provide a morphological basis for the elucidation of the roles of NGF, BDNF, NT-3, and NT-4 in adult primate brains.     

The neurotrophins BDNF, NT-3, and NGF display distinct patterns of retrograde axonal transport in peripheral and central neurons.

The pattern of retrograde axonal transport of the target-derived neurotrophic molecule, nerve growth factor (NGF), correlates with its trophic actions in adult neurons. We have determined that the NGF-related neurotrophins, brain-derived neurotrophic factor (BDNF) and neurotrophin-3 (NT-3), are also retrogradely transported by distinct populations of peripheral and central nervous system neurons in the adult. All three 125I-labeled neurotrophins are retrogradely transported to sites previously shown to contain neurotrophin-responsive neurons as assessed in vitro, such as dorsal root ganglion and basal forebrain neurons. The patterns of transport also indicate the existence of neuronal populations that selectively transport NT-3 and/or BDNF, but not NGF, such as spinal cord motor neurons, neurons in the entorhinal cortex, thalamus, and neurons within the hippocampus itself. Our observations suggest that neurotrophins are transported by overlapping as well as distinct populations of neurons when injected into a given target field. Retrograde transport may thus be predictive of neuronal types selectively responsive to either BDNF or NT-3 in the adult, as first demonstrated for NGF.     

Hippocampal neurotrophin levels in a kainate model of temporal lobe epilepsy: a lack of correlation between brain-derived neurotrophic factor content and progression of aberrant dentate mossy fiber sprouting

A significant upregulation of neurotrophins particularly brain-derived neurotrophic factor (BDNF) is believed to be involved in the initiation of epileptogenic changes such as the aberrant axonal sprouting and synaptic reorganization in the injured hippocampus. However, it is unknown which of the neurotrophins are upregulated during the peak period of aberrant mossy fiber sprouting in the chronically injured hippocampus. We measured chronic changes in the levels of BDNF, nerve growth factor (NGF) and neurotrophin-3 (NT-3) in the adult hippocampus using enzyme-linked immunosorbent assay (ELISA) after a unilateral intracerebroventricular administration of kainic acid (KA), a model of temporal lobe epilepsy. For comparison, neurotrophins were also measured from the control intact hippocampus. Further, to see the association between changes in neurotrophin levels and the progression of mossy fiber sprouting, chronic changes in the mossy fiber distribution within the dentate supragranular layer (DSGL) were quantified. In the KA-lesioned hippocampus, the neurotrophins BDNF and NGF were upregulated at 4 days post-lesion, in comparison to their levels in the intact hippocampus. However, the concentration of BDNF reached the baseline level at 45 days post-lesion and dramatically diminished at 120 days post-lesion. In contrast, the upregulation of NGF observed at 4 days post-lesion was sustained at both 45 days and 120 days post-lesion. The concentration of NT-3 was upregulated at 45 days post-lesion but remained comparable to baseline levels at 4 days and 120 days post-lesion. Interestingly, analysis of mossy fiber sprouting revealed that most of the aberrant sprouting in the lesioned hippocampus occurs between 45 days and 120 days post-lesion. Taken together, these results suggest that the period of robust mossy fiber sprouting does not correlate with the phase of post-lesion BDNF upregulation. Rather, it shows a relationship with the time of upregulation of neurotrophins NGF and NT-3.     

NT-3 modulates BDNF and proBDNF levels in naïve and kindled rat hippocampus

Both mature and precursor forms of neurotrophins regulate nerve development, survival and plasticity. Brain-derived neurotrophic factor (BDNF) synthesis and secretion in turn are regulated by neuronal activity, such as epilepsy. Further, neurotrophins themselves are regulated by neurotrophin levels. Neurotrophin-3 (NT-3) and BDNF in particular can be co-expressed and each can regulate the levels of the other. This regulation is thought to be mediated through receptor tyrosine kinase (Trk) activity. It is not known whether this neurotrophin-neurotrophin interaction occurs in hippocampal tissue in vivo, or how it is influenced by neuronal activation. In this study, we explored the reciprocal influences of intraventricular infusions of NT-3 and BDNF in na?ve and kindled hippocampi of rats using Western blotting. We confirm that hippocampal kindling resulted in a significant increase in levels of BDNF both in cytochrome C (control) infused and NT-3 infused kindled rats. However, NT-3 infusion significantly reduced BDNF levels in both kindled and non-kindled hippocampi compared to their cytochrome C infused counterparts. These results are consistent with our earlier studies demonstrating lowered levels of TrkA and TrkC (NGF modulates BDNF levels via TrkA) following chronic NT-3 infusion. Although kindling led to an increase in BDNF, this was not accompanied by any detectable change in the levels of proBDNF. However, there was a significant increase in proBDNF following NT-3 infusions, suggesting NT-3 may reduce proBDNF processing. In contrast, neither NT-3 nor proNT-3 levels were affected by kindling or chronic BDNF infusions, consistent with down-regulation of TrkB by chronic BDNF infusion. Thus, modulation of BDNF by NT-3, likely mediated by Trk receptors, occurs in na?ve and kindled adult rat hippocampus.     

Phase advance of the light-dark cycle perturbs diurnal rhythms of brain-derived neurotrophic factor and neurotrophin-3 protein levels, which reduces synaptophysin-positive presynaptic terminals in the cortex of juvenile rats

In adult rat brains, brain-derived neurotrophic factor (BDNF) rhythmically oscillates according to the light-dark cycle and exhibits unique functions in particular brain regions. However, little is known of this subject in juvenile rats. Here, we examined diurnal variation in BDNF and neurotrophin-3 (NT-3) levels in 14-day-old rats. BDNF levels were high in the dark phase and low in the light phase in a majority of brain regions. In contrast, NT-3 levels demonstrated an inverse phase relationship that was limited to the cerebral neocortex, including the visual cortex, and was most prominent on postnatal day 14. An 8-h phase advance of the light-dark cycle and sleep deprivation induced an increase in BDNF levels and a decrease in NT-3 levels in the neocortex, and the former treatment reduced synaptophysin expression and the numbers of synaptophysin-positive presynaptic terminals in cortical layer IV and caused abnormal BDNF and NT-3 rhythms 1 week after treatment. A similar reduction of synaptophysin expression was observed in the cortices of Bdnf gene-deficient mice and Ca(2+)-dependent activator protein for secretion 2 gene-deficient mice with abnormal free-running rhythm and autistic-like phenotypes. In the latter mice, no diurnal variation in BDNF levels was observed. These results indicate that regular rhythms of BDNF and NT-3 are essential for correct cortical network formation in juvenile rodents.     

Neurotrophin expression in rat hippocampal slices: a stimulus paradigm inducing LTP in CA1 evokes increases in BDNF and NT-3 mRNAs.

We report that stimulation inducing long-term potentiation (LTP) in the CA1 pyramidal cell layer of the hippocampus evokes significant increases in both BDNF and NT-3 mRNAs in CA1 neurons. No changes in BDNF or NT-3 mRNA levels were seen in the nonstimulated regions of the pyramidal cell layer or the dentate. No change was seen in the levels of NGF mRNA at the time point examined. These results suggest that relatively normal levels of activity may regulate region-specific neurotrophin levels in the hippocampus. Given that known effects of NGF (and presumably of BDNF and NT-3) include elevation of neurotransmitter levels, elevation of sodium channels, and promotion of axonal terminal sprouting, activity-associated changes in neurotrophin levels may play a role in regulating neural connections in the adult as well as the developing nervous system.     

Differential Age-Dependent Trophic Responses of Nodose,Sensory, and Sympathetic Neurons to Neurotrophins and GDNF: Potencies for Neurite Extension in Explant Culture

The age-dependent trophic responses of sympathetic, sensory, and nodose neurons to the neuro-trophins NGF, BDNF, and NT-3 and to glial cell line-derived neurotrophic factor (GDNF) were examined by an explant culture system. Superior cervical ganglia (SCG), dorsal root ganglia (DRG), and nodose ganglia (NG) were removed from rat embryos (E18), neonatals ( 1 day old), young adults (3–6 months old), and aged adults (>24 months old). The ganglia were cultured with and without each neurotrophic factor; the neurite extension and neurite density were then assessed. The SCG from rats of all ages were significantly influenced by NGF, NT-3, and GDNF; the effects of NT-3 and GDNF were reduced after maturation. The DRG from embryos and neonates were influenced by all neurotrophic factors; however, the effects of BDNF and NT-3 disappeared after maturation. The GDNF showed little effect on adult DRG and no effect on aged DRG. The effect of NGF was preserved over all ages of DRG. The NG from embryonic rats were significantly responsive to BDNF and GDNF; their effects decreased in the neonatal NG, but a minimum effect remained in the aged NG. These results indicate that age-dependent profiles of trophic effects differ extensively among the lineages of the peripheral nervous system and also among the individual neurotrophic factors.     

Effects of acute and chronic treatment elicited by lamotrigine on behavior, energy metabolism, neurotrophins and signaling cascades in rats

The present study was aimed to investigate the behavioral and molecular effects of lamotrigine. To this aim, Wistar rats were treated with lamotrigine (10 and 20 mg/kg) or imipramine (30 mg/kg) acutely and chronically. The behavior was assessed using forced swimming test. Brain-derived neurotrophic factor (BDNF), nerve growth factor (NGF), Proteina Kinase B (PKB, AKT), glycogen synthase kinase 3 (GSK-3) and B-cell lymphoma 2 (Bcl-2) levels, citrate synthase, creatine kinase and mitochondrial chain (I, II, II-III and IV) activities were assessed in the brain. The results showed that both treatments reduced the immobility time. The BDNF were increased in the prefrontal after acute treatment with lamotrigine (20 mg/kg), and the BDNF and NGF were increased in the prefrontal after chronic treatment with lamotrigine in all doses. The AKT increased and Bcl-2 and GSK-3 decreased after both treatments in all brain areas. The citrate synthase and creatine kinase increased in the amygdala after acute treatment with imipramine. Chronic treatment with imipramine and lamotrigine (10 mg/kg) increased the creatine kinase in the hippocampus. The complex I was reduced and the complex II, II-III and IV were increased, but related with treatment and brain area. In conclusion, lamotrigine exerted antidepressant-like, which can be attributed to its effects on pathways related to depression, such as neurotrophins, metabolism energy and signaling cascade.     

Differential expression of mRNAs for neurotrophins and their receptors after axotomy of the sciatic nerve

The neurotrophin family includes NGF, brain-derived neurotrophic factor (BDNF), neurotrophin-3 (NT-3), and neurotrophin-4 (NT-4). Previous studies have demonstrated that expression of NGF and its low-affinity receptor is induced in nonneuronal cells of the distal segment of the transected sciatic nerve suggesting a role for NGF during axonal regeneration (Johnson, E. M., M. Taniuchi, and P. S. DeStefano. 1988. Trends Neurosci. 11:299-304). To assess the role of the other neurotrophins and the members of the family of Trk signaling neurotrophin receptors, we have here quantified the levels of mRNAs for BDNF, NT-3, and NT-4 as well as mRNAs for trkA, trkB, and trkC at different times after transection of the sciatic nerve in adult rats. A marked increase of BDNF and NT-4 mRNAs in the distal segment of the sciatic nerve was seen 2 wk after the lesion. The increase in BDNF mRNA was mediated by a selective activation of the BDNF exon IV promoter and adrenalectomy attenuated this increase by 50%. NT-3 mRNA, on the other hand, decreased shortly after the transection but returned to control levels 2 wk later. In Schwann cells ensheathing the sciatic nerve, only trkB mRNA encoding truncated TrkB receptors was detected with reduced levels in the distal part of the lesioned nerve. Similar results were seen using a probe that detects all forms of trkC mRNA. In the denervated gastrocnemius muscle, the level of BDNF mRNA increased, NT-3 mRNA did not change, while NT-4 mRNA decreased. In the spinal cord, only small changes were seen in the levels of neutrophin and trk mRNAs. These results show that expression of mRNAs for neurotrophins and their Trk receptors is differentially regulated after a peripheral nerve injury. Based on these results a model is presented for how the different neurotrophins could cooperate to promote regeneration of injured peripheral nerves.     

The nerve growth factor family

Nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF) and neurotrophin-3 (NT-3) are small, basic, secretory proteins that allow the survival of specific neuronal populations. In their biologically active form, after cleavage from their biosynthetic precursors, these three neurotrophic proteins, or neurotrophins, show about 50% amino acid identities. The genes coding for the neurotrophins are not only expressed during development, but also in the adult, in a variety of tissues including the central nervous system. In the adult brain, the hippocampal formation is the site of highest expression of the three neurotrophin genes. These genes are expressed in neurons, and the mRNA levels of two of them (NGF and BDNF) have been shown to be regulated by neurotransmitters. There are also convincing indications that the administration of NGF prevents the atrophy and death of axotomized cholinergic neurons in the adult central nervous system, and improves the performance of rats selected for their poor memory retention in simple behavioral tasks.     

Effects of maternal deprivation on adrenal and behavioural responses in rats with anterodorsal thalami nuclei lesions

There is evidence that repeated maternal isolation of neonatal rats may influence both emotional behavior and Hypothalamic-Pituitary Adrenal (HPA) activity. On the other hand the Anterodorsal Thalami Nuclei (ADTN) exerts an inhibitory influence on the hypophyso-adrenal system under basal and stressful conditions. In the present work we investigated whether neonatal maternal deprivation produces long term effects on the ADTN regulation of behavioral patterns (open field test) and on HPA axis activity. Specifically, we sought to determine whether adult female rats with ADTN lesions, previously isolated for 4.5 hours daily during the first 3 weeks of life, react in endocrinologically and behaviourally distinct manner as compared to controls. The examined groups were: non maternally deprived (NMD)/sham lesioned, NMD/lesioned, maternally deprived (MD)/sham lesioned, MD/lesioned with and without the open field test. At 3 months MD/sham lesioned animals showed a marked decrease in ambulation (P < 0.01), and with ADTN lesion, the rearing values were lower (P < 0.01) and grooming higher (P < 0.05) than NMD. This last data would indicate a high emotional index. Regarding the activity of the HPA axis, maternal deprivation induced a significant decrease in plasma ACTH concentration both in sham and lesioned animals (P < 0.001), and plasma Corticosterone (C) increased in sham animals (P < 0.001). This data would indicate a higher sensitivity of the adrenal glands. After the open field test ACTH and C were different between deprived and non-deprived animals depending on the ADTN lesion. Taking into consideration the increase of ACTH levels in sham lesioned MD animals exposed to the test, we could conclude that this new situation was a stressful situation. Finally in the present work, it was very difficult to relate the behavioral parameters with the endocrine data. It is known that depending on the context, corticosteroids may produce opposite effects on emotional behavior via different receptors in the brain.In summary, neonatal maternal deprivation induced alterations of behavioral patterns and affected the ADTN inhibitory influence on ACTH and C secretion.     

Chronic REM Sleep Restriction in Juvenile Male Rats Induces Anxiety-Like Behavior and Alters Monoamine Systems in the Amygdala and Hippocampus

Adolescence is marked by major physiological changes, including those in the sleep-wake cycle, such as phase delay, which may result in reduced sleep hours. Sleep restriction and/or deprivation in adult rats activate stress response and seem to be a risk factor for triggering emotional disorders. In the present study, we sought to evaluate the behavioral and neurobiological consequences of prolonged REM sleep restriction in juvenile male rats. Immediately after weaning, on postnatal day 21, three males from each litter were submitted to REM sleep deprivation and the other three animals were maintained in their home-cages. REM sleep restriction (REMSR) was accomplished by placing the animals in the modified multiple platform method for 18 h and 6 h in the home-cage, where they could sleep freely; the sleep restriction lasted 21 consecutive days, during which all animals were measured and weighed every 3 days. After the end of this period, all animals were allowed to sleep freely for 2 days, and then the behavioral tests were performed for evaluation of depressive and anxiety-like profiles (sucrose negative contrast test and elevated plus maze, EPM). Blood sampling was performed 5 min before and 30 and 60 min after the EPM for determination of corticosterone plasma levels. The adrenals were weighed and brains collected and dissected for monoamine levels and receptor protein expression. REMSR impaired the physical development of adolescents, persisting for a further week. Animals submitted to REMSR exhibited higher basal corticosterone levels and a greater anxiety index in the EPM, characteristic of an anxious profile. These animals also exhibited higher noradrenaline levels in the amygdala and ventral hippocampus, without any change in the expression of β1-adrenergic receptors, as well as higher serotonin and reduced turnover in the dorsal hippocampus, with diminished expression of 5-HT1_A. Finally, greater concentration of BDNF was observed in the dorsal hippocampus in chronically sleep-restricted animals. Chronic REMSR during puberty impaired physical development and induced anxiety-like behavior, attributed to increased noradrenaline and serotonin levels in the amygdala and hippocampus.     

Decrease in the levels of NGF and BDNF in brains of mice fed a tryptophan-deficient diet

The roles of dietary tryptophan (Trp) were evaluated in regulation of production of nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), and neurotrophin (NT)-3 in the various brain regions in ddY mice. Feeding the mice a Trp-deficient diet for 2 weeks significantly decreased in the hippocampal level of NGF but not those of BDNF and NT-3, as compared with feeding an adequate Trp diet. The mice fed excess Trp did not have different levels of any of these neurotrophins than in the mice fed an adequate Trp diet. The levels of BDNF in the cerebral cortex were also significantly lower in the mice fed on a Trp-deficient diet, while the levels of NGF and NT-3 in the region were not modulated upon feeding of the diet. The dietary Trp level had no significant effect on the levels of NGF, BDNF, or NT-3 in the entorhinal cortex nor septum of the mice. These results demonstrate that the brain levels of NGF and BDNF are dependent on the dietary content of tryptophan.     

Neuropeptide Y administration reverses tricyclic antidepressant treatment-resistant depression induced by ACTH in mice

Depression is one of the most common mental disorders and a primary cause of disability. To better treat patients suffering this illness, elucidation of the underlying psychopathological and neurobiological mechanisms is urgently needed. Based on the above-mentioned evidence, we sought to investigate the effects of neuropeptide Y (NPY) treatment in tricyclic antidepressant treatment-resistant depression induced by adrenocorticotropic hormone (ACTH) administration. Mice were treated with NPY (5.84, 11.7 or 23.4 mmol/μl) intracerebroventricularly (i.c.v.) for one or five days. The levels of serum corticosterone, tryptophan (TRP), kynurenine (KYN), serotonin (5-HT), 5-hydroxyindoleacetic acid (5-HIAA), brain-derived neurotrophic factor (BDNF), nerve growth factor (NGF) and indoleamine 2,3-dioxygenase (IDO) activity in the hippocampus were analyzed. The behavioral parameters (depressive-like and locomotor activity) were also verified. This study demonstrated that ACTH administration increased serum corticosterone levels, KYN, 5-HIAA levels, IDO activity (hippocampus), immobility in the forced swimming test (FST) and the latency to feed in the novelty suppressed feeding test (NSFT). In addition, ACTH administration decreased the BDNF and NGF levels in the hippocampus of mice. NPY treatment was effective in preventing these hormonal, neurochemical and behavioral alterations. It is suggested that the main target of NPY is the modulation of corticosterone and neuronal plasticity protein levels, which may be closely linked with pharmacological action in a model of tricyclic antidepressant treatment-resistant depression. Thus, this study demonstrated a protective effect of NPY on the alterations induced by ACTH administration in mice, indicating that it could be useful as a therapy for the treatment of tricyclic antidepressant treatment-resistant depression.