Subchronic treatment with imipramine ameliorates the decreased number in neuropeptide Y-positive cells in the hippocampus of learned helplessness rats

Evidence for the involvement of neuropeptide Y in the antidepressant effect of imipramine in type 2 diabetes

Depression is a major comorbidity factor of diabetes and the outcome of one disorder influences the other. Our aim is to scrutinize the link between the two, if any. Since neuropeptide Y (NPY) system plays an important role in regulating central glucose sensing mechanisms, and also depression-related behavior, we test the involvement of NPY in the modulation of depression in type 2 diabetic mice. The mice were fed on high-fat diet and administered with low dose of streptozotocin to induce type 2 diabetes. These animals showed augmented plasma glucose and increased immobility time in tail suspension test (TST) suggesting induction of diabetes and depression. Intracerebroventricular (icv) treatment with NPY or NPY Y1 receptor agonist [Leu(31), Pro(34)]-NPY and intraperitoneal treatment with imipramine decreased immobility time. However, opposite effect was produced by NPY Y1 receptor antagonist BIBP3226 (icv). Moreover, reduced immobility time by imipramine was potentiated by NPY and [Leu(31), Pro(34)]-NPY, but attenuated by BIBP3226. Immunohistochemical analysis of the different nuclei of the extended amygdala, the region primarily involved in affective disorders, was undertaken. A significant reduction in NPY immunoreactivity in the central nucleus of amygdala, nucleus accumbens shell and lateral division of bed nucleus of stria terminalis of the diabetic mice was noticed; the response was ameliorated in imipramine treated animals. The results suggest that decreased NPY expression in the extended amygdala might be causally linked with the depression induced following type 2 diabetes and that the antidepressant action of imipramine in diabetic mice might be mediated by NPY-NPY Y1 receptor system.

Fluoxetine, 17-β estradiol or folic acid combined with intra-lateral septal infusions of neuropeptide Y produced antidepressant-like actions in ovariectomized rats forced to swim

Folic acid is antidepressant, either alone or combined with several antidepressant drugs. However, the antidepressant-like actions of folic acid combined with intra-lateral septal (LSN) infusions of neuropeptide Y (NPY) in the forced swimming test (FST) have not been tested before. Thus, systemic injections of fluoxetine (20.0mg/kg, P<0.05; s.c.) or 17-β estradiol (10.0 μg/rat, P<0.05; s.c.) or oral administrations of folic acid (50.0 mg/kg, P<0.05; 75.0 mg/kg, P<0.05) or NPY intra-LSN (3.0 μg, P<0.05; 3.5 μg, P<0.05) reduced immobility of ovariectomized Wistar rats. Subthreshold doses of: folic acid (25.0 mg/kg) or 17-β estradiol (5.0 μg/rat, P<0.05) or fluoxetine (15.0 mg/kg, P<0.05; s.c.) combined with subthreshold doses of NPY (2.5 μg/rat, P<0.05; intra-LSN) and these combinations produced antidepressant-like actions; which were canceled by BIBP 3226 (a NPY-Y1 receptor antagonist). It is concluded that folic acid produced antidepressant-like effects probably through the participation of the NPY Y1 receptors found in the lateral septal nuclei.

A possible mechanism underlying an antidepressive-like effect of Kososan, a Kampo medicine, via the hypothalamic orexinergic system in the stress-induced depression-like model mice

Kososan, a Kampo (Japanese herbal) medicine, has an antidepressive-like effect in behavioral animal models of depression and has been used clinically for the improvement of depressive mood. However, mechanism(s) underlying the antidepressive-like effect of kososan remain unknown. Previous studies showed that orexin-A (OX-A), a neuropeptide that is involved in feeding and arousal, exhibits an antidepressive-like property via hippocampal cell proliferation. Here, we used immunohistochemical analysis with bromodeoxyuridine (BrdU), a marker of proliferating cells, to investigate the effect of long-term treatment with kososan on the orexinergic system and on hippocampal cell proliferation. Oral administration of kososan (1.0 g/kg) or milnacipran (60 mg/kg), a serotonin and noradrenaline reuptake inhibitor, for 28 d led to an antidepressive-like effect in the stress-induced depression-like model mice and reversed the stress-induced decrease in the number of OX-A-positive cells in the lateral hypothalamic area. In addition, both kososan and milnacipran alleviated the stress-induced decrease in the number of BrdU-positive cells in the hippocampal dentate gyrus. Moreover, the antidepressive-like effect and the increase in cell proliferation and in the number of neuropeptide Y (NPY, which is closely associated with orexinergic system)-positive cells in the dentate gyrus induced by kososan were blocked by treatment with SB-334867, an orexin receptor 1 antagonist. These results suggest that kososan exerts an antidepressive-like effect via the improvement of the stress-induced decrease in hippocampal cell proliferation and that the mechanism underlying the antidepressive-like effect of kososan, but not of milnacipran, may be associated with the regulation of orexinergic and/or NPYergic transmission.

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

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

Social isolation increases number of newly proliferated cells in hippocampus in female flinders sensitive line rats

Genetic background influences the responsiveness to stress and plays a crucial role in the pathophysiology of depression. In an animal model of depression, Flinders Sensitive Line rats, and Sprague Dawley controls we analyzed if 7 weeks of social isolation of adult animals affect the number of newly proliferated cells in the dentate gyrus or mRNAs of Neuropeptide Y (NPY), the NPY-Y1 receptor, nociceptin, BDNF, and the serotonin 5HT1A and 5HT2A receptors, which are molecules involved in hippocampal plasticity. Since depressive illness more frequently affects women than men, and females seem to respond differently to stressful experiences than males, female rats were used in this study. Bromodeoxyuridine, which is a thymidin analogue that is incorporated into the DNA of newly formed cells, was administered during 9 days to even out the effects of hormonal fluctuations. Social isolation increased the number of newly proliferated Bromodeoxyuridine-immunoreactive cells in the Flinders Sensitive Line rats, whereas it had no impact on the number of cells in the Sprague Dawley strain. Group housed Sprague Dawley rats had a higher expression of BDNF, NPY, and the serotonin 5HT2A receptor mRNA than "depressed" Flinders Sensitive Line. Social isolation downregulated these molecules in Sprague Dawley but not in Flinders Sensitive Line rats thereby eliminating the differences between the two strains. We demonstrate strain and gender specific responses to stress induced regulation of factors important for hippocampal plasticity.

Infusion of neuropeptide Y into CA3 region of hippocampus produces antidepressant-like effect via Y1 receptor

A couple of papers indicate that patients with depression show a decrease in serum neuropeptide Y (NPY). To study the role of NPY in depression, we examined the effects of infusion of NPY into the hippocampus of learned helplessness (LH) rats (an animal model of depression). Infusion of NPY into the cerebral ventricle of LH rats showed antidepressant-like effects. Infusion of NPY into the CA3 region, but not the dentate gyrus (DG), produced antidepressant-like effects in the LH paradigm. Infusion of NPY did not affect locomotor activity or aversive learning ability. Coadministration of BIBO3304 (a Y1 receptor antagonist) with NPY to the CA3 region blocked the antidepressant-like effects of NPY, whereas coadministration of NPY with BIIE0246 (a Y2 receptor antagonist) to the CA3 region failed to block antidepressant-like effects. Furthermore, infusions of [Leu(31) Pro(34)]PYY (a Y1 and Y5 receptor agonist) alone and BIIE0246 alone into the CA3 region produced the antidepressant-like effects in LH rats. These results suggest that infusion of NPY into the CA3 region of hippocampus of LH rats produces antidepressant-like activity through Y1 receptors and attenuating effects through Y2 receptors.

Physiology and gene regulation of the brain NPY Y1 receptor

Neuropeptide Y (NPY) is one of the most prominent and abundant neuropeptides in the mammalian brain where it interacts with a family of G-protein coupled receptors, including the Y(1) receptor subtype (Y(1)R). NPY-Y(1)R signalling plays a prominent role in the regulation of several behavioural and physiological functions including feeding behaviour and energy balance, sexual hormone secretion, stress response, emotional behaviour, neuronal excitability and ethanol drinking. Y(1)R expression is regulated by neuronal activity and peripheral hormones. The Y(1)R gene has been isolated from rodents and humans and it contains multiple regulatory elements that may participate in the regulation of its expression. Y(1)R expression in the hypothalamus is modulated by changes in energetic balance induced by a wide variety of conditions (fasting, pregnancy, hyperglycaemic challenge, hypophagia, diet induced obesity). Estrogens up-regulate responsiveness to NPY to stimulate preovulatory GnRH and gonadotropin surges by increasing Y(1)R gene expression both in the hypothalamus and the pituitary. Y(1)R expression is modulated by different kinds of brain insults, such as stress and seizure activity, and alteration in its expression may contribute to antidepressant action. Chronic modulation of GABA(A) receptor function by benzodiazepines or neuroactive steroids also affects Y(1)R expression in the amygdala, suggesting that a functional interaction between the GABA(A) receptor and Y(1)R mediated signalling may contribute to the regulation of emotional behaviour. In this paper, we review the state of the art concerning Y(1)R function and gene expression, including our personal contribution to many of the subjects mentioned above.

Hippocampal synapsin I, growth-associated protein-43, and microtubule-associated protein-2 immunoreactivity in learned helplessness rats and antidepressant-treated rats

Learned helplessness rats are thought to be an animal model of depression. To study the role of synapse plasticity in depression, we examined the effects of learned helplessness and antidepressant treatments on synapsin I (a marker of presynaptic terminals), growth-associated protein-43 (GAP-43; a marker of growth cones), and microtubule-associated protein-2 (MAP-2; a marker of dendrites) in the hippocampus by immunolabeling. (1) Learned helplessness rats showed significant increases in the expression of synapsin I two days after the attainment of learned helplessness, and significant decreases in the protein expression eight days after the achievement of learned helplessness. Subchronic treatment of naïve rats with imipramine or fluvoxamine significantly decreased the expression of synapsin I. (2) Learned helplessness increased the expression of GAP-43 two days and eight days after learned helplessness training. Subchronic treatment of naïve rats with fluvoxamine but not imipramine showed a tendency to decrease the expression of synapsin I. (3) Learned helplessness rats showed increased expression of MAP-2 eight days after the attainment of learned helplessness. Naïve rats subchronically treated with imipramine showed a tendency toward increased expression of MAP-2, but those treated with fluvoxamine did not. These results indicate that the neuroplasticity-related proteins synapsin I, GAP-43, and MAP-2 may play a role in the pathophysiology of depression and the mechanisms of antidepressants.