Clonidine administration increases neuropeptide Y immunoreactivity and neuropeptide Y mRNA in the rat cerebral cortex neurons

Agmatine in the hypothalamic paraventricular nucleus stimulates feeding in rats: involvement of neuropeptide Y

BACKGROUND AND PURPOSE

Agmatine, a multifaceted neurotransmitter, is abundantly expressed in the hypothalamic paraventricular nucleus (PVN). Our aim was to assess (i) the effect of agmatine on feeding behaviour and (ii) its association, if any, with neuropeptide Y (NPY).

EXPERIMENTAL APPROACH

Satiated rats fitted with intra-PVN cannulae were administered agmatine, alone or jointly with (i) α₂-adrenoceptor agonist, clonidine, or antagonist, yohimbine; (ii) NPY, NPY Y₁ receptor agonist, [Leu³¹, Pro³⁴]-NPY, or antagonist, BIBP3226; or (iii) yohimbine and NPY. Cumulative food intake was monitored at different post-injection time points. Furthermore, the expression of hypothalamic NPY following i.p. treatment with agmatine, alone or in combination with yohimbine (i.p.), was evaluated by immunocytochemistry.

KEY RESULTS

Agmatine robustly increased feeding in a dose-dependent manner. While pretreatment with clonidine augmented, yohimbine attenuated the orexigenic response to agmatine. Similarly, NPY and [Leu³¹, Pro³⁴]-NPY potentiated the agmatine-induced hyperphagia, whereas BIBP3226 inhibited it. Moreover, yohimbine attenuated the synergistic orexigenic effect induced by the combination of NPY and agmatine. Agmatine increased NPY immunoreactivity in the PVN fibres and in the cells of the hypothalamic arcuate nucleus (ARC) and this effect was prevented by pretreatment with yohimbine. NPY immunoreactivity in the fibres of the ARC, dorsomedial, ventromedial and lateral nuclei of the hypothalamus was not affected by any of the above treatments.

CONCLUSIONS AND IMPLICATIONS

The orexigenic effect of agmatine is coupled to increased NPY activity mediated by stimulation of α₂-adrenoceptors within the PVN. This signifies the importance of agmatine or α₂-adrenoceptor modulators in the development of novel therapeutic agents to treat feeding-related disorders.

Association between neuropeptide Y gene and its receptor Y1 gene and methamphetamine dependence

AIMS

Neuropeptide Y (NPY) is a 36-amino acid peptide that is widely distributed in the brain, adrenal medulla, and sympathetic nervous system. Several lines of evidence suggest a possible involvement of the NPY system in the physiological effects of several classes of abused substances including alcohol, phencyclidine, cocaine, and marijuana and in endogenous psychosis. Accordingly, it was hypothesized that the NPY system may also be involved in methamphetamine dependence or psychosis.

METHODS

The single nucleotide polymorphisms rs16147 of the NPY gene (-485C>T) and rs7687423 of the NPY receptor Y1 (NPY1R) gene were analyzed in 222 patients with methamphetamine dependence and psychosis and 288 age- and gender-matched controls.

RESULTS

Genotypic distribution of the NPY1R gene showed a significant association with methamphetamine dependence and psychosis (P = 0.04), whereas the NPY gene had no significant association with them.

CONCLUSION

It is possible that genetic variants of the NPY1R gene affect the NPY-NPY receptor type Y1 signaling system in the brain, which may result in susceptibility to methamphetamine dependence or the development of methamphetamine psychosis, but the present findings need to be confirmed on replication.

Pharmacological studies on the monoaminergic influence on the synthesis and expression of neuropeptide Y and corticotropin releasing factor in rat brain amygdala

Our earlier findings concerning the 6-OHDA lesion suggested dopaminergic regulation of neuropeptide Y (NPY) and corticotropin releasing factor (CRF) synthesis and expression in amygdala neurons. On the other hand, some other studies indicated that not only dopamine, but also other monoamines may modulate peptidergic neurons. Therefore the present study examined the effect of pharmacological deprivation of monoaminergic influences on NPY and CRF neurons in rat brain amygdala by means of in situ hybridization and immunohistochemical methods. It was found that NPY mRNA expression in the amygdala decreased after 24h blockade of dopaminergic D1 and D2 receptors, by haloperidol or SCH23390. At the same time the NPY-peptide expression measured immunohistochemically was not significantly changed. A prolonged, 14-day, blockade of dopaminergic receptors by haloperidol induced an opposite effect, an increase in NPY mRNA expression. Impairment of the serotonergic transmission by blockade of 5-HT synthesis using p-chlorophenylalanine, as well as attenuation of the noradrenergic transmission by NA depletion from terminals by DSP4, did not significantly change NPY mRNA expression or the mean number of NPY-immunoreactive neurons in the amygdala. Only a decrease in the staining intensity observed as a decreased number of darkly stained neurons was found after both compounds. Neither the dopamine receptor blockade nor the impairment of serotonergic or noradrenergic transmission changed CRF mRNA or the peptide expression in the amygdala. The obtained results indicate that in rat brain amygdala, of all the monoamines, dopamine seems to be the most important modulator of NPY biosynthesis and expression. The effect of blockade of dopaminergic receptors is biphasic: first it induces a decrease and then - after prolonged treatment an increase in NPY mRNA. Serotonergic and noradrenergic systems in the amygdala seem to be connected with regulation of NPY release rather than the biosynthesis.

Effect of 6-hydroxydopamine on neuropeptide Y and corticotropin-releasing factor expression in rat amygdala

The influence of dopaminergic denervation on neuropeptide Y and corticotropin-releasing factor-containing neurons in the amygdala was investigated in rats by examining the effects of a selective, unilateral 6-hydroxydopamine lesion of mesencephalic dopaminergic neurons in both the substantia nigra and the ventral tegmental area on these peptides and their messenger RNA expression, observed eight to 10 days after the lesion. The studies were conducted by immunocytochemical and in situ hybridization methods. Neuropeptide Y or corticotropin-releasing factor-immunoreactive neurons were counted in sections of the amygdala under a microscope, and the messenger RNA expression was measured as optical density units in autoradiograms. A significant increase in both neuropeptide Y and corticotropin-releasing factor messenger RNA expression was found in the amygdala on the lesioned side in comparison with the contralateral one, as well as with the ipsilateral side of vehicle-injected controls. Immunohistochemical studies showed that the number of neuropeptide Y-immunoreactive neurons increased in the whole amygdala on the lesioned side. At the same time, the number of corticotropin-releasing factor-immunoreactive neurons grouped in the central amygdaloid nucleus declined, and so did the staining intensity. The obtained results indicate that dopaminergic denervation stimulates the synthesis of neuropeptide Y and corticotropin-releasing factor in rat amygdala, but the peptide levels are differently regulated, which points to a diverse release of these peptides.

Circulating neuropeptide Y (NPY) and catecholamines in rat under resting and stress conditions. Arguments for extra-adrenal origin of NPY, adrenal and extra-adrenal sources of catecholamines

Neuropeptide Y (NPY) is found in cell bodies of neurons in the brain and co-localized with noradrenaline (NA) in sympathetic nerves as well as with NA and adrenaline (A) in the adrenal chromaffin cells. The purpose of the present work is to determine whether NPY and catecholamines found in the plasma of the rat under resting and stress conditions (ether inhalation, restraint) arise from the adrenals or from extra-adrenal sites. We used adrenalectomized (adx) rats and sham-adx ones. Adrenalectomy increased plasma adrenocorticotrophic hormone (ACTH) levels but decreased drastically circulating corticosterone (B) and A (-97%). However, resting NA was slightly but not significantly decreased and NPY not affected. Ether inhalation (3 min) increased plasma levels of ACTH, B, NA and A in sham-adx rats, ACTH, NA and, weakly, A in adx ones. Restraint (30 min) increased B, NA and A in sham-adx rats, NA and, poorly, A, in adx ones. In contrast, plasma levels of NPY were not significantly affected by these stress conditions. The present data suggest that NA found in rat plasma at rest and during ether or restraint stress could arise from both adrenal medulla and noradrenergic nerve endings while A arises mainly from the adrenergic chromaffin cells of the adrenals. In contrast, NPY found in the circulation, at rest and under stress conditions, is not derived from the adrenals but emanates mainly from an extra-adrenal source.