Effects of neuropeptide Y on forskolin, alpha 2- and beta-adrenoceptor-regulated cAMP levels in the rat brain slice

GABA activity mediating cytosolic Ca2+ rises in developing neurons is modulated by cAMP-dependent signal transduction

In the majority of developing neurons, GABA can exert depolarizing actions, thereby raising neuronal Ca2+. Ca2+ elevations can have broad consequences during development, inducing gene expression, altering neurite outgrowth and growth cone turning, activating enzyme pathways, and influencing neuronal survival. We used fura-2 and fluo-3 Ca2+ digital imaging to assess the effects of inhibiting or activating the cAMP signal transduction pathway on GABA activity mediating Ca2+ rises during the early stages of in vitro hypothalamic neural development. Our experiments stemmed from the finding that stimulation of transmitter receptors shown to either activate or inhibit adenylyl cyclase activity caused a rapid decrease in Ca2+ rises mediated by synaptically released GABA. Both the adenylyl cyclase activator forskolin and the inhibitor SQ-22,536 reduced the Ca2+ rise elicited by the synaptic release of GABA. Bath application of the membrane-permeable cAMP analogs 8-bromo-cAMP (8-Br-cAMP) or 8-(4-chlorophenylthio)-cAMP (0.2-5 mM) produced a rapid, reversible, dose-dependent inhibition of Ca2+ rises triggered by synaptic GABA release. Potentiation of GABAergic activity mediating Ca2+ rises was observed in some neurons at relatively low concentrations of the membrane-permeable cAMP analogs (20-50 microM). In the presence of tetrodotoxin (TTX), postsynaptic Ca2+ rises triggered by the bath application of GABA were only moderately depressed (13%) by 8-Br-cAMP (1 mM), suggesting that the inhibitory effects of 8-Br-cAMP were largely the result of a presynaptic mechanism. The protein kinase A (PKA) inhibitors H89 and Rp-3', 5'-cyclic monophosphothioate triethylamine also caused a large reduction (>70%) in Ca2+ rises triggered by synaptic GABA release. Unlike the short-term depression elicited by activation of the cAMP signal transduction pathway, Ca2+ depression elicited by PKA inhibition persisted for an extended period (>30 min) after PKA inhibitor washout. Postsynaptic depression of GABA-evoked Ca2+ rises triggered by H89 (in the presence of TTX) recovered rapidly, suggesting that the extended depression observed during synaptic GABA release was largely through a presynaptic mechanism. Long-term Ca2+ modulation by cAMP-regulating hypothalamic peptides may be mediated through a parallel mechanism. Together, these results suggest that GABAergic activity mediating Ca2+ rises is dependent on ongoing PKA activity that is maintained within a narrow zone for GABA to elicit a maximal Ca2+ elevation. Thus, neuromodulator-mediated changes in the cAMP-dependent signal transduction pathway (activation or inhibition) could lead to a substantial decrease in GABA-mediated Ca2+ rises during early development.

Localization of neuropeptide Y Y1 receptor-like immunoreactivity in catecholaminergic neurons of the rat medulla oblongata

Neuropeptide Y receptors in the medulla oblongata participate in central cardiovascular control. The neuropeptide Y1 receptor subtype gene and amino acid sequence have been identified by molecular cloning studies. In this study, a C-terminal peptide representing amino acids 355-382 of the neuropeptide Y1 receptor was synthesized and cross-linked to thyroglobulin to produce an antibody against a partial sequence of the neuropeptide Y1 receptor, used to localize neuropeptide Y1 receptor-like immunoreactivity in the catecholaminergic neurons of the medulla oblongata. The double colour immunofluorescence technique with a polyclonal antibody against the neuropeptide Y1 receptor and a monoclonal antibody against tyrosine hydroxylase revealed that in the rat medulla oblongata, a weak (the C3 cell group) to moderately intense (the A1, A2, C1 and C2 cell groups), diffuse cytoplasmic neuropeptide Y1 receptor-like immunoreactivity was distributed primarily in the noradrenergic and adrenergic cell bodies and occasionally seen in the noradrenergic and adrenergic cell processes. Almost all tyrosine hydroxylase-like immunoreactive cell bodies in the A1, A2, C1, C2 and C3 cell groups showed neuropeptide Y1 receptor-like immunoreactivity. The neuropeptide Y1 receptor-like immunoreactivity in the A2 cell group was somewhat stronger. The present findings show localization of specific neuropeptide Y1 receptor-like immunoreactivity in the vast majority of the noradrenergic and adrenergic cell bodies of the A1, A2, C1, C2 and C3 cell groups, which are putative cardiovascular regions. The results support the view that neuropeptide Y1 receptors in the medulla oblongata are involved in central cardiovascular control and may coexist with another important receptor, the alpha 2A-adrenoceptor, also involved in central, cardiovascular regulation, since the alpha 2A-adrenoceptor-like immunoreactivity has been shown to exist in almost all noradrenergic and adrenergic cell bodies in the brainstem. In conclusion, centrally administered neuropeptide Y may act in part via neuropeptide Y1 receptors located on the soma and dendrites of noradrenergic and adrenergic neurons, where it may interact with alpha 2-adrenoceptors at least in the noradrenergic A2 neurons. This noradrenaline system may be involved in at least part of the vasodepressor actions of neuropeptide Y, noradrenaline and adrenaline in the nucleus tractus solitarii in view of the present findings.

Anorectic and neurochemical effects of pituitary adenylate cyclase activating polypeptide in rats

Pretreatment of rats with intrahypothalamic injections of pituitary adenylate cyclase activating peptide (PACAP) 10 min prior to the injection of neuropeptide Y (NPY) significantly reduced food and water intake during the 4-h measurement period. Intrahypothalamic injection of PACAP in schedule-fed rats also reduced food and water intake for 2 h. A smaller 1-h reduction of water intake was observed in water-deprived rats, suggesting that the anticonsummatory effects of PACAP were primarily against food intake. PACAP treatment did not alter hypothalamic concentration of NPY, nor were neurotransmitters, precursors, or metabolites altered substantially in corpus striatum or nucleus accumbens regions. These results demonstrate primary anorectic effects of intrahypothalamic injection of PACAP. The demonstration of these anorectic effects may suggest a role of cyclic AMP activation and inhibition in the control of satiety and hunger.

Coinjections of NPY(1-36) or [Leu31,Pro34]NPY with adrenaline in the nucleus tractus solitarius of the rat counteract the vasodepressor responses to adrenaline

The cardiovascular effects of adrenaline microinjected alone or together with neuropeptide Y (NPY) receptor agonists into the nucleus tractus solitarius (Sol) of the anaesthetized rat have been investigated in order to evaluate NPY/adrenergic receptor interactions. In the dose range 0.05-20 nmol, adrenaline microinjected unilaterally into the Sol produced significant dose-related reductions in mean arterial blood pressure and heart rate. The vasodepressor action of a close to ED50 dose of adrenaline (0.5 nmol) was significantly counteracted by a threshold dose of NPY (1-36) (1 pmol) and of the NPY Y1 receptor agonist [Leu31,Pro34]NPY (2.5 pmol) microinjected into the Sol, but not by a threshold dose of NPY(13-36)(50 fmol), a selective Y2 receptor agonist. The present study provides evidence for an antagonistic NPY Y1/adrenergic receptor interaction in the Sol of the rat, involved in cardiovascular regulation.

Neuropeptide Y-induced inositol phospholipid hydrolysis in blood vessels from normotensive and spontaneously hypertensive rats

1. Neuropeptide Y (NPY) increased inositol phosphate (IP) formation in the femoral artery and vein of adult Wistar Kyoto (WKY) and spontaneously hypertensive (SHR) rats. 2. Noradrenaline (NA, 10(-6) M) induced IP accumulation in both strains of rats. 3. Subthreshold concentrations of NPY (3 x 10(-9) M for femoral vein and 10(-8) M for femoral artery) failed to modify NA (10(-6) M)-induced IP formation in both vessels. 4. These results suggest that the direct contractile effects but not the potentiation of NA-induced contractions may be directly linked to phosphatidylinositol turnover in adult SHR and WKY rats.