Neuropeptide Y--a cotransmitter with noradrenaline and adenosine 5'-triphosphate in the sympathetic nerves of the mouse vas deferens? A biochemical, physiological and electropharmacological study

Adenosine and neuropeptide Y enhance alpha 1-adrenoceptor-induced accumulation of inositol phosphates and attenuate forskolin-induced accumulation of cyclic AMP in rat vas deferens

The action on alpha 1-adrenoceptor-coupled polyphosphoinositide breakdown of two modulators of adrenergic neurotransmission, adenosine and neuropeptide Y (NPY), was studied in pieces of rat vas deferens. Both adenosine and NPY dose-dependently increased the accumulation of inositol phosphates induced by phenylephrine (50 microM), but neither of the two compounds had any effect alone on inositol phosphate accumulation. In parallel experiments, adenosine and NPY dose-dependently decreased forskolin-induced cyclic AMP accumulation without affecting resting levels. Phenylephrine slightly increased forskolin (1 microM)-induced cyclic AMP accumulation, whereas treatment with agents that increase or mimic cyclic AMP (forskolin, prostaglandin E2, 8-Br-cyclic AMP) had no significant effect on phenylephrine-induced inositol phosphate accumulation. The previously described potentiation of the alpha 1-adrenoceptor-mediated contractile responses of the rodent vas deferens by adenosine and NPY is suggested to result from an enhanced alpha 1-adrenoceptor-induced accumulation of inositol triphosphate. Possible mechanisms are discussed.

A new microdissection technique for regional biochemical analysis of the rat spinal cord: serotonin, norepinephrine, dopamine and uric acid

This report described a new microdissection procedure to evaluate the regional distribution of neuromediators in the rat spinal cord. Different segments are first divided into sagittal slices. From these, different grey and white matter regions can be microdissected. This permits selective biochemical measurements in different laminae, including the area around the central canal. White and grey matter can also be differentially analysed. Using HPLC with electrochemical detection, we report on the regional analysis of biogenic amines as well as uric acid. An increase in 5-hydroxytryptamine (5-HT) levels was observed from cervical to lumbar segments. 5-HT levels were highest in the motoneurone samples (lamina IX) of the lumbar cord. The next highest levels were found in lamina X, followed by the intermediate grey matter laminae and the dorsal horn. Small amounts of 5-HT were detected in the white matter. Interestingly, the ratio of 5-hydroxyindoleacetic acid (5-HIAA) to 5-HT was greatest in the white matter and least in the motoneurone sample. Norepinephrine (NE) levels were higher in the thoracic than in the cervical or the lumbar cord. The highest levels were found in the lamina X in thoracic segments. With this exception, no marked laminar difference in NE levels was observed. Dopamine (DA) levels were highest in the dorsal horn of the cervical and the thoracic cord, the next highest levels were found in the intermediate grey matter and lamina X in the same segments. The distribution of uric acid (UA) was comparable to that of NE: UA levels were highest in the thoracic cord, but no marked laminar difference was observed. On the other hand, UA levels in white matter generally exceeded those in the grey matter. These data indicate the value of a sagittal regional microdissection of the spinal cord. The ability to separately analyse different laminae of the cord (as well as differentiating grey and white matter) should prove useful in future studies of experimentally evoked changes in neurotransmitters within functionally distinct regions of the spinal cord.

[Cholinergic nerve endings: cellular function and molecular structure]

Progress made in the study of the cellular and molecular function of cholinergic nerve terminals suggests that the textbook schemes need to be extended. Vesicles contained in cholinergic nerve terminals not only store acetylcholine but also ATP and Ca2+ as well as peptides. These substances when co-released by exocytosis may modulate transmission both pre- and postsynaptically.

Neuropeptide Y receptors and the inhibition of adenylate cyclase in the human frontal and temporal cortex

The presence of a single class of high affinity, saturable binding sites for [3H]neuropeptide Y (NPY) was demonstrated in membranes from human frontal and temporal cortex. The specific binding of [3H]NPY was sensitive to guanosine 5'-triphosphate (GTP) and guanylyl-imidodiphosphate (GMPP(NH)P; 100 microM) which lowered the total binding capacity (Bmax) value (35 +/- 2 fmol/mg in the frontal cortex and 82 +/- 3 fmol/mg in the temporal cortex) by 50%. GTP and GMPP(NH)P did not affect the dissociation constant (Kd) value which was 0.25 +/- 0.03 nM in a frontal cortex sample and 0.76 +/- 0.06 nM in the sample from the temporal cortex. The affinity and GTP sensitivity of the [3H]NPY binding to human brain membranes parallels that found in the rat brain. It was demonstrated that occupancy of NPY receptors by NPY (1 microM) inhibits the basal and forskolin (10 microM)-stimulated adenylate cyclase activity by 18-30% in a crude membrane preparation from human frontal cortex.

Presynaptic effects of neuropeptide Y on [3H]noradrenaline and [3H]acetylcholine release

The electrically evoked release of radioactivity from mouse vas deferens and rat hypothalamic slices preloaded with [3H]noradrenaline was measured. In addition the release of [3H]acetylcholine from longitudinal muscle strip of guinea-pig ileum was also measured. Neurochemical evidence has been obtained that neuropeptide Y (NPY), although it co-exists and is released with (-)-noradrenaline (NA), it behaves differently as far as its effect on presynaptic modulation of chemical neurotransmission is concerned. It exerts a frequency-dependent presynaptic inhibitory effect on noradrenaline release from mouse vas deferens but has no effect on the electrically evoked release of NA from rat hypothalamus. Unlike NA, NPY does not influence the release of [3H]acetylcholine from the longitudinal muscle strip of guinea-pig ileum and does not potentiate the presynaptic effect of NA. It seems very likely, that the inhibitory effect of NPY is mediated via receptors. Its action is concentration dependent. While exogenous noradrenaline inhibited the release of noradrenaline by 91%, the maximum inhibition reached with NPY was not higher than 60%, indicating that either the intrinsic activity of NPY is lower or much less axon terminals are equipped with NPY receptors. Peptide YY (PYY) also reduced the release of NA from mouse vas deferens.