Histamine-n-methyltransferase activity of the nervous system of the chick during development

Histamine H(2) -like receptors in chick cerebral cortex: effects on cyclic AMP synthesis and characterization by [(3) H]tiotidine binding

In this study, histamine (HA) receptors in chick cerebral cortex were characterized using two approaches: (1) analysis of the effects of HA-ergic drugs on the cAMP-generating system, and (2) radioreceptor binding of [(3) H]tiotidine, a selective H(2) antagonist. HA was a weak activator of adenylyl cyclase in a crude membrane preparation of chick cerebrum. On the other hand, HA (0.1-1000 microm) potently and concentration dependently stimulated cAMP production in [(3) H]adenine pre-labelled slices of chick cerebral cortex, displaying an EC(50) value (concentration that produces 50% of maximum response) of 2.65 microm. The effect of HA was mimicked by agonists of HA receptors with the following rank order of potency: HA >or= 4-methylHA (H(2)) >or= N alpha,N alpha-dimethylHA (H(3) >> H(2) = H(1)) >> 2-methylHA (H(1)) >> 2-thiazolylethylamine (H(1)) >or= R alpha-methylHA (H(3)) >> amthamine, dimaprit (H(2)), immepip (H(3), H(4)). The HA-evoked increase in cAMP production in chick cerebral cortex was antagonized by selective H(2) receptor blockers (aminopotentidine >or= tiotidine > ranitidine >> zolantidine), and not significantly affected by mepyramine and thioperamide, selective H(1) and H(3) /H(4) receptor blockers, respectively. A detailed analysis of the antagonistic action of aminopotentidine (vs. HA) revealed a non-competitive mode of action. The binding of [(3) H]tiotidine to chick cortical membranes was rapid, stable and reversible. Saturation analysis resulted in a linear Scatchard plot, suggesting binding to a single class of receptor binding site with high affinity [equilibrium dissociation constant (K (d)) = 4.42 nm] and high capacity [maximum number of binding sites (B (max) ) = 362 fmol/mg protein]. The relative rank order of HA-ergic drugs to inhibit [(3) H]tiotidine binding to chick cerebrum was: antagonists - tiotidine >> aminopotentidine = ranitidine >or= zolantadine >> thioperamide - triprolidine; agonists - HA >or= 4-methylHA >> 2-methylHA >or=R alpha-methylHA - dimaprit. In conclusion, chick cerebral cortex contains H(2) -like HA receptors that are linked to the cAMP-generating system and are labelled with [(3) H]tiotidine. The pharmacological profile of these receptors is different from that described for their mammalian counterpart. It is suggested that the studied receptors represent either an avian-specific H(2) -like HA receptors or a novel subtype of HA receptors.

Histamine in the chick pineal gland: origin, metabolism, and effects on the pineal function

The chick pineal gland contains histamine and tele-methylhistamine. The levels of both substances are elevated after treatment of chicks with the amino acid precursor of histamine, L-histidine (1 g/kg, ip). In control and L-histidine-loaded animals the pineal levels of histamine and tele-methylhistamine are higher in light-exposed than in dark-adapted animals (measured at the end of the light phase and in the middle of the dark phase of 12 hr light, 12 hr dark illumination cycle, respectively). The chick pineal gland contains histamine-immunofluorescent cells displaying mast cell morphology; they are seen in the vicinity of the capsule and in the parenchyma. Enzymatic studies showed the presence of the activity of histamine synthesizing and inactivating enzyme, i.e., L-histidine decarboxylase (HDC) and histamine-methyltransferase (HMT). The detected enzyme activities were sensitive to specific inhibitors of HDC (alpha-fluoromethylhistidine and alpha-hydrazinohistidine) and HMT (quinacrine and metoprine); inhibitors of aromatic amino acid decarboxylase alpha-methyl-DOPA and NSD-1015 were inactive on HDC. Exogenous histamine added to organ-cultured chick pineals strongly stimulated endogenous cyclic AMP accumulation and moderately increased melatonin secretion. The data, considered collectively, suggest that in avians histamine, probably originating from the pineal mast cell compartment, may function as a regulator of pineal gland activity.

Histamine and histamine-N-methyltransferase in the goat brain

Histamine concentrations and histamine-N-methyltransferase (HMT) (EC 2.1.1.8) activities were assayed in the goat brain, since this animal has been used for the purpose of assessing the physiological role of histamine in the central nervous system. The highest histamine concentrations were found in the hypothalamus (616 +/- 88 ng/g), 'thalamus' (244 +/- 41), preoptic area (242 +/- 95) and 'area postrema' (170 +/- 52), and are three to tenfold higher than the average concentration in the whole brain (76 +/- 9). The pineal body and choroid plexus contained very high concentrations of histamine (5800 and 5400 ng/g, respectively) and the pituitary gland had about the same as the hypothalamus (564 +/- 248 ng/g). There was little variation in the HMT activity in various parts of the brain and in the glands. In the cerebrospinal fluid both histamine concentration and HMT activity were very low, some increase occurred post mortem, but not within 20 minutes of death. The results indicate that the distribution of histamine and that of HMT in the goat brain are fairly similar to those in other mammalian brains, supporting the assumption that histamine might have a physiological function in the brain, especially in the hypothalamus.

Effect of Wallerian degeneration on histamine concentration of the peripheral nerve

One sciatic nerve of a White Leghorn hen was severed and the distal portion was allowed to undergo Wallerian degeneration. The change in histamine and DNA concentration and mast cell number was measured at different times following nerve sectioning in the proximal regenerating, distal degenerating, and intact, contralateral nerves. The experimental results revealed a significant accumulation of histamine in the proximal desheathed segment and in the contralateral "functional nerve," whereas the biogenic amine in the distal desheathed nerve significantly decreased. The pattern of change of histamine in the distal and proximal nerve sheaths was different: it dropped at 2 h and then rose in the later stages of Wallerian degeneration. In the distal desheathed nerves and in both the proximal and distal nerve sheaths DNA increased significantly by 14 days. The number of mast cells appeared to be highest in the 14-day distal nerve and in the 7-day proximal nerve sheaths. These results support a dual localization of histamine in the peripheral nerve, and are consistent with the interpretation that the amine has either some role in neurotransmission or in the process of growth and regeneration.

Hydroxyindole-O-methyltransferase (HIOMT), catechol-O-methyltransferase (COMT) and histamine-N-methyltransferase (HNMT) in the pineal gland of the vizcacha (Lagostomus maximus maximus)

The activities of three methylating enzymes HIOMT, COMT, and HNMT were determined in pineal glands from 2 groups of adult vizcachas of both sexes, one (I) maintained under permanent lighting (15 days) and the other (II) kept in darkness. The control determinations (III) were carried out in pineal glands from animals hunted and killed during the night. In (I) the HIOMT activity decreased and the COMT activity increased; no changes were exhibited by HNMT. In (II) showed a diminished HIOMT activity. In captivity illumination affected HIOMT and COMT activites in a similar form to that observed in other species of rodents. The decrease in HIOMT activity in (II) suggests that captivity may affect pineal function, possibly as a consequence of a decrease in locomotor activity.

Ontogenesis of histamine in the chick nervous system

Tissues from the central and peripheral nervous systems of the chick were analyzed for concentration of histamine (Hm) during development. Of the three CNS organs examined, cerebral hemispheres had the highest Hm content. Expressed on the bases of wet weight, protein, and DNA concentrations, sciatic nerve and the pineal gland had the highest levels of this biogenic amine of the five tissues investigated. The concentration of Hm was higher in the cerebellum, cerebral hemispheres, and thalamus of adult animals than in the 15 to 17-day-old embryos. The level of Hm rose markedly in the sciatic nerve and pineal gland after the 15th day of embryonic development. These data might indicate a possible involvement of Hm in controlling the course of maturation of certain organs in the nervous system.