Ontogenesis and regional distribution of histamine and histamine-N-methyltransferase in the guinea pig brain

The potentiating effects of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) on paraquat-induced neurochemical and behavioral changes in mice

Although the etiology of Parkinson's disease (PD) is not fully understood, there are numerous studies that have linked the increased risk for developing PD to pesticides exposure including paraquat (PQ). Moreover, the exposure to a combination of compounds or chemical mixtures has been suggested to further increase this risk. In the current study, the effects of PQ on the nigrostriatal dopaminergic system in male C57BL6 mice exposed to 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) were examined to assess the impact of toxic substance mixtures exposure on neurochemical and behavioral changes. In this study, a low non-toxic dose of MPTP (10mg/kg) was injected once a day for 5 days and was followed by PQ (7 mg/kg) once a day for 6 days (subacute protocol) or once a week for 10 weeks (chronic protocol). The results from the subacute protocol showed that PQ reduced the turnover of dopamine (DA) as indicated by a 21% and a 22.3% decrease in dihydroxyphenyl acetic acid (DOPAC), homovanillic acid and increased S-adenosyl methionine/S-adenosyl homocysteine index (SAM/SAH) by 100%. However, the administration of PQ to MPTP primed mice resulted in the decrease of DOPAC, HVA, DA, by 35.8%, 35.2% and 22.1%, respectively. In addition, PQ decreased the total number of movements (TM) by 28% but MPTP plus PQ decreased TM by 41%. The SAM/SAH index showed that MPTP increased methylation by 33.3%, but MPTP plus PQ increased methylation by 81%. In the chronic protocol, the data showed that MPTP administration did not affect DA, DOPAC, and HVA levels. The administration of PQ led to significant decrease in DOPAC, HVA, and TD by 31.6%, 19.9%, and 21.2% respectively with no effect on DA levels. The MPTP plus PQ group showed reduced DA, DOPAC, HVA, and total distance traveled by 58.4%, 82.8%, 55.8%, and 83.9%, respectively. Meanwhile, PQ administration caused a reduction in tyrosine hydroxylase immunoreactivity in the substantia nigra, and this effect was more pronounced in MPTP pretreated mice. It was concluded from this study that prior treatment with MPTP potentiated the effects of PQ in reducing DA, DOPAC, HVA, TH immunoreactivity, locomotor activity, and increasing the methylation index. The enhanced effects of PQ following MPTP administration further support the role of toxic substance mixtures in causing Parkinson's disease.

Neuronal and vascular localization of histamine N-methyltransferase in the bovine central nervous system

Histamine N-methyltransferase (HMT) (EC 2.1.1.8) plays a crucial role in the inactivation of the neurotransmitter histamine in the CNS. However, the localization of HMT remains to be determined. In the present study, we investigated immunohistochemical localization of HMT in the bovine CNS using a polyclonal antibody against bovine HMT. The HMT-like immunoreactivity was observed mainly in neurons. Strongly immunoreactive neurons were present in the oculomotor nucleus and ruber nucleus in the midbrain, the facial nucleus in the pons, the dorsal vagal nucleus and hypoglossal nucleus in the medulla oblongata and in the anterior horn as well as intermediolateral zone of the spinal cord. Intermediately immunoreactive neurons were present in the piriform cortex and the inferior olivary nucleus. The grey matter of the forebrain regions was diffusely and faintly stained. In the cerebellum and the striatum, the nerve fibres in the white matter were positive. The tuberomammillary nucleus, where histaminergic neurons are present, were weakly positive. The other immunoreactive structures in the CNS were blood vessels. Almost all of the blood vessel walls, irrespective of whether they were arterial or venous, were variably stained. The glial fibrillary acidic protein- (GFAP-) immunoreactive astrocytes were not stained. These findings indicated that histamine released from histaminergic nerve terminals or varicose fibres is methylated mainly in postsynaptic or extrasynaptic neurons rather than in astrocytes. The localization of HMT in the blood vessel wall may mean that blood-borne histamine and histamine released from mast cells associated with the blood vessels are catabolized in this structure.

Depletion of nigrostriatal and forebrain tyrosine hydroxylase by S-adenosylmethionine: a model that may explain the occurrence of depression in Parkinson's disease

The loss of nigrostriatal tyrosine hydroxylase (TH), dopamine and dopaminergic neurons are the major pathology of Parkinson's disease (PD). These catecholaminergic changes are responsible for the symptoms of tremor, hypokinesia and rigidity. Depression is also a major symptom in PD, but the cause is unknown. The impairments of catecholaminergic fibers in the frontal lobe may be involved, because the frontal lobe of the cerebrum is involved in the regulation of mood, and decreased catecholaminergic activity in the frontal lobe is related to behavioral depression. The changes that damage the nigrostriatal dopamine system and induce motor impairments may also damage the forebrain catecholamine fibers and induce depression. It means that manipulations that damage the nigrostriatum (NS) and induce parkinsonism may also deplete TH in the frontal cortex. Such an effect would suggests a basis for the depression seen in PD. The injection of S-adenosyl-L-methionine (SAM), the biological methyl donor, into the brain of rats damaged the NS, depleted TH and caused tremor and hypokinesia. SAM may interfere also with the forebrain TH, which may help to explain the occurrence of depression in PD. Experiments were designed to test such a hypothesis. The results showed that SAM caused a loss of immunoreactive nerve fibers and it decreased the intensity of TH-immunoreactivity (IR) in the frontal cortex. These changes were accompanied with the loss of cells and the depletion of TH-IR from nerve fibers in the SN and the caudate nucleus. Other studies showed that SAM depletes DA and since SAM induces PD-like changes the results may be relevant to the co-occurrence of PD symptoms and depression. A single biological manipulation may impair the nigrostriatal dopaminergic neurons as well as the frontal cortex catecholaminergic fibers.

Striatal dopamine depletion, tremors, and hypokinesia following the intracranial injection of S-adenosylmethionine: a possible role of hypermethylation in parkinsonism

The major symptoms of Parkinson disease (PD) are tremors, hypokinesia, rigidity, and abnormal posture, caused by the degeneration of dopamine (DA) neurons in the substantia nigra (SN) and deficiency of DA in the neostriatal DA terminals. Norepinephrine (NE) and serotonin (5-HT) levels in the neostriatum and tyrosine hydroxylase and melanin pigments in the substantia nigra are also decreased, and brain cholinergic activity is increased. The cause of PD is unknown, but PD is an age-related disorder, suggesting that changes that occur during the aging process may help to precipitate PD. Methylation increases in aging animals. Increased methylation can deplete DA, NE, and 5-HT; increase acetylcholine; and cause hypokinesia and tremors. These effects are similar to changes seen in PD, and interestingly also, they are similar to some of the changes that are associated with the aging process. It is suggested, therefore, that increased methylation may be an inducing factor in parkinsonism. Accordingly, the effects of an increase in methylation in the brain of rats were studied. S-adenosylmethionine (AdoMet), the limiting factor in the methylation process, was injected into the lateral ventricle of rats. Specific behavioral changes that resemble changes seen in PD were investigated. The results showed that AdoMet caused tremors, rigidity, hypokinesia, and depleted DA. The hypokinetic effects of a single dose of AdoMet lasted for about 90 min. AdoMet has a dose-dependent hypokinetic effect. A dose of 9.4 nmol reduced movement time (MT) by 68.9% and increased rest time (RT) by 20.7%, and a dose of 400 nmol reduced MT by 92.4% and increased RT by 27.6%. The normethyl analog of AdoMet, S-adenosylhomocysteine, did not cause hypokinesia or tremors, but it blocked the AdoMet-induced motor effects. L-dopa, the precursor of DA, also blocked the AdoMet-induced motor effects. These data suggest that the methyl group of AdoMet as well as DA depletion are involved in the AdoMet-induced motor effects. A dose of 0.65 mumol of AdoMet depleted DA in the ipsilateral caudate nucleus (CN) or neostriatum by 50.1%, and DA in the contralateral CN was reduced by 9.3%. Double the dose of AdoMet did not increase the depletion of DA on the ipsilateral CN, but DA in the contralateral CN was decreased by 26.3%. Taken together, the results suggest that increased methylation may contribute to the symptoms of PD.

Diurnal and age-related changes in cerebrospinal fluid tele-methylhistamine levels during infancy and childhood

Histamine is a neurotransmitter participating in many physiological functions and behavior, including control of arousal and modulation of the circadian rhythms. Diurnal variation in cerebrospinal fluid (CSF) levels of tele-methylhistamine (t-MH), the main histamine metabolite, has been detected in several animal studies. In humans, such changes have not been described. Little is known on the development of histaminergic neurons in human brain. In children, the levels of CSF t-MH are not known. Therefore, we have measured the concentrations of CSF t-MH in 81 children, age ranging from 3 months to 14.6 years. t-MH levels were higher in infants, and near adult values were measured in adolescents, the relation between CSF t-MH and age being; CSF t-MH = -0.217 years + 7.31 (n = 81, r = 0.26, p = 0.021). The mean t-MH concentration was higher during the daytime (7.07 +/- 0.46 pmol/ml, mean +/- SEM) than in the night (5.35 +/- 0.60 pmol/ml, p = 0.0019, ANOVA). The results show a development change in the concentration of t-MH during childhood and a difference in t-MH levels between the daytime and night indicating a more active metabolism of brain HA in the waking period.

Substantia nigra degeneration and tyrosine hydroxylase depletion caused by excess S-adenosylmethionine in the rat brain. Support for an excess methylation hypothesis for parkinsonism

The major symptoms of Parkinson's disease (PD) are tremors, hypokinesia, rigidity, and abnormal posture, caused by degeneration of dopamine (DA) neurons in the substantia nigra (SN) and deficiency of DA in the neostriatal dopaminergic terminals. Norepinephrine, serotonin, and melanin pigments are also decreased and cholinergic activity is increased. The cause of PD is unknown. Increased methylation reactions may play a role in the etiology of PD, because it has been observed recently that the CNS administration of S-adenosyl-L-methionine (SAM), the methyl donor, caused tremors, hypokinesia, and rigidity; symptoms that resemble those that occur in PD. Furthermore, many of the biochemical changes seen in PD resemble changes that could occur if SAM-dependent methylation reactions are increased in the brain, and interestingly, L-DOPA, the most effective drug used to treat PD, reacts avidly with SAM. So methylation may be important in PD; an idea that is of particular interest because methylation reactions increase in aging, the symptoms of PD are strikingly similar to the neurological and functional changes seen in advanced aging, and PD is age-related. For methylation to be regarded as important in PD it means that, along with its biochemical reactions and behavioral effects, increased methylation should also cause specific neuronal degeneration. To know this, the effects of an increase in methylation in the brain were studied by injecting SAM into the lateral ventricle of rats. The injection of SAM caused neuronal degeneration, noted by a loss of neurons, gliosis, and increased silver reactive fibers in the SN. The degeneration was accompanied with a decrease in SN tyrosine hydroxylase (TH) immunoreactivity, and degeneration of TH-containing fibers. At the injection site in the lateral ventricle it appears that SAM caused a weakening or dissolution of the intercellular substances; observed as a disruption of the ependymal cell layer and the adjacent caudate tissues. SAM may also cause brain atrophy; evidenced by the dilation of the cerebral ventricle. Most of the SAM-induced anatomical changes that were observed in the rat model are similar to the changes that occur in PD, which further support a role of SAM-dependent increased methylation in PD.

Monoamine oxidase: distribution in the cat brain studied by enzyme- and immunohistochemistry: recent progress

Localization of MAO-containing neurons, fibers and glial cells has been described by recent progress in MAO histochemistry and immunohistochemistry. It does not necessarily correspond to those containing monoamines. MAO-A is demonstrated in many noradrenergic cells, but it is hardly detectable in DA cells. Increase of 5-HT and DA concentration after inhibition of MAO-A indicates the possible existence of MAO-A in such neuronal structures. MAO-A is also undetectable in neurons containing 5-HT, a good substrate for MAO-A. These neurons contain MAO-B. There still remain contradictions to be solved in future. MAO is present in astroglial cells, in which monoamines released in extracellular space may be degraded. In glial cells, MAO may also play a role to regulate concentration of telemethylhistamine and trace amines. Such cells appear to transform MPTP to MPP+, a neurotoxin for nigral DA neurons.

Histamine inactivation in the brain: aspects of N-methylation

This report deals with molecular and anatomical site of histamine N-methylation assumed to be the exclusive route of HA inactivation. The methyl transfer from the -S-CH3 of S-adenosyl-L-methionine to the ring (tele)-nitrogen of histamine, appears as much more complex than a one-step transformation. It seems that -S-CH3 is transformed before being transferred to the nitrogen of the acceptor probably via methanol (formaldehyde) formation. For localizations of transmethylation of neuronal histamine we assume at least a two-compartment model in which glia participate to a significant extent. The uptake of neuronal HA into glial cells might be the first step of histamine inactivation.

Histamine, histidine decarboxylase and histamine-N-methyltransferase in brain areas of spontaneously hypertensive rats

Histamine levels, histidine decarboxylase and histamine-N-methyltransferase activities were determined in various brain areas of young (9-week old) and adult (18-week old) normotensive rats (WKY) and hypertensive rats (SHR). When compared with WKY, histamine levels were increased in the anterior and posterior hypothalamus of young and adult SHR, as well as in the brainstem of young SHR. Histidine decarboxylase activity was unchanged in the posterior hypothalamus and in the medulla oblongata of young and adult SHR as well as in the anterior hypothalamus of young SHR, but it was slightly decreased in the anterior hypothalamus of adult SHR. Histidine decarboxylase activity was enhanced in the cortex-midbrain of young, as well as adult SHR, histamine-N-methyltransferase in the cortex-midbrain of young SHR. The following differences were found between young and adult rats: histamine levels were elevated in the cortex-midbrain of adult WKY and SHR. In the cortex-midbrain and brainstem of adult WKY and SHR histidine decarboxylase activity was also increased, while histamine-N-methyltransferase activity was elevated in the cortex-midbrain of adult WKY. The findings show changes in histamine levels, histidine decarboxylase and histamine-N-methyltransferase activities in SHR and suggest involvement of histaminergic neurons in hypertension. The activity of histaminergic neurons of adult rats seems to be higher than that of young animals.

Development of histamine-immunoreactive neurons in the rat brain

This study was undertaken to reveal the cellular stores of histamine in developing rat brain and to determine the stage of development during which the histamine-immunoreactive neurons can first be detected. Rats from embryonal day 12 to postnatal day 14 were studied. The brains were fixed in 4% 1-ethyl-3(3-dimethylaminopropyl)carbodiimide and standard immunofluorescence technique was used. The first histamine-immunoreactive neurons were seen on embryonic day 13 in the border of mesencephalon and metencephalon. On embryonic day 15 immunoreactive neurons were detected in ventral mesencephalon and rhombencephalon. In caudal, tuberal, and postmammillary caudal magnocellular nuclei histamine-immunoreactive neurons were first detected on embryonic day 20 while those in the hindbrain had disappeared. Histamine-immunoreactive nerve fibers were first detected on embryonic day 15 in rhombencephalon and mesencephalon and in some areas of diencephalon including the mammillary bodies and frontal cortex. On embryonic day 18 the number of immunoreactive nerve fibers in the hindbrain had decreased considerably, but the olfactory bulb, septal and hypothalamic area, and the cerebral cortex showed immunoreaction in fibers. The density of histamine-immunoreactive fiber networks increased until postnatal day 14 when an adultlike pattern of neurons and fibers had developed. Histamine-immunoreactive neurons are present in embryonal CNS and they develop extensive projections to various brain areas.

Ontogeny of histidine-decarboxylase-immunoreactive neurons in the tuberomammillary nucleus of the rat hypothalamus: time of origin and development of transmitter phenotype

The ontogeny of the histidine decarboxylase (HDC)-immunoreactive neurons of the tuberomammillary (TM) nucleus was studied in the rat brain. The time of origin of TM neurons was studied by counting the percentage of HDC-immunopositive neurons double labelled by autoradiography in adult progeny of dams injected with [3H]-thymidine at various times during gestation. Neurogenesis began on embryonic day (E) 13, peaked on E16, and was complete by E18. HDC immunoreactivity was first detected in the fetal rat brain on E16. Experiments utilizing short-survival [3H]-thymidine autoradiography combined with HDC immunohistochemistry demonstrated that TM neurons undergo their final mitotic division prior to expression of their transmitter phenotype.

The histaminergic system in the guinea pig central nervous system: an immunocytochemical mapping study using an antiserum against histamine

Using an antiserum against conjugated histamine we mapped the histaminergic somata and their fiber projection areas in carbodiimide-fixed guinea pig central nervous system. The neurons were large and they were found exclusively in the posterior hypothalamus, as in the rat, but in the guinea pig they were more numerous and distributed more widely in thin layer around the posterior mammillary nucleus, scattered between and within the medial mammillary nuclei, and in a dense cell cluster emerging from the caudal magnocellular nucleus and extending to the medial preoptic area. The density of histamine-immunopositive fibers was very high in the olfactory tubercle, diagonal band of Broca, nucleus accumbens, medial and cortical amygdaloid nuclei, periventricular and lateral basal hypothalamus, paraventricular thalamus, and in a region from the medial central gray to the locus coeruleus and the parabrachial nucleus. Dense fiber networks were found in the piriform and entorhinal cortex, septum, dentate gyrus, and subiculum, in most parts of amygdala, and in many areas of the hypothalamus, thalamus, substantia nigra, raphe nuclei, inferior olivary, solitary tract and medial vestibular nuclei, and neurohypophysis. Medium fiber density was observed in the internal layers of the olfactory bulb, anterior olfactory nuclei, neocortex, zone CA1 of hippocampus, and many midbrain and hindbrain regions. Low density was present in the outer layers of the olfactory bulb, other parts of hippocampus, the globus pallidus, most of the caudatus-putamen, the cerebellar cortex, and the dorsal horn of the spinal cord. The retina and most of the myelinated white matter had single or no histaminergic fibers. It may be concluded from the results that most fibers seem to follow a ventromedial route to the forebrain, reaching the amygdala ventral to the medial forebrain bundle, the hippocampus via subiculum, and the hindbrain structures via the medial central gray. As compared to the rat, the fiber projections in the guinea pig brain were denser, particularly in the hippocampus, thalamus, pons-medulla, and neurohypophysis. The fiber densities in various regions of the guinea pig brain are compared to histamine receptor densities and the possible functions of histamine are discussed.

Enzymatic histamine catabolism in vertebrate ontogenesis. A comparative study

1. The synthesizing and degrading activities of histamine were determined in the liver and small intestine of developing guinea pig and chick embryos. 2. Though increasing with age, HDC values were always 2-3 orders of magnitude lower than those of degrading enzymes. 3. DAO activity on the other hand was 10-100 fold higher than HMT at all ages studied, suggesting a decisive role for oxidative deamination in control of tissue histamine levels. 4. Generally histamine levels were higher in tissues of developing guinea pig than chick embryo, however, in the laying hen intestine histamine concentration was approximately 5 times greater than in the adult guinea pig intestine.

Histamine levels and activity of histidine decarboxylase (HD) and histamine-methyltransferase (HMT) in neonate and adult human brain

The adult human brain contained histamine (HI), and showed well-expressed histidine decarboxylase (HD), histamine-methyltransferase (HMT) and monoamine oxidase (MAO) activity. The neonate human brain contained HI, and showed HMT and MAO activity; there was no HD activity. Neither the adult nor neonate brains possessed diamine oxidase activity.

Delayed ontogenesis of histamine in the hypothalamus of the homozygous Brattleboro rat

The ontogenetic development of histamine was studied in the diabetes insipidus rat to clarify the possible interference between the lack of vasopressin and the development of histaminergic systems in the hypothalamus. Rat pups were decapitated at different ages between the 2nd and 38th postnatal days. In addition to homozygous Brattleboro (diabetes insipidus) rats, Long Evans controls and heterozygous animals were studied. In all three genotypes hypothalamic histamine was almost equal during the first 6 postnatal days. In homozygous Brattleboro rats the period of most rapid increase occurred between days 14 to 26, which was significantly later than in Long Evans rats. In the remainder of the brain no such difference was seen. On the contrary, histamine values were highest in the youngest animals. It remains to be elucidated whether the delayed ontogenesis is causally related to vasopressin deficiency and what is the underlying mechanism.

Histidine transport into rat brain synaptosomes

Histidine transport and metabolism in rat brain synaptosomes were investigated to study the possible role of histidine uptake in the synthesis of the putative neurotransmitter histamine (HA). Histidine uptake was found to be regionally distributed and temperature sensitive, and was not totally independent of sodium or potassium ions. Transport was inhibited by metabolic inhibitors, as well as by promethazine and quinacrine. A number of other HA-related agents and several histidine metabolites had no effect. Kinetic analyses of histidine transport revealed the presence of both high- and low-affinity systems in cerebral cortex. Histidine uptake increased following preexposure of synaptosomes to depolarizing concentrations of potassium. This effect was dependent on the presence of calcium ions during the preincubation. No newly formed [3H]HA was detectable in rat brain synaptosomes following [3H]histidine transport. Lesions of the medial forebrain bundle did not alter histidine uptake in the hippocampus or cerebral cortex. Ontogenic studies indicated that the histidine uptake system developed rapidly and reached a peak during postnatal days 12-17. Overall, the present findings do not support a role for histidine transport in the regulation or maintenance of neurotransmitter pools of HA in rat brain.

High histamine levels in specific hypothalamic nuclei of Brattleboro rats lacking vasopressin

Histamine levels were determined in whole hypothalamus and specific hypothalamic nuclei of male 9-week-old homozygous Brattleboro rats lacking vasopressin and presenting the syndrome of diabetes insipidus (DI rats). These levels were compared to those in heterozygous Brattleboro rats with a partial deficit in vasopressin (HZ rats) and those in Long Evans control rats (LE rats). In whole hypothalamus, histamine levels in DI rats were higher than those found in HZ and LE rats. DI rats showed histamine levels higher than those present in LE rats in the nuclei supraopticus, paraventricularis and suprachiasmatis and in the area retrochiasmatica. Vasopressin replacement produced a selective decrease in histamine levels of DI rats, restricted to the area retrochiasmatica and nuclei supraopticus and paraventricularis. In contrast, vasopressin increased histamine levels in the area retrochiasmatica and eminentia mediana of HZ rats. In other areas normally rich in vasopressin such as the nucleus arcuatus and the eminentia mediana, the histamine content was not different among LE, HZ or DI rats. Our results suggest a physiological interaction between vasopressin and histamine systems in specific hypothalamic areas of the rat and support the hypothesis of a role of brain histamine on the central control of water balance.

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.

Phylogeny of histamine in vertebrate brain

Measurement of histamine and its metabolizing enzymes in a variety of chordate species indicated that histamine and histamine methyltransferase were present in brain of all vertebrate species with a recognizable brain structure. Diamine oxidase was absent in mammalian brain but was present in brain of lower vertebrates. Histamine levels were especially high in amphibia and fish brains, in which the phylogenetically newer parts of the brain were less well-developed. In the spiny dogfish (as in mammals), brain histamine levels were highest in the midbrain regions. In contrast to brain, histamine levels were low in muscle, skin and intestine of all aquatic species.

Ontogeny of histaminergic neurotransmission in the rat brain: concomitant development of neuronal histamine, H-1 receptors, and H-1 receptor-mediated stimulation of phospholipid turnover

The ontogeny of histaminergic neurotransmission in the rat brain was studied by assessing development of histamine levels in brain regions, along with H-1 receptor binding of [3H]mepyramine and H-1 receptor-mediated cellular events. In the hypothalamus, which is rich in histaminergic innervation, levels of the amine were low at birth, increased sharply at 8 days of age, and reached adult concentrations shortly thereafter; this pattern is typical of most neurotransmitters. In contrast, regions poor in neuronal histamine showed an initially high histamine level and a subsequent decline with development, as is known to occur during general growth of tissues. The developmental profile of H-1 receptor binding sites resembled that of the neuronal histamine pool, and the increases with age resulted from changes in the number of binding sites without alterations in Kd. Cellular responses to H-1 receptor activation were assessed by determining the stimulation of phospholipid turnover evoked by intracisternally administered histamine, a process that has been shown to involve only the neuronal compartment. Again, the developmental profile was superimposable upon that of H-1 receptor binding and that of hypothalamic histamine levels. These studies indicate that ontogeny of histaminergic neurotransmission is a coordinated process, with simultaneous development of neuronal histamine, its key biosynthetic enzyme, and H-1 receptors coupled directly to cellular events.

Vasopressin release by histamine in the conscious goat

The vasopressin releasing activity of histamine was studied in conscious goats. Histamine was infused into the brain ventricles or intravenously and serial blood samples were taken from the jugular vein. Plasma vasopressin was assayed by a radioimmunoassay for arginine vasopressin (AVP). After i.v. infusions of 300 micrograms and 1 mg of histamine, a pronounced increase in plasma AVP up to greater than 100 pg/ml occurred. This was considered secondary to hypotension, since it only occurred with doses that markedly decreased arterial blood pressure. When given i.c.v. even smaller doses of histamine increased plasma AVP without any concomitant decrease in blood pressure. There was a simultaneous decrease in renal free water clearance in hydrated animals. Up to the dose of 300 microgramshistamine, the increase in AVP was modest. Histamine 1 mg i.c.v., given to either hydrated or non-hydrated animals, increased plasma AVP about tenfold, up to 38.3 +/- 23.3 pg/ml and 56.7 +/- 19.0 pg/ml, respectively. In individual experiments the correlation between the AVP level and the degree of antidiuresis was less apparent, since the kidney seemed to be very sensitive even to small changes in plasma AVP. It is concluded that histamine releases vasopressin through a central mechanism and it is reasonable to suppose that histamine may act as a neurotransmitter in the vasopressin releasing system.

Antidiuresis induced by infusions of histamine into the brain ventricles of conscious hydrated goats

Histamine was infused into the third or lateral ventricle of conscious hydrated goats, and urine samples were analyzed for volume, osmolality and electrolytes. Doses of 10--1000 microgram of histamine induced dose-dependent antidiuretic responses both as to the maximum osmolality and the duration of the osmolality increase. Urine osmolality began to rise within a few minutes, reached its maximum within 0.5--2 h and was elevated for 1.5--4 h, depending on the dose. Thereafter a second increase in osmolality often occurred, which lengthened the effect of histamine dose-dependently up to about 10 h with the largest dose of histamine. Histamine (50--300 microgram) and the control solution given into the lateral ventricle increased the excretion of Na+ into the urine. After the largest dose of histamine (1000 microgram), however, the excretion of Na+ was significantly lower than in the control experiments. After the larger doses of histamine, effects on motor or autonomic functions were seen. These included decreased spontaneous motor activity, increased respiratory rate, defecation and miosis. It is suggested that the site of action of histamine is central, and that the release of vasopressin through the activation of the neurosecretory system is probably involved. In addition the changes in electrolytes may suggest an involvement of the release of other factors such as prolactin.

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.