Histamine increases ornithine decarboxylase activity in primary cultures of cerebellar granule cells

Polyamine uptake in cultured cerebellar granule neurons

In the present study, we have examined the transport of polyamines in cultured cerebellar granule cells. Our results suggest the existence of two different transporters for polyamines in these neurons. Putrescine and spermidine uptake (K ap m = 2.17 and 1.39 microM, respectively), were affected when extracellular sodium was replaced with choline (about 30% inhibition over controls) or sucrose (about 2.5-fold potentiation over controls). By contrast, the substitution of sodium by choline or sucrose did not modify spermine uptake (K ap m = 13.53 microM) in cerebellar granule cells. Accordingly, alteration of membrane potential with ouabain was able to block putrescine (50% inhibition) and spermidine (60% inhibition) uptake but not spermine uptake. These results indicate that putrescine and spermidine transport in cerebellar granule cells is membrane potential dependent, whereas spermine uptake is not modulated by membrane potential.

Signal transduction by histamine in the cerebellum and its modulation by N-methyltransferase

Histamine has been suggested to have roles as a neurotransmitter or a neuromodulator. Direct fiber connections between the hypothalamus and the cerebellum have recently been demonstrated and it is suggested that the cerebellum is involved in the control of autonomic and emotional functions. These fibers include histaminergic fibers. The components of histaminergic signal transmission are demonstrated in the cerebellum as follows: (1) the histaminergic fibers are visualized immunohistochemically in the cerebellar cortex of rat, guinea pig and human; (2) histamine H1 receptors are visualized by autoradiographic studies in the molecular layer of mouse and guinea pig. In situ hybridization study also detects the expression of H1 receptors in the Purkinje cells. H2 receptors are expressed in the Purkinje cells and granule cells of guinea pig; and (3) the application of histamine to the slices of guinea pig or rat cerebellar cortex elicits an increase in the turnover of phosphoinositides, so H1 receptors in the cerebellum are functional. Additionally, we have recently shown in the guinea pig that Purkinje cells express one of the histamine inactivating enzymes, and that inhibition of this enzyme enhances phosphoinositide turnover by histamine. Therefore, all the components of histaminergic neurotransmission are demonstrated in the cerebellum. These data suggest that histamine is involved in the signal transmission from the hypothalamus to the cerebellum. Here we review each component of histaminergic neurotransmission in the cerebellum.

The prenatal exposure to delta 9-tetrahydrocannabinol affects the gene expression and the activity of tyrosine hydroxylase during early brain development

We have previously reported that the exposure of pregnant female rats to delta 9-tetrahydrocannabinol (THC) during the perinatal period affected the gene expression and the activity of tyrosine hydroxylase (TH) in the brain of their male offspring. Those studies were done in animals perinatally exposed to THC but tested at peripubertal and adult ages. In the present work, we explored whether these effects also appear during early fetal brain development, when TH expression plays an important role in neuronal development. To this end, TH-mRNA concentrations were measured by Northern blot analysis with a specific TH probe in the brain of fetuses at gestational days 14 and 16 which had been prenatally exposed to THC or vehicle from day 5 of gestation. In parallel, measurements of TH activity and catecholamine contents by HPLC were also done. The results obtained were as follows. The prenatal exposure to THC markedly affected the expression of the TH gene in the brain of fetuses at gestational day 14. Thus, the amounts of TH-mRNA at this age were higher (2-fold) in THC-exposed fetuses than in controls. This corresponded with a marked increase in the activity of this enzyme (3-fold) at this age. Normalization was found in both parameters at gestational day 16. In summary, the prenatal exposure to THC affected the expression of the TH gene and the activity of this enzyme in brain catecholaminergic neurons during early fetal brain development. These results support the notion that cannabinoids are able to act at the level of the gene expression of specific key proteins for brain development.

Induction of ornithine decarboxylase by N-methyl-D-aspartate receptor activation is unrelated to potentiation of glutamate excitotoxicity by polyamines in cerebellar granule neurons

Polyamines positively modulate the activity of the N-methyl-D-aspartate (NMDA)-sensitive glutamate receptors. The concentration of polyamines in the brain increases in certain pathological conditions, such as ischemia and brain trauma, and these compounds have been postulated to play a role in excitotoxic neuronal death. In primary cultures of rat cerebellar granule neurons, exogenous application of the polyamines spermidine and spermine (but not putrescine) potentiated the delayed neurotoxicity elicited by NMDA receptor stimulation with glutamate. Furthermore, both toxic and nontoxic concentrations of glutamate stimulated the activity of ornithine decarboxylase (ODC)--the key regulatory enzyme in polyamine synthesis--and increased the concentration of ODC mRNA in cerebellar granule neurons but not in glial cells. Glutamate-induced ODC activation but not neurotoxicity was blocked by the ODC inhibitor difluoromethylornithine. Thus, high extracellular polyamine concentrations potentiate glutamate-triggered neuronal death, but the glutamate-induced increase in neuronal ODC activity may not play a determinant role in the cascade of intracellular events responsible for delayed excitotoxicity.