Uptake of 3H-noradrenaline and 3H-5-hydroxytryptamine in cultured rat brainstem

Autoradiographic studies on the uptake of 3H-dopamine by neurons and astrocytes in explant and primary cultures of rat CNS: effects of uptake inhibitors

The cellular localization of the uptake of 3H-dopamine was studies in explant and primary cultures from various regions of rat central nervous system by means of autoradiography. In explant cultures of substantia nigra, 3H-dopamine was taken up by cell bodies and processes of many neurons. In cultures from striatum, cerebellum and spinal cord, neuronal cell bodies were not labelled, whereas outgrowing nerve fibres revealed intense uptake of the monoamine. Uptake of 3H-dopamine by neurons was Na(+)- and temperature-dependent, suggesting an active uptake mechanism. In explant cultures, astrocytes did not accumulate 3H-dopamine, whereas in primary cultures, which were prepared from the same regions of rat central nervous system as the explant cultures, astrocytes also revealed uptake of this monoamine. The intensity of labelling was dependent on the incubation time. Little uptake of 3H-dopamine was observed after an incubation time of 5 min and only after 10-15 min did the astrocytes show moderate labelling. Uptake of 3H-dopamine by astrocytes was not Na(+)- and temperature-dependent, indicating that glial cells do not possess an active uptake mechanism for this monoamine. This is consistent with biochemical investigations by other laboratories, demonstrating that astrocytes accumulate 3H-dopamine by a facilitated diffusion system. Addition of the uptake inhibitors nomifensine or GBR 12909 to explant cultures markedly reduced or inhibited uptake of 3H-dopamine by neurons at a concentration of 10(-6) M. In contrast, accumulation of 3H-dopamine by astrocytes in primary cultures was only slightly affected by nomifensine at 10(-6) M. At the highest concentration used (10(-5) M), nomifensine also blocked the uptake of 3H-dopamine by astrocytes. Our finding that GBR 12909 almost completely inhibited the uptake of 3H-dopamine by astrocytes already at 10(-6) M suggests that this compound is a more potent inhibitor of the glial uptake of dopamine than nomifensine.

Autoradiographic studies on the uptake of 3H-noradrenaline and 3H-serotonin by neurones and astrocytes in explant and primary cultures of rat CNS: effects of antidepressants

Autoradiographic studies were made on the uptake of 3H-noradrenaline and 3H-serotonin in explant cultures and primary astrocyte cultures from various regions of rat central nervous system (cortex, cerebellum, locus coeruleus, nucleus raphé, spinal cord). In explant cultures from locus coeruleus and nucleus raphé cell bodies and processes of many neurones revealed intense labelling by 3H-noradrenaline and 3H-serotonin, respectively. In cultures from cortex, cerebellum and spinal cord the cell bodies of neurones did not show labelling by the monoamines but many nerve fibres in the outgrowth zone had taken up 3H-noradrenaline and 3H-serotonin. Astrocytes in explant cultures did not take up 3H-noradrenaline and 3H-serotonin whereas astrocytes in primary cultures showed heavy uptake of both monoamines. In contrast, amino acid transmitters such as 3H-GABA and 3H-glutamate were accumulated by astrocytes in explant as well as in primary cultures. Uptake of both 3H-noradrenaline and 3H-serotonin by neurones and astrocytes was considerably reduced or inhibited in Na(+)-free incubation medium or at low temperature, suggesting an active uptake mechanism. Addition of the antidepressants maprotiline and (+)oxaprotiline inhibited the uptake of 3H-noradrenaline by neuronal cell bodies and fibres in explant cultures and by astrocytes in primary cultures. The uptake of 3H-serotonin by neurones and astrocytes was blocked by citalopram and paroxetine. Our studies demonstrate that astrocytes in primary cultures are able to actively take up 3H-noradrenaline and 3H-serotonin whereas there was no uptake of monoamines into astrocytes in explant cultures, suggesting that there is a difference between astrocytes in different culture systems (explant cultures vs primary cultures) with respect to the uptake of monoamine transmitters.

Binding sites for [3H]dopamine and dopamine-antagonists on cultured astrocytes of rat striatum and spinal cord: an autoradiographic study

The cellular localization of binding sites for [3H]dopamine, and dopamine-antagonists (D1 and D2) was studied in organotypic cultures of rat striatum and spinal cord by means of autoradiography. In both types of cultures, many astrocytes were labelled by [3H]dopamine, the D1-antagonist [3H]cis-flupenthixol and the D2-antagonists [3H]domperidone and [3H]spiperone (10(-9) to 10(-8) M). Addition of unlabelled dopamine and antagonists at high concentrations (10(-6) to 10(-4) M) inhibited or markedly reduced binding of the radioligands indicating 'specific' binding of the compounds. Our autoradiographic studies are consistent with biochemical investigations by other authors, suggesting that astrocytes possess receptors for dopamine.

Amino acid and monoamine transport in primary astroglial cultures from defined brain regions

The uptake of L-[3H]glutamate, L-[3H]aspartate, gamma-[3H]aminobutyric acid (GABA), [3H]dopamine, DL-[3H]norepinephrine and [3H]5-hydroxytryptamine (5-HT) was studied in astrocytes cultured from the cerebral cortex, striatum and brain stem of newborn rat and grown for 2 weeks in primary cultures. The astrocytes exhibited a high-affinity L-glutamate uptake with Km values ranging from 11 to 110 microM. Vmax values were 4.5 in cerebral cortex, 39.1 in striatum, and 0.4 in brain stem, nmol per mg cell protein per min. There was a less prominent high-affinity uptake of L-aspartate with Km values from 88 to 187 microM. Vmax values were 7.4 in cerebral cortex, 37.1 in striatum, and 3.1 in brain stem, nmol per mg cell protein per min. The high-affinity GABA uptake exhibited Km values ranging from 5 to 17 microM and Vmax values were 0.01 for cerebral cortex, 0.04 for striatum, and 0.1 for brain stem, nmol per mg cell protein per min. No high-affinity, high-capacity uptake was found for the monoamines. The results demonstrate a heterogeneity among the astroglial cells cultivated from the different brain regions concerning the uptake capacity of amino acid neurotransmitters. Furthermore, amino acid transmitters and monoamines are taken up by the cells in different ways.

Autoradiographic localization of binding sites for [3H]histamine and H1- and H2-antagonists on cultured neurones and glial cells

By means of autoradiography we have studied the cellular localization of binding of [3H]histamine and H1- and H2-antagonists in explant cultures of rat cerebellum, brain stem and spinal cord. In brain stem and spinal cord cultures, a relatively great number of neurones revealed binding sites for [3H]histamine and to a lesser extent also for the H1-antagonist [3H]pyrilamine and for the H2-antagonist [3H]tiotidine. In contrast, only a small number of labelled neurones was found in cerebellar cultures. The intensity of labelling was usually much stronger for [3H]histamine than for its antagonists, suggesting that binding sites for histamine might reflect both H1- and H2-receptors. Glial cells also showed binding sites for [3H]histamine and the H1- and H2-antagonists, the number of labelled astrocytes by these radioligands was, however, smaller than that observed with [3H]noradrenaline and alpha- and beta-adrenergic antagonists. It is suggested that in addition to alpha- and beta-adrenoceptors, glial cells also possess receptors for histamine.

Enzyme activities of monoamine oxidase, catechol-O-methyltransferase and gamma-aminobutyric acid transaminase in primary astroglial cultures and adult rat brain from different brain regions

The activities of monoamine oxidase (MAO), catechol-O-methyltransferase (COMT) and gamma-aminobutyric acid transaminase (GABA-T) were measured in primary cultures from newborn rat cultivated from 6 different brain regions. These primary cultures contained mostly astroglial cells, evaluated by the presence of the glial fibrillary acidic protein (GFAp, alpha-albumin) and the S-100 protein. The enzyme activities in the corresponding brain area from adult rat were also quantified. MAO activities were on the same level in 14-day old cultures and in adult rat brain homogenates, with significantly lower values in brain stem as compared to the other brain regions examined. COMT activities were on a higher level in the cultures than in adult rat brain homogenates. Astroglial cells from hippocampus were found to have the highest and those from brain stem the lowest COMT-activities. GABA-T activities were lower in the cultures than in adult rat homogenates. No significant differences were seen in the various astroglial cultures. Accumulation of [3H]dopamine and [3H]gamma-aminobutyric acid (GABA) visualized by autoradiography showed only a slight uptake of dopamine in comparison with the uptake of GABA. It is concluded that astroglial cells in culture have enzymatic properties similar to those of astroglial cells in different brain regions of adult rat brain. Studies are in progress to evaluate if the regional heterogeneity observed among cultivated astroglial cells is affected by in vivo differentiation until cultivation and/or time in culture.

Accumulation of putative amino acid neurotransmitters, monoamines and D-Ala2-Met-enkephalinamide in primary astroglial cultures from various brain areas, visualized by autoradiography

The accumulation of amino acids, monoamines and D-Ala2-Met-enkephalinamide (Enk) was visualized by autoradiography in astroglial primary cultures from different well-defined brain areas. The most prominent accumulation of grains was seen after incubating astroglial cultures from cerebral cortex, hippocampus and striatum with glutamate. Less uptake was seen in brainstem and cerebellar cultures. Similar results were found with aspartate but at a lower uptake level. The accumulation of GABA was moderate in all cultures studied. Dopamine, norepinephrine and 5-hydroxytryptamine (5-HT) showed only a slight accumulation and enkephaline did not accumulate at all. The results demonstrate that astroglial cells are not general inactivators for neurotransmitters, as monoamines are taken up only slightly and enkephalin not at all, while the cells have the capacity to accumulate at least some amino acid neurotransmitters. Furthermore, astroglial cells from different brain regions have different capacities to accumulate the various amino acid neurotransmitters supporting the view of regionally specialized astroglial cells.

Development of catecholaminergic phenotypic characters in the mouse locus coeruleus in vivo and in culture

While abundant studies have begun to elucidate ontogeny of the peripheral nervous system, molecular mechanisms underlying brain development remain obscure. To approach this problem, we initiated parallel in vivo and in vitro studies of the mouse locus coeruleus (l.c.), a brainstem noradrenergic nucleus. The catecholaminergic enzymes tyrosine hydroxylase (TH) and dopamine-beta-hydroxylase (DBH) were used to monitor phenotype expression and development. TH catalytic activity and immunocytochemical reactivity were initially detectable on gestational Day 13 (E-13) in vivo, and adult levels of activity were approximately by the third postnatal week. Immunotitration studies indicated that the developmental increase was due to accumulation of enzyme molecules and not enzyme activation. The in vivo developmental profile of DBH approximated that of TH. To begin defining regulatory mechanisms, explants of embryonic brainstem were placed in culture. Explantation on E-12, prior to expression of TH or DBH, resulted in the de novo appearance of these phenotypic characters after 4 days. Explantation on E-18, after the enzymes are already expressed, was followed by a striking sixfold rise in TH activity. Immunotitration studies revealed that the increase in TH activity in E-18 cultures was attributable to increased molecule number, reproducing the in vivo results. Moreover, the E-18 explants, cultured for 3 weeks, attained higher plateau levels of TH activity than E-12 cultures, and this differences was due to increased molecule number. Morphometric analysis indicated that 3-week E-12 cultures actually had more l.c. cells than E-18 cultures, indicating that differences in TH were not due to increased cells in the E-18 l.c. Finally, systemic study revealed that the development of TH activity in culture increased progressively from E-11 to E-12 to E-13, suggesting that critical regulatory events occur at this time. Our studies suggest that the l.c. is an excellent model for the study of brain development in vivo and in vitro. Initial phenotypic expression and dramatic development occur in culture in the absence of normal targets, normal afferent innervation and, presumably, normal humoural milieu.

Evidence for the existence of alpha- and beta-adrenoceptors on neurones and glial cells of cultured rat central nervous system--an autoradiographic study

The cellular localization of the binding of radioactive noradrenaline and alpha- and beta-adrenoceptor antagonists was studied in organotypic cultures of rat cerebellum, brain stem and spinal cord using autoradiography. In cerebellar cultures, many neurones, which appeared to be Purkinje cells, were labelled by [3H]noradrenaline and by the beta-antagonists [3H]dihydroalprenolol and [3H]carazolol, whereas no binding of the alpha-antagonists [3H]prazosin and [3H]rauwolscine was detected. In cultures of spinal cord and brain stem, [3H]noradrenaline and the beta-antagonists were bound to many large neurones. Binding of [3H] alpha-antagonists was observed to a small number of brain stem and spinal neurones, the labelling being much weaker than that produced by the [3H] beta-antagonists. The antidepressant [3H]desmethylimipramine was bound to many neurones and glial cells in cerebellar, brain stem and spinal cord cultures. Glial cells also possessed binding sites for [3H]noradrenaline and alpha- and beta-adrenoceptor antagonists, findings that are consistent with recent electrophysiological observations which indicate the existence of alpha- and beta-adrenoceptors on cultured astrocytes.

Calcium-sensitive accumulation of norepinephrine in rat cerebral cortex

The accumulation of high and low concentrations of [3H]-norepinephrine has been examined in a crude synaptosomal preparation of rat cerebral cortex in the presence and absence of uptake1 inhibitors. When uptake1 was blocked, [3H]-norepinephrine accumulation exhibited very rapid initial rates. It was not inhibited by 10 mM normetanephrine, a potent inhibitor of peripheral uptake2, but it was inhibited by 10 mM metaraminol. This accumulation was markedly reduced when calcium ions were omitted from the incubation medium, and is named here 'calcium-sensitive accumulation' (CSA) to distinguish it functionally from the sodium-dependent, high affinity, uptake1 process. CSA may be localized in nerve endings since it was found predominantly i the synaptosomal fraction of homogenates subjected to density gradient centrifugation in sucrose or in Ficoll-in-sucrose. At high concentrations of [3H]l-norepinephrine (1.0 microM) and short incubation times, CSA accounted for most of the total accumulation of [3H]l-norepinephrine whereas uptake1 contributed only a small portion. Since extracellular concentrations of brain norepinephrine are thought to reach levels in excess of 1.0 microM, CSA may be a significant factor in noradrenergic neuronal transmission.

Glial uptake of monoamines in primary cultures of rat median raphe nucleus and cerebellum. A combined monoamine fluorescence and glial fibrillary acidic protein immunofluorescence study

Glial uptake of serotonin and dopamine was studied in primary cultures of the median raphe nucleus and cerebellum by using consecutive demonstration of monoamine fluorescence and glial fibrillary acidic protein immunofluorescence. Most of the glial cells taking up monoamines were glial fibrillary acidic protein positive. Astrocytes with a strong immunoreactivity exhibited monoamine fluorescence only occasionally, although such cells did take up L-dopa readily. Glial fibrillary acidic protein negative cells--morphologically identified as astrocytes--were seen to exhibit monoamine fluorescence after exposure. Glial uptake of serotonin at a concentration of 10(-4) M was detected in cerebellar cultures but not in cultures from the median raphe nucleus. When the concentration was 10(-3) M uptake of serotonin took place in both the areas but was weaker in cultures from the median raphe nucleus. At concentrations greater than 10(-5) M glial uptake of dopamine was detected in cultures from both the regions studied. No region dependent differences in glial uptake of dopamine was demonstrated, however. Based on these observations astrocytes and astrocyte-like glial cells take up dopamine and serotonin. Also glial cells with a remarkably high content of the glial fibrillary acidic protein are more resistant to monoamine uptake than cells exhibiting less intense or no glial fibrillary acidic protein immunofluorescence. The existence of regional differences in uptake of serotonin between the median raphe nucleus and cerebellum suggests that glial uptake of monoamines is not an entirely passive mechanism but may be actively controlled by glial cells in a region dependent manner.

Innervation of hippocampal explants by central catecholaminergic neurons in co-cultured fetal mouse brain stem explants

The ability of central catecholaminergic neurons to grow into and establish functional connections with the hippocampus in vitro was studied using organotypic tissue culture. Brain stem explanted from the region of the locus coeruleus and hippocampal explants, from 18-day fetal mice, were maintained as co-cultures and were also grown separately. After 1-4 weeks these tissues were analyzed by glyoxylic acid-induced histofluorescence, by light and electron microscopic radioautography after incubation with [3H]norepinephrine, and by electrophysiology. Brain stem explants exhibited specifically fluorescent catecholaminergic cell bodies and varicose fibers after 2-4 weeks in culture. In contrast, no fluorescent cells or neurites could be seen in isolated hippocampal cultures grown for 2-3 weeks in vitro. When hippocampal explants were grown near brain stem explants, catecholaminergic fibers grew out of the brain stem and entered the hippocampus. In additional experiments, co-cultures of brain stem and hippocampus were incubated with [3H]norepinephrine (0.5 micron) and the monoamine oxidase inhibitor nialamide (100 micron). Radioautographic analyses revealed that brain stem neurites which entered the hippocampus took up norepinephrine, whereas neurites in the isolated hippocampal explants did not. Electron microscopic studies of the hippocampus showed varicose axon terminals within the hippocampus to be preferentially labeled. Although close relationships could be seen between labeled axons and dendrites, junctions exhibiting the membranous modifications associated with synapses were never seen. Electrophysiological studies suggested that the catecholaminergic neurites within the hippocampus were functional. Complex synaptically mediated slow wave discharges could be evoked by electrical stimuli in isolated hippocampal explants. Introduction of the beta adrenergic antagonist propranolol (0.4-4.3 micron) did not alter, or slightly depressed, these hippocampal discharges. On the other hand, in hippocampus-brain stem co-cultures, these concentrations of propranolol enhanced the complex hippocampal responses to brain stem or hippocampal stimuli. Similar enhancement of hippocampal responses by propranolol also occurred in these cocultures after acute surgical extirpation of the brain stem explant. The data suggest, therefore, that the action of propranol was probably to block adrenergic inhibitory connections with hippocampal synaptic networks. These experiments provide morphological and electrophysiological evidence that catecholaminergic neurons from fetal mouse brain stem maintained in organotypic tissue culture can grow into and functionally innervate the hippocampus.

Uptake of L-glutamate and L-aspartate in neurones and glial cells of cultured human and rat spinal cord

Autoradiographic investigations on the uptake of L-glutamate and L-aspartate have shown that the amino acids were taken up by neurones as well as by glial cells of cultured human and rat spinal cord. The activity of glutamate and aspartate varied considerably between individual neurones, whereas glial cells showed a more even distribution of the labelled amino acids. Our results suggest that both neurones and glial cells are involved in the uptake of amino acid transmitters.