Uptake and Subcellular Localization of Neurotransmitters in the Brain

Neurochemical aspects of the ontogenesis of GABAnergic neurons in the rat brain

Examination of various biochemical characteristics of the GABAnergic nervous system in the rat brain was made between 15 days of gestation and adulthood. At birth, the concentration of GABA in whole brain and most regions is approximately 50% of adult levels, whereas the medulla-pons has achieved adult levels by this time. Compared to GABA levels, there is a marked lag in the development of the activity of glutamic acid decarboxylase in all areas studied; however, the activity of the enzyme increases in a linear fashion from birth to adulthood. The development of the uptake of GABA into particulate fractions prepared from whole brain and regions differs markedly from that of GABA and glutamic acid decarboxylase, with uptake near adult levels by birth, peaking considerably above that of the adult between one to two weeks after birth and then declining toward adult activity by 4 weeks after birth. Examination of the kinetics of GABA uptake into resuspended P2 fractions demonstrates that the developmental changes in the uptake reflects differences in the Vmax whereas the Kt remains constant; Studies on the development of the apparent postsynaptic receptor for GABA reveals that in all regions binding is approximately 25% of adult up to 8 days after birth, at which time it increases dramatically, approximating adult levels by 4 weeks after birth. The rise in the density of the apparent postsynaptic GABA receptor after 8 days postpartum correlates best with the increase in the activity of glutamic acid decarboxylase, a presynaptic marker.

Comparative study of the effects of mianserin, a tetracyclic antidepressant, and of imipramine on uptake and release of neurotransmitters in synaptosomes

The effects of mianserin, a tetracyclic antidepressant, on uptake and release of [3H]noradrenaline (3H-NA), [3H]dopamine (3H-DA), [3H]-5-hydroxytryptamine(3H-5-HT) and [3H]gamma-amino-butyric acid (3H-GABA) in synaptosomes from different areas of the rat brain were investigated in a comparative study with the tricyclic antidepressant imipramine. Mianserin and imipramine were inhibitors of 3H-NA uptake in the hypothalamus, but could not increase 3H-NA release from noradrenergic nerve endings. This behaviour was similar to that of (+)-amphetamine. Both mianserin and imipramine had essentially no effect on 3H-DA transport mechanisms in striatal synaptosomes. (+)-Amphetamine, in contrast, strongly affected both 3H-DA uptake and release. Imipramine was stronger than mianserin in inhibiting 3H-5-HT accumulation by striatal synaptosomes. In contrast, mianserin stimulated 3H-5-HT release whereas imipramine was ineffective. Mianserin had virtually no inhibitory activity on 3H-5-HT uptake by rat blood platelets. Imipramine was a modest inhibitor of 3H-GABA accumulation by whole brain synaptosomes; mianserin had no effect. Both drugs did not alter 3H-GABA release. These results indicate that mianserin interferes in a way different from that to tricyclic antidepressants with the neurotransmitter transport mechanisms at the presynaptic level.

d-Amphetamine as a releaser or reuptake inhibitor of biogenic amines in synaptosomes

The effect of d-amphetamine on the release of tritiated norepinephrine (NE), dopamine (DA) and 5-hydroxytryptamine (5-HT) was analyzed in synaptosomes from different brain area. 3H-NE release was unaffected in the hypothalamus, a region which is rich in noradrenergic terminals, and in cerebellum and pons-medulla, but was substantially increased in corpus striatum and moderately in cerebral cortex. 3H-DA release was strongly enhanced in corpus striatum, a region rich in dopaminergic terminals, substantially increased in cerebral cortex, and slightly increased in the hypothalamus. Since the regional pattern of d-amphetamine-stimulated release was similar with the two catecholamines, but the stimulation was greater with 3H-DA than with 3H-NE, and was more evident in areas richer in dopaminergic terminals, it is suggested that the drug can release 3H-DA or artificially stored 3H-NE from dopaminergic terminals, but not 3H-NE, from noradrenergic terminals. d-Amphetamine also seems capable of releasing 3H-5-HT from serotoninergic terminals. In contrast with the two catecholamines, 3H-5-HT release was more enhanced in cerebral cortex than in corpus striatum.

Synaptic organization of the amine-containing interplexiform cells of the goldfish and Cebus monkey retinas

Fluorescence microscopy has revealed a new type of amine-containing retinal neuron, the interplexiform cell, that extends processes in both plexiform layers. After intravitreal injection of 5,6-dihydroxytryptamine in goldfish and Cebus monkey, the processes of these cells can be identified by electron microscopy. In goldfish, the processes are pre- and postsynaptic to amacrine cells in the inner plexiform layer and presynaptic to bipolar and horizontal cells in the outer plexiform layer. Interplexiform cells thus provide an intraretinal centrifugal pathway from inner to outer plexiform layers.

The effect of the chronic administration of D-amphetamine upon circadian changes in amino acids in the pineal and pituitary glands of the rat

The formation of dansyl derivatives of amino acids, 5-hydroxyindoleacetic acid and histamine, and their separation on polyamide plates provided a reliable and sensitive method for studying circadian changes in single pineal and pituitary glands of the rat. There appears to be no correlation between the circadian changes in concentrations of these substances in the pineal and pituitary glands. Chronically administered D-amphetamine altered the circadian rhythms of five amino acids in the pituitary, including the putative transmitters taurine, glycine, and glutamate; in the pineal gland only the rhythmical changes of lysine and 5-hydroxyindoleacetic acid were affected.

Serotonin storage in platelets: estimation of storage-packet size

Storage-body diameter and volume, and the number of molecules of serotonin contained in a storage body, were estimated for blood platelets. In the human, 5.23 x 10(5) molecules of serotonin are contained in a storage body 198 nanometers in diameter, while in the cat, 31.2 x 10(5) molecules of this amine are contained in a storage body 298 nanometers in diameter.

The effect of narcotic analgesics on the uptake of 5-hydroxytryptamine and (-)-metaraminol by blood platelets

1. The effects of narcotic analgesic and related drugs were studied on the uptake of 5-hydroxytryptamine (5-HT) and (-)-metaraminol by blood platelets.2. The most potent drug in inhibiting the uptake of 5-HT (10 muM) by human platelets was methadone, followed by pentazocine>piminodine approximately pethidine approximately anileridine approximately cyclazocine approximately thebaine > dextropropoxyphene. Alphaprodine, papaverine, apomorphine, nalorphine, codeine, and morphine were almost without effect. Methadone was slightly less active than desipramine, and had 10% of the activity of imipramine under similar conditions. Naloxone did not antagonize the effect of methadone on 5-HT uptake.3. The most potent inhibitor of metaraminol (3 muM) uptake by human platelets was piminodine, followed by pentazocine>/=anileridine>cyclazocine=methadone > dextropropoxyphene approximately thebaine >/= papaverine approximately alphaprodine >pethidine>morphine. The activity of morphine was 1% of that of piminodine. Piminodine was more potent than desipramine and protriptyline under similar conditions. The order of potency of drugs studied in inhibiting the uptake of metaraminol by rabbit platelets was similar to that obtained with human platelets.4. The effects of the analgesics studied on inhibiting uptake of monoamines did not correlate with their pain-relieving properties.

Dopamine: stimulation-induced release from central neurons

Dopamine, synthesized in rat brain slices from labeled L-tyrosine or L-dopa, can be released by electrical stimulation of a type known to induce neuronal depolarization. Pretreatment of the animals with 6-hydroxydopamine, which destroys central catecholamine-containing nerve terminals, substantially reduced the release of dopamine synthesized from [(14)C]tyrosine or from a low concentration of [(3)H]dopa, whereas the release of dopamine formed from a high concentration of [(3)H]dopa remained essentially unchanged. The observations that at high concentrations L-dopa may enter noncatecholaminergic cells, undergo decarboxylation to dopamine, and subsequently be liberated in response to depolarization suggest that dopamine may act as a substitute central transmitter, possibly in serotonergic neurons. This mechanism may contribute to L-dopa's clinical effects in parkinsonian patients.