Accumulation and disappearance of 3H-5-hydroxytryptamine formed from 3H-tryptophan in mouse brain; effect of LSD-25

Tetanus intoxication causes an increment of serotonin in the central nervous system

Mice injected with tetanus toxin (TTx) showed an increase of 5-hydroxytryptamine (serotonin, 5-HT) levels in the central nervous system. The increment was not uniform throughout the central nervous system. Particularly significant were the 25% and 80% increases observed, respectively, in whole brain and spinal cord. The levels of dopamine and norepinephrine remained unchanged. The subsequent studies of 5-HT turnover revealed a synthesis rate in the tetanic animals that was almost double that of controls. The degradation rate of the amine as well as the levels of 5-hydroxyindolacetic acid were unaffected.

Pharmacological evidence for the existence of multiple functional pools of brain serotonin: analysis of brain perfusate from conscious rats

The serotonin reuptake inhibitor fluoxetine significantly reduced levels of endogenous 5-hydroxyindoleacetic acid (5-HIAA) in brain perfusate of rats implanted with push-pull cannulas. This occurred in conjunction with its suppressant effect upon fixed-ratio operant behavior. Behavior suppressed with the serotonin agonist lysergic acid diethylamide (LSD) occurred in conjunction with a reduction of 5-HIAA only after 5-HIAA was elevated, shortly before, by 5 mg/kg of the serotonin precursor 5-hydroxytryptophan. Our data demonstrate the likely existence of multiple functional pools of serotonin in brain and support the notion that LSD preferentially affects a newly synthesized pool of this transmitter.

Neurophysiological and psychopharmacological approaches to sensory deprivation phenomena

1. Research concerned with neurophysiological aspects of sensory deprivation phenomena is surveyed. 2. A theory is developed regarding the neurophysiological processes involved in sensory deprivation phenomena. It is postulated that the high amplitude bursts of slow waves observed in the visual cortex and lateral geniculate nucleus in deafferentation studies represent a PGO-like substrate of dream initiation. Concurrent neurochemical alterations are hypothesized to consist of a decrease in central serotonergic activity and an increase in norepinephrine level. 3. Hallucinogenic drugs, which produce subjective effects similar to those reported in sensory deprivation, are noted to induce neurochemical changes similar to those hypothesized for sensory deprivation. 4. New directions for research in this field are suggested.

LSD mescaline and serotonin injected into medial raphe nucleus potentiate apomorphine hypermotility

Microinjections of LSD (0.05 microgram), mescaline (0.5 microgram) and serotonin (10 microgram) into the medial raphe nucleus of rats resulted in a strong potentiation of apomorphine (1 mg/kg i.p.)-induced hypermotility. The potentiating effect of LSD or serotonin was suppressed by simultaneous injections of methysergide (0.05 microgram) or cyproheptadine (0.05 microgram) into the medial raphe nucleus. The same doses of LSD injected into the dorsal raphe nucleus and of LSD and mescaline injected into the nucleus accumbens failed to influence locomotor activity, whereas injections of higher doses of LSD and mescaline into the nucleus accumbens inhibited spontaneous and apomorphine-stimulated locomotor activity. It is concluded that the potentiating effect of systemically administered low doses of hallucinogens was triggered by preferential actions on the serotonergic system in the medial raphe nucleus.

Kinetic characteristics of newly synthesized 3H-5-HT in the brain of control and reserpinized mice. Evidence for the heterogeneous distribution of 5-HT in serotoninergic neurons

Following an intravenous administration of 3H-tryptophan to mice, 3H-serotonin rapidly accumulated in the brain, with a maximum around the 20th min after the injection. In mice whole monoamine oxidase activity was blocked by pargyline (75 mg/kg i.p.), reserpine pretreatment (5 mg/kg, 24 h before death) did not alter the initial accumulation of 3H-5-HT indicating that the rate of 5 HT synthesis was similar in control and reserpinized animals. When monoamine oxidase was not blocked, the accumulation of 3H-5-HT was significantly lower in reserpine-treated mice than in controls. However, the specific activity of 3H-5-HT accumulated in brain was 2-3 times higher in reserpinized (45 h) than in control mice. Since neither the specific activity of the precursor 3H-tryptophan, the reuptake process for 3H-5-HT nor the absolute synthesis rate of 5-HT was altered in the brain of reserpinized mice, it is proposed that the differences observed in the specific activity of 3H-5-HT reflected the presence of 3H-5-HT in different compartments in control and reserpinized mice. Serotonin would be distributed in a "storage" and a "functional" compartments in serotoninergic neurons under normal conditions whereas only the functional compartment would exist 18-48 h after the administration of reserpine.

Effects of para-methoxyamphetamine and 2,5-dimethoxyamphetamine on serotonergic mechanisms

A comparison of serotonergic effects of (+/-)-para-methoxyamphetamine (PMA) and (+/-)-2,5-dimethoxyamphetamine (2,5-DMA) was studied in rats. The activation of myoclonic twitch activity (MTA) of suprahyoideal muscle in urethane-anesthetized rats has been reported previously to involve central serotonergic and dopaminergic mechanisms. PMA (0.1--3.2 mg/kg i.v.) and 2,5-DMA (2--16 mg/kg i.v.) increased the MTA. The increased MTA caused by both PMA and 2,5-DMA was blocked by a 5-HT receptor blocker, methysergide, indicating that a serotonergic mechanism was involved. The increased MTA induced by PMA was reduced by a 5-HT synthesis inhibitor, para-chlorphenylalanine, (pCPA), and by a 5-HT uptake inhibitor, chlorimipramine. On the other hand, the increased MTA induced by 2,5-DMA was not blocked by pCPA or chlorimipramine. Using a ventricular perfusion technique in urethane-anesthetized rats, PMA (1.6 mg/kg) effectively increased the release of 3H-radioactivity from brain preloaded with 3H-5-HT before the initiation of perfusion whereas 2,5-DMA (16 mg/kg) decreased the release of 3H-radioactivity. Analysis of the perfusate by thin layer chromatography for 3H-5-HT and 3H-5-HIAA revealed an increased release of unchanged 3H-5-HT in the perfusate after the injection of PMA. The ratio of 3H-5-HT to 3H-5-HIAA was markedly increased after PMA but no alteration of this ratio was observed after 2,5-DMA. It is concluded that PMA elicits its pharmacological action indirectly by releasing 5-HT while 2,5-DMA acts directly on 5-HT receptors.

Effect of clozapine on the metabolism of serotonin in rat brain

Clozapine, but not chlorpromazine, haloperidol, thioridazine, or loxapine, increases the concentrations of tryptophan, serotonin, and 5-hydroxyindoleacetic acid in the brain of the rat. This effect of clozapine is due to an increased serotonin synthesis as demonstrated by an enhanced accumulation of 3H-serotonin in the brain after i.v. infusion of 3H-tryptophan. Clozapine also elevates the plasma concentration of free tryptophan, and reduces the plasma concentration of total tryptophan. Therefore, clozapine may increase the brain serotonin concentration by enhancing the availability of tryptophan in the brain, thereby promoting serotonin synthesis. Measurement of the rate of disappearance from the brain of 3H-serotonin or of endogenous serotonin after synthesis inhibition with 6-fluorotryptophan shows that clozapine has no direct effect on the release and degradation of serotonin. The effect of clozapine on brain serotonergic systems may possibly be related to the pronounced sedative and sleep-inducing properties of this drug.

Stereospecific binding of D-lysergic acid diethylamide (LSD) to brain membranes: relationship to serotonin receptors

D-[3H]LSD binds saturably, reversibly, and with a high affinity (KD = 10 nM) to rat brain membranes. The association and dissociation rates of binding are temperature dependent and fastest at 37 degrees C. Binding is enriched in crude microsomal (P3) membranes. D-[3H]LSD binding is stereospecific as L-LSD, the psychotropically inactive enatiomer, is 1000 times weaker than D-LSD as a displacing agent. The potencies of other LSD analogues parallel their psychotropic activity with the exception of 2-bromo-LSD (psychotropically inactive) which is as potent as D-LSD in displacing bound D-[3H]LSD. Serotonin is the only putative neurotransmitter with affinity (ED50 = 3 muM) for the LSD binding site, and psychotropically active alkylindoleamines are also potent displacing agents. Destruction of presynaptic serotonin neuronal elements by lesioning the midbrain raphe nuclei does not chang the affinity or maximum number of detectable in vitro D-[3H]LSD bindind sites. The regional distribution in monkey brain of D-[3H]LSD binding and high affinity [3h]serotonin uptake, a marker for pre-synaptic serotonin nerve terminal density, shows some correlation. The most notable exceptions are cerebral cortical areas which are highest in D-[3H]LSD binding and only intermediate in [3h]serotonin uptake. Our evidence suggests that D-[3H]LSD binds to post-synaptic serotonin receptors.

An evaluation of the use of intraventricularly administered [3H]5-hydroxytryptamine as a marker for endogenous brain 5-hydroxytryptamine

Following the intraventricular injection of a small amount of [3H]5-hydroxytryptamine ([3H]5-HT), the amount of radioactivity in telencephalic structures on the injected side was 6--7 times larger than that in corresponding areas on the opposite side. Moreover, a multiphasic disappearance of [3H]5-HT from whole brain or midbrain was found after the intraventricular injection of the labeled amine. However, after the intraventricular injection of [3H]tryptophan, the levels of [3H]5-HT in midbrain declined in a monophasic manner. A significant portion of the labeled amine derived from intraventricularly administered [3H]5-HT was resistant to the depleting effect of Ro4-1284 or to that elicited by destruction of the midbrain raphe nuclei, both of which caused an almost complete loss of endogenous 5-HT and labeled 5-HT formed from tryptophan. It thus appears that the intraventricular injection of [3H]5-HT leads to the formation of artifactual pools which are not present if the amine is synthesized in vivo. Studies with 6-hydroxydopamine suggested, however, that uptake of [3H]5-HT into adrenergic neurons did not occur to any great extent.

Effects of single and multiple dose LSD on endogenous levels of brain tyrosine and catecholamines

The effects on brain catecholamines of seven daily doses of d-LSD 520 mug/kg injected i.p. to Sprague-Dawley rats on a tolerance dosage schedule (L X 7) were compared with the effects of a single dose of LSD (L X 1) 520 mug/kg or 1040 mug/kg, over a 90 min time course. Compared to saline controls, after a single dose of 520 mug/kg LSD, there was a significant decrease in brain norepinephrine at 30 to 60 min, a rise in dopamine at 60 min, and a small rise in brain tyrosine at early time points followed by significant decline from control levels after 60 min. The effects of a single dose of 1040 mug/kg LSD were similar to the 520 mug/kg dose but were greater in both magnitude and duration of the brain catecholamine changes. After a tolerance dosage schedule there were significant changes in the response of brain catecholamines to 520 mug/kg LSD. The rise in brain dopamine at 60 min was abolished, brain tyrosine was uniformly below both saline and L times 1 animals, and brain norepinephrine returned to control levels slightly faster.

Effect of ergot drugs on central 5-hydroxytryptamine neurons: evidence for 5-hydroxytryptamine release or 5-hydroxytryptamine receptor stimulation

In combined biochemical and functional studies it has been possible to show that ergocornine (0.5-5 mg/kg) and the ergolene derivative (5R,8R)-8-(4-p-methoxyphenyl-1-piperazinylmethyl)-6-methylergolene (PTR 17402; MPME) (0.25-5 mg/kg) reduce in a dose-dependent way brain 5-hydroxytryptamine (5-HT) turnover in rat as evaluated with the tryptophan hydroxylase inhibitor, alpha-propyl-dopacetamide (H 22/54), whereas 2-Br-alpha-ergocryptine (CB 154; Br-EC) had no effect on brain 5-HT turnover. Effects on 5-HT receptor activity were evaluated using the extensor hindlimb reflex of acutely spinalized rats. It was found that ergocornine increased the 5-HT receptor activity independent of presynaptic 5-HT stores and that it didnot have any effects on uptake, retention and spontaneous overflow of 3-H-5-HT in vitro but reduced the fiedl stimulation-induced release of 3-H-5-HT in vitro. Therefore, it is suggested that ergocornine is a 5-HT recpetor-stimulating agent, an effect which may lead to reduction of nervous impulse flow in the 5-HT neurons and subsequently of 5-HT release and turnover. MPME, on the other hand, seems to increase 5-HT receptor release of 5-HT stores, mainly from extragranular sites. Thus, the increase in extensor reflex activity found after MPME was reduced by reserpine and H 22/54 and enhanced by nialamide and in vitro MPME markedly increased 3-H-5-HT overflow in cortical slices of nialamide-pretreated rats and inhibited uptake and retention of 3-H-5-HT (EC50 equals 1.6 times 10-minus 6 M) in cortical slices of normal rats. Inhibition of the 5-HT membrane pump does not seem to be of any major importance, since chlorimipramine was only weakly active on the extensor reflex in the pharmacological models used and since MPME did not block but rather enhanced the 5-HT depletion caused by 4-methyl-alpha-ethyl-m-tyramine. It is suggested that MPME is a releaser of extragranular 5-HT stores leading to increased 5-HT receptor activity and reduction of 5-HT turnover in the same way as indicated for ergocornine. This new ergolene derivative may represent a new class of antidepressant drugs acting via release of extragranular 5-HT stores.

A fluorimetric method for the determination of tryptophan in animal tissues

Tryptophan, tryptamine and peptides containing N-terminal tryptophan give two highly fluorescent products on treatment with dithiothreitol and acid ninhydrin reagent 1 or 2. The first fluorescent product (product A) gives an emission at 500nm on activation at 390-400nm and is stable for 20min. The second product (product B), which gives an emission at 530nm on activation at 470nm, is detectable within 1h after the reaction. It gives almost maximum intensity in 4h and is stable for at least 48h. Except lysine, which in equimolar amounts gives less than 1% of a product similar to product B, no other naturally occurring amino compounds give fluorescent products. A procedure is given for the determination of 0.05-34nmol of tryptophan in tissue extracts. By using this procedure rat brain was found to contain 17.56+/-0.76 (s.e.m.) nmol/g wet wt.

Persistent increase in brain serotonin turnover after chronic administration of LSD in the rat

Lysergic acid diethylamide at doses of 20 micrograms per kilogram per day was administered orally to rats for I month. Eighteen hours after the final dose a 25 to 30 percent increase in the synthesis and turnover of serotonin was noted, as well as a moderate but significant increase in the concentration of tryptophan (18 percent) and serotonin (13 percent) in the brain.