J. Knoll

The striatal dopamine dependency of life span in male rats. Longevity study with (−)deprenyl

Long-term experiments on male rats revealed that better performers in the mating test are better learners in the shuttle box and the more active animals live significantly longer than their less active peers. It was established by the aid of (-)deprenyl, a highly specific chemical tool, which increases superoxide dismutase activity in the striatum, facilitates the activity of the nigrostriatal dopaminergic neurons with utmost selectivity, and protects these neurons from their age-related decay, that the efficiency of a male rat in behavioral tests, as well as the duration of its life are striatal dopamine dependent functions. As a measure of striatal function, sexual activity was tested once a week in a group of male rats (n = 132) from the 24th month of their life. Because of the age-related decay of this function none of the 2-year-old animals displayed full scale sexual activity. By dividing the group equally the rats were treated with saline (1 ml/kg, s.c.) and deprenyl (0.25 mg/kg, s.c.), respectively, three times a week. In the saline-treated group (n = 66) the last signs of sexual activity vanished to the 33rd week of treatment. (-)Deprenyl treatment restored full scale sexual activity in 64 out of 66 rats. The longest living rat in the saline-treated group lived 164 weeks. The average lifespan of the group was 147.05 +/- 0.56 weeks. The shortest living animal in the (-)deprenyl-treated group lived 171 weeks and the longest living rat died during the 226th week of its life. The average lifespan was 197.98 +/- 2.36 weeks, i.e. higher than the estimated maximum age of death in the rat (182 weeks). This is the first instance that by the aid of a well-aimed medication members of a species lived beyond the known lifespan maximum.

Evidence that acetylcholine released by gastrin and related polypeptides contributes to their effect on gastrointestinal motility.

Abstract Gastrin- and cholecystokinin-like polypeptides have been found to release acetylcholine from the Auerbach plexus of longitudinal muscle strips of guinea pig ileum. The evidence is consistent with the view that contractions of intestine in response to these peptides are due to the acetylcholine released. Tetrodotoxin inhibited actions of peptides both on acetylcholine release and on mechanical responses of intestine; however, hexamethonium failed to affect their actions, indicating that their site of action is situated on non-nicotinic receptors of ganglionic cells. C-terminal octapeptide amide of cholecystokinin-pancreozymin and caerulein produced significant acetylcholine release in concentrations as low as 9 × 10 −10 and 7.5 × 10 −10 M, respectively. Human gastrin I was much less effective, its threshold concentration being 7 × 10 −8 M. Both exogenous and endogenous noradrenaline reduced both the acetylcholine release and the contractions of longitudinal muscle produced by peptides. Noradrenaline acted at a presynaptic site and its action was mediated through α receptors. It is concluded that gastrointestinal hormones may play a role as hormonal factors in regulating gastrointestinal motility, and their effect is continuously controlled by the tonic activity of the sympathetic nervous system which reduces acetycholine release.

Striatal dopamine, sexual activity and lifespan. Longevity of rats treated with (-) deprenyl

The influence of longterm deprenyl treatment on the sexual performance and lifespan of male rats was studied. One hundred and thirty two rats were treated from the end of their 2nd year of life either with saline (1 ml/kg, s.c.) (n = 66) or with deprenyl (0.25 mg/kg, s.c.) (n = 66) three times a week until death. Whereas none of the two-year-old saline-treated rats displayed full scale sexual activity, this appeared in 64 out of 66 rats on deprenyl. The longest living rat in the saline-treated group lived 164 weeks. The lifespan of the group was 147.05 +/- 0.56 weeks. The shortest living animal in the (-)deprenyl-treated group lived 171 weeks and the longest living rat died during the 226th week of its life. The lifespan was 191.91 +/- 2.31 weeks. This is the first instance that a well aimed medication prolonged lifespan of members of a species beyond their maximum age of death (182 weeks in the rat). A close relation between sexual activity and lifespan was detected.

Novel (-)deprenyl-derived selective inhibitors of B-type monoamine oxidase. The relation of structure to their action

Abstract A structure-activity relationship study has revealed the importance of the aromatic ring and the optimum length of the chain between the aromatic ring and the nitrogen for the selective inhibition of MAO-B. Among the (−)deprenyl derived new compounds described in this study N -methyl- N -propargyl-(2-furyl-1-methyl)-ethylammonium. HCl(U-1424) seems to be the most promising selective inhibitor of MAO-B.

Neuronal peptide (enkephalin) receptors in the ear artery of the rabbit

Methionine-enkephalin methylester (MEM) and leucine-enkephalin (LE) inhabit the vasoconstrictor responses of the rabbit ear artery to nerve stimulation by acting on a specific neuronal peptide (enkephalin)-receptor insensitive to opiate agonists. The tetrapeptide: H-Tyr-Gly-Phe-Leu-OCH3 is ineffective. This is the first instance of enkephalins acting in an organ devoid of receptors. In a new test for the analysis of opiate receptors, MEM (ID50=6.9 X 10(-9) M) was a potent inhibitor of transmission. The presence was shown of opiate receptors in the brain which were insensitive to high i.v. or intraventricular doses of enkephalins. It is concluded that enkephalins are not natural ligands to the opiate receptors, but that some of the receptors confuse these structures because of similar characteristics which determine the binding of both opiates and peptides.

Does the B form selective monoamine oxidase inhibitor lose selectivity by long term treatment

Abstract Rats were treated subcutaneously with different doses of the “B form” selective monoamine oxidase (MAO) inhibitors deprenyl (phenylisopropylmethylpropargylamine), U-1424 (N-methyl-N-propargyl-[2-furyl-1-methyl]-ethylammonium) and J-508 (N-methyl-N-propargyl-[1-indenyl]-ammonium. HCl) in order to study the changes of their selectivity during 21 days of treatment. When the daily dose of (−) deprenyl and U-1424 was 0.05 or 0.25 mg/kg body wt (similar to the human dosage of deprenyl in clinical trials), in spite of their repeated administration, a fairly selective inhibition pattern was maintained. In this case at a low rate of oxidation of beta-phenylethylamine (MAO-B form specific substrate) the conversion of serotonin (MAO-A form specific substrate) was near to the untreated value. When 1.0 mg/kg of these inhibitors were repeatedly administered they also inhibited the A form of MAO. As J-508 is a more potent MAO inhibitor than deprenyl and U-1424. even the lowest dose (0.05 mg/kg) used in this study proved to inhibit MAO-A. All the compounds tested were less effective on liver than on brain MAO; thus their selectivity was more pronounced on liver homogenate.

Enhanced catecholaminergic and serotoninergic activity in rat brain from weaning to sexual maturity: Rationale for prophylactic (-)deprenyl (selegiline) medication

Food deprived rats in the late developmental phase of life (2 months of age) are significantly more active than those in the early postdevelopmental phase (4 months of age), pointing to enhanced catecholaminergic activity during the developmental phase. We therefore measured the resting release of dopamine from the striatum, substantia nigra and tuberculum olfactorium, and of noradrenaline from the locus coeruleus, as an indicator of the basic activity of catecholaminergic neurons in the brain, in 2,4,8,16 and 32 weeks old male and female rats. We also measured the release of serotonin from the raphe. Both in male and female rats, the resting release of transmitters from brain catecholaminergic and serotoninergic neurons between weaning and the end of the 2nd month of age, i.e. during the crucial developmental phase of their life, was significantly higher than either before or after that period, signalling a transition from a developmental to a postdevelopmental (aging) phase of life and indicating that safe and effective measures are needed to maintain the catecholaminergic system at a higher activity level during the postdevelopmental phase. Daily administration of low doses (0.01-0.25 mg/kg) of (-)deprenyl for 21 days significantly enhances the resting release of catecholamines and diminishes that of serotonin, providing a rationale for prophylactic medication with this drug during the postdevelopmental lifespan. We also show that (-)methamphetamine, the parent compound of (-)deprenyl and (-)1-phenyl-2-propylaminopentane (PPAP), a deprenyl analogue free of MAO-B inhibitory potency but otherwise possessing the same pharmacological profile as (-)deprenyl, act similarly, furnishing direct evidence that enhancement of catecholaminergic activity in the brain by multiple, small dose administration of (-)deprenyl is unrelated to MAO-B inhibition.

Phenylethylamine and tyramine are mixed-acting sympathomimetic amines in the brain.

On the helical strip of a capacitance vessel, the pulmonary artery of the rabbit, phenylethylamine (PEA) and tyramine act solely via displacement of noradrenaline from their storage sites and this effect is inhibited by desmethylimipramine (DMI). In contrast, on a resistance vessel, the perfused central ear artery of the rabbit, PEA enhances stimulation induced contractions in 0.2-0.8 microgram/ml concentration [catecholaminergic activity enhancer (CAE) effect], and increases smooth muscle tone (noradrenaline displacing effect) in 4-6 micrograms/ml concentration. This latter effect only is blocked by DMI. Tyramine acts similarly and is more potent than PEA. On the isolated brain stem PEA, tyramine and (-)methamphetamine are, in the presence of cocaine and DMI, highly potent enhancers of stimulation induced release of 3H-noradrenaline, 3H-dopamine and 3H-serotonin. Compounds with specific CAE effect in the brain, (-)deprenyl and 1-phenyl-2-propylaminopentane [(-)PPAP], antagonize tetrabenazine-induced depression of performance of rats in the shuttle box. PEA and tyramine, which are rapidly metabolized in vivo, are ineffective in this test up to 40 mg/kg, whereas (-)methamphetamine, the stable PEA derivative, is highly effective. Compounds with CAE effect enhance at low concentrations the slow inward Ca2+ current in the sino-auricular fibers of the frog heart and inhibit it in high concentration. PEA and tyramine enhance Ca2+ influx from 0.05 to 4 micrograms/ml and inhibit it in 8 micrograms/ml. In conclusion, PEA and tyramine stimulate primarily coupling of action potential to transmitter release in the catecholaminergic neurons in the brain and displace catecholamines in higher concentration only.

(−)1-(Benzofuran-2-yl)-2-propylaminopentane, [(−)BPAP], a selective enhancer of the impulse propagation mediated release of catecholamines and serotonin in the brain

The brain constituents β‐phenylethylamine (PEA) and tryptamine enhance the impulse propagation mediated transmitter release (exocytosis) from the catecholaminergic and serotoninergic neurons in the brain (‘catecholaminergic/serotoninergic activity enhancer, CAE/SAE, effect’). (−)Deprenyl (Selegiline) and (−)1‐phenyl‐2‐propylaminopentane [(−)PPAP] are amphetamine derived CAE substances devoid of the catecholamine releasing property. By changing the aromatic ring in PPAP we developed highly potent and selective CAE/SAE substances, structurally unrelated to the amphetamines. Out of 65 newly synthetized compounds, a tryptamine derived structure, (−)1‐(benzofuran‐2‐yl)‐2‐propylaminopentane [(−)BPAP] was selected as a potential follower of (−)deprenyl in the clinic and as a reference compound for further analysis of the CAE/SAE mechanism in the mammalian brain. (−)BPAP significantly enhanced in 0.18 μmol 1−1 concentration the impulse propagation mediated release of [3H]‐noradrenaline and [3H]‐dopamine and in 36 nmol 1−1 concentration the release of [3H]‐serotonin from the isolated brain stem of rats. The amount of catecholamines and serotonin released from isolated discrete rat brain regions (dopamine from the striatum, substantia nigra and tuberculum olfactorium, noradrenaline from the locus coeruleus and serotonin from the raphe) enhanced significantly in the presence of 10−12–10−14 M (−)BPAP. BPAP protected cultured hippocampal neurons from the neurotoxic effect of β‐amyloid in 10−14 M concentration. In rats (−)BPAP significantly enhanced the activity of the catecholaminergic and serotoninergic neurons in the brain 30 min after acute injection of 0.1 μg kg−1 s.c. In the shuttle box, (−)BPAP in rats was about 130 times more potent than (−)deprenyl in antagonizing tetrabenazine induced inhibition of performance.

(−)Deprenyl and (−)1-phenyl-2-propylaminopentane, [(−) PPAP] act primarily as potent stimulants of action potential — transmitter release coupling in the catecholaminergic neurons

The activity of the catecholaminergic neurons in the rat brain is enhanced significantly 30 min after the subcutaneous injection of very small doses of (-)deprenyl (threshold doses: 0.01 mg/kg for noradrenergic neurons and 0.025 mg/kg for dopaminergic neurons). As a catecholaminergic activity enhancer (CAE) substance (-)deprenyl is about ten times more potent than its parent compound, (-)methamphetamine. While the (+)methamphetamine is 3-5 times more potent than (-)methamphetammine in releasing catecholamines, the (-)methamphetamine is the more potent CAE substance. The mechanism of the CAE effect of (-)deprenyl and (-)PPAP, a deprenyl-derived substance devoid of MAO inhibitory potency, was studied in rats by measuring: a) the release of catecholamines from striatum, substantia nigra, tuberculum olfactorium and locus coeruleus; b) the stimulation induced release of 3H-noradrenaline from the isolated brain stem; and c) the antagonistic effect against tetrabenazine-induced depression of learning in the shuttle box. The CAE effect was found to be unrelated: a) to the inhibition of MAO activity; b) to the inhibition of presynaptic catecholamine receptors; c) to the inhibition of the uptake of catecholamines; and d) to the release of catecholamines. It was concluded that (-)deprenyl and (-)PPAP act primarily as potent stimulants of action potential-transmitter release coupling in the catecholaminergic neurons of the brain. We show that both (-)deprenyl and (-)PPAP enhance the inward Ca2+ current in sino-auricular fibers of the frog heart. (-)PPAP was much more potent than either (+)PPAP or (-)deprenyl in this test.