Yoshiro Okano

Electrophoretic study of pipecolic acid, a biogenic imino acid, in the mammalian brain ☆

Pipecolic acid (PA), one of the imino acids, is a normal constituent in the mammalian brain. It is said that PA is a major intermediate of lysine metabolism in the rat brain. Biochemical studies have suggested that PA may be involved in the regulation of synaptic mechanism in the CNS. Moreover, the pathophysiological significance of PA has been also suggested by some investigators. However, there has so far been no good evidence based on the comprehensive electrophysiological experiments. Using unit recording and microelectrophoretic technique, the action of PA on single neuron activities in the rat brain was examined. PA depressed the firing of 88 out of 115 cortical neurons tested. Only 2 were excited and 25 remained unaffected. All the identified hippocampal pyramidal neurons examined were uniformly inhibited. It has been reported that PA inhibits the uptake of GABA into the brain slices and enhances the release of GABA from the slices. Thus, it is likely that the inhibitory response due to PA may have some connections with GABAergic transmission. On the other hand, it remains to be clarified whether the specific PA sensitive receptors exist in the brain. Our findings provide a clue to the elucidation of the presumed synaptic involvement of PA in the CNS.

Pipecolic acid in the dog brain

Abstract Pipecolic acid is an intermdiary metabolite of lysine and is decarboxylated to produce piperidine, an endogenous synaptotropic substance. In the present study, the existence of pipecolic acid in the dog brain was confirmed. It was present in highest concentration in the cerebellum followed by the diencephalon and caudate nucleus, and this distribution resembles that of piperidine in dog brain. It seems to be evident that pipecolic acid is a precursor of piperidine in the brain.

Effects of cyclodextrins on chlorpromazine-induced haemolysis and central nervous system responses

Cyclodextrins (CyDs) protected the human erythrocytes from haemolysis induced with chlorpromazine (CPZ) in isotonic solution, depending upon the magnitude of the stability constant of CPZ‐CyD complexes (β‐> γ‐> α‐CyD). From the observations of CPZ uptake into erythrocytes and changes in surface activity of CPZ, the protective effects of CyDs in vitro appeared to be due to the decrease in effective haemolytic concentration of CPZ through inclusion complex formation rather than the direct interaction of CyDs with the erythrocyte membrane. The effect of β‐CyD on some central nervous system (c.n.s.) actions of CPZ in rats was also investigated to see if there were any advantages in the use of β‐CyD complexes given by injection. The results suggest that β‐CyD does not alter the time‐course or magnitude of the effects of CPZ on the c.n.s.

Pipecolic acid: a new type of α-amino acid possessing bicuculline-sensiti action in the mammalian brain

Using unit recording and electrophoretic techniques, pharmacological properties of pipecolic acid (PA) were studied in the brain neurons of rats. PA response was blocked by bicuculline more effectively than GABA response but not blocked by strychnine. Stereochemical findings obtained using the HGS-model demonstrated that PA structure is almost the same as a part of bicuculline structure. The present results suggest that PA might be a new type of substance possessing bicuculline-sensitive action. The site of the action of PA was also discussed.

Simultaneous analysis of pipecolic acid with proline in the brain by selected ion-monitoring technique

Abstract A method for the simultaneous analysis of pipecolic acid and proline in the brain is developed. The qualification and quantification of pipecolic acid and proline are accomplished with gas chromatography/mass spectrometry including a selected ion-monitoring technique by using deuterium-labeled proline as an internal standard, after the amino and carboxylic groups of these cyclic amino acids are derivatized with boron trifluoride methanol complex and heptafluorobutyric anhydride. The lower limit of quantification for the method is picomole levels and the concentration of pipecolic acid and proline in rat whole brain is determined to be 1.05 and 71.50 nmol/g of tissue, respectively.

Effects of intracerebral administration of piperidine on EEG and behavior

Summary Effects of intracerebral administration of piperidine, a normal constituent of the mammalian brain, on EEG and behavior were examined in freely moving cats. 1) Administration into hippocampus or amygdalae caused resting and calmness in small doses, and seizure discharge accompanied by hyperemotionality in large doses. 2) Administration into pontine reticular formation induced slow wave and fast wave sleeps. 3) Administration into cerebellum caused remarkable changes in the extrapyramidal function. The findings seem to support our presumption that piperidine affects neural mechanisms serving regulation of emotional behavior, sleeping and extrapyramidal function.

Analysis of physiological variations of piperidine levels in tissues by mass fragmentography

Abstract By use of a mass fragmentographic technique the distribution of piperidine in tissues and changes in levels under physiological conditions were examined. Only trace amounts of piperidine existed in the brain of several animal species, although higher concentrations were detected in other species. In the brain of rats and rabbits, some regional differences were seen and high concentrations were found in the striatum. Piperidine levels in the brain and adrenal gland similarly showed the daily and seasonal rhythmic fluctuations.

Pipecolic acid enhancement of GABA response in single neurons of rat brain

Using unit recording and microelectrophoresis, influence of pipecolic acid (PA), a major metabolite of lysine in the brain, on GABA and glycine responses was studied in the cerebral cortical and hippocampal pyramidal neurons of rats. With small currents, PA had no effect on the single neuron activities but enhanced GABA response without affecting glycine response. The finding provides a new evidence that PA may have a connection with central GABA system.

Potentiation of phenobarbital-induced anticonvulsant activity by pipecolic acid

Pipecolic acid (PA) is an intermediate of lysine metabolism in the mammalian brain. Recent findings suggest a functional connection of PA as neuromodulator in GABAergic transmission. Since many drugs are postulated to produce their effects by interaction with the central GABA system, the influence of PA on the anticonvulsant activity of phenobarbital was examined. Pretreatment of mice with 50 mg . kg-1 of PA potentiated the suppressing effects of the barbiturate on electrically and chemically induced convulsions. However, there was no potentiation of the behavioral effects and hypothermia induced by phenobarbital. PA itself had no or only little effect on the convulsions, motor function and rectal temperature when given in i.p. doses up to 500 mg . kg-1. Intraventricular administration of 500 microgram of PA also did not suppress either type of convulsion, although it produced ptosis, hypotonia, sedation and hypothermia. The results are discussed in relation to GABA system.

Analysis of regional concentrations of piperidine in the brain by mass fragmentography

Piperidine, a normal constituent in the mammalian brain 3,6,s,12,17,19-22, affects synaptic mechanisms in the CNS10, 23 and influences neural mechanisms governing regulation of emotional behavior, sleeping and extrapyramidal functionsg, 14. There are enzyme systems within the brain that synthesize and metabolize piperidine 7,11,1s. Taken together, these findings suggest a physiological role of piperidine in the nervous system, although observations3, 21 that piperidine is present only in trace amounts in the brain seem not to support the role assigned to the amine 5,14,22. On the other hand, reliable data have shown an apparent lack of specific regional concentration ofpiperidine in the brain3,5, 21. By the use of a mass fragmentographic technique with deuteriumlabeled piperidine as an internal standard, we have recently revealed that piperidine levels in the whole brain and adrenal gland show rhythmic daily and seasonal fluctuations 15. This finding, being of particular interest in view of piperidines suggested role in the mechanisms of regulation of emotional behavior, sleep and hibernation 5,9,14, led us to the study on regional distribution of piperidine in the brain to clarify a possible involvement of piperidine in the neuroendocrine as well as neural functions. We report here that piperidine is highly concentrated in the pituitary and pineal glands. New Zealand White rabbits (1.8-2.2 kg, 10-week-old) were maintained for a minimum of two weeks in a 12 h l ight-dark cycled room with constant temperature and humidity control. The experiments were carried out during September in 1979, and the total number of rabbits used was 31. The rabbits were sacrificed by bleeding at 10.00 to 11.00 h. Usually 6 rabbits were killed in one session. The brain was removed