Katsuo Toide

Effects of Cholinergic Drugs on Extracellular Levels of Acetylcholine and Choline in Rat Cortex, Hippocampus and Striatum Studied by Brain Dialysis

A brain dialysis technique was used to investigate the effects of cholinergic drugs on acetylcholine (ACh) release and on the extracellular choline levels. Scopolamine (0.5 mg/kg s.c.) markedly increased ACh release in frontal cortex, hippocampus and corpus striatum. Conversely, it significantly decreased choline levels in extracellular spaces of these three regions. Oxotremorine (0.5 mg/kg i.p.) induced no significant ACh release in these three regions, probably due to the presence of highly concentrated physostigmine in the perfusate, while it induced an increase of the choline levels in both frontal cortex and hippocampus but not in corpus striatum. Nicotine (0.5 mg/kg s.c.) significantly increased the ACh release in these three regions with no change in choline levels. Nicotine had a biphasic effect on ACh release in frontal cortex and hippocampus but not in corpus striatum. It should be noted that all such cholinergic drugs, in our time course determinations, yielded certain differences among these brain regions for both the magnitude and the response pattern of ACh and choline levels. The present investigation appears to indicate that the in vivo brain dialysis technique can be useful for probing cholinergic neurotransmission of cholinergic drugs via presynaptic terminals.

Effect of a novel prolyl endopeptidase inhibitor, JTP-4819, on prolyl endopeptidase activity and substance P- and arginine-vasopressin-like immunoreactivity in the brains of aged rats

Abstract: The effects of a novel prolyl endopeptidase (PEP) inhibitor, (S)‐2‐[[(S)‐2‐(hydroxyacetyl)‐1‐pyrrolidinyl]carbonyl]‐N‐(phenylmethyl)‐1‐pyrrolidinecarboxamide (JTP‐4819), on the PEP activity in the brain and on the contents of substance P (SP)‐ and arginine‐vasopressin (AVP)‐like immunoreactivity (LI) in the cerebral cortex and hippocampus of young and aged rats were investigated using enzyme immunoassay. JTP‐4819 exhibited a concentration‐dependent in vitro inhibitory action on PEP activity in the brains of both young and aged rats, with IC50 values of ∼0.7 and 0.8 nM, respectively. A single dose of JTP‐4819 (3 mg/kg, p.o.) increased the SPLI content in the cerebral cortex but not the hippocampus of aged rats (23–24 months old). In addition, repeated administration of JTP‐4819 (1 mg/kg, p.o., for 21 days) increased the SPLI content in the cerebral cortex and restored the SPLI content in the hippocampus, which had decreased with aging. In contrast, single (1 mg/kg, p.o.) and repeated (1 mg/kg, p.o., for 21 days) administration of JTP‐4819 only tended to increase the AVPLI content of the hippocampus and cerebral cortex in aged rats, respectively. These results indicate that JTP‐4819 increases the cerebral and hippocampal SPLI content in aged rats by inhibiting the action of PEP.

Effect of a Novel Prolyl Endopeptidase Inhibitor, JTP-4819, on Spatial Memory and Central Cholinergic Neurons in Aged Rats

The effects of a novel prolyl endopeptidase inhibitor (PEP), (S)-2-[[(S)-2-(hydroxyacetyl)-1-pyrrolidinyl]carbonyl]-N-(phenylmethyl)- 1-pyrrolidinecar-boxamide (JTP-4819), on performance of the Morris water maze task and on central cholinergic function were investigated in aged rats. Spatial memory (escape latency, path length, and swimming speed to the platform) was impaired in aged rats performing the Morris water maze task when compared to young rats. Administration of JTP-4819 (1 mg/kg, p.o.) for 14 days improved this memory deficit in aged rats, as shown by the decrease in escape latency and path length. In addition, when JTP-4819 (at doses of 1 and 3 mg/kg, p.o.) was administered for 3 wk, it reversed the age-related increase of ChAT activity in the cerebral cortex and the decrease of 3H-choline uptake in the hippocampus. These data suggest that JTP-4819 ameliorates age-related impairment of spatial memory and partly reverses central cholinergic dysfunction, possibly due to the enhancement of neuropeptide function by inhibition of PEP mediated degradation of substance P, arginine-vasopressin, and thyrotropin-releasing hormone.

Effects of a novel thyrotropin-releasing hormone analogue, JTP-2942, on extracellular acetylcholine and choline levels in the rat frontal cortex and hippocampus.

The effects of a novel thyrotropin-releasing hormone (TRH) analogue, N alpha-[(1S,2R)-2-methyl-4-oxocyclopentanecarbonyl]-L-histidyl-L-pr olinamide (JTP-2942) on acetylcholine (ACh) release and on the extracellular choline level were investigated in rat frontal cortex and hippocampus by microdialysis, and were compared with effects of TRH. JTP-2942 (0.3 mg/kg i.p.) produced a marked (> 300%) and persistent increase of ACh release in both the frontal cortex and hippocampus, while TRH (3 mg/kg i.p.) caused a significant but transient increase of ACh to about 200% in the frontal cortex. Both drugs significantly decreased the choline levels in both brain regions. Investigation of the effects of JTP-2942 (0.001-1 mM) and TRH (1 and 10 mM) on ACh release and choline levels when perfused through the dialysis probe revealed that JTP-2942 had a greater effect than TRH in both the frontal cortex and the hippocampus. The action of JTP-2942 was about 1000-fold more potent than that of TRH in both brain regions. Oral administration of JTP-2942 at a dose of 10 mg/kg markedly and persistently increased the release of ACh and at doses of 1-10 mg/kg decreased the extracellular choline level in the frontal cortex and hippocampus. These results also suggest that JTP-2942 has some selectivity for the hippocampus compared to the frontal cortex after both systemic administration and local injection. The increase of ACh release caused by JTP-2942 was completely antagonized by perfusion with tetrodotoxin (TTX, 1 microM), suggesting that the action of JTP-2942 on cholinergic neurons was mediated via neuronal activity.

Effect of a novel prolyl endopeptidase inhibitor, JTP-4819, on neuropeptide metabolism in the rat brain

The effect of a novel prolyl endopeptidase (PEP) inhibitor, (S)-2-[[(S)-2-(hydroxyacetyl)-l-pyrrolidinyl] carbonyl]-N-(phenylmethyl)-l-pyrrolidinecarboxamide (JTP-4819), on neuropeptide metabolism was investigated in the rat brain.JTP-4819 exhibited a strong in vitro inhibitory effect on cortical and hippocampal PEP activity, with the IC50 values being approximately 0.58 ± 0.02 and 0.61 ± 0.06 nM, respectively. JTP-4819 also inhibited the in vitro degradation of substance P (SP), arginine-vasopressin (AVP), and thyrotropin-releasing hormone (TRH) by rat brain supernatants, with the IC50 values being respectively 3.4, 2.1, and 1.4 nM in the cerebral cortex and 3.3, 2.8, and 1.9 nM in the hippocampus. Oral administration of JTP-4819 at doses of 1 and 3 mg/kg increased SP-like immunoreactivity (LI) and AVP-LI in the cerebral cortex. JTP-4819 also increased hippocampal SP-LI and AVP-LI at doses of 1 and 3 mg/kg, as well as hippocampal TRH-LI at a dose of 3 mg/kg.These findings suggest that JTP-4819 inhibited the degradation of SP, AVP, and TRH in the rat brain secondary to the inhibition of PEP, and thus increased cortical and hippocampal SP-LI and AVP-LI as well as hippocampal TRH-LI.

Pharmacological studies of a novel prolyl endopeptidase inhibitor, JTP-4819, in rats with middle cerebral artery occlusion

We studied behavioral and pharmacological effects of a novel prolyl endopeptidase inhibitor, (S)-2-[[(S)-2-(hydroxyacetyl)- 1-pyrrolidinyl]carbonyl]-N-(phenylmethyl)-1-pyrrolidine-car boxamide (JTP-4819), in rats with middle cerebral artery occlusion. Administration of JTP-4819 (0.1 and 1 mg/kg p.o for 7 days) significantly prolonged passive avoidance latency, while the latency of rats with middle cerebral artery occlusion receiving the vehicle was significantly shorter than that of sham-operated rats. The prolonged escape latency in the Morris water maze task in rats with middle cerebral artery occlusion was also significantly reduced by administration of JTP-4819 (0.3 and 1 mg/kg p.o.). Interestingly, administration of JTP-4819 (0.3-3 mg/kg p.o. for 15 days) restored the decreased cortical thyrotropin-releasing hormone (TRH)-like immunoreactivity content of rats with middle cerebral artery occlusion but did not affect the cortical and hippocampal substance P- or arginine vasopressin-like immunoreactivity content. These results suggest that JTP-4819 ameliorates memory impairment due to middle cerebral artery occlusion by restoring the cortical TRH content.

A Novel Prolyl Endopeptidase Inhibitor, JTP-4819 - Its Behavioral and Neurochemical Properties for the Treatment of Alzheimer's Disease

Formation of beta-amyloid and neurofibrillary tangles in the brain due to genetic or other factors is the most frequent cause of Alzheimers disease. In addition, marked reduction of certain brain neuropeptide levels is a consistent finding in patients with Alzheimers disease, together with the deterioration of cholinergic neurons. Currently, there is great demand for the development of new drugs to improve memory deficits or to delay the neurodegenerative process in conditions such as Alzheimers disease. In this report, the pharmacological actions of JTP-4819, a novel specific prolyl endopeptidase (PEP) inhibitor devised for the treatment of Alzheimers disease, are reviewed with respect to its effects on PEP activity, neuropeptidergic and cholinergic neurons, and memory-related behavior in rats. We also discuss the possible beneficial effect of JTP-4819 on beta-amyloid metabolism and its potential neuroprotective properties.

Effect of a novel prolyl endopeptidase inhibitor, JTP-4819, on spatial memory and on cholinergic and peptidergic neurons in rats with ibotenate-induced lesions of the nucleus basalis magnocellularis

We conducted behavioral and neurochemical studies of a novel prolyl endopeptidase inhibitor, (S)2-[[(S)-2-(hydroxyacetyl)-1pyrrolidinyl]carbonyl]-N-(phenylmeth yl)-1-pyrrolidine-carboxamide (JTP-4819), in rats with lesions of the nucleus basalis magnocellularis (NBM-lesioned rats) induced by ibotenate. Administration of JTP-4819 (1 and 3 mg/kg, p.o.), on and after the 8th day, significantly shortened the escape latency in the Morris water maze as compared to the vehicle-treated group. JTP-4819 also significantly increased the path length in the quadrant with the platform removed in the spatial probe trial. Neurochemical studies of brains removed after the Morris water maze task showed that choline acetyltransferase activity in the cerebral cortex, but not the hippocampus, was significantly reduced by NBM lesioning, while there were no changes of muscarinic M1 receptor binding activity detected using [3H]pirenzepine. JTP-4819 had almost no effect on these cholinergic parameters in NBM-lesioned rats. Substance P-like immunoreactivity (LI), thyrotropin-releasing hormone (TRH)-LI, and arginine-vasopressin-LI were not significantly changed in the cerebral cortex and hippocampus of NBM-lesioned rats as compared to sham-operated rats. However, these neuropeptide levels were significantly increased in both brain regions by repeated administration of JTP-4819 (1, 3 and/or 10 mg/kg, p.o.). These results suggest that JTP-4819 ameliorated memory impairment due to NBM lesioning by potentiating SP, TRH and AVPergic neurons secondary to PEP inhibition.

A novel prolyl endopeptidase inhibitor, JTP-4819, with potential for treating Alzheimer's disease

The pharmacological actions of JTP-4819, a new prolyl endopeptidase (PEP) inhibitor targeted for the treatment of Alzheimers disease, are reviewed with respect to its effects on PEP activity, brain neurotransmitters, and memory-related behaviour in rats. JTP-4819 was shown to be a very potent and specific inhibitor of PEP. At nanomolar concentration, JTP-4819 inhibited the degradation of substance P, arginine-vasopressin, and thyrotropin-releasing hormone by PEP in supernatants of the rat cerebral cortex and hippocampus. Repeated administration of JTP-4819 reversed the aging-induced decrease in brain substance P-like and thyrotropin-releasing hormone-like immunoreactivity, suggesting that this drug may be able to improve the imbalance of peptidergic neuronal systems that develops with senescense by inhibiting PEP activity. JTP-4819 increased acetylcholine release from the frontal cortex and hippocampus, regions closely associated with memory, in both young and aged rats. In addition, it improved performance in several memory and learning-related tests (e.g., the Morris water maze task in aged or MCA-occluded rats and the passive avoidance test). This memory-enhancing effect of JTP-4819 may result from prevention of the metabolic degradation of brain neuropeptides by PEP as well as from the enhancement of acetylcholine release. Taken together, these unique and potent pharmacological actions of JTP-4819 suggest that it may have the potential to be used for treating Alzheimers disease.

Effect of JTP-2942, a novel thyrotropin-releasing hormone analogue, on pentobarbital-induced anesthesia in rats

The effects of a novel thyrotropin-releasing hormone (TRH) analogue, N alpha-((1S,2R)-2-methyl-4-oxocyclopentylcarbonyl)-L-histidyl-L-pro linamide monohydrate (JTP-2942), on pentobarbital-induced anesthesia in rats were investigated and compared with those of TRH. Intravenous administration of both JTP-2942 and TRH caused a dose-dependent decrease in the recovery time from pentobarbital-induced anesthesia. The minimum effective doses of JTP-2942 and TRH were respectively 0.03 and 1 mg/kg. The effect of JTP-2942 was antagonized by intraperitoneal scopolamine (0.5 mg/kg). Intraperitoneal JTP-2942 (1 mg/kg) caused an increase of acetylcholine release and a decrease of choline release in the frontal cortex and hippocampus of pentobarbital-treated rats. In addition, JTP-2942 ameliorated the decrease of hemicholinium-3-sensitive high-affinity choline uptake and the increase of acetylcholine in these brain regions. However, JTP-2942 had no effect on choline acetyltransferase activity or the choline content, which were also not changed by pentobarbital. Our results indicate that the effect of JTP-2942 on pentobarbital-induced anesthesia was about 30 times more potent than that of TRH, and suggest that JTP-2942 may act by accelerating acetylcholine turnover.