Yoshiyuki Shishido

Effect of nordihydroguaiaretic acid on behavioral impairment and neuronal cell death after forebrain ischemia.

The purpose of this study was to evaluate the neuroprotective effect of nordihydroguaiaretic acid (NDGA), an antioxidant and/or 5-lipoxygenase inhibitor, on ischemia-reperfusion injury behavioral pharmacologically and histologically in vivo. First, the antioxidant activity of NDGA was evaluated in vitro by measuring the production of thiobarbituric acid reactive substances (TBARS) in rat brain homogenate. Second, the effect of NDGA on learning and memory impairment induced by rat four-vessel occlusion transient ischemia was investigated with the Morris water-maze task. Third, the effect of NDGA on pyramidal cell loss in the hippocampus after transient ischemia was examined. NDGA inhibited the production of TBARS with an IC(50) of 0.1 microM, and significantly attenuated postischemic learning and memory impairment at 10 mg/kg. Furthermore, consecutive 4-day administration of NDGA at 10 mg/kg significantly reduced the postischemic neuronal death. NDGA was found to be potent and effective as an anti-ischemia-reperfusion injury agent in terms of behavioral pharmacology and histology. The present results suggest that NDGA has beneficial effects on behavioral deficits and histological injury caused by ischemia-reperfusion.

Effects of prolyl endopeptidase inhibitors and neuropeptides on delayed neuronal death in rats.

We investigated the effects of the prolyl endopeptidase inhibitors 1-[1-(Benzyloxycarbonyl)-L-prolyl]prolinal (Z-Pro-Prolinal) and N-benzyloxycarbonyl-thioprolyl-thioprolinal-dimethylaceta l (ZTTA) on delayed neuronal death induced by four-vessel-occlusion transient ischemia in rats. We also examined the effects of [pGlu4, Cyt6, ArgS]vasopressin (vasopressin-(4-9)) and thyrotropin-releasing hormone (TRH) on the delayed neuronal death. Furthermore, we investigated the role of vasopressin receptors in the effects of vasopressin and prolyl endopeptidase inhibitors. Z-Pro-Prolinal, vasopressin-(4-9) and TRH protected pyramidal cells in the CA1 subfield of the rat hippocampus from delayed neuronal death after 10-min ischemia. The effect of vasopressin-(4-9) was abolished by vasopressin receptor antagonists. The effect of Z-Pro-Prolinal was also abrogated by the antagonists. These results suggest that the neuroprotective effect of prolyl endopeptidase inhibitors is mediated by neuropeptides such as [Arg8]vasopressin and TRH, and indicate the involvement of vasopressin receptors in the neuroprotective effect of vasopressin-(4-9) and prolyl endopeptidase inhibitors.

ZTTA, a postproline cleaving enzyme inhibitor, improves cerebral ischemia-induced deficits in a three-panel runway task in rats.

We investigated the effect of N-benzyloxycarbonyl-thioprolyl-thioprolinal-dimethylaceta l (ZTTA), a novel postproline cleaving enzyme (prolyl endopeptidase, PPCE) inhibitor, on the in vitro activity of rat brain PPCE and memory impairment induced by cerebral ischemia. ZTTA noncompetitively inhibited rat brain PPCE (ki = 2.9 microM). Cerebral ischemia for 5 min increased the number of errors in a working memory task with a three-panel runway paradigm. ZTTA at 6 mg/kg, administered immediately after blood flow reperfusion, significantly reduced the increase in working memory errors expected to occur 24 h after 5 min of ischemia. The antiamnesic action of ZTTA may be ascribable to a neuroprotective effect on the central nervous system due to some neuropeptides that are substrates of PPCE in the brain.

Facilitatory effect of vasopressin on the ischemic decrease of the CA1 presynaptic fiber spikes in rat hippocampal slices

We investigated the effects of vasopressin-related neuropeptides on the hypoxia/hypoglycemia (ischemia)-induced decrease of the CA1 presynaptic potential elicited by stimulation of Schaffer collaterals in rat hippocampal slices. Treatment with arginine-vasopressin (AVP) potentiated the ischemic decrease of the CA1 presynaptic potential. In contrast, a V1 receptor antagonist produced a dose-dependent neuroprotective effect, whereas a V2 receptor antagonist had no effect. The AVP-induced decrease of the CA1 presynaptic potential was completely blocked by simultaneous application of the V1 receptor antagonist. Because AVP4-9 is regarded as the major proteolytic product of AVP in the rat brain, we examined its effect on the ischemic decrease of the CA1 presynaptic potential. Treatment with AVP4-9 produced a more marked reduction of the potential than treatment with AVP itself. The present study demonstrates that stimulation of the V1 receptor has a detrimental effect on the development of ischemic damage whereas V1 receptor blockade has a neuroprotective effect, suggesting that AVP may potentiate ischemic neuronal deficits via V1 receptor stimulation.

Effects of Arginine-Vasopressin Fragment 4–9 on Rodent Cholinergic Systems

Arginine-vasopressin fragment 4-9 (AVP4-9) has been demonstrated in animal studies to facilitate learning and memory. To clarify the mechanisms of this facilitation, we focused on the effects of AVP4-9 on rodent cholinergic systems. AVP4-9 (0.1 microM) enhanced the basal and the high-potassium-evoked acetylcholine (ACh) release from rat hippocampal slices (122.4 and 120.0% of control, respectively) in the presence of 1.3 mM calcium (physiological level) at 60 min after the incubation at 37 degrees C. The AVP4-9-stimulated basal ACh release was inhibited by a V1-selective antagonist ([(beta-mercapto-beta,beta-cyclopentamethylene propionic acid)1, O-methyl-Tyr2, Arg8] vasopressin), but not by a V2-selective antagonist ([adamantaneacetyl1, O-ethyl-D-Tyr2, Val4, aminobutyryl6, Arg8,9]-vasopressin). In addition, AVP4-9 did not affect the basal ACh release under the calcium-free condition at 37 degrees C or in the presence of 1.3 mM calcium at 4 degrees C. However, AVP4-9 facilitated the passive-avoidance response of scopolamine (a cholinergic blocker)-induced memory-deficient mice. These findings demonstrate that AVP4-9 stimulates ACh release via mediation by V1-like vasopressin receptors, and shows dependence on calcium ion and temperature. The results also suggest that the mechanism of the facilitative effects of AVP4-9 on learning and memory consist of the observed stimulation of cholinergic systems and other parallel pathways that would not be inhibited by cholinergic blocking.

Facilitation of Passive Avoidance Response by Newly Synthesized Cationized Arginine Vasopressin Fragment 4-9 in Rats

The effects of a newly synthesized cationized arginine vasopressin fragment 4-9 analogue (C-AVP-(4-9)) on learning and memory in rats were studied by the passive avoidance test. C-AVP-(4-9) and its parent peptide, arginine vasopressin fragment 4-9 (AVP-(4-9)), a well known potent neuropeptide, were subcutaneously injected 1.5 hr prior to the retention test. The most effective doses of C-AVP-(4-9) and AVP-(4-9) were 8.6 x 10(-2) and 1.3 nmol/kg, respectively. To evaluate the distribution of C-AVP-(4-9) in the control nervous system (CNS), apparent tissue-plasma concentration rations (Kp.app) of intravenously administered radioiodinated C-AVP-(4-9) (125I-C-AVP-(4-9)) in the CNS in mice were determined. At the apparent steady state of plasma concentration of 125I-C-AVP-(4-9), the Kp.app values of the 125I-C-AVP-(4-9) in the cerebrum, cerebellum and spinal cord were over 12 times higher than that of the vascular space marker which slightly penetrates the BBB. Moreover, the rat cerebral homogenate converted C-AVP-(4-9) into its parent peptide AVP-(4-9). These results suggest that the potent effects of C-AVP-(4-9) on learning and memory may be due to AVP-(4-9) generated as a result of distribution and metabolism of peripherally administered C-AVP-(4-9) in the CNS.