Long-term potentiation (LTP) is thought to be particularly important in the acquisition of hippocampus-associated memory, in part because it develops quickly and persists for indefinite periods. Extracellular proteolysis has been hypothesized to contribute to LTP by modifying adhesive relations of synapses and thus the morphology of excitatory synapses. Here we report that neuropsin (NP), an extracellular serine protease, is critically involved in the formation of both the potentiation effect and hippocampus-dependent forms of memory. NP-knockout mice were significantly impaired in the Morris water maze and Y-mazes and failed to exhibit early phase LTP induced by a single tetanus. Potentiation was also impaired or completely blocked by in vivo application of a specific inhibitor or a neutralizing monoclonal antibody for NP. Intriguingly, recombinant (r-) NP alone, without tetanic stimulation, elicited either long-lasting potentiation or depression, depending on the applied dose. The r-NP-elicited potentiation was occluded by prior induction of LTP, while theta-burst-elicited LTP was occluded by application of r-NP alone, suggesting that the two forms of plasticity have a common signalling pathway. r-NP-elicited potentiation and depression increased phosphorylation at different sites on the GluR1 subunit of the AMPA receptor that had previously been associated with LTP or long-term depression. Thus, we conclude that NP is necessary for establishment of LTP and has a significant role in memory acquisition.

No abstract

Abstract. We investigated the effect of TTC-909, a drug preparation of the stable prostaglandin I 2 analogue clinprost (isocarbacyclin methylester; methyl 5-{(1S,5S,6R,7R)-7-hydroxy-6-[(E)-(S)-3-hydroxy-1-octenyl] bicyclo[3.3.0]oct-2-en-3-yl} pentanoate) incorporated into lipid microspheres, on cerebral infarction 7 days after permanent occlusion of the middle cerebral artery (MCA) in stroke prone spontaneously hypertensive rats (SHRSP). Under the anesthesia, the MCA was permanently occluded above the rhinal fissure. In schedule 1, vehicle or TTC-909 was injected i.v. once daily over 7 days starting immediately after MCA occlusion. In schedule 2, vehicle or TTC-909 was infused for 3 h starting immediately after MCA occlusion. In schedule 3, vehicle or TTC-909 was infused for 3 h starting immediately after MCA occlusion followed by bolus injection once daily over 6 days. Seven days later, the infarct volume was estimated following hematoxylin and eosin staining. Cerebral infarction produced by permanent occlusion of MCA was limited to the cerebral cortex. While this volume was reduced significantly in case of schedule 3, the infarct volume was not reduced significantly in schedules 1 and 2. Ozagrel, a thromboxane A 2 synthetase inhibitor, had no effect on the infarct volume in schedule 3. These results suggest that cerebral infarction can be developed progressively not only during the first few hours but also after a permanent occlusion of MCA in SHRSP. TTC-909 inhibited cerebral infarction, maybe by improving cerebral blood flow and by protecting against neuronal damage.

No abstract

Histamine H3 receptor antagonists/inverse agonists are known to enhance the activity of histaminergic neurons in the brain, thereby promoting arousal and cognition. Here, we report the in vitro and in vivo pharmacological profiles for a newly synthesized histamine H3 receptor antagonist/inverse agonist: [1-(4-{3-[(2R)-2-methylpyrrolidin-1yl]propoxy}phenyl)-1H-pyrazol-4-yl](morpholin-4-yl)methanone monohydrochloride (enerisant hydrochloride). In vitro assays showed that enerisant was a competitive antagonist/inverse agonist with a high affinity and selectivity for human and rat histamine H3 receptors. Enerisant showed antagonist activity in vivo, as assessed using R-αmethylhistamine (a histamine H3 receptor agonist)-induced dipsogenia, and occupied the histamine H3 receptor in the frontal cortex in a dose-dependent manner. Enerisant also enhanced the extracellular levels of histamine in the posterior hypothalamus and the levels of dopamine and acetylcholine in the medial prefrontal cortex of rats. Enerisant exerted a pro-cognitive effect or reversed scopolamine-induced cognitive impairment in a social recognition test and a novel object recognition test in rats at doses at which less than 50% of the histamine H3 receptor were occupied (0.03-0.3 mg/kg, p.o.). In contrast, higher doses (3-10 mg/kg, p.o.) at which nearly all the histamine H3 receptor were occupied were needed to exert wake-promoting effects in rats.