Effect of minaprine on cycloheximide-induced amnesia in mice

Ameliorating effect of emodin, a constitute of Polygonatum multiflorum, on cycloheximide-induced impairment of memory consolidation in rats

The aim of the present study was intended to investigate the ameliorating effects of emodin on memory consolidation via cholinergic, serotonergic and GABAergic neuronal systems in rats. First, we evaluated the ameliorating effects of emodin on cycloheximide (CXM)-induced impairment of passive avoidance response in rats. Secondly, we clarified the role of cholinergic, serotonergic or GABAergic system on the ameliorating effect of emodin by using 5-HT1A receptor partial agonist, 5-HT2 receptor antagonist, GABAB agonist, GABAA antagonist and muscarinic receptor antagonist. Emodin protected the rat from CXM-induced memory consolidation impairment. The beneficial effect of emodin on CXM-induced memory consolidation impairment was amplified by 8-OH-DPAT (5-HT1A receptor partial agonist) and ritanserin (5-HT2 receptor antagonist), but reduced by scopolamine. These results suggested that the beneficial effect of emodin on CXM-induced memory consolidation impairment was amplified by serotonergic 5-HT1A-receptor partial agonist and 5-HT2 receptor antagonist but reduced by muscarinic receptor antagonist.

Microinjection of ritanserin into the CA1 region of hippocampus improves scopolamine-induced amnesia in adult male rats

The effect of ritanserin (5-HT2 antagonist) on scopolamine (muscarinic cholinergic antagonist)-induced amnesia in Morris water maze (MWM) was investigated. Rats were divided into eight groups and bilaterally cannulated into CA1 region of the hippocampus. One week later, they received repeatedly vehicles (saline, DMSO, saline+DMSO), scopolamine (2 microg/0.5 microl saline/side; 30 min before training), ritanserin (2, 4 and 8 microg/0.5 microl DMSO/side; 20 min before training) and scopolamine (2 microg/0.5 microl; 30 min before ritanserin injection)+ritanserin (4 microg/0.5 microl DMSO) through cannulae each day. Animals were tested for four consecutive days (4 trial/day) in MWM during which the position of hidden platform was unchanged. In the fifth day, the platform was elevated above the water surface in another position to evaluate the function of motor, motivational and visual systems. The results showed a significant increase in escape latencies and traveled distances to find platform in scopolamine-treated group as compared to saline group. Ritanserin-treated rats (4 microg/0.5 microl/side) showed a significant decrease in the mentioned parameters as compared to DMSO-treated group. However, scopolamine and ritanserin co-administration resulted in a significant decrease in escape latencies and traveled distances as compared to the scopolamine-treated rats. Our findings show that microinjection of ritanserin into the CA1 region of the hippocampus improves the scopolamine-induced amnesia.

Localization of 5-HT2A receptor in rat cerebral cortex and olfactory system revealed by immunohistochemistry using two antibodies raised in rabbit and chicken

Serotonin 2A receptor (5-HT2A receptor) is widely distributed in the central nervous system, and has been suggested to be involved in a variety of behavioral conditions and neuropsychiatric disorders. Two polyclonal antibodies were raised against the N-terminus peptide of rat 5-HT2A receptor in chickens (5-HT2A-N) and a glutathione S-transferase fusion protein that contained the C-terminus of the mouse 5-HT2A receptor in rabbits (5-HT2A-C). Affinity-purified 5-HT2A-N and -C antibodies reacted strongly with a single band of 77-78 kDa in postsynaptic density proteins prepared from the rat cortex. The distribution pattern of immunoreactive structures in the rat brain was virtually the same for the two antibodies. The highest levels of immunoreactivity were observed in the olfactory bulb, neocortex, claustrum, piriform cortex, mamillary bodies, pontine nuclei, red nucleus and cranial motor nuclei. In the olfactory bulb, mitral cells were intensely labeled. In the neocortex, many immunoreactive neurons were found in layers II-VI. In layer IV of the neocortex, strong neuropil labeling was observed. In a double-labeling study using chicken 5-HT2A-N and rabbit anti-glial fibrillary acidic protein (GFAP) antibody, a considerable number of GFAP positive cells also showed 5-HT2A immunoreactivity. By using an immunoelectron microscopic technique, 5-HT2A receptor immunoreaction was shown to be localized just beneath the postsynaptic membrane thickening of asymmetric synapses.

Effects of oral administration of soybean lecithin transphosphatidylated phosphatidylserine on impaired learning of passive avoidance in mice

Soybean lecithin transphosphatidylated phosphatidylserine (SB-tPS) was investigated for its effect on the impaired learning of a passive avoidance task by mice induced by scopolamine or cycloheximide. SB-tPS (240, 360, 480 mg/kg) administered orally significantly prolonged the step-through latency shortened by scopolamine. SB-tPS (240 mg/kg) administered orally also prolonged the step-through latency shortened by cycloheximide. These results suggest that the effect of SB-tPS on the impaired learning behavior may be related not only to the cholinergic system but also the serotonergic system.

Minaprine facilitates acquisition and retrieval of an active avoidance response in the rat

The nootropic activity of 3-(2-morpholino-ethylamino)-4-methyl-6-phenyl-pyridazine dihydrochloride (minaprine) has been investigated in intact male, adult Long Evans rats by means of an active avoidance paradigm. In the light-dark box apparatus, the rat had to learn the active avoidance response of going out of the normally preferred dark chamber to avoid electric foot-shocks. These were administered during one trial per day for 3 consecutive days (acquisition period). After a 72-h interval, rats underwent, for 3 consecutive days, one trial per day in which punishments were omitted (retrieval period). In the first experiment, rats were injected IP with minaprine (5, 10, and 25 mg/kg b.w.) 30 min before each trial of both periods. Rats injected with the two lower dosages showed better responding during the retrieval period than controls (saline). On the contrary, the highest dosage impaired active avoidance during both periods. In Experiment 2, minaprine (10 mg/kg b.w.) was administered either only during the acquisition or only during the retrieval period. In both instances, active avoidance was equally enhanced, if compared to controls (saline), only during the retrieval period. The results are discussed on the basis of the known facilitating activity on cholinergic systems of this compound. It is concluded that minaprine acts positively both on acquisition and retrieval of mnemonic traces.

Minaprine cancels scopolamine effects on the rat's acquisition of passive avoidance responses in two multitrial paradigms

The antiamnesic activity of minaprine has been studied in male Wistar rats. Two multitrial paradigms were employed: the light-dark box test (aversive stimulus: 0.6-mA foot-shocks) and the tail-handling test (aversive stimulus: manual tail-handling). In both paradigms, intraperitoneal scopolamine administration 30 min before testing significantly impaired the acquisition of the passive avoidance conditioned response. There were no significant differences in either paradigm between control rats and those to whom scopolamine and minaprine were simultaneously administered. These results show that minaprine fully protects the acquisition process of conditioned responses against scopolamine impairment not only in one-trial tests but also in multitrial paradigms. The effects of minaprine in reversing memory deficits are discussed in relation to its stimulating activity on central cholinergic systems.

Involvement of serotonergic neuronal systems in the anti-amnesic action of naftidrofuryl oxalate

The effects of naftidrofuryl oxalate on cycloheximide- and 5-hydroxytryptophan (5-HTP)-induced amnesia were investigated using a passive avoidance task in mice. Naftidrofuryl oxalate significantly improved the cycloheximide-induced amnesia. This effect of naftidrofuryl oxalate was antagonized by 5-HTP, a serotonin (5-HT) precursor, and by p-chloroamphetamine (PCA), a 5-HT releaser. Single administration of 5-HTP in combination with pargyline, a monoamine oxidase inhibitor, induced amnesia (5-HTP-induced amnesia). This amnesia was attenuated by ritanserin, a 5-HT2-selective antagonist, but not by pindolol, a 5-HT1-selective antagonist. Naftidrofuryl oxalate also attenuated the 5-HTP-induced amnesia. A binding study revealed that naftidrofuryl oxalate inhibited the binding of [3H]ketanserin to 5-HT2 receptors in mouse brain synaptic membrane in a dose-dependent fashion (IC50 = 1.42 x 10(-7) M), but did not inhibit that of [3H]serotonin to 5-HT1 receptors. These results suggest that naftidrofuryl oxalate may attenuate cycloheximide- and 5-HTP-induced amnesia by blocking 5-HT2 receptor subtypes.

Blockade of voltage-dependent 42K efflux from rat brain synaptosome by minaprine and tetrahydroaminoacridine

The effect of minaprine (3-(2-morpholinoethylamino)-4-methyl-6-phenylpyridazine) on the K+ channels was studied by means of 42K efflux from rat brain synaptosomes, comparing the effects of 4-aminopyridine and 9-amino-1,2,3,4-tetrahydroacridine (THA). 42K efflux from rat brain synaptosomes was classified into five components: a resting component (R), a rapidly inactivating, voltage-dependent component (T), a slowly inactivating, voltage-dependent component (S) and a voltage-dependent, Ca(2+)-dependent component which is divided into a fast phase (CT) and a slower phase (CS). 4-Aminopyridine selectively inhibited 42K efflux of component T. THA blocked both S and T components. The inhibitory effect of THA on the 42K efflux of component S was quite pronounced compared with that of component T. Minaprine inhibited the 42K efflux of components S and T but the inhibitory effect on component S was observed with a lower dose of minaprine than that needed for the effect on component T. Minaprine had no effect on the Ca(2+)-dependent component while THA blocked component CT. 42K efflux of the resting component was not changed by minaprine, THA or 4-aminopyridine. These results suggest that minaprine blocks Ca2+ independent voltage-dependent K+ channel is involved in the pharmacological actions of minaprine.