Cyclosporine A inhibits acetylcholinesterase activity in selected parts of the rat brain

Cyclosporine A (CsA) is the major immunosuppressive drug used for organ and neural transplantation and the therapy of selected autoimmune diseases. We investigated the effect of CsA on the activity of acetylcholinesterase (AChE) in the frontal cortex, hippocampus, septum, and basal ganglia. AChE was determined spectrophotometrically with acetylthiocholine as substrate and 5,5-bis-2-nitrobenzoic acid as chromogen. CsA was administered in single doses of 20 or 45 mg/kg perorally; in the case of the higher dose we also performed a repeated administration of CsA in three consecutive doses separated by 24 h intervals. Both lower and higher doses of CsA decreased AChE activity in the frontal cortex and hippocampus to practically the same extent. On the contrary, AChE activity was more diminished in the case of the higher dose of CsA used in the septum and basal ganglia. Repeated administration of the higher dose of CsA did not lead, with the exception of the hippocampus, to a further decrease in AChE activity in the brain structures observed. These findings contribute to rare evidence concerning the interaction of CsA and the cholinergic system in the brain.     

Influence of estradiol on acetylcholinesterase activity in several female rat brain areas and adenohypophysis

We investigated the relationship of estradiol (E₂) with cholinergic transmission in 7 brain areas and adenohypophysis of ovariectomized rats by measuring the activity, and induction by this steroid hormone of acetylcholinesterase (AChE). We found that, in comparison with untreated controls, E₂ significantly increased AChE activity in the adenohypophysis and amygdala at 4 h post-injection of the hormone.     

Effect of acute noise stress on acetylcholinesterase activity in discrete areas of rat brain

Effect of various stressor agents on the adrenergic system in brain had been studied extensively. However, reports on the effect of stress on various parameters of central cholinergic system are scanty. And very little is known about the effect of noise stress on the cholinergic system in brain. Hence, it was decided to elucidate the effect of acute noise stress on the activity of the enzyme acetylcholinesterase in discrete areas of brain in albino rats. Male albino rats of Wistar strain were subjected to acute noise stress for 30 minutes. The noise of pure sine wave tone was produced by using a function generator and was amplified. The frequency of noise generated was 1 kHz and the intensity was set at 100 dB. The total acetylcholinesterase activity was determined in the tissues of cerebral cortex, corpus striatum, hypothalamus and hippocampus of brain in these rats. The enzyme activity was estimated by colorimetric method using acetylthiocholine iodide as the substrate. The values were compared with the enzyme activity in the control rats. The activity of the enzyme increased significantly in all the four regions of the brain in rats after exposure to noise stress for 30 minutes. The results of the study indicate that the exposure to acute noise stress could modulate the cholinergic system in these areas of brain in rat.     

Typifying presynaptic M-cholinergic receptors in different structures of rat brain

Pre- and postsynaptic M-cholinergic receptors are typified by radioligand analysis with selective cholinoblockers by comparing ligand binding in homogeneous and synaptosomal fractions of different structures of rat brain. It is found that presynaptic receptors of the hemispheres belong to M₃ subtype and those of the brain stem are probably of M₄ subtype. Translated fromByulleten' Eksperimental'noi Biologii i Meditsiny, Vol. 122, No. 7, pp. 75–77, July, 1996     

Serotonin activates presynaptic and postsynaptic receptors in rat globus pallidus

Although recent histological, behavioral, and clinical studies suggest that serotonin (5-HT) plays significant roles in the control of pallidal activity, only little is known about the physiological action of 5-HT in the pallidum. Our recent unit recording study in monkeys suggested that 5-HT provides both presynaptic and postsynaptic modulations of pallidal neurons. The present study using rat brain slice preparations further explored these presynaptic and postsynaptic actions of 5-HT. Bath application of 5-HT or the 5-HT(1A/1B/1D/5/7) receptor (R) agonist 5-carboxamidotryptamine maleate (5-CT) depolarized some and hyperpolarized other pallidal neurons. Pretreatments of slices with blockers of the hyperpolarization-cyclic nucleotide-activated current or with the 5-HT(2/7)R-selective antagonist mesulergine occluded 5-CT-induced depolarization. The 5-HT(1A)R-selective blocker N-[2[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-N-2-pyridinylcyclohex-anecarboxamide maleate occluded the 5-CT-induced hyperpolarization. These results suggested involvement of 5-HT(7)R and 5-HT(1A)R in the postsynaptic depolarization and hyperpolarization, respectively. 5-CT presynaptically suppressed both internal capsule stimulation-induced excitatory postsynaptic currents (EPSCs) and striatal stimulation-induced inhibitory postsynaptic currents (IPSCs). The potencies of 5-CT on the presynaptic effects were 20- to 25-fold higher than on postsynaptic effects, suggesting that 5-HT mainly modulates presynaptic sites in the globus pallidus. Experiments with several antagonists suggested involvement of 5-HT(1B/D)R in the presynaptic suppression of EPSCs. However, the receptor type involved in the presynaptic suppression of IPSCs was inconclusive. The present results provided evidence that 5-HT exerts significant control over the synaptic inputs and the autonomous activity of pallidal neurons.     

KA-672 inhibits rat brain acetylcholinesterase in vitro but not in vivo

KA-672, a lipophilic benzopyranone derivative which is currently under development as a cognitive enhancer and antidementia drug, has previously been shown to have facilitatory effects on learning and memory in rats at doses of 0.1-1 mg/kg. We now report that KA-672 inhibited the activity of acetylcholinesterase (AChE), measured in vitro in rat brain cortical homogenate, with an IC50 value of 0.36 microM indicating that KA-672 may improve cognitive functions as a consequence of AChE inhibition. However, when we employed the microdialysis procedure to monitor acetylcholine (ACh) release from rat hippocampus, no effect of KA-672 (0.1-10 mg/kg) was found, indicating a lack of inhibition of brain AChE under in vivo-conditions. [14C]-labelled KA-672 was found to easily penetrate the blood-brain barrier, and an apparent concentration of 0.22 nmol/g brain (equivalent to 0.39 microM tissue concentration) was calculated following an i.p. injection of 1 mg/kg KA-672. However, no labelled substance could be detected in hippocampal microdialysates or in cerebrospinal fluid (CSF) taken from the cisterna magna, indicating that the concentration of KA-672 in brain extracellular fluid must have been below 0.01 microM. We conclude that KA-672 is a potent AChE inhibitor, an activity which, however, does not contribute to its behavioural effects in vivo because the lipophilic drug does not reach sufficient concentrations in the extracellular fluid, apparently due to cellular sequestration.     

Amitriptyline-induced ultrastructural changes in various structures of rat brain

The immediate effect of amitriptyline on various brain structures is characterized by the standard ultrastructural changes in neurons: emergence of numerous coated vesicles in the cytoplasm and formation of cisternae within a 3-h period. These changes are most pronounced in the sensorimotor cortex. Changes in the structure of cytoplasmic organelles are reversible; they disappear 24 h after administration of amitriptyline. Astrocytes respond to the preparation by activation of lysosomes, being the most sensitive cell type of the neuroglia. Numerous synaptic vesicles are seen in the axodendritic synapses. Newly formed fibers in the neuropile may be associated with the antidepressant effect of amitriptyline. Translated fromByulleten' Eksperimental'noi Biologii i Meditsiny, Vol. 122, No. 10, pp. 457–461, October, 1996     

Changes of acetylcholinesterase activity in the brain following septal lesions in the rat

Acetylcholinesterase activity in different parts of the limbic system (hippocampus, hypothalamus and amygdala) was decreased following medial septal lesions. On the other hand, this activity in the thalamus, frontal cortex, bulbus olfactorius, nucleus ruber, substantia nigra and basal ganglia was unaffected.These results raise the possibility that there is a functional relationship of the medial septum and those parts of the limbic system that we have studied.     

Dynorphin exerts both postsynaptic and presynaptic effects in the Globus pallidus of the rat

The opioids contained in striato-pallidal axons are thought to play a significant role in motor control. We examined post- and presynaptic effects of the kappa (kappa)-receptor agonist dynorphin A (1-13) (DYN13) on the globus pallidus (GP) neurons in rat brain slice preparations using the whole cell recording method. DYN13 hyperpolarized and decreased the input resistance of approximately one-quarter of neurons examined. All of these DYN13-sensitive neurons had medium-sized somata, large aspiny dendrites and generated repetitive firing without strong accommodation. The hyperpolarization was blocked by barium and was independent of TTX and intracellular chloride levels. The hyperpolarization was also selectively blocked by the kappa-antagonist nor-binaltorphimine dihydrochloride but not by the mu- or delta-antagonists. These data suggested that DYN13 activates barium-sensitive potassium currents in some GP neurons. Low- and high-intensity stimulation of the neostriatum (Str) evoked long- and short-latency GABAergic responses, respectively. Previous data suggested that the long- and the short-latency responses were due to activation of the striato-pallidal axons and the local collaterals of pallido-striatal axons, respectively. DYN13 diminished the amplitude of both the short- and long-latency GABAergic responses in all the neurons tested. The effects of DYN13 on GABAergic postsynaptic responses were also selectively blocked by a kappa-antagonist. To investigate whether the effects were pre- or postsynaptic, the effects of DYN13 on spontaneous inhibitory postsynaptic potentials (IPSPs) and TTX-independent miniature-inhibitory postsynaptic currents (IPSCs) were examined. DYN13 decreased the frequency, but not the amplitude, of spontaneous IPSCs and calcium-dependent miniature-IPSCs. However, DYN13 did not alter the cadmium-insensitive miniature-IPSCs. These results suggested that DYN13 suppressed GABA release from presynaptic terminals. This possibility was tested using a paired-stimulation test. DYN13 reduced the probability of evoking IPSCs to the first stimulation and greatly increased the success probability to the second stimulus. The amplitude of successfully evoked IPSCs was not changed with DYN13. DYN13 did not affect the excitatory postsynaptic potentials (EPSPs) or the response to iontophoretically applied GABA and glutamate. Together, these results suggest that DYN released from striato-pallidal axons controls the activity of GP neurons 1) by directly hyperpolarizing a population of neurons and 2) by presynaptically inhibiting GABA release from striato-pallidal and intrapallidal terminals.     

Tetrahydroaminoacridine inhibits human and rat brain monoamine oxidase

The inhibitory effects of 1,2,3,4-tetrahydro-9-aminoacridine (THA) on monoamine oxidase (MAO; EC 1.4.3.4) enzyme activities in human hippocampal and rat striatal homogenates have been studied. The activities of MAO-A and MAO-B were estimated radiochemically, in-vitro, in human hippocampus and rat striatum in the presence of various concentrations of THA with [2-14C]hydroxytryptamine binoxalate (100 microM) and beta-[ethyl-14C]phenylethylamine hydrochloride (20 microM) as substrates for the respective enzyme form. THA was found to inhibit both MAO-A and MAO-B activities reversibly and competitively, with inhibition constants (Ki) of 12.5 microM and greater than 500 microM respectively, of the rat striatal enzymes. From this it can be extrapolated that at therapeutic tissue concentrations of THA (10(-8) to 10(-6) M), more than 20% of the MAO-A activity should be inhibited. Thus it is possible that inhibition of MAO may be involved in the therapeutic action of THA in Alzheimer's disease.     

Enkephalinas activity in various brain structures of naloxone-treated and morphine-insensitive rats

Morphine injected subcutaneously in a dose of 2 mg/kg body weight exerted an analgesic effect in some Wistar rats (morphine-sensitive animals), as was indicated by a significantly prolonged latency of the tail-flick response, butfailed to produce analgesia in others (morphine-insensitive animals). In morphine-sensitive rats, the striatum had the highest enkephalinase A activity, followed in decreasing order by the mesencephalon, hippocampus, pons, cortex, medulla oblongata, and hypothalamus. Thirty minutes after intraperitoneal administration of naloxone (0.3 mg/kg body weight) to morphine-sensitive rats, enkephalinase activity fell significantly in the hippocampus, striatum, and cortex, remained unchanged in the pons and medulla oblongata, and rose significantly in the mesencephalon and insignificantly in the hypothalamus; generally similar differences in enkephalinase activity from naloxone-untreated morphine-sensitive rats were recorded in the brain structures of morphine-insensitive rats given saline instead of naloxone. Translated fromByulleten' Eksperimental'noi Biologii i Meditsiny, Vol. 120, N ^o 11, pp. 492–494, November, 1995 Presented by K. V. Sudakov, Member of the Russian Academy of Medical Sciences     

Donepezil markedly potentiates memantine neurotoxicity in the adult rat brain

The NMDA antagonist, memantine (Namenda), and the cholinesterase inhibitor, donepezil (Aricept), are currently being used widely, either individually or in combination, for treatment of Alzheimer's disease (AD). NMDA antagonists have both neuroprotective and neurotoxic properties; the latter is augmented by drugs, such as pilocarpine, that increase cholinergic activity. Whether donepezil, by increasing cholinergic activity, might augment memantine's neurotoxic potential has not been investigated. In the present study, we determined that a dose of memantine (20mg/kg, i.p.), considered to be in the therapeutic (neuroprotective) range for rats, causes a mild neurotoxic reaction in the adult rat brain. Co-administration of memantine (20 or 30 mg/kg) with donepezil (2.5-10mg/kg) markedly potentiated this neurotoxic reaction, causing neuronal injury at lower doses of memantine, and causing the toxic reaction to become disseminated and lethal to neurons throughout many brain regions. These findings raise questions about using this drug combination in AD, especially in the absence of evidence that the combination is beneficial, or that either drug arrests or reverses the disease process.     

Effect of aflatoxicosis on acetylcholinesterase activity in the brain and adenohypophysis of the male rat

The effects of 7 or 42 48-hourly i.p. injections of 20 micrograms aflatoxin B1 (AFB) on the acetylcholinesterase activity (AChE) in 8 brain areas and the adenohypophysis of the adult male rat were studied. Aflatoxicosis increased adenohypophysial AChE in direct proportion to the duration of intoxication, which also altered the distribution of AChE in the rat brain. With acute treatment, AChE was depressed in the cerebellum and hippocampus while in the chronically dosed rats AChE was drastically elevated in the mesencephalon and amygdala. Results suggest that AFB changes the ACh turnover and hence the cholinergic transmission in the brain and adenohypophysis. This may result in behavioural deficits and/or performance decrements via a disturbance of the hypothalamo-hypophysial axis.     

Effect of muramyl dipeptides on postsynaptic GABA, NMDA, and AMPA receptors and presynaptic NMDA receptors in rat brain

We studied the effect of muramyl dipeptides on postsynaptic GABA, NMDA, and AMPA receptors and presynaptic NMDA receptors. L,D-Dipeptide more potently than L,L-dipeptide inhibited postsynaptic NMDA receptors, potentiated GABA and AMPA receptors, and inhibited ⁴⁵Ca²⁺ uptake in synaptosomes from of rat brain cortex. Our results indicate that muramyl dipeptides modulate function of glutamate and GABA receptors. Translated from Byulleten' Eksperimental'noi Biologii i Meditsiny, Vol. 146, No. 9, pp. 247–249, September, 2008     

Nexin-1 inhibits the activity of human brain trypsin

Trypsin and other trypsin-like serine proteases have been shown to play important roles in neural development, plasticity and neurodegeneration. Their activity is modulated by serine protease inhibitors, serpins. However, for human brain trypsin, trypsin-4, no brain-derived inhibitors have been described. Here, we report that nexin-1 inhibits trypsin-4, and forms stable complexes only with this trypsin-isoenzyme. This result suggests that nexin-1 could modulate trypsin activity in brain where both nexin-1 and trypsin-4 are expressed.     

Acute starvation decreases acetylcholinesterase activity in different regions of rat brain.

The activity of acetylcholinesterase (AChE) was assayed spectrophotometrically in four brain regions of rats that had been deprived of food for 96 h. A significant decrease in the total AChE activity (by 4-45%) as well as in its specific activity (by 14-28%) was observed in the supernatant and total particulate fractions from cerebral hemispheres, cerebellum, brainstem and diencephalon + basal ganglia. Similarly, blood glucose, body weight and protein content of subcellular fractions from most brain regions showed decreases after starvation.     

Oxytocin enhances presynaptic and postsynaptic glutamatergic transmission between rat olfactory bulb neurones in culture

Although oxytocin (OT) within the olfactory bulb has been implicated in maternal behaviour and olfactory recognition, the cellular mechanisms of action remain to be clarified. We examined the effects of OT on glutamatergic spontaneous excitatory postsynaptic currents (sEPSCs) in cultured granule cells with the use of whole-cell patch-clamp recordings. OT reversibly increased both the frequency and amplitude of sEPSCs. The effects of OT on sEPSCs were blocked by the selective OT receptor antagonist desGly-NH(2)(9),d (CH(2))(5)-[Thy(Me)(2),Thr(4)]-ornithine vasotocin. OT had no detectable effect, however, on high voltage-activated Ca2+ currents in mitral/tufted cells, suggesting that OT acts presynaptically on step(s) in the release process downstream from calcium influx. OT augmented the membrane current in granule cells evoked by exogenous application of glutamate, indicating a postsynaptic site of action. These results indicate that OT facilitates sEPSCs in granule cells by both pre- and postsynaptic mechanisms.