Dietary restriction of choline reduces hippocampal acetylcholine release in rats: In vivo microdialysis study

We fed rats with a diet deficient in choline for 12 weeks and studied how dietary choline deficiency affected their behavior and their ability to release acetylcholine in discrete regions of rat brain using step-through passive avoidance task and in vivo microdialysis. In comparison with the control, rats fed the choline-deficient diet showed poorer retention of nociceptive memory in the passive avoidance task. Average choline level in cerebrospinal fluid in the choline-deficient group was significantly less (33.1%) than that of control rats. In vivo microdialysis showed no difference in the pattern of acetylcholine release enhanced by intraperitoneal administration of scopolamine hydrochloride (2 mg/kg) in the striatum between the two groups, whereas in the hippocampus, the maximum and subsequent increase of acetylcholine from the baseline by scopolamine injection was significantly lower in the choline-deficient group than in the control. From the results of our study, we speculate that long-term dietary restriction of choline can affect extra- and intracellular sources of substrates required for acetylcholine synthesis, and eventually limit the ability to release acetylcholine in the hippocampus. Reduced capacity to release acetylcholine in the hippocampus implies that the mechanism, maintaining acetylcholine synthesis on increased neuronal demand, may vary in discrete regions of the brain in response to dietary manipulation. The vulnerability of the mechanism in the hippocampus to dietary choline restriction is indicated by impaired mnemonic performance we observed.     

CPP and amlodipine alter the decrease in basal acetylcholine and choline release by audiogenic stimulus in hippocampus of ethanol-withdrawn rats in vivo

Effects of N-methyl-D-aspartate (NMDA) receptor and Ca2+ channel antagonists on extracellular acetylcholine and choline release in the hippocampus of ethanol-withdrawn rats were investigated by in vivo microdialysis. Ethanol was administered to Wistar rats in a liquid diet for 28 days. Basal acetylcholine and choline levels significantly increased at the 24th hour of ethanol withdrawal syndrome (EWS). Either an NMDA receptor antagonist (+/-)-3-(2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid (CPP) or a calcium channel antagonist amlodipine was administered, and 15 min later, an audiogenic stimulus (100 dB, 1 min) was applied to rats. While audiogenic stimulus increased acetylcholine and had no effect on choline release in control rats, it decreased acetylcholine and increased choline release in ethanol-withdrawn rats. CPP (15 mg/kg) and amlodipine (20 mg/kg) reversed the decrement in acetylcholine and increment in choline release in EW rats. Their effects on acetylcholine and choline release were not different from saline in control rats. Therefore, our findings suggest that, (a) because of adaptive changes in EWS, decrease of the acetylcholine release following audiogenic stimulus may play a role in the triggering of seizures, (b) hippocampal glutamatergic pathway may play a role in the audiogenic stimulus induced decrement of acetylcholine release in EWS, (c) inhibition of this pathway by NMDA receptor and calcium channel antagonists may prevent triggering of the seizures.     

Catecholamine and acetylcholine levels of the kidney in weanling rats fed a choline-deficient diet

Summary A disturbed renal circulation due to an imbalance between vasoconstrictor catecholamines and a vasodilator such as acetylcholine, caused by a decrease in acetylcholine, has been postulated as the basic mechanism of hemorrhagic degeneration of the kidneys in choline deficiency. To explore this hypothesis further a group of male weanling Wistar rats was fed on a choline-deficient diet for 10 days (group CD). A control group was fed on the same basal diet supplemented with choline (group CS). Food intake and body weights were registered. The kidneys of choline-supplemented and choline-deficient rats were studied grossly and histologically. The levels of catecholamines (noradrenaline and adrenaline) and acetylcholine were determined. Pathological changes of the kidneys were present in 30 out 57 choline-deficient rats, permitting the separation of data obtained from deficient rats into those not associated with renal injury (CDa rats) and those associated with renal injury (CDb rats). A marked increase in the levels of renal catecholamines was observed in both CDa and CDb rats. On the other hand, the content of acetylcholine remained unchanged. It is noteworthy that the changes in tissue catecholamine levels occurred before there were changes in kidney weight and morphology. The findings support the concept that an imbalance between sympathetic and parasympathetic systems plays an important role in the pathogenesis of the renal injury of choline-deficient weanling rats; and this imbalance would be the result of an excess of catecholamines in the kidneys.     

Maternal choline availability alters the localization of p15Ink4B and p27Kip1 cyclin-dependent kinase inhibitors in the developing fetal rat brain hippocampus

Previously we have shown that changes in maternal dietary choline are associated with permanent behavioral changes in offspring. Importantly, in adult male rats, feeding a choline-deficient diet increases the localization of cyclin-dependent kinase inhibitors (CDKIs) in the liver, whereas young adult CDKI knockout mice (p15Ink4B or p27Kip1) exhibit behavioral abnormalities. Thus, maternal dietary choline-CDKI interactions could underlie the changes we observe in fetal hippocampal development and cognitive function in offspring. Here, timed-pregnant rats on embryonic day E12 were fed the AIN-76 diet with varying levels of dietary choline for 6 days, and, on E18, fetal brain sections were collected, and the localization of CDKI proteins was studied using immunohistochemistry and an unbiased image analysis method. In choline-supplemented animals compared to controls, the number of cells with nuclear immunoreactivity for p15Ink4b CDKI protein was decreased 2- to 3-fold in neuroepithelial ventricular zones and adjacent subventricular zones corresponding to the fimbria, primordial dentate gyrus and Ammon's horn regions in the fetal hippocampus. In contrast, maternal dietary choline deficiency significantly decreased nuclear p15Ink4b immunoreactivity in the neuroepithelial layer of the dentate gyrus. Unlike p15Ink4b, the CDKI protein p27Kip1 was observed almost exclusively in the cytoplasm, though the protein was distributed throughout the proliferating and postmitotic zones in the E18 fetal hippocampus. Maternal dietary choline supplementation decreased the cytoplasmic staining intensity for p27Kip1 throughout the fetal hippocampus compared to control animals. Choline deficiency increased the staining intensity of p27Kip1 throughout the hippocampus in association with increased expression of MAP-1 and vimentin proteins. These results link maternal dietary choline availability to CDKI protein immunoreactivity and commitment to differentiation during fetal hippocampal development.     

Long-term voluntary ethanol consumption affects neither spatial nor passive avoidance learning, nor hippocampal acetylcholine release in alcohol-preferring rats.

Long-term ethanol consumption in humans and laboratory animals is associated with morphological and functional alterations of brain structures involved in cognitive processes. In the present experiments, we assessed whether voluntary long-term consumption of ethanol by alcohol-preferring (sP) rats under free choice condition with water (also) caused alterations in memory performance and hippocampal acetylcholine (ACh) release in vivo. A group of sP rats were offered a 10% v/v ethanol solution in a free choice with water for 36 weeks; controls had only tap water available. After withdrawal of ethanol, rats were tested in one trial passive avoidance test and thereafter were trained in a food-reinforced radial arm maze task for 12 days. One day after the last session in the radial-arm maze, rats were implanted with a microdialysis probe in the dorsal hippocampus and dialysate concentrations of ACh were measured. No significant differences were observed between sP drinking and control rats in retention latencies in the passive avoidance test, in radial arm-maze performance or in basal levels of hippocampal ACh release. These results show that long-term ethanol consumption by sP rats is not associated with cognitive impairments or with alterations in the hippocampal cholinergic function. To the extent that chronic ethanol intoxication can be considered a causal factor in the development of memory and neurochemical alterations, these results suggest that sP rats self-regulate ethanol consumption so as to avoid intoxication. These findings may challenge the notion that sP rat lines can be considered a valid model of human alcoholism.     

Changes in Cholinergic Neurons and Failure in Learning Function After Microsphere Embolism-Induced Cerebral Ischemia

Central cholinergic neurons play an important role in learning and memory functions. The present study was undertaken to elucidate the pathological changes in learning function and acetylcholine metabolism of the cerebral cortex and hippocampus, following microsphere embolism in rats. Microspheres (48

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) were injected into the right internal carotid artery of the rats. Learning function was determined using a passive avoidance task on the seventh day after the embolism. In the biochemical study, acetylcholine and choline contents, and choline acetyltransferase activity were measured in the cerebral cortex and hippocampus. Cortical acetylcholinesterase-containing fibers were quantitatively estimated in the embolized rat. Passive avoidance was impaired in the microsphere-embolized rat. Microsphere embolism decreased the acetylcholine concentration and choline acetyltransferase activity in the cerebral cortex and hippocampus. In the histochemical study, the length of cortical acetylcholinesterase-containing fibers was decreased, but cell density was unchanged in the ipsilateral hemisphere of the microsphere-embolized rat. The results suggest that microsphere embolism induces severe damage to cholinergic neurons, which may be related to the impairment of learning function in the ischemic brain.     

Choline availability to the developing rat fetus alters adult hippocampal long-term potentiation

Supplementation with choline during pregnancy in rats causes a long-lasting improvement of visuospatial memory of the offspring. To determine if the behavioral effects of choline are related to physiological changes in hippocampus, the effect of perinatal choline supplementation or deficiency on long-term potentiation (LTP) was examined in hippocampal slices of 6-8 and 12-14 month old rats born to dams consuming a control, choline-supplemented, or a choline-free diet during pregnancy. Stimulating and recording electrodes were placed in stratum radiatum of area CA1 to record extracellular population excitatory postsynaptic potentials (pEPSPs). To induce LTP, a theta-like stimulus train was generated. The amplitude of the stimulus pulses was set at either 10% or 50% of the stimulus intensity which had induced the maximal pEPSP slope on the input/output curve. We found that at both ages, a significantly smaller percentage of slices from perinatally choline-deficient rats displayed LTP after 10% stimulus intensity (compared with control and choline-supplemented rats), and a significantly larger percentage of slices from choline-supplemented rats displayed LTP at 50% stimulus intensity (compared with control and choline-deficient rats). Results reveal that alterations in the availability of dietary choline during discrete periods of development lead to changes in hippocampal electrophysiology that last well into adulthood. These changes in LTP threshold may underlie the observed enhancement of visuospatial memory seen after prenatal choline supplementation and point to the importance of choline intake during pregnancy for development of brain and memory function.     

Memory-improving action of glucose: indirect evidence for a facilitation of hippocampal acetylcholine synthesis

The effect of a 3 g/kg glucose injection on the velocity of the sodium-dependent high-affinity choline uptake mechanism in the hippocampus was both measured in quiet control mice and in mice immediately after training in an operant bar pressing task. Glucose did not significantly change high-affinity choline uptake in resting animals. High-affinity choline uptake in the hippocampus was increased by training in the operant bar pressing task. Glucose significantly reduced the amplitude of the increase in high-affinity choline uptake observed in the trained animals. Similarly, a 3 g/kg glucose injection also attenuated the increase in high-affinity choline uptake observed in animals injected with 1 mg/kg scopolamine. Finally, a 3 g/kg glucose injection significantly attenuated the amnesia produced by a post-training 1 mg/kg scopolamine injection in mice trained for an operant bar pressing task. These results provide additional evidence for an action of glucose on hippocampal cholinergic activity under conditions of high acetylcholine demand. This action may be mediated via an increase in acetyl coenzyme A availability, one of the precursors of acetylcholine. This facilitative effect of glucose on hippocampal acetylcholine synthesis may constitute the physiological basis for its facilitative action on memory and its attenuation of scopolamine amnesia.     

Effects of raloxifene and estradiol on hippocampal acetylcholine release and spatial learning in the rat

The effects of raloxifene on acquisition of a delayed matching to position (DMP) T-maze task and on hippocampal acetylcholine release were evaluated and compared with estradiol, to determine whether raloxifene has estrogenic effects on cognitive performance and hippocampal cholinergic activity. Ovariectomized rats received continuous treatment with raloxifene (one of two doses), estradiol, or vehicle for 30 days, followed by behavioral training, and then in vivo microdialysis assessment of basal and potassium-stimulated acetylcholine release. The data show that estradiol significantly enhanced DMP acquisition, whereas raloxifene did not. In contrast, both estradiol and the higher dose of raloxifene significantly increased potassium-stimulated acetylcholine release in the hippocampus. These data suggest that, despite increasing evidence for estrogenic effects of raloxifene in brain, raloxifene does not mimic the effects of estrogen on cognitive performance as assessed by acquisition of a simple spatial memory task in ovariectomized rats.     

MKC-231, a choline uptake enhancer: (2) Effect on synthesis and release of acetylcholine in AF64A-treated rats

The effect of MKC-231 on acetylcholine (ACh) synthesis and release was studied in the hippocampus of normal and AF64A-treated rats. AF64A (3 nmol/brain, i.c.v.) produced significant reduction of high-affinity choline uptake (HACU) and high K+-induced ACh release in hippocampal synaptosomes. Treatments with MKC-231 (10(-8) and 10(-7) M) showed significant reverse of the decrease in both HACU and ACh release. In hippocampal slices superfused with choline-containing artificial cerebro-spinal fluid (ACSF), high K+-induced ACh release was gradually decreased by repeated alteration of resting and high K+ stimulations in AF64A-treated rats. However, addition of MKC-231 (10(-8) to 10(-7) M) in the superfusate reduces this decrease. In vivo microdialysis studies indicate MKC-231 (10 mg/kg, p.o.) significantly reversed reduction of basal ACh concentrations in AF64A-treated rats, measured by radioimmunoassay without a cholinesterase inhibitor in the perfusate. These results indicate MKC-231 improves AF64A-induced cholinergic hypofunction by enhancing HACU, subsequently facilitating ACh synthesis and release in vitro and in vivo.     

Protective effect of adrenergic blocking agents against kidney hemorrhagic necrosis of choline deficiency

Summary A disturbed renal circulation due to an imbalance between vasoconstrictor catecholamines and a vasodilator such as acetylcholine, caused by a decrease in acetylcholine, has been postulated as the basic mechanism of hemorrhagic degeneration of the kidneys in choline deficiency. In previous works from our laboratory we have shown a marked increased in the levels of renal catecholamines in choline-deficient rats in comparison to choline supplemented animals, while the content of acetylcholine remained unchanged. Since the changes in tissue catecholamines occurred before there were kidney lesions, we have suggested that an autonomic imbalance, due to an excess of catecholamines, plays an important role in the pathogenesis of renal injury in choline-deficient rats. A series of experiments were then planned to explore this theory further by administering adrenergic blocking agents (alpha-methyldopa and reserpine) attempting to prevent the development of the renal injury in choline deficiency. Young male Wistar rats from our outbred colony were allocated into two experiments. In experiment I the animals were divided at random in 4 groups: group CS-I, was fed a cholinesupplemented diet; group CSD-I, was fed a choline-supplemented diet and treated with alpha-methyldopa; group CD-I, was fed a choline-deficient diet; and group CDD-I, was fed a choline deficient diet and treated with alpha-methyldopa. Groups CSD-I and CDD-I received daily intraperitoneal injections of alpha-methyldopa (300 mg/kg of body weight). In experiment II the animals were divided at random in 4 groups: group CS-II, was fed a choline-supplemented diet; group CSR-II, was fed a choline-supplemented diet and treated with reserpine; group CD-II, was fed a choline-deficient diet; and group CDR-II, was fed a choline-deficient diet and treated with reserpine. The appropriate groups received daily intraperitoneal injections of reserpine (0.4 mg/kg of body weight).The kidneys of all surviving rats were studied grossly and histologically, and the levels of noradrenaline and adrenaline determined. All animals from controls groups (CS-I, CSD-I, CS-II and CSR-II) showed essentially normal kidneys on gross and light microscopic examination. On the other hand, while CD-I and CD-II rats showed severe hemorrhagic degeneration of the kidneys, the renal lesions of animals given alpha-methyldopa (CDD-I) and reserpine (CDR-II) were significantly less pronounced. The total content of noradrenaline and adrenaline in the kidneys of CDD-I and CD-I rats were not statistically different, although the CDD-I animals tended to have lower levels of catecholamines. The content of noradrenaline and adrenaline of rats from group CD-I was significantly higher than the corresponding values in CS-I rats. Besides, the total content of renal noradrenaline of CDD-I animals was found to be unaltered when compared to CS-I rats, while their content of adrenaline was found to be higher than the corresponding value in CS-I group. The noradrenaline levels of CS-I and CSD-I rats were similar, but the latter group had a higher renal adrenaline content than the former. The total content of noradrenaline and adrenaline of the group CDR-II was lower than that of the group CD-II and did not differ than that of the group CS-II. Besides, the total content of noradrenaline in the kidneys of CSR-II animals was lower than that of the CS-II animals, while the content of adrenaline did not differ in these groups.The findings of the present investigation, besides confirming our previous observations, clearly show that alpha-methyldopa and reserpine afforded a protective effect against the renal injury of choline deficiency, thus giving strong additional support to the theory that the kidney hemorrhagic necrosis of choline deficiency in young rats is in all probability due to an autonomic imbalance.     

Role of high-affinity choline uptake on extracellular choline and acetylcholine evoked by NMDA

Previous studies have shown that NMDA evokes a calcium-dependent and region-specific increase in extracellular choline that is associated with a reduction of membrane phosphatidylcholine and precedes neuronal cell death. We investigated, using in vivo microdialysis, the contribution of high-affinity choline uptake on the increase in extracellular choline evoked by NMDA. Dialysis was performed in the presence of Neostigmine (0.5 microM), an acetylcholinesterase inhibitor, in prefrontal cortex or hippocampus of freely moving rats. Drugs were administered through the dialysis probe. In cholinergic denervation experiments, rats were subjected to sham or AMPA-induced lesion of cholinergic nuclei at least 2 weeks before microdialysis. Excitotoxic lesion of the medial septum / ventral diagonal band nuclei reduced hippocampal choline acetyltransferase activity by 74%, [(3)H]hemicholinium-3 binding by 32%, and completely abolished potassium-evoked acetylcholine release. Despite this reduction of presynaptic cholinergic function, perfusion of NMDA (300 microM) by retrodialysis produced an increase in hippocampal extracellular choline (249 +/- 22% of basal levels) that was similar to that observed in sham controls (301 +/- 35%). Inhibition of choline uptake with hemicholinium-3 in nonlesioned rats produced a sustained increase in dialysate choline (163 +/- 8%) and reduced acetylcholine to 33 +/- 2% of basal levels, consistent with a depletion of the acetylcholine pool due to precursor deficit. Simultaneous perfusion of hemicholinium-3 and NMDA produced a synergistic increase in dialysate choline (664 +/- 95% of basal levels), indicating that part of the choline released by NMDA is taken up. In contrast, NMDA antagonized the decrease of acetylcholine produced by hemicholinium-3. These results show that NMDA-evoked choline release is not mediated by inhibition of high-affinity choline uptake and indicate that choline released by NMDA can be used to sustain acetylcholine synthesis when there is a precursor deficit secondary to uptake inhibition.     

Dysregulated hippocampal acetylcholine neurotransmission and impaired cognition in M2, M4 and M2/M4 muscarinic receptor knockout mice

Among the five different muscarinic receptors that have been cloned and characterized, M2 and M4 receptors are localized both post- and presynaptically and are believed to have a pronounced autoreceptor role. The functional importance of these receptors in the regulation of acetylcholine release in the hippocampus and in cognitive processes was investigated by using M2 and M4 receptor single knockout (KO) as well as M2/M4 receptor double KO mice. We found profound alterations in acetylcholine homeostasis in the hippocampus of both M2- and M4-KO mice as well as of the combined M2/M4-KOs, as assessed by in vivo microdialysis. Basal acetylcholine efflux in the hippocampus was significantly increased in M4-KO and was elevated further in M2/M4-KOs. The increase in hippocampal acetylcholine induced by local administration of scopolamine was markedly reduced in M2-KO and completely abolished in M2/M4-KOs. In M2-KO and much more in M2/M4-KOs, the increase in hippocampal acetylcholine triggered by exposure to a novel environment was more pronounced both in amplitude and duration, with a similar trend observed for M4-KOs. Dysregulation of cholinergic function in the hippocampus, as it could result from perturbed autoreceptor function, may be associated with cognitive deficits. Importantly, M2- and M2/M4-KO, but not M4-KO, animals showed an impaired performance in the passive avoidance test. Together these results suggest a crucial role for muscarinic M2 and M4 receptors in the tonic and phasic regulation of acetylcholine efflux in the hippocampus as well as in cognitive processes.     

Choline supplementation during prenatal development reduces proactive interference in spatial memory

Previous research has demonstrated that increasing dietary choline during early development can have long-lasting effects on cholinergic (Ch) function that are correlated with improvement of spatial memory ability in rats. The present study is designed to further our understanding of these organizational changes in brain and behavior by examining the effects of spaced vs. massed trials. A third of the rats (n=10) were supplemented with choline chloride prenatally by adding it to the drinking water of their dams. Another third were made deficient of choline during early development by removing choline from the dams diet. The remaining rats served as untreated controls. Postnatally, the offspring were maintained on a choline-sufficient diet and at 120 days of age they began 12-arm radial maze training. The maze data revealed two major effects of early choline availability: (1) Both choline-supplemented and choline-deficient rats performed more accurately than control littermates when trials were spaced. These differences in spatial ability did not appear to be a function of differential response or cue-use strategies. (2) Choline-supplemented rats showed little proactive interference when trials were massed; whereas control rats demonstrated moderate levels and choline-deficient rats exhibited high levels of proactive interference as a function of massed trials. These data suggest that the behavioral consequences of early dietary availability of choline may involve the modification of the discriminative abilities used to attend to stimuli that demarcate the end of one trial and the start of another as well as the capacity for remembering the locations that have been visited during a trial.     

The decrease of serotonin release induced by a tryptophan-free amino acid diet does not affect spatial and passive avoidance learning

We assessed whether consumption of a diet lacking in tryptophan (TRP) resulted in alteration in learning and memory performance and hippocampal 5-HT release in rats. Two hours after the acute administration of TRP-free (T) and balanced (B) diet rats were trained in a one-trial passive avoidance task. The two groups of rats showed no significant difference in retention latencies. Two other groups of rats, fed with the above diets during the acquisition of a radial-arm maze task, showed no difference in baseline performance. The acute ingestion of the T diet produced a significant and long lasting decrease of hippocampal and cortical 5-HT release in rats when compared to the B diet, while the 12th day of the T diet, 5-HT was not detectable in the dialysate. These data indicate that the diminished brain release of 5-HT induced by a T diet is not sufficient to impair cognitive processes.     

Choline availability alters embryonic development of the hippocampus and septum in the rat

Choline availability in the diet during pregnancy alters fetal brain biochemistry with resulting behavioral changes that persist throughout the lifetime of the offspring. In the present study, the effects of dietary choline on cell proliferation, migration, and apoptosis in neuronal progenitor cells in the hippocampus and septum were analyzed in fetal brains at different stages of embryonic development. Timed-pregnant rats on day E12 were fed AIN-76 diet with varying levels of dietary choline for 6 days, and, on days E18 or E20, fetal brain sections were collected. We found that choline deficiency (CD) significantly decreased the rate of mitosis in the neuroepithelium adjacent to the hippocampus. An increased number of apoptotic cells were found in the region of the dentate gyrus of CD hippocampus compared to controls (5.5+/-0.7 vs. 1.9+/-0.3 apoptotic cells per section; p<0.01). Using a combination of bromodeoxyuridine (BrdU) labeling and an unbiased computer-assisted image analysis method, we found that modulation of dietary choline availability changed the distribution and migration of precursor cells born on E16 in the fimbria, primordial dentate gyrus, and Ammon's horn of the fetal hippocampus. CD also decreased the migration of newly born cells from the neuroepithelium into the lateral septum, thus indicating that the sensitivity of fetal brain to choline availability is not restricted to the hippocampus. We found an increase in the expression of TOAD-64 protein, an early neuronal differentiation marker, in the hippocampus of CD day E18 fetal brains compared to controls. These results show that dietary choline availability alters the timing of the genesis, migration, and commitment to differentiation of progenitor neuronal-type cells in fetal brain hippocampal regions known to be associated with learning and memory processes in adult brain.     

Increases in the concentration of brain alpha-bungarotoxin binding sites induced by dietary choline are age-dependent

We have previously reported that a diet supplemented with choline induces an increase in the concentration of a brain nicotinic-like receptor, as measured by alpha-bungarotoxin (BuTX) binding. Here we report the effects of choline administered in the drinking water on BuTX binding in the cortex, midbrain and brainstem of rats at 3 ages. In comparison with animals fed a choline-free diet, choline supplementation produced increases averaging 50% in 23-day-old rats and increases of approximately 30% in 60-day-old rats. Increases were also found in 6-month-old animals (averaging 16%), but the differences were generally not statistically significant. The mechanism responsible for the increase in the concentration of BuTX binding sites following the administration of dietary choline is not known, but the results are discussed in terms of choline as a precursor for the biosynthesis of acetylcholine and the biosynthesis of phospholipids. These data indicate that the administration of dietary choline is not likely to be effective in reversing cholinergic deficits by increasing the concentration of nicotinic-like receptors in aging rats.     

Antiamnesic effects of azaindolizinone derivative ZSET845 on impaired learning and decreased ChAT activity induced by amyloid-beta 25-35 in the rat

Antiamnesic effects of a newly synthesized azaindolizinone derivative ZSET845 were assessed in rats made learning ability deficient by amyloid-beta (Abeta)25-35 treatment. Intracerebroventricular injection of Abeta25-35 induced a marked decrease in step-through latency in passive avoidance task and reduction in choline acetyltransferase (ChAT) activity in the medial septum and hippocampus, but not in the basal forebrain and cortex. The number of ChAT-immunoreactive cells was decreased in the medial septum. Oral administration of ZSET845 at a dose of 1 or 10 mg/kg ameliorated learning impairment in passive avoidance task and enhanced ChAT activity in the basal forebrain, medial septum and hippocampus, and increased in the number of ChAT-immunoreactive cells in the medial septum in Abeta-treated rats to the levels of vehicle-injected control rats. These results suggest that ZSET845 is worth testing for further preclinical study aimed for the treatment of senile dementia such as Alzheimer's disease.     

Antiamnesic effects of azaindolizinone derivative ZSET845 on impaired learning and decreased ChAT activity induced by amyloid-β 25–35 in the rat

Antiamnesic effects of a newly synthesized azaindolizinone derivative ZSET845 were assessed in rats made learning ability deficient by amyloid-beta (Abeta)25-35 treatment. Intracerebroventricular injection of Abeta25-35 induced a marked decrease in step-through latency in passive avoidance task and reduction in choline acetyltransferase (ChAT) activity in the medial septum and hippocampus, but not in the basal forebrain and cortex. The number of ChAT-immunoreactive cells was decreased in the medial septum. Oral administration of ZSET845 at a dose of 1 or 10 mg/kg ameliorated learning impairment in passive avoidance task and enhanced ChAT activity in the basal forebrain, medial septum and hippocampus, and increased in the number of ChAT-immunoreactive cells in the medial septum in Abeta-treated rats to the levels of vehicle-injected control rats. These results suggest that ZSET845 is worth testing for further preclinical study aimed for the treatment of senile dementia such as Alzheimer's disease.     

Raised glucose levels enhance scopolamine-induced acetylcholine overflow from the hippocampus: an in vivo microdialysis study in the rat.

Behavioural studies in both humans and animals have shown that an acute rise in circulating glucose levels at or around the time of training enhances subsequent retention performance and can also afford protection from the amnesia produced by posttraining injections of scopolamine. In an attempt to directly investigate the neurochemical basis for these effects of glucose we have tested the hypothesis that raised glucose levels may enhance acetylcholine (ACh) synthesis and release in the brain during conditions of increased neuronal activity, induced either by training or pharmacological challenge, via a microdialysis study using rats. Microdialysate concentrations of ACh overflow from the hippocampus of fasted rats induced by i.p. injections of scopolamine (1 mg/kg) combined with concurrent s.c. injections of either glucose (2 g/kg) or saline were compared in successive 15-min samples using an on-line HPLC system. Scopolamine injections resulted in an immediate 10-20-fold increase in hippocampal ACh overflow which subsequently progressively declined over a 4-h period to pretreatment baseline levels. The combined injection of glucose with scopolamine resulted in a highly significant enhancement (19.4%; P less than 0.01) in ACh content of the first two samples as compared to saline-injected controls. These results provide the first direct experimental evidence that raised glucose levels, via increased availability of acetyl-coenzyme A (acetyl-coA), transiently facilitates ACh synthesis and release during conditions of increased neuronal activity. This enhancement of ACh availability during states of cholinergic neuronal activation may underlie the previously observed facilitatory effects of glucose on memory performance and its protection from scopolamine-induced amnesia.