Brain acetylcholine concentration and acetylcholinesterase activity in selectively-bred strains of rats

Significant differences in whole brain and in brain area acetylcholine concentration have been observed between two strains of rats selectively bred for differences in speed of acquisition of conditioned avoidance. Brain acetylcholinesterase activity was similar in the strains. The strain showing poor conditioned avoidance behaviour possessed the highest brain concentration of acetylcholine. The finding supports a theory which describes a central cholinergic inhibitory system which may be active in the control of certain types of learning behaviour.     

Strain specific cholinergic changes in response to stress: Analysis of a time-dependent avoidance variation

Investigators have established that the performance of an incompletely learned avoidance task is a U shaped function of the time since the original partial acquisition. Thus rats perform more poorly when retested at intermediate time intervals (1-8 hr) after training than they do when tested at longer post-acquisition intervals (24-48 hr). Studies have suggested that such time-dependent deficits are not related to changes in learning ability, but rather result from shock-induced motor suppression which interferes with active avoidance responding. Pharmacological studies utilizing drugs which effect cholinergic function have indicated that an inhibitory cholinergic system may be involved in mediating post-shock motor suppression. To obtain direct biochemical evidence for possible cholinergic mediation of post-shock motor suppression, measurements of high affinity choline uptake and acetylcholine turnover were made at varying time intervals following partial active avoidance training in F-344 rats. An increase in cholinergic function was found in the dorsal, but not the ventral hippocampus 30 min, 1 hr and 4 hr following acquisition training. These biochemical alterations were temporally correlated with deficits in active avoidance responding. We have reported that the immediate behavioral suppression observed in another rat strain (Sprague-Dawley, Zivic Miller Laboratories), which exhibits inferior active avoidance performance, is similarly correlated with cholinergic activation in the dorsal hippocampus [17]. These data support the hypothesis that the dorsal-hippocampal cholinergic system is involved in the mediation of stress-induced behavioral suppression.(ABSTRACT TRUNCATED AT 250 WORDS)     

Subsets of acetylcholine-stimulated 86Rb+ efflux and [125I]-epibatidine binding sites in C57BL/6 mouse brain are differentially affected by chronic nicotine treatment

Nicotinic cholinergic receptor (nAChR) sites that bind nicotine with high affinity (likely 4β2-nAChR) increase following chronic nicotine treatment. Effects of chronic treatment on other nAChR binding sites and functional responses of nAChRs are less well studied. Therefore, C57BL/6 mice were intravenously infused for 10 days with saline or nicotine (five doses, 0.25–4.0 mg/kg/h) and nAChR function and three different nicotinic binding sites in 12 brain regions were assessed. Plasma nicotine and cotinine increased linearly with dose. ⁸⁶Rb⁺ efflux with higher sensitivity to acetylcholine tended to decrease with increasing dose, whereas efflux with lower sensitivity to acetylcholine tended to increase. As anticipated, likely 4β2-nAChR [¹²⁵I]-epibatidine binding sites increased with treatment (estimated dosage for one-half maximal increase was 0.44 mg/kg/h, plasma nicotine ≈20 ng/ml). ⁸⁶Rb⁺ efflux with higher sensitivity to acetylcholine and cytisine-sensitive [¹²⁵I]-epibatidine binding are predominantly 4β2-nAChR. A high correlation between these parameters was observed across brain regions and slopes of these regression lines decreased with treatment dose, suggesting a decrease in function per unit receptor. Likely 3β4-nAChR binding sites were unaffected even at the highest dose (4.0 mg/kg/h, ≈210 ng/ml). A third set of diverse nAChR binding sites increased in some brain regions, but only after high-dose treatment.     

Cerebral acetylcholine and choline contents and turnover following low-dose acetylcholinesterase inhibitors treatment in rats

Male Sprague-Dawley rats were treated for 3 weeks with (1) regular tap drinking water plus subcutaneous (s.c.) saline (0.5 ml/kg) injections three times/week, (2) pyridostigmine bromide (PB) in drinking water (80 mg/L) plus s.c. saline injections three times/week, (3) regular tap drinking water plus s.c. sarin (0.5 × LD₅₀) injections three times/week, or (4) PB in drinking water plus s.c. sarin injections three times/week. Repeated doses of sarin, in the presence or absence of PB, were devoid of acute toxicity during the three-week treatment period. Two, 4, and 16 weeks post-treatment, animals were given an intravenous pulse injection of choline labeled with 4 deuterium atoms (D4Ch) followed, after 1 min, by microwave fixation of the brain in vivo. Tissue levels of endogenous acetylcholine (D0ACh), endogenous choline (D0Ch), D4Ch, and ACh synthesized from D4Ch (D4ACh) were measured by gas-chromatography mass-spectrometry in hippocampus, infundibulum, mesencephalon, neocortex, piriform cortex, and striatum. Ch uptake from blood and ACh turnover were estimated from D4Ch and D4ACh concentrations in brain tissue, respectively. Statistically significant differences among brain regions were found for D0Ch, D4Ch, D0ACh and D4ACh at 2, 4 and 16 weeks post-treatment. However, differences in the values of these parameters between control and drug treatments were found only for D0ACh and D0Ch at 2 and 4 weeks, but not at 16 weeks post-treatment. In conclusion, the results from these experiments do not support a delayed or persistent alteration in cholinergic function after exposure to low doses of PB and/or sarin.     

Comparison of two methods for estimating the acetylcholine turnover in discrete rat brain structures

The acetylcholine turnover rate was determined in olfactory tubercle, nucleus accumbens and striatum of rat brain. The calculation of turnover rates was carried out by means of two different methods: a two compartment analysis and the finite differences method. After pulse injection of [3H]choline the radioactivity of both [3H]acetylcholine and [3H]choline was measured in the above mentioned brain areas. The contents of acetylcholine and choline were measured radioenzymatically. By using the two compartment model the following acetylcholine turnover rates were obtained: olfactory tubercle, 0.577; nucleus accumbens, 0.679; striatum, 1.110 (mumoles/g X hr). When using the finite differences method the values were: olfactory tubercle, 0.517; nucleus accumbens, 0.822; striatum, 1.115 (mumoles/g X hr). This demonstrates that the results obtained by applying the two different methods are nearly identical. Advantages and disadvantages of the two methods are discussed.     

Strain specific alterations in hippocampal cholinergic function following acute footshock

Previous studies have shown that differences between Z-M and F-344 rats in active avoidance acquisition are due to variation in stress-induced motor response, rather than to differences in general learning ability. Thus F-344 rats, which become active when exposed to shock, are more likely to make avoidance responses and learn to associate an active response with ommision of shock than are Z-M rats, which reduce their activity in response to shock. The hypothesis that cholinergic neurons in the hippocampus contribute to the stress-induced motor suppression seen in Z-M rats derives from pharmacologic studies employing micro-injection of cholinergic antagonists. The present studies further investigate this hypothesis through assessment of acetylcholine turnover and high affinity choline uptake in discrete brain regions of Z-M and F-344 rats. Increases in cholinergic function in the dorsal hippocampus were observed in Z-M, but not F-344 rats following acute footshock. Cholinergic alterations were not seen in the ventral hippocampus or striatum of Z-M rats. The strain specific alterations in dorsal hippocampal cholinergic function correlate with documented motor suppression in Z-M rats and motor activation in F-344 rats during acute shock, and suggest that this cholinergic system mediates a suppressive behavioral response to environmental stress.     

Strain differences in lead intoxication in rats

In preliminary experiments it was observed that lactating rats of an albino Wistar strain did not readily accept diets containing lead acetate, with the resulting death of the litters by starvation during the first week of life. In the present study, blood and tissue lead concentrations were determined in rats of the black-and-white Hooded strain exposed to various concentrations of lead acetate in the diet, and the results compared with those in similarly exposed Wistar animals. It was observed that: (1) the Hooded rats accepted the diets containing lead acetate more readily; (2) the growth of the lead-intoxicated Hooded litters was less retarded; (3) the blood and tissue lead concentrations in the Hooded litters at 3 weeks of age were lower than in the age-matched Wistar animals; and (4) 30% of the Wistar suckling rats fed a diet containing 2.0% lead acetate became paralyzed by 5 weeks of age, whereas no paralysis was seen in any of the Hooded rats. Furthermore, a crossfostering experiment showed that the strain of the lactating dam had no effect on the blood and tissue lead concentrations in the pups. Using appearance of various physical features and reflexes as an index of progress of development, it was found that most of the physical features and reflexes fully mature 1–2 days earlier in the Hooded pups. It was concluded that the faster rate of development of the Hooded rat contributed to the observed difference in the toxicity of lead between these strains.     

Brain aldehyde dehydrogenase activity in rat strains with high and low ethanol preferences

The activity of aldehyde dehydrogenase in subcellular fractions of whole brain homogenates from the AA and ANA rat strains developed respectively for high and low ethanol preferences has been studied. No significant strain or sex differences between naive AA and ANA rats were found. In ethanol-experienced rats some strain and sex differences were found, the most consistent being higher enzyme activity in AA females than in males both with aliphatic and aromatic aldehyde substrates. However, contrary to previous findings no relation between brain aldehyde dehydrogenase activity and drinking behavior was found in the AA and ANA rat strains.     

Inhibition of choline incorporation into brain lipids in rats by urethane,a proposed mechanism of depression of the central nervous system

Summary Concentrations and specific radioactivities of choline, acetylcholine, phosphorylcholine, lipid choline, and sn-glycero-3-phosphorylcholine after i.v. injection of methyl-¹⁴C-choline were measured in the brain of untreated controls and of rats anesthesized with urethane.The specific activity was found to be decreased during deep anesthesia by 40% in acetylcholine, 20–30% in phosphorylcholine, 50–75% in lipid choline, and 30–40% in sn-glycero-3-phosphorylcholine. No significant change was detected in the specific activity of choline. The brain concentration of acetylcholine was increased by 40%, the concentration of sn-glycero-3-phosphorylcholine, however, was diminished by 10% during anesthesia. No change was found in the concentration of the other choline containing compounds investigated.Measuring choline incorporation into 4 subcellular fractions of brain tissue specific activities were found to be decreased by the same percentage, although 2 fractions (nuclei and microsomes) were higher labelled than the 2 other fractions (crude mitochondria with synaptosomes and lysosomes).A correlation between the biochemical and the functional alterations is supported by the dose-effect relationships on both parameters.It is suggested that urethane reduces turnover of lipids and by that mechanism inhibits the exocytotic release of the transmitter from presynaptic nerve endings.     

Lesions of cholinergic forebrain nuclei: Changes in avoidance behavior and scopolamine actions

The acquisition of active (shuttle-box) and passive avoidance conditioned responses and the effects of scopolamine on acetylcholine (ACh) output in freely moving rats and on conditioned responses were investigated 20 days after placing a unilateral lesion in the magnocellular forebrain nuclei (MFN). In the lesioned rats spontaneous ACh output from the cerebral cortex ipsilateral to the lesion was slightly decreased, while on the other hand the increase in ACh output elicited by scopolamine was strongly reduced. Sham operated rats always performed more active avoidance responses than MFN lesioned rats in the daily training shuttle-box sessions, and the facilitating effect of scopolamine (1 mg/kg IP) on the shuttle-box performance was suppressed. However the lesion did not disrupt the shuttle-box performance whenever training had taken place before the lesion. In the lesioned rats retested 30 min after the training trial, an impairment of the passive avoidance response was found. The effect of the lesion was potentiated by scopolamine. The results show therefore that MFN lesions impair the cortical cholinergic mechanisms, whose activity seems to play an important role in cognitive functions.     

Avoidance conditioning in different strains of rats: Neurochemical correlates

Two-way avoidance conditioning was compared in three strains of rats: Roman high avoiders (RHA), Roman low avoiders (RLA) and control Sprague-Dawleys (SD). RHAs performed more and RLAs fewer avoidance responses than SDs. RLAs injected with d-amphetamine improved their performance to levels comparable to SDs; however, d-amphetamine caused a time-dependent increase in intertrial crossings for the RLAs. Of the three strains, the RLAs had the lowest activities of tyrosine hydroxylase, dopamine--hydroxylase and phenylethanolamine-N-methyltransferase in their adrenal glands. Although there were no significant differences among the strains in respect to tyrosine hydroxylase activity in whole brain or regions, RLAs had higher dopamine--hydroxylase activity in the whole brain and cerebral cortex as compared to the SDs. RLAs and RHAs together had a significantly different turnover of intracisternally administered ³H-norepinephrine than SDs. After the intracisternal injection of ³H-L-tyrosine, twice as much ³H-dopamine accumulated in the brains of RLAs as compared to RHAs and SDs.     

大鼠胸主动脉舒缩反应节段性差异的等效转换

目的: 通过相关分析消除离体动脉不同节段反应差异对实验结果的影响.方法: 以生理多道记录仪记录离体大鼠胸主动脉环从下到上4节段舒缩张力反应,用回归方程对舒缩反应节段性差异作等效转换.结果: 大鼠胸主动脉下段对苯肾上腺素收缩反应高于次下段、次上段和上段,次下段高于次上段、上段 (P<0.05);下段对乙酰胆碱舒张反应高于次下段、次上段和上段,次下段高于次上段和上段(P<0.05).相关分析显示节段间收缩反应呈直线相关;舒张反应上段对下段呈曲线相关,余呈直线相关.按相关方程等效转换各动脉节段的舒缩反应,可消除反应的节段差异(P>0.05).结论: 通过回归方程作等效转换可消除动脉舒缩反应的节段性差异.     

Changes in regional brain acetylcholine levels during drug-induced convulsions

Acetylcholine (ACh) levels were determined in the brain of rats killed by decapitation or focussed microwave radiation during drug-induced convulsions. During metrazol or strychnine-induced convulsions a diffuse decrease in ACh levels was found in rats killed by decapitation. When the rats were killed by radiation and the brain was only divided into three large regions, strychnine caused no changes in ACh levels; metrazol caused a decrease in the cerebral cortex and lower brainstem. When discrete brain regions were investigated in rats killed by radiation, metrazol-induced convulsions were associated with a decrease in ACh level in all regions dissected and strychnine-induced convulsions with a decrease in the hippocampus and caudate nucleus only. Picrotoxin-induced convulsions were associated with a decrease in ACh level in the cerebral cortex, hippocampus, midbrain and medullapons, those induced by bicuculline with an increase in ACh level in the frontal cortex, hippocampus, midbrain and medulla-pons, by dimefline with an increase in the frontal cortex, midbrain and medulla-pons and a decrease in the caudate nucleus. The experiments show that each type of convulsant affects ACh levels in discrete brain regions in a different way.     

Differences in the behaviour of Sprague--Dawley and Lewis rats during repeated passive avoidance procedure: effect of amphetamine.

The present paper investigated the differences in passive avoidance learning between Sprague--Dawley and Lewis rats. After initial habituation (experimental Part 1), measured as latencies to enter the dark, preferable compartment, the effect of treatment with amphetamine (8 mg kg(-1)b.w.), the retention performance compared with controls (saline) was tested in both rat strains in Parts 2--4. The intervals between Parts 2--4 were 24 or 49 days. Each experimental part consisted of testing lasting 6 days. On the 7th day the rats received drug treatment 1 h before the application of foot shock. The differences between rat strains were already detectable at the beginning of the study. During the repeated exposures of rats in Part 1, only Lewis rats, in contrast to Sprague--Dawley rats, exhibited the habituation. The repeated testing of rats in Parts 2--4, due to previous experience with an aversive stimulus, was considered as the retention test. In Parts 2--3 we observed only minor differences in the responses of both rat strains tested. Also no significant differences were observed between rat strains after amphetamine treatment that induced an amnesia-like effect in all retention trials. However, data shown in Part 4 revealed the largest differences between both strains. Control Lewis rats exhibited significantly higher retention responses than Sprague--Dawley rats. In the latter strain we observed no differences in avoidance latencies between controls and amphetamine treated rats. In Lewis rats the difference in avoidance performance between controls and amphetamine treated animals was highly significant due to their enhanced retention performance. In conclusion, the results presented in this study extend the known behavioural differences in tested rat strains to the passive avoidance procedure that, in addition, was performed for a total period of 4 months. Due to a known deficiency of hypothalamo-pituitary-adrenal axis activity in Lewis rats it can be hypothesized that the behavioural dissociation of this strain from Sprague--Dawley rats could be related to the different activity of this regulatory axis in the rat strains tested.     

(-),(+)黄皮酰胺对樟柳碱引起的小鼠脑内乙酰胆碱含量降低及记忆障碍的影响

为证实黄皮酰胺体内抗记忆缺失作用是否也存在手性选择性,并且进一步探讨其作用的机制,用高效液相色谱 电化学检测器法测定乙酰胆碱含量并结合行为学实验,比较了(-),(+)黄皮酰胺对小鼠脑内乙酰胆碱含量及对小鼠记忆障碍的影响。结果表明:(-)黄皮酰胺剂量依赖性地对抗樟柳碱引起的脑皮层、海马、纹状体内乙酰胆碱含量降低,(+)黄皮酰胺在同样剂量却无此作用。行为学实验也得到相似结果。提示:黄皮酰胺的药理作用存在手性选择性;(-)黄皮酰胺能改善樟柳碱所致的记忆障碍,这与其逆转樟柳碱引起的脑内乙酰胆碱含量降低作用相关。     

Effects of acute and repeated systemic administration of ketamine on prefrontal acetylcholine release and sustained attention performance in rats

RATIONALE: The effects of non-competitive N-methyl- D-aspartate (NMDA) receptor antagonists model aspects of schizophrenic symptomatology. Because effects on both cortical cholinergic transmission and attentional processes have been hypothesized to represent components of the properties of psychotogenic drugs, the present study investigated the effects of ketamine on the activity of cortical cholinergic inputs and attentional performance. OBJECTIVE: To determine the effects of acute and repeated ketamine administration on cortical acetylcholine release and performance of rats in an operant task designed to assess sustained attention performance. METHODS: Experiment 1 assessed the effects of ketamine (2.0-20.0 mg/kg, i.p.) on medial prefrontal acetylcholine release using in vivo microdialysis. In experiment 2, animals were pretreated with 2.0 mg/kg or 25.0 mg/kg ketamine for 7 days. Cortical acetylcholine release was assessed in these rats following the subsequent administration of a 'challenge' dose of 2.0 mg/kg on days 1, 8, and 15 following completion of the pretreatment regimen. Experiment 3 assessed the effects of acute ketamine administration (2.0, 4.0, and 8.0 mg/kg, i.p.) on sustained attention performance. In experiment 4, animals trained in the sustained attention task were pretreated with 25.0 mg/kg ketamine or vehicle for 7 days. In these animals, the performance effects of 2.0 mg/kg ketamine administered 1, 8, or 15 days after completion of the pretreatment regimen were assessed. RESULTS: The acute administration of ketamine dose dependently increased cortical acetylcholine release by up to 250% above baseline and for over 40 min following the highest dose of ketamine. Pretreatment with 2.0 mg or 25.0 mg/kg did not robustly alter the effects of subsequent ketamine administration on cortical acetylcholine release. In animals performing the sustained attention task, administration of the highest dose of ketamine resulted in high levels of errors of omission, while the administration of the two smaller doses did not affect performance. Pretreatment with 25.0 mg/kg disrupted the attentional performance during the pretreatment period, but it did not affect the baseline performance thereafter. Furthermore, ketamine pretreatment did not systematically alter the performance effects of subsequent ketamine administration. CONCLUSIONS: The robust stimulation of cortical acetylcholine release represents a potent component of the pharmacological effects of ketamine. The effects of acute ketamine on attentional performance were limited to high rates of omissions. Repeated ketamine administration 'sensitized' neither cortical acetylcholine release nor attentional performance. These effects of repeated ketamine differ substantially from those of another major psychotogenic drug, amphetamine, and thus support the view that ketamine and amphetamine model fundamentally different aspects of schizophrenia.     

Effects of chronic lead exposure on levels of acetylcholine and choline and on acetylcholine turnover rate in rat brain areas in vivo

Rats were exposed to lead acetate from birth, and were killed at the age of 44–51 days for analysis of levels and turnover rates of acetylcholine (ACh). Steady-state levels of ACh were not altered in midbrain, cortex, hippocampus, or striatum of lead-exposed rats. Similarly, no changes in choline (Ch) concentrations were found in cortex, hippocampus, or striatum. In the midbrain, however, a 30% reduction in Ch levels was observed. Changes in specific activity of Ch and ACh were measured as a function of time in selected brain areas of rats infused with a radio-labeled precursor of Ch. Specific activities of ACh were not altered. Ch specific activities were, however, significantly elevated in all brain areas examined, as compared with age-matched control rats. The in vivo ACh turnover rate in cortex, hippocampus, midbrain, and striatum was diminished by 35%, 54%, 51% and 33%, respectively. These findings provide direct evidence for an inhibitory effect of lead exposure from birth on central cholinergic function in vivo. Since a significant reduction of body weight was found in those animals treated with lead acetate, the alteration of central cholinergic function may partially be attributed to malnutrition observed in the lead-exposed animals.Part of this work was presented in abstract form (Fed. Proc. 36. 977 (1977))     

Effect of prolonged isolation on learning, biogenic amine turnover and aggressive behaviour in three strains of mice

Two albino strains (MF-1 and CF-1) and one non-albino inbred strain (DBA/2J) of mice were compared for shuttle-box avoidance acquisition and fighting behaviour following a 5-week isolation period. Brain levels and turnover rates of norepinephrine and serotonin were also measured in groups of isolated mice. Mice housed in groups of five (aggregated) served as control subjects. Only the albino strains became aggressive after isolation; DBA/2J mice did not fight when paired. Results obtained in order of increasing facility of avoidance acquisition and a higher level of spontaneous activity were: DBA/2J mice > CF-1 mice > MF-1 mice. These results were correlated with whole-brain steady-state levels of norepinephrine among the strains. No differences in avoidance acquisition or serotonin levels and turnover rates were observed between isolated and aggregated mice within the same strain. CF-1 mice had lower levels and a faster turnover rate of serotonin compared with the other strains. Norepinephrine turnover rates were unchanged in CF-1 and DBA/2J mice following isolation, but were significantly slowed in MF-1 isolated mice compared with their controls. It is concluded that no clear-cut relationship exists among learning ability, aggressive behaviour and biogenic amine turnover rates in isolated or aggregated mice.     

Supersensitivity of cortical neurones of the rat to acetylcholine and L-glutamate following chronic morphine treatment

Summary The effect of microelectrophoretically applied L-glutamate and acetylcholine on discharge activity of cortical neurones was studied in naive and in morphine-tolerant/dependent rats. The thresholds for increase in discharge activity elicited by these 2 putative neurotransmitters were 3 times lower in the tolerant/dependent rats than in the naive rats, indicating the development of supersensitivity.     

Brain tryptophan metabolism on the 5-hydroxytryptamine and kynurenine pathways in a strain of rats with a deficiency in platelet 5-HT

1 Brain 5-hydroxytryptamine (5-HT) metabolism has been compared in albino (Sprague-Dawley; SD) and in Fawn-Hooded (FH) rats, which have an inherited platelet 5-HT deficiency. 2 It was confirmed that blood 5-HT levels in the FH rats were about one quarter of those in the SD rats. 3 Brain 5-HT and 5-HIAA were however higher in FH rats on a per gram basis; there was no difference between the strains on a per brain basis, because of the smaller brain weights of the FH rats. 4 Brain and plasma tryptophan were not significantly different in the two strains. Plasma kynurenine was higher in the FH rats, and brain kynurenine was also higher either on a per gram or on a per brain basis. 5 The reserpine-releasable brain 5-HT was the same proportion of total brain 5-HT in the two strains. 6 Experiments with pargyline suggested that the turnover of 5-HT was somewhat higher in the FH rats on a per gram basis, but not significantly so on a per brain basis. 7 It is concluded that although brain tryptophan metabolism may be somewhat accelerated along both the 5-HT and kynurenine pathways in the FH rats there is no gross deficiency in the binding of 5-HT in their brains analogous to that found in their platelets.