Age-related differences in brain choline acetyltransferase, cholinesterases and muscarinic receptor sites in two strains of rats.

The age-related changes in choline acetyltransferase (ChAT), cholinesterases (ChE) and muscarinic receptor sites (measured as Bmax of 3H-QNB binding) were evaluated in the cerebral cortex, hippocampus and striatum of Fischer 344 and Wistar male rats at the ages of 3 and 24 months. In the aged Fischer rats there was a significant decline of ChAT (except the hippocampus), ChE and muscarinic receptor densities in the regions analyzed. In the aged Wistar rats cortical and hippocampal ChAT as well as cortical muscarinic receptors remained constant while striatal ChAT, hippocampal and striatal muscarinic receptors decreased significantly; ChE were reduced in all regions analyzed. Factorial analysis of variance (2 strains x 2 ages ANOVA) showed significant strain-related differences in ChAT and muscarinic receptor sites in the three brain areas (about 1.5 times higher levels in the Fischer rats). The same analysis showed significant interactions between strain and age for ChAT and muscarinic receptors in the cerebral cortex, but not in the hippocampus and striatum; no interactions were found for ChE in the regions analyzed. This means that cortical ChAT and muscarinic receptors behave differently in aging in the two strains of rats, i.e., their alterations are strain-specific. Conversely, all other age-related changes (or lack of them for hippocampal ChAT) cannot be considered strain-specific. Moreover, an additional group of 33-month Wistar rats showed a significant decline of cortical muscarinic receptors with respect to 24 month rats but not of other markers in any area. The data underscore the need to consider genotype in the assessment of age-related cholinergic deficits in animal models.

Differential reactivation by HI-6 in vivo of paraoxon-inhibited rat brain acetylcholinesterase molecular forms.

The effects of the cholinesterase reactivator HI-6, [1-(((4-(aminocarbonyl)-piridinio)methoxy)methyl-2-(hydroxy- imino)methyl pyridinium dichloride], on paraoxon-inhibited brain acetylcholinesterase (AChE) and its molecular forms were studied in rats. Treatment with paraoxon (0.25 mg/kg s.c.) caused approx. 60% inhibition of total AChE from frontal cerebral cortex, while that including HI-6 (140 mg/kg i.m.) and atropine (50 mg/kg i.m.) reduced such inhibition to only 25%. Two molecular forms of the enzyme, 10S and 4S, corresponding to globular tetrameric (G4) and monomeric (G1), were detected by sucrose gradient sedimentation. In paraoxon treated rats the G4 form was inhibited by approx. 65% while G1 only by 35%. The G4 form was considerably and selectively reactivated by HI-6 while the G1 form was not reactivated at all. The data show that HI-6 penetrates the blood-brain barrier and reactivates the molecular forms preferentially inhibited by paraoxon and involved in synaptic neurotransmission.

Transient global brain hypoxia-ischemia in adult rats: neuronal damage, glial proliferation, and alterations in inositol phospholipid hydrolysis.

A model of ischemic-hypoxic brain injury which combines bilateral occlusion of common carotid arteries for 10 min and mild hypoxia (15% O2 for 10 min before and during occlusion) was developed. Global ischemia was assessed by a simplified EEG recording indicating isoelectric line, i.e. full arrest of cortical electrical activity. Histological examination of brain 7 days after ischemic insult showed from moderate to severe damage, mainly in the cerebral cortex (layers III, V and VI) and hippocampus (mainly CA1 subfield). The injury consisted of neuronal degeneration and necrosis with nuclear pyknosis and karyorrhexis. Immunohistochemical staining for gliofibrillar acidic protein showed a marked glial proliferation in the cerebral cortex and hippocampus. In the cortical slices, inositol phosphates accumulation stimulated by excitatory amino acid agonists (ACPD, ibotenate and quisqualate), as well as by norepinephrine and carbachol, was enhanced significantly (p < 0.01) with respect to sham-operated rats 7 days, but not 24 h, after the ischemic insult. The overall data show that the relatively simple transient brain hypoxia/ischemia rat model produces full arrest of cortical EEG, histopathological alterations and those relative to post-receptor neurochemical mechanisms characteristic of four-vessel occlusion model.

Subcutaneous dirofilariasis in Okinawa, Japan.

A nematode within a subcutaneous nodule excised from an elderly Okinawan man has been tentatively identified in sections as an immature Dirofilaria repens--the first to be reported from Japan.

Change in the distribution of acetylcholinesterase molecular forms in frontoparietal cortex of the rat following nucleus basalis lesions with kainic acid.

The unilateral injection of kainic acid into the nucleus basalis magnocellularis (NBM) resulted in an alteration of the distribution of acetylcholinesterase (AChE) molecular forms in frontoparietal cortex ipsilaterally to the lesion. The G4/G1 ratio fell from 5.4 +/- 0.8 in contralateral to 3.0 +/- 0.5 in ipsilateral cortex. The NBM lesion effect thus, mimicks, the loss of tetrameric G4 form reported for various brain cortical areas of Alzheimer's disease (AD) patients. The data support the suggestion that G4 form is enriched in presynaptic nerve terminals.

Postnatal maturation of brain cholinergic systems in the precocial murid Acomys cahirinus: comparison with the altricial rat.

The spiny mouse (Acomys cahirinus) is the only precocial murid species. It has some neuroanatomical peculiarities such as a relatively thin cerebral cortex and a large hippocampus. The levels of choline acetyltransferase, membrane-bound acetylcholinesterase and muscarinic receptor sites (measured as [3H]quinuclidynil benzilate binding) were assessed in the whole brain on days 1, 7, 14, 21, 28 and 80 (adult), and compared with those of Wistar rats of the corresponding ages. At birth choline acetyltransferase was significantly higher in spiny mice than in rats but the adult levels were similar, with an overall increase of about 5.2- and 14-fold for the former and the latter species, respectively. Membrane-bound acetylcholinesterase level and maximal density of muscarinic receptor sites in spiny mice were considerably higher at birth, in contrast adult levels were significantly lower than in rats with a respective overall increase of about 1.5- and over 4.5-fold. The high degree of maturity attained at birth by spiny mice partially depends on the long gestation period. However, if we consider postconception age, the maturation of choline acetyltransferase appears to be delayed at birth in the spiny mice, probably in relation to the lack of external stimulation during intrauterine life. In the cerebral cortex, hippocampus and striatum of adult spiny mice, when compared with the rats, there were similar levels of choline acetyltransferase but lower levels of membrane-bound acetylcholinesterase and, in the cerebral cortex, lower density of muscarinic receptor sites.

Increased responsiveness of the cerebral cortical phosphatidylinositol system to noradrenaline and carbachol in senescent rats.

The responsiveness of cerebral cortical alpha 1-adrenoceptors and cholinergic muscarinic M1 receptors was assessed in young (3 months) and aged (24 months) male Sprague-Dawley rats. The measure of responsiveness was the accumulation of inositol phosphate (IP) formed in [3H]myo-inositol-preloaded cerebral cortical slices in the presence of lithium, following stimulation with various concentrations of noradrenaline (1-300 microM) and carbachol (5-1000 microM). In old rats the maximum response to noradrenaline was higher by 80%, and that to carbachol by 33%, indicating an increased responsiveness of the investigated receptors in senescence.

Brain acetylcholinesterase and its molecular forms in a precocial murid, Acomys cahirinus, and rat during post-natal development.

Brain acetylcholinesterase (AChE) and its molecular forms of a precocial murid, Acomys cahirinus, characterized by a large hippocampus, were measured during post-natal development and compared with rat. The activity of soluble AChE in Acomys increased slightly up to 4 weeks after birth. The total AChE activity increased somewhat more but, in rats, this increase was still greater. Three main molecular forms of AChE were separated by 7.5% polyacrylamide gel electrophoresis. Their close similarity to the rat AChE forms was assessed by gradient polyacrylamide gel electrophoresis and electrofocusing. Maturation of these forms, i.e., conversion of simple into more complex forms in the soluble fraction of AChE was, however, considerably delayed reaching only after 4 weeks the pattern comparable to that of rat.

Effect of dietary rapeseed oil on hepatic hexobarbital metabolism in mice.

The effect of dietary rapeseed oil (RSO) on hepatic hexobarbital metabolism has been studied in short-term experiments in mice by measuring both the activity of mixed function oxidase system in microsomal preparations in vitro and the in vivo hexobarbital-induced sleeping time. Moreover, the fatty acid pattern of liver tissue, with particular regard to erucic and gadoleic acids, was analyzed gas-chromatographically. The hexobarbital metabolism in young RSO-fed (RSO containing 52% of erucic acid and 7.4% of gadoleic acid; 50 cal% for 3 days) is lower by about 44% than in controls treated in the same way with peanut oil, independently of sex. RSO did not have a statistically significant effect of hexobarbital metabolism in adult animals of both sexes. As to the dose-response study, the prolongation of the hexobarbital-induced sleeping time in young male is statistically significant when fed with 30 cal% in RSO for 3 days, while it is not more statistically significant in mice fed 15 cal% in RSO. In RSO mice (50 cal%) erucic and gadoleic acid account both for about 10% of the total fatty acids in the liver tissue, while they are quite absent in controls. It causes a relative deficiency of linoleic and arachidonic acids, known to be essential for synthesis and maintenance of the membranes supporting hepatic microsomal enzymes responsible for the metabolism of some drugs.

Glutamate-dependent mechanisms in the induction of a calcium long-term potentiation-like phenomenon.

The electric synaptic efficacy, in terms of extracellular electrical potentials, and the intracellular postsynaptic efficacy, in terms of inositol phosphate (IP) accumulation, were evaluated in rat hippocampal slices exposed for a brief period (10 min) to a high concentration of calcium (+2.7 mM). In addition, the effects of N-methyl-D-asparate (NMDA) ionotropic and metabotropic glutamate receptor (mGluR) antagonists on the induction and the establishment or maintenance of enhanced synaptic efficacy of CA1 pyramidal neurons due to high-calcium exposure were also tested. Elevation of the calcium concentration from 1.3-4 mM in the medium bathing hippocampal slices produced a long-lasting (80 over 90 min) increase in the slope of the CA1 somatic excitatory postsynaptic potential and the amplitude of the population spike (PS). Slice perfusion with NMDA antagonists cyclazocine and cis-4-phosphonomethyl-2-piperidine-carboxylic acid (CGS 19755) or with mGluR antagonists L-2-amino-3-phosphonopropionic acid (AP3) or alpha-methyl-4-carboxyphenyl-glycine (all 0.1 mM), during the 10-min period of exposure to high-calcium prevented the induction of such changes. By contrast, slice perfusion with the same concentration of CGS 19755 or L-AP3 did not affect the already established long-lasting increase in amplitude of CA1 PS induced by high-calcium. Moreover, high-calcium failed to produce any significant modification of the basal IP accumulation or of the IP accumulation elicited by mGluR agonist 1S,3R-trans-amino cyclo-pentane-1,3-dicarboxylic acid (ACPD). In conclusion, the results confirm that high-calcium induces a long-lasting increase in synaptic efficacy in rat hippocampal slices. Both NMDA ionotropic and mGluR receptors are involved in the induction, but not in the maintenance, of this phenomenon. In line with these data no modifications of basal or ACPD-induced phosphoinositide hydrolysis have been found during the maintenance stage.

Adaptive processes of the central and autonomic cholinergic neurotransmitter system: age-related differences.

Potential age-related differences in the response of the ileum strip longitudinal and circular muscle to repeated treatment with diisopropyl fluorophosphate (DFP) were evaluated in Sprague-Dawley rats. The response was measured in terms of both biochemical parameters (acetylcholinesterase-AChE inhibition, muscarinic acetylcholine receptor binding sites-mAChRs, choline acetyltransferase-ChAT) and functional responsiveness (contractility of the isolated ileum stimulated by cholinergic agonists). The biochemical data were compared with those obtained for the cerebral cortex. Male 3- and 24-month old rats were s.c. injected with DFP on alternate days for 2 weeks (doses in mg/kg: first 1.1, two of 0.7 and four of 0.35). They were killed 48 hr and 7, 14, 21, 28 and 35 days after the last treatment. In the ileum strip of control rats there was a significant age-related decline of AChE, maximal density of 3H-QNB binding sites (Bmax) and ChAT. During the first week of DFP treatment the cholinergic syndrome was more pronounced in aged than in young rats, resulting in 35% and 10% mortality, respectively; subsequently the syndrome attenuated. At the end of DFP treatment ileal AChE were inhibited by about 30%; the down-regulation of mAChRs was about 50% in young and 35% in aged rats. No significant differences in the recovery rate of AChE were noted between young and aged rats (normalization within 7 days). On the contrary, mAChRs normalized within 5 weeks in young and 3 weeks in aged rats. This was probably due to more adaptive decline in the former group. There was a post-treatment increase of ChAT, transitory in young and persistent in aged rats. In spite of age-related marked loss of ileal mAChRs there were only little, although significant, changes in the contractile responsiveness of the isolated ileum to cholinergic agonists. Considerable DFP-induced down-regulation of mAChRs was not accompanied by changes in contractility stimulated by the agonists. The overall data indicate that age- and treatment-induced changes of AChE, mAChRs and ChAT in the ileum strip differ considerably from those observed in the cerebral cortex of the same rats.

Altered modulation by excitatory amino acids of cortical phosphatidylinositol system stimulated by carbachol in rats poisoned by an anti-cholinesterase compound, diisopropyl fluorophosphate.

The effects of glutamate and N-methyl aspartate (NMDA) on carbachol-induced inositol phosphate (IP) accumulation were evaluated in slices of the cerebral cortex of rats treated with diisopropyl fluorophosphate (DFP) for 2 weeks. This induced an about 75% inhibition of cholinesterases. The IP accumulation induced by carbachol (expressed as ratio stimulated/basal IP content) was lower in DFP rats than in controls when incorporation of [3H]-myoinositol into membrane phospholipids and their hydrolysis were measured (no washing step between labeling and hydrolytic incubation). There were no differences in carbachol induced IP accumulation between control and DFP rats when only phosphoinositide hydrolysis was determined (hydrolytic incubation of prelabeled washed slices). When both incorporation of [3H]-myoinositol and the hydrolysis were measured, 0.5 mM glutamate and 0.1 mM NMDA caused a significant, about 40%, decrease of carbachol-induced IP accumulation in control rats; the inhibitory effects of glutamate and NMDA were not significant in DFP rats. When only hydrolytic IP accumulation by carbachol was studied, the inhibitory effects of glutamate and NMDA were very similar in control and DFP rats. Additional experiments on inositol phospholipid synthesis showed a significantly lesser [3H]-myoinositol incorporation (by about 30%) in DFP rats. This may explain the differences between the results obtained by the two methods. The overall data suggest that the attenuation of glutamate and NMDA effects in DFP-rats depends on a decrease of carbachol-induced IP accumulation or phosphoinositide synthesis rather than on the EAA specific action.

Effects of diisopropyl fluorophosphate on muscarinic-M1-receptors and on receptor-mediated responsiveness of the phosphatidyl-inositol system in the cerebral cortex of rats.

The effects of acute and repeated treatments with an anticholinesterase (anti-ChE) compound, diisopropylfluorophosphate (DFP) on M1-acetylcholine receptor (M1-AChRs) density and on M1-mediated breakdown of inositol phospholipids were studied in the cerebral cortex of rats. The DFP doses induced an about 75% inhibition of cortical ChE 48 hr after the last treatment. The acute treatment did not change Bmax of M1-AChRs (measured as 3H-pirenzepine binding), while 1-week and 2-weeks treatments induced their significant down-regulation, by 14 and 29%, respectively. The responsiveness of M1-AChRs was measured in cortical prisms as accumulation of inositol phosphate (IP) following stimulation with a cholinergic agonist, carbachol (from 10 to 1000 microM). The IP accumulation (expressed as ratio stimulated/basal IP content) was lower in acute DFP rats than in controls at few carbachol concentrations, and after 2 weeks at most carbachol concentrations. This resulted in a significant increase of EC50. The data indicate the involvement of cortical phosphatidyl inositol system during intoxication by anti-ChE agents, namely a decreased efficiency of post-receptor mechanisms.

Impaired recovery of brain muscarinic receptor sites following an adaptive down-regulation induced by repeated administration of diisopropyl fluorophosphate in aged rats.

Potential age-related differences in the recovery rate of brain cholinesterase activity (ChE) and muscarinic acetylcholine receptor binding sites (mAChRs) following reduction induced by repeated treatment with diisopropyl fluorophosphate (DFP) were evaluated in Sprague-Dawley rats. Male 3- and 24-month old rats were s.c. injected with DFP (doses in mg/kg: first 1.1, two of 0.7 and four of 0.35) on alternate days for 2 weeks and killed 48 hr and 7, 14, 21, 28 and 35 days after the last treatment. In the hippocampus and striatum, but not in the cerebral cortex, of control rats there was a significant age-related decline of ChE activity and maximal density of 3H-QNB binding sites (Bmax). The repeated administration of DFP during the first week caused a syndrome of cholinergic stimulation both in aged and young rats. The syndrome was more pronounced, in terms of intensity and duration (for many hours after each injection), in aged than in young animals resulting in 40 and 12% mortality, respectively; during the second week the syndrome attenuated in the two age-groups. The percentage inhibition of brain ChE at the end of DFP treatment (about 70%) did not differ between young and surviving aged rats. The down-regulation of mAChRs (without changes in affinity) was present in the three brain regions of both young and aged rats (from 20 to 40%). Factorial analysis of variance (2 ages x 2 recoveries ANOVA) showed significant differences for age, recovery rate, and significant interaction between age and recovery rate, both for ChE and mAChRs in the three brain areas. For example, cortical ChE in young rats reached pretreatment levels within 3 weeks, while hippocampal and striatal ChE activity recovered within 4 weeks; at these intervals ChE activity in aged rats was still considerably reduced (except in the striatum). Cortical and striatal mAChRs in young rats almost normalized within 1 week and hippocampal mAChR binding sites normalized within 2 weeks; at these intervals Bmax in aged rats were markedly below control levels. The overall data indicate that the recovery rate to normal baseline levels of ChE activity and mAChRs, following the termination of repeated treatment with the antiChE agent, is impaired in brain of aged rats. The delay in recovery rate is particularly evident in the cerebral cortex.

Muscarinic receptor plasticity in the brain of senescent rats: down-regulation after repeated administration of diisopropyl fluorophosphate.

Potential age-related differences in the response of Fischer 344 rats to subchronic treatment with diisopropylfluorophosphate (DFP) were evaluated in terms of brain cholinesterase (ChE) inhibition and muscarinic receptor sites. Male 3- and 24-month old rats were sc injected with sublethal doses of DFP (first dose 1.6, subsequent doses 1.1 mg/kg on alternate days) for 2 weeks and killed 48 hrs after the last treatment. In the cerebral cortex, hippocampus and striatum of control rats a significant age-related reduction of ChE and of maximum number of 3H-QNB binding sites (Bmax) was observed. The administration of DFP to senescent rats resulted in more pronounced and longer lasting syndrome of cholinergic stimulation, with marked body weight loss and 60% mortality. The percentage inhibition of brain ChE induced by DFP (over 80% in all regions) did not differ between young and senescent rats. As expected, in young rats DFP caused a significant decrease of Bmax (without apparent changes in affinity), which in the cerebral cortex reached about 40%. In the surviving senescent rats, the percentage decrease of Bmax due to DFP with respect to age-matched controls was very similar to that of young animals, especially in the cerebral cortex. Thus, there is great variability in the response of aged rats to DFP treatment, from total failure of adaptive mechanisms resulting in death to considerable muscarinic receptor plasticity. The data support the view that the ability of central neurotransmitter systems to compensate for pathological or xenobiotic induced insult is an essential part of the aging process.

Molecular forms of cholinesterases in CSF of Alzheimer's disease/senile dementia of Alzheimer type patients and matched neurological controls.

Acetylcholinesterase, pseudocholinesterase and their molecular forms were measured in the CSF of patients affected by Alzheimer's disease and of matched neurological controls. Three different molecular forms of ChE were found in the CSF of both groups of patients, but only two of them belonged to 'true' AChE. No differences were found between Alzheimer's disease patients and neurological controls in all the examined parameters.

Differential inhibition of rat brain acetylcholinesterase molecular forms by 7-methoxytacrine in vitro.

The effects of 7-methoxytacrine (7-MEOTA), a less toxic derivative of tetrahydroaminoacridine, on the activity of acetylcholinesterase (AChE) molecular forms were investigated in vitro. AChE molecular forms were separated by sucrose gradient sedimentation from homogenates of the frontal cerebral cortex prepared with buffer containing Triton X-100 (soluble + membrane-bound enzyme). Two molecular forms, namely 10S and 4S corresponding to globular tetrameric (G4) and monomeric (G1) forms, respectively, were detected; their molecular weights were 220,000 and 54,000 Da. A significantly higher sensitivity to 7-MEOTA of G4 than of G1 forms was observed. The Ki values were 0.21 +/- 0.07 microM for the former and 0.70 +/- 0.15 microM for the latter. The differential inhibition of AChE molecular forms by 7-MEOTA is discussed in relation to its possible clinical application for treatment of disorders such as Alzheimer's disease, in which a reduction of brain cholinergic neurotransmission is believed to play a role.

Age-related changes in muscarinic receptor and post-receptor mechanisms in brain and ileum strip of rats.

Age-related differences in the response of the cerebral cortex and ileum strip to a repeated treatment with an anticholinesterase compound, diisopropyl fluorophosphate (DFP) were evaluated in 3- and 24-month Sprague-Dawley rats. The response was measured in terms of acetylcholinesterase (AChE) inhibition and total muscarinic receptor density (MAChRs, measured as 3H-QNB binding). At the end of DFP treatment there was a 75% inhibition of brain AChE and 30% inhibition of ileal AChE, independently of age. The adaptive down-regulation of brain MAChRs was more pronounced in aged than in young rats (50 and 25%, respectively), while that of ileal MAChRs was greater in young than in aged rats (50 and 35%). The normalization of cortical MAChRs was delayed in aged rats that of ileal MAChRs was delayed in young rats. As regards age-related changes of AChE and MAChRs in untreated rats, there was a 30% decrease of cortical and ileal AChE, no changes in Bmax of cortical MAChRs and a 45% deficit of ileal MAChRs. This was accompanied by only a little age-related decrease in sensitivity of the isolated ileum to cholinergic agonists. Additional experiments on the responsiveness of phosphatidyl inositol system stimulated with carbachol showed that accumulation of inositol phosphate both in cortical and ileum strip slices was higher in aged than in young rats. The overall data indicate that treatment- and age-related changes of AChR mechanisms in the ileum strip differ considerably from those in the brain. However, the increased efficiency of post-receptor mechanisms in old age is their common feature.

Age-related differences in the recovery rate of brain cholinesterases, choline acetyltransferase and muscarinic acetylcholine receptor sites after a subacute intoxication of rats with the anticholinesterase agent, isofluorophate.

The recovery rate of brain cholinesterase activity (ChE) and muscarinic acetylcholine receptor sites (MAChRs) following a reduction due to a repeated treatment (2 weeks) with the antiChE agent, isofluorophate (diisopropyl fluorophosphate, DFP) was studied in young (3 months) and aged (24 months) male Sprague-Dawley rats. At the end of DFP treatment the inhibition of ChE in the cerebral cortex, hippocampus and striatum did not differ between young and aged rats (about 70%); the down-regulation of MAChRs (without changes in affinity) varied from 20 to 40% for various areas of brains of rats belonging to the two age-groups, and was the most pronounced in the cerebral cortex of aged rats. As assessed by factorial analysis of variance (2 ages x 2 recoveries ANOVA) there were age-related differences in the recovery rate of both ChE and MAChRs during 5 weeks from the end of DFP treatment. The impairment of recovery observed in aged rats was present in three brain areas and was the most pronounced in the cerebral cortex. Choline acetyltransferase (ChAT) was not influenced by the age and/or treatment in the cerebral cortex and hippocampus while in the striatum an age-related decline was observed. The overall data appear of interest in relation to the recent use of antiChE organophosphorus compounds in the therapy of age-related memory disorders.

Responsiveness of brain muscarinic acetylcholine receptors in aged rats.

In the first part of the investigation the age-related changes in cortical, hippocampal and striatal cholinesterases (ChE), choline acetyltransferase (ChAT) and muscarinic acetylcholine receptors (mAChRs, measured as Bmax of 3H-QNB binding) were compared in male Wistar, Fischer 344 and Sprague-Dawley rats aged 3 and 24 months. Fischer rats exhibited 1.5 fold higher levels of ChAT and mAChRs than Wistar and Sprague-Dawley rats in the areas analyzed. The age-related decline of cortical ChAT and mAChRs was present in Fischer rats but not in those of the other two strains, i.e. was strain-dependent. There were no age-related changes in hippocampal ChAT in any strain. The decline of striatal ChAT, hippocampal and striatal mAChRs and ChE in the three regions analyzed were present in Wistar, Fischer and Sprague-Dawley aged rats. Thus, these deficits (or lack of changes) appeared to be not strain-dependent. The overall data indicate the importance of genotype in the rate of aging, and an accelerated aging for Fischer 344 rats. In the second part of the investigation the responsiveness of cortical mAChRs, ChE and ChAT to a repeated treatment with an indirect cholinergic agonist (an antiChE agent, diisopropyl fluorophosphate-DFP) was studied in two independent experiments on Fischer 344 and Sprague Dawley rats aged 3 and 24 months. The s.c. administration of DFP (first dose 1.6, subsequent six doses of 1.1 mg/kg on alternate days) to senescent Fischer rats caused a considerably more pronounced syndrome of cholinergic stimulation than in young ones, resulting in 60 and 14% mortality, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)