Regional distribution of cholinergic parameters within the rat striatum

The topographical distribution of choline acetyltransferase, muscarinic receptor binding and high affinity choline uptake was studied in 21 separate areas of the rat striatum. The areas of the nucleus chosen represented dorsolateral, dorsomedial, ventrolateral and ventromedial regions along the rostrocaudal aspect of the striatum, such that a three-dimensional distribution of the cholinergic parameters could be obtained.Within any given rostrocaudal section, no significant dorsoventral differences were noted for any of the cholinergic parameters. On the other hand, marked differences were found in a comparison of the medial and lateral striatum. Choline acetyltransferase, muscarinic receptor binding and high affinity choline uptake were more concentrated in the lateral striatum than the medial striatum, and the magnitude of this medio-lateral disparity increased from rostral to caudal regions of the nucleus. The lateral striatum exhibited no significant rostrocaudal variations in the cholinergic parameters; however, the medial portion of the striatum did exhibit differences along its rostrocaudal extent, with the rostral-most sections being enriched relative to the more caudal sections.These results suggest that the cholinergic system in the striatum is heterogeneously distributed within this nucleus, with the lateral portion possessing a greater cholinergic innervation than the medial portion. They further suggest that future neurochemical studies of cholinergic alterations in the striatum should include a consideration of the possibility of regional effects within the nucleus rather than treating the striatum as a homogeneous tissue.     

Effects of long-term dietary choline and phosphatidylcholine administration on muscarinic receptors in aged mouse brain

It has been suggested that choline and/or phosphatidylcholine may be beneficial in improving the memory deficits associated with aging and Alzheimer's disease. The effects of long-term choline or phosphatidylcholine treatment on cholinergic receptors in the brain have been investigated. Mice were maintained on one of four diets from 50 days of age until sacrificed at 20-24 months. [3H]-QNB binding in the cortex, hippocampus and striatum was specific, saturable and of high affinity. Animals treated with a phosphatidylcholine-enriched diet displayed a down-regulation of muscarinic receptors in the cortex and hippocampus, reflected by a decrease in Bmax. There were no significant differences in the binding affinities among the treatment groups. Choline levels were unaffected by the various diets, however phosphatidylcholine treatment resulted in an increase in phosphatidylcholine in the cortex and somewhat in the hippocampus. This study indicates that choline and phosphatidylcholine have different effects after long-term dietary administration. Phosphatidylcholine treatment results in a down-regulation of muscarinic receptors in certain brain areas which appears to be related to an increase in phosphatidylcholine concentration. Any potentially beneficial effects derived from chronic phosphatidylcholine treatment must overcome the apparent down-regulation of muscarinic receptors which may occur.     

Expression of cholinergic markers in the developing chick embryo spinal cord

The expression of cholinergic neurotransmission in the developing spinal cord was followed with pre- and postsynaptic cholinergic markers and histoautoradiographic determinations of cholinergic receptors and ultrastructural studies. Two distinct steps in the development of cholinergic markers were evident. The first step of cholinergic expression occurs early in development and its characterized by a sudden and large increase in choline acetyltransferase activity, whereas the high affinity choline uptake mechanism remains undetectable and few muscarinic receptors are detectable. This phenomenon possibly reflects the expression of high choline acetyltransferase gene activity in developing neurons which are still not synaptically connected. The second step is also characterized by a sharp rise of choline acetyltransferase activity. This rise parallels an active development of high affinity choline uptake and big increase in both number and density of muscarinic receptors. Also nicotine receptors increase, as revealed by histoautoradiography. Specific morphogenetic events, such as the increase of synaptic junctions with postsynaptic thickenings and numerous presynaptic clear vesicles, occur at the same time. Such interactions may contribute to the full maturity of cholinergic neurotransmission of the spinal cord.     

Effects of aging on nicotinic and muscarinic autoreceptor function in the rat brain: relationship to presynaptic cholinergic markers and binding sites

The main objective of the present work was to determine whether the regulation of ACh release by nicotinic and muscarinic autoreceptors is compromised in the aged rat brain. For this, the effects of the nicotinic agonist N-methylcarbamylcholine (MCC) and the muscarinic-M2 antagonist AF-DX 116 on ACh release from brain slices of young (3-month-old), adult (9-month-old), and aged (27-month-old) rats were tested. The ability of MCC to enhance spontaneous ACh release in hippocampal, cerebral cortical, and cerebellar slices was only modestly altered with age. In contrast, the sensitivity of muscarinic autoreceptors in the aged hippocampus and cerebral cortex, but not the striatum, to blockade by the muscarinic-M2 antagonist AF-DX 116 was severely attenuated. To assess whether the age-related changes in cholinergic autoreceptor function may be due to deficits in presynaptic cholinergic markers, we tested whether choline acetyltransferase (ChAT) activity, basal and evoked ACh release, and nicotinic and muscarinic binding sites are altered in the aged rats. ChAT activity in forebrain regions was decreased in the aged compared to the young and mature adult rats. Furthermore, the potassium-evoked, but not the spontaneous, release of ACh was markedly depressed in striatal, hippocampal, and cortical slices of aged rats. The densities of nicotinic and muscarinic-M2 binding sites, assessed using 3H-MCC and 3H-AF-DX 116 as selective ligands, respectively, were markedly reduced in homogenates of the striatum, hippocampus, cerebral cortex, and thalamus of aged rats. In contrast, muscarinic-M1 sites, selectively labeled with 3H-pirenzepine, were not affected. Therefore, it appears that age-related decrements in ChAT activity and in muscarinic-M2, but not nicotinic, binding sites in the rat brain are reflected in a decreased function of muscarinic-M2 autoreceptors. However, the positive correlation between loss of ChAT activity, decreased muscarinic-M2 binding sites, and impaired muscarinic autoreceptor function is clearly tissue dependent.     

Lasting influence of amygdaloid kindling on cholinergic neurotransmission

Possible biochemical changes in cholinergic systems were investigated in nine brain regions of rats kindled by daily amygdaloid stimulation. Choline acetyltransferase (CAT) activity in the kindled animals was significantly decreased bilaterally in the frontal cortex, amygdala, and hippocampus. No such bilateral changes were found in specific muscarinic cholinergic receptor binding. In the stimulated hemisphere, muscarinic cholinergic receptor binding was decreased in the frontal cortex but increased in the amygdala. In the nonstimulated hemisphere, that receptor binding increased in the pyriform cortex. These results imply persistent effects of amygdaloid kindling on cholinergic neurotransmission.     

ELISA methods to measure cholinergic markers and nerve growth factor receptors in cortex, hippocampus, prefrontal cortex, and basal forebrain from rat brain

The central cholinergic system has a fundamental role in normal cognitive function, and in diseases that exhibit cognitive dysfunction. The purpose of this study was to design ELISA methods to measure proteins that have essential functions in the central cholinergic system. We were particularly interested in quantifying proteins that respond directly or indirectly to nerve growth factor (NGF). ELISAs offer advantages over Western blot analyses and other methods, such as increased sensitivity, decreased assay variability, increased efficiency, and decreased cost. We developed indirect ELISA methods for: choline acetyltransferase (ChAT); the vesicular acetylcholine transporter (VAChT); the high affinity choline transporter (HACT/CHT); TrkA, the high affinity NGF receptor; the p75 neurotrophin receptor (p75^NTR). A sandwich ELISA was developed to measure tyrosine-phosphorylated TrkA in brain lysates. We used these ELISAs to compare levels of the above proteins in important memory-related brain regions – basal forebrain, hippocampus, cortex, and prefrontal cortex – from old and young rats. We identified age-related differences in the levels of the aforementioned proteins (e.g., VAChT and HACT/CHT in hippocampus). Thus, these ELISA methods should be particularly useful for comparing the effects of age, disease, drugs, and toxicants on brain levels of key cholinergic and growth factor-related proteins.     

Changes in high affinity choline uptake in rat cortex following lesions of the magnocellular forebrain nuclei

High affinity choline uptake (HACU) and choline acetyltransferase (CAT) were measured in the cerebral cortex of rats 4 and 20 days after placing electrolytic lesions in the magnocellular forebrain nuclei (MFN) or in the pallidum.Four days after MFN lesion a 40–50% decrease in ipsilateral cortical HACU was found and a slightly smaller decrease was found 4 days after the pallidum lesion. Twenty days after the lesion, HACU activity returned to control values in the ipsilateral parietal cortex, its decrease was smaller than 4 days postlesion in the ipsilateral frontal cortex and a significant increase was found in the contralateral cortex.CAT activity showed a 40% decrease in the frontal, parietal and occipital ipsilateral cortex 4 days after MFN lesion. The same decrease was found 20 days postlesion. However, at this time a significant increase in CAT activity was detected in the contralateral cortex.The ipsilateral recovery of HACU activity 20 days after the lesions and the contralateral increase in HACU and CAT activity demonstrate the remarkable and widespread functional adjustment associated with discrete brain lesions. The existence of a large cholinergic pathway projecting to the neocortex from the basal forebrain region is also confirmed.     

Evidence for specific immunolysis of nerve terminals using antisera against choline acetyltransferase, glutamate decarboxylase and tyrosine hydroxylase

Synaptosomes prepared from striatum or cerebral cortex of rat brain were incubated with antibodies raised against three neurotransmitter biosynthetic enzymes, choline acetyltransferase, glutamate decarboxylase and tyrosine hydroxylase in the presence or absence of complement. Immunolysis was first assessed by measuring the release of lactic dehydrogenase or reduction in potassium from synaptosomes, and lysis of neurochemically specific subpopulation of synaptosomes was detected by measuring release of either transmitters, their biosynthetic enzymes or by blockade of sodium-dependent uptake of transmitter or precursor. In both striatum and cortex, antibodies to choline acetyltransferase lysed only cholinergic while those against glutamate decarboxylase only lysed GABAergic nerve terminals. Antibodies against tyrosine hydroxylase lysed only the dopaminergic terminals in striatum but not noradrenergic terminals in cortex. The lysis occurred only in the presence of complement, and was never observed in the absence of complement. The studies indicate that antibodies to the neurotransmitter biosynthetic enzymes recognize antigens in the synaptosomal membrane specific only to neurons harboring the transmitters. The results suggest that the antibody-positive peptides in the membrane and neurotransmitter biosynthetic enzyme share common antigenic sites, probably common peptides.     

Regional adaptation of muscarinic receptors and choline uptake in brain following repeated administration of diisopropylfluorophosphate and atropine

The specific [³H]QNB binding and high-affinity uptake of [¹⁴C]choline in 8 brain regions (cerebral cortex, hippocampus, hypothalamus, thalamus, striatum, midbrain, cerebellum and brainstem) after repeated administration of DFP and atropine to guinea-pigs were simultaneously measured. Following repeated DFP administration, AChE was markedly depressed in each brain region. In these animals, there was a significant decrease in specific [³H]QNB binding in the cerebral cortex, hippocampus and striatum, whereas the [³H]QNB binding in the rest of brain regions was unchanged. Scatchard analysis revealed a 36% decrease in the B_max value for the striatal [³H]QNB binding without a change in theK_d value, suggesting a change in the receptor density. In contrast, repeated atropine administration produced a significant enhancement in the [³H]QNB binding only in the hippocampus and striatum. The B_max value in the striatum increased by 21% without a change in theK_d value.In addition to the receptor alteration, high affinity uptake of [¹⁴C]choline in the hippocampus and striatum was significantly decreased by DFP treatment, while that in the striatum increased by atropine treatment. Thus the present study has demonstrated that a prolonged activation and blockade of central muscarinic receptors resulted in specific adaptation in both the receptor density and ACh availability at the synapses in the cerebral cortex, hippocampus and striatum.     

Choline in the aging brain

Proton magnetic resonance spectroscopy has been increasingly utilized in brain research to monitor non-invasively metabolites such as N-acetyl aspartate (NAA), creatine (Cr) and choline (Cho). We present here studies of the effect of aging on the ratios of these metabolites measured in the rat brain in vivo and on choline transport and lipid synthesis in rat brain slices, in vitro. The in vivo studies indicated that the ratios of Cho/NAA and Cho/Cr increased in the aged hippocampus, whereas the ratio of Cr/NAA was similar in the aged and adult hippocampus. These three ratios remained similar in the cortex of adult and aged rats. The in vitro studies revealed that in the aged cortex and the aged hippocampus the activity of the low-affinity choline uptake increased, possibly compensating for a decrease in the high-affinity uptake activity and the rate of choline diffusion. The incorporation of choline into phospholipids exhibited high and low affinity kinetics which were not modified by aging.     

Age-dependent loss and compensatory changes of septohippocampal cholinergic neurons in two rat strains differing in longevity and response to stress

Inbred Wistar-Kyoto rats which are behaviorally more reactive to stress have a shorter life span than Brown-Norway rats. This is paralleled by higher basal activity and more pronounced changes in the septohippocampal cholinergic system of Wistar-Kyotos after stress. Age- and strain-dependent differences were therefore characterized in the septohippocampal system of 3- and 24-month-old (aged) Wistar-Kyotos and Brown-Norways, and in 30-month-old Brown-Norways. High affinity [3H]choline uptake and newly synthesized [3H]acetylcholine release served as markers for cholinergic terminals in the hippocampus. [3H]Quinuclidinylbenzilate binding served as a marker of muscarinic receptors in the hippocampus. Choline acetyltransferase activity served as a marker for cholinergic neurons and their terminals in the septum and hippocampus respectively. Acetylcholinesterase histochemical staining served to localize cholinergic neurons and their terminals in the septum and hippocampus respectively. In the hippocampus of aged Wistar-Kyotos choline uptake and acetylcholine release were reduced by approximately 50% compared to their young counterparts, but remained unchanged in aged Brown-Norways. Hippocampal choline acetyltransferase activity, acetylcholinesterase staining and muscarinic binding were unchanged in aged rats of both strains. Pyramidal cell loss (observed in Cresyl violet stained sections) was detected in hippocampus of 24-month-old Wistar-Kyotos and 30-month-old, but not younger Brown-Norways. Numbers of acetylcholinesterase-stained cells in the septum were reduced by 45 and 25% in 24-month-old Wistar-Kyotos and Brown-Norways respectively, and by 50% in 30-month-old Brown-Norways. Mean diameter of these cells was increased only in aged Wistar-Kyotos (approximately 46%) and in 30-month-old Brown-Norways (40%). The results indicate: (1) there is an ongoing age-dependent degeneration of septohippocampal cholinergic neurons which is associated with two principal compensatory changes in remaining cholinergic neurons: (a) hypertrophy of perikarya and (b) relative increase in activity of presynaptic markers in terminals with unchanged regional distribution, suggesting possible collateral sprouting; (2) age-dependent loss of septal cholinergic neurons precedes loss of hippocampal pyramidal neurons and (3) loss of pyramidal neurons in the hippocampus is associated with a compensatory increased muscarinic binding by remaining target hippocampal neurons. The results imply that higher basal and stress-induced activity of septohippocampal cholinergic neurons may be correlated with an accelerated and more pronounced age-dependent degeneration of this cholinergic system.(ABSTRACT TRUNCATED AT 400 WORDS)     

Evidence for Normal Aging of the Septo-Hippocampal Cholinergic System in apoE (−/−) Mice but Impaired Clearance of Axonal Degeneration Products Following Injury

The association of the ε4 allele of apoE with increased risk for Alzheimer's disease (AD) and with poor clinical outcome after certain acute brain injuries has sparked interest in the neurobiology of apoE. ApoE (−/−) mice provide a tool to investigate the role of apoE in the nervous systemin vivo.Since integrity of the basal forebrain cholinergic system is severely compromised in AD, with severity of dysfunction correlating with apoE4 gene dosage, the present study tested the hypothesis that apoE is required to maintain the normal integrity of basal forebrain cholinergic neurons (BFCNs). Histological and biochemical analyses of the septo-hippocampal cholinergic system were performed in apoE (−/−) mice during aging and following injury. Using unbiased quantitative methods, there was little or no evidence for defects in the septo-hippocampal cholinergic system, as assessed by p75^NTR-immunoreactive neuron number and size in the medial septum, cholinergic fiber density in the hippocampus, and choline acetyltransferase activity in the hippocampus, cortex, and striatum in aged apoE (−/−) mice (up to 24 months of age) as compared to age-matched wild-type mice of the same strain. In addition, cholinergic neuronal survival and size following fimbria–fornix transection in apoE (−/−) mice did not differ from controls. However, following entorhinal cortex lesion, there was persistence of degeneration products in the deafferented hippocampus in apoE (−/−) mice. These data suggest that although apoE is not required for the maintenance of BFCNsin vivo,it may play a role in the clearance of cholesterol-laden neurodegeneration products following brain injury.     

Development of high affinity choline uptake and associated acetylcholine synthesis in the rat fascia dentata

The ontogenic development of hemicholinium-sensitive, high affinity choline uptake and the synthesis of acetylcholine from exogenous choline have been studied in particulate preparations of the rat fascia dentata. Between 6 days of age and adulthood the rate of high affinity choline uptake increases 3-fold, when expressed with respect to protein, and 125-fold, when expressed independently of protein. This process develops most rapidly during the period around 16-17 days of age, similar to the ontogenesis of choline acetyltransferase activity. This observation supports the idea that cholinergic septohippocampal boutons develop mainly at this time. Unlike choline acetyltransferase activity, the velocity of high affinity choline uptake increases to as much as 161% of the adult value at about 30 days of age. It is suggested that at 25-31 days of age a relatively high endogenous septohippocampal firing rate increases the rate of choline uptake. At 6 days of age we detected no synthesis of acetylcholine from the accumulated choline. Uptake-synthesis coupling develops mainly between 6 and 13 days of age, earlier than any other presynaptic cholinergic property. Acetylcholine synthesis from exogenous choline develops in paralled with high affinity choline uptake, but developmental increases in uptake velocity result in comparable increases in synthesis rate only after a delay of several days. Some limiting factor other than choline acetyltransferase activity appears to link the accumulation of exogenous choline to acetylcholine synthesis during development.     

Regional- and Age-Specific Neurochemical Alterations in Rats Rendered Microencephalic by Differentially Timed Gestational Methylazoxymethanol Treatment

Rats with different degrees of microencephaly were obtained by injecting pregnant mothers with methylazoxymethanol acetate (MAM) at gestational days 13.5 or 16.5. Specific markers for cholinergic (choline acetyltransferase, ChAT), GABAergic (glutamate decarboxylase, GAD), and glutamatergic (D-3H aspartate high affinity uptake) neurons, were measured in several brain regions (cortex, hippocampus, anterior and posterior striatum, medial septum plus nucleus of the diagonal band, globus pallidus) in young and adult microencephalic rats. In adult rats born to mothers injected with MAM at gestational day 16.5 (G16.5) ChAT level was increased in the cortex, hippocampus and striatum but decreased in the septal complex; GAD was decreased in the globus pallidus and, to a little extent, in the hippocampus while D-3H aspartate uptake was decreased in the striatum. One month old rats belonging to the same group showed comparable differences with the exception of larger increase of ChAT in the cortex and striatum. In adult rats born from mothers injected with MAM at gestational day 13.5 (G13.5) differences in the cholinergic marker were in general less pronounced; GAD was not decreased in the globus pallidus and D-3H aspartate uptake was unchanged in the striatum but significantly decreased in the hippocampus. The results are correlated with morphological brain alterations caused by differentially timed MAM treatment and with available information on the generation time of various neuronal populations. They show that the balance between different neurotransmitter systems can be experimentally altered and suggest that MAM treatment may provide an experimental tool for studying the development of this balance.     

Effects of dihydroergotoxine on central cholinergic neuronal systems and discrimination learning test in aged rats.

We evaluated changes in the cholinergic neuronal system and learning ability with aging. Choline acetyltransferase (ChAT) activity, a presynaptic index of the cholinergic system, was decreased in the cerebral cortex, hippocampus, striatum, and hypothalamus in the brain of aged rats compared with young adults. Muscarinic cholinergic binding sites (receptors, MCR), a postsynaptic index of the cholinergic system, were markedly decreased in all areas of the brain. However, intraperitoneal injection of 1 mg/kg of dihydroergotoxine (DHET) for 14 days normalized both ChAT and MCR in the cerebral cortex and hippocampus. In the striatum, ChAT was normalized, but MCR did not recover. Aged rats showed marked learning impairment in a 30-day operant type brightness discrimination learning test. Daily DHET administration restored the discrimination ability in the aged rats to nearly the young adult level. DHET had no effects on central cholinergic indices or learning test results in young adult rats. These findings suggest that learning is impaired in aged rats due to impairment in the central cholinergic neuronal system, and that DHET normalizes the decreased function in this system, restoring the learning ability.     

Decreased [H]hemicholinium binding to high-affinity choline uptake sites in aged rat brain

The binding of [³H]hemicholinium ([³H]HCh-3) to sodium-dependent high-affinity choline uptake sites provides a useful neuroanatomical and functional marker of the cholinergic system. We examined the autoradiographic distribution of [³H]HCh-3 binding sites in the forebrain of young (4–6 months) and old (32 months) rats. There was a widespread reduction of [³H]HCh-3 binding site density in the aged rat brain. This loss presented regional differences with maximal reduction in the medial and posterior striatum (55%) and in the dentate gyrus (47%), in limbic areas such as basolateral amygdala, tubercle olfactorium and piriform cortex the autoradiographic signal was about 25–30% lower. In aged hippocampus and cerebral cortex the density of [³H]HCh-3 binding sites was about 40% lower, the difference between young and senescent animals being less evident in the medial septum and basal nucleus. No significant alterations were observed in interpeduncular nucleus from old rats. These data are in agreement with the functional results obtained by measuring other cholinergic parameters in the aged rat and confirm the vulnerability of cholinergic system during aging     

High-affinity choline uptake carrier in Alzheimer''s disease: implications for the cholinergic hypothesis of dementia

We examined the density and the state of affinity of [3H]hemicholinium-3 ([3H]HC-3) binding sites, a marker of the presynaptic high-affinity choline uptake (HACU) carrier, in 4 representative regions of 13 postmortem Alzheimer's disease (AD) brains, as well as in 12 matched control brains. Significant reductions in the densities of [3H]HC-3 binding sites were found both in frontal cortex (-44.7%) and hippocampus (-36.5%) of AD brains in comparison to controls. On the other hand the densities of [3H]HC-3 binding sites in AD brains in caudate-putamen and cerebellar cortex showed no significant differences when compared to controls. No significant change in the state of affinity of these sites could be observed in the saturation assays carried out in hippocampus and frontal cortex. Our findings concur with the reported data by using other presynaptic cholinergic markers in AD and confirm that some degree of cholinergic degeneration, highly specific for the basal forebrain neurons, occurs in AD. However, these results, obtained in a group of AD brains belonging to severely demented patients, do not show a dramatic loss of the HACU in many AD brains. Although this fact could be due to the existence of a compensatory mechanism, our results probably suggest that dementia in AD cannot be explained only by the loss of neocortical cholinergic presynaptic terminals arising from the basal forebrain and also may clarify as to why the acetylcholine precursors or the muscarinic agonists are not effective in AD dementia.     

Brain muscarinic cholinergic receptors in Huntington's disease

Summary Muscarinic cholinergic receptors and choline acetyltransferase (ChAT) activity were studied in postmortem brain tissue from patients with Huntington's disease and matched control subjects. In comparison with controls, reductions in ChAT activity were found in the hippocampus, but not in the temporal cortex in Huntington's disease. Patients with Huntington's disease showed reduced densities of the total number of muscarinic receptors and of M-2 receptors in the hippocampus while the density of M-1 receptors was unaltered. Muscarinic receptor binding was unchanged in the temporal cortex. These results indicate a degeneration in Huntington's disease of the septo-hippocampul cholinergic pathway, but no impairment of the innominato-cortical cholinergic system.     

Cholinergic deficits in the septal-hippocampal pathway of the SAM-P/8 senescence accelerated mouse

Senescence accelerated prone mouse strains (SAM-P) and resistant strains (SAM-R) have proven useful in elucidating aspects of the aging process. The senescence accelerated mouse SAM-P/8 strain exhibits severe age-related learning and memory impairments well before the median age of survival. Disruption of the brain cholinergic system produces learning and memory impairments as severe as those seen in aging SAM-P/8 mice. Therefore, we compared the effects of aging on cholinergic parameters in the septal-hippocampal pathway, a region known to play a role in learning and memory, in SAM-P/8 mice and mice of the senescence resistant SAM-R/1 strain. Between 4 and 12 months of age we observed a 40-50% decrease in choline acetyltransferase (ChAT) activity in two of three subregions of the hippocampus in the SAM-P/8, but not the SAM-R/1 strain. Between 4 and 12 months, SAM-P/8 mice also showed a 40-50% decrease in ChAT activity in the septal region that was maximal by 8 months of age. By contrast, these age-related changes were not observed in the control SAM-R/1 mouse strain. The changes in ChAT in the SAMP/8 mouse strain were limited to the septal-hippocampal cholinergic pathway. There were no differences in ChAT activity in the nucleus basalis of Meynert, nor any of several neocortical areas to which it projects. To determine the neurochemical specificity of these alterations, the activity of glutamic acid decarboxylase (GAD), was also measured in the septum and hippocampus of SAM-P/8 mice. There were no age-related alterations in the hippocampus, but a significant 50% increase in GAD activity in the septal nucleus at 12 months of age. There were no age-related alterations in either nicotinic (3H-cytisine) or muscarinic (3H-QNB) cholinergic receptor binding in the cortex or hippocampus of SAM-P/8 mice. However, there were significant strain differences. At 2 months of age, 3H-QNB binding was higher in hippocampus of the SAM-R/1 than in SAM-P/8 mice. Similarly, 3H-cytisine binding in cortex of SAM-R/1 mice was higher at both 2 and 13 months than in SAM-P/8 mice. The results suggest that a compromised septal-hippocampal cholinergic pathway may contribute to the previously reported early onset of impaired learning and memory in the SAM-P/8 mouse strain.     

Effect of Venezuelan equine encephalomyelitis virus infection on brain choline acetyltransferase and acetylcholinesterase activities

Mice and rats infected with the Venezuelan equine encephalomyelitis virus showed a significant decrease in the choline acetyltransferase activity of caudate nucleus, hypothalamus, midbrain, hippocampus and frontal cortex. Acetylcholinesterase activity was not affected in any of the same brain regions analyzed. In surviving rats no alterations were observed in the activities of choline acetyltransferase, tyrosine hydroxylase, and glutamate decar☐ylase 3 months after the infection.