Recent developments in biochemical investigations of cholinergic transmission

Roles of the Functional Interaction between Brain Cholinergic and Dopaminergic Systems in the Pathogenesis and Treatment of Schizophrenia and Parkinson's Disease

Most physiologic processes in the brain and related diseases involve more than one neurotransmitter system. Thus, elucidation of the interaction between different neurotransmitter systems could allow for better therapeutic approaches to the treatments of related diseases. Dopaminergic (DAergic) and cholinergic neurotransmitter system regulate various brain functions that include cognition, movement, emotion, etc. This review focuses on the interaction between the brain DAergic and cholinergic systems with respect to the pathogenesis and treatment of schizophrenia and Parkinson’s disease (PD). We first discussed the selection of motor plans at the level of basal ganglia, the major DAergic and cholinergic pathways in the brain, and the receptor subtypes involved in the interaction between the two signaling systems. Next, the roles of each signaling system were discussed in the context of the negative symptoms of schizophrenia, with a focus on the α7 nicotinic cholinergic receptor and the dopamine D₁ receptor in the prefrontal cortex. In addition, the roles of the nicotinic and dopamine receptors were discussed in the context of regulation of striatal cholinergic interneurons, which play crucial roles in the degeneration of nigrostriatal DAergic neurons and the development of L-DOPA-induced dyskinesia in PD patients. Finally, we discussed the general mechanisms of nicotine-induced protection of DAergic neurons.

MicroRNAs Induce a Permissive Chromatin Environment that Enables Neuronal Subtype-Specific Reprogramming of Adult Human Fibroblasts

Directed reprogramming of human fibroblasts into fully differentiated neurons requires massive changes in epigenetic and transcriptional states. Induction of a chromatin environment permissive for acquiring neuronal subtype identity is therefore a major barrier to fate conversion. Here we show that the brain-enriched miRNAs miR-9/9^∗ and miR-124 (miR-9/9^∗-124) trigger reconfiguration of chromatin accessibility, DNA methylation, and mRNA expression to induce a default neuronal state. miR-9/9^∗-124-induced neurons (miNs) are functionally excitable and uncommitted toward specific subtypes but possess open chromatin at neuronal subtype-specific loci, suggesting that such identity can be imparted by additional lineage-specific transcription factors. Consistently, we show that ISL1 and LHX3 selectively drive conversion to a highly homogeneous population of human spinal cord motor neurons. This study shows that modular synergism between miRNAs and neuronal subtype-specific transcription factors can drive lineage-specific neuronal reprogramming, providing a general platform for high-efficiency generation of distinct subtypes of human neurons.

Emerging Treatments: Replacement Therapy with Choline or Lecithin in Neurological Diseases

This review evaluates the theoretical background and experimental data behind a new development: the replacement therapy of deficient central cholinergic systems with the dietary precursors choline or lecithin. Cholinergic deficiency states are possibly present in five neurological entities: Huntington's chorea, Tardive Dyskinesia, Gilles de la Tourette's disease, Friedreich's ataxia and presenile dementia. Preliminary data from various laboratories, including our own, in each of these disorders indicate that some clinical improvement can occasionally be seen, and that this approach deserves further investigation.

Vagal projections to the pylorus in the domestic pig (Sus scrofa domestica)

The goal of the present study was to examine the precise localization of the brainstem motor and primary sensory (nodose ganglion) vagal perikarya supplying the pylorus in the domestic pig. Using the Fast Blue retrograde tracing technique it has been established that all the vagal motor neurons projecting to the pylorus (about 337 ± 59 cells per animal) were localized bilaterally in the dorsal motor nucleus of the vagus nerve (DMX, 171 - left; 167 - right) and all other regions of the porcine brainstem were devoid of labeled neurons. The vagal perikarya supplying the porcine pylorus were dispersed throughout the whole rostro-caudal extent of the DMX and no somatotopic organization of these neurons was observed. The labeled neurons occurred individually or in groups up to five cell bodies per nuclear transverse cross section area (in the middle part of the nucleus). An immunocytochemical staining procedure disclosed that all Fast Blue labeled motor neurons were choline acetyltransferase (ChAT) immunoreactive, however some differences in immunofluorescence intensity occurred. The primary sensory vagal neurons were observed within the left (215±37 cells/animal) and right (148±21 cells/animal) nodose ganglion. The traced neurons were dispersed throughout the ganglia and no characteristic arrangement of these neurons was observed. The present experiment precisely indicates the sources of origin of the vagal motor and primary sensory neurons supplying the pyloric region in the pig, the animal of an increasing significance in biomedical research.

Determination of high-affinity choline uptake (HACU) and choline acetyltransferase (ChAT) activity in the same population of cultured cells

Cholinergic neurons are a major constituent of the mammalian central nervous system. Acetylcholine, the neurotransmitter used by cholinergic neurons, is synthesized from choline and acetyl CoA by the enzymatic action of choline acetyltransferase (ChAT). The transport of choline into the cholinergic neurons, which results in synthesis of ACh, is hemicholinium-sensitive and is referred to as high-affinity choline uptake (HACU). Thus, the formation of acetylcholine in cholinergic neurons largely depends on both the levels of choline being transported into the cells from the extracellular space and the activity of ChAT. Several methods were described previously to measure HACU and ChAT simultaneously in synaptosomes, but the same for cultured cells is lacking. We describe a procedure to measure HACU and ChAT at the same time in cultured cells by simple techniques employing radionuclides. In this procedure, we determined quantitatively hemicholinium-sensitive choline uptake and ChAT enzyme activity in a small number of differentiated human neuroblastoma (SK-N-SH) cells. We also determined the kinetics of choline uptake in the SK-N-SH cells. We believe that these simple methods can be used for neurochemical and drug discovery studies in several models of neurodegenerative disorders including Alzheimer's disease.

Nicotine and Parkinson's disease: implications for therapy

Accumulating evidence suggests that nicotine, a drug that stimulates nicotinic acetylcholine receptors, may be of therapeutic value in Parkinson's disease. Beneficial effects may be several-fold. One of these is a protective action against nigrostriatal damage. This possibility stems from the results of epidemiological studies that consistently demonstrate an inverse correlation between tobacco use and Parkinson's disease. This reduced incidence of Parkinson's disease has been attributed to the nicotine in tobacco products, at least in part, based on experimental work showing a protective effect of nicotine against toxic insults. Second, several studies suggest a symptomatic effect of nicotine in Parkinson's disease, although effects are small and somewhat variable. Third, recent data in nonhuman primates show that nicotine attenuates levodopa-induced dyskinesias, a debilitating side effect that develops in the majority of patients on levodopa therapy. Collectively, these observations suggest that nicotine or CNS selective nicotinic receptor ligands hold promise for Parkinson's disease therapy to reduce disease progression, improve symptoms, and/or decrease levodopa-induced dyskinesias.

Paraquat exposure reduces nicotinic receptor-evoked dopamine release in monkey striatum

Paraquat, an herbicide widely used in the agricultural industry, has been associated with lung, liver, and kidney toxicity in humans. In addition, it is linked to an increased risk of Parkinson's disease. For this reason, we had previously investigated the effects of paraquat in mice and showed that it influenced striatal nicotinic receptor (nAChR) expression but not nAChR-mediated dopaminergic function. Because nonhuman primates are evolutionarily closer to humans and may better model the effects of pesticide exposure in man, we examined the effects of paraquat on striatal nAChR function and expression in monkeys. Monkeys were administered saline or paraquat once weekly for 6 weeks, after which nAChR levels and receptor-evoked [(3)H]dopamine ([(3)H]DA) release were measured in the striatum. The functional studies showed that paraquat exposure attenuated dopamine (DA) release evoked by alpha3/alpha6beta2(*) (nAChR that is composed of the alpha3 or alpha6 subunits, and beta2; the asterisk indicates the possible presence of additional subunits) nAChRs, a subtype present only on striatal dopaminergic terminals, with no decline in release mediated by alpha4beta2(*) (nAChR containing alpha4 and beta2 subunits, but not alpha3 or alpha6) nAChRs, present on both DA terminals and striatal neurons. Paraquat treatment decreased alpha4beta2(*) but not alpha3/alpha6beta2(*) nAChR expression. The differential effects of paraquat on nAChR expression and receptor-evoked [(3)H]DA release emphasize the importance of evaluating changes in functional measures. The finding that paraquat treatment has a negative impact on striatal nAChR-mediated dopaminergic activity in monkeys but not mice indicates the need for determining the effects of pesticides in higher species.

Nicotine reduces levodopa-induced dyskinesias in lesioned monkeys

OBJECTIVE

Levodopa, the gold standard for Parkinson's disease treatment, is associated with debilitating abnormal involuntary movements or dyskinesias, for which few treatments are currently available. Studies have implicated numerous neurotransmitters in the development of levodopa-induced dyskinesias. However, the cholinergic system has received little attention despite an extensive overlap between dopaminergic terminals and cholinergic interneurons in the striatum and the well-known ability of nicotine to stimulate striatal dopamine release. Our objective, therefore, was to determine whether nicotine treatment reduced levodopa-induced dyskinesias.

METHODS

The effect of nicotine (provided in the drinking water) was determined on dyskinesias induced by levodopa (5 mg/kg twice daily by oral gavage) in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated monkeys.

RESULTS

Nicotine pretreatment reduced peak and total levodopa-induced dyskinesias in levodopa-naive monkeys over an 8-week period, with a decrease in total dyskinesias of about 50%. A crossover study was then done in which levodopa-treated monkeys originally receiving vehicle were administered nicotine, whereas the levodopa-treated animals initially receiving nicotine were placed on vehicle. Nicotine treatment to levodopa-primed monkeys led to an approximately 35% reduction in total dyskinesias that lasted for at least 8 weeks, at which time the study was ended. In contrast, a significant increase in levodopa-induced dyskinesias was observed in the group of animals that had previously received nicotine and were then switched to vehicle. Nicotine treatment did not appear to affect the antiparkinsonian action of levodopa.

INTERPRETATION

These data suggest that nicotine or selective nicotinic agonists may represent a useful treatment strategy to reduce levodopa-induced dyskinesias.

Nicotinic receptors as CNS targets for Parkinson's disease

Parkinson's disease is a debilitating neurodegenerative movement disorder characterized by damage to the nigrostriatal dopaminergic system. Current therapies are symptomatic only and may be accompanied by serious side effects. There is therefore a continual search for novel compounds for the treatment of Parkinson's disease symptoms, as well as to reduce or halt disease progression. Nicotine administration has been reported to improve motor deficits that arise with nigrostriatal damage in parkinsonian animals and in Parkinson's disease. In addition, nicotine protects against nigrostriatal damage in experimental models, findings that have led to the suggestion that the reduced incidence of Parkinson's disease in smokers may be due to the nicotine in tobacco. Altogether, these observations suggest that nicotine treatment may be beneficial in Parkinson's disease. Nicotine interacts with multiple nicotinic receptor (nAChR) subtypes in the peripheral and central nervous system, as well as in skeletal muscle. Work to identify the subtypes affected in Parkinson's disease is therefore critical for the development of targeted therapies. Results show that striatal alpha6beta2-containing nAChRs are particularly susceptible to nigrostriatal damage, with a decline in receptor levels that closely parallels losses in striatal dopamine. In contrast, alpha4beta2-containing nAChRs are decreased to a much smaller extent under the same conditions. These observations suggest that development of nAChR agonists or antagonists targeted to alpha6beta2-containing nAChRs may represent a particularly relevant target for Parkinson's disease therapeutics.

Upregulation of Bax protein and increased DNA degradation in ALS spinal cord motor neurons

OBJECTIVES

To investigate if degeneration of motor neurons in amyotrophic lateral sclerosis (ALS) is related to altered levels of the apoptosis regulating proteins Bcl-2 and Bax. In addition, immunoreactivity of the cysteine protease ICH-IL and detection of motor neurons with DNA fragmentation, indicative of apoptosis, was also studied.

MATERIAL AND METHODS

The immunoreactivity of Bcl-2, Bax and ICH-1L were compared in ALS and control spinal cord motor neurons by immunohistochemical analysis and motor neurons with DNA fragmentation were identified by the TUNEL-method.

RESULTS

The results demonstrate an increased expression of Bax in the ALS material as compared to controls but no change in Bcl-2 and ICH-1L expressions. Moreover, a larger proportion of motor neurons stained positive for TUNEL in ALS spinal cords.

CONCLUSION

Present study suggest an upregulation of the cell death promoting protein Bax and increased DNA degradation, indicative of apoptosis, in spinal motor neurons of ALS patients.

Transport of choline in rat brain slices

Enzyme-modified amperometric microsensors have been utilized in the investigation of acetylcholine and choline diffusion in solution and choline uptake and diffusion in rat brains. A small amount of the substance of interest was introduced by pressure injection and transport to the sensor was monitored. The apparent diffusion coefficients for acetylcholine and choline in agarose gel perfused with physiological solutions were determined to be 5.2 +/- 0.7 x 10(-6) cm2/s and 6.1 +/- 0.8 x 10(-6) cm2/s, respectively. Choline transport was monitored in two brain regions: the caudate and anterior hypothalamus. The transport time of choline in the caudate was concentration dependent, but was unaffected by the presence of a competitive, high-affinity uptake inhibitor, hemicholinium-3. The apparent diffusion coefficient (D) and uptake rate (k) for choline in the caudate and anterior hypothalamus were calculated using a model for point source diffusion coupled with first-order uptake kinetics. The effect of the sensors' response time on the measurements was removed by deconvolution. The D and k were 1.8 +/- 0.1 x 10(-6) cm2/s and 2.0 +/- 0.1 x 10(-2) s-1 in the caudate and 1.9 +/- 0.1 x 10(-6) cm2/s and 3.2 +/- 0.6 x 10(-2) s-1 in the anterior hypothalamus. The reduced diffusion coefficient determined in brain tissue compared to agar gel is consistent with the increased tortuosity of the brain microenvironment. A substance in brain tissue, presumably acetylcholinesterase, prevents the use of differential measurements of acetylcholine because choline sensors became sensitive to acetylcholine.

Development of high-affinity choline transport sites in rat forebrain: a quantitative autoradiography study with [3H]hemicholinium-3

The development of cholinergic terminals in rat brain has been quantitatively analyzed by [3H]hemicholinium-3 autoradiography. [3H]Hemicholinium-3 binds to high affinity choline transport sites, a specific marker for cholinergic neurons. In neonatal animals, kinetic and pharmacologic binding characteristics and regional distribution of [3H]hemicholinium-3 sites are consistent with specific cholinergic localization, as in the adult. The distribution of cholinergic terminals is described in the adult rat brain and during development, including heterogeneity of binding within several regions such as the striatum, nucleus accumbens, olfactory tubercle, cortex, and hippocampus. Early development and maturation vary greatly between brain regions. At embryonic day E18 and day 0, specific binding density is high only in the medial habenula. Development occurs primarily during the postnatal period in most brain regions examined. Many brain regions exhibit a lull in development between days 5 and 10, although the rate of development is highly region specific. Specific binding increases 2-12-fold between day 5 and adult animals, with adult density being achieved anywhere from day 15 to after day 21. The ontogeny of [3H]hemicholinium-3 binding sites generally occurs in a rostral to caudal direction. In the striatal body the characteristic lateral to medial gradient of binding site density is apparent by day 5, and development is more rapid in the lateral striatum. Patches of dense [3H]hemicholinium-3 binding coincident with acetylcholinesterase are observed on day 5 in the caudal striatum. The various patterns of cholinergic terminal development suggest that factors regulating cholinergic development are regional and complex.

Global in vivo replacement of choline by N-aminodeanol. Testing a hypothesis about progressive degenerative dementia: II. Physiological and behavioral effects

We have examined the progressive effects of replacement of dietary choline with NADe for a period of 120 days on a broad spectrum of behavioral and physiological functions known to involve the cholinergic system. The magnitudes of these effects tended to increase with time on the NADe diet, but those related to learning and memory were largely confined to the 60-120-day period. Neurochemical effects were concomitant with the replacement of Ch by NADe, being consistent with a hypocholinergic state as found in such progressive degenerative dementias as Alzheimer's disease. As cholinergic functioning was progressively impaired, basic physiological ("vegetative") processes appeared not to be affected. Apparently the rate at which the hypofunctional state developed was sufficiently slow for adjustments to occur, allowing the animal to adapt at a survival level to neurochemical changes. More complex behavioral functions were affected progressively, cognitive processes (e.g., learning and memory) being most sensitive and showing the least adaptability. We propose that the syndrome generated by NADe replacement of Ch represents an experimental model of progressive degenerative dementia.

Effect of intrathecal proctolin administration on the behaviour evoked by the thyrotrophin-releasing hormone (TRH) analogue (RX 77368) and the indoleamine, TRH, substance P and calcitonin gene-related peptide levels and choline acetyltransferase activity in the rat spinal cord

The behavioral effects and the biochemical changes produced following either a single or repeated intrathecal injection respectively, of the insect peptide proctolin (Arg-Tyr-Leu-Pro-Thr-OH) have been compared with the effects of a stable analogue of thyrotrophin-releasing hormone (TRH) in rats. Intrathecal proctolin (1-100 micrograms) did not produce any marked behavioural effects on its own, while intrathecal TRH analogue (RX 77368, 0.5 microgram) administration produced wet-dog shakes and forepaw-licking behaviours. Proctolin (10 micrograms) significantly attenuated the wet-dog shake and forepaw-licking behaviours evoked by intrathecal RX 77368 administration when it was given 30 min before, but not when given in combination with RX 77368. Repeated intrathecal proctolin administration (10 micrograms twice daily for 5 days) significantly reduced the 5-hydroxytryptamine (5-HT), 5-hydroxyindoleacetic acid and TRH levels in the ventral, but not in the dorsal, horn of the spinal cord nor in the brainstem, and elevated hypothalamic TRH without affecting plasma free thyroxine levels when compared with values in saline-treated controls. Repeated proctolin injection did not alter substance P levels in any brain region examined, nor did it affect the choline acetyltransferase activity or the calcitonin gene-related peptide-like immunoreactive levels in the ventral horn of the spinal cord, both of which are principally located in motoneurones in this cord region.(ABSTRACT TRUNCATED AT 250 WORDS)

Cholinergic innervation of the main and the accessory olfactory bulbs of the rat as revealed by a monoclonal antibody against choline acetyltransferase

The main and accessory olfactory bulbs (MOB and AOB) of the rat were immunohistochemically stained with a monoclonal antibody against choline acetyltransferase (ChAT) in order to know the difference in the distribution patterns of cholinergic fibers between these two structures. A few ChAT-immunoreactive cell bodies were found in the superficial and middle parts of the external plexiform layer (EPL) of the MOB, in the granule cell layer (GCL) of the MOB, and in the GCL of the AOB. The frequency in appearance of these cells was 0.9 cells/section in the MOB and 0.3 cells/section in the AOB. While the glomerular layer (GL) and the superficial part of the EPL were most densely innervated in the MOB, the internal plexiform layer received the richest innervation in the AOB. There were no immunoreactive structures in the olfactory nerve layer of the MOB and in the vomeronasal nerve layer and glomerular layer of the AOB. In addition to a relatively homogenous distribution of cholinergic fibers in the MOB and AOB, there were several foci of very dense network of immunoreactive fibers at the posterior level of the OB. These foci formed a part of the modified glomerular complex that was recently identified using 2-deoxyglucose method and was presumed to be related to suckling behaviour in the neonatal rat.

Spinal effects of chronic intrathecal administration of the thyrotrophin-releasing hormone analogue (CG 3509) in rats

The effect of repeated intrathecal administration of a thyrotrophin-releasing hormone (TRH) analogue (CG 3509; 2 micrograms twice daily for 5 days) on wet-dog shake (WDS) and forepaw-licking (FPL) behaviours and spinal cord TRH and indoleamine levels and choline acetyltransferase (ChAT) activity was examined in adult rats. A rapid behavioural tolerance developed to repeated intrathecal injections of CG 3509; WDS and FPL behaviours were reduced by 57% and 34%, respectively, following the fifth injection and remained reduced at the ninth injection. Repeated CG 3509 administration selectively elevated ChAT activity and the level of 5-hydroxytryptamine (5-HT) in the ventral but not in the dorsal horn of the spinal cord, while 5-hydroxyindoleacetic acid (5-HIAA) and TRH levels were unaltered in either region. As ventral horn ChAT activity is principally located within motoneurones this data implies that TRH exerts a trophic-like influence on mature rat motoneurones in vivo. The results also suggest that long-term intrathecal TRH administration may decrease the release of 5-HT from bulbospinal raphe neurones.

Regionally selective manifestations of neostriatal aging

Presynaptic and postsynaptic markers of the cholinergic and dopaminergic systems have characteristic topographical distributions within the striatum. Aside from the dopaminergic afferents, several other afferent systems exhibit a heterogeneous distribution in the striatum. The net result is that each part of the striatum receives a specific and unique combination of afferents. Moreover, the intrinsic striatal systems also have unique distributions, so each part of the striatum consists of a unique combination of afferent and intrinsic neurotransmitter systems. In view of these points, one may expect that the striatum is functionally very complex, integrating information from a wide variety of brain areas. One may also assume from these facts that the striatum is a functionally heterogeneous structure. Consistent with that conclusion, behavioral and pharmacological studies show that interruption of neurotransmission in localized regions of the striatum produces very specific behavioral and physiological effects. Age-related neurochemical changes are also confined to specific striatal regions. Which regions are affected will depend on a variety of factors, including the neurochemical parameter studied and the species or strain of animal. However, we still do not know what factors make a particular striatal area vulnerable to the effects of aging or disease. Moreover, a question that remains to be answered is whether the regions that are affected by neurodegenerative diseases are the same ones affected during normal aging. If so, then this may provide a clue as to why neurodegenerative diseases of the basal ganglia increase in frequency with advancing age. Nevertheless, discrete regional neurochemical alterations may underlie specific symptoms of these diseases. Further study of this relationship may provide the basis for treatments that better target the source of the symptoms. Not only would this increase the effectiveness of the treatment, it would help reduce potential side effects. This may be particularly important, for example, with respect to the use of tissue explants in the treatment of diseases of the basal ganglia.

Effects of spinal cord lesions and rhizotomies on cholinergic and opiate receptor binding sites in rat spinal cord

Changes in the distribution of [3H]quinuclidinylbenzilate ([3H]QNB), [3H] alpha-bungaro-toxin ([3H]alpha-Btx) and [3H]etorphine binding sites were studied autoradiographically, and cholinacetyltransferase (ChAT) activity radioenzymatically, in the C6-7 segments of rats 1-20 days after combined dorsal and ventral C3-8 rhizotomies and spinal cord lesions at C3. After dorsal and ventral rhizotomies the number of [3H]QNB, [3H]alpha-Btx and [3H]etorphine binding sites were reduced ipsilaterally in the dorsal horn and those of [3H]QNB and [3H]alpha-Btx in the ventral horn. In the ventral horn ChAT activity was significantly reduced. After a unilateral spinal cord lesion at C3, ChAT activity was reduced in the ipsilateral ventral horn at C6-7 caudal to the lesions, whereas no change in receptor binding sites was observed.

Cholinergic and GABAergic afferents to the olfactory bulb in the rat with special emphasis on the projection neurons in the nucleus of the horizontal limb of the diagonal band

We have examined the location of cholinergic and GABAergic neurons that project to the rat main olfactory bulb by combining choline acetyltransferase (ChAT) and glutamic acid decarboxylase (GAD) immunohistochemistry with retrograde fluorescent tracing. Since many of the projection neurons are located in subcortical basal forebrain structures, where the delineation of individual regions is difficult, particular care was taken to localize projection neurons with respect to such landmarks as the ventral pallidum (identified on the basis of GAD immunoreactivity), the diagonal band, and medial forebrain bundle. In addition, sections with fluorescent tracers or immunofluorescence were counterstained for Nissl substance in order to correlate tracer or immunopositive neurons with the cytoarchitecture of the basal forebrain. The majority of the cholinergic bulbopetal neurons are located in the medial half of the nucleus of the horizontal limb of the diagonal band (HDB), whereas only a few are located in its lateral half. A substantial number of cholinergic bulbopetal cells are also found in the sublenticular substantia innominata. A small number of cholinergic bulbopetal neurons, finally, are located in the ventrolateral portion of the nucleus of the vertical limb of the diagonal band. At the level of the crossing of the anterior commissure, approximately 17% of the bulbopetal neurons in the HDB are ChAT-positive. The noncholinergic bulbopetal cells are located mainly in the lateral half of the HDB. GAD-containing bulbopetal neurons are primarily located in the caudal part of the HDB, especially in its lateral part. About 30% of the bulbopetal projection neurons in the HDB are GAD-positive. A few GAD-positive bulbopetal cells, furthermore, are located in the ventral pallidum, anterior amygdaloid area, deep olfactory cortex, nucleus of the lateral olfactory tract, lateral hypothalamic area, and tuberomamillary nucleus. The topography of bulbopetal neurons was compared to other projection neurons in the HDB. After multiple injections of fluorescent tracer in the neocortex, retrogradely labeled neurons were concentrated in the most medial part of the HDB, while neurons projecting to the olfactory and entorhinal cortices were located in the ventral part of the HDB. These results show that the cells of the HDB can be divided into subpopulations based upon projection target as well as transmitter content. Furthermore, these subpopulations correspond, at least to a considerable extent, to areas that can be defined on cyto- and fibroarchitectural grounds.

Accumulation, acetylation, and releasability of diethylhomocholine from a sympathetic ganglion

Superior cervical ganglia of the cat perfused with [14C]diethylhomocholine [( 14C]DEHCh) synthesized acetyldiethylhomocholine (ADEHCh), but rather little of this ester was released by subsequent preganglionic nerve stimulation. Stimulation evoked the release of an appreciable amount of unchanged DEHCh when ganglia had been exposed to the analogue in the absence of choline (Ch), but did not do so when exposed to both Ch and DEHCh. The release of DEHCh was Ca2+ dependent, and was not the result of the release and subsequent hydrolysis of ADEHCh. This is the first clear demonstration of the release of an unacetylated compound from mammalian tissue; therefore, the characteristics of the transmitter release mechanism are further defined. The effect of preganglionic nerve stimulation on the uptake and acetylation of DEHCh was also measured. Stimulated ganglia accumulated approximately 4 times more labeled analogue and synthesized 7.5 times more ADEHCh than did rested ganglia. Stimulated ganglia perfused with 2-(4-phenylpiperidino)cyclohexanol, a compound considered to inhibit acetylcholine (ACh) release by inhibiting its transport into synaptic vesicles, accumulated 3.4 times as much and acetylated 6 times as much DEHCh as did rested ganglia. When the concentration of Mg2+ in the perfusion medium was increased to block ACh release, accumulation of the labelled analogue was enhanced by stimulation, but its acetylation was increased much less than during perfusion with normal medium. It is concluded that the synthesis of ADEHCh is subject to the same regulation as is ACh synthesis and that the activation of ester synthesis during activity can be dissociated from ester release.(ABSTRACT TRUNCATED AT 250 WORDS)

Postnatal development of neurons containing choline acetyltransferase in rat spinal cord: an immunocytochemical study

A monoclonal antibody to choline acetyltransferase (ChAT) has been used in an immunocytochemical study of the postnatal development of ChAT-containing neurons in cervical and thoracic spinal cord. Specimens from rat pups ranging in age from 1 to 28 days postnatal (dpn) were studied and compared with adult specimens (Barber et al., '84). The development of established cholinergic neurons, the somatic motoneurons and sympathetic preganglionic cells, has been described as has that of previously unidentified ChAT-positive neurons in the dorsal, intermediate, and central gray matter. Cell bodies of somatic and visceral motoneurons contained moderate amounts of ChAT-positive reaction product at birth that gradually increased in intensity until 14-21 dpn. The most intensely stained ChAT-positive neurons in 1-5-dpn specimens were named partition cells because this cell group extended from the central gray to an area dorsal to the lateral motoneurons, and thereby divided the spinal cord into dorsal and ventral halves. Partition cells were medium to large in size with 5-7 primary dendrites, and axons that, in fortuitous sections, could be traced into the ventrolateral motoneuron pools, the ventral funiculi, or the ventral commissure. Small ChAT-positive cells clustered around the central canal and scattered in laminae III-VI of the dorsal horn were detectable at birth. These neurons were moderately immunoreactive at 11-14 dpn and intensely ChAT positive by 21 dpn. The band of ChAT-positive terminal-like structures demonstrated in lamina III of adult specimens (Barber et al., '84) was first visible in 11-14-dpn specimens. By 28 dpn, both laminae I and III contained punctate bands that approximated the density of those observed in adult spinal cord. This investigation has demonstrated ChAT within individual neurons of developing spinal cord, and has identified a group of neurons, the partition cells, that exhibit intense ChAT-positive immunoreactivity earlier than any other putative cholinergic cells in spinal cord, including motoneurons. Another important observation has been that each ChAT-positive neuronal type achieves adult levels of staining intensity at different times during development. A likely explanation for this differential staining is that various groups of neurons acquire their mature concentration of ChAT molecules at different developmental stages. In turn, this may correlate with the maturation of cholinergic synaptic activity manifest by individual cells or groups of neurons.

Electron microscopic localization of choline acetyl transferase activity in the electric organ of Torpedo marmorata

The light microscopic method for demonstration of choline acetyltransferase (CAT) activity based on the formation of a lead mercaptide of free SH-acetyl Coenzyme A was adapted for electron microscopy. In samples of electric organ of Torpedo marmorata CAT activity was found to be restricted to synaptic vesicles and cysternae. The precipitate formed was mostly fine grained and distributed more or less evenly throughout the vesicles. Generally, the reaction product seemed not to adhere to the inner side of the vesicle membrane. CAT activity was found only in the presynaptic region of the synapse, neither the synaptic cleft nor the postsynaptic region reacted positively. CAT activity was found also within synaptic vesicles in nerve endings prepared from electric organ. Samples of Torpedo brain reacted positively too. Complete suppression of CAT activity with inhibitors, judged on the basis of lead mercaptide deposited, was rather difficult to achieve. From a group of 10 presumed enzyme inhibitors, only 2 compounds reacted satisfactorily, namely trans-1,2-dihydro-2-imino-4-(1-naphthylvinyl)-1-pyridine-ethanol hydrobromide and 5,5-dithio-bis-(2-nitrobenzoic acid) (3,3'-6). On the whole, the results obtained show the viability of the method used and furthermore it offers also some new insight into the turnover of acetylcholine, since it may be deduced from the results that under certain circumstances acetylcholine may be synthesized in synaptic vesicles.

Regional distribution of cholinergic neurons in human spinal cord transections in the patients with and without motor neuron disease

Regional distribution of enzymic activities in acetylcholine (ACh) metabolism was examined on thinly-sectioned transverse slices of human spinal cords obtained during autopsy of 5 motor neuron disease (MND) and 5 control patients without MND. Choline acetyltransferase (ChAT) activity was highly concentrated in the ventral horn regions (gray and white matters) of cervical, thoracic and lumbar spinal cord of non-MND patients. This enzyme activity was found to be remarkably low in the ventral gray and white matter of MND patients compared with that of the controls. Although the distribution of acetylcholinesterase (AChE) activity was found to be high in both ventral and dorsal gray matter of the spinal cord, little difference was observed between each corresponding region of MND and control patients, except relatively low enzyme activity in the cervical ventral horn region of MND patients. Muscarinic cholinergic receptors, examined as specific [3H]quinuclidinylbenzilate ([3H]QNB) binding, was also highly concentrated in the ventral and dorsal gray matter of the control spinal cord, and was strongly reduced in the ventral horn region of MND patients, indicating a quite similar distribution pattern of ChAT activity. These biochemical changes of cholinergic transmission system may be paralleled to the morphological degeneration of the spinal lower motor neurons in MND patients. Activity of 2',3'-cyclic nucleotide-3'-phosphodiesterase (CNPase), a marker enzyme of central myelin structure, was evenly distributed throughout the whole spinal cord section, without regard to the gray and white matter, of both MND and control patients.

Choline chloride fails to improve cognition of Alzheimer's disease

Seven mildly to moderately demented patients with Alzheimer's disease were treated with either placebo or choline chloride (50, 100 and 200 mg/kg/24 hrs) in a double blind, crossover study. Detailed psychometric analysis was carried out at the end of each two-week period of drug or placebo administration. No subjects showed significant overall improvement at any dose level despite more than a doubling of the baseline plasma choline level.

Topographical localization of choline acetyltransferase within the human spinal cord and a comparison with some other species

Choline acetyltransferase (ChAT), which is known to be a specific marker of cholinergic structures, was assayed in small tissue samples punched out from cryosections of human, bovine, cat and rat spinal cords. The relative distribution patterns of spinal ChAT were similar between the different species. An area of high activity in the ventrolateral part of the ventral horn was found. This activity is probably located in the motor neurons, as it could be traced into the ventral root region. In addition, in the dorsal horn of the cord from man and cow another area with high ChAT activity was found. Subcellular studies suggest that this activity is mainly located at nerve terminals.

Subcellular origin of cholinergic transmitter release from mouse brain

Samples of minced mouse forebrain were treated in a way that resulted in a high ratio of false cholinergic transmitter (acetylhomocholine) to true transmitter (acetylcholine) in a synaptic vesicle fraction, and a low ratio of false to true transmitter in the nerve terminal cytoplasm. The spontaneous release of cholinergic transmitters from this minced tissue occurred independently of calcium and had a ratio of false to true transmitter similar to that of the cytoplasm, whereas the evoked transmitter release required calcium and had a ratio of false to true transmitter similar to that of the vesicular fraction.

Changes in the monoamine containing neurones of the human CNS in senile dementia

In thirteen cases of senile dementia of the Alzheimer type severe loss of nerve cells from the locus caeruleus was frequently seen together with reductions in nucleolar volume and cytoplasmic RNA in surviving cells, averaging 14 and 21 per cent respectively. These histological findings were matched in two cases by biochemical measurements of loss of noradrenaline from all brain regions examined, ranging from 10 per cent in temporal cortex to 53 per cent in hypothalamus. By contrast, neither nucleolar volume nor cytoplasmic RNA was altered in cells of the substantia nigra, nor was dopamine content significantly altered in most regions. In vascular dementia neither noradrenaline nor dopamine metabolism was changed except in regions of local circulatory deficiency. These findings provide evidence of a primary degeneration of the noradrenergic system in Alzheimer type dementia.

Striatal nondopaminergic neurons: possible involvement in feeding and drinking behavior

Intracaudate injections of kainic acid destroy striatal neurons containing acetylcholine and gamma-aminobutyric acid but leave dopaminergic nerve terminals in this brain region intact. Rats injected with the drug are aphagic and adipsic, and have other behavioral abnormalities strikingly similar to those seen in animals with lesions in the dopaminergic nigrostriatal bundle.

Cholinergic Vesicles: Ability to Empty and Refill Independently of Cytoplasmic Acetylcholine

Incubation of minced mouse-forebrain tissues in lithium Krebs solution reduces the acetylcholine content of the vesicular fraction 70 percent without altering that of the cytoplasmic fraction. Depleted vesicular-bound acetylcholine can be restored with newly synthesized acetylcholine (formed from extracellular choline) independently of the cytoplasmic pool. Depletion of vesicular-bound acetylcholine does not facilitate the movement of preformed extracellular acetylcholine into vesicles.

The effect of disuse on cholinergic enzymes

1. The effects of disuse on the activity of choline acetyltransferase (ChAT) and acetylcholinesterase (AChE) have been investigated in the sciatic nerve and leg muscles of the rat. 2. Disuse was produced by blockade of nerve conduction by repeated subperineurial injection of tetrodotoxin (TTX), and the effects were compared to those of denervation. 3. After 8 days of disuse there was no change in neural ChAT activity in the sciatic nerves, anterior roots or intramuscular terminals. By contrast, surgical section of the sciatic nerve resulted in a marked decrease of ChAT in the nerve terminals. 4. Similarly, after 8 days of disuse there was no change in neural AChE activity in the sciatic nerves or anterior roots. 5. AChE activity in the disused muscles decreased by more than 50%, which was comparable to the effect of surgical denervation. 6. These results indicate that disuse produced by TTX blockade of nerve conduction does not affect the cholinergic enzymes ChAT and AChE in nerves, but does lead to a significant decrease in muscle AChE.

Ultrastructural localization of choline acetyltransferase in the CNS of rat

The ultrastructural localization of choline acetyltransferase in various regions of rat's CNS is studied. It is established that the reaction product is located in some structures of the neuronal perikarya--on the outer surface of the rough endoplasmic reticulum sacs, along the vesicular profiles and in the mitochondria. Electron dense material is found in the axon terminal as well as, where enzyme activity is detected in the cytoplasm, on the membrane of spherical and flat synaptic vesicles and in the mitochondria. These findings, the control results and literature data are discussed.