Cross-species and intraspecies reactivities of monoclonal antibodies against choline acetyltransferase

Topographic mapping between basal forebrain cholinergic neurons and the medial prefrontal cortex in mice

The basal forebrain cholinergic innervation of the medial prefrontal cortex (mPFC) is crucial for cognitive performance. However, little is known about the organization of connectivity between the basal forebrain and the mPFC in the mouse. Using focal virus injections inducing Cre-dependent enhanced yellow fluorescent protein expression in ChAT-IRES-Cre mice, we tested the hypothesis that there is a topographic mapping between the basal forebrain cholinergic neurons and their axonal projections to the mPFC. We found that ascending cholinergic fibers to the mPFC follow four pathways and that cholinergic neurons take these routes depending on their location in the basal forebrain. In addition, a general mapping pattern was observed in which the position of cholinergic neurons measured along a rostral to caudal extent in the basal forebrain correlated with a ventral to dorsal and a rostral to caudal shift of cholinergic fiber distribution in mPFC. Finally, we found that neurons in the rostral and caudal parts of the basal forebrain differentially innervate the superficial and deep layers of the ventral regions of the mPFC. Thus, a frontocaudal organization of the cholinergic system exists in which distinct mPFC areas and cortical layers are targeted depending on the location of the cholinergic neuron in the basal forebrain.

Multiple origins of cholinergic innervation of the cochlear nucleus

Acetylcholine (Ach) affects a variety of cell types in the cochlear nucleus (CN) and is likely to play a role in numerous functions. Previous work in rats suggested that the acetylcholine arises from cells in the superior olivary complex, including cells that have axonal branches that innervate both the CN and the cochlea (i.e. olivocochlear cells) as well as cells that innervate only the CN. We combined retrograde tracing with immunohistochemistry for choline acetyltransferase to identify the source of ACh in the CN of guinea pigs. The results confirm a projection from cholinergic cells in the superior olivary complex to the CN. In addition, we identified a substantial number of cholinergic cells in the pedunculopontine tegmental nucleus (PPT) and the laterodorsal tegmental nucleus (LDT) that project to the CN. On average, the PPT and LDT together contained about 26% of the cholinergic cells that project to CN, whereas the superior olivary complex contained about 74%. A small number of additional cholinergic cells were located in other areas, including the parabrachial nuclei.The results highlight a substantial cholinergic projection from the pontomesencephalic tegmentum (PPT and LDT) in addition to a larger projection from the superior olivary complex. These different sources of cholinergic projections to the CN are likely to serve different functions. Projections from the superior olivary complex are likely to serve a feedback role, and may be closely tied to olivocochlear functions. Projections from the pontomesencephalic tegmentum may play a role in such things as arousal and sensory gating. Projections from each of these areas, and perhaps even the smaller sources of cholinergic inputs, may be important in conditions such as tinnitus as well as in normal acoustic processing.

Cholinergic cells in the tegmentum send branching projections to the inferior colliculus and the medial geniculate body

The pontomesencephalic tegmentum (PMT) provides cholinergic input to the inferior colliculus (IC) and the medial geniculate body (MG). PMT cells are often characterized as projecting to more than one target. The purpose of this study was to determine whether individual PMT cholinergic cells, (1) innervate the auditory pathways bilaterally via collateral projections to left and right auditory thalamus; or, (2) innervate multiple levels of the auditory pathways via collateral projections to the auditory thalamus and inferior colliculus. We used multiple retrograde tracers to identify individual PMT cells that project to more than one target. We combined the retrograde tracer studies with immunohistochemistry for choline acetyltransferase to determine whether the projecting cells were cholinergic. We found that individual PMT cells send branching axonal projections to two or more auditory targets in the midbrain and thalamus. The collateral projection pattern that we observed most frequently was to the ipsilateral IC and ipsilateral MG. Cells projecting to both MGs were somewhat less common, followed by cells projecting to the contralateral IC and ipsilateral MG. Both cholinergic and non-cholinergic cells contribute to each of these projection patterns. Less often, we found cells that project to one IC and both MGs; there was no evidence for non-cholinergic cells in this projection pattern. It is likely that collateral projections from PMT cells could have coordinated effects bilaterally and at multiple levels of the ascending auditory pathways.

Cholinergic and non-cholinergic projections from the pedunculopontine and laterodorsal tegmental nuclei to the medial geniculate body in Guinea pigs

The midbrain tegmentum is the source of cholinergic innervation of the thalamus and has been associated with arousal and control of the sleep/wake cycle. In general, the innervation arises bilaterally from the pedunculopontine tegmental nucleus (PPT) and the laterodorsal tegmental nucleus (LDT). While this pattern has been observed for many thalamic nuclei, a projection from the LDT to the medial geniculate body (MG) has been questioned in some species. We combined retrograde tracing with immunohistochemistry for choline acetyltransferase (ChAT) to identify cholinergic projections from the brainstem to the MG in guinea pigs. Double-labeled cells (retrograde and immunoreactive for ChAT) were found in both the PPT (74%) and the LDT (26%). In both nuclei, double-labeled cells were more numerous on the ipsilateral side. About half of the retrogradely labeled cells were immunonegative, suggesting they are non-cholinergic. The distribution of these immunonegative cells was similar to that of the immunopositive ones: more were in the PPT than the LDT and more were on the ipsilateral than the contralateral side. The results indicate that both the PPT and the LDT project to the MG, and suggest that both cholinergic and non-cholinergic cells contribute substantially to these projections.

Projections from auditory cortex to midbrain cholinergic neurons that project to the inferior colliculus

We have shown that auditory cortex projects to cholinergic cells in the pedunculopontine tegmental nucleus (PPT) and laterodorsal tegmental nucleus (LDT). PPT and LDT are the sources of cholinergic projections to the inferior colliculus, but it is not known if the cortical inputs contact the cholinergic cells that project to the inferior colliculus. We injected FluoroRuby into auditory cortex in pigmented guinea pigs to label cortical projections to PPT and LDT. In the same animals, we injected Fast Blue into the left or right inferior colliculus to label PPT and LDT cells that project to the inferior colliculus. We processed the brain to identify cholinergic cells with an antibody to choline acetyltransferase, which was visualized with a green fluorescent marker distinguishable from both FluoroRuby and Fast Blue. We then examined the PPT and LDT to determine whether boutons of FluoroRuby-labeled cortical axons were in close contact with cells that were double-labeled with the retrograde tracer and the immunolabel. Apparent contacts were observed ipsilateral and, less often, contralateral to the injected cortex. On both sides, the contacts were more numerous in PPT than in LDT. The results indicate that auditory cortex projects directly to brainstem cholinergic cells that innervate the ipsilateral or contralateral inferior colliculus. This suggests that cortical projections could elicit cholinergic effects on both sides of the auditory midbrain.

Sources of cholinergic input to the inferior colliculus

We combined retrograde tracing with immunohistochemistry for choline acetyltransferase to identify the source of cholinergic input to the inferior colliculus (IC) in guinea pigs. Injection of a retrograde tracer into one IC labeled cells in many brainstem nuclei. Retrogradely-labeled cells that were also immunoreactive for choline acetyltransferase were identified in two nuclei in the midbrain tegmentum: the pedunculopontine tegmental nucleus (PPT) and the laterodorsal tegmental nucleus (LDT). More PPT and LDT cells project ipsilaterally than contralaterally to the IC and, on both sides, there are more projecting cells in the PPT than in the LDT. Double-labeled cells were not found in any other brainstem nucleus. A common feature of cholinergic cells in PPT and LDT is collateral projections to multiple targets. We placed different retrograde tracers into each IC to identify cells in PPT and LDT that project to both ICs. In both PPT and LDT, a substantial proportion (up to 57%) of the immunoreactive cells that contained tracer from the contralateral IC also contained tracer from the ipsilateral IC. We conclude that acetylcholine in the IC originates from the midbrain tegmental cholinergic nuclei: PPT and LDT. These nuclei are known to participate in arousal, the sleep/wake cycle and prepulse inhibition of acoustic startle. It is likely that the cholinergic input to the IC is directly associated with these functions.

Distribution of cholinergic cells in guinea pig brainstem

We used an antibody to choline acetyltransferase (ChAT) to label cholinergic cells in guinea pig brainstem. ChAT-immunoreactive (IR) cells comprise several prominent groups, including the pedunculopontine tegmental nucleus, laterodorsal tegmental nucleus, and parabigeminal nucleus, as well as the cranial nerve somatic motor and parasympathetic nuclei. Additional concentrations are present in the parabrachial nuclei and superior colliculus. Among auditory nuclei, the majority of ChAT-IR cells are in the superior olive, particularly in and around the lateral superior olive, the ventral nucleus of the trapezoid body and the superior paraolivary nucleus. A discrete group of ChAT-IR cells is located in the sagulum, and additional cells are scattered in the nucleus of the brachium of the inferior colliculus. A group of ChAT-IR cells lies dorsal to the dorsal nucleus of the lateral lemniscus. A few ChAT-IR cells are found in the cochlear nucleus and the ventral nucleus of the lateral lemniscus. The distribution of cholinergic cells in guinea pigs is largely similar to that of other species; differences occur mainly in cell groups that have few ChAT-IR cells. The results provide a basis for further studies to characterize the connections of these cholinergic groups.

Distribution of choline acetyltransferase immunoreactivity in the brain of an elasmobranch, the lesser spotted dogfish (Scyliorhinus canicula)

Although the distribution of cholinergic cells is remarkably similar across the vertebrate species, no data are available on more primitive species, such as cartilaginous fishes. To extend the evolutionary analysis of the cholinergic systems, we studied the distribution of cholinergic neurons in the brain and rostral spinal cord of Scyliorhinus canicula by immunocytochemistry using an antibody against the enzyme choline acetyltransferase (ChAT). Western blot analysis of brain extracts of dogfish, sturgeon, trout, and rat showed that this antibody recognized similar bands in the four species. Putative cholinergic neurons were observed in most brain regions, including the telencephalon, diencephalon, cerebellum, and brainstem. In the retrobulbar region and superficial dorsal pallium of the telencephalon, numerous small pallial cells were ChAT-like immunoreactive. In addition, tufted cells of the olfactory bulb and some cells in the lateral pallium showed faint immunoreactivity. In the preoptic-hypothalamic region, ChAT-immunoreactive (ChAT-ir) cells were found in the preoptic nucleus, the vascular organ of the terminal lamina, and a small population in the caudal tuber. In the epithalamus, the pineal photoreceptors were intensely positive. Many cells of the habenula were faintly ChAT-ir, but the neuropil of the interpeduncular nucleus showed intense ChAT immunoreactivity. In the pretectal region, ChAT-ir cells were observed only in the superficial pretectal nucleus. In the brainstem, the somatomotor and branchiomotor nuclei, the octavolateral efferent nucleus, and a cell group just rostral to the Edinger-Westphal (EW) nucleus contained ChAT-ir neurons. In addition, the trigeminal mesencephalic nucleus, the nucleus G of the isthmus, some locus coeruleus cells, and some cell populations of the vestibular nuclei and of the electroreceptive nucleus of the octavolateral region exhibited ChAT immunoreactivity. In the reticular areas of the brainstem, the nucleus of the medial longitudinal fascicle, many reticular neurons of the rhombencephalon, and cells of the nucleus of the lateral funiculus were immunoreactive to this antibody. In the cerebellum, Golgi cells of the granule cell layer and some cells of the cerebellar nucleus were also ChAT-ir. In the rostral spinal cord, ChAT immunoreactivity was observed in cells of the motor column, the dorsal horn, the marginal nucleus (a putative stretch-receptor organ), and in interstitial cells of the ventral funiculus. These results demonstrate for the first time that cholinergic neurons are distributed widely in the central nervous system of elasmobranchs and that their cholinergic systems have evolved several characteristics that are unique to this group.

Calbindin D-28k and choline acetyltransferase are expressed by different neuronal populations in pedunculopontine nucleus but not in nucleus basalis in squirrel monkeys

Single- and double-immunostaining procedures were used to study the distribution of the acetylcholine synthesizing enzyme choline acetyltransferase (ChAT) and the calcium binding protein calbindin D-28k in the nucleus basalis of Meynert (nbM) and in the pedunculopontine nucleus (PPN) of the squirrel monkey (Saimiri sciureus). As expected from previous studies in other primates, including humans, the nbM in the squirrel monkey is enriched with large ChAT-immunoreactive neurons that form clusters in the substantia innominata. Some ChAT-positive neurons are also scattered more dorsally within the internal and external medullary laminae of the pallidal complex. A smaller number of calbindin-immunoreactive cells occur in the same locations and their mean cross-sectional somatic area (424 microns 2) is not significantly different from that of the ChAT-immunoreactive cells (450 microns 2). Furthermore, 60% of the ChAT-immunopositive cells in the nbM display calbindin immunoreactivity. Most of these double-immunoreactive neurons occur in the typical clusters of the nbM, whereas the large neurons scattered in between the clusters display ChAT immunoreactivity only. In the PPN, ChAT-positive neurons are scattered around and partly within the superior cerebellar peduncle and also form a dense cluster in the lateral portion of the mesopontine tegmentum. Calbindin-immunoreactive cells also abound around the superior cerebellar peduncle, but they are more sparsely distributed and cover a larger sector of the tegmentum than the ChAT-positive neurons. These calbindin-immunoreactive cells are significantly smaller (200 microns 2) than the ChAT-immunoreactive cells (471 microns 2) and no double-immunostained neurons are present in the PPN.(ABSTRACT TRUNCATED AT 250 WORDS)

Organization of central cholinergic neurons revealed by combined in situ hybridization histochemistry and choline-O-acetyltransferase immunocytochemistry

Digoxigenin-labeled riboprobes and in situ hybridization of choline-O-acetyltransferase mRNA, both alone and in combination with immunohistochemical procedures for the synthetic enzyme of acetylcholine, were used to map the topography of putative cholinergic neurons in the rat central nervous system. Only the anti-sense riboprobe yielded specific labeling, which was absent in brain sections processed with sense riboprobe. Telencephalic neurons demonstrating the mRNA for choline-O-acetyltransferase and choline-O-acetyltransferase-like immunoreactivity were found in the caudate-putamen nucleus, nucleus accumbens, olfactory tubercule, Islands of Calleja complex, medial septal nucleus, vertical and horizontal limbs of the diagonal band, substantia innominata, nucleus basalis, and nucleus of the ansa lenticularis, as well as occasionally in the amygdala. Neurons in the cerebral cortex, hippocampus, and primary olfactory structures did not demonstrate hybridization signal, even though some cells in those areas were observed to exhibit choline-O-acetyltransferase-like immunopositivity. Thalamic cells were devoid of hybrido- and immunoreactivity, with the exception of several neurons located primarily in the ventral two-thirds of the medial habenula. A few cell bodies labeled with riboprobe and co-localizing choline-O-acetyltransferase-like immunopositivity were found in the lateral hypothalamus, caudal extension of the internal capsule, and zona incerta. Neurons in the pedunculopontine and laterodorsal tegmental nuclei evinced moderate hybridization signal, whereas cells of the parabigeminal nucleus were very weakly reactive. In contrast, motor neurons of the cranial nerve nuclei demonstrated high levels of choline-O-acetyltransferase mRNA and choline-O-acetyltransferase-like immunoreactivity. Putative cholinergic somata in the ventral horns and intermediolateral cell columns of the spinal cord and around the central canal were also labeled with riboprobe. It is concluded that hybridocytochemistry with digoxigenin-labeled riboprobes confirms the existence of cholinergic neurons in most of the neural regions believed to contain them on the basis of acetylcholinesterase pharmacohistochemistry and choline-O-acetyltransferase immunocytochemistry, with the prominent exceptions of the cerebral cortex, hippocampus, olfactory bulb, anterior olfactory nucleus, and caudal raphe nuclei, which apparently do not possess neurons expressing detectable levels of the mRNA for the synthetic enzyme of acetylcholine.

Cholinergic neurons in the rat central nervous system demonstrated by in situ hybridization of choline acetyltransferase mRNA

Digoxigenin-labeled RNA probes and in situ hybridization histochemistry were used to examine choline acetyltransferase gene expression in the rat central nervous system. Hybridization signal was present only in brain sections processed with the antisense riboprobe. The sense probe did not yield labeling, further validating the specificity of tissue reactivity. Telencephalic neurons containing the mRNA for the cholinergic synthetic enzyme were found in the caudate-putamen nucleus, nucleus accumbens, olfactory tubercule, islands of Calleja complex, medial septal nucleus, vertical and horizontal limbs of the diagonal band, substantia innominata, nucleus basalis, and nucleus of the ansa lenticularis. Some somata evincing hybridization signal were observed in the anterior amygdalar area, and an occasional such cell was seen in the basolateral and central amygdalar nuclei. Neurons in the cerebral cortex, hippocampus, and primary olfactory structures did not demonstrate hybridocytochemically detectable amounts of choline acetyltransferase mRNA. Thalamic cells were devoid of reactivity, with the exception of several neurons located primarily in the ventral two-thirds of the medial habenula. A few somata labeled with riboprobe were found in the lateral hypothalamus, caudal extension of the internal capsule, and zona incerta. Neurons in the pedunculopontine and laterodorsal tegmental nuclei were moderately reactive, whereas cells of the parabigeminal nucleus exhibited a very weak hybridization signal. No somata in the brainstem raphe nuclei, including raphe obscurus and raphe magnus, were observed to bind riboprobe. In contrast, motor neurons of the cranial nerve nuclei demonstrated relatively large amounts of choline acetyltransferase mRNA. Putative cholinergic somata in the ventral horns and intermediolateral cell columns of the spinal cord were also labeled with riboprobe, as were a few cells around the central canal. We conclude that hybridocytochemistry with digoxigenin-labeled riboprobes confirms the existence of cholinergic neurons (i.e. those that synthesize and use acetylcholine as a neurotransmitter) in most of the neural regions deduced to contain them on the basis of previous histochemical and immunocytochemical data. Notable exceptions are the cerebral cortex and hippocampus, which do not possess neurons expressing detectable levels of choline acetyltransferase mRNA.

Comparative effects of ibotenic acid- and quisqualic acid-induced lesions of the substantia innominata on attentional function in the rat: further implications for the role of the cholinergic neurons of the nucleus basalis in cognitive processes

Two experiments examined the effects of excitotoxic lesions of the substantia innominata on cholinergic activity in the neocortex and on performance in a paradigm measuring selective attention in the rat. In Expt. 1, ibotenate-induced lesions produced approximately 30% reductions in cortical choline acetyltransferase (ChAT) activity, and damage to wide regions of the substantia innominata and ventral pallidum. The rats were impaired in their ability to localize brief visual targets in a serial reaction time task, as measured by reduced choice accuracy. This impairment was particularly evident at short stimulus durations, but the lesioned rats did not exhibit evidence of primary visual sensory dysfunction and exhibited only minor deficits when the stimuli were presented unpredictably. The deficit was exacerbated when distracting white noise was interpolated into the task. The rats with lesions were also slower to respond correctly, probably resulting partly from the adoption of a speed/error trade-off strategy, and were slower to collect earned food pellets, although they made no more errors of omission than controls. In Expt. 2, quisqualate-induced lesions produced fewer signs of non-specific damage and 50% reductions in cortical ChAT activity. This lesion produced generally qualitatively similar, but weaker effects to those of ibotenate-induced lesions. It was notable that many of the deficits following either ibotenate- or quisqualate-induced lesions lasted for several months after surgery. The results are discussed in terms of the cholinergic hypothesis of cognitive dysfunction. It is argued that lesions of the substantia innominata, including the magnocellular cholinergic neurons of the nucleus basalis of Meynert, produce deficits in attentional processing, which may not result from damage specifically to cholinergic cells. However, the longevity of the effects makes these preparations suitable for further exploration of the restorative effects of cholinergic treatments.

Comparative effects of quisqualic and ibotenic acid-induced lesions of the substantia innominata and globus pallidus on the acquisition of a conditional visual discrimination: differential effects on cholinergic mechanisms

Two experiments tested the hypothesis that the deficits in conditional discrimination learning produced by ibotenic acid-induced lesions of the ventral pallidum and substantia innominata are produced by loss of the magnocellular cholinergic cells in the nucleus basalis and adjacent regions. Experiment 1 replicated the previously reported deficit in conditional learning produced by ibotenate-induced lesions of the ventral pallidum/substantia innominata, but failed to demonstrate any restoration of learning by a subchronic regimen of the acetylcholinesterase inhibitor physostigmine sufficient to produce significant (30%), but equivalent, degrees of inhibition in the frontal cortex of ventral pallidum/substantia innominata-lesioned or sham-operated rats. Experiment 2 examined the effects of quisqualic acid-induced lesions of the ventral pallidum/substantia innominata. According to most of the measures of learning employed, the quisqualic acid-induced lesion of the ventral pallidum/substantia innominata failed to impair conditional learning, even though the quisqualate-induced lesion produced greater degrees of cholinergic neuron destruction than the ibotenate-induced lesion, as measured in terms of reductions in cortical choline acetyltransferase activity (44% vs 27%). Although consideration of individual data suggested that very high (60%) levels of choline acetyltransferase reduction in Experiment 2 might have detrimental effects of conditional learning, the overall failure of the quisqualate-induced lesions of the ventral pallidum/substantia innominata to impair learning is to be contrasted with the significant behavioural effects of ibotenate-induced lesions. Histological and immunocytochemical analysis showed that the quisqualate-induced lesion, unlike that produced by ibotenate, tended to produce less damage to the overlying dorsal globus pallidus and to parvocellular neurons of the ventral pallidum/substantia innominata, thus implicating these nonspecific effects of ibotenate-induced lesions in their behavioural effects. The present results question previous interpretations of the behavioural effects of ibotenate-induced lesions of the ventral pallidum/substantia innominata in terms of damage inflicted on the cortically-projecting cholinergic cells of the nucleus basalis, and suggest that quisqualic acid, although also nonspecific in its excitotoxic effects, is nevertheless more selective for producing damage to cholinergic neurons in the ventral pallidum/substantia innominata than ibotenic acid.

Distribution and some projections of cholinergic neurons in the brain of the common marmoset, Callithrix jacchus

The distribution of choline acetyltransferase-immunoreactive (ChAT-IR) neurons was studied in the brain of the common marmoset by using immunohistochemistry. ChAT-IR neurons were found in the medial septal nucleus, vertical and horizontal limb nuclei of the diagonal band, the nucleus basalis of Meynert, pedunculopontine nucleus and laterodorsal tegmental nucleus, and also in the striatum, habenula, and brainstem cranial nerve motor nuclei. The organization of ChAT-IR neurons in the basal forebrain, midbrain, and pons is consistent with the Ch1-Ch6 nomenclature introduced by Mesulam et al. ('83). The combination of the retrograde transport of HRP-WGA with ChAT immunohistochemistry revealed the distribution of neurons in the Ch4 cell group projecting to the dorsolateral prefrontal cortex. The activity of ChAT was highest in limbic cortical structures, such as the hippocampus, and lowest in association areas of the neocortex. Lesions at various loci in the basal forebrain resulted in differential patterns of ChAT loss in the cortex, which suggests some degree of topographical organization of Ch4 projections to the cortical mantle.

Immunohistochemistry of choline acetyltransferase in the guinea pig brain

Choline acetyltransferase (ChAT) was localized immunohistochemically within the brain of the guinea pig using a monoclonal antibody. ChAT was found in the cytoplasm of cell bodies and primary dendrites of neurons located in striatum, basal forebrain, cranial nerve motor nuclei and scattered cells in the pons. The greatest numbers of immunoreactive neurons were located in the diagonal band of Broca, medial septum and striatum. Distinct immunoreactive fibers were not visible using this antibody, although a diffuse immunostaining was present in the same nuclear regions as well as in the nerve roots of cranial nerve nuclei and the interpeduncular nuclei. Results of the present study agree closely with other previous reports of acetylcholine distributions.

Molecular biology and neurobiology of choline acetyltransferase

In the 45 years since the first description of choline acetyltransferase (ChAT; EC 2.3.1.6.), significant progress has been made in characterizing the molecular properties of this important neurotransmitter synthetic enzyme. We are now on the verge of understanding its genetic regulation and biological function(s). The Drosophila cDNA has been cloned, sequenced, and expressed in both a eucaryotic and a procaryotic system. The levels of ChAT specific mRNA have been determined during Drosophila development. Monoclonal and polyclonal antibodies have been produced to the enzyme from a variety of sources and used for biochemical and immunocytochemical studies. Two well characterized genetic systems have identified the ChAT gene and described a series of useful alleles. As a nervous system specific protein expressed only in the subset of neurons using acetylcholine as a neurotransmitter, ChAT is a good model for uncovering the processes and factors responsible for regulating genes involved in neurotransmitter phenotype selection and maintenance. Recent studies have described the purification of a cholinergic factor from muscle conditioned medium and indicated the potential importance of nerve growth factor (NGF) for regulating ChAT expression in the central nervous system. These factors, or ones remaining to be discovered, may be involved in the etiology or disease process of neurodegenerative nervous system disorders such as Alzheimer's disease.

The effects of excitotoxic lesions of the substantia innominata, ventral and dorsal globus pallidus on the acquisition and retention of a conditional visual discrimination: implications for cholinergic hypotheses of learning and memory

The effects of ibotenic acid-induced lesions of the ventral pallidum/substantia innominata region, the dorsal pallidum or both on the acquisition and retention of a conditional visual discrimination have been studied in the rat. Lesions of the ventral pallidum and large lesions of the dorsal and ventral pallidum severely impaired both the acquisition and retention of the conditional discrimination. Dorsal pallidal lesions had similar, but less marked effects. The same lesions also impaired the retention of a passive avoidance task, but had no effect on a conditioned taste aversion. Neurobiological investigations revealed that the lesions destroyed cholinergic neurons in the magnocellular nucleus basalis and caused reductions in cortical choline acetyltransferase activity of about 30-40%. Tract-tracing experiments indicated that the lesions destroyed, in particular, cholinergic neurons projecting to the frontal dorsolateral cortex and also those projecting to more posterior cortex, but not the occipital lobes. Contingency analysis of the behavioural, neurochemical and neuroanatomical data indicated that those animals with the largest decreases in choline acetyltransferase activity, or the largest areas of neuronal loss in the ventral and dorsal globus pallidus, were most impaired in the retention of the conditional discrimination. The results do not, therefore, indicate a simple relationship between cholinergic neuronal loss and the retention of response rules essential for performance of the task ("reference memory"). The relevance of the results to cholinergic hypotheses of learning and memory is discussed.

Choline acetyltransferase immunohistochemical staining in the goldfish (Carassius auratus) brain: evidence that the Mauthner cell does not contain choline acetyltransferase

In the hatchetfish, the Mauthner cell (M-cell) is thought to be cholinergic based on electrophysiological studies using cholinergic agents and on the localization of acetylcholinesterase (AChE) and alpha-bungarotoxin to M-cell-giant fiber synapses. Immunocytochemical studies have shown that mammalian and non-mammalian cholinergic neurons stain positive for choline acetyltransferase (ChAT), the enzyme responsible for synthesizing acetylcholine. We processed tissue from the goldfish (Carassius auratus) for the immunohistochemical detection of ChAT using the monoclonal antibody AB8 and the peroxidase-antiperoxidase procedure. ChAT immunoreactivity was found in selected areas of the goldfish brain including the cranial nerve nuclei and the ventral horn motoneurons of the spinal cord. Interestingly, the M-cell soma which stains positive for AChE was ChAT negative. This immunohistochemical evidence does not support cholinergic functioning of the Mauthner cell.

Ultrastructural characterization of choline acetyltransferase-containing neurons in the basal forebrain of rat: evidence for a cholinergic innervation of intracerebral blood vessels

The ultrastructural morphology and vascular associations of cholinergic neurons in the horizontal limb of the nucleus of the diagonal band of Broca (nDBBhl) and amygdala of rat were determined by the immunocytochemical localization of choline acetyltransferase (ChAT), the acetylcholine biosynthetic enzyme. Within the nDBBhl peroxidase reaction product was distributed throughout the cytoplasm of selectively labeled neuronal perikarya and dendrites. Labeled perikarya were characterized by an oval cell body (7-10 microns X 17-26 microns in diameter) in which was located a large nucleus and often a prominent nucleolus. Dendrites were by far the most numerous immuno-labeled profiles in the nDBBhl. The labeled dendrites had a cross-sectional diameter of 0.4-4.6 microns and contained numerous mitochondria and microtubules. Approximately 10% of all immunolabeled dendrites received synaptic contacts from unlabeled presynaptic boutons. In contrast to the relatively large number of ChAT-labeled dendrites within the nDBBhl, ChAT-positive axons were less frequently observed and immunolabeled axon terminals were never detected. The labeled axons had an outside diameter of 0.4-1.4 micron and were myelinated. The absence or relative paucity of immunolabeled terminals in the nDBBhl indicates that most if not all of the cholinergic perikarya within this nucleus are efferent projection neurons. The nDBB is known to have widespread projections to many areas of the neocortex, hippocampus, and amygdala. In the present study we examined the amygdala and observed many ChAT-labeled axon boutons. The immunolabeled varicosities contained numerous agranular vesicles and although ChAT-positive terminals were in direct contact with unlabeled neuronal elements within the amygdala, few if any synaptic densities were detected in a single plane of section. With respect to the vasculature, immunolabeled perikarya and dendrites within the nDBBhl and axon terminals in the amygdala were often in direct apposition to blood vessels. In many instances the labeled profile was observed lying directly on the basal lamina of a capillary endothelial cell. In no instance, however, were membrane densities observed. The presence of cholinergic neuronal elements contacting the vessel wall provides morphologic evidence suggesting that the neurogenic control of cerebral vasculature is in part mediated via a cholinergic mechanism.

The distribution of choline acetyltransferase in the rat amygdaloid complex and adjacent cortical areas, as determined by quantitative micro-assay and immunohistochemistry

The distribution of choline acetyltransferase (ChAT) within the amygdaloid complex has been studied to evaluate what should primarily represent the terminal field of the cholinergic projection from the basal forebrain. Two currently available methods have been combined for the comparison: immunohistochemistry with a monoclonal antibody against ChAT, by a double peroxidase-antiperoxidase procedure, and quantitative histochemistry involving micro-assay of the ChAT activity of contiguous microdissected samples. Both methods indicate prominent ChAT activity in the basolateral amygdaloid nucleus (especially rostrally), the nucleus of the lateral olfactory tract (especially layer II), and the amygdalohippocampal area. Regions of lower ChAT activity were not accurately represented by the immunohistochemistry, but could be discriminated by the quantitative assays. Lowest activity was found in the medial nucleus of the amygdala. Most other regions had activities at least as high as average brain or neocortex. Gradients of enzyme activity were found within several regions, including the basolateral and lateral amygdaloid nuclei and the nearby posterior piriform cortex. In the piriform cortex, a region of particularly high ChAT activity was found at its medial edge near the nucleus of the lateral olfactory tract. The immunohistochemical method shows a few intensely reactive somata in layer III within this zone. Comparison of the results seen with immunohistochemistry and quantitative histochemistry suggests an advantage in using them together, since their respective strengths and weaknesses tend to complement each other.

The localization of central cholinergic neurons

Over the past decade our understanding of the localization of central cholinergic neurons has greatly increased. Interest in these systems has also intensified due to the involvement of cholinergic mechanisms in Alzheimer's disease. The distribution of central cholinergic neurons is reviewed, focusing on recent work in experimental animals. The pharmacohistochemical procedure for acetylcholinesterase and the development of antibodies to choline acetyltransferase are two of the major technical advances that have shaped our knowledge of the distribution of central cholinergic neurons. The results, advantages and limitations of both techniques are discussed. A discussion of the phenomenon of coexistence of acetylcholine with neuroactive peptides in central neurons is also included.

Distribution of central cholinergic neurons in the baboon (Papio papio). I. General morphology

The morphological characteristics of cholinergic neurons in the central nervous system (CNS) of the baboon (Papio papio) were studied by choline acetyltransferase (ChAT) immunohistochemistry and acetylcholinesterase (AChE) pharmacohistochemistry. The distributions of central cholinergic neurons as visualized by these two histochemical techniques were similar in most, but not all regions of the brain and spinal cord. Based upon these observations, central cholinergic neurons that are immunoreactive to ChAT and intensely stained for AChE by the pharmacohistochemical procedure can be divided into four major groups: (1) those in the caudate nucleus, putamen, nucleus accumbens and anterior perforated substance. These ChAT-containing and AChE-intense neurons are large and multipolar, and are scattered throughout these structures. (2) The rostral cholinergic column, which consists of a continuous mass of cholinergic perikarya situated in the medial septal nucleus, nucleus of the diagonal band, and nucleus basalis (Meynert). The ChAT-immunoreactive and AChE-intense cell bodies of the nucleus basalis are a prominent feature in the basal forebrain of the baboon. The labeled neurons are large, multipolar, and hyperchromic and show a tendency to aggregate in cell clusters. These cells are distributed within the full extent of the substantia innominata, often being associated with subcortical fiber networks such as the medullary laminae of the globus pallidus. (3) The caudal cholinergic column, which consists of a continuous group of cholinergic neurons in the caudal midbrain and pontine tegmentum. The rostral component of this group of cells is the nucleus tegmenti pedunculopontinus (subnucleus compacta) and it extends caudally to include the laterodorsal tegmental nucleus. Compared to that in other species the nucleus tegmenti pedunculopontinus in the baboon appears to occupy a relatively greater volume and is composed of a greater number of cholinergic neurons. The cells of the caudal column are large and hyperchromic. (4) Nuclei of origin of somatic and visceral efferents of the cranial nerves (III, IV, V, VI, VII, IX, X, XI, XII) and spinal nerves. In addition to these major cholinergic cell groups, a small population of ChAT-positive and AChE-intense cell bodies can be observed at the floor of the fourth ventricle and in lamina VII and X of the cervical cord. The present findings indicate that although some differences exist, the overall distribution and morphological features of cholinergic cell bodies identified in the baboon brain and spinal cord are similar to those demonstrated previously in investigations of the rhesus monkey and nonprimates.

Monoclonal antibodies in enzyme research: present and potential applications

Hybridoma antibodies are powerful tools. Their impact is already apparent in many areas of basic and applied research. In contrast, their impact is just beginning to be felt in enzymology. The existing literature on monoclonal antibodies to enzymes and isozymes, reviewed in this article, is as yet largely descriptive. However, the potential applications discussed herein promise to revolutionize existing strategies of unraveling the basic biochemistry, immunochemistry, and developmental, somatic cell, and molecular genetics of enzymes and isozymes. At a clinical level, monoclonal antibodies to enzymes promise to radically improve the current modalities of diagnosis and therapy in clinical enzymology and oncology. It is becoming increasingly apparent that the future applications of hybridoma antibodies to enzymes and isozymes appear to be limited only by our imagination.

Immunocytochemical identification of cholinergic neurons in the monkey central nervous system using monoclonal antibodies against choline acetyltransferase

A monoclonal antibody directed against rat brain choline acetyltransferase (ChAT) was used to stain cholinergic nerve cells within the brain and spinal cord of macaques. ChAT immunoreactivity was seen in motor neurons of the brainstem and spinal cord, in large neurons of the striatum, and in large neurons in the basal forebrain (medial septum--diagonal band--nucleus basalis complex); each of these groups of neurons is believed to be cholinergic. The ability to visualize cholinergic neurons in the nervous system of primates provides a new approach to the study of cholinergic systems in health and disease.

A comparison of the distribution of central cholinergic neurons as demonstrated by acetylcholinesterase pharmacohistochemistry and choline acetyltransferase immunohistochemistry

The topographical distribution of cholinergic cell bodies has been studied in the rat brain and spinal cord by choline acetyltransferase (ChAT)-immunohistochemistry and acetylcholinesterase (AChE)-pharmacohistochemistry using diisopropylfluorophosphate (DFP). The ChAT-containing cells and the cells that stained intensely for AChE 4-8 hr after DFP were mapped in detail on an atlas of the forebrain (telencephalon, diencephalon) hindbrain (mesencephalon, rhombencephalon) and cervical cord (C2, C6). Striking similarities were observed between ChAT-positive cells and neuronal soma that stained intensely for AChE both in terms of cytoarchitectural characteristics, and with respect to the distribution of the labelled cells in many areas of the central nervous system (CNS). In the forebrain these areas include the caudatoputamen, nucleus accumbens, medial septum, nucleus of the diagonal band, magnocellular preoptic nucleus and nucleus basalis magnocellularis. In contrast, a marked discrepancy was observed in the hypothalamus and ventral thalamus where there were many neurons that stained intensely for AChE, but where there was an absence of ChAT-positive cells. No cholinergic perikarya were detected in the cerebral cortex, hippocampus, amygdala and dorsal diencephalon by either histochemical procedure. In the hindbrain, all the motoneurons constituting the well-established cranial nerve nuclei (III-VII, IX-XII) contained ChAT and exhibited intense staining for AChE. Further, a close correspondence was observed in the distribution of labeled neurons obtained by the two histochemical procedures in the midbrain and pontine tegmentum, including the laterodorsal tegmental nucleus, some areas in the caudal pontine and bulbar reticular formation, and the central gray of the closed medulla oblongata. On the other hand, AChE-intense cells were found in the nucleus raphe magnus, ventral part of gigantocellular reticular nucleus, and flocculus of the cerebellum, where ChAT-positive cells were rarely observed. According to both techniques, no positive cells were seen in the cerebellar nuclei, the pontine nuclei, or the nucleus reticularis tegmenti pontis. Large ventral horn motoneurons and, occasionally, cells in the intermediomedial zone of the cervical cord displayed ChAT-immunoreactivity and intense AChE staining. On the other hand, AChE-intense cells were detected in the dorsal portion of the lateral funiculus, but immunoreactive cells were not found in any portion of the spinal cord white matter.(ABSTRACT TRUNCATED AT 400 WORDS)

Distribution of cholinergic neurons in rat brain: demonstrated by the immunocytochemical localization of choline acetyltransferase

The neuroanatomical location and cytological features of cholinergic neurons in the rat brain were determined by the immunocytochemical localization of the biosynthetic enzyme, choline acetyltransferase (ChAT). Perikarya labeled with ChAT were detected in four major cell groups: (1) the striatum, (2) the magnocellular basal nucleus, (3) the pontine tegmentum, and (4) the cranial nerve motor nuclei. Labeled neurons in the striatum were observed scattered throughout the neostriatum (caudate, putamen) and associated areas (nucleus accumbens, olfactory tubercle). Larger ChAT-labeled neurons were seen in an extensive cell system which comprises the magnocellular basal nucleus. This more or less continuous set of neuronal clusters consists of labeled neurons in the nucleus of the diagonal band (horizontal and vertical limbs), the magnocellular preoptic nucleus, the substantia innominata, and the globus pallidus. Labeled neurons in the pontine tegmentum were seen as a group of large neurons in the caudal midbrain, dorsolateral to the most caudal part of the substantia nigra, and extended in a caudodorsal direction through the midbrain reticular formation into the area surrounding the superior cerebellar peduncle. The neurons in this latter group constitute the pedunculopontine tegmental nucleus (PPT). An additional cluster of cells was observed medially adjacent to the PPT, in the lateral part of the central gray matter at the rostral end of the fourth ventricle. This group corresponds to the laterodorsal tegmental nucleus. Large ChAT-labeled neurons were also observed in all somatic and visceral motor nerve nuclei. The correspondence of the distribution of ChAT-labeled neurons identified by our methods to earlier immunocytochemical and acetylcholinesterase histochemical studies and to connectional studies of these groups argues for the specificity of the ChAT antibody used.

Co-localization of acetylcholinesterase and choline acetyltransferase in the rat cerebrum

Acetylcholinesterase-histochemistry has been widely used for localizing cholinergic neurons despite specificity problems. The distribution of cells stained with this method has never been directly compared on a histochemical level with the specific cholinergic marker, choline acetyltransferase. We recently reported the immunohistochemical localization of choline acetyltransferase using monoclonal antibodies [Levey A. I., Armstrong D., Atweh S. F., Terry R. D. & Wainer B. H. (1983) J. Neurosci 3, 1-9]. Here we report the development of a combined histochemical and immunohistochemical method for the co-localization of the 2 cholinergic markers, and their comparison in the rat cerebrum. Although the precise relationship between the markers was complex, the important results were: (1) all neurons which contained choline acetyltransferase also contained some acetylcholinesterase; (2) many acetylcholinesterase-containing neurons did not contain any demonstrable choline acetyltransferase; (3) all neurons which stained intensely for acetylcholinesterase in the neostriatum and basal forebrain also contained choline acetyltransferase; and (4) many choline acetyltransferase-containing neurons did not stain intensely for acetylcholinesterase. The results corroborate the assumption that choline acetyltransferase is a more specific marker for cholinergic neurons than acetylcholinesterase. Intense staining for acetylcholinesterase can be reliably used in some regions of the cerebrum for identifying cholinergic neurons, however, it should be recognized that this criterion s not essential for all cholinergic neurons.

Immunochemical studies of bovine and human choline-O-acetyltransferase using monoclonal antibodies

Immunochemical properties of bovine and human choline acetyltransferase (ChAT, EC 2.3.1.6, acetyl-CoA:choline-O-acetyltransferase) were studied using six monoclonal antibodies (AB1, AB5, AB6, AB7, AB8, and AB9) reactive with the enzyme. All antibodies except AB1 bound specifically to two proteins of 68,000 and 70,000 MW on "Western" blots of sodium dodecyl sulfate-polyacrylamide gels containing human or bovine ChAT. The enzyme was specifically absorbed to immobilized antibody and could not be eluted by low pH and/or high salt concentrations although the enzyme retained activity on the immunoabsorbent. Pure bovine enzyme consisting of the same two proteins as seen in the Western blotting studies was eluted from immobilized AB1 in the presence of sodium dodecyl sulfate. Although active enzyme could not be eluted from immobilized antibodies by standard conditions, various combinations of free and immobilized antibodies were effective in competing off bound enzyme. Free antibody AB1 quantitatively eluted the active enzyme from immobilized AB1. The different capacities of the antibodies to elute enzyme from various immunoabsorbents reflect interesting properties of both the enzyme and the antibodies.