The localization of central cholinergic neurons

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.

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.

Suckling rat brain regional distribution of acetylcholinesterase activity in galactosaemia in vitro

We aimed to evaluate the effect of in vitro galactosaemia on acetylcholinesterase (AChE) activity in different suckling rat brain regions. Various concentrations of galactose (Gal), galactose-1-phosphate (Gal-1-P) and/or galactitol (Galtol) were preincubated for 1 h with homogenates from frontal cortex, hippocampus and for 1-3 h with hypothalamus homogenates at 37( composite function)C. AChE activity was determined spectrophotometrically. Mixture A (Gal-1-P (2 mM), Galtol (2 mM), and Gal (4 mM) (=brain concentrations in classical galactosaemia)) or mixture B (Galtol (2 mM) and Gal (1 mM) (=brain concentrations in galactokinase deficiency galactosaemia)) inhibited by 18-20% (P < 0.01) AChE activity in frontal cortex or hippocampus homogenates. Gal-1-P (2-8 mM) reduced AChE activity by 20% (P < 0.01) on frontal cortex and hippocampus homogenates. Galtol (2-8 mM) resulted in an AChE inhibition (20-22% (P < 0.01)) in hippocampus, 2 mM of the substance had the same effect (20%, P < 0.01) on frontal cortex, whereas higher concentrations (4-8 mM) failed to decrease the enzyme activity anymore. Gal (1-8 mM) did not change AChE activity in the studied areas. Additionally, the hypothalamus enzyme activity was measured considerably high and remained unaltered in the presence of the above compounds. In conclusion, AChE activity was significantly higher in hypothalamus compared with those in frontal cortex and hippocampus. Frontal cortex and hippocampus AChE was significantly inhibited by Gal derivatives, whereas hypothalamus AChE activity remained unaltered possibly due to the histologically different innervation of this area.

Distribution of choline acetyltransferase-immunoreactive structures in the lamprey brain

The distribution of cholinergic neurons and fibers was studied immunohistochemically in the brain of two species of lampreys (Petromyzon marinus and Lampetra fluviatilis), by using an antiserum against choline acetyltransferase (ChAT). The results obtained in both species were similar, but there appeared some interspecies differences. In the forebrain, cholinergic cells were present in the striatum, preoptic region, paraventricular nucleus, pineal and parapineal organs, habenula, and pretectum. The cranial nerve motoneurons (III, IV, V, VI, VII, IX, and X), the first and second spino-occipital nerves (so), and the ventral horn of the spinal cord showed a strong ChAT immunoreactivity. Additional cholinergic neurons were observed: the mesencephalic M5 nucleus of Schober, two different cell populations in the isthmic region, the efferent component of the eighth nerve, putative preganglionic parasympathetic cells, cells in the solitary tract nucleus, and the rhombencephalic reticular formation. Cholinergic fibers were widely distributed in the brain. Comparison with previous studies in other vertebrates suggests that major cholinergic pathways, like tectal innervation from the isthmic region, are also present in lampreys. Of particular interest was the prominent projection to the neurohypophysis from cholinergic neurons in the preoptic region and paraventricular nucleus. Present data were analyzed within the segmental paradigm, as was previously done in other vertebrates. Our results reveal that the organization of many cholinergic systems in the lamprey as, for example, in the striatal, preoptic, and isthmic regions, comprises features of the anamniote brain that remain common to all living amniotes studied so far, thus being conservative to a surprisingly high degree. Therefore, the distribution of ChAT-immunoreactive structures in the lamprey brain is, in general, comparable to that previously described in other vertebrate species.

Distribution of choline acetyltransferase immunoreactivity in the pigeon brain

We have investigated the distribution of cholinergic perikarya and fibers in the brain of the pigeon (Columba livia). With this aim, pigeon brain sections were processed immunohistochemically by using an antiserum specific for chicken choline acetyltransferase. Our results show cholinergic neurons in the pigeon basal telencephalon, the hypothalamus, the habenula, the pretectum, the midbrain tectum, the dorsal isthmus,the isthmic tegmentum, and the cranial nerve motor nuclei. Cholinergic fibers were prominent in the dorsal telencephalon, the striatum, the thalamus, the tectum, and the interpeduncular nucleus. Comparison of our results with previous studies in birds suggests some major cholinergic pathways in the avian brain and clarifies the possible origin of the cholinergic innervation of some parts of the avian brain. In addition, comparison of our results in birds with those in other vertebrate species shows that the organization of the cholinergic systems in many regions of the avian brain (such as the basal forebrain, the epithalamus, the isthmus, and the hindbrain) is much like that in reptiles and mammals. In contrast, however, birds appear largely to lack intrinsic cholinergic neurons in the dorsal ("neocortex-like") parts of the telencephalon.

Distribution of choline acetyltransferase immunoreactivity in the brain of the lizard Gallotia galloti

The aim of the present study is to provide a complete description of the distribution of choline acetyltransferase (ChAT) immunoreactivity (i) in the brain of the lizard Gallotia galloti, on the basis of two different primary antisera: rat anti-ChAT and rabbit anti-chicken ChAT. Considering that the brain is a segmented structure, we have analysed our data with respect to transverse segmental domains (or neuromeres), which have been previously described by several authors in the brain of vertebrates. In the telencephalon, ChATi neurons are seen in the cortex, anterior dorsal ventricular ridge, basal ganglia, diagonal band, and bed nucleus of the stria terminalis. Further caudally, ChATi cell bodies are located in the preoptic area, hypothalamus, habenula, isthmus, and all motor efferent centers of the brainstem and spinal cord. Plexuses of ChATi fibers are observed in the areas containing cholinergic cell bodies. In addition, distinct plexuses are found in the cortex, the posterior dorsal ventricular ridge, the neuropiles of all primary visual centers of the diencephalon and mesencephalon, and several non-visual nuclei of the brainstem. The distribution of ChAT immunoreactivity in the brain of G. galloti resembles in many respects that of other vertebrates, and differences are mainly observed in the pretectum and midbrain tectum. Transverse segmental domains were identified in the brainstem and forebrain of Gallotia when the cranial nerve roots and fiber tracts were used as a reference, and most cranial motor nuclei were found to occupy the same segmental positions as have been reported in the chick.

Comparative alterations of nicotinic and muscarinic binding sites in Alzheimer's and Parkinson's diseases

We have recently reported on the differential alterations of various cholinergic markers in cortical and subcortical regions in Alzheimer's disease (AD). The main purpose of the present study was to determine if cholinergic deficits observed in patients with AD are unique to this disorder or can be generalized to others such as idiopathic Parkinson's disease (PD) and PD with Alzheimer-type dementia (PD/AD). Muscarinic M1, M2, and nicotinic receptor binding parameters (KD and Bmax) were determined in various cortical and subcortical areas using selective radioligands ([3H]pirenzepine, [3H]AF-DX 116, and N[3H]methylcarbamylcholine). Choline acetyltransferase activity was also determined as a marker of the integrity of cholinergic innervation. Alterations of cholinergic markers are comparable in cortical areas in AD, PD, and PD/AD brains. In frontal and temporal cortices, as well as in the hippocampus, choline acetyltransferase activity and binding capacities of M2 and nicotinic binding sites are similarly decreased in these three disorders compared with age-matched control values. M1 receptor binding parameters are not significantly modified in cortical areas in patients with these disorders. In contrast, important differences between AD and PD brain tissues are found in subcortical areas such as the striatum and the thalamus. The density of M1 sites is significantly increased in striatal areas only in patients with AD, whereas densities of nicotinic sites are decreased in thalamus and striatum in PD and PD/AD, but not AD, brain tissues. The binding capacity of M2 sites is apparently unchanged in subcortical areas in all three disorders, although tendencies toward reductions are observed in the striatum of PD and PD/AD patients. Thus, although comparable alterations of various cholinergic markers are observed in cortical areas in the three neurological disorders investigated in the present study, important differences are seen in subcortical areas. This may be relevant to the respective etiological and clinical profiles of AD and PD.

Ultrastructural study of cholinergic neurons in the medial septal nucleus and vertical limb of the diagonal band of broca in the basal forebrain of the rat

The morphology, ultrastructure and synaptic relationships of the cholinergic and non-cholinergic neurons in the medial septal nucleus (MS) and vertical limb of the diagonal band of Broca (VDB) in the basal forebrain of the rat were studied at the light and electron microscopic levels. The cholinergic neurons were localized immunocytochemically using a monoclonal antibody against choline acetyltransferase (ChAT). Morphometric and statistical analyses showed that ChAT-labelled cells presented a predominantly oval morphology in both nuclei. The sizes of the neurons were significantly larger in the VDB nucleus. Within the two nuclei, two populations of cholinergic neurons were differentiated. One of the large immunolabelled neurons presented deep indentations and prominent nucleoli in their non-immunoreactive nuclei. Their cytoplasm contained a well-organized endomembrane system composed of short cisternae of rough endoplasmic reticulum (RER). One or two lamellar bodies with a peculiar ultrastructure were frequently found intercalated in this system. The Golgi areas presented numerous coated vesicles, sequestration and multivesicular bodies, which was indicative of an intense metabolic activity in these cells. The second population of small immunolabelled neurons exhibited reduced cytoplasm with a poorly developed endomembrane system and apparent absence of lamellar bodies. The neighbouring non-immunolabelled neurons presented a different type of organization of the endomembrane system which was composed of scattered and loosely arranged elongated cisternae of RER and infrequent lamellar bodies, with a structure different from that seen in the large cholinergic neurons. We propose that the structural differences in composition of the endomembrane system and lamellar bodies observed in the three types of neurons in this study indicate different metabolic activities. Symmetrical and asymmetrical synaptic contacts were observed on somata and dendrites of labelled neurons, the latter being more frequent. ChAT-labelled axon boutons were never seen. The absence of immunolabelled axon terminals and the presence of immunolabelled myelinated axons leads us to suggest that the majority of neurons in these areas are of the long projecting type.

Choline acetyltransferase in bovine pineal gland

Recent studies from our laboratories have shown that the bovine pineal gland contains a muscarinic cholinergic receptor with a Kd value of 0.423 +/- 0.010 nM and a Bmax value of 69.75 +/- 20.91 fmol/mg protein. In order to substantiate further the possible existence of a pineal cholinergic transmission, we have measured the activity of choline acetyltransferase and delineated its kinetic properties in the bovine pineal gland. This enzyme exhibited an activity of 0.0339 +/- 0.0042 nmol/mg protein/min. Furthermore, the bovine pineal choline acetyltransferase possessed a Km value of 124.86 +/- 24.06 microM and a Vmax value of 0.0598 +/- 0.0034 nmol/mg protein/min for acetyl CoA, and a Km value of 3.11 +/- 0.94 mM and a Vmax value of 0.0155 +/- 0.0016 nmol/mg protein/min for choline. The presence of muscarinic cholinergic receptors along with a specific choline acetyltransferase are supportive evidences that the bovine pineal gland may receive cholinergic innervation.

Ontogeny of cholinergic neurons in the mouse forebrain

The development of cholinergic neurons in the mouse forebrain was studied by immunocytochemistry with a monoclonal antibody to choline acetyltransferase (ChAT), the rate-limiting enzyme for acetylcholine synthesis. Since this antibody stained dividing cells in ventricular germinal zones as well as differentiating neurons, likely routes of migration could be inferred on the basis of the location of immunoreactive (IR) cells at different gestational ages. Germinal zones for cholinergic cells were observed in all ventricular zones of the forebrain with the ventral zones generating the earliest cells by gestational day 13.5 (GD13.5). On GD14, ChAT IR cells were visible in the germinal zones of the eye, olfactory ventricle, anterior horn, and dorsolateral aspect of the lateral ventricle, lateral ganglionic eminence, ventro- and dorsolateral third ventricle, and in the pineal anlage (epiphysis). ChAT IR neurons continued to develop in these and additional germinal zones on GD15, including the medial, dorsal, and dorsomedial walls of the lateral ventricle, and the medial and dorsal ganglionic eminence. On GD16, ChAT IR neurons were located in the prelimbic, pyriform, and parietal cortices and the lamina terminalis, and a cluster of IR cells was observed in the ventricular zone of the caudatopallial angle. On GD17-18, neurons in the anterior olfactory nucleus, olfactory tubercle, horizontal and vertical nucleus of the diagonal band, and medial septal nucleus stained more darkly and were multipolar, whereas immature bipolar neurons appeared to continue their migration into the hippocampus and along major fiber tracts, such as the corpus callosum, external capsule, fornix and anterior commissure. This study provides a comprehensive view of the zones of origin, probable routes of migration, and final destination of cholinergic neurons in the mouse forebrain.

Studies on the properties of muscarinic cholinergic receptor sites in bovine pineal gland

1. Using the tritiated muscarinic receptor antagonist, quinuclidinyl benzilate ([3H]QNB) as a ligand, muscarinic cholinergic receptors have been identified and characterized in the pineal glands of cow and swamp buffalo. 2. At 25 degrees C, the specific binding reached equilibrium within 60 min and remained constant for an additional two hours. Furthermore, the specific binding was saturable, reversible and tissue dependent in nature. 3. The kinetic analyses of muscarinic cholinergic receptor sites revealed KD values of 0.423 +/- 0.01 nM and 0.218 +/- 0.01 nM, and Bmax values of 69.75 +/- 20.91 fmol/mg protein and 74.19 +/- 32.73 fmol/mg protein for the cow's- and the swamp buffalo's pineal glands, respectively. 4. The presence of muscarinic cholinergic receptor sites originating from cholinergic innervation of the pineal gland is suggested.

Time of origin of cholinergic neurons in the rat basal forebrain

The timing of the final mitotic division of basal forebrain cholinergic neurons was studied by injecting [3H]thymidine into timed pregnant rats and processing the brains of their progeny as young adults for immunohistochemistry with a monoclonal antibody to choline acetyltransferase (ChAT) followed by autoradiography. ChAT-positive neurons located caudally in the basal forebrain were found to become postmitotic mostly on embryonic (E) days 12 and 13, whereas the peak final mitosis of more rostrally located ChAT-positive neurons occurred increasingly later, with the most rostral ChAT-immunoreactive neurons leaving their final mitotic cycles on E15 and E16. In all basal forebrain regions, cholinergic neurogenesis was complete by E17. These results indicate that the cholinergic neurons in the basal forebrain become postmitotic in a caudal-to-rostral gradient over about 5 days. The continuity of the gradient suggests that these cholinergic neurons may derive from the same germinal source.

The immunohistochemical localization of choline acetyltransferase in the cat brain

The distribution of neurons displaying choline acetyltransferase (ChAT) immunoreactivity was examined in the feline brain using a monoclonal antibody. Groups of ChAT-immunoreactive neurons were detected that have not been identified previously in the cat or in any other species. These included small, weakly stained cells found in the lateral hypothalamus, distinct from the magnocellular rostral column cholinergic neurons. Other small, lightly stained cells were also detected in the parabrachial nuclei, distinct from the caudal cholinergic column. Many small ChAT-positive cells were also found in the superficial layers of the superior colliculus. Other ChAT-immunoreactive neurons previously detected in rodent and primate, but not in cat, were observed in the present study. These included a dense cluster of cells in the medial habenula, together with outlying cells in the lateral habenula. Essentially all of the cells in the parabigeminal nucleus were found to be ChAT-positive. Additional ChAT-positive neurons were detected in the periolivary portion of the superior olivary complex, and scattered in the medullary reticular formation. In addition to these new observations, many of the cholinergic cell groups that have been previously identified in the cat as well as in rodent and primate brain such as motoneurons, striatal interneurons, the magnocellular rostral cholinergic column in the basal forebrain and the caudal cholinergic column in the midbrain and pontine tegmentum were confirmed. Together, these observations suggest that the feline central cholinergic system may be much more extensive than previous studies have indicated.

Physiological evidence for subpopulations of cortically projecting basal forebrain neurons in the anesthetized rat

Sixty-three cortically projecting basal forebrain neurons were identified in chloral hydrate anesthetized rats by antidromic activation from the cerebral cortex. Two subpopulations were noted: type I neurons exhibited two antidromic action potentials of constant latency and identical waveform in response to double pulse cortical stimulation. In contrast, type II neurons exhibited two antidromic action potentials of constant latency but differing waveforms in response to the double pulse paradigm. The phenomenon exhibited by type II cortically projecting basal forebrain neurons is interpreted as evidence for loss of the somatodendritic portion of the antidromic action potential with high frequency stimulation. The median latency to antidromic activation of type II neurons (13.5 ms) was significantly longer than that of type I neurons (3.9 ms). Spontaneous firing rates varied over a wide range (0-49 Hz), and there was no significant difference between the rates of type I and type II neurons. These data underscore the physiological heterogeneity of this presumptive cholinergic cortical afferent system. Anatomical studies have shown that most, but possibly not all cortically projecting basal forebrain neurons are cholinergic. The relative proportions of type I (87%) and type II (13%) neurons encountered in this study suggest that type I neurons might be cholinergic and type II neurons non-cholinergic. If substantiated, this hypothesis would permit cholinergic and non-cholinergic cortically projecting basal forebrain neurons to be distinguished using a simple test of antidromicity.