Cholinergic interneuron characteristics and nicotinic properties in the striatum

The neostriatum (dorsal striatum) is composed of the caudate and putamen. The ventral striatum is the ventral conjunction of the caudate and putamen that merges into and includes the nucleus accumbens and striatal portions of the olfactory tubercle. About 2% of the striatal neurons are cholinergic. Most cholinergic neurons in the central nervous system make diffuse projections that sparsely innervate relatively broad areas. In the striatum, however, the cholinergic neurons are interneurons that provide very dense local innervation. The cholinergic interneurons provide an ongoing acetylcholine (ACh) signal by firing action potentials tonically at about 5 Hz. A high concentration of acetylcholinesterase in the striatum rapidly terminates the ACh signal, and thereby minimizes desensitization of nicotinic acetylcholine receptors. Among the many muscarinic and nicotinic striatal mechanisms, the ongoing nicotinic activity potently enhances dopamine release. This process is among those in the striatum that link the two extensive and dense local arbors of the cholinergic interneurons and dopaminergic afferent fibers. During a conditioned motor task, cholinergic interneurons respond with a pause in their tonic firing. It is reasonable to hypothesize that this pause in the cholinergic activity alters action potential dependent dopamine release. The correlated response of these two broad and dense neurotransmitter systems helps to coordinate the output of the striatum, and is likely to be an important process in sensorimotor planning and learning.     

NMDA-induced acetylcholine release in mouse striatum: role of NO synthase isoforms

Striatal cholinergic interneurons are stimulated by glutamatergic inputs from thalamus and cortex via NMDA receptors. The present microdialysis study was designed to characterize the role of nitric oxide (NO) in this process and to identify the NO synthase (NOS) isoform responsible for this effect. For this purpose, we studied the effects of NMDA and 3-morpholino sydnonimine (SIN-1) perfusions on the release of acetylcholine (ACh) in mouse striatum. In wild-type C57/Bl6 mice, perfusion of NMDA (100 micro m) induced a two-fold stimulation of ACh release. This effect was attenuated in mice lacking endothelial NOS but was completely absent in mice lacking neuronal NOS. Local perfusion of SIN-1 (300 micro m), an NO donor, increased ACh release by more than two-fold in all three mouse lines. We conclude that NO synthesized by neuronal NOS provides a nitrergic link in the glutamatergic stimulation of striatal cholinergic interneurons.     

Inhibitory interneurons in hippocampus

In the hippocampus and DG, a small number of morphologically and physiologically diverse interneurons controls the neuronal activity of large numbers of the principal excitatory output cells. The inhibitory interneurons are themselves regulated by glutamatergic and GABA-ergic intrinsic hippocampus afferents, as well as by extrinsic afferents, including cholinergic and serotonergic projections from the basal forebrain and the brainstem, respectively. In addition to the slow modulatory effects of the neurotransmitters released from these extrinsic pathways (11), recent evidence has revealed rapid effects of ACh and 5-HT mediated by ligand-gated ion channel receptors for these neurotransmitters. The direct, rapid excitatory action of ACh and 5-HT on hippocampus interneurons can explain many of the effects of these neurotransmitters on neuronal activity in the hippocampus circuit. Because the hippocampus receives both serotonergic and cholinergic innervation, there is strong potential for fast cholinergic and serotonergic synaptic transmission between these fibers and hippocampus interneurons, such as has been reported in other brain regions (e.g., visual cortex) (36). Moreover, these receptors may play important roles in the cognitive functions of the hippocampus, and show impaired function in certain neurological disorders, such as neurodegeneration. Recently McQuiston and Madison (77) have recorded functional nAChR-mediated responses in other interneuronal layers in the CA1 region of the rat hippocampus, and recently nAChR-mediated fast excitatory synaptic transmission has been provided in area CA1 of the rat hippocampus (78, 79). See Jones et al. (80) for a recent review.     

Cholinergic neurotransmission from mechanosensory afferents to giant interneurons in the terminal abdominal ganglion of the cricket Gryllus bimaculatus

Crickets respond to air currents with quick avoidance behavior. The terminal abdominal ganglion (TAG) has a neuronal circuit for a wind-detection system to elicit this behavior. We investigated neuronal transmission from cercal sensory afferent neurons to ascending giant interneurons (GIs). Pharmacological treatment with 500 muM acetylcholine (ACh) increased neuronal activities of ascending interneurons with cell bodies located in the TAG. The effects of ACh antagonists on the activities of identified GIs were examined. The muscarinic ACh antagonist atropine at 3-mM concentration had no obvious effect on the activities of GIs 10-3, 10-2, or 9-3. On the other hand, a 3-mM concentration of the nicotinic ACh antagonist mecamylamine decreased spike firing of these interneurons. Immunohistochemistry using a polyclonal anti-conjugated acetylcholine antibody revealed the distribution of cholinergic neurons in the TAG. The cercal sensory afferent neurons running through the cercal nerve root showed cholinergic immunoreactivity, and the cholinergic immunoreactive region in the neuropil overlapped with the terminal arborizations of the cercal sensory afferent neurons. Cell bodies in the median region of the TAG also showed cholinergic immunoreactivity. This indicates that not only sensory afferent neurons but also other neurons that have cell bodies in the TAG could use ACh as a neurotransmitter.     

Striatal interneurons in dissociated cell culture

In addition to the well-characterized direct and indirect projection neurons there are four major interneuron types in the striatum. Three contain GABA and either parvalbumin, calretinin or NOS/NPY/somatostatin. The fourth is cholinergic. It might be assumed that dissociated cell cultures of striatum (typically from embryonic day E18.5 in rat and E14.5 for mouse) contain each of these neuronal types. However, in dissociated rat striatal (caudate/putamen, CPu) cultures arguably the most important interneuron, the giant aspiny cholinergic neuron, is not present. When dissociated striatal neurons from E14.5 Sprague–Dawley rats were mixed with those from E18.5 rats, combined cultures from these two gestational periods yielded surviving cholinergic interneurons and representative populations of the other interneuron types at 5 weeks in vitro. Neurons from E12.5 CD-1 mice were combined with CPu neurons from E14.5 mice and the characteristics of striatal interneurons after 5 weeks in vitro were determined. All four major classes of interneurons were identified in these cultures as well as rare tyrosine hydroxylase positive interneurons. However, E14.5 mouse CPu cultures contained relatively few cholinergic interneurons rather than the nearly total absence seen in the rat. A later dissection day (E16.5) was required to obtain mouse CPu cultures totally lacking the cholinergic interneuron. We show that these cultures generated from two gestational age cells have much more nearly normal proportions of interneurons than the more common organotypic cultures of striatum. Interneurons are generated from both ages of embryos except for the cholinergic interneurons that originate from the medial ganglionic eminence of younger embryos. Study of these cultures should more accurately reflect neuronal processing as it occurs in the striatum in vivo. Furthermore, these results reveal a procedure for parallel culture of striatum and cholinergic depleted striatum that can be used to examine the function of the cholinergic interneuron in striatal networks.     

Optogenetic release of ACh induces rhythmic bursts of perisomatic IPSCs in hippocampus

Acetylcholine (ACh) influences a vast array of phenomena in cortical systems. It alters many ionic conductances and neuronal firing behavior, often by regulating membrane potential oscillations in populations of cells. Synaptic inhibition has crucial roles in many forms of oscillation, and cholinergic mechanisms regulate both oscillations and synaptic inhibition. In vitro investigations using bath-application of cholinergic receptor agonists, or bulk tissue electrical stimulation to release endogenous ACh, have led to insights into cholinergic function, but questions remain because of the relative lack of selectivity of these forms of stimulation. To investigate the effects of selective release of ACh on interneurons and oscillations, we used an optogenetic approach in which the light-sensitive non-selective cation channel, Channelrhodopsin2 (ChR2), was virally delivered to cholinergic projection neurons in the medial septum/diagonal band of Broca (MS/DBB) of adult mice expressing Cre-recombinase under the control of the choline-acetyltransferase (ChAT) promoter. Acute hippocampal slices obtained from these animals weeks later revealed ChR2 expression in cholinergic axons. Brief trains of blue light pulses delivered to untreated slices initiated bursts of ACh-evoked, inhibitory post-synaptic currents (L-IPSCs) in CA1 pyramidal cells that lasted for 10's of seconds after the light stimulation ceased. L-IPSC occurred more reliably in slices treated with eserine and a very low concentration of 4-AP, which were therefore used in most experiments. The rhythmic, L-IPSCs were driven primarily by muscarinic ACh receptors (mAChRs), and could be suppressed by endocannabinoid release from pyramidal cells. Finally, low-frequency oscillations (LFOs) of local field potentials (LFPs) were significantly cross-correlated with the L-IPSCs, and reversal of the LFPs near s. pyramidale confirmed that the LFPs were driven by perisomatic inhibition. This optogenetic approach may be a useful complementary technique in future investigations of endogenous ACh effects.     

Substantia nigra dopaminergic neurons and striatal interneurons are engaged in three parallel but interdependent postnatal neurotrophic circuits

The striatum integrates motor behavior using a well‐defined microcircuit whose individual components are independently affected in several neurological diseases. The glial cell line‐derived neurotrophic factor (GDNF), synthesized by striatal interneurons, and Sonic hedgehog (Shh), produced by the dopaminergic neurons of the substantia nigra (DA SNpc), are both involved in the nigrostriatal maintenance but the reciprocal neurotrophic relationships among these neurons are only partially understood. To define the postnatal neurotrophic connections among fast‐spiking GABAergic interneurons (FS), cholinergic interneurons (ACh), and DA SNpc, we used a genetically induced mouse model of postnatal DA SNpc neurodegeneration and separately eliminated Smoothened (Smo), the obligatory transducer of Shh signaling, in striatal interneurons. We show that FS postnatal survival relies on DA SNpc and is independent of Shh signaling. On the contrary, Shh signaling but not dopaminergic striatal innervation is required to maintain ACh in the postnatal striatum. ACh are required for DA SNpc survival in a GDNF‐independent manner. These data demonstrate the existence of three parallel but interdependent neurotrophic relationships between SN and striatal interneurons, partially defined by Shh and GDNF. The definition of these new neurotrophic interactions opens the search for new molecules involved in the striatal modulatory circuit maintenance with potential therapeutic value.     

Dopaminergic control of corticostriatal long-term synaptic depression in medium spiny neurons is mediated by cholinergic interneurons

Long-term depression (LTD) of the synapse formed between cortical pyramidal neurons and striatal medium spiny neurons is central to many theories of motor plasticity and associative learning. The induction of LTD at this synapse is thought to depend upon D(2) dopamine receptors localized in the postsynaptic membrane. If this were true, LTD should be inducible in neurons from only one of the two projection systems of the striatum. Using transgenic mice in which neurons that contribute to these two systems are labeled, we show that this is not the case. Rather, in both cell types, the D(2) receptor dependence of LTD induction reflects the need to lower M(1) muscarinic receptor activity-a goal accomplished by D(2) receptors on cholinergic interneurons. In addition to reconciling discordant tracts of the striatal literature, these findings point to cholinergic interneurons as key mediators of dopamine-dependent striatal plasticity and learning.     

Whole-Brain Mapping of Inputs to Projection Neurons and Cholinergic Interneurons in the Dorsal Striatum

The dorsal striatum integrates inputs from multiple brain areas to coordinate voluntary movements, associative plasticity, and reinforcement learning. Its projection neurons consist of the GABAergic medium spiny neurons (MSNs) that express dopamine receptor type 1 (D1) or dopamine receptor type 2 (D2). Cholinergic interneurons account for a small portion of striatal neuron populations, but they play important roles in striatal functions by synapsing onto the MSNs and other local interneurons. By combining the modified rabies virus with specific Cre- mouse lines, a recent study mapped the monosynaptic input patterns to MSNs. Because only a small number of extrastriatal neurons were labeled in the prior study, it is important to reexamine the input patterns of MSNs with higher labeling efficiency. Additionally, the whole-brain innervation pattern of cholinergic interneurons remains unknown. Using the rabies virus-based transsynaptic tracing method in this study, we comprehensively charted the brain areas that provide direct inputs to D1-MSNs, D2-MSNs, and cholinergic interneurons in the dorsal striatum. We found that both types of projection neurons and the cholinergic interneurons receive extensive inputs from discrete brain areas in the cortex, thalamus, amygdala, and other subcortical areas, several of which were not reported in the previous study. The MSNs and cholinergic interneurons share largely common inputs from areas outside the striatum. However, innervations within the dorsal striatum represent a significantly larger proportion of total inputs for cholinergic interneurons than for the MSNs. The comprehensive maps of direct inputs to striatal MSNs and cholinergic interneurons shall assist future functional dissection of the striatal circuits.     

NGF receptor reexpression and NGF-mediated cholinergic neuronal hypertrophy in the damaged adult neostriatum

Adult cholinergic interneurons of the neostriatum are not immunoreactive for monoclonal antibody to NGF receptor, whereas the developing neostriatum is immunoreactive for this same antibody. Chronic NGF infusion into the adult neostriatum resulted in reexpression of the NGF receptor such that many cholinergic interneurons became immunoreactive for NGF receptor. NGF infusion dramatically increased the size and choline acetyltransferase immunoreactivity of these same cholinergic neurons. Additionally, in situ hybridization demonstrated an increase in the number of cells expressing NGF receptor mRNA in the NGF-infused striatum. These findings indicate that central cholinergic neurons which lose their NGF receptors during postnatal development will resume their NGF responsiveness when the tissue is damaged. Such a damage-induced mechanism may act to enhance the action of trophic factors, including NGF, released at the site of injury and enhance the responsiveness of damaged CNS neurons to exogenously administered trophic factors.     

Acetylcholine activates cerebral interneurons and feeding motor program in Limax maximus

The cellular and network effects of acetylcholine (ACh) on the control system for feeding in Limax maximus were measured by intracellular recordings from feeding command-like interneurons and whole nerve recordings from buccal ganglion motor nerve roots that normally innervate the ingestive feeding muscles. The buccal ganglion motor nerve root discharge pattern that causes rhythmic feeding movements, termed the feeding motor program (FMP), was elicited either by attractive taste solutions applied to the lip chemoreceptors or by ACh applied to the cerebral ganglia. The ability of exogenous ACh applied to the cerebral ganglia to trigger FMP was blocked by the cholinergic antagonists curare and atropine. If the strength of the lip-applied taste stimulus was in the range of 1-2 times threshold, cerebral application of the cholinergic antagonists blocked or greatly decreased the ability of lip-applied taste solutions to trigger FMP (5 of 8 trials). The cerebral feeding interneurons, some of which activate FMP when stimulated intracellularly, are excited by small pulses of ACh applied directly to the cell body from an ACh-filled micropipette. A pulse of ACh that activates several of the feeding interneurons simultaneously triggers FMP. The data suggest that under certain stimulus conditions an obligatory set of cholinergic synapses onto the feedininterneurons must be activated for taste inputs to trigger ingestion. The determination of ACh's action within the feeding control system is necessary for understanding how enhanced cholinergic transmission leads to prolonged associative memory retention (Sahley, et al., 1986).     

GABAergic Modulation of Striatal Cholinergic Interneurons: An In Vivo Microdialysis Study

Abstract: Striatal cholinergic interneurons have been shown to receive input from Striatal γ-aminobutyric acid (GABA)-containing cell elements. GABA is known to act on two different types of receptors, the GABA_A and the GABA₆ receptor. Using in vivo microdialysis, we have studied the effect of intrastriatal application of the GABA_A-selective compounds muscimol and bicuculline and the GA- BA_B-selective compounds baclofen and 2-hydroxysaclofen, agonists and antagonists, respectively, at GABA receptors, on the output of Striatal acetylcholine (ACh). Intrastriatal infusion of 1 and 10 μmol/L concentrations of the GABA_A antagonist bicuculline resulted in a significant increase in Striatal ACh output, whereas infusion of 1 and 10 /μmol/L concentrations of the GABA_A agonist muscimol significantly decreased the output of Striatal ACh. Both compounds were ineffective in changing the output of Striatal ACh at lower concentrations. Infusion of concentrations up to 100 μmol/L of the GABA_B-selective antagonist 2-hydroxy-saclofen failed to affect Striatal ACh output, whereas infusion of 10 and 100 μmol/L baclofen, but not 0.1 and 1 μmol/L baclofen, significantly decreased the output of Striatal ACh. Thus, agonist-stimulation of GABAA and GABA_B receptors decreases the output of striatal ACh in a dose-dependent fashion, whereas the GABAergic system appears to inhibit tonically the output of striatal ACh via GABA_A receptors, but not via GABA_B receptors. We hypothesize that although GABA_A mediated regulation of striatal ACh occurs via GABA receptors on the cholinergic neuron, the GABA_B mediated effects may be explained by presynaptic inhibition of the glutamatergic input of the striatal cholinergic neuron.     

Neurotensin Regulation of Endogenous Acetylcholine Release from Rat Striatal Slices Is Independent of Dopaminergic Tone

The effects of neurotensin (NT) alone or in combination with the dopamine antagonist sulpiride were tested on the release of endogenous acetylcholine (ACh) from striatal slices. NT enhanced potassium (25 mM)-evoked ACh release from striatal slices in a dose-dependent manner. This effect was tetrodotoxin-insensitive, suggesting an action directly on cholinergic elements. The dopamine antagonist sulpiride (5 x 10(-5) M) significantly increased (63%) potassium-evoked ACh release from striatal slices; potassium-evoked ACh release was further increased (90%) in the presence of NT (10(-5) M) and sulpiride (5 x 10(-5) M). The second set of experiments tested the effects of 6-hydroxydopamine (6-OHDA) lesions of the substantia nigra on NT-induced increases of potassium-evoked ACh release. These lesions did not alter the NT regulation of potassium-evoked ACh release from striatal slices, but did significantly increase spontaneous (33%) and potassium-evoked (40%) ACh release from striatal slices. Striatal choline acetyltransferase activity was not affected by 6-OHDA lesions. In addition, following 6-OHDA lesions, sulpiride was ineffective in altering ACh release from striatal slices. Furthermore, evoked ACh release in the presence of the combination of NT and sulpiride was not different from that in the presence of NT alone. These results suggest that in the rat striatum, NT regulates cholinergic interneuron activity by interacting with NT receptors associated with cholinergic elements. Moreover, the NT modulation of cholinergic activity is independent of either an interaction of NT with D2 dopamine receptors or the sustained release of dopamine.     

Somatostatin stimulates striatal acetylcholine release by glutamatergic receptors: an in vivo microdialysis study

The modulation of striatal cholinergic neurons by somatostatin (SOM) was studied by measuring the release of acetylcholine (ACh) in the striatum of freely moving rats. The samples were collected via a transversal microdialysis probe. ACh level in the dialysate was measured by the high performance liquid chromatography method with an electrochemical detector. Local administration of SOM (0.1, 0.5 and 1 microM) produced a long-lasting and concentration-dependent increase in the basal striatal ACh output. The stimulant effect of SOM was antagonized by the SOM receptor antagonist cyclo(7-aminopentanoyl-Phe-D-Trp-Lys-Thr[BZL]) (1 microM). In a series of experiments, we studied the effect of 6,7-dinitroquinoxaline-2, 3-dione (DNQX), a selective non-NMDA (N-methyl-D-aspartate) glutamatergic antagonist, on the basal and SOM-induced ACh release from the striatum. DNQX, 2 microM, perfused through the striatum had no effect on the basal ACh output but inhibited the SOM (1 microM)-induced ACh release. The non-NMDA glutamatergic receptor antagonist 1-(4-aminophenyl)-4-methyl-7,8-methylendioxy-5H-2,3- benzodiazepine (GYKI-52466), 10 microM, antagonized the SOM (1 microM)-induced release of ACh in the striatum. Local administration of the NMDA glutamatergic receptor antagonist, 2-amino-5-phosphonopentanoic acid (APV), 100 microM, blocked SOM (1 microM)-evoked ACh release. Local infusion of tetrodotoxin (1 microM) decreased the basal release of ACh and abolished the 1 microM SOM-induced increase in ACh output suggesting that the stimulated release of ACh depends on neuronal firing. The present results are the first to demonstrate a neuromodulatory role of SOM in the regulation of cholinergic neuronal activity of the striatum of freely moving rats. The potentiating effect of SOM on ACh release in the striatum is mediated (i) by SOM receptor located on glutamatergic nerve terminals, and (ii) by NMDA and non-NMDA glutamatergic receptors located on dendrites of cholinergic interneurones of the striatum.     

Enhanced muscarinic M1 receptor gene expression in the corpus striatum of streptozotocin-induced diabetic rats

Acetylcholine (ACh), the first neurotransmitter to be identified, regulate the activities of central and peripheral functions through interactions with muscarinic receptors. Changes in muscarinic acetylcholine receptor (mAChR) have been implicated in the pathophysiology of many major diseases of the central nervous system (CNS). Previous reports from our laboratory on streptozotocin (STZ) induced diabetic rats showed down regulation of muscarinic M1 receptors in the brainstem, hypothalamus, cerebral cortex and pancreatic islets. In this study, we have investigated the changes of acetylcholine esterase (AChE) enzyme activity, total muscarinic and muscarinic M1 receptor binding and gene expression in the corpus striatum of STZ – diabetic rats and the insulin treated diabetic rats. The striatum, a neuronal nucleus intimately involved in motor behaviour, is one of the brain regions with the highest acetylcholine content. ACh has complex and clinically important actions in the striatum that are mediated predominantly by muscarinic receptors. We observed that insulin treatment brought back the decreased maximal velocity (V_max) of acetylcholine esterase in the corpus striatum during diabetes to near control state. In diabetic rats there was a decrease in maximal number (B_max) and affinity (K_d) of total muscarinic receptors whereas muscarinic M1 receptors were increased with decrease in affinity in diabetic rats. We observed that, in all cases, the binding parameters were reversed to near control by the treatment of diabetic rats with insulin. Real-time PCR experiment confirmed the increase in muscarinic M1 receptor gene expression and a similar reversal with insulin treatment. These results suggest the diabetes-induced changes of the cholinergic activity in the corpus striatum and the regulatory role of insulin on binding parameters and gene expression of total and muscarinic M1 receptors.     

In Vivo Regulation of [3H]Acetylcholine Recognition Sites in Brain by Nicotinic Cholinergic Drugs

The in vivo regulation of [3H]acetylcholine [( 3H]ACh) recognition sites on nicotinic receptors in rat brain was examined by administering drugs that increase stimulation of nicotinic cholinergic receptors, either directly or indirectly. After 10 days of treatment with the cholinesterase inhibitor diisopropyl fluorophosphate, [3H]ACh binding in the cortex, thalamus, striatum, and hypothalamus was decreased. Scatchard analyses indicated that the decrease in binding in the cortex was due to a reduction in the apparent density of [3H]ACh recognition sites. In contrast, after repeated administration of nicotine (5-21 days), the number of [3H]ACh recognition sites was increased in the cortex, thalamus, striatum, and hypothalamus. Similar effects were observed in the cortex and thalamus following repeated administration of the nicotinic agonist cytisin. The nicotinic antagonists mecamylamine and dihydro-beta-erythroidine did not alter [3H]ACh binding following 10-14 days of administration. Further, concurrent treatment with these antagonists and nicotine did not prevent the nicotine-induced increase in these binding sites. The data indicate that [3H]ACh recognition sites on nicotinic receptors are subject to up- and down-regulation, and that repeated administration of nicotine results in a signal for up-regulation, probably through protracted desensitization at the recognition site.     

Cholinergic interneurons in the feeding system of the pond snail Lymnaea stagnalis. II. N1 interneurons make cholinergic synapses with feeding motoneurons.

The N1 neurons are a population of interneurons active during the protraction phase of the feeding rhythm. All the N1 neurons are coupled by electrical synapses which persist in a high Mg/low Ca saline which blocks chemical synapses. Individual N1 spikes produce discrete electrotonic postsynaptic potentials (PSPS) in other N1 cells, but the coupling is not strong enough to ensure 1:1 firing. Bursts of N1 spikes generate compound PSPS in the feeding motoneurons. The sign (excitation or inhibition) of the N1 input corresponds with the synaptic barrage recorded during the protraction phase. Discrete PSPS are only resolved in a Hi-Di saline. Their variation in latency and number can be explained by variation in electrotonic propagation within the electrically coupled network of N1 cells. The excitatory postsynaptic potentials (ESPS) in the 1 cell are reduced by 0.5 mM antagonists hexamethonium (HMT), atropine (ATR), curare (d-TC) and by methylxylocholine (MeXCh), all of which block the excitatory cholinergic receptor (Elliott et al. (Phil. Trans. R. Soc. Lond. 336, 157-166 (Preceding paper.) (1992)). The 1 cell EPSPS were transiently blocked by phenyltrimethylammonium (PTMA), which is both an agonist and antagonist at the 1 cell excitatory acetylcholine (ACh) receptor (Elliott et al. 1992). The inhibitory postsynaptic potential (IPSP) in the 3 cell is blocked by bath applications of MeXCh and PTMA, which both abolish the response of the 3 cell to ACh (Elliott et. al. 1992). The effects of the cholinergic antagonists on the response of 4 cluster and 5 cells to N1 stimulation matches their response to ACh (Elliott et al. 1992). It is concluded that the population of N1 cells are multiaction, premotor cholinergic interneurons.     

The non-competitive AMPA receptor antagonist (GYKI 52466) blocks quisqualate-induced acetylcholine release from the rat hippocampus and striatum: an in vivo microdialysis study

The effects of the non-N-methyl-D-aspartate (NMDA) agonist quisqualate (QUIS) and selective AMPA/kainate receptor antagonist 1-(aminophenyl)-methyl-7, 8-methyilendioxy-5H-2,3-benzodiazepine (GYKI 52466) on the release of acetylcholine (ACh) from the hippocampus and striatum of freely moving rats were studied by transversal microdialysis. Acetylcholine level in the dialisate was measured by the high performance liquid chromatography (HPLC) method with an electrochemical detector. The QUIS (100 microM) perfused through the striatum induced an increase of extracellular ACh level (250%) which lasted for over 1h and gradually returned to basal values. Local perfusion of GYKI 52466 (10-100 microM) to the striatum did not change the basal release of ACh. GYKI 52466 (10 microM) administered together with QUIS (100 microM) in he striatum antagonized the stimulant effect of QUIS on the ACh release.Local administration of the QUIS (100 microM) through the microdialysis fiber implanted in the hippocampus, caused a long lasting increase of extracellular hippocampal ACh level (360%) which was reversed when the drug was withdrawn from the perfusion solution. The stimulant effect of QUIS was antagonized by concomitant perfusion of GYKI (10 microM). No effect was seen on the basal ACh release when GYKI (10-100 microM) was perfused through the hippocampus.Local perfusion with tetrodotoxin (1 microM) decrease the basal release of ACh and prevented the QUIS-induced increase of ACh both in the hippocampus and striatum.Our in vivo neurochemical results indicate that hippocampal and striatal cholinergic systems are regulated by non-NMDA (probably AMPA) glutamatergic receptors located in the hippocampus and striatum.     

Differential effects of acetylcholine in the chicken auditory neostriatum and hyperstriatum ventrale — studies in vivo and in vitro

1. The effect of acetylcholine (ACh) on the response properties of single units in the caudal auditory telencephalon was studied both in awake chickens and in an in vitro slice preparation. 2. Two types of electrophysiological behavior in response to ACh were observed: an inhibition of cell firing typical for the majority of neurons in the auditory hyperstriatum ventrale and a facilitation of neuronal responses seen predominantly in neostriatal auditory units. 3. The facilitatory effect of ACh is also present in hyperstriatal cells, but is usually dominated by an indirect inhibition. 4. ACh-induced facilitation on single unit responses could be mimicked in awake birds by applying potentially arousing sensory stimuli. 5. The effects of ACh are antagonized by the muscarinic receptor blocker scopolamine. 6. Inhibitory responses can also be antagonized by the GABA-antagonist bicuculline and thus can be attributed to an ACh-induced activation of GABAergic inhibitory interneurons. Evidence is given that the facilitatory responses result from a closure of voltage-dependent potassium channels. 7. The results are discussed with respect to a possible role of cholinergic afferents in telencephalic processing of auditory information and in comparison with the cholinergic influences in the mammalian neocortex.     

Muscarinic Receptors Modulate Dopamine-Activated Adenylate Cyclase of Rat Striatum

We investigated the effect of acetylcholine (ACh) on the activation of adenylate cyclase by dopamine (DA) in a lysed synaptosomal preparation from rat striatum. ACh reduced both basal and the DA-activated adenylate cyclase with an apparent IC50 of approximately 1 microM. From a kinetic analysis it appeared that ACh reduced the Vmax for activation by DA but not the activation constant for DA. For most preparations the Vmax was reduced by 30-40%. The presence of atropine did not affect the activation of the enzyme by DA but it blocked the inhibition by ACh. Following 6-hydroxydopamine lesion of the nigrostriatal pathway, the enzyme became supersensitive to activation by DA and also more sensitive to inhibition by ACh. Inhibition of adenylate cyclase by ACh appeared to be rather specific for activation by DA, as ACh had no effect on activation of adenylate cyclase by the adenosine analogue N6-(L-2-phenylisopropyl)adenosine. These results indicate that some striatal muscarinic and dopaminergic receptors are probably coupled to the same adenylate cyclase domain. Moreover, they suggest a biochemical model for the dynamic balance of cholinergic and dopaminergic neurons that innervate the striatum.