The effect of 1,2,3,4-tetrahydro-9-aminoacridine (THA) on quantal transmitter release was examined at the frog neuromuscular junction. THA (3 μM) caused an increase in m (no. of quanta released) as measured by K+-evoked miniature endplate potential (MEPP) frequency. This was due to an increase in p (probability of release), as n (no. of functional release sites) was unchanged. The increase in p was dose-dependent over a range of 0.3-10 μM. By contrast, physostigmine (3 μM) caused a decrease in p, and neostigmine, which does not cross the nerve membrane, had no consistent effect on p. At the postsynaptic site, neostigmine produced the largest increase in MEPP size (79.2%), and THA produced the smallest (17.5%). The divergent effects of THA and physostigmine on p indicate a fundamental difference in their actions at the nerve terminal.

Trimethyltin (TMT) is known to produce substantial damage to the hippocampal formation. It also destroys neurons within the entorhinal cortex, thereby causing degeneration of perforant path afferents that terminate in the outer molecular layer (OML) of the dentate gyrus. Surgical destruction of the entorhinal cortex also causes the perforant path to degenerate. This leads to reactive synpatogenesis (axonal sprouting) of septal afferents to the dentate gyrus. The purpose of the present study was to determine whether administration of 6 mg/kg of TMT by gavage to rats would cause axonal sprouting within the septodentate projection. A histochemical stain for acetycholinesterase (AChE) was used. Compared to control subjects rats given TMT exhibited significantly denser AChE staining in the dentate OML. This is putative indication of reactive synaptogenesis within the cholinergic projection to this layer of the dentate and is somewhat surprising because other neurotoxins, such as lead and ethanol, that affect neurons within the hippocampal formation reduce the capacity for reactive synaptogenesis in response to lesions of the entorhinal cortex.

Trimethyltin (TMT) destroys specific subfields of the hippocampus in the rat. TMT also increases choline acetyltransferase (ChAT) activity in CA1 of Ammon's horn and the outer molecular layer of the dentate gyrus. This observation suggests that axonal sprouting occurs in the cholinergic septohippocampal system in response to TMT. However, neither does-response nor time course data are available for the effects of TMT on this enzyme. The effects of three dose levels of TMT on ChAT activity in CA1 and the dentate gyrus were determined in Experiment 1 and ChAT activity in these two areas was measured at six time points following exposure to TMT in Experiment 2. Only the highest dose of TMT (6 mg/kg) significantly increased ChAT activity. ChAT activity in the dentate gyrus increased significantly by 3 d after administration and continued to increase until 21 d after exposure. A significant increase was not observed in CA1 until 7 d after exposure to TMT. Asymptotic levels were still reached at d 21. These results indicate a steep dose-response curve for TMT-induced changes in ChAT activity in the hippocampal formation and that this marker of cholinergic activity is more sensitive to perturbation by TMT in the dentate gyrus than Ammon's horn.

Substance P and neurokinin A are tachykinins that are co-localized with calcitonin gene-related peptide (CGRP) in a unique subpopulation of cardiac afferent nerve fibers. These neurons are activated by nociceptive stimuli and exhibit both sensory and motor functions that are mediated by the tachykinins and/or CGRP. Sensory signals (e.g., cardiac pain) are transmitted by peptides released at central processes of these neurons, whereas motor functions are produced by the same peptides released from peripheral nerve processes. This review summarizes our current understanding of intracardiac actions of the tachykinins. The major targets for the tachykinins within the heart are the intrinsic cardiac ganglia and coronary arteries. Intrinsic cardiac ganglia contain cholinergic neurons that innervate the heart and coronary vasculature. Tachykinins can stimulate NK3 receptors on these neurons to increase their excitability and evoke spontaneous firing of action potentials. This action provides a mechanism whereby tachykinins can indirectly influence cardiac function and coronary tone. Tachykinins also have direct effects on coronary arteries to decrease or increase tone. Stimulation of NK1 receptors on the endothelium causes vasodilation mediated by nitric oxide. This effect is normally dominant, but NK2 receptor-mediated vasoconstriction can also occur and is augmented when NK1 receptors are blocked. It is proposed that these ganglion stimulant and vascular actions are manifest by endogenous tachykinins during myocardial ischemia.

Very little is known about the development of cardiac parasympathetic ganglia and cholinergic innervation of the mouse heart. Accordingly, we evaluated the growth of cholinergic neurons and nerve fibers in mouse hearts from embryonic day 18.5 (E18.5) through postnatal day 21(P21). Cholinergic perikarya and varicose nerve fibers were identified in paraffin sections immunostained for the vesicular acetylcholine transporter (VAChT). Satellite cells and Schwann cells in adjacent sections were identified by immunostaining for S100β calcium binding protein (S100) and brain-fatty acid binding protein (B-FABP). We found that cardiac ganglia had formed in close association to the atria and cholinergic innervation of the atrioventricular junction had already begun by E18.5. However, most cholinergic innervation of the heart, including the sinoatrial node, developed postnatally (P0.5-P21) along with a doubling of the cross-sectional area of cholinergic perikarya. Satellite cells were present throughout neonatal cardiac ganglia and expressed primarily B-FABP. As they became more mature at P21, satellite cells stained strongly for both B-FABP and S100. Satellite cells appeared to surround most cardiac parasympathetic neurons, even in neonatal hearts. Mature Schwann cells, identified by morphology and strong staining for S100, were already present at E18.5 in atrial regions that receive cholinergic innervation at later developmental times. The abundance and distribution of S100-positive Schwann cells increased postnatally along with nerve density. While S100 staining of cardiac Schwann cells was maintained in P21 and older mice, Schwann cells did not show B-FABP staining at these times. Parallel development of satellite cells and cholinergic perikarya in the cardiac ganglia and the increase in abundance of Schwann cells and varicose cholinergic nerve fibers in the atria suggest that neuronal-glial interactions could be important for development of the parasympathetic nervous system in the heart.

Cardiac autonomic neuropathy is a frequent complication of diabetes and often presents as impaired cholinergic regulation of heart rate. Some have assumed that diabetics have degeneration of cardiac cholinergic nerves, but basic knowledge on this topic is lacking. Accordingly, our goal was to evaluate the structure and function of cardiac cholinergic neurons and nerves in C57BL/6 mice with streptozotocin-induced diabetes. Electrocardiograms were obtained weekly from conscious control and diabetic mice for 16. weeks. Resting heart rate decreased in diabetic mice, but intrinsic heart rate was unchanged. Power spectral analysis of electrocardiograms revealed decreased high frequency and increased low frequency power in diabetic mice, suggesting a relative reduction of parasympathetic tone. Negative chronotropic responses to right vagal nerve stimulation were blunted in 16-week diabetic mice, but postjunctional sensitivity of isolated atria to muscarinic agonists was unchanged. Immunohistochemical analysis of hearts from diabetic and control mice showed no difference in abundance of cholinergic neurons, but cholinergic nerve density was increased at the sinoatrial node of diabetic mice (16. weeks: 14.9 ± 1.2% area for diabetics versus 8.9 ± 0.8% area for control, P< 0.01). We conclude that disruption of cholinergic function in diabetic mice cannot be attributed to a loss of cardiac cholinergic neurons and nerve fibers or altered cholinergic sensitivity of the atria. Instead, decreased responses to vagal stimulation might be caused by a defect of preganglionic cholinergic neurons and/or ganglionic neurotransmission. The increased density of cholinergic nerves observed at the sinoatrial node of diabetic mice might be a compensatory response.

Dysfunction of the intrinsic cardiac nervous system is implicated in the genesis of atrial and ventricular arrhythmias. While this system has been studied extensively in animal models, far less is known about the intrinsic cardiac nervous system of humans. This study was initiated to anatomically identify neurotransmitters associated with the right atrial ganglionated plexus (RAGP) of the human heart. Biopsies of epicardial fat containing a portion of the RAGP were collected from eight patients during cardiothoracic surgery and processed for immunofluorescent detection of specific neuronal markers. Colocalization of markers was evaluated by confocal microscopy. Most intrinsic cardiac neuronal somata displayed immunoreactivity for the cholinergic marker choline acetyltransferase and the nitrergic marker neuronal nitric oxide synthase. A subpopulation of intrinsic cardiac neurons also stained for noradrenergic markers. While most intrinsic cardiac neurons received cholinergic innervation evident as punctate immunostaining for the high affinity choline transporter, some lacked cholinergic inputs. Moreover, peptidergic, nitrergic, and noradrenergic nerves provided substantial innervation of intrinsic cardiac ganglia. These findings demonstrate that the human RAGP has a complex neurochemical anatomy, which includes the presence of a dual cholinergic/nitrergic phenotype for most of its neurons, the presence of noradrenergic markers in a subpopulation of neurons, and innervation by a host of neurochemically distinct nerves. The putative role of multiple neurotransmitters in controlling intrinsic cardiac neurons and mediating efferent signaling to the heart indicates the possibility of novel therapeutic targets for arrhythmia prevention.

Objective: The strong association between ADHD and cigarette smoking and the known effects of nicotine on cognition has lead to interest in the role of cholinergic function in ADHD cognitive deficits. We have previously demonstrated that acute nicotine improves behavioral inhibition in adolescents with ADHD. This study examined acute nicotine in young adults with ADHD-Combined type on cognitive domains including behavioral inhibition, delay aversion, and recognition memory. Methods: 15 non-smoking young adults (20 ± 1.7 years) diagnosed with ADHD-C received acute nicotine (7 mg patch for 45 min) and placebo on separate days. Cognitive tasks included the Stop Signal Task, Choice Delay task, and the High-Low Imagery Task (a verbal recognition memory task). Three subjects experienced side effects and their data was excluded from analysis of cognitive measures. Results: There was a significant (p < .05) positive effect of nicotine on the Stop Signal Reaction Time measure of the Stop Signal Task. The SSRT was improved without changes in GO reaction time or accuracy. There was a trend (p = .09) for nicotine to increase tolerance for delay and a strong trend (p = .06) for nicotine to improve recognition memory. Conclusions: Non-smoking young adults with ADHD-C showed improvements in cognitive performance following nicotine administration in several domains that are central to ADHD. The results from this study support the hypothesis that cholinergic system activity may be important in the cognitive deficits of ADHD and may be a useful therapeutic target.

The present study was done to characterize the effects of endogenous tachykinins on heart rate in urethane-anesthetized guinea pigs. Intravenous injection of capsaicin (32 nmol/kg) was used to evoke release of tachykinins and calcitonin gene-related peptide (CGRP) from cardiac sensory nerve fibers. Such injections caused a brief decrease in heart rate (- 37 ± 7 beats/min, n = 6) that was followed by a more prolonged increase (+ 44 ± 10 beats/min). Blood pressure was lowered by - 11 ± 2 mmHg. Bilateral vagotomy did not affect the chronotropic or depressor responses to capsaicin, but atropine (1 μmol/kg) nearly abolished the bradycardic response (- 8 ± 3 beats/min, n = 7). Combined blockade of NK2 and NK3 receptors, with SR48968 and SR14801 respectively, also caused a significant reduction of capsaicin-evoked bradycardia (- 14 ± 3 beats/min, n = 4) but did not affect bradycardia evoked by vagal nerve stimulation. Blockade of CGRP receptors eliminated capsaicin-evoked tachycardia and prolonged the capsaicin-evoked bradycardia. These findings suggest that capsaicin-evoked bradycardia in the anesthetized guinea pig is mediated by tachykinins that stimulate cardiac cholinergic neurons. This effect appears to be truncated by the positive chronotropic action of CGRP that is also released from cardiac afferents by capsaicin.

This study was done to determine if pituitary adenylate cyclase-activating peptide (PACAP)-immunoreactive nerve fibers occur in cardiac muscle as well as intracardiac ganglia of rats and guinea pigs and to clarify the chronotropic actions of PACAP27 in the same species using isolated heart preparations. PACAP nerve fibers were not detected in atrial or ventricular muscle of rat or guinea pig but a few stained nerve fibers occurred in the atrioventricular bundle of the guinea pig. Stained nerve fibers were prominent in intracardiac ganglia of both species. PACAP27 caused a dose-dependent tachycardia in isolated rat hearts (+39 ± 3 beats/min with 1 nmol, n = 6). Positive and/or negative chronotropic responses were evoked by PACAP27 in guinea pig heart, depending on dose and prior exposure to the peptide. PACAP27 also caused arrhythmias in several guinea pig hearts. Treatment with atropine eliminated or prevented PACAP-evoked bradycardia and arrhythmias, implicating cholinergic neurons in these responses. Positive chronotropic responses to PACAP were unaffected by beta-adrenergic receptor blockade in either species, suggesting that tachycardia resulted from a direct action on the heart. These observations support the conclusion that endogenous PACAP could have a role in regulating parasympathetic input to the heart but through different mechanisms in rats versus guinea pigs. A direct positive chronotropic influence of endogenous PACAP is unlikely since atrial muscle lacks PACAP-immunoreactive nerve fibers.