Infusion Of Carbachol Research Articles

Cholinergic action of spleen‐derived cardioprotective factors

IntroductionThere is an ambivalent relationship between the spleen and the heart in myocardial infarction (Circ Res 124; 2019; 26‐8). Sympathetic activation of the spleen initially increases myocardial inflammatory infiltration but resolves it later by initiating a myocardial healing response. Vagal activation of the spleen induces the release of cardioprotective factors: Perfusion of an isolated rat spleen with the vagomimetic carbachol resulted in the release of factors which then reduced infarct size (IS) in an isolated perfused rat heart.AimTo characterize cardioprotection of spleen‐derived factors, with a focus on their cholinergic action.MethodsRat spleens and hearts were isolated and buffer‐perfused at constant pressure. Isolated spleens were either challenged by infusion of saline (as control) or the vagomimetic carbachol (500 pmol/L), and splenic effluate (SEff; 100 mL) was sampled after saline infusion (SEffsaline) or carbachol infusion (SEffcarbachol), respectively. Cell‐free SEff was prepared by centrifugation and filtration. SEffsaline or SEffcarbachol was infused into isolated hearts which were then subjected to 30 min global ischemia and 120 min reperfusion (I/R). In subsets of experiments, the hearts were pretreated with the nicotinic receptor antagonist hexamethonium (50 µmol/L) or the muscarinic receptor antagonist atropine (100 pmol/L). IS was demarcated by triphenyltetrazolium chloride staining and calculated as percent of ventricular mass. To study the relevance of spleen‐derived protection on the cardiomyocyte level, adult rat ventricular cardiomyocytes were prepared. Cells were incubated for 30 minutes with SEffsaline or SEffcarbachol, respectively, and then subjected to 30 min hypoxia/ 5 min reoxygenation (H/R) or exposed to SEffsaline or SEffcarbachol for 35 minutes as time control (TC). Since nicotinic and muscarinic receptors are also expressed on cardiomyocytes, all experiments were repeated after pretreatment with hexamethonium (1 µmol/L) or atropine (100 nmol/L). Cardiomyocyte viability was quantified before (baseline) and after H/R or TC, as the percent fraction of rod‐shaped, unstained (5% trypan blue) cells over all cells. The estimated final concentration of carbachol in the SEffcarbachol of ≤10 pmol/L and the SEffsaline did neither reduce IS in isolated perfused rat hearts nor improve cardiomyocyte viability in isolated rat cardiomyocytes.ResultsWith SEffsaline, IS was 34±7%. With SEffcarbachol, IS was reduced to 19±8%. Hexamethonium or atropine had no impact on IS per se in hearts with SEffsaline (33±8%; 34±6%), but attenuated the cardioprotection by SEffcarbachol (27±10%; 26±10%; Figure A). The viability of cardiomyocytes subjected to H/R was better preserved with SEffcarbachol than with SEffsaline or saline alone. Again, this protection was attenuated by hexamethonium or atropine (Figure B, insert).ConclusionThe cardioprotection by spleen‐derived factors, which were released in response to the vagomimetic carbachol, is mediated through nicotinic and muscarinic receptors within the heart. Apparently, this protection does not need to involve neuronal structures within the myocardium – nicotinic and muscarinic receptors on cardiomyocytes per se mediate protection.

Urodynamic Characterization of Aged Ossabaw Miniature Pigs Mimics Human Detrusor Underactivity

Detrusor underactivity (DU) and its clinical correlate, underactive bladder (UAB), are common urologic conditions experienced by up to 20 million Americans, however, its pathophysiology is poorly understood and treatment is limited. This highlights the need for a high fidelity animal model that has similar bladder characteristics that will allow direct testing of new treatment modalities. Building on our previous study in metabolic syndrome pigs (Comp. Med. PMID 32972487), we hope to further establish the Ossabaw swine as a translational model for human bladder dysfunction, highlighting its comparable bladder capacity and function as major strengths. We hypothesized that the aged Ossabaw model will demonstrate detrusor underactivity on urodynamic measures due to similar age-related loss of bladder contractility and degeneration of neural and non-neural function. Ossabaw pigs were catheterized via transurethral access when possible or suprapubic cystostomy under general anesthesia. Urodynamic studies were conducted on old (N=3; 10.7 ± 2.6 y) and young (N=10; 3.2 ± 1.0 y) pigs to confirm detrusor underactivity. Fisher's exact test and two sample t-test were performed for comparisons between demographic and urodynamic parameters. Intravesical pressure at capacity with saline was significantly reduced in old vs. young pigs (6.4 ± 3.5 vs. 27.2 ± 17.5 cm H2O; p < 0.001), while compliance was significantly increased (201.4 ± 120.9 vs. 74.6 ± 73.4 mL/cm H2O; p = 0.03). Carbachol infusion revealed significantly reduced maximal pressure during active contraction in aged pigs (29.1 ± 4.0 vs. 44.5 ± 16.7; p = 0.03), but no significant changes in compliance. This characteristic hallmark of detrusor underactivity in aged Ossabaw miniature swine demonstrates its powerful utility as a translational model for age-related bladder dysfunction due to its human-sized bladder more closely approximating human urinary physiology.

NMDA Receptor-Dependent Cholinergic Modulation of Mesolimbic Dopamine Cell Bodies: Neurochemical and Behavioral Studies.

Substance abuse disorders are devastating, costly, and difficult to treat. Identifying the neurochemical mechanisms underlying reinforcement promises to provide critical information in the development of effective treatments. Several lines of evidence suggest that striatal dopamine (DA) release serves as a teaching signal in reinforcement learning, and that shifts in DA release from the primary reward to reward-predicting stimuli play a critical role in the self-administration of both natural and non-natural rewards. However, far less is known about the reinforcing effects of motivationally neutral sensory stimuli, or how these signals can facilitate self-administration behavior. Thus, we trained rats ( n = 7) to perform a visual stimulus-induced instrumental task, which involved lever pressing for activation of a stimulus light. We then microinfused vehicle (phosphate buffered saline), carbachol (acetylcholine receptor agonist), or carbachol in the presence of an N-methyl-d-aspartate (NMDA) receptor-specific drug (NMDA itself, or the antagonist, AP5) into the ventral tegmental area (VTA). This enabled us to directly evaluate how chemical modulation of dopamine cell bodies affects the instrumental behavior, as well as the nature of extracellular dopamine transients recorded in the nucleus accumbens shell (NAc shell) using fast-scan cyclic voltammetry (FSCV). Intra-VTA infusion of carbachol enhanced the magnitude and frequency of dopamine transients in the NAc shell and potentiated active lever responding without altering inactive lever responding, as compared to infusion of vehicle. Coinfusion of carbachol with AP5 abolished dopamine transients recorded in the NAc and attenuated active lever responding without altering inactive lever responding. Finally, coadministration of carbachol and NMDA into the VTA restored both lever pressing and dopaminergic signals recorded in the striatum. Together, these results suggest that acetylcholine and glutamate synergistically act at dopamine cells in the VTA to modulate VTA-NAc shell dopaminergic output, and this underlies motivation to lever press for a motivationally neutral visual stimulus.

Vagal Hyperactivity Due to Ventromedial Hypothalamic Lesions Increases Adiponectin Production and Release

In obese humans and animals, adiponectin production and release in adipose tissue are downregulated by feedback inhibition, resulting in decreased serum adiponectin. We investigated adiponectin production and release in ventromedial hypothalamic (VMH)-lesioned animals. VMH-lesioned mice showed significant increases in food intake and body weight gain, with hyperinsulinemia and hyperleptinemia at 1 and 4 weeks after VMH-lesioning. Serum adiponectin was elevated in VMH-lesioned mice at 1 and 4 weeks, despite adipocyte hypertrophy in subcutaneous and visceral adipose tissues and increased body fat. Adiponectin production and mRNA were also increased in both adipose tissues in VMH-lesioned mice at 1 week. These results were replicated in VMH-lesioned rats at 1 week. Daily atropine administration for 5 days or subdiaphragmatic vagotomy completely reversed the body weight gain and eliminated the increased adiponectin production and release in these rats, with reversal to a normal serum adiponectin level. Parasympathetic nerve activation by carbachol infusion for 5 days in rats increased serum adiponectin, with increased adiponectin production in visceral and subcutaneous adipose tissues without changes of body weight. These results demonstrate that activation of the parasympathetic nerve by VMH lesions stimulates production of adiponectin in visceral and subcutaneous adipose tissues and adiponectin release, resulting in elevated serum adiponectin.

Formation and Reverberation of Sequential Neural Activity Patterns Evoked by Sensory Stimulation Are Enhanced during Cortical Desynchronization

Memory formation is hypothesized to involve the generation of event-specific neural activity patterns during learning and the subsequent spontaneous reactivation of these patterns. Here, we present evidence that these processes can also be observed in urethane-anesthetized rats and are enhanced by desynchronized brain state evoked by tail pinch, subcortical carbachol infusion, or systemic amphetamine administration. During desynchronization, we found that repeated tactile or auditory stimulation evoked unique sequential patterns of neural firing in somatosensory and auditory cortex and that these patterns then reoccurred during subsequent spontaneous activity, similar to what we have observed in awake animals. Furthermore, the formation of these patterns was blocked by an NMDA receptor antagonist, suggesting that the phenomenon depends on synaptic plasticity. These results suggest that anesthetized animals with a desynchronized brain state could serve as a convenient model for studying stimulus-induced plasticity to improve our understanding of memory formation and replay in the brain.

Autoregulation of renal blood flow during the infusion of acetylcholine or carbachol in anaesthetized dogs.

Whether renal blood flow autoregulation is abolished by acetylcholine was re-examined by kidney perfusion experiments in anaesthetized dogs. Renal blood flow was dose-dependently increased by the renal arterial infusion of acetylcholine (2 and 5 micrograms min-1) or another muscarinic agent, carbachol (2 and 5 micrograms min-1) and was maintained at an increased level during the infusion. When perfusion pressure was changed stepwise between 60 and 200 mmHg, the infusion of acetylcholine or carbachol caused no impairment of autoregulation. It is concluded that autoregulation is independent of muscarinic stimulation of vascular smooth muscle in the kidney.

Cholinergic Pairing with Visual Activation Results in Long-Term Enhancement of Visual Evoked Potentials

Acetylcholine (ACh) contributes to learning processes by modulating cortical plasticity in terms of intensity of neuronal activity and selectivity properties of cortical neurons. However, it is not known if ACh induces long term effects within the primary visual cortex (V1) that could sustain visual learning mechanisms. In the present study we analyzed visual evoked potentials (VEPs) in V1 of rats during a 4–8 h period after coupling visual stimulation to an intracortical injection of ACh analog carbachol or stimulation of basal forebrain. To clarify the action of ACh on VEP activity in V1, we individually pre-injected muscarinic (scopolamine), nicotinic (mecamylamine), α7 (methyllycaconitine), and NMDA (CPP) receptor antagonists before carbachol infusion. Stimulation of the cholinergic system paired with visual stimulation significantly increased VEP amplitude (56%) during a 6 h period. Pre-treatment with scopolamine, mecamylamine and CPP completely abolished this long-term enhancement, while α7 inhibition induced an instant increase of VEP amplitude. This suggests a role of ACh in facilitating visual stimuli responsiveness through mechanisms comparable to LTP which involve nicotinic and muscarinic receptors with an interaction of NMDA transmission in the visual cortex.

The Cholinomimetic Agent Carbachol Induces Headache in Healthy Subjects

The parasympathetic nervous system is likely to be involved in migraine pathogenesis. We hypothesized that the cholinomimetic agonist carbachol would induce headache and vasodilation of cephalic and radial arteries. Carbachol (3 microg/kg) or placebo was randomly infused into 12 healthy subjects in a double-blind crossover study. Headache was scored on a verbal rating scale from 0-10. Velocity in the middle cerebral artery (V(MCA)) and diameter of the superficial temporal artery (STA) and radial artery (RA) were recorded. Nine participants developed headache after carbachol compared with three after placebo. The area under the curve for headache was increased after carbachol compared with placebo both during infusion (0-30 min) (P = 0.042) and in the postinfusion period (30-90 min) (P = 0.027). Carbachol infusion caused a drop in V(MCA) (P = 0.003) and an increase in STA diameter (P = 0.006), but no increase in the RA diameter (P = 0.200). In conclusion, the study demonstrated that carbachol caused headache and dilation of cephalic arteries in healthy subjects.

Boosting cholinergic activity in gustatory cortex enhances the salience of a familiar conditioned stimulus in taste aversion learning.

The cholinergic system is important for learning, memory, and responses to novel stimuli. Exposure to novel, but not familiar, tastes increases extracellular acetylcholine (ACh) levels in insular cortex (IC). To further examine whether cholinergic activation is a critical signal of taste novelty, in these studies carbachol, a direct cholinergic agonist, was infused into IC before conditioned taste aversion (CTA) training with a familiar taste. By mimicking the cholinergic activation generated by novel taste exposure, it was hypothesized that a familiar taste would be treated as novel and therefore a salient target for aversion learning. As predicted, rats infused with the agonist were able to acquire CTAs to familiar saccharin. Effects of carbachol infusion on patterns of neuronal activation during conditioned stimulus-unconditioned stimulus pairing were assessed using Fos-like immunoreactivity (FLI). Familiar taste-illness pairing following carbachol, but not vehicle, induced significant elevations of FLI in amygdala, a region with reciprocal connections to IC that is also important for CTA learning. These results support the view that IC ACh activity provides a critical signal of taste novelty that facilitates CTA acquisition.

PERIPHERAL DOPAMINE D2‐LIKE RECEPTORS HAVE A REGULATORY EFFECT ON CARBACHOL‐, HISTAMINE‐ AND PENTAGASTRIN‐STIMULATED GASTRIC ACID SECRETION

It has been documented that dopamine, an important regulator of gastric function in the brain-gut axis, has an inhibitory effect on the gastric acid secretion. It has also been suggested that dopamine D1, D2 and D5 receptor proteins are present in the gastrointestinal tract from the stomach through to the distal colon. Therefore, we hypothesized that peripheral D2 receptors may be involved in the control of stimulated gastric acid secretion. To address this question, we examined the effect of quinpirole, a selective D2 receptor-like agonist, and domperidone, a peripheral D2 receptor antagonist, on rat gastric acid secretion. Quinpirole (0.0001-0.5 mg/kg, i.p.) was administered simultaneously with intravenous infusions of histamine, pentagastrin, and carbachol. In some experiments, domperidone (3 and 7 mg/kg) was administered 30 min before quinpirole injection. We found that intraperitoneal injection of quinpirole (0.0001-0.5 mg/kg) suppressed stimulated gastric acid secretion induced by histamine (0.08 mg/100 g per h), pentagastrin (1 microg/100 g per h) and carbachol (4 microg/100 g per h) in a dose-dependent manner. This inhibitory effect of quinpirole persisted until the end of the experiments (90-120 min) and was completely suppressed by domperidone (7 mg/kg). In conclusion, the results of the present study suggest that peripheral D2-like receptors have an inhibitory effect on histaminergic-, pentagastrin- and cholinergic-stimulated gastric acid secretion. This inhibitory effect may be mediated by enteric dopaminergic neurons and/or non-neuronal membranes.

Pulmonary Vein Region Ablation in Experimental Vagal Atrial Fibrillation

Pulmonary vein (PV) -encircling radiofrequency ablation frequently is effective in vagal atrial fibrillation (AF), and there is evidence that PVs may be particularly prone to cholinergically induced arrhythmia mechanisms. However, PV ablation procedures also can affect intracardiac autonomic ganglia. The present study examined the relative role of PVs versus peri-PV autonomic ganglia in an experimental vagal AF model. Cholinergic AF was studied under carbachol infusion in coronary perfused canine left atrial PV preparations in vitro and with cervical vagal stimulation in vivo. Carbachol caused dose-dependent AF promotion in vitro, which was not affected by excision of all PVs. Sustained AF could be induced easily in all dogs during vagal nerve stimulation in vivo both before and after isolation of all PVs with encircling lesions created by a bipolar radiofrequency ablation clamp device. PV elimination had no effect on atrial effective refractory period or its responses to cholinergic stimulation. Autonomic ganglia were identified by bradycardic and/or tachycardic responses to high-frequency subthreshold local stimulation. Ablation of the autonomic ganglia overlying all PV ostia suppressed the effective refractory period-abbreviating and AF-promoting effects of cervical vagal stimulation, whereas ablation of only left- or right-sided PV ostial ganglia failed to suppress AF. Dominant-frequency analysis suggested that the success of ablation in suppressing vagal AF depended on the elimination of high-frequency driver regions. Intact PVs are not needed for maintenance of experimental cholinergic AF. Ablation of the autonomic ganglia at the base of the PVs suppresses vagal responses and may contribute to the effectiveness of PV-directed ablation procedures in vagal AF.

Effects of chronic trimetazidine treatment on myocardial preconditioning in anesthetized rats

Trimetazidine is a widely used anti-ischemic agent, but effects of its chronic treatment on myocardial preconditioning in anesthetized animals have not been investigated. The aim of this study was to examine the effects of 15-day treatment of trimetazidine on ischemic preconditioning and carbachol-induced preconditioning in anesthetized rats. Ischemic preconditioning, induced by 5 min of coronary artery occlusion and 5 min of reperfusion, significantly decreased the total number of ventricular ectopic beats, the incidence of ventricular tachycardia and abolished the occurrence of ventricular fibrillation (VF) during 30 min of ischemia. Trimetazidine (10 mg/kg/day, i.p. for 15 days and 10 mg/kg, i.v.) itself attenuated these arrhythmia parameters with no marked effect on hemodynamic effects. In the presence of trimetazidine, anti-arrhythmic effects of ischemic preconditioning were present. Carbachol infusion induced preconditioning with a marked depression of mean arterial blood pressure, heart rate and the total number of ventricular ectopic beats. No VF was observed in carbachol-induced preconditioning. The marked reductions in arrhythmia parameters that induced carbachol-induced preconditioning were also preserved in the presence of trimetazidine. Arrhythmia scores and myocardial infarct size were reduced significantly with ischemic preconditioning or carbachol-induced preconditioning and were not modified by trimetazidine. Lactate and malondialdehyde levels were suppressed significantly with preconditioning or trimetazidine + preconditioning groups. These results show that chronic treatment of trimetazidine protects the heart against ischemia-induced arrhythmias, reduces myocardial infarct size, plasma lactate and malondialdehyde levels, and preserves the effects of ischemic and pharmacological preconditioning in anesthetized rats.

Carbachol injections into the nucleus accumbens induce 50 kHz calls in rats

In rats, different types of vocalization can be observed. High frequency vocalizations (so called 50 kHz calls) are believed to indicate an appetitive state of the emitting animal. This is supported by studies demonstrating that infusions of the dopamine agonist amphetamine into the nucleus accumbens (NAC), a key structure for appetitive behaviors, induce 50 kHz calls. Several studies during the last years demonstrated that not only infusions of dopamine agonists such amphetamine but also infusions of acetylcholine receptor agonists into the NAC stimulate the appetitive system. In present study, we tested whether infusions of the unspecific cholinergic agonist carbachol into the NAC are able to induce 50 kHz calls. Indeed, we observed a high number of 50 kHz calls after intra-NAC infusions of carbachol. The main frequency of the these calls was between 40 and 70 kHz, and the duration was mainly between 10 and 50 ms. We hypothesize that acetylcholine transmission within the NAC plays an important role in the induction of those ultrasonic calls indicating an appetitive state.

Continuous carbachol infusion promotes peripheral cell proliferation and mimics vagus hyperactivity in a rat model of hypothalamic obesity

Lesions of the ventromedial hypothalamus (VMH) result in obesity and enhanced cellular proliferation in various organs, including the pancreas, gastrointestinal tract, and liver. Previous studies have suggested that vagal hyperactivity, rather than overeating, induces the peripheral cell proliferation in VMH-lesioned rats. The goal of the present study was to investigate the mechanism of peripheral cell proliferation in VMH-lesion-induced obesity by infusing rats with the acetylcholine agonist, carbachol, and then measuring cellular proliferation in the pancreas and duodenum using immunohistochemistry. The ventromedial hypothalamus was bilaterally lesioned in five rats. In other rats, the bilateral vagus nerves were ligated (vagotomized), and saline or carbachol was continuously administered by an osmotic minipump (n = 5 in each group). Three days later, rats were killed, and cell proliferation was assessed in the pancreas and the duodenum using immunohistochemistry for proliferating cell nuclear antigen (PCNA). Additionally, cellular proliferation in the duodenum was more precisely examined by assessing incorporation of 5-bromo-2'-deoxyuridine (BrdU). Cellular proliferation was higher in rats that received carbachol infusions and in rats with VMH-lesions when compared with control rats (P < 0.05, respectively). The pancreatic PCNA-expressing cells were predominantly identified as the B-cells of the islets of Langerhans. These data demonstrate that carbachol infusion can induce pancreatic and duodenal cell proliferation to a degree that was comparable to that in vagal hyperactivity induced by VMH lesions.

Carbachol injections into the nucleus accumbens disrupt acquisition and expression of fear-potentiated startle and freezing in rats

The nucleus accumbens is involved in different types of emotional learning, ranging from appetitive instrumental learning to Pavlovian fear conditioning. In previous studies, we found that temporary inactivation of the nucleus accumbens blocked both the acquisition and expression of conditioned fear. This was not due to altered dopaminergic activity as we have also found that intra-nucleus accumbens infusions of the dopamine agonist amphetamine do not affect either the acquisition or the expression of conditioned fear. Therefore, in the present study we examined whether cholinergic activity in the nucleus accumbens is involved in the acquisition and expression of conditioned fear. Specifically, the effect of intra-nucleus accumbens infusions of the unselective cholinergic agonist carbachol on the acquisition and expression of conditioned fear was assessed. Across several experiments, we measured fear to visual and acoustic conditioned stimuli and to the experimental context. Further, two different measures of conditioned fear were recorded: fear potentiation of startle and freezing. Intra-nucleus accumbens carbachol infusions disrupted acquisition as well as expression of conditioned fear, regardless of the modality of the fear-eliciting stimulus or of the specific measure of conditioned fear. This disruption of conditioned fear was not simply a by-product of enhanced motor activity which also occurred after intra-nucleus accumbens carbachol infusions. Interestingly, despite the substantial effect of intra-nucleus accumbens carbachol on expression of conditioned fear, the results of the final experiment suggest that these rats extinguish similarly to control rats. Taken together, the present results indicate that acetylcholine within the nucleus accumbens is important for the learning and retrieval of conditioned fear.

Spatiotemporal Gating of Sensory Inputs in Thalamus during Quiescent and Activated States

The main role of the thalamus is to relay sensory inputs to the neocortex according to the regulations dictated by behavioral state. Hence, changes in behavioral state are likely to transform the temporal and spatial properties of thalamocortical receptive fields. We compared the receptive fields of single cells in the ventroposterior medial thalamus (VPM) of urethane-anesthetized rats during quiescent states and during aroused (activated) states. During quiescent states, VPM cells respond to stimulation of a principal whisker (PW) and may respond modestly to one or a few adjacent whiskers (AWs). During either generalized forebrain activation or selective thalamic activation caused by carbachol infusion in the VPM, the responses to AWs enhance so that VPM receptive fields become much larger. Such enlargement is not observed at the level of the principal trigeminal nucleus, indicating that it originates within the thalamus. Interestingly, despite the increase in AW responses during activation, simultaneous deflection of the PW and AWs produced VPM responses that resembled the PW response, as if the AWs were not stimulated. This nonlinear summation of sensory responses was present during both quiescent and activated states. In conclusion, the thalamus suppresses the excitatory surround (AWs) of the receptive field during quiescent states and enlarges this surround during arousal. But, thalamocortical cells represent only the center (PW) of the receptive field when the center (PW) and surround (AWs) are stimulated simultaneously.

Effects of trimetazidine on myocardial preconditioning in anesthetized rats

Trimetazidine is a widely used anti-ischemic agent, but its effect on myocardial preconditioning in anesthetized animals has not been investigated. The aim of this study was to examine the effects of trimetazidine on ischemic preconditioning and carbachol preconditioning in anesthetized rats. Ischemic preconditioning, induced by 5-min coronary artery occlusion and 5-min reperfusion, decreased the incidence of ventricular tachycardia and abolished the occurrence of ventricular fibrillation during 30-min ischemia. Trimetazidine (10 mg/kg, i.v.) alone attenuated these parameters of arrhythmia. Carbachol infusion induced preconditioning with a marked depression of mean arterial blood pressure, heart rate and ventricular tachycardia. The marked reductions in parameters of arrhythmia induced by ischemic preconditioning and carbachol preconditioning were preserved in the presence of trimetazidine. Arrhythmia scores and myocardial infarct size were significantly reduced with ischemic preconditioning or carbachol preconditioning and were not inhibited by trimetazidine. These results show that trimetazidine protects the heart against ischemia-induced arrhythmias, reduces myocardial infarct size, preserves the effects of ischemic preconditioning and pharmacological preconditioning, and is able to mimic ischemic preconditioning in anesthetized rats.

Timing of administration mediates the memory effects of intraseptal carbachol infusion

Medial septal neurons innervate the entire hippocampal formation. This input provides a potent regulation of hippocampal formation physiology (e.g. theta) and memory function. Medial septal neurons are rich in cholinergic receptors and thus are potential targets for the development of cognitive enhancers. Direct intraseptal infusion of cholinomimetics alters hippocampal physiology and can produce either promnestic or amnestic effects. Several variables (e.g. age of animal, integrity of septohippocampal circuits, task difficulty) may influence treatment outcome. We have previously demonstrated that intraseptal carbachol (12.5–125 ng) infusion immediately after the sample session of a delayed-non-match-to-sample radial maze paradigm produces a dose-dependent amnesia. The present study examined whether manipulating the timing of intraseptal carbachol infusion with respect to the sample session would alter the amnestic effect. A within-subjects design was used to examine the effect of intraseptal carbachol (125 ng/0.5 μl) in a delayed-non-match to sample radial maze task. During a sample session, rats retrieved rewards from six of 12 maze arms. At the test session (3 h later), only the alternate set contained reward and entries into the sample set arms constituted errors. Intraseptal carbachol was administered: 1) 30 min prior; 2) immediately prior; 3) immediately after and 4) 90 min after the sample session. Intraseptal carbachol prior to the sample had no effect on any index of accuracy. Infusion immediately after the sample, or delayed 90 min into the retention interval, produced an acute amnesia. These findings demonstrate that the timing of treatment is a critical variable in determining the memory effects of septohippocampal manipulations and that dynamic changes in cholinergic tone are important for memory.

Intraseptal infusion of the cholinergic agonist carbachol impairs delayed-non-match-to-sample radial arm maze performance in the rat.

The medial septal nucleus regulates the physiology and emergent functions (e.g., memory formation) of the hippocampal formation. This nucleus is particularly rich in cholinergic receptors and is a putative target for the development of cholinomimetic cognitive enhancing drugs. A large number of studies have demonstrated that direct intraseptal drug infusions can produce amnestic or promnestic effects. While a few studies have examined the effects of direct intraseptal infusion of cholinomimetics on spatial memory performance (with drug "on-board" at the time of testing), the effects of post-acquisition infusions have not been assessed. We hypothesized that post-acquisition intraseptal infusion of cholinomimetics, by promoting hippocampal theta and suppressing the occurrence of hippocampal sharp waves, may disrupt the long-term retention and consolidation of memory. The present study examined the effects of intraseptal infusion of the cholinergic agonist carbachol in a delayed-non-match-to-sample radial maze task. Treatments were administered immediately following (within 1 min) the sample session with a retention session 2 h later. Carbachol infusions (12.5-125 ng in 0.5 microl) produced a linear dose-dependent decrease in correct entries and increase in retroactive errors, without any change in proactive errors or latency-per-choice. These findings suggest that post-acquisition intraseptal cholinergic treatments can produce amnesia. These findings are discussed with regard to multi-stage models of hippocampal-dependent memory formation and the further development of therapeutic strategies in the treatment of mild cognitive impairment as well as age-related cognitive decline and Alzheimer's dementia.

The interaction between the locus coeruleus and dorsal raphe nucleus studied with dual-probe microdialysis

The interaction between the locus coeruleus and dorsal raphe nucleus was investigated by means of dual-probe microdialysis in conscious rats. The release of noradrenaline and 5-hydroxytryptamine (5-HT) after inhibition or stimulation of locus coeruleus and dorsal raphe activity was sampled in both nuclei and analysed by high-pressure liquid chromatography (HPLC). The inhibition of locus coeruleus activity by the infusion of the α 2-adrenoceptor agonist clonidine (100 μM) decreased the release of noradrenaline to 20% in the locus coeruleus and 30% in the dorsal raphe, whilst the release of 5-HT decreased to 80% of control in the two brain areas. The excitation of locus coeruleus activity by the muscarinic receptor agonist carbachol (100 μM) led to an increase in the release of noradrenaline to 240% and 220% of control in the locus coeruleus and dorsal raphe, respectively. The release of 5-HT in both nuclei did not respond to the carbachol infusion into the locus coeruleus. Infusion of the 5-HT 1A receptor agonist flesinoxan into the dorsal raphe (1 μM) significantly decreased the release of 5-HT in the dorsal raphe and locus coeruleus to 45% and 65% of control, respectively. The release of noradrenaline was decreased in the dorsal raphe to 45% by flesinoxan, whereas no changes were seen in the release of noradrenaline in the locus coeruleus. In conclusion, the innervation of the dorsal raphe by the locus coeruleus has a slight excitatory effect on the release of 5-HT in the dorsal raphe. The dorsal raphe does not exert a direct inhibitory influence on the release of noradrenaline in the locus coeruleus. Finally, the release of noradrenaline in the dorsal raphe may be locally regulated by 5-HT 1A receptors.