Rat Nucleus Basalis Research Articles

Propofol Causes Consciousness Loss by Affecting GABA-A Receptor in the Nucleus Basalis of Rats.

Objective Propofol is a classical anesthetic and induces consciousness loss, and gamma-aminobutyric-acid-type-A (GABA-A) receptor is its target. Righting reflex is associated with conscious response. The nucleus basalis (NB) acts as a major relay between the reticular activating system and the frontal cortex (FC). Propofol may mediate righting reflex by affecting GABA-A receptor in NB. Methods Fifty male SD rats (250-350 g) were divided into parts I and II. In part I, 20 male SD rats were randomly divided into control group (CG) and NB-lesion group (NG, ibotenic acid-induced NB lesion). In part II, 30 male SD rats were treated with saline (0.9% NaCl, SG group), muscimol (a GABA-A receptor agonist, MG group), and gabazine (a GABA-A receptor antagonist, GG group) in NB, respectively. Two weeks later, the activity of the rats was measured between CG and NG groups. The rats were intravenously injected with propofol (50 mg/kg/h) to test the time of loss of righting reflex (LORR) in all rats. When LORR occurred, the rats received single administration of propofol (12 mg/kg) to measure the time of return of righting reflex (RORR). Electroencephalogram (EEG) activity of the frontal cortex (FC) was recorded. Results The numbers of NB neurons were reduced by 44% in the NG group compared to the CG group (p < 0.05) whereas the activity of rats was reduced a little in the NG group when compared with the CG group, but the statistical difference was insignificant (p < 0.05) whereas the activity of rats was reduced a little in the NG group when compared with the CG group, but the statistical difference was insignificant (p < 0.05) whereas the activity of rats was reduced a little in the NG group when compared with the CG group, but the statistical difference was insignificant (p < 0.05) whereas the activity of rats was reduced a little in the NG group when compared with the CG group, but the statistical difference was insignificant (p < 0.05) whereas the activity of rats was reduced a little in the NG group when compared with the CG group, but the statistical difference was insignificant (p < 0.05) whereas the activity of rats was reduced a little in the NG group when compared with the CG group, but the statistical difference was insignificant (Conclusions The unilateral NB lesion increased the recovery time and FC delta power, and the NB region might be involved in the emergence after propofol administration. Propofol plays a crucial role for causing conscious loss by affecting GABA-A receptor in NB.

Imidafenacin has no influence on learning in nucleus basalis of Meynert-lesioned rats

The prevalence of overactive bladder (OAB) and Alzheimer's disease (AD) increases with age, and much attention has been paid to the risk of cognitive impairment which may be induced by antimuscarinics used for OAB in patients with AD. Imidafenacin, an antimuscarinic agent for OAB treatment, has been reported not to affect learning in normal animals. However, under the condition in which sensitivity to learning impairment by antimuscarinics is increased, it remains unclear whether imidafenacin still does not impair the learning. Therefore, the influences of imidafenacin on passive avoidance response were investigated in sham-operated and nucleus basalis of Meynert (nbM)-lesioned rats and compared with oxybutynin hydrochloride and tolterodine tartrate. The learning-inhibitory doses of intravenous oxybutynin hydrochloride and tolterodine tartrate were 0.3 and 3 mg/kg in sham-operated rats and 0.1 and 1 mg/kg in nbM-lesioned rats, respectively. Thus, the learning impairments by those antimuscarinics were more sensitive in nbM-lesioned rats than in sham-operated rats. On the other hand, intravenous administration of imidafenacin had no influence on learning in either case of the rats. In normal rats, however, intracerebroventricular administration of imidafenacin impaired learning to the same degree as that of oxybutynin hydrochloride. Thus, the present study suggests that imidafenacin, unlike the other antimuscarinics used, has no significant risk of enhancing learning impairment even in models whose sensitivity to learning impairment by antimuscarinics is commonly increased, probably because of its low brain penetration.

High volume microinfusion suppresses local astrocyte response within nucleus basalis of rat.

Our study investigates the impact of different volume sham control and excitotoxin microinfusions in vivo on local reactive astroglial response within rat nucleus basalis (NB). We followed the effects of unilateral 200, 100, and 50 nL of sham-control (phosphate buffer PBS) versus ibotenic acid (IBO) microinfusions, mechanical NB lesion (10 µL Hamylton syringe needle positioned into NB for 5 min), or physiological control (intact brain), on the local reactive astroglial response within the NB site, by immunoreactivity against glial fibrillary acidic protein (GFAP). NB lesions were identified by NADPHdiaphorase histochemistry. Local astrocytes responses within NB were suppressed by both high volume microinfusions, PBS and IBO (200 and 100 nL) versus mechanical lesion. Our study has proved, for the first time, the volume of microinfusion as critical for any selective pharmacological stimulation or lesion in vivo, and suggest the microinfusion volume less than 50nL as protective for physiological astroglial reactivity.

Selective brain region activation by histamine H3 receptor antagonist/inverse agonist ABT-239 enhances acetylcholine and histamine release and increases c-Fos expression

Histamine axons originate solely from the tuberomamillary nucleus (TMN) to innervate almost all brain regions. This feature is consistent with a function for histamine over a host of physiological processes, including regulation of appetite, body temperature, cognitive processes, pain perception and sleep–wake cycle. An important question is whether these diverse physiological roles are served by different histamine neuronal subpopulations. Here we report that systemic administration of the non-imidazole histamine H3 receptor antagonist 4-(2-{2-[(2R)-2-methylpyrrolidinyl]ethyl}-benzofuran-5-yl)benzonitrile (ABT-239, 3 mg/kg) increased c-Fos expression dose-dependently in rat cortex and nucleus basalis magnocellularis (NBM) but not in the nucleus accumbens (NAcc) nor striatum, and augmented acetylcholine and histamine release from rat prefrontal cortex. To further understand functional histaminergic pathways in the brain, dual-probe microdialysis was used to pharmacologically block H3 receptors in the TMN. Perfusion of the TMN with ABT-239 (10 μM) increased histamine release from the TMN, NBM, and cortex, but not from the striatum or NAcc. When administered locally, ABT-239 increased histamine release from the NBM, but not from the NAcc. Systemic as well as intra-TMN administration of ABT-239 increased c-Fos expression in the NBM, and cortex, but not in the striatum or NAcc. Thus, as defined by their sensitivity to ABT-239, histaminergic neurons establish distinct pathways according to their terminal projections, and can differentially modulate neurotransmitter release in a brain region-specific manner. This implies independent functions of subsets of histamine neurons according to their terminal projections, with relevant consequences for the development of specific compounds that affect only subsets of histamine neurones, thus increasing target specificity.

High volume microinfusion suppresses local astrocyte response within nucleus basalis of rat

Our study investigates the impact of different volume sham control and excitotoxin microinfusions in vivo on local reactive astroglial response within rat nucleus basalis (NB). We followed the effects of unilateral 200, 100, and 50 nL of sham-control (phosphate buffer - PBS) versus ibotenic acid (IBO) microinfusions, mechanical NB lesion (10 µL Hamylton syringe needle positioned into NB for 5 min), or physiological control (intact brain), on the local reactive astroglial response within the NB site, by immunoreactivity against glial fibrillary acidic protein (GFAP). NB lesions were identified by NADPH- diaphorase histochemistry. Local astrocytes responses within NB were suppressed by both high volume microinfusions, PBS and IBO (200 and 100 nL) versus mechanical lesion. Our study has proved, for the first time, the volume of microinfusion as critical for any selective pharmacological stimulation or lesion in vivo, and suggest the microinfusion volume less than 50nL as protective for physiological astroglial reactivity.

Chronic Dietary Administration of Valproic Acid Protects Neurons of the Rat Nucleus Basalis Magnocellularis from Ibotenic Acid Neurotoxicity

Valproic acid (VPA) has been used for many years as a drug of choice for epilepsy and mood disorders. Recently, evidence has been proposed for a wide spectrum of actions of this drug, including antitumoral and neuroprotective properties. Valproic acid-mediated neuroprotection in vivo has been so far demonstrated in a limited number of experimental models. In this study, we have tested the neuroprotective potential of chronic (4 + 1 weeks) dietary administration of VPA on degeneration of cholinergic and GABAergic neurons of the rat nucleus basalis magnocellularis (NBM), injected with the excitotoxin, ibotenic acid (IBO), an animal models that is relevant for Alzheimer's disease-like neurodegeneration. We show that VPA treatment significantly protects both cholinergic and GABAergic neurons present in the injected area from the excitotoxic insult. A significant level of neuroprotection, in particular, is exerted towards the cholinergic neurons of the NBM projecting to the cortex, as demonstrated by the substantially higher levels of cholinergic markers maintained in the target cortical area of VPA-treated rats after IBO injection in the NBM. We further show that chronic VPA administration results in increased acetylation of histone H3 in brain, consistent with the histone deacetylase inhibitory action of VPA and putatively linked to a neuroprotective action of the drug mediated at the epigenetic level.

Increased expression of PAD2 after repeated intracerebroventricular infusions of soluble Aβ25–35 in the Alzheimer’s disease model rat brain: Effect of memantine

Peptidylarginine deiminases (PADs) convert the arginine residues in proteins into citrulline residues in a Ca2+-dependent manner. We previously showed that a bilateral injection of ibotenic acid into the rat nucleus basalis magnocellularis elevated the PAD2 activity in the hippocampus and striatum. In this study, we examined whether repeated intracerebroventricular infusions of soluble Aβ25–35 would affect the PAD2 expression in any regions of the rat brain. We also assessed the protective effect of memantine on Aβ-induced PAD2 alterations. The infusion of Aβ25–35 increased the activity and protein level of PAD2 in the hippocampus, and co-treatment with memantine suppressed these changes. An immunohistochemical analysis showed that an increased level of PAD2 was coincident with GFAP-positive astrocytes and CD11b-positive microglia. In addition, immunofluoresecence staining revealed that citrullinepostive immunoreactivity coincided with the occurrence of GFAP-positive astrocytes. Co-treatment with memantine reversed the activation of the astrocytes and microglia, thus attenuating the PAD2 increment. These biochemical and immunohistochemical results suggest that PAD2 might play an important role in the pathology of early Alzheimer’s disease, and may correlate with the changes in glial cells that are recovered by memantine treatment.

Mechanisms of the spatial memory deficits induced by injection of okadaic acid into the Meynert nucleus basalis of rats

We previously reported that the injection of okadaic acid (OA) into the Meynert nucleus basalis of rats induced spatial memory deficits. The present study was designed to further explore the underlying mechanisms. We found that the level of acetylcholine (Ach) in the hippocampus significantly decreased 24 h after injection of OA into the Meynert nucleus basalis of rats. Simultaneously, spatial memory deficit, PP-2A inhibition and tau hyperphosphorylation at Ser-198/Ser-199/Ser-202 (Tau-1 epitope) and Ser-396/Ser-404 (PHF-1 epitope) were observed. With the restoration of hippocampus Ach to normal levels at 48 and 72 h after the injection, the spatial memory deficits, PP-2A inhibition and tau hyperphosphorylation were reversed. It is suggested that injection of OA into the Meynert nucleus basalis of rats may impair the hippocampus-dependent spatial memory through damaging the cholinergic projection between the Meynert nucleus basalis and the hippocampus and the selective inhibition of PP-2A and tau hyperphosphorylation may be at least part of the underlying mechanisms.

Selective cholinergic lesions in the rat nucleus basalis magnocellularis with limited damage in the medial septum specifically alter attention performance in the five-choice serial reaction time task

Selective immunotoxic cholinergic lesions in the nucleus basalis magnocellularis (NBM) impair visuospatial attention performance in a 5-choice serial reaction time task (5-CSRT task). The features of the reported deficits, however, do not perfectly match among studies, in which some lesions may have been too weak while others largely encroached onto the septal region. Using the 5-CSRT task, we therefore re-assessed the effects of NBM lesions that produced minimal septal damage. Long-Evans adult male rats were trained to stable 5-CSRT task performance (stimulus duration: 0.5 s) and subsequently subjected to intra-NBM injections of 192 IgG-saporin (200 ng/side). The lesions induced more than 90% loss of choline acetyltransferase–positive neurons in the NBM vs. only 28% in the medial septum. The decrease of the optical density of acetylcholinesterase reaction products was significant in the cortex (−91%), not in the hippocampus. In the 5-CSRT task, the lesions resulted in increased omissions (from 10% to 30%) and decreased correct responses (from 80% to 60%), with negligible or no effects on all other usually collected variables. This deficit disappeared with lengthened stimulus duration (i.e. 0.5–1 and then 5 s). Furthermore, overall performance levels decreased when the stimulus duration was shortened (i.e. 0.5–0.2 s) or its intensity attenuated, and rats with cholinergic lesions remained consistently impaired vs. controls. These results show that disruption of sustained visual attention functions by damage to the NBM cholinergic neurons can be evidenced despite weak or no effects on variables accounting for motivational, locomotion- or impulsivity-related biases. Discrepancies with previously reported results are discussed in terms of differences in lesion extent/specificity and training levels.

Regulatable Acetylcholine-Producing Fibroblasts Enhance Cognitive Performance

Regulatable gene therapy systems provide a method to alter neurotransmitter levels in vivo. We developed a rodent fibroblast cell line expressing the choline acetyltransferase (ChAT) cDNA that is silenced by doxycycline (DOX) administration. The ability of the cell line to improve cognition was tested by grafting after cholinergic lesions. Ibotenic acid was injected bilaterally into the nucleus basalis of rats, which were distributed into three groups. One group received no treatment, while the second group received cortical transplants (Graft). The third group received identical grafts but was treated with DOX to turn off ChAT expression (Graft/DOX). An unlesioned group served as control. Water maze acquisition was significantly better in the Graft group compared to the Graft/DOX group, an effect also seen in the retention and spatial probe trials. However, cognitive enhancement was restricted to spatial tasks, as inhibitory avoidance or open-field activity measures were unchanged. Molecular and biochemical analyses confirmed that DOX regulated transgene transcription and ACh levels. This study demonstrates that regulatable gene therapy has therapeutic value for single-gene disorders and also provides a mechanism to deliver small molecules in a spatiotemporal pattern to delineate the role of these compounds in discrete behavioral tasks.

Verapamil prevents, in a dose-dependent way, the loss of ChAT-immunoreactive neurons in the cerebral cortex following lesions of the rat nucleus basalis magnocellularis

In the present study we analysed the neuroprotective effect of the L-type voltage-dependent calcium channel antagonist verapamil on cholineacetyltransferase (ChAT)-immunoreactive neurons in the cerebral cortex of rats with bilateral electrolytic lesions of the nucleus basalis magnocellularis (NBM). Treatment with verapamil (1.0, 2.5, 5.0 and 10.0 mg/kg/12 h i.p.) started 24 h after NBM lesions and lasted 8 days. Animals were sacrificed on day 21 after NBM-lesions. The bilateral NBM-lesions produced significant loss of ChAT-immunoreactive neurons in frontal, parietal and temporal cortex. Although the number of ChAT-positive neurons was significantly higher in NBM-lesioned animals treated with verapamil at a dose of 2.5, 5.0 and 10.0 mg/kg than in saline treated ones, the most significant effect was obtained at a dose of 5 mg/kg. This is, to our knowledge, the first report showing an inverted U-shape mode of neuroprotective action of the calcium antagonist verapamil, at morphological level in this particular model of brain damage. The demonstrated beneficial effect of verapamil treatment suggests that the regulation of calcium homeostasis during the early period after NBM lesions might be a possible treatment to prevent neurodegenerative processes in the rat cerebral cortex.

Spatial memory deficit and Tau hyperphosphorylation induced by inhibiting PP2A in rat brain

Hyperphosphorylation of Tau in Alzheimer’s disease (AD) brain appears to be caused by a down-regulation of protein phosphatase 2A (PP2A). In this study, we selectively inhibited PP2A by injection of okadaic acid (OA) into the Meynert nucleus basalis of rats and found that 0.4 pmol of OA injection induced approximately 60% inhibition of PP2A 24 h after injection, 13% inhibition 48 h after injection and no obvious inhibition 72 h after injection. Hyperphosphorylation of Tau at Ser-198/Ser-199/Ser-202 and Ser-396/Ser-404 and spatial memory deficit of, rats were induced 24 h after 0. 1 pmol of OA injection. This study suggests that a down-regulation of PP2A may underlie abnormal hyperphosphorylation of cytoskeletal proteins leading to neurofibrillary degeneration in AD.

Progression of age‐associated cognitive impairment correlates with quantitative and qualitative loss of TrkA receptor protein in nucleus basalis and cortex

A direct correlation between disease progression and reduced expression of TrkA receptor in cholinergic neurons has been documented in neurocognitive pathologies including Alzheimer's disease. We investigated whether reduced expression of TrkA protein might also correlate with the level of cognitive impairment in age-associated cognitive impairment. Quantitative and qualitative measurements of TrkA protein levels in the cortex and nucleus basalis of aged rats that had been well-characterized behaviorally as 'unimpaired', 'mildly impaired' or 'fully impaired' demonstrated significant changes in TrkA expression. In the mildly impaired cognitive state phenotypic silencing of TrkA was detected in neurons expressing TrkA at high density but before cholinergic atrophy or loss of TrkA+ neurons was detected. In the fully impaired cognitive state a significant loss in TrkA+ cholinergic neurons together with a more significant phenotypic silencing of TrkA expression then took place. These data suggest that TrkA+ cholinergic cells are associated with cognition, TrkA could be a biomarker of the cognitive state and phenotypic loss of TrkA precedes neuronal loss and probably sensitizes cells to death. We speculate that neurotrophic deficits may be a shared mechanism for cognitive decline in aging and Alzheimer's disease.

Differential effects of typical and atypical antipsychotics on nerve growth factor and choline acetyltransferase expression in the cortex and nucleus basalis of rats

Previously we reported that chronic exposure to haloperidol (HAL), but not the atypical antipsychotics risperidone (RISP) or clozapine (CLOZ), resulted in reductions in brain choline acetyltransferase (ChAT) immunoreactivity and impaired water maze task performance in rats. In the present study, we compared the effects of these antipsychotic drugs on the expression of nerve growth factor (NGF) as well ChAT the in the rat cortex and nucleus basalis of Meynert (NBM) in an effort to determine the underlying mechanism for the differential drug effects observed previously. We also evaluated the effects of these compounds in a crossover design to evaluate specific neurochemical consequences of switching between typical and atypical antipsychotics, a common practice observed in the clinical setting. Male Wistar rats (250–300 g) were exposed to HAL (2.0 mg/kg/day), RISP (2.5 mg/kg/day), or CLOZ (20 mg/kg/day) for 45 days or a pre-treatment regimen consisting of administering either RISP/HAL (i.e., RISP followed by HAL) or CLOZ/HAL, or a post-treatment regimen consisting of administering: HAL/RISP or HAL/CLOZ. The duration of each treatment in the crossover study was also 45 days. NGF and ChAT immunoreactivity were measured by quantitative immunohistochemistry in some sub-cerebral cortical regions and NBM after drug exposures. NGF protein was also measured by an enzyme-linked ImmunoSorbent assay (ELISA) in rat sensorimotor cortex. The results indicated that HAL (but not RISP or CLOZ) significantly reduced NGF levels in some sub-cortical regions and ChAT immunoreactivity in both cortex and NBM. However, pre-treatment with CLOZ prevented the HAL-associated decreases in NGF and ChAT, while post-treatment with either RISP or CLOZ (i.e., after the administration of HAL) appeared to restore NGF and ChAT to control levels. These data indicate that antipsychotic drugs exert dissimilar effects on the levels of NGF and ChAT in the brain, which may contribute to their differential effects on cognitive function. The crossover data further suggest that certain atypical antipsychotic drugs (e.g., clozapine) may have the potential to prevent or reverse the deleterious effects of HAL on important neurochemical substrates of cognitive function.

Effect of memantine on the levels of glial cells, neuropeptides, and peptide-degrading enzymes in rat brain regions of ibotenic acid-treated alzheimer's disease model

It has been implicated that glia activation plays a critical role in the progression of Alzheimer's disease (AD). However, the precise mechanism of glia activation is not clearly understood yet. In our present studies, we confirmed our previous results where change the levels of neuropeptides and peptidases in ibotenic acid (IBO) infusion into the rat nucleus basalis magnocellularis, an animal model of AD. Furthermore, we extended our study to investigate a possible protection effect of co-administration on the changes of neuropeptides, and neuronal and glial cells in IBO-infused rat brain by memantine treatment. The levels of substance P and somatostatin were decreased in the striatum and frontal cortex 1 week after IBO infusion, and recovered to the control level by memantine treatment, indicating the involvement of neuropeptides in AD pathology. Furthermore, the immunohistochemical and enzymatic studies of GFAP and CD 11b, and peptidylarginine deiminase, markers of glia, in the striatum and frontal cortex showed the increase in IBO-treated rat brain as compared with controls, while co-administration of memantine and IBO no increase of astrocytes and microglia activation was observed. The present biochemical and immunohistochemical results suggest that glia activation might play an important role to the pathology of AD, and correlate with the changes of neuropeptide levels in AD brain that is recovered by memantine treatment.

Single-cell RT-PCR analysis of GIRK channels expressed in rat locus coeruleus and nucleus basalis neurons

G protein-coupled inward rectifier potassium channels (GIRK, Kir3) play a crucial role in determining neuronal excitability. Currently, four mammalian GIRK members (GIRK1–4) have been genetically identified. We have been investigating physiological properties of GIRKs in cultured noradrenergic neurons from the locus coeruleus (LC) and cholinergic neurons from the nucleus basalis (NB). Yet, precise information is lacking about which types of GIRK channels are present in these neurons. We performed single-cell RT-PCR on these cultured neurons. In 13 noradrenergic LC neurons, GIRK1, GIRK2, GIRK3, and GIRK4 mRNAs existed in 12, 13, nine, and six neurons, respectively. In six cholinergic NB neurons, GIRK1, GIRK2, GIRK3, and GIRK4 mRNAs existed in six, four, one, and three neurons, respectively. Therefore, GIRK1 and GIRK2 mRNAs are most frequently encountered in both LC and NB neurons.

Injection of okadaic acid into the meynert nucleus basalis of rat brain induces decreased acetylcholine level and spatial memory deficit

Abnormal hyperphosphorylation of tau and cholinergic deficit occur in the early stage of Alzheimer's disease (AD) and relate to the dementia symptom. Hyperphosphorylation of tau, neurofilament (NF) and other proteins in AD brain appears to be caused by a down-regulation of protein phosphatase 2A (PP2A), but the mechanism leading to cholinergic deficit is still unknown. In this study, we selectively inhibited PP2A by injection of okadaic acid (OA) into the Meynert nucleus basalis of rats. We found that injection of OA induced hyperphosphorylation of tau and NF and decreased acetylcholine (ACh) level in the nucleus basalis of Meynert. These alterations were accompanied by spatial memory deficit in OA-injected rats. We also demonstrated that the OA-induced ACh reduction may be due to a failure of intraneuronal transport of choline acetyltransferase (ChAT) from cell body to the neuronal terminals rather than an alteration of activity of ChAT or acetylcholinesterase. This study suggests that a down-regulation of PP2A may underlie both abnormal hyperphosphorylation of cytoskeletal proteins leading to neurofibrillary degeneration and cholinergic deficiency in AD.

Effect of memantine on the levels of glial cells, neuropeptides, and peptide-degrading enzymes in rat brain regions of ibotenic acid-treated alzheimer's disease model

It has been implicated that glia activation plays a critical role in the progression of Alzheimer's disease (AD). However, the precise mechanism of glia activation is not clearly understood yet. In our present studies, we confirmed our previous results where change the levels of neuropeptides and peptidases in ibotenic acid (IBO) infusion into the rat nucleus basalis magnocellularis, an animal model of AD. Furthermore, we extended our study to investigate a possible protection effect of co-administration on the changes of neuropeptides, and neuronal and glial cells in IBO-infused rat brain by memantine treatment. The levels of substance P and somatostatin were decreased in the striatum and frontal cortex 1 week after IBO infusion, and recovered to the control level by memantine treatment, indicating the involvement of neuropeptides in AD pathology. Furthermore, the immunohistochemical and enzymatic studies of GFAP and CD 11b, and peptidylarginine deiminase, markers of glia, in the striatum and frontal cortex showed the increase in IBO-treated rat brain as compared with controls, while co-administration of memantine and IBO no increase of astrocytes and microglia activation was observed. The present biochemical and immunohistochemical results suggest that glia activation might play an important role to the pathology of AD, and correlate with the changes of neuropeptide levels in AD brain that is recovered by memantine treatment.

GABAB receptor transduction mechanisms, and cross-talk between protein kinases A and C, in GABAergic terminals synapsing onto neurons of the rat nucleus basalis of Meynert.

The transduction mechanisms underlying presynaptic GABAB receptor-mediated inhibition of transmitter release have been characterized for a variety of synapses in the central nervous system (CNS). These studies have suggested a range of transduction mechanisms, including a role for second messengers such as protein kinases A (PKA) and C (PKC). In the present study, we have examined the intracellular signalling pathways underlying baclofen-induced inhibition of GABA release from terminals synapsing onto rat basalis of Meynert neurons using patch-clamp recordings. Baclofen, a selective GABAB receptor agonist, reversibly decreased both evoked and spontaneous, miniature, GABAergic inhibitory postsynaptic currents (eIPSCs and mIPSCs, respectively). Such baclofen actions were completely abolished by CGP55845A, a selective GABAB receptor antagonist, and by staurosporine, a non-selective PKA and PKC inhibitor. The mIPSC frequency was still decreased by baclofen even in the presence of 4 AP, a K+ channel blocker, and Cd2+, a voltage-dependent calcium channel blocker. Pharmacological activation or inhibition of PKC activity affected basal GABA release and mildly affected the response to baclofen. Inhibition of the cAMP/PKA cascade also affected basal GABA release and, in a subset of neurons, occluded the effects of baclofen, suggesting that the GABAB receptor-mediated inhibitory action on GABA release was mediated via decreases in PKA activity. In addition, PKA inhibition occluded the effects of PKC modulation on both basal GABA release and on the response to baclofen. Our results characterize the transduction pathway of baclofen at these nucleus basalis of Maynert (nBM) synapses and show, for the first time, some cross-talk between the cAMP/PKA and PKC pathways in mammalian presynaptic nerve terminals.

GABAB receptor transduction mechanisms, and cross-talk between protein kinases A and C, in GABAergic terminals synapsing onto neurons of the rat nucleus basalis of Meynert

The transduction mechanisms underlying presynaptic GABAB receptor-mediated inhibition of transmitter release have been characterized for a variety of synapses in the central nervous system (CNS). These studies have suggested a range of transduction mechanisms, including a role for second messengers such as protein kinases A (PKA) and C (PKC). In the present study, we have examined the intracellular signalling pathways underlying baclofen-induced inhibition of GABA release from terminals synapsing onto rat basalis of Meynert neurons using patch-clamp recordings. Baclofen, a selective GABAB receptor agonist, reversibly decreased both evoked and spontaneous, miniature, GABAergic inhibitory postsynaptic currents (eIPSCs and mIPSCs, respectively). Such baclofen actions were completely abolished by CGP55845A, a selective GABAB receptor antagonist, and by staurosporine, a non-selective PKA and PKC inhibitor. The mIPSC frequency was still decreased by baclofen even in the presence of 4 AP, a K+ channel blocker, and Cd2+, a voltage-dependent calcium channel blocker. Pharmacological activation or inhibition of PKC activity affected basal GABA release and mildly affected the response to baclofen. Inhibition of the cAMP/PKA cascade also affected basal GABA release and, in a subset of neurons, occluded the effects of baclofen, suggesting that the GABAB receptor-mediated inhibitory action on GABA release was mediated via decreases in PKA activity. In addition, PKA inhibition occluded the effects of PKC modulation on both basal GABA release and on the response to baclofen. Our results characterize the transduction pathway of baclofen at these nucleus basalis of Maynert (nBM) synapses and show, for the first time, some cross-talk between the cAMP/PKA and PKC pathways in mammalian presynaptic nerve terminals.