Does the release of acetylcholine in septal slices originate from intrinsic cholinergic neurons bearing p75ntr receptors? a study using 192 IgG-saporin lesions in rats

In previous studies electrically-evoked release of acetylcholine in septal slices was demonstrated. The present experiment aimed at verifying if this release involved intrinsic neurons bearing p75(NTR) receptors. Long-Evans rats sustained injections of 192 IgG-saporin into the medial septum/diagonal band of Broca (0.8 microg). Sham-operated rats served as controls. Two to 3.5 weeks later, the electrically-evoked release of acetylcholine ([(3)H]ACh) was measured in slices from the lateral septum (LS), medial septum (MS) and diagonal band of Broca (DBB). Choline acetyltransferase (ChAT) and acetylcholinesterase (AChE) activity, and monoamine concentrations were measured in the septum, cortex and hippocampus. The lesion extent was also assessed by ChAT immunostaining in a separate series of rats. In the septum, the number of ChAT-positive neurons was depleted dramatically (>90% at the level of the injection site). In the hippocampus, the lesions reduced ChAT and AChE activity by 91% and 84%, respectively. In the cortex, this reduction was weaker (-55% and -47%). In the septal region, the reduction was either weak or not significant. The evoked release of acetylcholine in septal slices was not reduced, except in the slices from the LS (-64%). The effects of physostigmine and atropine confirmed the presence of autoreceptors. Our data exclude that a major part of the acetylcholine released by MS and DBB slices derived from intrinsic neurons bearing p75(NTR) receptors. In the LS, part of the released acetylcholine might be from projections of such neurons located in the LS, MS and/or DBB. These data also suggest that the MS and the DBB may be the target of extrinsic cholinergic innervation that does not bear p75(NTR) receptors

Neurotransmitter release and its presynaptic modulation in the rat hippocampus after selective damage to cholinergic or/and serotonergic afferents

Male Long-Evans rats sustained injections of 5,7-dihydroxytryptamine (5,7-DHT) into the fimbria-fornix and the cingular bundle or/and intraseptal injections of 192 IgG-saporin to induce serotonergic or/and cholinergic hippocampal denervations; Sham-operated rats served as controls. Four to ten weeks after lesioning, we measured (i). the electrically evoked release of acetylcholine ([3H]ACh), noradrenaline ([3H]NA) and serotonin ([3H]5-HT) in hippocampal slices in the presence of drugs acting on auto- or heteroreceptors, (ii). the nicotine-evoked release of NA and (iii). the choline acetyltransferase (ChAT) activity and the concentration of monoamines in homogenates. Saporin lesions reduced the accumulation of [3H]choline, the release of [3H]ACh and the ChAT activity, but increased the concentration of NA and facilitated the release of [3H]NA evoked by nicotine. 5,7-DHT lesions reduced the accumulation and the release of [3H]5-HT, the concentration of 5-HT, and also facilitated the release of [3H]NA evoked by nicotine. Accumulation and electrically evoked release of [3H]NA were not altered by either lesion. The combination of both toxins resulted in an addition of their particular effects. The 5-HT(1B) receptor agonist, CP 93129, and the muscarinic agonist, oxotremorine, reduced the release of [3H]ACh in control and 5,7-DHT-lesioned rats; in rats injected with saporin, their effects could not be measured reliably. CP 93129 and the alpha(2)-adrenoceptor agonist, UK 14304, reduced the release of [3H]5-HT in all groups by about 65%. IN CONCLUSION: (i). selective neurotoxins can be combined to enable controlled and selective damage of hippocampal transmitter systems; (ii). 5-HT exerts an inhibitory influence on the nicotine-evoked release of NA, but partial serotonergic lesions do not influence the release of ACh at a presynaptic level and (iii). presynaptic modulatory mechanisms involving auto- and heteroreceptors may be conserved on fibres spared by the lesions

3D Reconstruction of the Neurovascular Unit Reveals Differential Loss of Cholinergic Innervation in the Cortex and Hippocampus of the Adult Mouse Brain

Increasing evidence supports a role for cerebrovasculature dysfunction in the etiology of Alzheimer’s disease (AD). Blood vessels in the brain are composed of a collection of cells and acellular material that comprise the neurovascular unit (NVU). The NVU in the hippocampus and cortex receives innervation from cholinergic neurons that originate in the basal forebrain. Death of these neurons and their nerve fibers is an early feature of AD. However, the effect of the loss of cholinergic innervation on the NVU is not well characterized. The purpose of this study was to evaluate the effect of the loss of cholinergic innervation of components of the NVU at capillaries, arteries and veins in the hippocampus and cortex. Adult male C57BL/6 mice received an intracerebroventricular injection of the immunotoxin p75NTR mu-saporin to induce the loss of cholinergic neurons. Quadruple labeling immunohistochemistry and 3D reconstruction were carried out to characterize specific points of contact between cholinergic fibers and collagen IV, smooth muscle cells and astrocyte endfeet. Innate differences were observed between vessels of the hippocampus and cortex of control mice, including a greater amount of cholinergic contact with perivascular astrocytes in hippocampal capillaries and a thicker basement membrane in hippocampal veins. Saporin treatment induced a loss of cholinergic innervation at the arterial basement membrane and smooth muscle cells of both the hippocampus and the cortex. In the cortex, there was an additional loss of innervation at the astrocytic endfeet. The current results suggest that cortical arteries are more strongly affected by cholinergic denervation than arteries in the hippocampus. This regional variation may have implications for the etiology of the vascular pathology that develops in AD

Selective Cholinergic Depletion in Medial Septum Leads to Impaired Long Term Potentiation and Glutamatergic Synaptic Currents in the Hippocampus

Cholinergic depletion in the medial septum (MS) is associated with impaired hippocampal-dependent learning and memory. Here we investigated whether long term potentiation (LTP) and synaptic currents, mediated by alpha-amino-3-hydroxy-5-methyl-isoxazole-4-propionate (AMPA) and N-methyl-D-aspartate (NMDA) receptors in the CA1 hippocampal region, are affected following cholinergic lesions of the MS. Stereotaxic intra-medioseptal infusions of a selective immunotoxin, 192-saporin, against cholinergic neurons or sterile saline were made in adult rats. Four days after infusions, hippocampal slices were made and LTP, whole cell, and single channel (AMPA or NMDA receptor) currents were recorded. Results demonstrated impairment in the induction and expression of LTP in lesioned rats. Lesioned rats also showed decreases in synaptic currents from CA1 pyramidal cells and synaptosomal single channels of AMPA and NMDA receptors. Our results suggest that MS cholinergic afferents modulate LTP and glutamatergic currents in the CA1 region of the hippocampus, providing a potential synaptic mechanism for the learning and memory deficits observed in the rodent model of selective MS cholinergic lesioning

Does the release of acetylcholine in septal slices originate from intrinsic cholinergic neurons bearing p75ntr receptors? a study using 192 IgG-saporin lesions in rats

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5,7-dihydroxytryptamine lesions enhance and serotonergic grafts normalize the evoked overflow of acetylcholine in rat hippocampal slices: Serotonin depletion facilitates acetylcholine release

Adult rats were subjected to intracerebroventricular injections of 5,7-dihydroxytryptamine (5,7-DHT; 150 micro g) and, 15 days later, to intrahippocampal grafts of fetal raphe cell suspensions. About 11 months later, we assessed baseline and electrically evoked release of tritium ([3H]) in hippocampal slices, preloaded with tritiated ([3H])choline or [3H]serotonin (5-HT), in the presence or absence of the 5-HT1B receptor agonist CP-93,129 and the 5-HT receptor antagonist methiothepine. HPLC determinations of monoamine concentrations were also performed. The lesions reduced the concentration of 5-HT (-90%) and the accumulation (-80%) as well as the evoked release (-90%) of [3H]5-HT. They also decreased the inhibitory effects of CP-93,129 on the evoked release of [3H]5-HT. Most interestingly, they facilitated the evoked release of [3H]acetylcholine (+20%). In slices from rats subjected to lesions and grafts, the responsiveness of the serotonergic autoreceptors (presumably located on the terminals of the grafted neurons) and the release of acetylcholine were close to normal. These results confirm that grafts rich in serotonergic neurons may partially compensate for the dramatic effects of 5,7-DHT lesions on serotonergic hippocampal functions. The lesion-induced reduction of the 5-HT1B autoreceptor-mediated inhibition of evoked 5-HT release may be an adaptation enhancing serotonergic transmission in the (few) remaining terminals. The facilitated release of acetylcholine is probably caused by a reduced serotonergic tone on the inhibitory 5-HT1B heteroreceptors of the cholinergic terminals. When related to data in the literature, this facilitation may be of particular interest in terms of transmitter-based strategies developed to tackle cognitive symptoms related to neurodegenerative diseases

Ethanol, 3,4-Methylenedioxymethamphetamine (Ecstasy) and Their Combination: Long-Term Behavioral, Neurochemical and Neuropharmacological Effects in the Rat

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