The effect of hippocampal sympathetic ingrowth and cholinergic denervation on hippocampal M2 cholinergic receptors

doi:10.1016/0006-8993(95)00386-5

Brain Research

Volume 684, Issue 2, 3 July 1995, Pages 201-205

https://doi.org/10.1016/0006-8993(95)00386-5 Get rights and content

Abstract

After cholinergic denervation of the hippocampus, via medial septal (MS) lesions, peripheral sympathetic fibers, originating from the superior cervical ganglia, grow into the hippocampus. In this study, we sought to determine the effect of hippocampal sympathetic ingrowth (HSI) on the M₂ subtype of muscarinic cholinergic receptors, by examining the membrane bindingo of [³H]AF-DX 384 in hippocampal tissue from control rats, rats with HSI and rats with MS lesions+ concurrent ganglionectomy (CD group). In dorsal hippocampus, K_d was found to be increased while B_max was decreased in the CD group as compared with both the HSI and control group which did not differ from one another. In ventral hippocampus, K_d was found to be increased while B_max was decreased in the CD group when compared only with the control group. These results suggest that sympathetic ingrowth, which has its greatest concentration in dorsal hippocampus, can ‘normalize’ the M₂ receptor in hippocampus.

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Cited by (11)

Apoptotic protein expression and activation of caspases is changed following cholinergic denervation and hippocampal sympathetic ingrowth in rat hippocampus
2000, Neuroscience
Following cholinergic denervation of the hippocampus by medial septal lesions, an unusual neuronal reorganization occurs in which peripheral adrenergic fibers arising from superior cervical ganglia grow into the hippocampus (hippocampal sympathetic ingrowth). Recent studies suggest that a similar process, in which sympathetic noradrenergic axons invade the hippocampus, can occur in Alzheimer’s disease patients. In the last few years, the occurrence of apoptotic cell death has been studied in Alzheimer’s disease patients and in animal models of this disorder. Several studies suggest that the hippocampus is an important area to be considered for apoptotic cell death. In our studies in the rat hippocampus, we have measured the expression of inducers and blockers of apoptosis in membrane, cytosolic and mitochondrial fractions, and the activity of caspases. The level of cytosolic Fas was increased in cholinergic denervation compared to control and hippocampal sympathetic ingrowth groups. The membrane Fas ligand expression was significantly increased in hippocampal sympathetic ingrowth and in cholinergic denervation compared to the control group. The level of caspase-3 (CPP32) was increased in the cholinergic denervation group compared to control and hippocampal sympathetic ingrowth groups. The cytosolic expression of bcl-x was increased in hippocampal sympathetic ingrowth compared to control and cholinergic denervation. The cytosolic activity of caspase-3 appeared to be significantly decreased in hippocampal sympathetic ingrowth and increased in cholinergic denervation groups compared to control and cholinergic denervation/hippocampal sympathetic ingrowth, respectively.
From the present results, we suggest that cholinergic denervation may be responsible for pro-apoptotic responses, while hippocampal sympathetic ingrowth may protect neurons from apoptosis in rat dorsal hippocampus.
Effect of phospholipase C and protein kinase C following cholinergic denervation and hippocampal sympathetic ingrowth in rat hippocampus
2000, Neuroscience
Following cholinergic denervation of the hippocampus by medial septal lesions, an unusual neuronal reorganization occurs in which peripheral adrenergic fibers arising from the superior cervical ganglia grow into the hippocampus (hippocampal sympathetic ingrowth). We have reported previously that cholinergic denervation and hippocampal sympathetic ingrowth differentially affected cholinergically stimulated phosphoinositide hydrolysis, concentration and affinity of muscarinic receptors, Go-protein level and protein kinase C activity. To complete these studies, we determined whether cholinergic denervation and hippocampal sympathetic ingrowth influenced phospholipase C and protein kinase C expression in dorsal hippocampal membranes and cytosol. Using immunoblotting methods, the results showed that the 100,000 mol. wt subunit of phospholipase Cβ was increased in the membrane fraction in the hippocampal sympathetic ingrowth group by 45% compared to controls and the 150,000 mol.wt subunit was increased by 75% and 59% compared to controls and cholinergic denervation, respectively. For protein kinase C detection, immunoblots were prepared using antibodies selective for “classical” protein kinase C members (α, β, γ) and for the “novel” protein kinase C subfamily members (δ, θ). Membrane protein kinase Cβ was decreased in hippocampal sympathetic ingrowth by 35% compared to controls and by 41% compared to cytosolic hippocampal sympathetic ingrowth. Membrane protein kinase Cβ was decreased in cholinergic denervation by 28% compared to controls. When compared to membranes from controls and the cholinergic denervation group, and to cytosolic fractions from the hippocampal sympathetic ingrowth groups, respectively, the following membrane protein kinase isoforms were found to be decreased by hippocampal sympathetic ingrowth: γ by 55%, 40% and 57%; δ by 91.5%, 70% and 120%; θ by 95%, 100% and 86%.
In conclusion, our results may indicate the connection between the previously reported differential influence of hippocampal sympathetic ingrowth and cholinergic denervation on cholinergically stimulated phosphoinositol hydrolysis. The “normalization” of phosphoinositol hydrolysis found in hippocampal sympathetic ingrowth may be due to the increase in phospholipase Cβ expression in hippocampal sympathetic ingrowth membrane fractions. Since the activation of protein kinase C is known to block phosphoinositol hydrolysis, hippocampal sympathetic ingrowth “normalization” of phosphoinositol hydrolysis may result from a reduction in protein kinase expression in hippocampal sympathetic ingrowth membranes.
Ectopic noradrenergic hyperinnervation does not functionally compensate for neonatal forebrain acetylcholine lesion
2000, Brain Research
Citation Excerpt :
In support of this possibility is the finding that NE fibers from the superior cervical ganglion, which are known to innervate the hippocampus following fimbria/fornix transection in adult rats [7,8,11], have been shown to alter hippocampal muscarinic receptor function. Specifically, the presence of these fibers seemingly normalizes muscarinic receptors by preventing the upregulation of receptor number and decreases in phosphoinositol turnover normally produced by cholinergic denervation [17,31]. It is also possible that elevated cortical and hippocampal NE reflects a compensatory neurochemical response of the axonal innervation of these areas from the locus coeruleus.
Adult rats who have undergone neonatal 192 IgG-saporin induced lesions of forebrain acetylcholine (ACH) neurons are normal on many behavioral tasks. In this study we determined whether ectopic hippocampal ingrowths, a documented consequence of these neonatal cholinergic lesions, functionally compensate for ACH denervation in these rats. Neonatal rats underwent systemic 6-hydroxydopamine (6-OHDA) injections on postnatal days (PND) 1–3 to prevent the ingrowths, and/or intraventricular 192 IgG-saporin injections on PND 7. The 192 IgG-saporin profoundly reduced basal forebrain p75 neurotrophin receptor (p75^NTR) immunoreactive (IR) neurons. The 6-OHDA treatment abolished hippocampal and cortical dopamine-beta-hydroxylase (DBH) IR terminals, indicating the absence of normal norepinephrine (NE) innervation. Ectopic DBH IR and p75^NTR IR varicosities which occurred in the hippocampus of 192 IgG-saporin treated rats were also eliminated by 6-OHDA treatment. Behavioral testing in adulthood indicated no effect of the treatments on the Morris water maze. 192 IgG-saporin treatment caused perseveration during delayed spatial alternation (DSA) and increased working but not reference memory errors on the radial arm maze (RAM). The 6-OHDA plus 192 IgG-saporin treated rats did not differ from the 192 IgG-saporin only rats on any task. These results indicate that ectopic hippocampal NE ingrowths do not functionally compensate for neonatal ACH lesions. Neonatal forebrain ACH lesion impairs working memory on the RAM but the absence of an effect on DSA contraindicates a basic dysfunction of short term memory. Despite severe combined neonatal loss of forebrain ACH and NE innervation, behavior is remarkably intact.
Effects of pertussis toxin and Gα-protein-specific antibodies on phosphoinositide hydrolysis in rat brain membranes after cholinergic denervation and hippocampal sympathetic ingrowth
2000, Experimental Neurology
Cholinergic denervation of the hippocampal formation, via medial septal lesions, induces peripheral noradrenergic fibers, originating from the superior cervical ganglion, to grow into the hippocampus. We have previously reported that cholinergic denervation and hippocampal sympathetic ingrowth differentially affect guanosine-5′-O-(3-thiotriphosphate)- as well as guanosine-5′-O-(3-thiotriphosphate) + carbachol-stimulated polyphosphoinositide hydrolysis, suggesting an alteration in G proteins and/or the entire receptor complex. To examine the type of G protein which may be involved in these effects, rat dorsal hippocampal membranes were preincubated with pertussis toxin in the presence of guanosine-5′-O-(3-thiotriphosphate) and guanosine-5′-O-(3-thiotriphosphate) + carbachol. Pertussis toxin reduced guanosine-5′-O-(3-thiotriphosphate) in all groups, while guanosine-5′-O-(3-thiotriphosphate) + carbachol-stimulated phosphoinositide hydrolysis was reduced in controls and animals without sympathetic ingrowth but not in animals with hippocampal sympathetic ingrowth. This suggests that pertussis toxin-sensitive G proteins may be involved in the mediation of phosphoinositide hydrolysis. To confirm this hypothesis, membranes were preincubated with antibodies to Gαo and Gq/11. The Go antibody significantly decreased guanosine-5′-O-(3-thiotriphosphate) in all groups, while guanosine-5′-O-(3-thiotriphosphate) +carbachol-stimulated phosphoinositide hydrolysis was reduced only in hippocampal sympathetic ingrowth. Impairment of guanosine-5′-O-(3-thiotriphosphate) and carbachol-stimulated phosphoinositide hydrolysis was also decreased in all groups when preincubated with Gq/11 antibody. To determine whether hippocampal sympathetic ingrowth or cholinergic denervation altered the concentration of various G proteins, immunoblotting methodology was utilized. Gq/11 concentrations were found to be equivalent among groups. The density of Go1, Go2, and Go3 isoforms was significantly increased in the cholinergic denervation, while in the hippocampal sympathetic ingrowth only group Go3 was significantly increased. When assessed as total Go protein, density was increased significantly only in the cholinergic denervation group. Overall, these results suggest that hippocampal sympathetic ingrowth and cholinergic denervation induce alterations in phosphoinositide hydrolysis through both the Gq/11 and the Go proteins and that the coupling between muscarinic receptor and G protein is the possible site which affects changes in phosphoinositide turnover. Our results also suggest that cholinergic denervation and hippocampal sympathetic ingrowth may mediate phosphoinositide hydrolysis through an effect on different isoforms of the same G protein.
Modulation of 5-hydroxytryptamine release in hippocampal slices of rats: Effects of fimbria-fornix lesions on 5-HT(1B)-autoreceptor and α<inf>2</inf>- heteroreceptor function
1999, Brain Research Bulletin
Fimbria-fornix lesions disrupt important parts of serotonergic and noradrenergic hippocampal afferents and elicit sprouting of sympathetic fibers from the superior cervical ganglion. Since 5-hydroxytryptamine (5-HT) release in the hippocampus is modulated by 5-HT_1B auto- and α₂-heteroreceptors, we investigated whether such lesions may alter these presynaptic mechanisms. Hippocampal slices of sham-operated (SHAM) and fimbria-fornix–lesioned (LES) rats (14 months after surgery) were preincubated with [³H]5-HT, superfused continuously, and stimulated electrically using two stimulation conditions: either (a) 360 pulses 3 Hz, or (b) 20 pulses 100 Hz (2 ms, 28 mA, 4 V/chamber). The amount of [³H]5-HT taken up by slices from LES rats was significantly reduced, whereas the evoked 5-HT release (in percent of tissue-³H) was unchanged compared to that of SHAM rats. The 5-HT_1B agonist CP 93,129 or the α₂-agonist UK 14,304 reduced the evoked 5-HT release more potently in slices from LES rats, but only using stimulation condition (a), which permits inhibition by endogenously released transmitters. In LES rats, the facilitatory effect of the 5-HT antagonist metitepine was weaker, whereas that of the α₂-antagonist idazoxane was more pronounced than in SHAM rats. In LES rats, hippocampal 5-HT content was reduced to about 45% of SHAM levels, whereas that of noradrenaline was increased by about 30% (high-performance liquid chromatography). We conclude: (1) despite LES-induced changes in tissue levels of endogenous ligands, there is no down- or upregulation of 5-HT_1B-autoreceptors or α₂-heteroreceptors on serotonergic neurons in the denervated rat hippocampus. (2) The reduced endogenous autoinhibition (by 5-HT) seems to be compensated for by an increased heteroinhibition (by noradrenaline).
Cholinergic denervation and sympathetic ingrowth result in persistent changes in hippocampal muscarinic receptors
1997, Neuroscience
Our laboratory has been utilizing the model of hippocampal sympathetic ingrowth, which has been suggested to occur in Alzheimer's disease, to investigate the effects of cholinergic denervation and hippocampal rearrangements. After cholinergic denervation by medial septal lesions, peripheral sympathetic fibres originating from the superior cervical ganglia grow into the rat hippocampus. This hippocampal sympathetic ingrowth can be prevented by superior cervical ganglionectomy. We examined the long-term effects of these treatments on muscarinic receptors by comparing [³H]quinuclidinyl benzilate binding in rat dorsal hippocampus four and 12 weeks post lesion. Four groups of animals were employed, including controls (sham lesion + sham ganglionectomy), animals with ingrowth (medial septal lesion + sham ganglionectomy), animals with cholinergic denervation alone (medial septal lesion + ganglionectomy), and ganglionectomy alone (sham lesion + ganglionectomy) animals. In dorsal hippocampus four weeks post lesion, binding affinity was similar among all groups, while muscarinic receptor number was increased in ingrowth animals as compared to both the control (P<0.0002) and ganglionectomy animals (P<0.01). By 12 weeks, receptor affinity was significantly decreased in ingrowth (P<0.0001) and cholinergic denervation (P<0.0003) groups, and receptor number remained significantly elevated in ingrowth animals as compared to control (P<0.01), ganglionectomy (P<0.02) and cholinergic denervation (P<0.01) groups.
The decrease in muscarinic receptor affinity may provide some insight into the ineffectiveness of cholinomimetic therapies in Alzheimer's disease, in that agonist efficacy would be reduced at the receptor.

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The effect of hippocampal sympathetic ingrowth and cholinergic denervation on hippocampal M2 cholinergic receptors

Abstract

J. Neurosci.

Eur. J. Pharmacol.

Brain Res.

Brain Res. Rev.

Pharmacol. Biochem. Behav.

Exp. Neurol.