1
|
Whitley K, Briggs SB, Sharma K, Parent MB. Don't ignore the middle: Distinct mnemonic functions of intermediate hippocampus. Hippocampus 2024. [PMID: 39096197 DOI: 10.1002/hipo.23629] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/29/2023] [Revised: 06/21/2024] [Accepted: 07/18/2024] [Indexed: 08/05/2024]
Abstract
The dorsal region of the hippocampus (dHC) mediates many of the mnemonic functions traditionally associated with the hippocampus proper, such as spatial and episodic memory, whereas ventral hippocampus (vHC) has been extensively implicated in emotional memory and motivational processes. By contrast, the functions of the intermediate hippocampus (iHC) are far less understood. In this study, we aimed to investigate the mnemonic functions of iHC by reversibly inactivating iHC prior to testing memory in behavioral tasks dependent on the integrity of dHC, iHC, or vHC, namely, rapid place water maze, inhibitory avoidance, spontaneous alternation, and temporal ordering of odors. Given our previous findings showing that dHC and vHC are involved in mnemonic control of ingestive behavior, we also assessed the effects of iHC inactivation on sucrose intake. The results showed that pharmacological inhibition of iHC impairs rapid place water maze memory, which has been previously shown to be dependent on iHC but not dHC or vHC. iHC inactivation does not impact memory dependent on dHC (spontaneous alternation), vHC (temporal odor memory), or either dHC or vHC (inhibitory avoidance), and only modestly affects sucrose intake. These findings provide support for the involvement of iHC in mnemonic functions that are distinct from dHC and vHC and highlight the need to further advance our understanding of the functions of this hippocampal region that has been relatively understudied.
Collapse
Affiliation(s)
- Kathryn Whitley
- Neuroscience Institute, Georgia State University, Atlanta, Georgia, USA
| | - Sherri B Briggs
- Neuroscience Institute, Georgia State University, Atlanta, Georgia, USA
| | - Karan Sharma
- Neuroscience Institute, Georgia State University, Atlanta, Georgia, USA
| | - Marise B Parent
- Neuroscience Institute, Georgia State University, Atlanta, Georgia, USA
| |
Collapse
|
2
|
Anderson T, Sharma S, Kelberman MA, Ware C, Guo N, Qin Z, Weinshenker D, Parent MB. Obesity during preclinical Alzheimer's disease development exacerbates brain metabolic decline. J Neurochem 2024; 168:801-821. [PMID: 37391269 DOI: 10.1111/jnc.15900] [Citation(s) in RCA: 6] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2023] [Revised: 05/29/2023] [Accepted: 06/13/2023] [Indexed: 07/02/2023]
Abstract
Alzheimer's disease (AD) is the most common form of dementia. Obesity in middle age increases AD risk and severity, which is alarming given that obesity prevalence peaks at middle age and obesity rates are accelerating worldwide. Midlife, but not late-life obesity increases AD risk, suggesting that this interaction is specific to preclinical AD. AD pathology begins in middle age, with accumulation of amyloid beta (Aβ), hyperphosphorylated tau, metabolic decline, and neuroinflammation occurring decades before cognitive symptoms appear. We used a transcriptomic discovery approach in young adult (6.5 months old) male and female TgF344-AD rats that overexpress mutant human amyloid precursor protein and presenilin-1 and wild-type (WT) controls to determine whether inducing obesity with a high-fat/high-sugar "Western" diet during preclinical AD increases brain metabolic dysfunction in dorsal hippocampus (dHC), a brain region vulnerable to the effects of obesity and early AD. Analyses of dHC gene expression data showed dysregulated mitochondrial and neurotransmission pathways, and up-regulated genes involved in cholesterol synthesis. Western diet amplified the number of genes that were different between AD and WT rats and added pathways involved in noradrenergic signaling, dysregulated inhibition of cholesterol synthesis, and decreased intracellular lipid transporters. Importantly, the Western diet impaired dHC-dependent spatial working memory in AD but not WT rats, confirming that the dietary intervention accelerated cognitive decline. To examine later consequences of early transcriptional dysregulation, we measured dHC monoamine levels in older (13 months old) AD and WT rats of both sexes after long-term chow or Western diet consumption. Norepinephrine (NE) abundance was significantly decreased in AD rats, NE turnover was increased, and the Western diet attenuated the AD-induced increases in turnover. Collectively, these findings indicate obesity during prodromal AD impairs memory, potentiates AD-induced metabolic decline likely leading to an overproduction of cholesterol, and interferes with compensatory increases in NE transmission.
Collapse
Affiliation(s)
- Thea Anderson
- Neuroscience Institute, Georgia State University, Atlanta, Georgia, USA
| | - Sumeet Sharma
- Department of Psychiatry and Behavioral Sciences, Emory University School of Medicine, Atlanta, Georgia, USA
| | - Michael A Kelberman
- Department of Human Genetics, Emory University School of Medicine, Atlanta, Georgia, USA
| | - Christopher Ware
- Neuroscience Institute, Georgia State University, Atlanta, Georgia, USA
| | - Nanxi Guo
- Department of Biostatistics and Bioinformatics, Emory University, Atlanta, Georgia, USA
| | - Zhaohui Qin
- Department of Biostatistics and Bioinformatics, Emory University, Atlanta, Georgia, USA
| | - David Weinshenker
- Department of Human Genetics, Emory University School of Medicine, Atlanta, Georgia, USA
| | - Marise B Parent
- Neuroscience Institute, Georgia State University, Atlanta, Georgia, USA
- Department of Psychology, Georgia State University, Georgia, USA
| |
Collapse
|
3
|
Chuluun B, Pittaras E, Hong H, Fisher N, Colas D, Ruby NF, Heller HC. Suprachiasmatic lesions restore object recognition in down syndrome model mice. Neurobiol Sleep Circadian Rhythms 2020; 8:100049. [PMID: 32195448 PMCID: PMC7075983 DOI: 10.1016/j.nbscr.2020.100049] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2019] [Revised: 02/04/2020] [Accepted: 02/12/2020] [Indexed: 01/03/2023] Open
Abstract
The Ts65Dn mouse is a well-studied model of trisomy 21, Down syndrome. This mouse strain has severe learning disability as measured by several rodent learning tests that depend on hippocampal spatial memory function. Hippocampal long-term potentiation (LTP) is deficient in these mice. Short-term daily treatment with low-dose GABA receptor antagonists rescue spatial learning and LTP in Ts65Dn mice leading to the hypothesis that the learning disability is due to GABAergic over-inhibition of hippocampal circuits. The fact that the GABA receptor antagonists were only effective if delivered during the daily light phase suggested that the source of the excess GABA was controlled directly or indirectly by the circadian system. The central circadian pacemaker of mammals is the suprachiasmatic nucleus (SCN), which is largely a GABAergic nucleus. In this study we investigated whether elimination of the SCN in Ts65Dn mice would restore their ability to form recognition memories as tested by the novel object recognition (NOR) task. Full, but not partial lesions of the SCN of Ts65Dn mice normalized their ability to perform on the NOR test. These results suggest that the circadian system modulates neuroplasticity over the time frame involved in the process of consolidation of recognition memories.
Collapse
|
4
|
Heller HC, Ruby NF. Functional Interactions Between Sleep and Circadian Rhythms in Learning and Learning Disabilities. Handb Exp Pharmacol 2019; 253:425-440. [PMID: 30443786 DOI: 10.1007/164_2018_176] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/13/2023]
Abstract
The propensity for sleep is timed by the circadian system. Many studies have shown that learning and memory performance is affected by circadian phase. And, of course it is well established that critical processes of memory consolidation occur during and depend on sleep. This chapter presents evidence that sleep and circadian rhythms do not just have separate influences on learning and memory that happen to coincide because of the circadian timing of sleep, but rather sleep and circadian systems have a critical functional interaction in the processes of memory consolidation. The evidence comes primarily from research on two models of learning disability: Down's syndrome model mice and Siberian hamsters. The Down's syndrome model mouse (Ts65Dn) has severe learning disability that has been shown to be due to GABAergic over-inhibition. Short-term, chronic therapies with GABAA antagonists restore learning ability in these mice long-term, but only if the antagonist treatments are given during the dark or sleep phase of the daily rhythm. The Siberian hamster is a model circadian animal except for the fact that a light treatment that gives the animal a phase advance on one day and a phase delay on the next day can result in total circadian arrhythmia for life. Once arrhythmic, the hamsters cannot learn. Learning, but not rhythmicity, is restored by short-term chronic treatment with GABA antagonists. Like many other species, if these hamsters are made arrhythmic by SCN lesion, their learning is unaffected. However, if made arrhythmic and learning disabled by the light treatment, subsequent lesions of their SCNs restore learning. SCN lesions also appear to restore learning in the Ts65Dn mice. The collective work on these two animal models of learning disability suggests that the circadian system modulates neuroplasticity. Our hypothesis is that a previously unrecognized function of the circadian system is to dampen neuroplasticity during the sleep phase to stabilize memory transcripts during their transfer to long-term memory. Thus, sleep and circadian systems have integrated roles to play in memory consolidation and do not just have separate but coincident influences on that process.
Collapse
Affiliation(s)
- H Craig Heller
- Biology Department, Stanford University, Stanford, CA, USA.
| | - Norman F Ruby
- Biology Department, Stanford University, Stanford, CA, USA
| |
Collapse
|
5
|
Supplementation with zinc in rats enhances memory and reverses an age-dependent increase in plasma copper. Behav Brain Res 2017; 333:179-183. [PMID: 28693861 DOI: 10.1016/j.bbr.2017.07.007] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2017] [Revised: 07/03/2017] [Accepted: 07/06/2017] [Indexed: 12/26/2022]
Abstract
Zinc and copper are essential trace elements. Dyshomeostasis in these two metals has been observed in Alzheimer's disease, which causes profound cognitive impairment. Insulin therapy has been shown to enhance cognitive performance; however, recent data suggest that this effect may be at least in part due to the inclusion of zinc in the insulin formulation used. Zinc plays a key role in regulation of neuronal glutamate signaling, suggesting a possible link between zinc and memory processes. Consistent with this, zinc deficiency causes cognitive impairments in children. The effect of zinc supplementation on short- and long-term recognition memory, and on spatial working memory, was explored in young and adult male Sprague Dawley rats. After behavioral testing, hippocampal and plasma zinc and copper were measured. Age increased hippocampal zinc and copper, as well as plasma copper, and decreased plasma zinc. An interaction between age and treatment affecting plasma copper was also found, with zinc supplementation reversing elevated plasma copper concentration in adult rats. Zinc supplementation enhanced cognitive performance across tasks. These data support zinc as a plausible therapeutic intervention to ameliorate cognitive impairment in disorders characterized by alterations in zinc and copper, such as Alzheimer's disease.
Collapse
|
6
|
Gold PE, Newman LA, Scavuzzo CJ, Korol DL. Modulation of multiple memory systems: from neurotransmitters to metabolic substrates. Hippocampus 2014; 23:1053-65. [PMID: 23929581 DOI: 10.1002/hipo.22182] [Citation(s) in RCA: 40] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 08/02/2013] [Indexed: 01/14/2023]
Abstract
This article reviews evidence showing that neurochemical modulators can regulate the relative participation of the hippocampus and striatum in learning and memory tasks. For example, relative release of acetylcholine increases in the hippocampus and striatum reflects the relative engagement of these brain systems during learning of place and response tasks. Acetylcholine release is regulated in part by available brain glucose levels, which themselves are dynamically modified during learning. Recent findings suggest that glucose acts through astrocytes to deliver lactate to neurons. Brain glycogen is contained in astrocytes and provides a capacity to deliver energy substrates to neurons when needed, a need that can be generated by training on tasks that target hippocampal and striatal processing mechanisms. These results integrate an increase in blood glucose after epinephrine release from the adrenal medulla with provision of brain energy substrates, including lactate released from astrocytes. Together, the availability of peripheral and central energy substrates regulate the processing of learning and memory within and across multiple neural systems. Dysfunctions of the physiological steps that modulate memory--from hormones to neurotransmitters to metabolic substrates--may contribute importantly to some of the cognitive impairments seen during normal aging and during neurodegenerative diseases.
Collapse
Affiliation(s)
- Paul E Gold
- Department of Biology, Syracuse University, Syracuse, New York
| | | | | | | |
Collapse
|
7
|
Gold PE, Korol DL. Forgetfulness during aging: an integrated biology. Neurobiol Learn Mem 2014; 112:130-8. [PMID: 24674745 DOI: 10.1016/j.nlm.2014.03.005] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2013] [Revised: 03/10/2014] [Accepted: 03/13/2014] [Indexed: 01/07/2023]
Abstract
Age-related impairments in memory are often attributed to failures, at either systems or molecular levels, of memory storage processes. A major characteristic of changes in memory with increasing age is the advent of forgetfulness in old vs. young animals. This review examines the contribution of a dysfunction of the mechanisms responsible for modulating the maintenance of memory in aged rats. A memory-modulating system that includes epinephrine, acting through release of glucose from liver glycogen stores, potently enhances memory in young rats. In old rats, epinephrine loses its ability to release glucose and loses its efficacy in enhancing memory. Brain measures of extracellular levels of glucose in the hippocampus during memory testing show decreases in glucose in both young and old rats, but the decreases are markedly greater in extent and duration in old rats. Importantly, the old rats do not have the ability to increase blood glucose levels in response to arousal-related epinephrine release, which is retained and even increased in aged rats. Glucose appears to be able to reverse fully the increased rate of forgetting seen in old rats. This set of findings suggests that physiological mechanisms outside of the brain, i.e. changes in neuroendocrine functions, may contribute substantially to the onset of rapid forgetting in aged animals.
Collapse
Affiliation(s)
- Paul E Gold
- Department of Biology, Syracuse University, Syracuse, NY 13244, United States.
| | - Donna L Korol
- Department of Biology, Syracuse University, Syracuse, NY 13244, United States
| |
Collapse
|
8
|
Ruby NF, Fernandez F, Garrett A, Klima J, Zhang P, Sapolsky R, Heller HC. Spatial memory and long-term object recognition are impaired by circadian arrhythmia and restored by the GABAAAntagonist pentylenetetrazole. PLoS One 2013; 8:e72433. [PMID: 24009680 PMCID: PMC3756994 DOI: 10.1371/journal.pone.0072433] [Citation(s) in RCA: 58] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2013] [Accepted: 07/09/2013] [Indexed: 11/18/2022] Open
Abstract
Performance on many memory tests varies across the day and is severely impaired by disruptions in circadian timing. We developed a noninvasive method to permanently eliminate circadian rhythms in Siberian hamsters (Phodopussungorus) so that we could investigate the contribution of the circadian system to learning and memory in animals that are neurologically and genetically intact. Male and female adult hamsters were rendered arrhythmic by a disruptive phase shift protocol that eliminates cycling of clock genes within the suprachiasmatic nucleus (SCN), but preserves sleep architecture. These arrhythmic animals have deficits in spatial working memory and in long-term object recognition memory. In a T-maze, rhythmic control hamsters exhibited spontaneous alternation behavior late in the day and at night, but made random arm choices early in the day. By contrast, arrhythmic animals made only random arm choices at all time points. Control animals readily discriminated novel objects from familiar ones, whereas arrhythmic hamsters could not. Since the SCN is primarily a GABAergic nucleus, we hypothesized that an arrhythmic SCN could interfere with memory by increasing inhibition in hippocampal circuits. To evaluate this possibility, we administered the GABAA antagonist pentylenetetrazole (PTZ; 0.3 or 1.0 mg/kg/day) to arrhythmic hamsters for 10 days, which is a regimen previously shown to produce long-term improvements in hippocampal physiology and behavior in Ts65Dn (Down syndrome) mice. PTZ restored long-term object recognition and spatial working memory for at least 30 days after drug treatment without restoring circadian rhythms. PTZ did not augment memory in control (entrained) animals, but did increase their activity during the memory tests. Our findings support the hypothesis that circadian arrhythmia impairs declarative memory by increasing the relative influence of GABAergic inhibition in the hippocampus.
Collapse
Affiliation(s)
- Norman F Ruby
- Biology Department, Stanford University, Stanford, California, USA.
| | | | | | | | | | | | | |
Collapse
|
9
|
Abstract
This article reviews some of the neuroendocrine bases by which emotional events regulate brain mechanisms of learning and memory. In laboratory rodents, there is extensive evidence that epinephrine influences memory processing through an inverted-U relationship, at which moderate levels enhance and high levels impair memory. These effects are, in large part, mediated by increases in blood glucose levels subsequent to epinephrine release, which then provide support for the brain processes engaged by learning and memory. These brain processes include augmentation of neurotransmitter release and of energy metabolism, the latter apparently including a key role for astrocytic glycogen. In addition to up- and down-regulation of learning and memory in general, physiological concomitants of emotion and arousal can also switch the neural system that controls learning at a particular time, at once improving some attributes of learning and impairing others in a manner that results in a change in the strategy used to solve a problem.
Collapse
Affiliation(s)
- Paul E Gold
- Department of Biology, Syracuse University Syracuse, NY, USA
| | | |
Collapse
|
10
|
Henderson YO, Smith GP, Parent MB. Hippocampal neurons inhibit meal onset. Hippocampus 2012; 23:100-7. [DOI: 10.1002/hipo.22062] [Citation(s) in RCA: 63] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 07/16/2012] [Indexed: 01/29/2023]
|
11
|
Albiston AL, Diwakarla S, Fernando RN, Mountford SJ, Yeatman HR, Morgan B, Pham V, Holien JK, Parker MW, Thompson PE, Chai SY. Identification and development of specific inhibitors for insulin-regulated aminopeptidase as a new class of cognitive enhancers. Br J Pharmacol 2012; 164:37-47. [PMID: 21470200 DOI: 10.1111/j.1476-5381.2011.01402.x] [Citation(s) in RCA: 65] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022] Open
Abstract
Two structurally distinct peptides, angiotensin IV and LVV-haemorphin 7, both competitive high-affinity inhibitors of insulin-regulated aminopeptidase (IRAP), were found to enhance aversion-associated and spatial memory in normal rats and to improve performance in a number of memory tasks in rat deficits models. These findings provide compelling support for the development of specific, high-affinity inhibitors of the enzyme as new cognitive enhancing agents. Different classes of IRAP inhibitors have been developed including peptidomimetics and small molecular weight compounds identified through in silico screening with a homology model of the catalytic domain of IRAP. The proof of principal that inhibition of IRAP activity results in facilitation of memory has been obtained by the demonstration that the small-molecule IRAP inhibitors also exhibit memory-enhancing properties.
Collapse
Affiliation(s)
- Anthony L Albiston
- Howard Florey Institute, University of Melbourne, Parkville, Victoria, Australia
| | | | | | | | | | | | | | | | | | | | | |
Collapse
|
12
|
Krebs-Kraft DL, Parent MB. Septal co-infusions of glucose with the benzodiazepine agonist chlordiazepoxide impair memory, but co-infusions of glucose with the opiate morphine do not. Physiol Behav 2009; 99:438-44. [PMID: 20005883 DOI: 10.1016/j.physbeh.2009.12.002] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2009] [Revised: 11/24/2009] [Accepted: 12/04/2009] [Indexed: 10/20/2022]
Abstract
We have found repeatedly that medial septal (MS) infusions of glucose impair memory when co-infused with the gamma-amino butyric acid (GABA) agonist muscimol. The present experiments sought to determine whether the memory-impairing effects of this concentration of glucose would generalize to another GABA(A) receptor agonist and to an agonist from another neurotransmitter system that is known to impair memory. Specifically, we determined whether the dose of glucose that produces memory deficits when combined with muscimol in the MS would also impair memory when co-infused with the GABA(A) receptor modulator chlordiazepoxide (CDP) or the opiate morphine. Male Sprague-Dawley rats were given MS co-infusions and then 15 min later tested for spontaneous alternation or given shock avoidance training (retention tested 48 h later). The results showed that MS infusions of the higher dose of glucose with morphine did not produce memory deficits, whereas, the performance of rats given MS co-infusions of CDP with glucose was impaired. These findings suggest that the memory-impairing effects of brain glucose administration may involve an interaction with the GABA(A) receptor.
Collapse
Affiliation(s)
- Desiree L Krebs-Kraft
- Department of Psychology and Center for Behavioral Neuroscience, Georgia State University, Atlanta, GA 30303, USA.
| | | |
Collapse
|
13
|
Krebs-Kraft DL, Rauw G, Baker GB, Parent MB. Zero net flux estimates of septal extracellular glucose levels and the effects of glucose on septal extracellular GABA levels. Eur J Pharmacol 2009; 611:44-52. [PMID: 19345207 PMCID: PMC2866298 DOI: 10.1016/j.ejphar.2009.03.055] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2008] [Revised: 03/17/2009] [Accepted: 03/23/2009] [Indexed: 11/21/2022]
Abstract
Although hippocampal infusions of glucose enhance memory, we have found repeatedly that septal glucose infusions impair memory when gamma-aminobutyric acid (GABA) receptors are activated. For instance, hippocampal glucose infusions reverse the memory-impairing effects of co-infusions of the GABA agonist muscimol, whereas septal glucose infusions exacerbate memory deficits produced by muscimol. One potential explanation for these deleterious effects of glucose in the septum is that there are higher levels of endogenous extracellular fluid glucose concentrations in the septum than in the hippocampus. Another hypothesis is that septal glucose infusions impair memory by increasing septal GABA synthesis or release, which is possible because elevating glucose increases GABA levels in other brain regions. To test these hypotheses, Experiment 1 quantified extracellular fluid glucose levels in the septum and hippocampus using zero net flux in vivo microdialysis procedures in conscious, freely moving rats. Experiment 2 determined whether septal infusions of glucose would increase GABA concentrations in dialysates obtained from the septum. The results of Experiment 1 indicated that extracellular fluid glucose levels in the hippocampus and septum are comparable. The results of Experiment 2 showed that co-infusions of glucose with muscimol, at doses that did not affect memory on their own, decreased percent alternation memory scores. However, none of the infusions significantly affected GABA levels. Collectively, these findings suggest that the memory-impairing effects of septal infusions of glucose are not likely due to regional differences in basal extracellular fluid glucose concentrations and are not mediated via an increase in septal GABA release.
Collapse
|
14
|
Zhou L, Liu YW, Peoples RW, Yang M, Tian X, Ai YX, Pang YP, Li ZW, Han YF, Li CY. Mechanism of bis(7)-tacrine inhibition of GABA-activated current in cultured rat hippocampal neurons. Neuropharmacology 2009; 57:33-40. [PMID: 19393253 DOI: 10.1016/j.neuropharm.2009.04.004] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2009] [Accepted: 04/09/2009] [Indexed: 11/17/2022]
Abstract
Bis(7)-tacrine is a novel dimeric acetylcholinesterase inhibitor derived from tacrine that shows promise for the treatment of Alzheimer's disease. We have previously reported that bis(7)-tacrine inhibits GABA(A) receptors. In the present study we investigated the mechanism of bis(7)-tacrine inhibition of GABA(A) receptor function using whole-cell patch-clamp recording in cultured rat hippocampal neurons. Bis(7)-tacrine produced a gradual decline of GABA-activated current to a steady-state, but this was not an indication of use-dependence, as the gradually declining component could be eliminated by exposure to bis(7)-tacrine prior to GABA application. In addition, bis(7)-tacrine inhibition did not require the presence of agonist, and GABA-activated current recovered completely from inhibition by bis(7)-tacrine in the absence of agonist. The slow onset of inhibition by bis(7)-tacrine was not apparently due to an action at an intracellular site, as inclusion of 25 microM bis(7)-tacrine in the recording pipette did not alter inhibition by bis(7)-tacrine applied externally. Bis(7)-tacrine shifted the GABA concentration-response curve to the right in a parallel manner and the pA(2) value estimated from a Schild plot was 5.7. Bis(7)-tacrine increased the time constant of activation of GABA-gated ion channels without affecting the time constants of deactivation or desensitization. These results suggest that bis(7)-tacrine is a competitive GABA(A) receptor antagonist with slow onset and offset kinetics. The competitive inhibition of GABA receptors by bis(7)-tacrine could contribute to its ability to enhance memory.
Collapse
Affiliation(s)
- Li Zhou
- Department of Neurobiology, Tongji Medical College, Huazhong University of Science and Technology, Wuhan 430030, China
| | | | | | | | | | | | | | | | | | | |
Collapse
|
15
|
Reversible inactivation of the auditory thalamus disrupts HPA axis habituation to repeated loud noise stress exposures. Brain Res 2009; 1276:123-30. [PMID: 19379718 DOI: 10.1016/j.brainres.2009.04.023] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2008] [Revised: 03/26/2009] [Accepted: 04/10/2009] [Indexed: 10/20/2022]
Abstract
Although habituation to stress is a widely observed adaptive mechanism in response to repeated homotypic challenge exposure, its brain location and mechanism of plasticity remains elusive. And while habituation-related plasticity has been suggested to take place in central limbic regions, recent evidence suggests that sensory sites may provide the underlying substrate for this function. For instance, several brainstem, midbrain, thalamic, and/or cortical auditory processing areas, among others, could support habituation-related plasticity to repeated loud noise exposures. In the present study, the auditory thalamus was tested for its putative role in habituation to repeated loud noise exposures, in rats. The auditory thalamus was inactivated reversibly by muscimol injections during repeated loud noise exposures to determine if brainstem or midbrain auditory nuclei would be sufficient to support habituation to this specific stressor, as measured during an additional and drug-free loud noise exposure test. Our results indicate that auditory thalamic inactivation by muscimol disrupts acute HPA axis response specifically to loud noise. Importantly, habituation to repeated loud noise exposures was also prevented by reversible auditory thalamic inactivation, suggesting that this form of plasticity is likely mediated at, or in targets of, the auditory thalamus.
Collapse
|
16
|
Hippocampal-dependent learning requires a functional circadian system. Proc Natl Acad Sci U S A 2008; 105:15593-8. [PMID: 18832172 DOI: 10.1073/pnas.0808259105] [Citation(s) in RCA: 173] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Decades of studies have shown that eliminating circadian rhythms of mammals does not compromise their health or longevity in the laboratory in any obvious way. These observations have raised questions about the functional significance of the mammalian circadian system, but have been difficult to address for lack of an appropriate animal model. Surgical ablation of the suprachiasmatic nucleus (SCN) and clock gene knockouts eliminate rhythms, but also damage adjacent brain regions or cause developmental effects that may impair cognitive or other physiological functions. We developed a method that avoids these problems and eliminates rhythms by noninvasive means in Siberian hamsters (Phodopus sungorus). The present study evaluated cognitive function in arrhythmic animals by using a hippocampal-dependent learning task. Control hamsters exhibited normal circadian modulation of performance in a delayed novel-object recognition task. By contrast, arrhythmic animals could not discriminate a novel object from a familiar one only 20 or 60 min after training. Memory performance was not related to prior sleep history as sleep manipulations had no effect on performance. The GABA antagonist pentylenetetrazol restored learning without restoring circadian rhythms. We conclude that the circadian system is involved in memory function in a manner that is independent of sleep. Circadian influence on learning may be exerted via cyclic GABA output from the SCN to target sites involved in learning. Arrhythmic hamsters may have failed to perform this task because of chronic inhibitory signaling from the SCN that interfered with the plastic mechanisms that encode learning in the hippocampus.
Collapse
|
17
|
Albiston AL, Morton CJ, Ng HL, Pham V, Yeatman HR, Ye S, Fernando RN, De Bundel D, Ascher DB, Mendelsohn FAO, Parker MW, Chai SY. Identification and characterization of a new cognitive enhancer based on inhibition of insulin‐regulated aminopeptidase. FASEB J 2008; 22:4209-17. [DOI: 10.1096/fj.08-112227] [Citation(s) in RCA: 86] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Affiliation(s)
- Anthony L. Albiston
- Howard Florey Institute, Florey Neurosciences InstitutesParkvilleVictoriaAustralia
| | - Craig J. Morton
- St. Vincent's Institute of Medical ResearchFitzroyVictoriaAustralia
| | - Hooi Ling Ng
- St. Vincent's Institute of Medical ResearchFitzroyVictoriaAustralia
| | - Vi Pham
- Howard Florey Institute, Florey Neurosciences InstitutesParkvilleVictoriaAustralia
| | - Holly R. Yeatman
- Howard Florey Institute, Florey Neurosciences InstitutesParkvilleVictoriaAustralia
| | - Siying Ye
- Howard Florey Institute, Florey Neurosciences InstitutesParkvilleVictoriaAustralia
- Department of PhysiologyDartmouth Medical SchoolHanoverNHUSA
| | - Ruani N. Fernando
- Howard Florey Institute, Florey Neurosciences InstitutesParkvilleVictoriaAustralia
- Division of Molecular Neurobiology, Department of Medical Biochemistry and BiophysicsKarolinska InstituteStockholmSweden
| | - Dimitri De Bundel
- Howard Florey Institute, Florey Neurosciences InstitutesParkvilleVictoriaAustralia
- Research Group of Experimental Phar macology, Department of Pharmaceutical Chemistry, Drug Analysis and Drug InformationVrije UniversityBrusselBrusselsBelgium
| | - David B. Ascher
- St. Vincent's Institute of Medical ResearchFitzroyVictoriaAustralia
| | | | - Michael W. Parker
- Department of Biochemistry and Molecular BiologyBio21 Molecular Science and Biotechnology InstituteParkvilleVictoriaAustralia
- St. Vincent's Institute of Medical ResearchFitzroyVictoriaAustralia
| | - Siew Yeen Chai
- Howard Florey Institute, Florey Neurosciences InstitutesParkvilleVictoriaAustralia
- Centre for NeuroscienceUniversity of MelbourneParkvilleVictoriaAustralia
| |
Collapse
|
18
|
Fernando RN, Albiston AL, Chai SY. The insulin-regulated aminopeptidase IRAP is colocalised with GLUT4 in the mouse hippocampus - potential role in modulation of glucose uptake in neurones? Eur J Neurosci 2008; 28:588-98. [DOI: 10.1111/j.1460-9568.2008.06347.x] [Citation(s) in RCA: 69] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
|
19
|
Krebs-Kraft DL, Wheeler MG, Parent MB. The memory-impairing effects of septal GABA receptor activation involve GABAergic septo-hippocampal projection neurons. Learn Mem 2007; 14:833-41. [PMID: 18086826 DOI: 10.1101/lm.809407] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
Septal infusions of the gamma-aminobutyric acid (GABA)(A) agonist muscimol impair memory, and the effect likely involves the hippocampus. GABA(A) receptors are present on the perikarya of cholinergic and GABAergic septo-hippocampal (SH) projections. The current experiments determined whether GABAergic SH projections are involved in the memory-impairing effects of septal GABA(A) receptor activation. Experiment 1 tested whether combining septal co-infusions of subeffective doses of muscimol with scopolamine, a drug that selectively influences GABA SH projections, would produce memory deficits. Experiment 2 tested whether hippocampal infusions of a GABA(A) receptor antagonist would block the effects of septal muscimol infusions. Fifteen minutes prior to assessing spontaneous alternation (SA) or training in a multiple trial inhibitory avoidance (CMIA) task, male Sprague-Dawley rats were given septal infusions of vehicle, muscimol, scopolamine, or co-infusions of muscimol with scopolamine, or septal infusions of vehicle or muscimol combined with hippocampal infusions of vehicle or bicuculline. Septal co-infusions of muscimol with scopolamine significantly impaired SA and CMIA. Hippocampal bicuculline infusions blocked deficits produced by septal muscimol infusions in SA and attenuated deficits produced in CMIA. Combined, these findings suggest that GABAergic SH projections are involved in the memory-impairing effects of septal GABA receptor activation.
Collapse
|
20
|
Krebs-Kraft DL, Parent MB. Hippocampal infusions of glucose reverse memory deficits produced by co-infusions of a GABA receptor agonist. Neurobiol Learn Mem 2007; 89:142-52. [PMID: 17728160 PMCID: PMC2259438 DOI: 10.1016/j.nlm.2007.07.008] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2007] [Revised: 07/11/2007] [Accepted: 07/15/2007] [Indexed: 11/30/2022]
Abstract
Although septal infusions of glucose typically have positive effects on memory, we have shown repeatedly that this treatment exacerbates memory deficits produced by co-infusions of gamma-aminobutyric acid (GABA) receptor agonists. The present experiments tested whether this negative interaction between glucose and GABA in the medial septum would be observed in the hippocampus, a brain region where glucose typically has positive effects on memory. Specifically, we determined whether hippocampal infusions of glucose would reverse or exacerbate memory deficits produced by hippocampal co-infusions of the GABA receptor agonist muscimol. Fifteen minutes prior to either assessing spontaneous alternation (SA) or continuous multiple trial inhibitory avoidance (CMIA) training, male Sprague-Dawley-derived rats were given bilateral hippocampal infusions of vehicle (phosphate-buffered saline [PBS], 1 microl/2 min), glucose (33 or 50 nmol), muscimol (0.3 or 0.4 microg, SA or 3 microg, CMIA) or muscimol and glucose combined in one solution. The results indicated that hippocampal infusions of muscimol alone decreased SA scores and CMIA retention latencies. More importantly, hippocampal infusions of glucose, at doses that had no effect when infused alone, attenuated (33 nmol) or reversed (50 nmol) the muscimol-induced memory deficits. Thus, although co-infusions of glucose with muscimol into the medial septum impair memory, the present findings show that an opposite effect is observed in the hippocampus. Collectively, these findings suggest that the memory-impairing interaction between glucose and GABA in the medial septum is not a general property of the brain, but rather is brain region-dependent.
Collapse
Affiliation(s)
- Desiree L Krebs-Kraft
- Department of Psychology and Center for Behavioral Neuroscience, Georgia State University, P.O. Box 5010, Atlanta, GA 30302-5010, USA.
| | | |
Collapse
|
21
|
Krebs DL, Parent MB. Hippocampal infusions of pyruvate reverse the memory-impairing effects of septal muscimol infusions. Eur J Pharmacol 2006; 520:91-9. [PMID: 16150437 PMCID: PMC1668712 DOI: 10.1016/j.ejphar.2005.08.007] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2005] [Accepted: 08/05/2005] [Indexed: 10/25/2022]
Abstract
Hippocampal infusions of glucose reverse memory deficits in spontaneous alternation and in a continuous multiple trial inhibitory avoidance task. The current experiments tested whether glucose metabolism may participate in these effects of glucose. Specifically, these experiments determined whether the glycolytic metabolite pyruvate would mimic these effects of glucose. Male Sprague-Dawley rats were given septal infusions of vehicle or the gamma-aminobutyric acid (GABA) receptor agonist muscimol (0.15 nmol for spontaneous alternation or 5 nmol for continuous multiple trial inhibitory avoidance) combined with hippocampal infusions of vehicle or pyruvate (200 nmol) 15 min prior to assessing spontaneous alternation or training in a continuous multiple trial inhibitory avoidance task. The infusions of muscimol decreased percent alternation scores and continuous multiple trial inhibitory avoidance retention latencies tested 48 h after training. More importantly, hippocampal infusions of pyruvate reversed the deficits produced by septal infusions of muscimol on both tasks. These findings show for the first time that hippocampal infusions of pyruvate influence memory and suggest that glucose may affect memory via glycolytic metabolism.
Collapse
Affiliation(s)
- Desiree L. Krebs
- * Corresponding author. Tel.: +1 404 651 1755 (Lab), +1 404 651 3108 (Office); fax: +1 404 651 3929. E-mail address: (D.L. Krebs)
| | | |
Collapse
|
22
|
McNay EC, Canal CE, Sherwin RS, Gold PE. Modulation of memory with septal injections of morphine and glucose: effects on extracellular glucose levels in the hippocampus. Physiol Behav 2005; 87:298-303. [PMID: 16343563 DOI: 10.1016/j.physbeh.2005.10.016] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2005] [Revised: 09/19/2005] [Accepted: 10/19/2005] [Indexed: 11/26/2022]
Abstract
The concentration of glucose in the extracellular fluid (ECF) of the hippocampus decreases substantially during memory testing on a hippocampus-dependent memory task. Administration of exogenous glucose, which enhances task performance, prevents this decrease, suggesting a relationship between hippocampal glucose availability and memory performance. In the present experiment, spontaneous alternation performance and task-related changes in hippocampal ECF glucose were assessed in rats after intraseptal administration of morphine, which impairs memory on a spontaneous alternation task, and after co-administration of intraseptal glucose, which attenuates that impairment. Consistent with previous findings, spontaneous alternation testing resulted in a decrease in hippocampal ECF glucose levels in control rats. However, rats that received intraseptal morphine prior to testing showed memory impairments and an absence of the task-related decrease in hippocampal ECF glucose levels. Intraseptal co-administration of glucose with morphine attenuated the memory impairment, and ECF glucose levels in the hippocampus decreased in a manner comparable to that seen in control rats. These data suggest that fluctuations in hippocampal ECF glucose levels may be a marker of mnemonic processing and support the view that decreases in extracellular glucose during memory testing reflect increased glucose demand during memory processing.
Collapse
Affiliation(s)
- Ewan C McNay
- Section of Endocrinology, Yale University School of Medicine, USA
| | | | | | | |
Collapse
|
23
|
Canal CE, Stutz SJ, Gold PE. Glucose injections into the dorsal hippocampus or dorsolateral striatum of rats prior to T-maze training: modulation of learning rates and strategy selection. Learn Mem 2005; 12:367-74. [PMID: 16027177 PMCID: PMC1183254 DOI: 10.1101/lm.88205] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
The present experiments examined the effects of injecting glucose into the dorsal hippocampus or dorsolateral striatum on learning rates and on strategy selection in rats trained on a T-maze that can be solved by using either a hippocampus-sensitive place or striatum-sensitive response strategy. Percentage strategy selection on a probe trial (P(crit)) administered after rats achieved criterion (nine of 10 correct choices) varied by group. All groups predominately exhibited a response strategy on a probe trial administered after overtraining, i.e., after 90 trials. In experiment 1, rats that received intrahippocampal glucose injections showed enhanced acquisition of the T-maze and showed increased use of response solutions at P(crit) compared with that of unimplanted and artificial cerebral spinal fluid (aCSF)-treated groups. These findings suggest that glucose enhanced hippocampal functions to accelerate the rate of learning and the early adoption of a response strategy. In experiment 2, rats that received intrastriatal glucose injections exhibited place solutions early in training and reached criterion more slowly than did aCSF controls, with learning rates comparable to those of unoperated and operated-uninjected controls. Relative to unoperated, operated-uninjected and glucose-injected rats, rats that received intrastriatal aCSF injections showed enhanced acquisition of the T-maze and increased use of response solutions at P(crit). The unexpected enhanced acquisition seen after striatal aCSF injections suggests at least two possible interpretations: (1) aCSF impaired striatal function, thereby releasing competition with the hippocampus and ceding control over learning to the hippocampus during early training trials; and (2) aCSF enhanced striatal functioning to facilitate striatal-sensitive learning. With either interpretation, the results indicate that intrastriatal glucose injections compensated for the aCSF-induced effect. Finally, enhanced acquisition regardless of treatment was accompanied by rapid adoption of a response solution for the T-maze.
Collapse
Affiliation(s)
- Clinton E Canal
- The Neuroscience Program,University of Illinois, Urbana-Champaign, IL 61820, USA
| | | | | |
Collapse
|
24
|
Fernando RN, Larm J, Albiston AL, Chai SY. Distribution and cellular localization of insulin-regulated aminopeptidase in the rat central nervous system. J Comp Neurol 2005; 487:372-90. [PMID: 15906313 DOI: 10.1002/cne.20585] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
Central infusions of angiotensin IV enhance spatial learning, memory retention and retrieval, neurotransmitter release, and long-term potentiation via interaction with a specific, high-affinity binding site. This site was recently purified and identified as the insulin-regulated aminopeptidase (IRAP). This enzyme was previously characterized as the marker protein of specialized insulin-responsive vesicles containing GLUT4 in muscle and adipose tissue. The present study provides the first comprehensive description of IRAP distribution in the adult rat brain. By using immunohistochemistry, IRAP was found to be highly expressed in selected olfactory regions, in septal and hypothalamic nuclei, throughout the hippocampal formation and cerebral cortex, and in motor and motor associated nuclei. IRAP was expressed exclusively in neurons in these regions. At the cellular level, IRAP was localized within cell bodies, excluding the nucleus, in a punctate vesicular pattern of expression. IRAP-positive immunoreactivity was also found in some proximal processes but was not detected in synaptic nerve terminals. The neurochemical composition of IRAP-containing neurons was further characterized by dual-label immunohistochemistry. IRAP was expressed in cholinergic cell bodies of the medial septum, a source of cholinergic projections to the hippocampus and cerebral cortex. The distribution of IRAP in motor and motor-associated nuclei; the colocalization of the enzyme with potential in vivo substrates, oxytocin and vasopressin in the hypothalamus; and the colocalization with GLUT4 in selected nuclei all suggest diverse physiological roles for IRAP in the rat central nervous system.
Collapse
Affiliation(s)
- Ruani N Fernando
- Howard Florey Institute of Experimental Medicine and Physiology, The University of Melbourne, Parkville, Victoria 3010, Australia
| | | | | | | |
Collapse
|
25
|
Parent MB, Baxter MG. Septohippocampal acetylcholine: involved in but not necessary for learning and memory? Learn Mem 2004; 11:9-20. [PMID: 14747512 PMCID: PMC1668717 DOI: 10.1101/lm.69104] [Citation(s) in RCA: 148] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
The neurotransmitter acetylcholine (ACh) has been accorded an important role in supporting learning and memory processes in the hippocampus. Cholinergic activity in the hippocampus is correlated with memory, and restoration of ACh in the hippocampus after disruption of the septohippocampal pathway is sufficient to rescue memory. However, selective ablation of cholinergic septohippocampal projections is largely without effect on hippocampal-dependent learning and memory processes. We consider the evidence underlying each of these statements, and the contradictions they pose for understanding the functional role of hippocampal ACh in memory. We suggest that although hippocampal ACh is involved in memory in the intact brain, it is not necessary for many aspects of hippocampal memory function.
Collapse
Affiliation(s)
- Marise B Parent
- Department of Psychology and Center for Behavioral Neuroscience, Georgia State University, Atlanta, Georgia 30303, USA.
| | | |
Collapse
|
26
|
Chang Q, Gold PE. Impaired and spared cholinergic functions in the hippocampus after lesions of the medial septum/vertical limb of the diagonal band with 192 IgG-saporin. Hippocampus 2004; 14:170-9. [PMID: 15098723 DOI: 10.1002/hipo.10160] [Citation(s) in RCA: 67] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
To lesion the cholinergic input to the hippocampus, rats received injections of 192 IgG-saporin into the medial septum/vertical limb of the diagonal band (MS/VDB). The lesions produced near-total loss of choline acetyltransferase (ChAT)-positive neurons in the MS/VDB. The loss was accompanied, however, by only partial decreases (to 40% of control levels) in acetylcholine (ACh) release in the hippocampus. Moreover, ACh release in the hippocampus increased when lesioned and control rats were tested on a spontaneous alternation task, indicating that there was significant residual cholinergic function in the hippocampus. The lesions were sufficient to impair spontaneous alternation scores. However, this impairment could be reversed by either systemic or intra-hippocampal injections of the indirect cholinergic agonist, physostigmine, providing additional evidence of residual and effective cholinergic functions in the hippocampus of lesioned rats. Moreover, systemic injections of physostigmine at doses that produced mild tremors in control rats led to more severe tremors in the lesioned rats, suggesting upregulation of cholinergic mechanisms after saporin lesions, likely in brain areas other than the hippocampus. Thus, these findings provide evidence for decreases in cholinergic input to the hippocampus accompanied by deficits on a spontaneous alternation tasks. The findings also provide evidence for considerable residual cholinergic input to the hippocampus after saporin lesions of the MS/VDB. Together, the results suggest that 192 IgG-saporin lesions of the MS/VDB, using methods often employed, do not fully remove septohippocampal cholinergic input to the hippocampus but are nonetheless sufficient to produce impairments on a task impaired by hippocampal lesions.
Collapse
Affiliation(s)
- Qing Chang
- Department of Psychology, University of Illinois, 603 East Daniel Street, Champaign, IL 61820, USA
| | | |
Collapse
|
27
|
Abstract
This experiment examined the effects of co-infusing the GABA agonist muscimol (0.5 nmol) with 33 nmol of glucose, pyruvate, fructose or sorbitol into the medial septum on spontaneous alternation. Only co-infusions of muscimol with glucose or pyruvate impaired spontaneous alternation performance; none of the other infusions had any significant effects. The findings suggest that glucose metabolism rather than hyperosmolarity is involved in the memory-impairing interaction between glucose and muscimol.
Collapse
Affiliation(s)
- Akeel A Shah
- Department of Psychology, University of Alberta, Edmonton, AB, Canada
| | | |
Collapse
|
28
|
Degroot A, Kornecook T, Quirion R, DeBow S, Parent MB. Glucose increases hippocampal extracellular acetylcholine levels upon activation of septal GABA receptors. Brain Res 2003; 979:71-7. [PMID: 12850573 DOI: 10.1016/s0006-8993(03)02868-3] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
Activation of septal GABA receptors impairs learning and memory and this effect likely involves an influence on the hippocampus. We found previously that the memory-impairing effects of septal infusions of the GABA agonist muscimol are reversed by hippocampal infusions of glucose and suggested that glucose reverses these deficits by increasing hippocampal acetylcholine (ACh). In this study, we report that septal infusions of muscimol produce dose-dependent decreases in ACh levels in hippocampal dialysates. Importantly, increasing glucose levels in the hippocampus elevates hippocampal extracellular ACh levels in rats given septal infusions of muscimol, but not in rats given vehicle. Thus, glucose increases hippocampal extracellular ACh levels when the ACh system is inhibited, an effect that likely contributes to the effects of glucose on memory.
Collapse
Affiliation(s)
- Aldemar Degroot
- Department of Psychology, University of Alberta, AB, Edmonton, Canada
| | | | | | | | | |
Collapse
|
29
|
Shah AA, Parent MB. Septal infusions of glucose or pyruvate, but not fructose, produce avoidance deficits when co-infused with the GABA agonist muscimol. Neurobiol Learn Mem 2003; 79:243-51. [PMID: 12676523 DOI: 10.1016/s1074-7427(03)00007-8] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Abstract
Although glucose typically enhances memory or reverses memory deficits, glucose can also produce memory deficits when co-infused with the gamma-aminobutyric acid (GABA) agonist muscimol into the medial septum (Parent & Gold, 1997; Parent, Laurey, Wilkniss, & Gold, 1997). To date the mechanisms underlying the memory-impairing interaction between GABA and glucose remain unknown. Here we investigate whether this effect is the result of hyperosmolar conditions or may involve glucose metabolism. Male Sprague-Dawley rats were given one-trial inhibitory avoidance training after receiving septal infusions of vehicle (phosphate-buffered saline, 0.5 microl), the GABA(A) agonist muscimol (3 nmol), glucose (16.5, 33, or 66 nmol), fructose (33 nmol), pyruvate (33 nmol), or a solution containing muscimol combined with glucose, fructose, or pyruvate. Retention performance was tested 48 h later. Infusions of glucose, pyruvate, fructose, or muscimol alone did not affect retention performance. However, co-infusions of all doses of glucose (16.5, 33, or 66 nmol) or the glycolytic end product pyruvate with muscimol impaired retention performance. Co-infusions of fructose with muscimol did not affect retention performance. These results suggest that the memory-impairing interaction between glucose and muscimol does not result from hyperosmolar conditions, because equiosmolar concentrations of fructose do not mimic the effects of glucose and the memory deficits do not vary as a function of glucose concentration. The finding that pyruvate mimicked the effects of glucose and impaired memory when combined with muscimol suggests that glucose metabolism may be involved in the memory-impairing interaction between glucose and GABA(A) receptors in the medial septum.
Collapse
Affiliation(s)
- Akeel A Shah
- Department of Psychology, University of Alberta, Edmonton, Alb., T6G 2E9, Canada
| | | |
Collapse
|
30
|
Heininger K. The cerebral glucose-fatty acid cycle: evolutionary roots, regulation, and (patho)physiological importance. INTERNATIONAL REVIEW OF NEUROBIOLOGY 2003; 51:103-58. [PMID: 12420358 DOI: 10.1016/s0074-7742(02)51004-7] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Affiliation(s)
- Kurt Heininger
- Department of Neurology, Heinrich Heine University, D-40597 Düsseldorf, Germany
| |
Collapse
|
31
|
Talley CP, Clayborn H, Jewel E, McCarty R, Gold PE. Vagotomy attenuates effects of L-glucose but not of D-glucose on spontaneous alternation performance. Physiol Behav 2002; 77:243-9. [PMID: 12419400 DOI: 10.1016/s0031-9384(02)00850-8] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Abstract
Two peripheral signaling routes have been proposed to account for the ability of peripheral substances such as glucose to modulate memory processing in the brain. One possible signaling route is by crossing the blood-brain barrier to act directly on brain. A second route involves activation of peripheral nerves with resulting changes in neural activity carried by peripheral nerves to the brain. Because the vagus nerve is a major neural pathway between the periphery and brain, peripherally acting modulators of memory modulators may act via vagal afferents to the brain to enhance memory processing. In the present experiments, systemic injections of either D-glucose or L-glucose, a metabolically inactive enantiomer, facilitated performance of rats on a four-arm alternation task, but at very different doses (D-glucose, 250 mg/kg; L-glucose, 3,000 mg/kg). The enhanced performance seen with L-glucose, but not that seen with D-glucose, was attenuated by vagotomy. These findings suggest that the mechanisms by which these enantiomers act to enhance memory are quite different, with L-glucose acting via vagal afferents but D-glucose acting by other means, including direct modulation of central nervous system (CNS) processes by D-glucose.
Collapse
Affiliation(s)
- Cheryl P Talley
- School of Psychology, James Madison University, Harrisonburg, VA 22801, USA.
| | | | | | | | | |
Collapse
|
32
|
Degroot A, Parent MB. Infusions of physostigmine into the hippocampus or the entorhinal cortex attenuate avoidance retention deficits produced by intra-septal infusions of the GABA agonist muscimol. Brain Res 2001; 920:10-8. [PMID: 11716806 DOI: 10.1016/s0006-8993(01)02798-6] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Septal gamma-aminobutyric acid (GABA) receptor activation is known to disrupt memory formation, although the mechanisms underlying this impairment remain unclear. The present study explored the possibility that high levels of septal GABA receptor activity might impair memory by down-regulating acetylcholine (ACh) function in archicortex and entorhinal cortex. To test this possibility, rats were trained on an avoidance task 15 min after receiving intra-septal infusions of vehicle or muscimol (5 nmol/0.5 microl) combined with unilateral intra-hippocampal (10 microl/1 microl) or intra-entorhinal cortex (1.875 microg/0.25 microl) infusions of vehicle or the acetylcholinesterase inhibitor physostigmine. We demonstrate that these infusions do not alter acquisition performance on a continuous multiple trial inhibitory avoidance task. However, intra-septal infusions of muscimol dramatically impair retention performance 48 h later. More importantly, infusions of physostigmine into the hippocampus or the entorhinal cortex, at doses that do not influence acquisition or retention performance when infused alone, attenuate the impairing effects of the muscimol infusions on retention. We suggest that high levels of septal GABA receptor activity might impair memory by down-regulating ACh levels in the hippocampal region, and that such memory impairments can be ameliorated by increasing ACh levels in the hippocampus or entorhinal cortex.
Collapse
Affiliation(s)
- A Degroot
- Department of Psychology, University of Alberta, Alberta, T6G 2E9, Edmonton, Canada
| | | |
Collapse
|
33
|
Intrahippocampal infusions of k-atp channel modulators influence spontaneous alternation performance: relationships to acetylcholine release in the hippocampus. J Neurosci 2001. [PMID: 11160440 DOI: 10.1523/jneurosci.21-02-00609.2001] [Citation(s) in RCA: 61] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
One mechanism by which administration of glucose enhances cognitive functions may be by modulating central ATP-sensitive potassium (K-ATP) channels. K-ATP channels appear to couple glucose metabolism and neuronal excitability, with channel blockade increasing the likelihood of neurosecretion. The present experiment examined the effects of glucose and the direct K-ATP channel modulators glibenclamide and lemakalim on spontaneous alternation performance and hippocampal ACh release. Rats received either artificial CSF vehicle or vehicle plus drug for two consecutive 12 min periods via microdialysis probes (3 mm; flow rate of 2.1 microliter/min) implanted in the left hippocampus. During the second 12 min period, rats were tested for spontaneous alternation performance. Dialysate was simultaneously collected for later analysis of ACh content. Both glucose (6.6 mm) and glibenclamide (100 micrometer) significantly increased alternation scores compared with those of controls. Conversely, lemakalim (200 micrometer) significantly reduced alternation scores relative to those of controls. Simultaneous administration of lemakalim with either glucose or glibenclamide resulted in alternation scores not significantly different from control values. All drug treatments enhanced hippocampal ACh output relative to control values. The results demonstrate that K-ATP channel modulators influence behavior when administered directly into the hippocampus, with channel blockers enhancing and openers impairing spontaneous alternation performance, thus supporting the hypothesis that glucose enhances memory via action at central K-ATP channels. That lemakalim, as well as glibenclamide and glucose, increased hippocampal ACh output suggests a dissociation between the effects of K-ATP channel modulators on behavior and hippocampal ACh release.
Collapse
|
34
|
Sloley BD, Urichuk LJ, Lei L, Coutts RT, Baker GB, Shan JJ, Pang PK. Monoamine oxidase inhibition and neuroprotection by N1-propargylphenelzine. Drug Dev Res 2001. [DOI: 10.1002/ddr.1164] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
|
35
|
Degroot A, Parent MB. Increasing acetylcholine levels in the hippocampus or entorhinal cortex reverses the impairing effects of septal GABA receptor activation on spontaneous alternation. Learn Mem 2000; 7:293-302. [PMID: 11040261 PMCID: PMC311338 DOI: 10.1101/lm.32200] [Citation(s) in RCA: 44] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2000] [Accepted: 08/09/2000] [Indexed: 11/24/2022]
Abstract
Intra-septal infusions of the gamma-aminobutyric acid (GABA) agonist muscimol impair learning and memory in a variety of tasks. This experiment determined whether hippocampal or entorhinal infusions of the acetylcholinesterase inhibitor physostigmine would reverse such impairing effects on spontaneous alternation performance, a measure of spatial working memory. Male Sprague-Dawley rats were given intra-septal infusions of vehicle or muscimol (1 nmole/0.5 microL) combined with unilateral intra-hippocampal or intra-entorhinal infusions of vehicle or physostigmine (10 microg/microL for the hippocampus; 7.5 microg/microL or 1.875 microg/0.25 microL for the entorhinal cortex). Fifteen minutes later, spontaneous alternation performance was assessed. The results indicated that intra-septal infusions of muscimol significantly decreased percentage-of-alternation scores, whereas intra-hippocampal or intra-entorhinal infusions of physostigmine had no effect. More importantly, intra-hippocampal or intra-entorhinal infusions of physostigmine, at doses that did not influence performance when administered alone, completely reversed the impairing effects of the muscimol infusions. These findings indicate that increasing cholinergic levels in the hippocampus or entorhinal cortex is sufficient to reverse the impairing effects of septal GABA receptor activation and support the hypothesis that the impairing effects of septal GABAergic activity involve cholinergic processes in the hippocampus and the entorhinal cortex.
Collapse
Affiliation(s)
- A Degroot
- Division of Neuroscience, University of Alberta, Edmonton, Alberta T6G 2E9 Canada
| | | |
Collapse
|
36
|
Talley CE, Kahn S, Alexander LJ, Gold PE. Epinephrine fails to enhance performance of food-deprived rats on a delayed spontaneous alternation task. Neurobiol Learn Mem 2000; 73:79-86. [PMID: 10686125 DOI: 10.1006/nlme.1999.3920] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Increases in blood glucose levels after epinephrine injection appear to contribute to the hormone's effects on learning and memory. The present experiment evaluated whether epinephrine-induced enhancement of spontaneous alternation performance would be attenuated in fasted rats that had blunted increases in circulating glucose levels after injections of epinephrine. Rats deprived of food for 24 h prior to injection of epinephrine exhibited significant attenuation of the increase in blood glucose levels seen in fed rats. When the rats were tested on a delayed spontaneous alternation task, epinephrine enhanced performance in fed rats but not in rats deprived of food for 24 h. These findings are consistent with the view that hyperglycemia subsequent to epinephrine injections contributes to the memory-enhancing effects of epinephrine.
Collapse
Affiliation(s)
- C E Talley
- Department of Psychology, University of Virginia, 102 Gilmer Hall, Charlottesville, Virginia 22903, USA
| | | | | | | |
Collapse
|
37
|
Miller MM, Hyder SM, Assayag R, Panarella SR, Tousignant P, Franklin KB. Estrogen modulates spontaneous alternation and the cholinergic phenotype in the basal forebrain. Neuroscience 1999; 91:1143-53. [PMID: 10391490 DOI: 10.1016/s0306-4522(98)00690-3] [Citation(s) in RCA: 76] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
We report that a small population of neurons expresses both choline acetyltransferase and classical estrogen receptor immunoreactivity and they are found primarily in the bed nucleus of the stria terminalis. In short-term ovariectomized ageing mice (24 months, n = 5) there were 41.0 +/- 4.1% fewer of these double-labeled cells than in young (five months, n = 5) short-term ovariectomized C57BL/6J mice. To study cholinergic neuron estrogen responsiveness, young mice (n = 8) were ovariectomized at puberty (five weeks). After three months half of the mice (n = 4) were given physiological levels of 17beta estradiol for 10 days. Bed nucleus double-labeled neurons increased by 32.9% (P < or = 0.003) in the young mice given estrogen. In a gel shift assay, double-stranded oligonucleotides with putative estrogen response elements from the choline acetyltransferase gene were used as competitors against estrogen receptor binding to consensus estrogen response elements. A sequence with 60% homology to the vitellogenin estrogen response element was found to compete at 500- and 1000-fold excess. Young mice (five months) with ovaries demonstrated significantly (P < or = 0.04) better performance in the spontaneous alternation T-maze test than did old (19 month) mice with ovaries (young = 66.3 +/- 3.3% correct choices; vs old = 55.0 +/- 4.0% in old mice with ovaries). Young mice (five months old), ovariectomized for one month and treated with estrogen, showed significantly more spontaneous alternation than ovariectomized controls (69.1 +/- 2.8% vs 58.3 +/- 3.9%; P < or = 0.04). Estrogen also increased spontaneous alternation in old, short-term ovariectomized mice (61.5 +/- 2.7% vs 48 +/- 3.3%; P < or = 0.005). In either young or old ovariectomized mice, estrogen increased spontaneous alternation to levels seen in young animals with ovaries. Estrogen increases the number of choline acetyltransferase-immunoreactive and choline acetyltransferase/estrogen receptor-immunoreactive cells in old or young mice lacking estrogen, and enhances working memory in old or young mice lacking estrogen. Our data suggest that estrogen may act at the level of the choline acetyltransferase gene, but in view of the limited distribution of cholinergic cells expressing the classical estrogen receptor, it is unlikely that these cells can account for a memory enhancing effect of estrogen replacement.
Collapse
Affiliation(s)
- M M Miller
- Department of Obstetrics and Gynecology, Centre for Studies on Aging, McGill University, Montreal, Quebec, Canada
| | | | | | | | | | | |
Collapse
|
38
|
Spanis CW, Bianchin MM, Izquierdo I, McGaugh JL. Excitotoxic basolateral amygdala lesions potentiate the memory impairment effect of muscimol injected into the medial septal area. Brain Res 1999; 816:329-36. [PMID: 9878813 DOI: 10.1016/s0006-8993(98)01104-4] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
In rats, the septo-hippocampal system is important for memory encoding. Previous reports indicate that muscimol, a specific GABAergic agonist induces learning and memory deficits when infused into the medial septal area. The basolateral nucleus of the amygdala (BLA) modulates memory encoding in other brain areas, including the hippocampus. To explore the interactions between the septo-hippocampal system and amygdala in memory, we studied the effects of intra-medial septal infusions of muscimol in rats with BLA lesions. Animals received sham surgery or excitotoxic BLA lesions and were given infusions of either vehicle or muscimol (5 nmol) into the medial septal area 5 min prior to training sessions in inhibitory avoidance and water maze tasks. In the inhibitory avoidance task, muscimol-induced memory impairment was potentiated by BLA amygdala lesions. Additionally, in the water maze task, BLA-lesioned rats given muscimol infusions into the medial septal also showed memory impairment. These findings indicate that the MSA interacts with the BLA in the processing of memory storage.
Collapse
Affiliation(s)
- C W Spanis
- Biology Department, University of San Diego, San Diego, CA, 92110, USA
| | | | | | | |
Collapse
|