T-maze alternation,response patterning,and septo-hippocampal circuitry in rats

The effects of small electrolytic lesions in the posterodorsal septal area (aimed at the precommissural fornix) on acquisition and retention of either a spatio-temporal task (contingently reinforced T-maze alternation) or a temporal task (response patterning in a straight runway) were investigated in Long-Evans rats. Acquisition of T-maze alternation was impaired following posterodorsal septal lesions, but with extensive training there was evidence of learning. Postoperative retention of T-maze alternation was also impaired by posterodorsal septal lesions but, again, with continued practice the experimental animals relearned the task and came to perform as well as controls. Postoperative acquisition of response patterning in a runway was significantly but not greatly impaired by posterodorsal septal lesions. The experimental animals did pattern, but not as well as controls, even after substantial practice. Retention of response patterning was severely impaired following lesions in the posterodorsal septum but, as in the T-maze task, experimental animals improved significantly in performance with postoperative practice. The results were interpreted in the light of two recent formulations of the functions of the septo-hippocampal system: cognitive mapping and working memory. However, the data are not conclusive and suggest that inhibition theories of septo-hippocampal function are possibly relevant.     

Perception of species-specific vocalizations in rats : role of the cholinergic septo-hippocampal pathway and aging

The effect of a chemical lesion of the cholinergic septo-hippocampal pathway induced by ethylcholine aziridinium (AF64A) on brain potentials evoked by species-specific vocalization containing informations of high biological relevance was studied in young adult (10 months) and aged (24 months) rats by means of neocortical electroencephalographic recordings. In control rats, the perception of a rats vocalization in a life endangering situation (lasting 0.8 s) initiated an evoked potential followed by a late positive slow wave (LPSW)-complex and a direct current shift with a duration of up to 16 s. Four months after treatment with AF64A (2 nmol into each of the lateral ventricles), the main negative component of the initial acoustic evoked potential (peak latency of about 60 ms after stimulus onset) was reduced (P = 0.04) both in young adult and aged rats. Further changes included a decrease of the late positive wave amplitude in young adult rats (P = 0.001) and a shorter duration of the LPSW-complex in aged rats (P = 0.03). AF64A induced also changes in specific components revealed by Principle Component Analysis, but only in the group of young rats. A decrease in the slow wave component (factor 1, 3000–4000 ms after stimulus onset ; P = 0.02) was observed. Age per se affected the late positive potential shifts as indicated by a shorter latency of the late positive wave (P = 0.03).

A detailed analysis of the major neurotransmitter markers proved an almost exclusive reduction of the activity of choline acetyltransferase in the ventral and dorsal hippocampus (up to 60%), which was equal in young adult and aged rats. The irreversible loss in choline acetyltransferase activity, which was restricted to the hippocampus, was associated by a slight reduction in serotonergic function.

The present data suggest that the complex cognitive and emotional processes initiated by species-specific vocalization appear to be affected by aging. Furthermore, as a consequence of a cholinergic deficit in the hippocampus, the integration processes essential for the recognition of the biological meaning of a species-specific vocalization are considerably disturbed. These findings provide an experimental basis for studying disturbances in the perceptual response to stimuli of high emotional value in patients with hypocholinergic function as in Alzheimers disease.     

Aversive stimulus attenuates impairment of acquisition in a delayed match to position T-maze task caused by a selective lesion of septo-hippocampal cholinergic projections

Infusion of 192 IgG-saporin (SAP) into the medial septum (MS) of rats selectively destroys cholinergic neurons projecting to the hippocampus and impairs acquisition of a delayed matching to position (DMP) T-maze task. The present study evaluated whether introduction of a mild aversive stimulus 30 min prior to training would attenuate the deficit in DMP acquisition caused by the SAP lesions. Male Sprague-Dawley rats received medial septal infusions of either artificial cerebrospinal fluid or SAP (0.22 microg in 1.0 microl). Fourteen days later, all animals were trained to perform the DMP task. Half of the SAP-treated animals and controls received an intraperitoneal injection of saline each day, 30 min prior to training. Results show that intraperitoneal saline attenuated the impairment in DMP acquisition in SAP lesioned rats. These results suggest that a mild aversive stimulus can attenuate cognitive deficits caused by medial septal cholinergic lesions.     

The T-maze continuous alternation task for assessing the effects of putative cognition enhancers in the mouse

The T-maze continuous alternation task (T-CAT) assesses the spatial exploratory performance in mice. We performed a series of four experiments in order to establish the T-CAT in mice in our laboratory, to replicate published findings, and to investigate the effects of scopolamine and donepezil. In the first experiment, the task was found to be sensitive to differences between mouse strains, corroborating findings reported by Gerlai. HsdWin:CFW1 mice alternated below chance level, C57BL/6JIco and B6D2F1/JIco mice performed above chance level, and C57BL/6NTac and 129S6/SvEvTac mice performed at chance level. In the second experiment, donepezil (Aricept, E2020) at the dose of 3 mg/kg p.o. increased the rate of alternations above the level of the vehicle-treated control group in C57BL/6JIco mice, suggesting that this drug can act as cognition enhancer in normal animals. 1mg/kg scopolamine, administered intraperiteoneally (i.p.), impaired the spontaneous alternation behaviour of the mice. The slightly lower dose of 0.75 mg/kg did not affect alternation performance. The high dose of donepezil (3 mg/kg) was able to antagonise the scopolamine-induced performance deficit. With respect to time to complete a session, the results were inconclusive. In the third experiment, we found that scopolamine, administered i.p. at the dose of 1 mg/kg, or subcutaneously (s.c.) at the dose of 0.1 mg/kg, decreased the rate of spontaneous alternations in C57BL mice in the T-CAT and increased the time to complete a session. Most likely due to adverse side effects induced by the dose of 1mg/kg scopolamine, 4 out of 10 animals did not complete at least eight free-choice trials during the maximum session duration of 30min. No such adverse effects were seen after 0.1 mg/kg scopolamine, administered s.c. Finally, we evaluated whether the T-CAT yields replicable results. We conclude that the T-CAT provides a reliable tool for assessing the effects of cognition-modulating treatments in mice.     

Stain-dependent differences between the septo-hippocampal cholinergic system and hippocampal size

The activity of choline acetyltransferase is over twice as high in the hippocampus of Wistar Kyoto (WKY) than in Brown Norway (BN) rats, and this is paralleled by a comparable difference in acetylcholinesterase staining intensity within the hippocampal formation. However, the size of the whole hippocampus is smaller in WKY than in BN rats. There are no strain differences in the activities of the neurotransmitter-synthesizing enzymes: tyrosine hydroxylase in the septum and glutamic acid decarboxylase in the hippocampus. The findings indicate the existence of strain-dependent inverse relationship between the septo-hippocampal cholinergic system and the size of the hippocampus.     

Rapid task acquisition of spatial-delayed alternation in an automated T-maze by mice

The spatial-delayed alternation task using a T-maze is the standard method for testing working memory in rodents and is widely used. Until now, however, there has been a gap in the understanding of the underlying brain mechanisms. The development of new manganese-enhanced brain imaging methods now permit a more specific examination of these mechanisms by allowing behavioural brain stimulation to take place outside the MRI scanner and the scan identifying the activation of specific brain regions to take place subsequently. The requirements for this method are a frequent repetition of the behaviour of interest, a control group that differs in only one task parameter and the minimization of unspecific environmental factors to avoid irrelevant stimulation. To meet these requirements, a fully automated spatial-delayed alternation task in a T-maze was developed that used identity detectors and automated gates to route mice individually from their social home cage to the T-maze. An experimental and a control group of mice were trained in procedures that differed only in the parameter “working-memory based alternation”. Our data demonstrate that both groups can be trained concurrently with a rapid procedure using the automated T-maze. With its high level of stimulation, the minimization of unspecific stimulation through environmental factors and the simultaneous training of a control group that differs in only one task parameter our set-up and procedure met the requirements of new imaging techniques for the study of the influence of a specific cognitive component of spatial-delayed alternation on activity in specific brain regions.     

Erythropoietin improves spatial delayed alternation in a T-maze in fimbria-fornix transected rats

Systemically administered human recombinant erythropoietin (EPO) may have the potential to reduce the cognitive and behavioural symptoms of a mechanical brain injury. In a series of studies we address this possibility. We have previously found that EPO given to fimbria-fornix transected rats at the moment of injury is able substantially to improve the posttraumatic acquisition of allocentric place learning tasks administered in a water maze as well as in an 8-arm radial maze. It is, however, essential to evaluate this clinically important ability of EPO within other cognitive domains, as well. Consequently, we presently studied the effects of similarly administered EPO in fimbria-fornix transected and control operated rats, respectively--evaluating the posttraumatic behavioural/cognitive abilities in a spatial delayed alternation task performed in a T-maze. Administration of EPO to the hippocampally injured rats was associated with a substantial reduction of the lesion-associated behavioural impairment--while such an impairment was clearly seen in the saline injected fimbria-fornix transected group. In contrast, EPO had no detectable effect on the task acquisition of non-lesioned animals. The results of the present study confirm our previous demonstrations that EPO is able to reduce or eliminate the behavioural/cognitive consequences of mechanical injury to the hippocampus--and emphasize that this ability is present across a broader spectrum of cognitive domains.     

Denervation supersensitivity in the cholinergic septo-hippocampal pathway: a microiontophoretic study.

The purpose of this study was to determine whether denervation supersensitivity could be produced in an identified cholinergic pathway in the CNS of the rat. The mechanism for the development of this phenomenon was also explored. Cholinergic denervation of the hippocampus was accomplished by lesions of the medial septum. The response of hippocampal pyramidal cells to microiontophoretic application of acetylcholine (ACh) and carbachol in lesioned and unlesioned animals was determined by extracellular recording. There was a marked increase (6 X) in sensitivity to ACh 2-43 days following lesions. However, there was no increase in sensitivity to carbachol or glutamate. Other workers have shown that septal lesions cause a large decrease in hippocampal acetylcholinesterase (AChE) which is located mainly presynaptically. The absence of increase in sensitivity to carbachol, a cholinomimetic resistant to hydrolysis by AChE, suggests that the postlesion increase in sensitivity to ACh results from a decrease in its inactivation by AChE. A time course for the development of ACh supersensitivity was found to be similar to the time course of AChE loss previosly reported. Experiments using physostigmine, an AChE inhibitor, demonstrated that inhibition of AChE can potentiate the effects of ACh in unlesioned preparations, but not in lesioned preparations. We conclude: (1) denervation supersensitivity to ACh occurs in the septo-hippocampal pathway; and (2) the supersensitivity is probably due to decreased inactivation of ACh by AChE. The results suggest that presynaptic AChE plays a significant role in modulating the neurotransmitter function of ACh in the septo-hippocampal pathway.     

Altered NGF response but not release in the aged septo-hippocampal cholinergic system

An important aspect of aging and Alzheimer's disease (AD) pathology includes the degeneration of basal forebrain cholinergic neurons (BFCNs), possibly due to disrupted nerve growth factor (NGF) signaling. Previous studies on disrupted NGF signaling have focused on changes in retrograde transport. This study focuses on two other possible mechanisms for loss of trophic support: diminished release of NGF from hippocampal neurons or diminished TrkA receptor response of BFCNs to NGF. We measured NGF levels in the effluent of hippocampal slices from young and aged rats in response to potassium chloride and glutamate. We found that release of NGF was not altered in aged hippocampal slices compared to slices from young controls. To measure the in situ response of the BFCNs to NGF, we injected NGF intraparenchymally into the right hippocampus of young and aged rats. Injections of cytochrome C served as controls. Fifteen minutes post-administration, a dramatic increase in TrkA immunoreactivity was found in the cell bodies of medial septal neurons. We found that this rapid response was blunted in aged rats compared to young adult controls. To determine whether retrograde transport was necessary for this rapid response, we injected colchicine prior to NGF injection. The NGF-induced upregulation was not blocked by colchicine, suggesting that this acute response was not dependent on classical retrograde transport. Since cholinergic degeneration coupled with altered levels of NGF and TrkA receptors are also seen in human aging and AD, the loss of acute responsivity to NGF in the BFCNs may also play a role in these processes.     

The stress-induced response of the septo-hippocampal cholinergic system. A vectorial outcome of psychoneuroendocrinological interactions

Considerable data have emerged which strongly indicate that the septohippocampal cholinergic system is involved in the adaptive response to stress. Neurotransmitter regulatory mechanisms in cholinergic synaptic terminals of this part of the limbic system undergo adaptive changes in response to stress and recover slowly after stress. The initial stress-induced response is characterized by activation of hippocampal cholinergic terminals within minutes, as indicated by a rapid and transient elevation in high affinity choline uptake and increased newly synthesized acetylcholine release. The response of this cholinergic system to stress is influenced by both neuronal and hormonal stimuli. Among the several neuronal systems converging in the septum, terminals of the dopaminergic mesolimbic system have been found to be selectively involved in the early response to stress. Pharmacological interference with dopaminergic neurotransmission, with agonist and antagonist treatments, revealed that changes in the tonic inhibitory influence of septal dopaminergic terminals can modulate the response of hippocampal cholinergic terminals to stress. A similar activation of hippocampal cholinergic terminals as after short-term stress was observed after treatments with a large dose of either adrenocorticotropic hormone or corticosterone. Furthermore, glucocorticoids and not adrenocorticotropic hormone can directly enhance acetylcholine release, but only from excited terminals. This indicates that stress-induced activation of the septo-hippocampal system may occur secondary to, but not directly by, increased levels of pituitary-adrenocortical hormones. Yet, it is possible that under stressful conditions the increased glucocorticoid levels may modulate the activity of the stimulated hippocampal cholinergic terminals. Together the findings support the notion that the stress-induced response of the septo-hippocampal cholinergic system represents an integrated output of converging neuronal and hormonal stimuli which convey signals of stress to this limbic brain region.     

Impairment in T-maze reinforced alternation performance following nucleus basalis magnocellularis lesions in rats

Rats were trained on a reinforced alternation paradigm using an elevated T-maze. After pre-surgical training subjects received either ibotenic acid (4 micrograms/0.4 microliter) or vehicle (pH 7.4, 0.4 microliter) bilaterally into the region of the nucleus basalis magnocellularis--an important source of neocortical acetylcholine projections. Acetylcholinesterase staining of sectioned brains revealed a loss of neocortical, but not hippocampal staining in lesioned animals. On the T-maze task, lesioned rats showed significantly impaired choice performance relative to controls. They also demonstrated significant side biases, the degree of which was correlated with choice performance deficit.     

Pure Schwann cell suspension grafts promote regeneration of the lesioned septo-hippocampal cholinergic pathway

Regeneration of central nervous system (CNS) axons has been studied in the cholinergic septo-hippocampal system using various ‘bridges’ able to support fiber growth. In this study, a pure Schwann cell (Sc) suspension labeled with bisbenzimide (Hoechst 33342) was grafted in the lesioned septo-hippocampal pathway. At 2 weeks post-grafting, acetyl-cholinesterase (AChE)-positive fibers invaded the graft and grew in association with the Hoechst-labeled Sc, some of which expressed the low-affinity nerve growth factor receptor (NGF-R). At 2 months and 4 months post-grafting, the dorsal hippocampus was reinnervated with an apparently normal innervation pattern. Analysis of fiber growth in the hippocampus at four months post-grafting revealed a significant increase of reinnervation in the grafted animals (2 mm) compared to the non-grafted ones. No difference was observed in the number of cholinergic septal neurons expressing the NGF-R. These results demonstrate that a Sc suspension grafted into the lesioned septo-hippocampal system, integrates well into the host tissue, and supports axonal CNS outgrowth, implying that Sc by themselves provide an adequate environment for regeneration to occur.     

脑内注射乙酰胆碱受体抗体IgG对大鼠隔-海马胆碱能系统的损害

目的　探讨乙酰胆碱受体抗体 ( Ach Rab) Ig G对大鼠隔 -海马胆碱能系统的损害及对认知功能的影响。方法　 Ach Rab阳性 Ig G或健康人 Ig G注入大鼠一侧隔 -斜角带核区 ,跳台试验测试大鼠的学习记忆功能 ,乙酰胆碱酯酶 ( Ach E)组织化学法测定颞叶、海马 Ach E阳性纤维 ,免疫组化测定隔 -斜角带核区胆碱乙酰转移酶( Ch AT)阳性神经元。结果　实验组大鼠错误次数 ( 7.8± 1..5 )较对照组 ( 3.6± 1.3)明显增加 ;实验组大鼠颞叶及海马各区 Ach E纤维面密度均明显低于对照组 ( P<0 .0 1) ;实验组注射侧 Ch AT阳性细胞数 ( 30 .4 5± 5 .4 1)明显少于实验组非注射侧 ( 5 4 .0 0± 7.5 9)和对照组注射侧 ( 6 3.5 3± 5 .12 ) ;实验组非注射侧明显少于对照组非注射侧 ( 6 8.35± 4 .72 )。结论　内侧隔 -斜角带核区定向注射 Ach Rab Ig G可使胆碱能神经元损害 ,进而导致胆碱能系统功能障碍。因而认为 MG认知功能障碍与中枢胆碱能系统损害有关     

Erythropoietin improves spatial delayed alternation in a T-maze in rats subjected to ablation of the prefrontal cortex

Systemically administered human recombinant erythropoietin (EPO) may have the potential to reduce the cognitive and behavioural symptoms of mechanical brain injury. In a series of studies we address this possibility. Previously, we studied the effects of EPO given to fimbria-fornix transected rats at the moment of injury. We have found that such treatment improves substantially the posttraumatic acquisition of allocentric place learning tasks administered in a water maze and in an 8-arm radial maze as well as a spatial delayed alternation task administered in a T-maze. It is, however, essential also to evaluate this clinically important ability of EPO after other types of mechanical brain injury. Consequently, we presently studied the effects of similarly administered EPO in rats subjected to bilateral subpial aspiration of the anteromedial prefrontal cortex as well as control operated rats, respectively. We evaluated the posttraumatic behavioural/cognitive abilities of these animals in a spatial delayed alternation task performed in a T-maze. Administration of EPO to the prefrontally ablated rats was associated with a reduction of the lesion-associated behavioural impairment--while such an impairment was clearly seen in the saline injected prefrontally ablated group. In sham operated rats administration of EPO did not influence the task acquisition significantly. The results of the present study confirm our previous demonstrations that EPO is able to reduce the behavioural/cognitive consequences of mechanical brain injury. This ability is emphasized by its relative independence on the type of lesion as well as the neural structure affected.     

Hippocampal muscarinic cholinergic mediation of spontaneous alternation and fear in the developing rat

Spontaneous alternation was examined in young rats following microinjections of anticholinergic agents into 4 hippocampal sites: anterodorsal or posteroventral dentate gyrus, hippocampus or entorhinal complex. The rate of alternation remained around 40% at 5, 10, and 15 days, increased suddenly to 80% on day 17, did not vary until day 20, regressed partly and temporarily until day 30, and returned to a near-adult level on day 40. Concomitantly with the transient regression of alternation between days 20 and 40, fear responses to environment were seen to emerge (boluses and squeaks), to reach a maximum on day 30, and to return to a low level by day 40. Injections of atropine (4, 8 μg) or scopolamine (4, 10 μg) into any of the 4 sites significantly reduced the rate of alternation from day 17 on. Only the highest doses were active at 10 and 15 days. These results demonstrate that spontaneous alternation and hippocampal muscarinic cholinergic mechanisms develop simultaneously and progress suddenly on postnatal day 17. Atropine and scopolamine also affected fear responses, abolishing or potentiating them according to the site of injection, showing that hippocampal cholinergic mechanisms exert complex influences on fear-induced emotional reactions.     

Lesions of the dorsal noradrenergic bundle and rewarded running: The role of pretraining

Local injection of 6-hydroxydopamine was used to selectively destroy the dorsal ascending noradrenergic bundle (DB), producing 75% loss of hippocampal noradrenaline. Lesioned and control rats were trained to run in a straight alley for food reward with or without pretraining (handling and habituation to the apparatus). Lesioned rats ran more slowly than controls only if they had not been pretrained. This result may explain previous discrepancies in the literature; it is discussed in relation to existing hypotheses of DB function.     

Genetic variation in the morphology of the septo-hippocampal cholinergic and GABAergic systems in mice: II. Morpho-behavioral correlations

We investigated the contribution of the septo-hippocampal cholinergic and GABAergic system to spatial and nonspatial aspects of learning and memory that had previously been found to correlate with the extent of the hippocampal intra- and infrapyramidal mossy fiber projection in different inbred mouse strains. The following cholinergic and GABAergic markers were measured in the septi and hippocampi of male mice: the number of cholinergic and parvalbumin-containing neurons in the medial septum/vertical limb of the diagonal band of Broca (MS/vDB), the number of septo-hippocampal cholinergic and GABAergic projection neurons, the density of cholinergic fibers in different hippocampal subfields, and the density of muscarinic receptors (predominantly M1 and M2) in the hippocampus. In addition, animals were behaviorally tested for spatially dependent and activity-dependent variables in a water maze and spatial and nonspatial working and reference memory in different experimental set-ups in an eight-arm radial maze. Using only those variables for which significant strain differences were obtained, we looked for covariations between behavior and neuroanatomy. The density of cholinergic fibers in the dentate gyrus was significantly correlated with activity-dependent learning in the water maze, whereas the number of septo-hippocampal cholinergic projection neurons correlated with spatial and, to a lesser extent, also with nonspatial aspects of radial maze learning. Only weak correlations were found between receptor densities and behavioral traits. From these data we conclude that variations in the septo-hippocampal cholinergic system, like variations in the mossy fiber projection, entail functional consequences for different types of maze learning in mice. © 1996 Wiley-Liss, Inc.     

Genetic variation in the morphology of the septo-hippocampal cholinergic and GABAergic system in mice. I. Cholinergic and GABAergic markers

In the present study, variations of cholinergic and GABAergic markers in the medial septum/vertical limb of the diagonal band of Broca (MS/vDB) and the hippocampus of eight different inbred mouse strains were investigated. By means of immunocytochemistry against the acetylcholine-synthesizing enzyme choline acetyltransferase (ChAT), the cholinergic neurons were visualized and the number of ChAT-positive neuronal profiles in the MS/vDB was counted. Cholinergic and GABAergic septo-hippocampal projection neurons were detected with a combined retrograde tracing and immunocytochemical approach. In order to quantify the cholinergic innervation of various hippocampal subregions, we estimated the density of acetylcholinesterase (AChE)-containing fibers as visualized by AChE histochemistry. Additionally, the densities of muscarinic receptors (mainly the subtypes M1 and M2) in different hippocampal areas of seven inbred strains were measured by means of quantitative receptor autoradiography. We found significant strain differences for the number of ChAT-positive neurons in the MS/vDB; in the numbers of cholinergic septo-hippocampal projection neurons; in the density of cholinergic fibers in hippocampal subfields CA3c, CA1, and in the dentate gyrus; and in the density of muscarinic receptors in the hippocampus. In contrast, the GABAergic component of the septo-hippocampal projection did not differ between the strains investigated. The number of ChAT-reactive neurons in the MS/vDB was not correlated with either hippocampal cholinergic markers. This might be attributed to different collateralization of cholinergic neurons or to different projections of these neurons to other brain regions. These results show a strong hereditary variability within the septo-hippocampal cholinergic system in mice. In view of the role of the cholinergic system in learning and memory processes, strain differences in cholinergic markers might be helpful in explaining behavioral variation. © 1996 Wiley-Liss, Inc.     

Septal transplants ameliorate spatial deficits and restore cholinergic functions in rats with a damaged septo-hippocampal connection

Behavioral effects of septal lesion and fornix-fimbria transection were compared in absence and presence of a septal transplant in the hippocampus. The transplant grew in the hippocampus and projected acetylcholinesterase (AChE)-containing fibers throughout the extent of the denervated hippocampus. There were no differences in graft size or AChE reinnervation pattern after septal lesion or fornix transection. An increase in the density of M1 binding sites seen in hippocampal CA3 region after a cholinergic lesion, was restored back to normal after reinnervation of the hippocampus by the graft. Fornix-transected rats were more impaired in water maze acquisition than septal-lesioned rats which were impaired compared to controls. Septal-grafted rats were not different from lesioned rats in the behavioral tasks. However, an injection of physostigmine improved their performance relative to lesioned non-grafted rats. These experiments indicate that grafts can ameliorate behavioral deficits when the efficacy of acetylcholine of graft origin is enhanced.