Direct cell-cell interactions control apoptosis and oligodendrocyte marker expression of neuroepithelial cells

During brain development, the neuroepithelium generates neurons and glial cells. Proliferation and differentiation of neuroepithelial cells are controlled by a complex combination of secreted factors and more intrinsic or local mechanisms, such as lateral inhibition and asymmetric division. To obtain further insights into the signals governing neuroepithelial cell fate, we used the immortomouse to derive conditionally immortalised cell lines from mouse E10 neuroepithelium. We isolated a nestin-positive basic fibroblast growth factor (bFGF)-responsive cell line (SVE10-23) which mostly differentiate into astrocytes when cocultured with primary cortical cells. We found that, by simply lowering the cell density, SVE10-23 cells embarked on oligodendrocytic differentiation as indicated by the strong expression of galactocerebroside C and 2'3'-cyclic nucleotide 3'-phosphodiesterase. Apoptosis accompanied the differentiation, and all cells died within 1 week. We present here evidence that direct interactions between cells are the main mechanism regulating this oligodendrocytic differentiation. We demonstrate that SVE10-23 cells contact or proximity inhibit their differentiation, prevent apoptosis, and promote their proliferation. Similarly, others nestin-positive precursor cell lines and nonimmortalised bFGF-grown E10 cells were found to spontaneously differentiate at low density, thus generalising the idea that neural precursor fate is regulated by direct cell-cell interactions. The SVE10-23 cell line provides a valuable tool with which to study further the molecular components implicated in this mode of regulation.

Functional reconstruction of the hippocampus: fetal versus conditionally immortal neuroepithelial stem cell grafts

Late fetal CA1 hippocampal grafts and stem cell grafts from the conditionally immortal MHP36 clonal line derived from the H-2Kb-tsA58 transgenic mouse neuroepithelium both improved spatial deficits in rats with ischaemic CA1 damage induced by four-vessel occlusion (4VO). However, the distribution of fetal and MHP36 grafts differed. Fetal cells lodged in clumps around the implant sites and along the corpus callosum, whilst MHP36 grafts infiltrated the area of CA1 ischaemic damage, achieving apparent architectural reconstruction of the hippocampus. The migration of MHP36 cells is damage-dependent. Few cells were found in intact brain; after 15 min of 4VO cells repopulated only the discrete area of CA1 cell loss, whereas with more extensive damage after 30 min occlusion cells migrated to all hippocampal fields and to cortex. A higher proportion of grafted MHP36 cells differentiated into neurons in the host CA1 field than grafts of striatal or cortical expanded cell populations. Cortical population grafts were as effective as MHP36 grafts in improving water maze learning, whereas striatal or ventral mesencephalic cells were ineffective, indicating a degree of stem cell specificity. The efficacy of MHP36 cells extends to primates. In marmosets with profound impairments in conditional discrimination tasks after lesions of the CA1 field, MHP36 cells improved performance as effectively as fetal grafts and migrated evenly through the CA1 field, in contrast to clustered fetal cells. These findings suggest that MHP36 stem cell grafts are as effective as fetal grafts in functional repair of hippocampal damage, and that their preference for areas of cell loss and adoption of appropriate morphologies is consistent with a point-to-point repair mechanism.

Functional repair with neural stem cells

Approval to commence phase I/II clinical trials with neural stem cells requires proof of concept in well-accepted animal models of human neurological disease or injury. We initially showed that the conditionally immortal MHP36 line of hippocampal origin (derived from the H-2Kb-tsA58 transgenic mouse) was effective in repopulating CA1 neurons in models of global ischaemia and repairing cognitive function, and have now shown that this line is multifunctional. MHP36 cells are effective in restoring spatial memory deficits in rats after excitotoxic lesions of the cholinergic projections to cortex and hippocampus and in rats showing cognitive impairments due to normal ageing. Moreover, grafts of MHP36 cells are effective in reversing sensory and motor deficits and reducing lesion volume as a consequence of occlusion of the middle cerebral artery, the major cause of stroke. In contrast, MHP36 cell grafts were unable to repair motor asymmetries in rats with unilateral 6-hydroxydopamine lesions of the nigrostriatal dopamine system, the prototype rodent model of Parkinson's disease. These data show that conditionally immortal neuroepithelial stem cells are multifunctional, being able to repair diverse types of brain damage. However, there are limitations to this multifunctionality, suggesting that lines from different regions of the developing brain will be required to treat different brain diseases. ReNeuron is currently developing human neuroepithelial stem cell lines from different brain regions and with similar reparative properties to our murine lines.

Conditionally immortalized, multipotential and multifunctional neural stem cell lines as an approach to clinical transplantation

Experiments are described using rats with two kinds of brain damage and consequent cognitive deficit (in the Morris water maze, three-door runway, and radial maze): 1) ischemic damage to the CA1 hippocampal cell field after four-vessel occlusion (4VO), and 2) damage to the forebrain cholinergic projection system by local injection of excitotoxins to the nuclei of origin or prolonged ethanol administration. Cell suspension grafts derived from primary fetal brain tissue display a stringent requirement for homotypical cell replacement in the 4VO model: cells from the embryonic day (E)18-19 CA1 hippocampal subfield, but not from CA3 or dentate gyrus or from E16 basal forebrain (cholinergic rich) led to recovery of cognitive function. After damage to the cholinergic system, conversely, recovery of function was seen with cell suspension grafts from E16 basal forebrain or cholinergic-rich E14 ventral mesencephalon, but not with implants of hippocampal tissue. These two models therefore provided a test of multifunctionality for a clonal line of conditionally immortalized neural stem cells, MHP36, derived from the E14 "immortomouse" hippocampal anlage. Implanted above the damaged CA1 cell field in 4VO-treated adult rats, these cells (multipotential in vitro) migrated to the damaged area, reconstituted the gross morphology of the CA1 pyramidal layer, took up both neuronal and glial phenotypes, and gave rise to cognitive recovery. Similar recovery of function and restoration of species-typical morphology was observed when MHP36 cells were implanted into marmosets with excitotoxic CAI damage. MHP36 implants led to recovery of cognitive function also in two experiments with rats with excitotoxic damage to the cholinergic system damage, either unilaterally in the nucleus basalis or bilaterally in both the nucleus basalis and the medial septal area. Thus, MHP36 cells are both multipotent (able to take up multiple cellular phenotypes) and multifunctional (able to repair diverse types of brain damage).

Primary CA1 and conditionally immortal MHP36 cell grafts restore conditional discrimination learning and recall in marmosets after excitotoxic lesions of the hippocampal CA1 field

Common marmosets (Callithrix jacchus, n = 18) were trained to discriminate between rewarded and non-rewarded objects (simple discriminations, SDs) and to make conditional discriminations (CDs) when presented sequentially with two different pairs of identical objects signifying reward either in the right or left food well of the Wisconsin General Test Apparatus. After bilateral N-methyl-D-aspartate (0.12 M) lesions through the cornu ammonis-1 (CA1) field (7 microl in five sites), marmosets showed profound impairment in recall of CDs but not SDs, and were assigned to lesion only, lesion plus CA1 grafts and lesion plus Maudsley hippocampal cell line, clone 36 (MHP36) grafts groups matched for lesion-induced impairment. Cell suspension grafts (4 microl, 15-25 000 cells/microl) of cells dissected from the CA1 region of foetal brain at embryonic day 94-96, or of conditionally immortalized MHP36 cells, derived from the H-2Kb-tsA58 transgenic mouse neuroepithelium and labelled with [3H]thymidine, were infused at the lesion sites. The lesion plus MHP36 grafts group was injected five times per week with cyclosporin A (10 mg/kg) throughout testing. Lesion, grafted and intact control marmosets (n = 4-5/group) were tested on recall of SDs and CDs learned before lesioning and on acquisition of four new CDs over a 6-month period. Lesioned animals were highly impaired in recall and acquisition of CD tasks, but recall of SDs was not significantly disrupted. Both grafted groups of marmosets showed improvement to control level in recall of CDs. They were significantly slower in learning the first new CD task, but mastered the remaining tasks as efficiently as controls and were substantially superior to the lesion-only group. Visualized by Nissl staining, foetal grafts formed clumps of pyramidal-like cells within the denervated CA1 field, or jutted into the lateral ventricles. MHP36 cells, identified by beta-galactosidase staining and autoradiography, showed neuronal and astrocytic morphology, and were distributed evenly throughout the CA1 region. The results indicate that MHP36 cell grafts are as functionally effective as foetal grafts and appear to integrate into the host brain in a structurally appropriate manner, showing the capacity to differentiate into both mature neurons and glia, and to develop morphologies appropriate to the site of migration. These findings, which parallel the facilitative effects of foetal and MHP36 grafts in rats with ischaemic CA1 damage, offer encouragement for the development of conditionally immortal neuroepithelial stem cell lines for grafting in conditions of severe amnesia and hippocampal damage following recovery from cardiac arrest or other global ischaemic episodes.

Lesions of the nucleus basalis magnocellularis do not alter the proportions of pirenzepine- and gallamine-sensitive responses of somatosensory cortical neurones to acetylcholine in the rat

The effects of S-alpha-amino-3-hydroxy-4-isoxozolepropionic acid (AMPA) lesions of the nucleus basalis magnocellularis on the M1/M2 nature of the responses of somatosensory cortical neurones to acetylcholine (ACh) in Sprague-Dawley rats were investigated by iontophoretic application and extracellular single unit recording. The responses were characterised using pirenzepine, an M1 receptor antagonist, and gallamine, an M2 antagonist. Eighty two neurones in control and 94 neurones in lesioned animals were studied. In control animals, 37% of responses to ACh were sensitive to pirenzepine, gallamine or to both antagonists. This increased to 62% in lesioned animals, the proportions of pirenzepine- and gallamine-sensitive responses remaining unchanged. These results provide the first electrophysiological confirmation that both pirenzepine- and gallamine-sensitive (M1 and M2) receptors occur postsynaptic to afferent cholinergic terminals and that their postsynaptic stimulation may produce both inhibition and excitation.

Recovery of spatial learning by grafts of a conditionally immortalized hippocampal neuroepithelial cell line into the ischaemia-lesioned hippocampus

Transient global cerebral ischaemia in rats causes relatively circumscribed and specific damage to the CA1 pyramidal cells of the dorsal hippocampus, along with a cognitive deficit manifest as difficulties in the performance of a range of spatial learning and memory tasks. Our previous studies have shown that restoration of behavioural performance in ischaemic rats by neural grafts taken relatively late in fetal development occurs only after local replacement of cells homotypic to those lost through the ischaemic insult. This lesion-plus-behaviour model therefore offers a powerful means for establishing whether multipotent embryonic neuroepithelial cells will engraft the damaged CA1, develop into appropriate neuronal phenotypes and produce behavioural recovery. Here we report that, in rats subjected to 15 min of global cerebral ischaemia, intrahippocampal implants of a conditionally immortal, multipotent cell line, directly derived from the embryonic day 14 hippocampal neuroepithelium of the H-2Kb-tsA58 transgenic mouse, selectively repopulated the lesioned CA1 pyramidal layer and restored ischaemia-induced deficits in acquisition of a hidden platform location in the Morris water maze.

Long-term beneficial effects of BW619C89 on neurological deficit, cognitive deficit and brain damage after middle cerebral artery occlusion in the rat

4-Amino-2-(4-methyl-1-piperazinyl)-5-(2,3,5-trichlorophenyl)pyrimidine (BW619C89) is a sodium channel antagonist which when administered parenterally reduces neurological deficit and infarct volume after middle cerebral artery occlusion in rats. We have investigated whether BW619C89 administered orally before middle cerebral artery occlusion is cerebroprotective when rats are assessed at one day after stroke, and whether cerebroprotection is long lasting and related to functional recovery. A cerebroprotective oral dose of BW619C89 (20 mg/kg) was used to determine whether reduction in infarct volume is long lasting and can be enhanced with continued therapy, and whether behavioural deficits occurring after middle cerebral artery occlusion such as disturbances in cognition and motor coordination are ameliorated by treatment with BW619C89. Rats received sham surgery or middle cerebral artery occlusion with a single treatment of BW619C89 (20 mg/kg) 1 h before middle cerebral artery occlusion, a double treatment group receiving 20 mg/kg BW619C89 1 h before and 10 mg/kg 5 h after middle cerebral artery occlusion, or continued treatment with BW619C89 for up to five days. Neurological deficit, assessed from days 1 to 21, and at 70 days after middle cerebral artery occlusion, was reduced to a similar extent in all three groups of rats treated with BW619C89, compared with vehicle-treated controls. At 70 days after middle cerebral artery occlusion, all groups performed at control level. Vehicle-treated rats were impaired in the Morris water maze and step-through passive avoidance paradigm five to eight weeks after middle cerebral artery occlusion, when neurological deficit was minimal. These deficits were partially alleviated, to a similar extent, by all of the three treatments with BW619C89. Total volumes of brain damage, assessed at 70 days after middle cerebral artery occlusion in Luxol Fast Blue- and Cresyl Violet-stained coronal sections, were reduced in all three groups of BW619C89-treated rats, to 46% in the single, 50% in the double and 58% in the continued treatment group, compared with vehicle-treated rats. Extent of brain damage correlated with extent of impairment of the rats in the water maze. These findings suggest that BW619C89 has long-lasting cerebroprotective effects with advantageous functional consequences after single oral administration in a rodent model of stroke. Prolonged treatment with BW619C89 did not significantly enhance the cerebroprotective effects. Deficits in performance of rats in the water maze and step-through passive avoidance tasks indicate sustained cognitive impairment after middle cerebral artery occlusion. The reductions in brain damage by BW619C89 correlated with significant long-term functional improvement.

Cognitive deficits induced by global cerebral ischaemia: prospects for transplant therapy

Global ischaemia induced by interruption of cerebral blood flow results in damage to vulnerable cells, notably in the CA1 and hilar hippocampal fields, and is frequently associated with memory deficits. This review examines cognitive deficits that occur in animal models of global ischaemia in rats and monkeys, the extent to which these deficits are associated with CA1 cell loss, and the evidence for functional recovery following transplants of foetal CA1 cells and grafts of conditionally immortalised precursor cells. In rats, impairments are seen most consistently in tasks of spatial learning and spatial working memory dependent on use of allocentric environmental cues. In monkeys, ischaemic deficits have been shown to a moderate extent in delayed object recognition tasks, but animals with a selective excitotoxic CA1 lesion show a profound impairment in conditional discrimination tasks, suggesting that these may be a more sensitive measure of ischaemic impairments. Several studies have reported correlational links between the extent of CA1 cell loss following two or four vessel occlusion (2 VO, 4 VO) in rats and behavioural impairments, but recent findings indicate that at intermediate levels of damage these relationships are weak and variable, and emerge clearly only when animals with maximal CA1 cell loss are included, suggesting that the deficits involve more than damage to the CA1 field. Nevertheless, ischaemic rats and CA1-lesioned marmosets with grafts of foetal CA1 cells show substantial improvements; in rats these are not found with grafts from other hippocampal fields. Conditionally immortalised cell lines and trophic grafts are currently being assessed for their functional potential in animal models, because clinical use of foetal cells will not be practicable. Recent findings suggest that an expanded population of neuroepithelial cells derived from the conditionally immortalised H-2Kb-tsA58 transgenic mouse improve spatial learning as effectively as CA1 foetal grafts in rats subjected to 4 VO, and clonal lines from the same source show similar promise. Lines derived from precursor cells have the potential to develop into different types of cell (neuronal or glial) depending on signals from the host brain. These cell lines may therefore have the capacity to repair damaged host circuits more precisely than is possible with foetal grafts, and offer a promising, approach both to functional recovery and to elucidating graft-host interactions.

Changes in the sensitivity of frontal cortical neurones to acetylcholine after unilateral lesion of the nucleus basalis with alpha-amino-3-OH-4-isoxozole propionic acid (AMPA): effects of basal forebrain transplants into neocortex

Unilateral S-alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) lesions of the nucleus basalis magnocellularis (nbm), which produced persistent and extensive ChAT-positive cell loss within the nbm and depletion of cortical cholinergic markers in the frontal cortex, increased both the number and sensitivity of individual frontal cortical neurones responding to iontophoretic administration of ACh. The lesion also increased the sensitivity of individual neurones to carbachol but the increase in the number of neurones responding to carbachol was transient and had returned to normal 4 weeks after lesion. The sensitivity of individual neurones to glutamate was unchanged by the lesion. The percentage of cortical neurones responding to ACh, but not the sensitivity of individual neurones was restored to the prelesion level, 6-8 weeks after cholinergic transplants to the lesioned frontal cortex; cholinergic transplants to the more distant parietal cortex were only effective after 6 months whereas noncholinergic transplants were ineffective at both time intervals. Cholinergic transplants placed in the frontal cortex 6-8 weeks or 6 months before nbm lesion offered some protection from the effects of the lesion, particularly at 6 months but were ineffective when placed into the parietal cortex. Lesion of the nbm also reduced basal firing rate of spontaneously active neurones and this was not restored by any of the transplants. The results are discussed in the light of quantitative measurements of acetylcholinesterase-positive fibre outgrowth from the transplant into the recording area, which are described in the preceding manuscript [20].

Plastic changes in the cholinergic innervation of the rat cerebral cortex after unilateral lesion of the nucleus basalis with alpha-amino-3-OH-4-isoxozole propionic acid (AMPA): effects of basal forebrain transplants into neocortex

Unilateral AMPA lesions of the nucleus basalis magnocellularis (nbm) produced a nearly complete loss of cholinergic markers in the ipsilateral frontal and parietal cortices with no recovery at 6 months. The loss was associated with compensatory increases in AChE-positive fibre density in the contralateral cortex, in ipsilateral cortical regions not receiving their cholinergic innervation from the nbm and in the size of cholinergic magnocellular neurones in the contralateral nbm. The hypertrophy and increase in AChE-positive fibre density were apparent at 4-6 weeks after lesion and increased with time. Cholinergic transplants to cholinergically deafferented cortex prevented development of the compensatory increases in AChE-positive fibre density and restored AChE-positive fibre density and ChAT activity to control levels in ipsilateral cholinergically deafferented regions, partially after 6-8 weeks and completely after 6 months. In contrast, when cholinergic grafts were placed into unlesioned cortex, axonal outgrowth was localized to the vicinity of the transplant and did not develop with time. These results support the concept that vacant synapses promote and direct axonal outgrowth from transplanted neurones and that grafted cholinergic neurones integrate into the lesioned forebrain cholinergic projections system and prevent the lesion-induced changes in AChE-positive fibre density and ChAT activity.

Behavioural specificity of neocortical grafts of fetal basal forebrain tissue after unilateral lesion of the nucleus basalis with alpha-amino-3-OH-4-isoxozole propionic acid (AMPA)

The previous articles in this series [4,9] have shown that unilateral AMPA lesions of the nucleus basalis magnocellularis (nbm) produced widespread morphological and functional changes to the forebrain cholinergic projection system that could be reversed by transplants of fetal cholinergic tissue. At earlier postgraft time points, the effects of cholinergic grafts were specific to the neocortical region (frontal or parietal cortex) into which the grafts were targeted. Here we report that nbm lesion-induced spatial learning and memory deficits in the Morris water maze were reversed at 6-8 weeks postsurgery only by cholinergic grafts placed in the frontal cortex or frontal and parietal cortices combined. Similar grafts to parietal cortex only and noncholinergic fetal transplants to any cortical site were ineffective. In contrast, using separate groups of animals, deficits in sensorimotor function could be reversed in only one measure (open field turning) by cholinergic transplants targeted to the parietal (somatosensory) cortex or frontal and parietal cortex combined. These behavioural dissociations demonstrate that the frontal cortical cholinergic innervation from the nbm is necessary for effective spatial cognitive performance.

Contrasting effects of fetal CA1 and CA3 hippocampal grafts on deficits in spatial learning and working memory induced by global cerebral ischaemia in rats

Functional effects of fetal hippocampal field grafts were assessed in rats with spatial learning and memory impairments following global cerebral ischaemia. Experiment 1 examined effects of grafts dissected from fields CA1 and CA3 at embryonic day 19 and from the dentate gyrus at postnatal day 1. Cell suspensions (15,000 cells/site) were implanted bilaterally at two points above the dorsal CA1 area two weeks after four-vessel occlusion (electrocoagulation of the vertebral arteries followed the 24 h later by occlusion of the carotid arteries for 15 min). Histological examination showed that CA1 neuronal loss (60-70%) was equivalent in all ischaemic groups and that 80% of CA1 and 60% of CA3 grafts survived and were sited appropriately in the alveus or corpus callosum above the area of ischaemic CA1 damage in the host, but there was no survival of dentate grafts. Results from rats with poor pyramidal cell graft survival were excluded, but those from rats with non-surviving dentate grafts were retained as an additional control group. Acquisition in the water maze was examined nine and 25 weeks after transplantation, and spatial working memory was assessed in three-door runway and water maze matching-to-position tasks 19 and 28 weeks after grafting, respectively. For water maze acquisition rats were trained with two trails/day and a 10 min inter-trial interval for 10-12 days to locate a submerged platform. Ischaemic rats with CA1 grafts learned the platform position as rapidly as non-ischaemic controls, searched appropriately in the training quadrant and were accurate in heading towards the platform, but were initially impaired on recall of the precise platform position on probe trials with the platform removed. Performance of ischaemic controls and groups with CA3 and non-surviving dentate graft groups was significantly impaired relative to controls and to the CA1 grafted group. The CA1 grafted group was also as successful as controls in matching-to-position in the water maze and substantially superior to the other ischaemic groups, assessed using three trials/day, with a 30-s inter-trial interval and a different platform position on each day. In a more complex matching-to-position task in the three-door runway, the performance of the CA1 grafted group was significantly impaired relative to controls, although superior to that of the other ischaemic control and graft groups. Functional recovery with CA1, but not CA3, grafts in ischaemic rats was replicated in a second experiment which assessed water maze acquisition and working memory at 10 and 14 weeks after transplantation, in rats with 90% graft survival. These results indicate that long-lasting, task-dependent improvements can be seen in ischaemic rats with CA1 fetal grafts in both aversively and appetitively motivated spatial learning tasks. The findings suggest that functional recovery requires homotypic replacement of CA1 cells damaged by ischaemia, rather than provision of structurally similar glutamate-releasing CA3 pyramidal cells.

Relationship between up-regulation of nicotine binding sites in rat brain and delayed cognitive enhancement observed after chronic or acute nicotinic receptor stimulation

(-)-Nicotine tartrate (2 mg/kg), and a nicotinic agonist, RJR 2403 (1.4 mg/kg), and antagonist, mecamylamine (1 mg/kg), were administered to separate groups of rats SC twice daily for 10 days. Two other groups received the same doses of nicotine or RJR 2403 for 1 day followed by saline for 9 days. Twenty-four hours after the final injection, the rats were compared to a 10-day saline-injected group on acquisition of a hidden platform position in the Morris water maze (20 trials, 30-min inter-trial interval). The rats were killed 48 h after the last drug injection and frontal, entorhinal and posterior cingulate cortex and dorsal and ventral hippocampus assayed for [3H]-nicotine binding density. Chronic nicotine significantly increased the number of frontal and entorhinal cortical and dorsal hippocampal, but not posterior cingulate cortical or ventral hippocampal, nicotinic receptors, and improved rate of learning. Chronic mecamylamine and RJR 2403 also significantly increased the number of nicotinic receptors in frontal cortex, though not other regions, but retarded rate of learning. Nicotine given for 1 day 11 days earlier marginally increased nicotinic receptors in entorhinal cortex (but not other regions) and significantly increased rate of learning, though significantly less than 10-day nicotine. Entorhinal cortical and dorsal hippocampal nicotinic receptor numbers were positively associated with rate of learning but not performance at asymptote. Thus cognitive enhancement after chronic nicotine is in part a delayed consequence of nicotine administration 11 days earlier, and may reflect regional changes in nicotinic receptor up-regulation.

6-OHDA lesions of the nucleus accumbens accentuate memory deficits in animals with lesions to the forebrain cholinergic projection system: effects of nicotine administration on learning and memory in the water maze

The separate and combined effects of lesions to the forebrain cholinergic projections system (FCPS) and to dopamine (DA) terminals in the nucleus accumbens (n.acc) were assessed in two water maze tasks: (1) standard acquisition using two trials/day with a 10 min intertrial interval (ITI) for 15 days with the platform in the same position and (2) a working memory task requiring matching to a platform position located by chance on Trial 1, with four trials/day separated by a 30-s ITI and a different platform position on each of 4 days. Effects of nicotine (0.1 mg/kg) were also examined in animals with FCPS, n.acc, and combined lesions in order to determine whether facilatory effects of nicotine in FCPS lesioned animals are mediated by dopamine release in the n.acc. The FCPS and combined lesion groups were impaired in both tasks, but the combined lesion group was substantially worse than animals with FCPS lesions alone. The n.acc lesion group did not differ from controls. Nicotine did not affect acquisition in either the FCPS or combined lesion group, but impaired learning in animals with n.acc lesions. In the working memory task nicotine exerted a nonspecific facilatory effect in the FCPS and combined lesion groups, by reducing latency to find the platform both on the first trial and on the subsequent matching to position trials. Choline acetyltransferase (ChAT) activity was reduced in hippocampus and cortex in the FCPS lesion group, whereas DA levels in n.acc were increased. Conversely, in the n.acc lesion group accumbal DA levels were reduced, while cortical and hippocampal ChAT activity was increased, suggesting that reciprocal changes were induced by the separate lesions. However the combined lesion group showed mixed and more widespread effects; ChAT activity was unaltered in cortex and substantially reduced in hippocampus, and DA levels were reduced in both n.acc and caudate. The results indicate that combined FCPS and n.acc lesions impair spatial learning and working memory far more severely than FCPS lesions alone, although this does not reflect simple additive reductions in DA and ChAT activity. Nicotine improved spatial search strategy, and effect detected in the in the working memory task with daily changes in platform position, rather than in the standard acquistion task, but did not appear specifically to improve working memory. Since the facilitatory effect of nicotine was seen in both FCPS and combined lesion groups, the findings suggest that nicotine-induced improvements do not depend on accumbal DA release.

Sensitivity of rat frontal cortical neurones to nicotine is increased by chronic administration of nicotine and by lesions of the nucleus basalis magnocellularis: comparison with numbers of [3H]nicotine binding sites

The effects of chronic nicotine treatment and of unilateral AMPA lesion of the nucleus basalis magnocellularis (nbm) on the sensitivity of frontal cortical neurones to iontophoretically applied nicotine were studied. Chronic nicotine treatment increased the number of [3H]nicotine binding sites from 2.9 to 3.9 pmol g-1 wet weight, and increased the proportion of cortical neurones responding to nicotine from 32.3% to 60.0%. After unilateral nbm lesions, the densities of AChE-positive fibers and [3H]nicotine binding sites were reduced by approximately 97% and 55%, respectively, and the proportion of neurones responding to nicotine increased from 32.3% to 53.8%. The two treatments, chronic nicotine administration and nbm lesion, also increased the size of individual neuronal responses, prolonged their duration, and shortened the response latency. Responses to glutamate were unaffected by either procedures. The results show that the increase in [3H]nicotine binding produced by chronic nicotine administration is associated with an increased response to iontophoretically applied nicotine, suggesting that the receptor upregulation induced by the chronic treatment were functional. Less easily explained is the association between increased sensitivity of frontal cortical neurons to nicotine after nbm lesion with a decreased receptor density. It is suggested that a substantial proportion of nicotinic receptors are located presynaptically, and that their loss after lesion concealed an upregulation at postsynaptic sites.

Astrocyte transplants alleviate lesion induced memory deficits independently of cholinergic recovery

Basal forebrain tissue fragments taken from embryonic day 15 were separated into primary astrocytes and primary neurons in culture and grafted to rats with alpha-amino-3-hydroxy-5-methyl-4-isoxazole-propionic acid lesions to the nucleus basalis and medial septal regions. The two cell types were compared in two experimental paradigms for their behavioural, biochemical and histochemical effects; standard transplants of whole basal forebrain and sham transplants served as positive and negative controls, respectively. Each transplant cell type was characterised by in vitro immunocytochemistry to assess content and purity. Memory deficits produced by the lesions in a spatial win-stay T-maze task (Experiment 1) and a spatial plus associative radial maze task (Experiment 2) were significantly improved by the astrocyte, but not by the neuronal, primary cell transplants. The astrocyte graft groups performed as well as standard cholinergic rich basal forebrain groups, reaching control levels on both tasks, while the neuronal transplant groups were not significantly different to lesioned (sham transplanted) rats. There was no recovery in choline acetyltransferase activity in brain regions containing astrocyte grafts whereas activity in the neuronal graft regions was increased (often to control levels), similar to recovery produced by basal forebrain grafts. Grafts in all groups survived, transplanted neurons displaying similar morphology and placement in the host brain to unseparated basal forebrain grafts, while astrocytes showed evidence of migration. The cultured astrocytes were estimated to be > 95% pure, showing positive staining for all astrocyte markers and an absence of staining for neuronal markers. The results indicate that the restoration of cognitive function following fetal grafting is not dependent upon a restoration of cholinergic neuronal activity but is more likely mediated via diffuse graft-host communication, with trophic secretion a probable factor. This study emphasizes the usefulness of astrocytes in the repair of central nervous system injury and has implications for therapeutic potential.

The selective 5-HT3 receptor antagonist, WAY100289, enhances spatial memory in rats with ibotenate lesions of the forebrain cholinergic projection system

The effects of three doses (0.003, 0.03 and 1.0 mg/kg sc) of the 5-HT3 receptor antagonist, WAY 100289, on spatial learning and memory in the water maze were examined in rats before and after ibotenate lesions to the nucleus basalis and medial septal brain regions at the source of cholinergic projections to cortex and hippocampus. The representative cholinergic nicotinic and muscarinic receptor agonists nicotine (0.1 mg/kg) and arecoline (1.0 mg/kg) were also tested for comparison. Both arecoline and nicotine improved initial acquisition in rats before lesioning, in terms of latency to find a hidden platform and accuracy of search strategy. WAY100289 did not affect the performance of normal rats significantly, apart from some non-significant trends towards improvement with the highest dose. However, in animals showing transient navigational deficits in retention and relearning after lesioning, WAY100289 improved performance at all three doses, though ameliorative effects of nicotine and arecoline were more marked also in lesioned rats. These results show that WAY100289 improved spatial learning in animals impaired after lesions to cholinergic projection nuclei, which may reflect an interaction with cholinergic transmission to enhance cognitive function. However, in the present study, WAY100289 appeared to be less effective than direct cholinergic agonists.

Importance of forebrain cholinergic and GABAergic systems to the age-related deficits in water maze performance of rats

The present study investigated the performance of rats at 3-4 months and 21 months of age in the Morris water maze and correlated age-related cognitive deficits with changes in both cholinergic and GABAergic systems in the frontal cortex. The older rats were divided into two groups, unimpaired old and impaired old according to their ability to find a hidden submerged platform in the water maze, for electrophysiological, neurochemical, and morphological studies. The firing rate of frontal cortical neurones was recorded from the motor area of the frontal cortex under urethane anaesthesia and was found to be significantly slower in the two aged groups of rats compared to the young rats, but there were no differences between the two aged groups. The sensitivity of frontal cortex neurones of the impaired and unimpaired old age groups to ACh and to carbachol was significantly lower than that of the young group, but there were no differences between the two old age groups. In contrast, sensitivity of frontal cortex neurones to bicuculline was significantly higher in the aged rats compared with the young rats and was significantly greater in the impaired old rats than in the unimpaired old rats. The sensitivity of cortical neurones to glutamate was unaffected by age. There were also significant correlations between the percentages of cortical neurones responding to ACh and bicuculline and different parameters of water maze acquisition during days 7-8, but not during days 2-3, when spatial learning had not begun, and days 13-14, when spatial learning was complete. Biochemical and morphological analyses did not show any significant differences in ChAT activity and AChE-positive fibre density in the frontoparietal cortices of the three groups of rats. The results demonstrate that the learning deficit observed in old age rats cannot be adequately explained solely by a reduction in cholinergic receptor sensitivity and that an age-related increase in GABAergic tone may be a more important determinant of cognitive impairment.

Are the cognitive-enhancing effects of nicotine in the rat with lesions to the forebrain cholinergic projection system mediated by an interaction with the noradrenergic system?

Experiments were conducted to test the hypothesis that the enhancing effect of nicotine on water maze performance in rats with lesions of the forebrain cholinergic projection systems (FCPS) is mediated by an interaction with the noradrenergic system, in particular the ascending dorsal noradrenergic bundle (DNAB) and its projection areas. Three groups of rats received lesions of either: i) the nucleus basalis (NBM) and medial septal area/diagonal band (MSA/DB) by infusion of alpha-amino-3-hydroxy-4-izoxazole propionic acid (AMPA) (FCPS group), ii) DNAB, by infusion of 6-hydroxydopamine (6-OHDA) (NOR group), or iii) both FCPS plus DNAB (COMB group). Control animals received vehicle. Choline acetyltransferase activity was reduced in the cortex and hippocampus of the FCPS and COMB groups and in the hippocampus of the NOR group. NA level was reduced in the cortex and hippocampus of the FCPS and COMB groups, but not the FCPS group. In a reference memory task, the performance of both the NOR and COMB groups, but not the NOR group, was significantly worse than that of controls; there was no effect of nicotine administration (0.1 mg/kg) on escape latency or other measures in this task. In a working memory task, FCPS and COMB rats took longer to find the submerged platform on the second and following trials, and there was a significant enhancement of performance by nicotine in both groups, but not in controls. These results indicate that the enhancing effects of nicotine in rats with FCPS lesions are not mediated by an interaction with the DNAB.

Immunocharacterization of H-2Kb-tsA58 transgenic mouse hippocampal neuroepithelial cells

From dissected fragments of embryonic H-2Kb-tsA58 transgenic mouse hippocampal neuroepithelium, we have derived a population of rapidly proliferating, nestin-positive conditionally immortal hippocampal neuroepithelial cells. Treatment with dibutyryl cAMP in non-permissive culture conditions resulted in cessation of cell division and differentiation of the precursor cells into neuronal or glial phenotypes.

Fimbria-fornix lesions impair spatial performance and induce epileptic-like activity but do not affect long-term potentiation in the CA1 region of rat hippocampal slices

Groups of rats were given bilateral fimbria-fornix lesions and one month later grafted into the hippocampus with fetal cholinergic and non-cholinergic (hippocampal) neural tissue. Three weeks and 3 months after transplantation the animals were trained to find and then to retain the location of a hidden platform in the Morris water maze. After the final behavioral testing phase, electrophysiological studies of the short- and long-term potentiation (STP and LTP) and epileptiform activity of evoked responses were performed in vitro in the CA1 region of the hippocampus. The lesions produced a marked deficit in spatial function in the early testing phase which showed some recovery at the three month time point. Neither the cholinergic nor the non-cholinergic grafts improved spatial performance; indeed, on some measures these groups showed a significantly greater deficit than the lesion-alone group. Epileptiform activity, which was defined as the ratio of the sum of amplitudes of second and third population spikes to the amplitude of the first, before tetanization was not significantly different for all groups. After tetanization of the radiatum input, however, the epileptiform activity in the FFL group was significantly higher in comparison to that of the control groups. Grafting of cholinergic tissue decreased this parameter to the control level, but non-cholinergic grafts did not modify the lesion-induced epileptiform activity. Epileptiform activity after tetanization of the oriens input was approximately equal for all groups. There were no significant differences between surgical groups in STP and LTP for both the oriens and radiatum inputs.(ABSTRACT TRUNCATED AT 250 WORDS)

An iontophoretic study of the effects of alpha-amino-hydroxy-5-methyl-4-isoxazole propionic acid lesions of the nucleus basalis magnocellularis on cholinergic and GABAergic influences on frontal cortex neurones of rats

Unilateral lesions of the nucleus basalis magnocellularis (NBM) produced by alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid in rats caused, 8-10 weeks after the lesion, a 94% reduction in cortical acetylcholinesterase fibres and reduced activities of acetylcholinesterase and choline acetyltransferase by 70-80% in the frontal cortex ipsilateral to the lesion. In anaesthetized unlesioned control rats, iontophoretic administration of acetylcholine and carbachol produced atropine-sensitive inhibition and excitation of frontal cortical neurones, effects similar to those produced by electrically stimulating the NBM. The lesion reduced cortical neuronal firing rates but increased the percentage and sensitivity of neurones responding to acetylcholine, the predominant response changing from inhibition to excitation; response duration increased but latency was unaffected. The size of the response of individual neurones to carbachol, but not the percentage of sensitive neurones, was also increased in lesioned animals. The proportion of neurones responding to bicuculline and their individual sensitivities were increased by the lesion, suggesting that the lesion increased GABAergic tone; responses to glutamate were unchanged. The lesion did not affect the proportion of neurones in which acetylcholine modulated neuronal responses but reversed the nature of the modulation to predominantly excitatory; excitation was the predominant response to electrical forepaw stimulation in unlesioned control animals. This suggests a possible interaction between GABAergic and cholinergic mechanisms in selective attention and processing of cognitive information. Acute administration of di-isopropyl fluorophosphate to unlesioned animals significantly increased the number of frontal cortical neurones responding to acetylcholine, without affecting individual neuronal sensitivity or responses to carbachol and glutamate. The similarity of these effects to those of acetylcholine in lesioned animals suggests that the increased sensitivity to acetylcholine in the latter was due to loss of acetylcholinesterase, enabling diffusion of acetylcholine to more distant neurones. However, acetylcholinesterase does not hydrolyse carbachol and therefore it is necessary to postulate a different post-synaptic mechanism to explain the lesion-induced increases in the sensitivities of individual neurones to carbachol and to acetylcholine; interpretation of experimental findings should take these two mechanisms into account.

Unilateral AMPA lesions of nucleus basalis magnocellularis induce a sensorimotor deficit which is differentially altered by arecoline and nicotine

One week after unilateral alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) lesions of nucleus basalis magnocellularis, rats showed significant lateralised bias in spontaneous turning and in turning induced by tail pinch or by placing the rat on a 45 degrees grid. Turning was biased to the lesioned side and this side also showed increased responsiveness to pin-prick stimulation of the skin (somaesthesia), snout and whisker stimulation and ammonia olfaction. Arecoline (0.5 mg/kg), at a dose which did not affect responses to sensorimotor stimulation in sham-operated rats, corrected the lesion-induced biased turning to tail pinch and the 45 degrees grid test and reduced the bias in the open field. In contrast, nicotine (0.05 mg/kg), at a dose which also did not substantially affect responses to sensorimotor stimulation in sham-operated rats, switched the lesion-induced turning bias towards the contralateral side. Neither cholinoceptor agonist reduced the lesion-induced increased sensory responsiveness. The effects of nicotine were blocked by the centrally acting nicotinic antagonist, mecamylamine (1.0 mg/kg), but not by hexamethonium (1.0 mg/kg), or ondansetron (0.01 mg/kg). Amphetamine (up to 1.0 mg/kg) did not affect the lesion-induced motor asymmetry. The results confirm that the basal forebrain cholinergic system plays a role in sensorimotor cortical functions, but suggest different functional roles for muscarinic and nicotinic receptors.

Neuropathological sequelae of long-term allogeneic and syngeneic neural transplantation into the hippocampus

The long-term fate of multiple intrahippocampal allogeneic transplants of fetal basal forebrain tissue was studied in neonatally tolerised and immunised groups of rats with lesions of the fimbria-fornix. Despite the good survival of the allografts in all groups, unexpected transplant-associated host hippocampal neuropathology was discovered 12 months after transplantation, which consisted of (i) CA1 cell degeneration and (ii) abnormal accumulations of phosphorylated neurofilaments in neuronal perikarya and axonal swellings only within the host hippocampal neuropil and not of the transplanted tissue. This neurofilament abnormality, identified by RT97 immunohistochemistry, was significantly greater in the transplanted rats compared to the non-grafted lesion-only and sham-lesioned rats (p < 0.01). The same type of neurofilament abnormality was again observed in a second, separate experiment using unilateral and bilateral syngeneic and allogeneic transplants. The neuropathology was significantly (p < 0.05) greater in the transplanted side of the unilateral transplanted rats compared to the non-transplanted lesion-only control side of the same animals, showing that transplantation per se was a major factor involved in the pathogenesis of this neuropathology, irrespective of the type of transplant (syngeneic or allogeneic). In addition, a small degree of neurofilament abnormality was also found within the transplants in the second experiment, but not in the first. The results show that, under certain conditions, specific local neuropathological damage to the surrounding host neural tissue can develop in long-surviving allografted and syngrafted animals.

Foetal grafts from hippocampal regio superior alleviate ischaemic-induced behavioural deficits

Transitory global cerebral ischaemia produced in rats by four vessel occlusion for 15 min produced substantial loss of CA1 cells in dorsal hippocampus and minimal other intra- and extra-hippocampal damage. Ischaemic rats showed a long-lasting impairment in spatial navigation in the water maze, and such impairment was sensitive to task difficulty. Groups of ischaemic animals were implanted with foetal tissue dissected from hippocampal regio superior (SUP--containing CA1 field), regio inferior (INF--containing dentate gyrus), and basal forebrain, with grafts sited in the alveus above the damaged CA1 region. Behavioral testing in the water maze (acquisition, retention and a working memory task) was conducted over a period of 4 to 12 weeks after grafting. Only rats receiving the SUP graft showed consistent improvement in water maze performance, relative to ischaemic controls, when tested in retention and working memory. Although the selective effect of CA1-containing grafts suggests repairing of the damaged host circuit, functional recovery may have been related to the greater ability of SUP grafts to survive and grow in the host ischaemic hippocampus.

Extracellular recordings in the colchicine-lesioned rat dentate gyrus following transplants of fetal dentate gyrus and CA1 hippocampal subfield tissue

Grafts of fetal dentate gyrus (DG) and CA1 hippocampal subfield tissue were extruded into the dentate gyri of adult male Sprague-Dawley rats, 7-10 days after lesioning the granule cells with colchicine (0.06 microliter of 7 mg/ml solution at each of 5 sites/hippocampus). Graft area-host and host-graft area connectivities were investigated 4-6 months post-transplantation by recoding extracellular evoked response in hippocampal slice preparations. Following stimulation of the host mid-molecular layer, evoked field potential responses, showing considerable variation, were recorded in both types of graft. Evoked responses in the lesioned DG without grafts were recorded in very few slices. Stimulation of the area of DG tissue grafts occasionally evoked responses in the host CA3/CA4 and there was no evidence for CA1 graft area-CA3/CA4 connectivity; stimulation of DG and CA1 graft areas occasionally evoked responses in the host CA1. Responses in the area of both DG and CA1 grafts supported short-term potentiation following stimulation of the host mid-molecular layer but only DG graft areas supported long-term potentiation of the population spike amplitude. In the area of both types of transplant a tonic bicuculline-sensitive inhibition was present and paired-pulse stimulation paradigms provided some evidence for inhibition. It is possible that responses recorded within the area of grafted tissue to stimulation of the host are attributable to host-graft connectivity and similarly, responses recorded in the host to stimulation of the area of the graft may be attributable to graft-host connectivity. Only DG graft areas received host inputs which were capable of sustaining a long-term potentiation and establishing efferent contacts with the host CA3/CA4 subfield, suggesting that these would be more likely than CA1 grafts to reinstate normal functional circuitry.

Effects of fetal hippocampal field grafts on ischaemic-induced deficits in spatial navigation in the water maze

Transitory global cerebral ischaemia induced in rats by four vessel occlusion for 15 min produced substantial loss of CA1 cells in dorsal hippocampus, and minimal damage in other intra- and extrahippocampal forebrain regions examined. Ischaemic rats showed long-lasting deficits in spatial navigation in the water-maze, consisting of impaired learning to locate a hidden platform in a novel pool, a substantial increase in time spent searching close to the platform without finding it, and moderate deficits in matching to position in a working memory task. Groups of ischaemic rats were implanted with fetal tissue dissected from hippocampal CA1 field, containing glutamatergic CA1 pyramidal cells, from dentate gyrus, containing glutamatergic dentate granule cells, and from basal forebrain, containing cholinergic cells, with grafts sited in the alveus above the damaged CA1 region, for comparison with non-grafted ischaemic and non-ischaemic control groups, over a series of tests from four to 20 weeks after grafting. All ischaemic groups showed comparable acquisition deficits prior to transplantation, and similar loss of CA1 cells on post mortem examination. When tested in a familiar pool in retention and reversal learning of the original platform position, and a working memory task, all ischaemic rats performed better than in initial acquisition. However, rats receiving CA1 grafts showed the most consistent improvement relative to ischaemic controls. When tested in a second (i.e. novel) pool, ischaemic rats again showed marked impairment, whereas rats with CA1 grafts were significantly superior, and learned as rapidly as non-ischaemic controls. The performance of groups with dentate granule and basal forebrain grafts was similar to that of the non-grafted ischaemic control group throughout testing. These results suggest that ischaemic rats are impaired in the adaptive use of spatial information, as shown by acquisition and working memory deficits, but not in long- or short-term memory storage processes, and are also impaired in precise spatial localization. The effects of CA1 grafts in restoring spatial abilities, shown most clearly when rats were tested in a novel environment, suggest that these grafts may have assisted with repair to the damaged host circuit, rather than acted through the release of an appropriate neurotransmitter, since the glutamatergic dentate granule grafts were ineffective. However, CA1 grafts showed better survival and growth than the other types of transplant, so that functional recovery may have been related to graft viability rather than to the specific type of graft.

Direct evidence for axonal outgrowth from cholinergic grafts to cholinergically-deafferented rat cortex

True Blue, a retrograde fluorescent tracer, was used to investigate axonal outgrowth after grafting embryonic forebrain cholinergic tissue into the cholinergically-deafferented rat frontal cortex. Unilateral deafferentation was achieved by injecting alpha-amino-3-OH-4-isoxozole propionic acid (AMPA) into the ipsilateral nucleus basalis magnocellularis. Grafting occurred 3 weeks after the lesion. Eight to 10 weeks later, True Blue was injected bilaterally into the cortex at a superficial site which, on the transplanted side, was located at least 2 mm away from the transplant. Forty-eight h later, retrogradely labelled fluorescent neurones could be seen in the deepest part of the transplants. Some of these neurones were shown to be ChAt-positive, providing evidence of axonal outgrowth from transplanted cholinergic neurones into cholinergically-deafferented frontal cortex.

Chronic treatments with cholinoceptor drugs influence spatial learning in rats

Nicotine, scopolamine, oxotremorine, diisopropyl-fluorophosphate (DFP) and tetrahydroaminoacridine (THA) were administered chronically to different groups of rats in doses reported to alter central muscarinic and/or nicotinic receptor numbers. Beginning 24 h after final drug injection, the groups were compared to a vehicle control group on acquisition of a hidden platform position in the Morris water maze over 20 trials with a 30-min inter-trial interval. Chronic treatment with either nicotine or scopolamine significantly improved the rate of learning, but oxotremorine and DFP retarded learning and THA had no effect on learning. The chronic drug effects on behaviour were consistent with known effects of the injected drugs on muscarinic and nicotinic binding in the forebrain and on the sensitivity of frontal cortex neurones to iontophoretically applied cholinoceptor agonists. However, alternative explanations for the observed changes cannot be ruled out, since the drugs used are known to have a wide range of effects on other neurotransmitters.

Neural transplantation: problems and prospects for therapeutic application

Successful demonstrations of behavioural recovery in a variety of lesion and mutant animal models have encouraged the application of neural transplantation to the alleviation of neurodegenerative disease. Apart from the continuing shortage of foetal tissue, the major problems to be resolved for successful application of neural transplantation to humans are: first, immune rejection of allograft tissue and its pathological consequences to both graft and host tissue; and second, the establishment of normal and extensive graft-host connectivity. Recent developments in transplant research are beginning successfully to apply a number of strategies to resolve these problems.

Comparison of radial maze performance of rats after ibotenate and quisqualate lesions of the forebrain cholinergic projection system: effects of pharmacological challenge and changes in training regime

Rats with ibotenic or quisqualic acid lesions to cholinergic projections showed similar significant increases in both short-term working and long-term reference memory errors in radial maze spatial (place) and nonspatial (cue) tasks, throughout a period of 10 weeks after lesioning. All types of error were dose-relatedly reduced to a similar extent in lesioned rats after treatment with nicotine and the beta-carboline ZK93426. Performance of controls was not affected by nicotine, but errors were increased with the higher doses of ZK93426. In contrast, amphetamine increased errors in both control and lesioned rats. With extensive training, lesioned rats improved to control level, but were more disrupted than controls by a break in testing, which reinstated high error rates to an equivalent extent in lesioned groups. Choline acetyltransferase (ChAT) activity showed a comparable degree of depletion in quisqualate and ibotenate lesioned groups to around 60% of control level in cortex and 75% in hippocampus. These results indicate that at volumes and concentrations that produced an equivalent degree of ChAT depletion, detrimental effects of ibotenate and quisqualate lesions on radial maze performance were very similar. The time course of improvement with over-training and impairment after a break in training were also comparable with both lesioning agents. Reduced errors following compounds acting directly (nicotine) or possibly indirectly (ZK 93426) to enhance cholinergic function, but not after amphetamine, suggested that damage to cholinergic neurons contributed to the behavioural deficits induced by both ibotenic and quisqualic acid.

Survival and distribution of transplanted human IMR-32 neuroblastoma cells

The visualisation of transplanted cell lines is essential to determine both their viability and possible functional properties. Fluorescent latex microspheres were used to label cultured human neuroblastoma IMR-32 cells prior to transplantation. IMR-32 cells were first rendered amitotic by treatment with mitomycin C and bromodeoxyuridine and subsequently incubated with fluorescent microspheres for 3 days. Cell suspensions were prepared from these cultures and transplanted into the cortex and hippocampus of male Sprague-Dawley rats bearing ibotenate lesions of forebrain cholinergic projections. The animals were perfused at 4, 8 and 12 weeks post-transplantation and tissue was prepared for electron and light microscopy. IMR-32 cells containing fluorescent microspheres were clearly visualised in cryostat sections at all time points. Greater survival was seen in the hippocampus, with evidence of migration of cells from the site of implantation. Macrophages were seen at the electron and light microscope level, and were distinct from the discrete fluorescent labelled IMR-32 cells. Ultrastructurally, transplanted IMR-32 cells resembled cells in vitro, with microspheres clearly distinguished within the cytoplasm. Fluorescent microspheres provide a simple and direct labelling technique suitable for long-term transplant experiments using characterised cell lines.

The effects of ibotenic acid lesions of the nucleus basalis and cholinergic-rich neural transplants on win-stay/lose-shift and win-shift/lose-stay performance in the rat

Rats were trained to criterion performance in 2-lever operant conditional memory tasks that required them to follow either a Win-stay/Lose-shift, or else a Win-shift/Lose-stay response rule. Substantial impairments in performance of both pretrained conditional tasks were seen following ibotenic acid lesions of the nucleus basalis, but not of the globus pallidus. The deficit in both tasks was apparent at all inter-response retention intervals, indicating that nucleus basalis lesions produced a general impairment in the performance of the complex conditional operant tasks, and not a specific deficit in short-term memory. The nucleus basalis lesion rats were then divided into groups matched for equivalent performance. One group was given cell suspension grafts into neocortex of E15 cholinergic-rich forebrain tissue; a second group was given similar grafts of E17 hippocampal tissue; and a third group was given sham transplants. Testing beginning 3 months post-transplant showed that there was no evidence of recovery of performance on these tasks in the cholinergic-rich transplanted groups compared to the controls. However, the rats with cholinergic-rich transplants subsequently showed a significant improvement in retention of a step-through passive avoidance task. The results indicate that either cholinergic deafferentation of the neocortex is not critical for the observed deficits in the operant conditional tasks, or recovery of function following cholinergic-rich transplants is task-specific, in that more complex cognitive tasks may require different levels of graft-host neural integration.

Non-specific effects of the putative cholinergic neurotoxin ethylcholine mustard aziridinium ion in the rat brain examined by autoradiography, immunocytochemistry and gel electrophoresis

Autoradiographic localisation of [3H]-ethylcholine mustard aziridinium ion (ECMA) after microinjection into the rat striatum has revealed intracellular sequestration of the toxin by glial and endothelial cells; fewer neuronal cells were labelled. Intrastriatal injection of 200 pmol ECMA caused severe cavitation of the tissue, extensive gliosis and permanent damage to myelinated structures, as revealed by immunocytochemical detection of glial fibrillary acidic protein (GFAP) and myelin basic protein (MBP). These non-specific effects are in addition to ECMA's irreversible action on the choline carrier associated with cholinergic neurons, and only marginally protected by concomitant administration of the reversible choline transport inhibitor hemicholinium-3. They may instead be attributed to the powerful alkylating action that ECMA has on tissue proteins, as shown by fluorography of synaptosomal proteins treated with [3H]ECMA and separated by SDS-PAGE.

The effects of intra-subicular ibotenate on resistance to extinction after continuous or partial reinforcement

Intracerebral injections of ibotenate were used to produce, in rats, extensive cell loss in the subiculum. These rats and sham-operated controls were trained to run in a straight alley for food reward delivered on a continuous (CR) or partial (PR) reinforcement schedule. In controls PR training gave rise to the well-known partial reinforcement extinction effect (PREE), i.e., greater resistance to extinction than that observed in CR-trained animals. Previous experiments have shown that large aspiration lesions of the hippocampal formation eliminate the PREE; and that ibotenate-induced lesions of the subicular region plus either the hippocampus or the entorhinal cortex disrupt it. In contrast to these previous results, the PREE was unaltered in the present experiment by damage largely restricted to the subiculum. This lesion caused only relatively small changes in running speeds during acquisition. Thus the critical region(s) of damage within the hippocampal formation for disruption of the PREE remains uncertain.

The effects of fornix section on win-stay/lose-shift and win-shift/lose-stay performance in the rat

Two groups of rats were trained in 2-lever operant tasks that required them to follow either a Win-shift/Lose-stay rule, or else a Win-stay/Lose-shift rule. The rats in each testing condition attained a similar level of performance. Once the tasks had been learnt, half of the rats in each testing condition were given fornix lesions. These lesions produced a clear performance impairment at all inter-response retention intervals tested in those rats trained on the Win-shift/Lose-stay task, but impaired performance in rats trained on the Win-stay/Lose-shift condition only when the inter-response interval reached 10 s. The implications of these results for the working memory theory and for the temporal discontiguity theory are discussed.

Selective cytotoxic lesions of the hippocampal formation and DRL performance in rats

Rats were given injections of ibotenic acid that made lesions of neurons throughout the hippocampus (CHC), or restricted to area CA3 (CA3), or to the subiculum (SUB), and were trained to lever press on a differential reinforcement of low rates (DRL) schedule. Their performance efficiency was compared with that of sham-operated (SO) rats in three experiments. Acquisition of DRL 12 s was only slightly impaired by any of the lesions. Increasing the DRL requirement to 18 s did not affect asymptotic efficiency of responding in the SO, CA3, or SUB group but markedly reduced efficiency in the CHC group. Administration of scopolamine reduced efficiency to the same extent in rats in all surgical treatment groups. It is concluded that hippocampal lesions made with ibotenic acid resemble conventional hippocampal lesions in their behavioral effects on DRL performance; that the behavioral effects of scopolamine administration do not appear to depend on disruption of activity of cholinoceptive cells in the hippocampal formation; and that DRL schedules, although highly sensitive to septohippocampal system disruption, discriminate more between the extent than the location of lesions in the system.

The effects of intrahippocampal ibotenate on resistance to extinction after continuous or partial reinforcement

Intracerebral injections of ibotenate were used to produce, in rats, extensive cell loss in the hippocampus and dentate gyrus (complete hippocampal, CH), in the CH plus subiculum (SUB + CH), or in the subiculum plus entorhinal cortex (SUB + EC). These rats and sham-operated controls were trained to run in a straight alley for food reward delivered on a continuous (CR) or partial (PR) reinforcement schedule. In controls PR training gave rise to the well-known partial reinforcement extinction effect (PREE), i.e., greater resistance to extinction than that observed in CR-trained animals. Previous work had shown that large aspiration lesions of the hippocampal formation eliminate the PREE by increasing resistance to extinction in CR-trained animals and decreasing resistance to extinction in PR-trained animals. In the present experiments the PREE survived CH lesions, which increased resistance to extinction in both CR and PR training conditions; these effects were observed in the start and run (but not goal) sections of the alley. In contrast, subicular cell loss (in both SUB + CH and SUB + EC groups) abolished the PREE (but in the goal section only) by increasing resistance to extinction in the CR condition and decreasing resistance to extinction in the PR condition. In addition, some of the effects of PR training on start and run speeds during acquisition were altered by the CH and SUB + CH lesions. These results confirm previous data showing that the hippocampal formation plays a role in mediating the behavioural effects of PR training, but require modification of the model previously proposed to account for these data.

Selective cytotoxic lesions of the hippocampal formation and DRL performance in rats

Rats were given injections of ibotenic acid that made lesions of neurons throughout the hippocampus (CHC), or restricted to area CA3 (CA3), or to the subiculum (SUB), and were trained to lever press on a differential reinforcement of low rates (DRL) schedule. Their performance efficiency was compared with that of sham-operated (SO) rats in three experiments. Acquisition of DRL 12 s was only slightly impaired by any of the lesions. Increasing the DRL requirement to 18 s did not affect asymptotic efficiency of responding in the SO, CA3, or SUB group but markedly reduced efficiency in the CHC group. Administration of scopolamine reduced efficiency to the same extent in rats in all surgical treatment groups. It is concluded that hippocampal lesions made with ibotenic acid resemble conventional hippocampal lesions in their behavioral effects on DRL performance; that the behavioral effects of scopolamine administration do not appear to depend on disruption of activity of cholinoceptive cells in the hippocampal formation; and that DRL schedules, although highly sensitive to septohippocampal system disruption, discriminate more between the extent than the location of lesions in the system.

Hypothalamic modulation of energy expenditure

The acute effects of electrical stimulation of the hypothalamus on energy expenditure as measured by indirect calorimetry were investigated in 20 unanaesthetized rats. Thirty sec of stimulation increased both O2 consumption and respiratory quotient (R.Q.). The largest magnitude hypermetabolic response (39% mean peak increase in O2 consumption) was produced by stimulation of the ventromedial hypothalamic nucleus. Stimulation of the lateral hypothalamus produced hypermetabolic effects similar to but smaller than those produced by medial stimulation. A number of considerations suggest that the hypermetabolism is not secondary to changes in motor activity, carbohydrate utilization or blood glucose levels. Consequently, these data suggest that the hypothalamus modulates energy expenditure through changes in non-shivering thermogenesis. These metabolic changes may modulate the effects of various hypothalamic manipulations on body weight.

The effect of electrical stimulation of the hypothalamus on continuously-monitored blood glucose levels

The effects of hypothalamic stimulation on blood glucose levels were investigated in unanaesthetised rats with intracardiac catheters directly connected to a continuous glucose analyzer. Thirty sec of low level electrical stimulation produced hyperglycemia at 23 of the 34 sites stimulated. At the remaining 11 sites the electrical stimulation produced no changes in blood glucose levels. The hyperglycemia could be dissociated from the changes in motor activity produced by the stimulation. The highest probability of producing hyperglycemia was found at ventro-lateral sites although hyperglycemia was also observed after stimulation of dorsal and medial sites. Apart from this medio-lateral difference in the density of sites at which stimulation produced hyperglycemia, the effects were not well differentiated anatomically. In addition, in terms of latency, peak magnitude and duration of the hyperglycemia, stimulation of the various hypothalamic subdivisions appeared to be functionally equivalent. Thus with respect to hypothalamic involvement in the maintenance of blood glucose levels the present stimulation analysis suggests a medio-lateral functional similarity which is very different from the medio-lateral reciprocity of lesion effects on ingestive behaviour and body weight.

The effect of naloxone on intragastric ethanol self-administration

The acute effect of 1.25 and 2.50 mg/kg naloxone was tested in a group of male Wistar rats readily self-administering 10% w/v ethanol intragastrically following 12 days of forced ethanol intoxication. Compared to saline pretreatment, naloxone did not alter 24 hr intakes of food, water or ethanol. However, both does strongly and significantly inhibited lever pressing for ethanol during 2 hr following pretreatment. The results indicate that naloxones's inhibition of ethanol intake does have a transient postabsorptive component, although this component is unlikely to be specific to ethanol.

Dissociating the determinants of self-stimulation

Four experiments were conducted to elucidate the determinants of the initiation of and escape from electrical stimulation of the lateral hypothalamus under several different reinforcement schedules. The first experiment of this series used correlational and factor analytic techniques to show that, under continuous reinforcement, the vigour of initiation is determined more by forcement than by positive reinforcement. Forcement is defined as all of the performance changes directly elicited and potentiated by the stimulation. Escape is determined by adaptation of positive reinforcement, not by negative reinforcement or aversion. Continuous reinforcement schedules are, therefore, not appropriate for studying either the positive or negative reinforcement produced by brain stimulation. The second experiment used fixed-interval reinforcement schedules to eliminate the effects of forcement on initiation and adaptation of positive reinforcement on escape. Parametric manipulations indicate that activity in the positive reinforcement and escape systems is a simple function of stimulation charge. The combination of parameters which make up a given charge is of relatively little importance. However, the positive reinforcement system becomes maximally activated at far lower charges than does the escape system. The third experiment used a T-maze technique to show that, after 5 sec, anterior hypothalamic stimulation becomes negatively reinforcing, but posterior hypothalamic stimulation does not. Since the escape from posterior hypothalamic stimulation on a fixed-interval schedule can be dissociated from both negative reinforcement and adaptation of positive reinforcement, it is suggested that such escape is reinforced by a positive process triggered by the offset of stimulation (OFF positive reinforcement). The fourth experiment showed that stimulation trains longer than 10 sec are significantly less positively reinforcing than much shorter trains. This reduction in positive reinforcement confirms the development of negative reinforcement in long trains of hypothalamic stimulation, even at posterior electrodes. Negative reinforcement appears to be as general a property of hypothalamic stimulation as is positive reinforcement. Thus, depending on the reinforcement schedule and electrode site, the initiation of lateral hypothalamic stimulation may be determined by ON positive reinforcement, OFF positive reinforcement and forcement. Escape may be determined by OFF positive reinforcement, adaptation of positive reinforcement and negative reinforcement.(ABSTRACT TRUNCATED AT 400 WORDS)

Dopaminergic and noradrenergic inhibition of hypothalamic self-stimulation: differentiation of reward and performance effects

Dopaminergic and noradrenergic inhibition of lateral hypothalamic self-stimulation was investigated in a new signalled, discrete-trials shuttle-box paradigm. The differential inhibitory effects of drugs and stimulation frequency reductions within small blocks of trials differentiate reward inhibition from a variety of performance deficits. They further differentiate among the deficits produced by fatigue, sedation, dyskinesias, akinesia and sensory disruption. Pimozide's selective inhibition of the first response within each block of trials shows that its inhibition of self-stimulation is not due to either an inhibition of reward or to a general performance deficit. Instead, it suggests that pimozide specifically inhibits the initiation of motor responding. Pimozide-induced akinesia appears to be partly reversible by hypothalamic stimulation. Thus the pimozide data do not support a role for dopamine in mediating brain-stimulation reward. Since the inhibitory effects of clonidine were very similar to those of pimozide, it is suggested that clonidine also produces a stimulation-reversible akinesia. Thus the clonidine data do not support a role for noradrenaline in mediating brain-stimulation reward. LU 5-003, which selectively inhibits the presynaptic reuptake of noradrenaline, inhibited self-stimulation in almost exactly the same way as did reducing reward by reducing stimulation frequency. These data do support a primary role for noradrenaline in mediating brain-stimulation reward. However, it is suggested that LU 5-003 inhibits self-stimulation, not by inhibiting reward, but by enhancing reward and making the electrical stimulation superfluous.

Parameters of low-dose ethanol intravenous self-administration in the rat

Male Wistar rats were able to press on an operant lever 24 hr/day for intravenous infusions of saline or ethanol at doses of 0.5, 1.0 or 5.0 mg/kg/infusion. Only the 1.0 mg/kg/infusion group showed a significant increase in responding on the lever as a function of days, whereas the 5.0 mg/kg/infusion group showed a significant decrease in responding as a function of days. The results suggest that the reinforcing value of intravenous ethanol changes from rewarding to neutral or aversive in valence at dose-level below that expected to produce signs of intoxication.