Peripheral administration of novel anti-inflammatories can attenuate the effects of chronic inflammation within the CNS

In the present study we investigated whether nitroflurbiprofen (NFP) or nitro-aspirin can reduce the inflammatory response induced by continuous infusion of lipopolysaccharide (LPS) into the fourth ventricular space of the rat's brain for 30 days. The chronic LPS infusion produced an extensive inflammation that was particularly evident in the hippocampus, subiculum and entorhinal and piriform cortices. Daily peripheral administration of NFP dose-dependently, and significantly, attenuated the brain inflammation as indicated by the decreased density and reactive state of microglial cells. Daily peripheral administration of nitro-aspirin also attenuated the brain inflammation, but to a much lesser degree than NFP. The results demonstrated that nonsteroidal anti-inflammatory drugs (NSAIDs) could reduce brain inflammation and that NFP is an effective anti-inflammatory agent.

Pathological and biochemical consequences of acute and chronic neuroinflammation within the basal forebrain cholinergic system of rats

Inflammatory processes may play a critical role in the degeneration of basal forebrain cholinergic cells that underlies some of the cognitive impairments associated with Alzheimer's disease. In the present study, the proinflammagen lipopolysaccharide, from the cell wall of Gram-negative bacteria, was used to produce inflammation within the basal forebrain of rats. The effects of acute, high-dose injections of lipopolysaccharide (2, 20 or 40 microg) upon basal forebrain chemistry and neuronal integrity were compared with the effects of chronic, low-dose lipopolysaccharide infusions (0.18, 0.25, 1.8 or 5.0 microg/h) for either 14, 37, 74 or 112 days. Acute exposure to lipopolysaccharide decreased cortical choline acetyltransferase activity and the number of immunoreactive choline acetyltransferase-positive cells within a small region of the basal forebrain. Regional levels of five different neuropeptides were unchanged by acute, high-dose lipopolysaccharide injections. Chronic lipopolysaccharide infusions produced (i) a time-dependent, but not dose-dependent, decrease in cortical choline acetyltransferase activity that paralleled a decline in the number of choline acetyltransferase- and p75-immunoreactive cells within the basal forebrain, and (ii) a dense distribution of reactive astrocytes and microglia within the basal forebrain. Chronic neuroinflammation might underlie the genesis of some neuropathological changes associated with normal ageing or Alzheimer's disease.

Novel glycineB antagonists show neuroprotective activity in vivo

The degeneration or dysfunction of cholinergic neurons within the basal forebrain of patients with Alzheimer's disease (AD) may be related to the vulnerability of these cells to endogenous glutamate (Beal, 1995; Greenamyre and Young, 1989). The administration of drugs that attenuate the toxic actions of glutamate in the early stages of the disease might significantly delay its rate of progression. Two approaches to neuroprotection from endogenous glutamatergic function were investigated and found to be effective: blockade of voltage-dependent, NMDA-type glutamate receptor channels and antagonism of an NMDA-receptor related glycineB modulatory site.

The neural mechanisms underlying cholinergic cell death within the basal forebrain

The basal forebrain region includes a large group of cholinergic neurons within the medial septal area and nucleus basalis magnocellularis (NBM) that project to the hippocampus and throughout the neocortex, respectively. This chapter will consider the mechanisms that influence why cholinergic cells within the NBM die and discuss studies that have manipulated the features of these cells that could make them differentially vulnerable to degeneration with aging and Alzheimer's Disease (AD). This chapter will focus upon the NBM cholinergic system because this regions typically demonstrates a greater degree of cell loss with aging and AD.

Coadministration of galanin antagonist M40 with a muscarinic M1 agonist improves delayed nonmatching to position choice accuracy in rats with cholinergic lesions

The neuropeptide galanin is overexpressed in the basal forebrain in Alzheimer's disease (AD). In rats, galanin inhibits evoked hippocampal acetylcholine release and impairs performance on several memory tasks, including delayed nonmatching to position (DNMTP). Galanin(1-13)-Pro2-(Ala-Leu)2-Ala-NH2 (M40), a peptidergic galanin receptor ligand, has been shown to block galanin-induced impairment on DNMTP in rats. M40 injected alone, however, does not improve DNMTP choice accuracy deficits in rats with selective cholinergic immunotoxic lesions of the basal forebrain. The present experiments used a strategy of combining M40 with an M1 cholinergic agonist in rats lesioned with the cholinergic immunotoxin 192IgG-saporin. Coadministration of intraventricular M40 with intraperitoneal 3-(3-S-n-pentyl-1,2,5-thiadiazol-4-yl)-1,2,5, 6-tetrahydro-1-methylpyridine (TZTP), an M1 agonist, improved choice accuracy significantly more than a threshold dose of TZTP alone. These results suggest that a galanin antagonist may enhance the efficacy of cholinergic treatments for the cognitive deficits of AD.

Neuroprotection by novel antagonists at the NMDA receptor channel and glycineB sites

Glutamate may act via an N-methyl-D-Aspartate (NMDA)-sensitive receptor site to destroy cholinergic neurons within the nucleus basalis magnocellularis in age-associated neurodegenerative diseases. Multiple interesting properties of the NMDA receptor are relevant to its excitotoxic actions, e.g., glutamate is ineffective unless a glycine (gly) modulatory site is also occupied. Thus, the antagonism of glutamate receptor-related toxicity by blockade of either the NMDA-sensitive recognition site or the gly binding site may therefore have therapeutic applications. The current study investigated the ability of four novel noncompetitive antagonists at these two sites: one NMDA open channel antagonist (MRZ 2/579: 1-amino-1,3,3,5,5-pentamethyl-cyclohexane hydrochloride), and three glyB receptor antagonists (MRZ 2/570: 8-bromo-4-hydroxy-1-oxo-1,2-dihydropyridaziono [4,5-beta] quinoline-5-oxide choline salt; MRZ 2/57: 8-fluoro-4-hydroxy-1-oxo-1,2-dihydropyridaziono [4,5-beta] quinoline-5-oxide choline; MRZ 2/576: 8-chloro-4-hydroxy-1-oxo-1,2-dihydropyridaziono [4,5-beta] quinoline-5-oxide choline) administered acutely, to provide neuroprotection from a NMDA receptor agonist within the nucleus basalis magnocellularis of young rats. Injection of NMDA into the nucleus basalis magnocellularis significantly decreased cortical choline acetyltransferase activity. Acute administration (i.p.) of MRZ 2/579, 2/570, 2/571 and 2/576 provided significant neuroprotection from NMDA.

Chronic neuroinflammation in rats reproduces components of the neurobiology of Alzheimer's disease

Inflammatory processes may play a critical role in the pathogenesis of the degenerative changes and cognitive impairments associated with Alzheimer's disease (AD). In the present study, lipopolysaccharide (LPS) from the cell wall of gram-negative bacteria was used to produce chronic, global inflammation within the brain of young rats. Chronic infusion of LPS (0.25 microgram/h) into the 4th ventricle for four weeks produced (1) an increase in the number of glial fibrillary acidic protein-positive activated astrocytes and OX-6-positive reactive microglia distributed throughout the brain, with the greatest increase occurring within the temporal lobe, particularly the hippocampus, (2) an induction in interleukin-1 beta, tumor necrosis factor-alpha and beta-amyloid precursor protein mRNA levels within the basal forebrain region and hippocampus, (3) the degeneration of hippocampal CA3 pyramidal neurons, and (4) a significant impairment in spatial memory as determined by decreased spontaneous alternation behavior on a T-maze.

Analysis of galanin and the galanin antagonist M40 on delayed non-matching-to-position performance in rats lesioned with the cholinergic immunotoxin 192 IgG-saporin

Galanin is a 29-amino-acid neuropeptide that is overexpressed in Alzheimer's disease (AD) and impairs performance on rodent learning and memory tasks. M40, a peptidergic galanin receptor ligand, blocks galanin-induced impairments on delayed non-matching-to-position (DNMTP). The present experiments used the 192IgG-saporin lesion model of AD to evaluate the actions of galanin and M40 on DNMTP when cholinergic transmission was reduced. Hippocampal choline acetyltransferase levels were correlated with DNMTP choice accuracy in lesioned rats. Intracerebroventricular (icv) galanin reduced choice accuracy in both the lesioned and sham groups. M40 alone, either icv or intrahippocampal, did not affect choice accuracy in either group. These results suggest that excess galanin can produce further deficits in DNMTP performance in a lesion model of AD, but blocking endogenous galanin is not sufficient alone to improve performance in lesioned rats.

Analysis of galanin and the galanin antagonist M40 on delayed non-matching-to-position performance in rats lesioned with the cholinergic immunotoxin 192 IgG-saporin

Galanin is a 29-amino-acid neuropeptide that is overexpressed in Alzheimer's disease (AD) and impairs performance on rodent learning and memory tasks. M40, a peptidergic galanin receptor ligand, blocks galanin-induced impairments on delayed non-matching-to-position (DNMTP). The present experiments used the 192IgG-saporin lesion model of AD to evaluate the actions of galanin and M40 on DNMTP when cholinergic transmission was reduced. Hippocampal choline acetyltransferase levels were correlated with DNMTP choice accuracy in lesioned rats. Intracerebroventricular (icv) galanin reduced choice accuracy in both the lesioned and sham groups. M40 alone, either icv or intrahippocampal, did not affect choice accuracy in either group. These results suggest that excess galanin can produce further deficits in DNMTP performance in a lesion model of AD, but blocking endogenous galanin is not sufficient alone to improve performance in lesioned rats.

The effects of selective cholinergic basal forebrain lesions and aging upon expectancy in the rat

The effects of selective cholinergic cell loss within the basal forebrain (BF) were determined using a task that requires shifting of attention between two visual stimuli. Discriminability between two stimuli and response bias were determined in young and old F-344 rats given BF injections of IgG-192 saporin (100 ng). The lesion reduced ChAT activity in the frontal and parietal cortices, hippocampus, and olfactory bulbs. The lesion did not significantly alter Na+/K(+)-ATPase activity in cortex, hippocampus, or olfactory bulbs, or endogenous levels of neuropeptide Y and neurokinin B within the BF. The BF lesions impaired both stimulus discriminability and response bias in young and old rats. The BF lesions had a significantly greater effect upon stimulus discriminability and response bias in aged rats, compared to young rats, only when the stimulus duration was very brief, i.e., when the task was most difficult to solve. At longer stimulus durations, aging and lesions showed no interaction. The results suggest that the selective loss of cholinergic cells in the BF, but not normal aging, impairs the ability to discriminate between independent sensory stimuli. The loss of these cells confers a response bias in simple operant tasks involving motor responses to reward-related visual stimuli.

Differential effects of selective immunotoxic lesions of medial septal cholinergic cells on spatial working and reference memory

The effect of injection into the medial septum of a toxin selective for cholinergic neurons, 192 IgG-saporin, was examined in rats trained to perform 2 versions of the radial 8-arm maze task. Rats were first trained to perform a task with varying delays (0, 1, 2 min) imposed between the 4th correct arm choice and access to all 8 arms. Lesioned rats made significantly more errors in the first 4 choices compared with controls and significantly more errors after delays; however, this effect was not delay dependent. Rats were then trained on a different version of this 8-arm maze task in which they learned to avoid 2 arms that were never baited. There was no treatment effect on acquisition of this task. These data are consistent with the hypothesis that the cholinergic projection to the hippocampus facilitates the acquisition of information into the system responsible for short-term memory for locations visited (spatial working memory) but is not involved in retention of this information. It also appears to play no role in either the acquisition or retention of place-nonreward associations (spatial reference memory).

Rett syndrome: neurobiological changes underlying specific symptoms

Rett syndrome (RS) is a progressive disorder that is predominant in females. It is associated with cortical atrophy, stereotyped hand movements mimicking hand-washing, severe mental deficiency, and cortical and extrapyramidal dysfunction. The cause of RS is unknown; no consistent genetic abnormalities, at either the cellular or mitochondrial levels, have been identified. The diagnosis still depends solely upon clinical evidence. The clinical progression of RS is consistent with an arrested neuronal development that may be due to either impaired cellular differentiation or the lack of appropriate trophic factors. Neuropathological studies have confirmed (1) a generalized brain atrophy involving the cerebrum and cerebellum; (2) a decrease in neuronal cell size and increased cell packing density throughout the brain; (3) a reduction in the number of basal forebrain cholinergic neurons; (4) a reduction in the concentration of melanin-containing neurons in the substantia nigra. Biochemical studies have identified (1) a decrease in cholinergic markers in the neocortex, hippocampus, thalamus and basal ganglia; (2) inconsistent and variable changes in biogenic amine biomarkers in post-mortem tissues and cerebrospinal fluid (CSF); (3) an elevation of beta-endorphin levels in the thalamus and glutamate levels in the CSF; (4) no evidence for mitochondrial dysfunction. These data suggest that there is a primary deficit in cholinergic function that might underlie some of the higher cognitive impairments and extrapyramidal dysfunction. Overall, the clinical, biochemical and neuropathological data suggest that RS is a neurodevelopmental disorder that has its greatest effects upon a limited number of neural systems during the first few years of postnatal life.

The nucleus basalis magnocellularis cholinergic system: one hundred years of progress

The nucleus basalis magnocellularis (NBM) contains a population of large cholinergic (Ch) neurons that send their axons to the entire cortical mantle, the olfactory bulbs, and the amygdala. This is the centennial anniversary of the first exact description of this nucleus by Von Kölliker, who named it in honor of its discoverer. This review will focus upon recent attempts to understand the role of the NBM Ch neurons in higher cognitive function by the use of selective lesion analyses and electrophysiological recording techniques. Behavioral deficits associated with NBM lesions produced by injections of excitatory amino acid agonists have been demonstrated in a variety of tasks. Performance decrements produced by these lesions were initially interpreted as being the result of impairments in learning and memory abilities. However, the precise role of the Ch NBM neurons in these performance deficits could not be more thoroughly investigated until it became possible to produce selective and discrete lesions by injection of the immunotoxin, IgG-192 saporin. The results of investigations using this immunotoxin supported a role for NBM Ch neurons in the performance of tasks that require selected attentional abilities rather than learning and memory per se. These lesion analysis studies suggested that the corticopetal NBM Ch system may be involved in the control of shifting attention to potentially relevant, and brief, sensory stimuli that predict a biologically relevant event, such as a food reward. Electrophysiological evidence has implicated NBM Ch cells in the control of attentional processes, as well as a role in the control and maintenance of arousal and sleep states. Electrophysiological studies also suggest that NBM Ch neurons might influence cortical EEG activity in two ways, by its direct excitatory inputs and by an indirect inhibitory projection to the thalamic reticular nucleus. Taken together with the results of histological and anatomical studies of the basal forebrain, NBM Ch cells appear to be ideally located within the basal forebrain for evaluating sensory stimuli for their level of significance, via inputs from the midbrain and limbic system, and also to modulate intrinsic cortical responsiveness appropriately in order to attend to brief, highly salient sensory stimuli.

Neuroprotection of acetylcholinergic basal forebrain neurons by memantine and neurokinin B

The present study investigated whether chronic, low dose therapy with memantine could (1) prevent the loss of basal forebrain cholinergic cells induced by injection of N-methyl-D-aspartate (NMDA) into the nucleus basalis magnocellularis (NBM) of rats, and (2) attenuate impaired performance in the radial maze of rats with entorhinal cortex lesions. In addition, we investigated whether neuroprotection could be provided by neurokinin B (NKB). Following an injection of NMDA (0.015 M) into the NBM, rats were implanted with osmotic minipumps containing memantine (20 or 0.20 mg/kg/day for 2 weeks). Other rats were given unilateral NBM injections of 1.0 microliter of Solution A (0.5 microliter containing 8.26 mM NKB and 0.24 units of bacitracin and 0.5 microliter containing 0.03 M NMDA) or Solution B (0.5 microliter of PBS containing 0.24 U of bacitracin and 0.5 microliter containing 0.03 M NMDA). Two weeks later, the anterior cortex was analyzed for choline acetyltransferase (ChAT), a specific marker for the loss of acetylcholinergic neurons. Both chronic administration of memantine, and acute administration of NKB, prevented the decline in cortical ChAT activity associated with injection of NMDA into the NBM, and attenuated a reference memory deficit in the radial maze produced by entorhinal cortex lesions. Thus, memantine infusion at low doses leading to steady-state serum levels within a therapeutic range provides both neuroprotection and cognitive enhancement-an optimal combination for the treatment of neurodegenerative disorders.

Differential effects of selective immunotoxic lesions of medial septal cholinergic cells on spatial working and reference memory

The effect of injection into the medial septum of a toxin selective for cholinergic neurons, 192 IgG-saporin, was examined in rats trained to perform 2 versions of the radial 8-arm maze task. Rats were first trained to perform a task with varying delays (0, 1, 2 min) imposed between the 4th correct arm choice and access to all 8 arms. Lesioned rats made significantly more errors in the first 4 choices compared with controls and significantly more errors after delays; however, this effect was not delay dependent. Rats were then trained on a different version of this 8-arm maze task in which they learned to avoid 2 arms that were never baited. There was no treatment effect on acquisition of this task. These data are consistent with the hypothesis that the cholinergic projection to the hippocampus facilitates the acquisition of information into the system responsible for short-term memory for locations visited (spatial working memory) but is not involved in retention of this information. It also appears to play no role in either the acquisition or retention of place-nonreward associations (spatial reference memory).

Rett syndrome: evidence for normal dopaminergic function

Rett syndrome (RS) is a neurological disorder associated with cortical atrophy, stereotyped hand movements, dementia, and extrapyramidal dysfunction. In a small number of RS patients, dopaminergic function has been reported to be decreased throughout the neocortex and basal ganglia. The present study investigated for changes in endogenous levels of dopamine, its metabolite homovanillic acid, dopamine reuptake sites and dopamine type-2 receptors in the brains of 12 RS patients (4-30 yrs) and 14 normal female controls (2.5-20 yrs). The levels of each biomarker did not differ significantly between RS and controls in any brain region examined. These data support the hypothesis that dopaminergic neuronal function may be relatively normal in RS.

Choline acetyltransferase activity and vesamicol binding in Rett syndrome and in rats with nucleus basalis lesions

The decline in choline acetyltransferase activity has been identified previously within the brains of patients with Rett syndrome and Alzheimer's disease. The level of [3H]vesamicol binding to a terminal vesicular acetylcholine transporter is inversely related to the decline in cortical choline acetyltransferase activity in Alzheimer's disease, which may be due to compensatory processes within surviving cholinergic terminals. In order to investigate whether similar cholinergic compensatory processes are present in the Rett syndrome brain and are altered by normal aging, we investigated the density of cholinergic vesicular transporters in (i) the brains of Rett syndrome patients, and (ii) young and old rats with experimentally-induced cholinergic cell loss. In Rett syndrome, a significant decline in choline acetyltransferase activity within the putamen and thalamus was directly correlated with a decline in [3H]vesamicol binding. In both young and old rats, basal forebrain lesions decreased cortical choline acetyltransferase activity significantly, while [3H]vesamicol binding was unchanged. In contrast to young and old lesioned rats and patients with Alzheimer's disease, cholinergic cells in the brains of patients with Rett syndrome do not compensate for the loss of cholinergic cells by increasing acetylcholine vesicular storage.

The effects of mitochondrial failure upon cholinergic toxicity in the nucleus basalis

Increased glutamate or acetylcholine receptor stimulation may interact with mitochondrial failure to increase the vulnerability of cholinergic neurons within the nucleus basalis. Understanding of the mechanisms that underlie this vulnerability may lead to a therapy to prevent the degeneration of these neurons in Alzheimer's disease. In the presence of a mitochondrial energy deficit, excess stimulation of N-methyl-D-aspartate (NMDA) receptors was not required for cytotoxicity. Furthermore, stimulation of cholinergic receptors was cytotoxic to cholinergic neurons but this toxicity was not enhanced by NMDA stimulation. Chronic administration of NMDA antagonists, such as memantine, amantadine or MK-801, attenuated the effects of mitochondrial failure in the presence or absence of excessive cholinergic or NMDA receptor stimulation.

Age-related decrease in vulnerability to excitatory amino acids in the nucleus basalis

The present study investigated the effects of nucleus basalis magnocellularis (NBM) lesions in young (3 months), adult (9 months), and aged (24 months) rats by injections of either NMDA or AMPA upon performance of a delayed alternation task on a T maze. During phase 1 of testing, the interchoice interval (ICI) was 5 s and each rat was given 10 trials per day during phase 2, the ICI was 30 s across 10 trials per day; during phase 3, the ICI was 5 s across 20 trials per day. Analyses of variance revealed (a) a significant effect of age during phase 1 (i.e., 24-month-old rats performed worse than 3-month-old rats); (b) a significant effect of age and lesion in phase 2 (i.e., the lesions impaired choice accuracy equally in all age groups when the ICIs were 30 s); (c) a significant effect of age and lesions, and a significant interaction in phase 3 (i.e., young rats were more impaired by the lesions than were aged rats.

Neuroprotection and selective vulnerability of neurons within the nucleus basalis magnocellularis

Neurons within the nucleus basalis may die due to their selective vulnerability to endogenous excitatory amino acid neurotransmitters, nitric oxide and free radicals. The factors influencing the selective vulnerability of neurons within the nucleus basalis depend upon many different factors related to the presence of these agents and the neuron's ability to defend itself against the consequences of exposure. Many different mechanisms have been investigated to provide neuroprotection for neurons within the nucleus basalis and throughout the central nervous system. This review summarizes the results of studies that have investigated our current capability to either attenuate the neurotoxicity of endogenous excitatory amino acids, such as glutamate, or to provide effective neuroprotection during circumstances of neurotoxin exposure.

MK-801, memantine and amantadine show neuroprotective activity in the nucleus basalis magnocellularis

The activation of glutamate receptors by endogenuous glutamate has been implicated in the processes that underlie cell loss associated with ischemia and trauma and in the development of some neurodegenerative diseases. The antagonism of NMDA-sensitive glutamate receptors may therefore have therapeutic applications. The present study compared the side effects and neuroprotective potency of 1-aminoadamantane hydrochloride (amantadine), 1-amino-3,5-dimethyladamantane hydrochloride (memantine), and (+)-5-methyl-10,11-dihydro-5H-debenzocyclhepten-5,10-imine maleate ((+)-MK-801) against NMDA injected directly into the nucleus basalis magnocellularis of rats. Each drug significantly attenuated the loss of nucleus basalis magnocellularis cholinergic cells. The ED50s were respectively 0.077, 2.81 and 43.5 mg/kg for (+)-MK-801, memantine and amantadine, giving a relative potency ratio of 1:36:565. The ratio of the ED50 for the side effects observed, including ataxia, myorelaxation and stereotypy, and the ED50 for neuroprotective ability, was highest for memantine and the lowest for (+)-MK-801. The results suggest that a potential neuroprotective action of NMDA receptor antagonists, memantine and amantadine in particular, can be seen at low doses lacking side effects.

Effects of excitatory amino acid lesions upon neurokinin B and acetylcholine neurons in the nucleus basalis of the rat

The nucleus basalis magnocellularis (NBM) contains cholinergic neurons that project to the neocortex and is densely innervated by excitatory amino acid-containing terminals. A dysfunction in the balance of excitatory inputs or an alteration in the sensitivity of NBM cells to glutamate may underlie the selective vulnerability to aging. Some large NBM neurons contain neurokinin B (NKB) mRNA. The present study investigated whether alpha-2-amino-3-hydroxy-5-methyl-isoxazole-4-propionic acid (AMPA) or N-methyl-D-aspartate (NMDA) differentially destroy NKB-containing, NKB-receptive, or cholinergic NBM cells, and whether this vulnerability is altered by aging. Injections of AMPA or NMDA significantly decreased neocortical ChAT activity, as compared to control levels, across all three age groups, with no interaction between lesion and age group. The results of in situ hybridization histochemistry and NKB receptor studies suggest that NKB-containing neurons in the NBM, and the neurons they innervate, are not vulnerable to NMDA or AMPA in either young or old rats. While NKB mRNA-positive cells were diffusely distributed throughout the basal forebrain, only a small proportion of the large NBM cells contained NKB mRNA. The results suggest that NKB does not extensively colocalize with acetylcholine within the basal forebrain of rats and that NBM NKB neurons do not directly innervate cholinergic cells.

Alterations in dopaminergic function in Rett syndrome

Rett syndrome is a neurological disorder associated with cortical atrophy, stereotyped hand movements, dementia, and extrapyramidal dysfunction. Endogenous levels of dopamine and its metabolites are decreased throughout the neocortex and basal ganglia and the number of dopamine type 2 receptors are decreased in the putamen. The present study investigated changes in dopamine uptake sites and dopamine type-1 receptors in the brains of eleven Rett syndrome patients (4-30 yrs) and ten normal female controls (2.5-20 yrs). The number of dopamine type 1 receptors within the caudate nucleus were unchanged. The density of dopamine reuptake sites were unchanged in the cingulate and midfrontal gyri but decreased within the caudate nucleus and putamen. The results of the present study suggest that: 1) in the basal ganglia of Rett syndrome patients, dopamine receptive neurons are intact whereas the number and activity of dopamine terminals are decreased, and 2) in the midfrontal and cingulate cortex, dopaminergic neuronal activity may be increased in order to compensate for fewer terminals that contain less dopamine.

Behavioral, biochemical, histological, and electrophysiological effects of 192 IgG-saporin injections into the basal forebrain of rats

The behavioral, biochemical, histological, and electrophysiological effects of a basal forebrain injection of saporin, a ribosome-inactivating protein, coupled to a monoclonal antibody against the low-affinity NGF receptor (192 IgG) were investigated in adult rats. Within the basal forebrain region, the low-affinity NGF receptor is exclusively expressed by cholinergic neurons in the medial septal area, diagonal band, and nucleus basalis magnocellularis (NBM). The presence of this receptor upon these cells confers a degree of specificity to the 192 IgG-saporin that could not previously be achieved by previous lesioning techniques, such as excitatory amino acids. Rats with unilateral injections of different amounts of 192 IgG-saporin were prepared to determine the optimal conditions in order to produce a lesion restricted to the NBM that would not destroy cholinergic afferents to hippocampus or nearby regions. Electroencephalographic (EEG) recordings were taken from these lesioned rats before and during treatment with scopolamine (1 mg/kg, i.p.). Another group of rats received bilateral NBM injections of 192 IgG-saporin and were behaviorally tested using a rewarded, delayed-alternation task on a T-maze and a passive avoidance task. Finally, histological and biochemical investigations confirmed the effectiveness and specificity of the 192 IgG-saporin. The results showed that the 192 IgG-saporin did not destroy neurotensin, galanin, somatostatin, NADPH-diaphorase, or neuropeptide Y neurons within the NBM. Also, biomarkers of cholinergic function were significantly decreased throughout the neocortex and within the NBM, but not in the olfactory bulbs, hippocampus, or dorsal caudate nucleus. Intraperitoneal injections of scopolamine, but not NBM injections of 192 IgG-saporin, increased total power across all frequency bands; however, slow-wave frequencies showed a greater increase in power as compared to fast-wave frequencies. Acquisition, and performance of the delayed-alternation or passive avoidance tasks were not impaired by the lesions. These data confirm the effectiveness and specificity of this novel lesioning tool and suggest that selective loss of NBM cholinergic cells is not sufficient to impair performance in these behavioral tasks.