Amyloid plaques, neurofibrillary tangles and neuronal loss in brains of transgenic mice overexpressing a C-terminal fragment of human amyloid precursor protein

Alzheimer's disease (AD) affects more than 30% of people over 80 years of age. The aetiology and pathogenesis of this progressive dementia is poorly understood, but symptomatic disease is associated histopathologically with amyloid plaques, neurofibrillary tangles and neuronal loss primarily in the temporal lobe and neocortex of the brain. The core of the extracellular plaque is a derivative of the amyloid precursor protein (APP), referred to as beta/A4, and contains the amino-acid residues 29-42 that are normally embedded in the membrane-spanning region of the precursor. The cellular source of APP and the relationship of its deposition to the neuropathology of AD is unknown. To investigate the relationship between APP overexpression and amyloidogenesis, we have developed a vector to drive expression specifically in neurons of a C-terminal fragment of APP that contains the beta/A4 region, and have used a transgenic mouse system to insert and express this construct. We report here that overexpression of this APP transgene in neurons is sufficient to produce extracellular dense-core amyloid plaques, neurofibrillary tangles and neuronal degeneration similar to that in the AD brain.

Opportunities for treatment of psychoactive substance use disorders with serotonergic medications

The authors review both the preclinical and the clinical evidence for a role of serotonin (5-HT) systems in the regulation of drug-taking behavior. Animal studies show that pharmacologic treatments that enhance 5-HT function, notably selective reuptake inhibitors, reduce the self-administration of a variety of substances of abuse, including ethanol and cocaine. These treatments also tend to suppress consummatory behavior in general. In contrast to the broad spectrum of suppression following 5-HT enhancement, selective antagonists at the 5-HT3 receptor subtype have been reported to reduce ethanol but not cocaine or food intake. Although essentially limited to alcohol abusers, clinical studies seem to support the preclinical findings that a number of 5-HT reuptake inhibitors decrease interest in and intake of alcohol in mild-moderate ethanol-dependent individuals. Furthermore, other serotonergic drugs may show utility in the treatment of alcohol abuse. Another way in which serotonergic medications can be used in treating substance abuse is by the treatment of comorbid psychoactive illness for which such drugs are already known to be effective, e.g., depression and anxiety disorders.

Differential regulation of the low-affinity nerve growth factor receptor during postnatal development of the rat brain

We studied the temporal and spatial localization of the low-affinity nerve growth factor receptor (LNGF-R) during the early postnatal period in rat brain in order to understand better the relationship between nerve growth factor (NGF)-like responsiveness and the development of specific central neuronal populations. Four different developmental patterns of LNGF-R mRNA hybridization were found in this study. First, some neurons contain high levels of LNGF-R mRNA from postnatal time points into adulthood, as exemplified by neurons of the cholinergic basal forebrain and mesencephalic trigeminal nucleus. Second, several cell groups exhibit robust hybridization during the early postnatal period but contain much reduced levels of LNGF-R mRNA in the adult brain. These include striatal neurons, Purkinje cells of the cerebellum, and several medullary nuclei. A third group of cells produces the LNGF-R transiently during development, including cranial nerve nuclei of the brainstem, the periolivary nuclei complex, the reticular formation, and the deep cerebellar nuclei. Finally, cell populations which may exist only transiently during central nervous system (CNS) development, such as subplate neurons of the cerebral cortex, appear to express the LNGF-R during only a brief period. These results show that the LNGF-R gene is differentially regulated in a cell type-specific manner during development, and suggests that diverse neuronal populations require only transient growth factor sensitivity, while others exhibit NGF-like responsitivity into maturity.

Nerve growth factor receptor immunoreactivity in the new world monkey (Cebus apella) and human cerebellum

The present study used the NGFR-5 monoclonal antibody raised against human nerve growth factor receptor (NGFR) to determine the extent of NGFR immunoreactivity within the embryonic and young adult Cebus apella cerebellum as well as the human cerebellum. Immunohistochemically processed tissue revealed NGFR expressing Purkinje cell somata, axons, and dendrites, the latter being observed within the molecular layer of both adult species. Within all regions of the cerebellum we observed both darkly and lightly immunostained Purkinje cells. The proximal axons of these cells, which were visualized for short distances within the granular cell layer, appeared to contain bulbous aggregates of reaction product. In sagittal sections, the full extent of the Purkinje cell dendritic tree was observed in the more lightly stained portions of the cerebellum. In situ hybridization experiments revealed NGFR mRNA within Purkinje cells in a pattern similar to that seen with immunohistochemistry. The distribution of NGFR immunoreactivity within the cerebellum exhibits a general topographic organization with the heaviest and most consistent staining occurring within the archi- and neocerebellum and weaker staining within the paleocerebellum. In fetal Cebus monkey cerebellum obtained at gestational day 50 and 70, NGFR immunoreactivity was observed as a band composed of developing Purkinje cell neurites. These profiles were seen in the paleo- and neocerebellum, but not the archicerebellum. The present investigation is the first demonstration of NGFR immunoreactive profiles in the adult monkey and human cerebellum. These findings suggest that nerve growth factor may influence locomotor and vestibular behaviors that are mediated by cerebellar circuity. The precise mode of action for the NGF/NGFR system within the cerebellum remains to be determined.

Increased abundance of alternatively spliced forms of D2 dopamine receptor mRNA after denervation

The existence of two molecular forms of D2 dopamine receptors suggests that differences in the distribution or regulation of the two forms could be exploited for the pharmacological treatment of disease. Using probes selective for each alternatively spliced variant of D2 receptor mRNA, we determined that both variants were widely distributed in rat brain and pituitary but that the ratio of the forms varied among regions. mRNA for the 444-amino acid-long variant, D2(444), was the most abundant form in pituitary and neostriatum. Intermediate levels of both D2(444) mRNA and the short form, D2(415), were detected in midbrain, and low levels of D2(444) and D2(415) mRNAs were detected in all other regions examined, including hippocampus, cerebellum, and cortex. The D2(444)/D2(415) ratio was generally lower in the regions of low expression than in pituitary and neostriatum. Dopamine-depleting lesions increased the density of D2 receptors in the denervated neostriatum by 29% without altering the affinity of the receptors for [3H]spiperone. The proliferation of receptors appeared to be due to a lesion-induced increase of up to 120% in the abundance of both variants of mRNA in the neostriatum.

Survival and function of intrastriatally grafted primary fibroblasts genetically modified to produce L-dopa

A combination of gene transfer and intracerebral grafting may provide a powerful technique for examining the role of discrete substances in the development or functioning of the brain. In the present study, primary fibroblasts obtained from a skin biopsy from inbred Fischer rats were used as donor cells for genetic modification and grafting. When grafted to the striatum of Fischer rats with a prior 6-hydroxydopamine lesion, primary fibroblasts containing a transgene for either tyrosine hydroxylase (TH) or beta-galactosidase survived for 10 weeks and continued to express the transgene. TH synthesized by the implanted fibroblasts appeared to convert tyrosine to L-dopa actively, as observed in vitro, and to affect the host brain, as assessed through a behavioral measurement. These results suggest that primary fibroblasts genetically altered to express TH have the capacity to deliver L-dopa locally to the striatum in quantities sufficient to compensate partially for the loss of intrinsic striatal dopaminergic input.

Differential behavioural activation following intra-raphe infusion of 5-HT1A receptor agonists

Microinfusion of the selective 5-HT1A receptor agonist, 8-hydroxy-(di-N-propylamino)tetralin (8-OHDPAT), into the dorsal raphe nucleus (DRN) produced a marked behavioural hypoactivity and flat body posture. Injections of similar doses into the median raphe nucleus (MRN) elicited hyperactivity but no postural change. Reductions in rearing and grooming were also observed after DRN and MRN infusions of 8-OHDPAT. The behavioural profiles of other 5-HT1A selective compounds, gepirone and BMY7378 were found to be similar to 8-OHDPAT. The contrasting behavioural profiles of the 5-HT1A agents observed after DRN or MRN microinfusions are probably related to the differential innervation of forebrain structures by each raphe nucleus. Thus, the present data confirms and extends previous results illustrating the influence of 5-HT systems on motor behaviour in the rat and identifies unique behavioural profiles following activation of the DRN and MRN.

Evidence that the unilateral activation of 5-HT1D receptors in the substantia nigra of the guinea-pig elicits contralateral rotation

1. The effects of various 5-hydroxytryptamine (5-HT) receptor agonists were examined following unilateral infusion into the substantia nigra (SN) of the guinea-pig. 2. The 5-HT1 receptor agonists, 5-carboxamidotryptamine (5-CT) (2-25 micrograms), sumatriptan (10-25 micrograms) and RU24969 (25 micrograms) all induced a marked contralateral rotation. In contrast, the selective 5-HT1A receptor agonist 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH DPAT, 10-25 micrograms) produced only a very small response, whilst the selective 5-HT1C/5-HT2 receptor agonist (+-)-1-(4-iodo-2,5-dimethoxyphenyl)-2-aminopropane hydrochloride ((+/-)-DOI) (25 micrograms) and the 5-HT3 receptor agonist, 2-methyl 5-HT (2-Me5-HT, 25 micrograms) were without effect. 3. The contralateral rotation induced by 5-CT (10 micrograms) was attenuated following pretreatment with the non-selective 5-HT1/5-HT2 receptor antagonists methiothepin (1 mg kg-1, s.c.) and metergoline (5-10 mg kg-1, s.c.) but not the 5-HT1C/5-HT2 antagonist ritanserin (1 mg kg-1, s.c.) or the 5-HT3 antagonist, ondansetron (0.5 mg kg-1, s.c.). An involvement of dopaminergic systems in the rotational response to 5-CT was implied by the antagonism of 5-CT-induced rotation by haloperidol (0.3 mg kg-1, s.c.). 4. At doses lower than those required to produce contralateral rotation, 5-CT (0.08-0.4 micrograms) and sumatriptan (2 micrograms) induced a small, but nonetheless consistent, ipsilateral rotation. 5. The data with agonists and antagonists taken together suggest that 5-CT-induced contralateral rotation may be mediated by 5-HTID receptor activation but definitive classification of the receptor will not be possible until selective 5-HTID-antagonists become available. This may therefore represent the first model to study this receptor subtype in vivo.

Effects of 5-HT3 receptor antagonists on behavioural measures of naloxone-precipitated opioid withdrawal

The effect of the selective 5-HT3 receptor antagonists, ondansetron and MDL 72,222, against various behaviours elicited by naloxone-precipitated morphine withdrawal were examined. Rats made dependent upon morphine by the subcutaneous implantation of a 75 mg pellet, when challenged with naloxone (0.5 mg/kg SC), 3 or 4 days later exhibited a wide range of behaviours including wet dog shakes, paw shakes, salivation and a marked weight loss. Pre-treatment with ondansetron (0.01-1 mg/kg SC) or MDL 72,222 (1-3 mg/kg SC) failed to affect the incidence of these responses except weight loss, which was attenuated by both treatments. At doses similar to and below those required to elicit the withdrawal syndrome, naloxone produced a single-trial place aversion in morphine dependent rats. The place aversion produced by naloxone (0.05 mg/kg SC) was antagonized by pre-treatment of ondansetron (0.1-1 mg/kg SC) and MDL 72,222 (1 mg/kg SC) prior to conditioning. Chlordiazepoxide (10 mg/kg IP) but not gepirone (3-10 mg/kg SC) was similarly effective. It is concluded that 5-HT3 antagonists may attenuate some but not all behavioural signs associated with morphine withdrawal. Reasons for this apparent selectivity are discussed.

Induction of interleukin-1 beta mRNA in adult rat brain

The ability of the central nervous system to produce the cytokine interleukin-1 beta (IL-1 beta) in response to challenge by activators of the mononuclear phagocyte system has been examined in vivo. Unilateral injection of a mixture of gamma-interferon (IFN-gamma) and lipopolysaccharide (LPS) into the forebrain of adult rats induced expression of IL-1 beta mRNA. In situ hybridization of IL-1 beta mRNA showed a gradient of cellular hybridization, which was most intense at the site of IFN-gamma/LPS injection. The reverse transcription--polymerase chain reaction (RT-PCR) was used to demonstrate the presence of IL-1 beta mRNA in normal rat brain, and to confirm increases in IL-1 beta mRNA levels following IFN-gamma/LPS injection. These studies show that IL-1 beta can be induced to high levels within the CNS as a consequence of exposure to potent stimulators of macrophage activation.

Evidence that the amygdala is involved in the disinhibitory effects of 5-HT3 receptor antagonists

The effects of various 5-HT3 receptor antagonists were examined in the social interaction (SI) test following discrete microinjection into either the dorsal raphe nucleus (DRN) or amygdala of the rat. Following DRN injection, ondansetron, ICS205-930, and MDL72222 (5-500 ng) all failed to modify SI under high light/unfamiliar (HLU) test conditions relative to vehicle pretreated controls. The 5-HT3 receptor agonist, 2-Me 5-HT (100-2500 ng), was similarly ineffective under both HLU and low light/familiar (LLF) conditions, although 5-HT (20-100 ng) increased SI under the HLU paradigm. After amygdaloid injection, ondansetron (10-100 ng), granisetron (1-10 ng), ICS205-930 (10-100 ng), GR 65630 (1-10 ng), and MDL72222 (100-1000 ng) all significantly increased SI under the HLU but not LLF condition. Furthermore, a detailed behavioural analysis revealed that the behaviours underlying this increase were similar to those seen in vehicle pretreated animals tested in the LLF compared to HLU condition. The benzodiazepine, flurazepam (200 ng), increased both SI (HLU condition) and punished responding in a modified water-lick conflict model, after amygdaloid injection. Both ondansetron (10-1000 ng) and ICS205-930 (1-100 ng) were ineffective in the conflict test. Finally, 2-Me 5-HT and 5-HT (100-10,000 ng) reduced SI under the LLF test condition with no concomitant change in locomotor activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Behavioural effects of serotonin agonists and antagonists in the rat and marmoset

The present study was conducted to investigate the effects of various 5-hydroxytryptamine (5-HT) agonists and antagonists on motor behaviour in rats and marmosets. Various motor-based responses were assessed after central or peripheral administration of 5-HT agents to rats and marmosets. Drugs acting as agonists at the 5-HT1A receptor (8-OHDPAT, gepirone, BMY-7378, NAN-190, PAPP (LY165163) and flesinoxan) and 5-HT2/1C receptors (DOI) were found to reverse neuroleptic-induced catalepsy in the rat whereas 5-HT2/1C antagonists (mianserin, ritanserin and ICI-170,809) and the 5-HT1 antagonist ((+/-)pindolol) increased catalepsy. Agonists acting at 5-HT3 receptors (phenylbiguanide and 2-methyl-5-HT) had no effect on catalepsy. The putative 5-HT1A antagonist, (+/-) pindolol, attenuated the reversal of catalepsy by 8-OHDPAT. Although both 8-OHDPAT and BMY-7378 were tested, only the latter was found to reduce apomorphine-induced stereotypy. Bilateral or unilateral infusions of 8-OHDPAT, BMY-7378 or pindolol into the substantia nigra of non-lesioned rats had no effect on spontaneous locomotor or rotational activity, respectively. However, 8-OHDPAT and BMY-7378 were found to increase or decrease motor activity, after injection into the median or dorsal raphe nuclei, respectively. Finally, 8-OHDPAT and BMY-7378 were found to be inactive against MPTP-induced bradykinesia in the marmoset. It is concluded that both 5-HT1A and 5-HT2/1C receptors are involved in the anti-cataleptic effects of 5-HT agents. The 5-HT1A receptors are probably situated within the raphe, whereas the location of the 5-HT2/1C receptors remains undetermined.

The Alzheimer amyloid precursor-related transcript lacking the beta/A4 sequence is specifically increased in Alzheimer's disease brain

The deposition of cerebrovascular and plaque amyloid in the CNS is a primary feature of Alzheimer's disease and aged Down's syndrome pathology. The localization of the Alzheimer amyloid protein precursor (APP) gene on chromosome 21, along with its overexpression in Down's syndrome brain compared with normal brain, suggests that alterations in APP gene expression may play a role in the development of the neuropathology common to the two diseases. In the present report, we demonstrate that a specific spliced form of mRNA that is transcribed from the APP gene and that lacks the beta/A4 sequence is elevated in the nucleus basalis, occipitotemporal cortex, and parahippocampal gyrus in Alzheimer's disease brain relative to controls. These results are based on combined data from RNA slot blot analysis, in situ hybridization, and polymerase chain reaction quantification of specific mRNAs taken directly from tissue sections.

Cardiovascular effects of 5-HT1A receptor agonists injected into the dorsal raphe nucleus of conscious rats

The aim of this study was to investigate the cardiovascular effects of the 5-HT1A receptor agonists, 8-OH-DPAT (8-hydroxy-2-(di-n-propylamino)tetralin), flesinoxan and 5-carboxamidotryptamine (5-CT) following injection into the dorsal raphe nucleus of conscious rats. 8-OH-DPAT (0.5-2.5 micrograms), hypotension, bradycardia and flat body posture. In contrast, injection of 8-OH-DPAT (0.5 microgram) into the median raphe nucleus caused no cardiovascular changes or flat body posture. (-)Pindolol (0.5 microgram dorsal raphe nucleus) had little effect on cardiovascular parameters, but significantly attenuated the cardiovascular effects of 8-OH-DPAT (0.5 microgram dorsal raphe nucleus). N-Methylatropine (1 mg/kg i.v.) antagonised the cardiovascular effects of 8-OH-DPAT (0.5 microgram dorsal raphe nucleus), suggesting these were vagally mediated. Both pretreatments also appeared to reduce 8-OH-DPAT-induced flat body posture. The results suggest that 8-OH-DPAT activates 5-HT1A receptors in the dorsal raphe nucleus to cause hypotension and bradycardia.

Altered levels of amyloid protein precursor transcripts in the basal forebrain of behaviorally impaired aged rats

The beta/A4 protein is a constituent of plaque and vascular amyloid deposits in Alzheimer disease. Previous studies have shown increased levels of amyloid protein precursor (APP) mRNA in basal forebrain neurons in the disease. Morphological and neurochemical changes occur within the forebrain in Alzheimer disease and are also correlated with behavioral impairments in aged rats. Recent studies suggest that decreased nerve growth factor responsiveness of basal forebrain neurons is a feature of normal aging and of Alzheimer disease. We have used in situ hybridization to show that the abundance of specific forms of APP mRNA, which contain an inserted Kunitz-type serine protease inhibitor motif (APP-751, APP-770, and APP-related 563), are increased relative to the noninserted form (APP-695) of APP mRNA in the basal forebrain of aged rats. This increase appears to be specific to animals who exhibit spatial memory deficits but not aged rats without behavioral impairments.

NGF receptor gene expression is decreased in the nucleus basalis in Alzheimer's disease

Basal forebrain neuronal atrophy in Alzheimer's disease (AD) may be caused by a deficit in the NGF responsiveness of magnocellular cholinergic neurons which project to the cerebral cortex and hippocampal formation. We have used in situ hybridization to show that NGF-receptor (NGF-R) mRNA-positive neurons are lost within all divisions of the nucleus basalis of Meynert (Ch4 cell group) in AD patients as compared to normal aged controls. The posterior division of the nucleus basalis showed the largest decrease in NGF-R mRNA hybridization in the disease, with no overlap in neuronal number between AD cases and normal controls. Northern (RNA) blotting showed decreased levels of NGF-R mRNA in the nucleus basalis in the disease. No differences in the number of NGF-R mRNA-positive neurons between normal aged and AD patients were detected within the NGF-responsive cell groups of the medial septum (Ch1) and nucleus of the vertical limb of the diagonal band (Ch2). These results show that NGF-R gene expression is selectively reduced within basal forebrain neuronal populations which exhibit degenerative changes in AD.

Localization of nerve growth factor receptor messenger RNA and protein in the adult rat brain

We have used in situ hybridization and immunocytochemistry to map the cellular localization of NGF receptor (NGF-R) mRNA and protein in the adult rat brain. In addition to basal forebrain magnocellular neurons, NGF-R is widely expressed within the CNS, including neurons of the caudate/putamen, ventral premamillary nucleus, mesencephalic trigeminal nucleus, prepositus hypoglossal nucleus, raphe nucleus, nucleus ambiguous, and Purkinje cells of the cerebellum. Cells of the vestibulocochlear ganglion also contain NGF-R mRNA and protein. Ventricular subependymal cells and tanycytes are clearly stained by immunocytochemistry, yet only very weak hybridization is detectable in these cells. Also, greater amounts of NGF-R protein than of mRNA appear to be present in the glomeruli of the olfactory bulb, area postrema, and nucleus tractus solitarius. Areas that contain only NGF-R immunoreactive fibers and terminals can be distinguished from the cellular sites of NGF-R biosynthesis and include the suprachiasmatic nucleus, the principal olivary pretectal nucleus, the superior colliculus, the inferior olive, and the principal and spinal trigeminal nuclei. This study shows that NGF-R is widely expressed within individual neurons in different areas of the rat brain and identifies new potential CNS target sites of endogenous NGF.

The identification of a novel synaptosomal-associated protein, SNAP-25, differentially expressed by neuronal subpopulations

cDNA clones of a neuronal-specific mRNA encoding a novel 25-kD synaptosomal protein, SNAP-25, that is widely, but differentially expressed by diverse neuronal subpopulations of the mammalian nervous system have been isolated and characterized. The sequence of the SNAP-25 cDNA revealed a single open reading frame that encodes a primary translation product of 206 amino acids. Antisera elicited against a 12-amino acid peptide, corresponding to the carboxy-terminal residues of the predicted polypeptide sequence, recognized a single 25-kD protein that is associated with synaptosomal fractions of hippocampal preparations. The SNAP-25 polypeptide remains associated with synaptosomal membrane components after hypoosmotic lysis and is released by nonionic detergent but not high salt extraction. Although the SNAP-25 polypeptide lacks a hydrophobic stretch of residues compatible with a transmembrane region, the amino terminus may form an amphiphilic helix that may facilitate alignment with membranes. The predicted amino acid sequence also includes a cluster of four closely spaced cysteine residues, similar to the metal binding domains of some metalloproteins, suggesting that the SNAP-25 polypeptide may have the potential to coordinately bind metal ions. Consistent with the protein fractionation, light and electron microscopic immunocytochemistry indicated that SNAP-25 is located within the presynaptic terminals of hippocampal mossy fibers and the inner molecular layer of the dentate gyrus. The mRNA was found to be enriched within neurons of the neocortex, hippocampus, piriform cortex, anterior thalamic nuclei, pontine nuclei, and granule cells of the cerebellum. The distribution of the SNAP-25 mRNA and the association of the protein with presynaptic elements suggest that SNAP-25 may play an important role in the synaptic function of specific neuronal systems.