Colchicine lesions in the rat hippocampus mimic the alterations of several markers in Alzheimer's disease

Spontaneous and familial models of Alzheimer's disease: Challenges and advances in preclinical research

Alzheimer's disease (AD) is a debilitating neurodegenerative disorder that is progressive and irreversible in nature. Even after decades of dedicated research and paradigm-shifting hypotheses of AD etiology, very few well-founded credible improvements have been foreseen in understanding the actual underlying mechanisms involved in the development of the disorder. As for any disease to be well-comprehended, AD also requires optimal modelling strategies, which will then pave way for effective therapeutic interventions. Most of the clinical trials and research towards better treatment of AD fail in translation, due to the inefficacy of explored animal models to mimic the actual AD pathology, precisely. The majority of the existing AD models are developed based on the mutations found in the familial form of AD (fAD) which accounts for less than 5 % of the incidence of AD. Further, the investigations also face more challenges due to the additional complexities and lacunae found in etiology of sporadic form of AD (sAD), which accounts for 95 % of total AD. This review illustrates the gaps found in different models of AD, both sporadic and familial variants with additional focus on recent avenues for accurate simulation of AD pathology using in vitro and chimeric AD models.

Rodent Model Preclinical Assessment of PEGylated Block Copolymer Targeting Cognition and Oxidative Stress Insults of Alzheimer's Disease

Misfolded peptide amyloid beta (Aβ₄₂), neurofibrillary tangles of hyper-phosphorylated tau, oxidative damage to the brain, and neuroinflammation are distinguished determinants of Alzheimer's disease (AD) responsible for disease progression. This multifaceted neurodegenerative disease is challenging to cure under a single treatment regime until the key disease determinants are traced for their sequential occurrence in disease progression. In an early report, a novel side-chain tripeptide containing PEGylated block copolymer has been tested thoroughly in vitro and in silico for the early inhibition of Aβ₄₂ aggregation as well as degradation of preformed Aβ₄₂ fibril deposits. The present study demonstrates a preclinical assessment of the PEGylated block copolymer in colchicine-induced AD-mimicking rodent model. The colchicine-induced Wistar rats receiving an intranasal delivery of the block copolymer at a daily dosage of 100 µg/kg and 200 µg/kg body weights, respectively, for 14 days manifested a notable attenuation of behavioral deficit pattern, oxidative stress, and neurotransmitters' deficiency as compared to the untreated ones. The current study also reports the ameliorative property of the PEGylated compound for progressive neuroinflammation and decreased mitochondrial bioenergetics in astrocytoma cell line, viz., U87. A closer look into the drug mechanism of action of a compact 3D PEGylated block copolymer confirmed its disintegrative interaction with Aβ₄₂ fibril via in silico simulation. The results obtained from this study signify the potential of the novel PEGylated block copolymer to ameliorate the cognitive decline and progressive oxidative insults in AD and may envision a successful clinical phase trial. The amelioration of disease condition of colchicine-induced AD rat. Initially the rat has given colchicine via stereotaxic surgery which led to a mimicking condition of AD including neuronal death in hippocampal CA1 region. After recovery from the surgery, the rat was treated with the PEGylated block copolymer through intranasal delivery, and this has led to the decrease in neuronal death in hippocampal CA1 region. The mechanism of drug action has shown by the separation of monomer chains of Aβ₄₂.

Thymol in Trachyspermum ammi seed extract exhibits neuroprotection, learning, and memory enhancement in scopolamine-induced Alzheimer's disease mouse model

Several reports have stated the neuroprotective and learning/memory effects of Tachyspermum ammi seed extract (TASE) and its principal component thymol; however, little is known about its underlying molecular mechanisms and neurogenesis potential. This study aimed to provide insights into TASE and a thymol-mediated multifactorial therapeutic approach in a scopolamine-induced Alzheimer's disease (AD) mouse model. TASE and thymol supplementation significantly reduced oxidative stress markers such as brain glutathione, hydrogen peroxide, and malondialdehyde in mouse whole brain homogenates. Tumor necrosis factor-alpha was significantly downregulated, whereas the elevation of brain-derived neurotrophic factor and phospho-glycogen synthase kinase-3 beta (serine 9) enhanced learning and memory in the TASE- and thymol-treated groups. A significant reduction in the accumulation of Aβ 1-42 peptides was observed in the brains of TASE- and thymol-treated mice. Furthermore, TASE and thymol significantly promoted adult neurogenesis, with increased doublecortin positive neurons in the subgranular and polymorphic zones of the dentate gyrus in treated-mice. Collectively, TASE and thymol could  potentially act as natural therapeutic agents for the treatment of  neurodegenerative disorders, such as  AD.

Rodent model preclinical assessment of PEGylated block copolymer targeting cognition and oxidative stress insults of Alzheimer’s disease.. [DOI: 10.21203/rs.3.rs-1907312/v1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

Misfolded peptide amyloid beta (Aβ42), neurofibrillary tangles of hyper-phosphorylated tau, oxidative damage to the brain, neuroinflammation are distinguished determinants of Alzheimer’s disease (AD) responsible for disease progression. This multifaceted neurodegenerative disease is challenging to cure under a single treatment regime until the key disease-determinants are traced for their sequential occurrence in disease progression. In an early report, a novel side-chain tripeptide containing PEGylated block copolymer has been tested thoroughly in vitro and in silico for the early inhibition of Aβ42-aggregation as well as degradation of preformed Aβ42-fibril deposits. The present study demonstrates a preclinical assessment of the PEGylated block copolymer in colchicine-induced AD mimicking rodent model. The colchicine induced Wistar rats receiving an intranasal delivery of the block copolymer at a daily dosage of 100 µg/kg and 200 µg/kg body weights respectively for 14 days manifested a notable attenuation of behavioral deficit pattern, oxidative stress, and neurotransmitters’ deficiency as compared to the untreated ones. The current study also reports the ameliorative property of the PEGylated compound for progressive neuroinflammation and decreased mitochondrial bioenergetics in astrocytoma cell line viz. U87. A closer look into the drug mechanism of action of a compact three-dimensional PEGylated block copolymer confirmed its disintegrative interaction with Aβ42 fibril via in silico simulation. The results obtained herein this study signify the potential of the novel PEGylated block copolymer to ameliorate the cognitive decline and progressive oxidative insults in AD, and may envision a successful clinical phase trial.

Bacopa monnieri prevents colchicine-induced dementia by anti-inflammatory action

Inflammation is considered as an early event in the development of Alzheimer's disease (AD) that precedes the formation of Aβ plaques and neurofibrillary tangles. Therefore, strategies aimed at attenuating inflammation by phytochemicals may be a potential therapeutic intervention against AD. The present study was designed to evaluate if colchicine-induced inflammation and Aβ production could be prevented by Bacopa monnieri (BM) supplementation. Dementia was induced by a single intracerebroventicular injection of colchicine (15 μg/5 μl), whereas, BM extract was administered orally (50 mg/kg body weight, daily) for 15 days. Assessment of cognitive functions using Morris water maze revealed deficits in colchicine administered animals. This was accompanied by significant increase in oxidative stress in terms of accentuated ROS and NO production. Expression of pro-inflammatory cytokines (IL-6, TNF-α) and chemokine (MCP-1) increased in the brain regions. Furthermore, COX-2 and iNOS expression also increased significantly in the brain regions of colchicine-administered animals. In addition, BACE-1 activity increased in the colchicine treated animals, which was accompanied by enhanced Aβ production. On the other hand, BM supplementation was able to improve cognitive functions, suppress Aβ formation by reducing BACE-1 activity. Inflammatory and oxidative stress markers were attenuated in the brain regions of BM supplemented animals. Taken together, the findings reveal that BM reverses colchicine-induced dementia by its anti-inflammatory and anti-oxidant action suggesting that it may be an effective therapeutic intervention to ameliorate progression of AD.

ZnT3 Gene Deletion Reduces Colchicine-Induced Dentate Granule Cell Degeneration

Our previous study demonstrated that colchicine-induced dentate granule cell death is caused by blocking axonal flow and the accumulation of intracellular zinc. Zinc is concentrated in the synaptic vesicles via zinc transporter 3 (ZnT3), which facilitates zinc transport from the cytosol into the synaptic vesicles. The aim of the present study was to identify the role of ZnT3 gene deletion on colchicine-induced dentate granule cell death. The present study used young (3–5 months) mice of the wild-type (WT) or the ZnT3^−/− genotype. Colchicine (10 µg/kg) was injected into the hippocampus, and then brain sections were evaluated 12 or 24 h later. Cell death was evaluated by Fluoro-Jade B; oxidative stress was analyzed by 4-hydroxy-2-nonenal; and dendritic damage was detected by microtubule-associated protein 2. Zinc accumulation was detected by N-(6-methoxy-8-quinolyl)-para-toluenesulfonamide (TSQ) staining. Here, we found that ZnT3^−/− reduced the number of degenerating cells after colchicine injection. The ZnT3^−/−-mediated inhibition of cell death was accompanied by suppression of oxidative injury, dendritic damage and zinc accumulation. In addition, ZnT3^−/− mice showed more glutathione content than WT mice and inhibited neuronal glutathione depletion by colchicine. These findings suggest that increased neuronal glutathione by ZnT3 gene deletion prevents colchicine-induced dentate granule cell death.

Toxin-Induced Experimental Models of Learning and Memory Impairment

Animal models for learning and memory have significantly contributed to novel strategies for drug development and hence are an imperative part in the assessment of therapeutics. Learning and memory involve different stages including acquisition, consolidation, and retrieval and each stage can be characterized using specific toxin. Recent studies have postulated the molecular basis of these processes and have also demonstrated many signaling molecules that are involved in several stages of memory. Most insights into learning and memory impairment and to develop a novel compound stems from the investigations performed in experimental models, especially those produced by neurotoxins models. Several toxins have been utilized based on their mechanism of action for learning and memory impairment such as scopolamine, streptozotocin, quinolinic acid, and domoic acid. Further, some toxins like 6-hydroxy dopamine (6-OHDA), 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and amyloid-β are known to cause specific learning and memory impairment which imitate the disease pathology of Parkinson's disease dementia and Alzheimer's disease dementia. Apart from these toxins, several other toxins come under a miscellaneous category like an environmental pollutant, snake venoms, botulinum, and lipopolysaccharide. This review will focus on the various classes of neurotoxin models for learning and memory impairment with their specific mechanism of action that could assist the process of drug discovery and development for dementia and cognitive disorders.

Cox-2 Plays a Vital Role in the Impaired Anxiety Like Behavior in Colchicine Induced Rat Model of Alzheimer Disease

The anxiety status is changed along with memory impairments in intracerebroventricular colchicine injected rat model of Alzheimer Disease (cAD) due to neurodegeneration, which has been indicated to be mediated by inflammation. Inducible cox-2, involved in inflammation, may have important role in the colchicine induced alteration of anxiety status. Therefore, the present study was designed to investigate the role of cox-2 on the anxiety behavior (response to novelty in an elevated open field space) of cAD by inhibiting it with three different doses (10, 20, and 30 mg) of etoricoxib (a cox-2 blocker) in two time points (14 and 21 days). The results showed anxiolytic behavior in cAD along with lower serum corticosterone level, both of which were recovered at all the doses of etoricoxib on day 21. On day 14 all of the anxiety parameters showed similar results to that of day 21 at high doses but not at 10 mg/kg body weight. Results indicate that the parameters of anxiety were dependent on neuronal circuitries that were probably sensitive to etoricoxib induced blocking of neurodegeneration. The present study showed that anxiolytic behavior in cADr is predominantly due to cox-2 mediated neuroinflammation induced neurodegeneration in the brain.

Colchicine induced intraneuronal free zinc accumulation and dentate granule cell degeneration

Colchicine has been discovered to inhibit many inflammatory processes such as gout, familial Mediterranean fever, pericarditis and Behcet disease. Other than these beneficial anti-inflammatory effects, colchicine blocks microtubule-assisted axonal transport, which results in the selective loss of dentate granule cells of the hippocampus. The mechanism of the colchicine-induced dentate granule cell death and depletion of mossy fiber terminals still remains unclear. In the present study, we hypothesized that colchicine-induced dentate granule cell death may be caused by accumulation of labile intracellular zinc. 10 μg kg(-1) of colchicine was injected into the adult rat hippocampus and then brain sections were evaluated at 1 day or 1 week later. Neuronal cell death was evaluated by H&E staining or Fluoro-Jade B. Zinc accumulation and vesicular zinc were detected by N-(6-methoxy-8-quinolyl)-para-toluene sulfonamide (TSQ) staining. To test whether an extracellular zinc chelator can prevent this process, CaEDTA was injected into the hippocampus over a 5 min period with colchicine. To test whether other microtubule toxins also produce similar effects as colchicine, vincristine was injected into the hippocampus. The present study found that colchicine injection induced intracellular zinc accumulation in the dentate granule cells and depleted vesicular zinc from mossy fiber terminals. Injection of a zinc chelator, CaEDTA, did not block the zinc accumulation and neuronal death. Vincristine also produced intracellular zinc accumulation and neuronal death. These results suggest that colchicine-induced dentate granule cell death is caused by blocking axonal zinc flow and accumulation of intracellular labile zinc.

Spontaneous and induced nontransgenic animal models of AD: modeling AD using combinatorial approach

Alzheimer's disease (AD), the most common neurodegenerative and dementing disorder, is characterized by extracellular amyloid deposition, intracellular neurofibrillary tangle formation, and neuronal loss. We are still behind in AD research in terms of knowledge regarding understanding its pathophysiology and designing therapeutics because of the lack of an accurate animal model for AD. A complete animal model of AD should imitate all the cognitive, behavioral, and neuropathological features of the disease. Partial models are currently in use, which only mimic specific and not all of the components of AD pathology. Currently the transgenic animals are the popular models for AD research, but different genetic backgrounds of these transgenic animals remain a major confounding factor. This review attempts to summarize the current literature on nontransgenic animal models of AD and to highlight the potential of exploiting spontaneous and induced animal models for neuropathological, neurochemical, neurobehavioral, and neuroprotective studies of AD.

Neuroprotective effects of Bacopa monnieri in experimental model of dementia

Alzheimer disease (AD) is characterized by dementia that begins as mild short term memory deficit and culminates in total loss of cognitive and executive functions. The present study was conducted to evaluate the neuroprotective potential of Bacopa monnieri (BM), an Indian traditional medicinal plant effective against cognitive impairment, in colchicine-induced dementia. Intracerebroventricular administration of colchicine (15 μg/5 μl) induced cognitive impairment in rats as assessed by elevated plus maze. This was accompanied by a significant increase in oxidative stress in term of enhanced levels of lipid peroxidation and protein carbonyls. Concomitantly, decrease in activity of antioxidant enzymes was observed in colchicine treated animals. BM (50 mg/kg body weight) supplementation reversed memory impairment observed in the colchicine treated rats. BM administration attenuated oxidative damage, as evident by decreased LPO and protein carbonyl levels and restoration in activities of the antioxidant enzymes. The activity of membrane bound enzymes (Na(+)K(+) ATPase and AChE) was altered in colchicine treated brain regions and BM supplementation was able to restore the activity of enzymes to comparable values observed in controls. The results suggest therapeutic potential of BM in the treatment of AD associated cognitive decline.

Nootropic activity of acetaminophen against colchicine induced cognitive impairment in rats

Alzheimer’s disease is a devastating neurodegenerative disorder, the most common among the dementing illnesses. Acetaminophen has gaining importance in neurodegenerative diseases by attenuating the dopaminergic neurodegeneration in Caenorhabditis elegans model, decreasing the chemokines and the cytokines and increasing the anti apoptotic protein such as Bcl-2 in neuronal cell culture. The low concentration acetaminophen improved the facilitation to find the hidden platform in Morris Water Maze Test. Also some data suggest that acetaminophen could contribute in neurodegeneration. The present study was aimed to evaluate the effect of acetaminophen against colchicine induced cognitive impairment and oxidative stress in wistar rats. The cognitive learning and memory behaviour was assessed using step through passive avoidance paradigm and acetylcholine esterase activity. The parameters of oxidative stress were assessed by measuring the malondialdehyde, reduced glutathione and catalase levels in the whole brain homogenates. There was a significant memory improvement in the rats received acetaminophen treatment and it has also decreased the acetylcholine esterase enzyme level, confirming its nootropic activity. Acetaminophen neither increases nor decreases the reduced glutathione and catalase in the whole brain homogenates, showing that acetaminophen is devoid of any adverse effect on brain antioxidant defense system.

Protective role of curcumin on colchicine-induced cognitive dysfunction and oxidative stress in rats

Dementia is a syndrome of progressive nature, affects wide range of cognitive abilities like memory, language, calculation and so on, neuropsychiatric and social deficits to impair the routine social functions. The present study was designed to assess the effect of curcumin against colchicine-induced cognitive dysfunction and oxidative stress in rats and compare it with rivastigmine. Colchicine (15 µg/5µl) was administered to male Wistar rats intracerebroventricularly (i.c.v.) by stereotaxic apparatus to induce cognitive dysfunction. Administration of colchicine caused poor retention of memory in elevated plus maze, passive avoidance apparatus and Morris water maze paradigms. Chronic treatment with curcumin (100, 200 and 400 mg/kg, p.o.) twice daily and rivastigmine (2.5 mg/kg, p.o.) daily for a period of 28 days beginning 7 days prior to colchicine injection significantly improved colchicine-induced cognitive impairment. Biochemical assessment revealed that i.c.v. colchicine injection significantly increased lipid peroxidation, depleted reduced glutathione levels and decreased acetyl cholinesterase (AChE) activity in rat brains. Chronic administration of curcumin significantly reduced the elevated lipid peroxidation, restored the reduced glutathione levels and AChE activity; however, rivastigmine failed to prevent oxidative stress. The results of the current study indicate that curcumin (100, 200 and 400 mg/kg, p.o.) twice daily has a protective role against colchicine-induced cognitive impairment and associated oxidative stress.

Colchicine-induced apoptosis was prevented by glycogen synthase kinase-3 inhibitors in PC12 cells

The purpose of this study was to examine whether glycogen synthase kinase-3 (GSK-3) is involved in colchicine-induced cell death in PC12 cells by using GSK inhibitors. Colchicine increased apoptotic cell death with morphological changes characterized by cell shrinkage and nuclear condensation or fragmentation. GSK-3 inhibitors such as alsterpaullone, SB216763, and AR-A014418 prevented colchicine-induced cell death and caspase-3 activation. These results suggest that colchicine induces caspase-dependent apoptotic cell death and that GSK-3 activation is involved in cell death in PC12 cells.

Neuroprotective Effects of Centella asiatica against Intracerebroventricular Colchicine-Induced Cognitive Impairment and Oxidative Stress

Oxidative stress appears to be an early event involved in the pathogenesis of Alzheimer's disease. The present study was designed to investigate the neuroprotective effects of Centella asiatica against colchicine-induced memory impairment and oxidative damage in rats. Colchicine (15 mug/5 muL) was administered intracerebroventricularly in the lateral ventricle of male wistar rats. Morris water maze and plus-maze performance tests were used to assess memory performance tasks. Various biochemical parameters such as lipid peroxidation, nitrite, reduced glutathione, glutathione-S-transferase, superoxide dismutase, acetylcholinesterase were also assessed. ICV colchicine resulted marked memory impairment and oxidative damage. Chronic treatment with Centella asiatica extract (150 and 300 mg/kg, p.o.) for a period of 25 days, beginning 4 days prior to colchicine administration, significantly attenuated colchicine-induced memory impairment and oxidative damage. Besides, Centella asiatica significantly reversed colchicines administered increase in acetylcholinesterase activity. Thus, present study indicates protective effect of Centella asiatica against colchicine-induced cognitive impairment and associated oxidative damage.

Luminescence studies of perturbation of tryptophan residues of tubulin in the complexes of tubulin with colchicine and colchicine analogues

Tubulin, a heterodimeric (alphabeta) protein, the main constituent of microtubules, binds efficiently with colchicine (consisting of a trimethoxybenzene ring, a seven-member ring and methoxy tropone moiety) and its analogues, viz., demecolcine and AC [2-methoxy-5-(2',3',4'-trimethoxyphenyl)tropone]. Tubulin contains eight tryptophan (Trp) residues at A21, A346, A388, A407, B21, B103, B346, and B407 in the two subunits. The role of these eight Trp residues in this interaction and also their perturbation due to binding have been explored via time-resolved fluorescence at room temperature and low-temperature (77 K) phosphorescence in a suitable cryosolvent. Both the time-resolved fluorescence data and 77 K phosphorescence spectra indicate that the emitting residues move toward a more hydrophobic and less polar environment after complex formation. The environment of emitting Trps in the complex also becomes slightly more heterogeneous. Our analysis using the experimental results, the calculation of the accessible surface area (ASA) of all the Trps in the wild type and tubulin-colchicine complex [Ravelli, R. B. G., et al. (2004) Nature 428, 198-202], the distance of the Trp residues from the different moieties of the colchicine molecule, the knowledge of the nature of the immediate residues (<5 A) present near each Trp residue, and the calculation of the intramolecular Trp-Trp energy transfer efficiencies indicate that Trp A346, Trp A407, Trp B21, and Trp B407 are the major contributors to the emission in the free protein, while Trp B21 and Trp B103 are mainly responsible for the emission of the complexes. A comparative account of the photophysical aspects of the drug molecules bound to protein in aqueous buffer and in buffer containing 40% ethylene glycol has been presented. The quantum yield and average lifetime of fluorescence in tubulin and its complexes with colchicine are used to predict the possible donors and the energy transfer (ET) efficiency in the ET process from Trps to colchicine in the complex. This study is a unique attempt to identify the Trp residues contributing to the emission in the free protein and in a complex of a multi-Trp protein with a drug molecule without performing the mutation of the protein.

Effect of Curcumin on Intracerebroventricular Colchicine-Induced Cognitive Impairment and Oxidative Stress in Rats

This study was designed to investigate the protective effects of curcumin against colchicine-induced cognitive impairment and oxidative stress in rats. Male Wistar rats (weighing 150-200 g) received colchicine intracerebroventricularly (15 microg per rat), and cognitive dysfunctions were evaluated by the Morris water maze and the plus maze performance task and supported by biochemical tests. Central administration of colchicine caused memory deficit in both the Morris water maze and the elevated plus maze task paradigm tasks. Chronic treatment with curcumin (5-50 mg/kg, p.o.) twice daily for a period of 25 days beginning 4 days prior to colchicine injection significantly improved the colchicine-induced cognitive impairment. Biochemically, chronic administration of curcumin significantly reduced the elevated lipid peroxidation, restored the decreased reduced glutathione level and acetylcholinesterase activity, and attenuated the raised colchicine-induced elevated nitrite levels. The results of the present study indicate that curcumin has a protective role against colchicine-induced cognitive impairment and associated oxidative stress.

Anti-mitotic activity of colchicine and the structural basis for its interaction with tubulin

In this review, an attempt has been made to throw light on the mechanism of action of colchicine and its different analogs as anti-cancer agents. Colchicine interacts with tubulin and perturbs the assembly dynamics of microtubules. Though its use has been limited because of its toxicity, colchicine can still be used as a lead compound for the generation of potent anti-cancer drugs. Colchicine binds to tubulin in a poorly reversible manner with high activation energy. The binding interaction is favored entropically. In contrast, binding of its simple analogs AC or DAAC is enthalpically favored and commences with comparatively low activation energy. Colchicine-tubulin interaction, which is normally pH dependent, has been found to be independent of pH in the presence of microtubule-associated proteins, salts or upon cleavage of carboxy termini of tubulin. Biphasic kinetics of colchicines-tubulin interaction has been explained in light of the variation in the residues around the drug-binding site on beta-tubulin. Using the crystal structure of the tubulin-DAMAcolchicine complex, a detailed discussion on the pharmacophore concept that explains the variation of affinity for different colchicine site inhibitors (CSI) has been discussed.

Differential effects of cyclooxygenase inhibitors on intracerebroventricular colchicine-induced dysfunction and oxidative stress in rats

Alzheimer's disease is a progressive neurological and psychiatric disorder. Oxidative stress and neuroinflammation have been implicated in pathophysiology of Alzheimer's disease. Inflammatory cells, such as astrocytes and microglia, are activated in areas of the brain affected by amyloid plaques and inflammatory mediators including cytokines, chemokines, prostaglandins, oxygen free radicals and reactive nitrogen species may have a crucial role in Alzheimer's disease pathogenesis. Central administration of colchicine, a microtubule-disrupting agent, causes loss of cholinergic neurons and cognitive dysfunction that is associated with excessive free radical generation. The present study was aimed to evaluate the effects of cyclooxygenase inhibitors against colchicine-induced cognitive dysfunction and oxidative stress in rats. Following intracerebroventricular (i.c.v.) administration of colchicine (15 microg/5 microl), rats exhibited poor retention of memory in Morris water maze and elevated plus maze task paradigms and oxidative stress in rats. Chronic treatment with naproxen (per se; 20 and 40 mg/kg, p.o.) or valdecoxib (per se; 5 and 10 mg/kg, p.o.) daily respectively for a period of 25 days beginning 4 days prior to colchicine injection significantly improved colchicine-induced cognitive impairment. Intracerebroventricular colchicine injection resulted in free radical generation characterized by alterations in oxidative stress markers with a significant increase in malondialdehyde and nitrite levels and depletion of reduced glutathione levels in the brains of rats. It also caused a decrease in acetylcholinesterase activity. Besides, improving cognitive dysfunction, chronic administration of cyclooxygenase inhibitors (naproxen and valdecoxib) significantly reduced elevated malondialdehyde, nitrite levels and restored reduced glutathione levels and acetylcholinesterase activity. The results of the present study indicated that naproxen (per se; 20 and 40 mg/kg, p.o.) or valdecoxib (per se; 5 and 10 mg/kg, p.o.) treatment has a neuroprotective role against colchicine-induced cognitive impairment and associated oxidative stress. The present findings further support the potential use of cyclooxygenase inhibitors in treatment of neurodegenerative diseases such as Alzheimer's disease.

Neuroprotective Effects of Resveratrol against Intracerebroventricular Colchicine-Induced Cognitive Impairment and Oxidative Stress in Rats

Alzheimer's disease is a complex and multifactorial neurodegenerative disease. Central administration of colchicine, a microtubule-disrupting agent, causes loss of cholinergic neurons and cognitive dysfunction that is associated with excessive free radical generation. The present study was aimed at evaluating the effects of trans-resveratrol in the prevention of colchicine-induced cognitive impairment and oxidative stress in rats. Intracerebroventricular administration of colchicine (15 microg/5 microl) induced impaired cognitive functions in both the Morris water maze task and the elevated plus-maze task. Chronic treatment with resveratrol (10 and 20 mg/kg, p.o.) for a period of 25 days, beginning 4 days prior to colchicine injection, significantly improved the colchicine-induced cognitive impairment. Intracerebroventricular colchicine injection resulted in free radical generation characterized by alterations in oxidative stress markers with a significant increase in malondialdehyde (MDA) and nitrite levels and depletion of reduced glutathione (GSH) activity in the rat brains. It also showed a significant decrease in acetylcholinesterase activity. Besides improving cognitive dysfunction, chronic administration of resveratrol significantly reduced the elevated MDA and nitrite levels and restored the depleted GSH and acetylcholinesterase activity. Results of the present study indicated that trans-resveratrol has a neuroprotective role against colchicine-induced cognitive impairment and associated oxidative stress.

Apoptotic morphology does not always require caspase activity in rat cerebellar granule neurons

The death of a cell via apoptosis is characterized by morphological changes including cell shrinkage and nuclear condensation. Intracellularly, proteases, including caspases, are activated. In the present article we have compared the ability of three different neurotoxic agents to induce caspase activity in cerebellar granule cells (CGC). These compounds are the microtubule-disrupting agent colchicine and the oxidative stress-inducing agents hydrogen peroxide and methylmercury (MeHg). We have previously shown that each of these agents causes nuclear changes that are consistent with apoptosis, i.e., induction of chromatin condensation and DNA cleavage into fragments of regular size (700, 300 and 50 kbp). However, only colchicine causes a large increase in caspase activity, as monitored by the ability of whole cell extracts to cleave the synthetic caspase substrate DEVD-MCA. In contrast, MeHg and hydrogen peroxide do not induce any significant increase of DEVDase activity as compared to control cells. Immunocytochemistry confirms that active caspase-3 is abundant only in colchicine-exposed cells. In agreement with these findings, the pan-caspase inhibitor, z-VAD-fmk, is efficient in protecting CGC against colchicine, but not against hydrogen peroxide or MeHg. These data suggest that in CGC the activation of caspases is not always required to induce morphological changes and pattern of DNA fragmentation consistent with apoptosis.

Discovery of a novel compound: insight into mechanisms for acrylamide-induced axonopathy and colchicine-induced apoptotic neuronal cell death

The exposure of humans and experimental animals to certain industrial toxins such as acrylamide is known to cause nerve damage classified as axonopathy, but the mechanisms involved are poorly understood. Here we show that acrylamide induces morphological changes and tyrosine phosphorylation of focal adhesion kinase (FAK) and proline-rich tyrosine kinase 2 (Pyk2), a member of the FAK subfamily, in human differentiating neuroblastoma SH-SY5Y cells. Furthermore, we identified a novel molecule designated 'compound-1' that inhibits the morphological and biochemical events. Daily oral administrations of the compound also effectively alleviated behavioral deficits in animals elicited by acrylamide in inclined plane testing, landing foot spread testing and rota-rod performance testing. The compound also effectively inhibited the biological and biochemical responses caused by another axonopathy inducer, colchicine, including tyrosine phosphorylation of Pyk2, formation of an 85-kDa poly(ADP-ribose)polymerase (PARP) fragment and apoptosis-associated induction of the NAPOR gene as well as neuronal cell death. Our findings not only provide insight into FAK and Pyk2 functions in neuronal cells, but may also be important in the development of therapeutic agents for peripheral neuropathy and neurodegeneration.

Prenatal exposure to high levels of glucocorticoids increases the susceptibility of cerebellar granule cells to oxidative stress-induced cell death

There is growing concern that prenatal exposure to excessive glucocorticoids may have deleterious effects on the development of various organs, including the nervous system. This study aimed at evaluating whether prenatal exposure to high levels of glucocorticoids might produce long-term effects on neuronal cell survival. Pregnant rats were injected i.p. with 0.1 mg/kg dexamethasone (DEX) from day 14 postconception, and cerebellar granule cells (CGC) were prepared from 1-week-old rats from DEX-treated and control dams. After 7 days in culture, cells were exposed to H(2)O(2), methylmercury, or colchicine at concentrations known to induce apoptotic cell death. After exposure to H(2)O(2) or methylmercury, both inducing oxidative stress, the number of apoptotic cells was significantly higher in DEX- than in control-CGC. Because mitochondria play a key role in apoptosis, mitochondrial function was investigated, and a decrease in the threshold level of Ca(2+) necessary for induction of mitochondrial permeability transition, in Ca(2+) accumulation rate, and in oxygen consumption was detected in DEX-CGC. Moreover, the activity of the antioxidant enzyme catalase was significantly decreased in DEX-CGC. A similar decrease in catalase activity was observed in cerebellar homogenate from newborn and 40-day-old DEX-rats. In conclusion, these results indicate that prenatal exposure to high levels of glucocorticoids induces long-lasting changes in CGC rendering them more sensitive to oxidative stress. With the increasing use of multiple doses of glucocorticoids in preterm infants, the possibility that prenatal exposure to excess glucocorticoids may lead to long-term neurological consequences becomes a relevant issue.

Involvement of intracellular labile zinc in suppression of DEVD-caspase activity in human neuroblastoma cells

Age-related tissue Zn deficiency may contribute to neuronal and glial cell death by apoptosis in Alzheimer's dementia. To investigate this, we studied the effects of increasing or decreasing the levels of intracellular labile Zn on apoptosis of human neuroblastoma BE(2)-C cells in vitro. BE(2)-C cells were primed for 18 h with butyrate (1 mM) before addition of staurosporine (1 microM), an effector enzyme of apoptosis, for a further 3 h to induce DEVD-caspase activity. An increase in intracellular Zn using Zn ionophore pyrithione suppressed DEVD-caspase activity, while a decrease in intracellular Zn induced by Zn chelator TPEN mimicked staurosporine by activating DEVD-caspase in butyrate-primed cells. The distribution of intracellular Zn in the cells was demonstrated with the UV-excitable Zn-specific fluorophore Zinquin. Confocal images showed distinct cytoplasmic and cytoskeletal fluorescence. We propose that Zn decreases the level of apoptosis in neuronal cells exposed to toxins, possibly by stabilizing their cytoskeleton.

Colchicine administration in the rat central nervous system induces SNAP-25 expression

he arrest of axonal transport by colchicine administration has been extensively used in immunocytochemical studies to increase the levels of neuroactive compounds in neuronal somata. In order to study the accumulation rates of a variety of proteins with location and physiological action at the synaptic terminal, we analysed, by immunocytochemical methods, the neuronal cell body content of these synaptic proteins in colchicine-injected rats. In sham-injected animals, all synaptic proteins tested were essentially observed in nerve fibres and terminal boutons. After colchicine administration, intense SNAP-25 immunoreactivity was found in many neuronal cell bodies throughout the CNS. In contrast, immunostaining for the rest of the synaptic proteins analysed (syntaxin 1A and 1B, synaptobrevin I and II, Rab3A, synaptophysin, synapsin I, synaptotagmin I and GAP-43) was virtually absent in neuronal cell bodies in treated animals. Furthermore, northern blot and in situ hybridization analysis revealed an increase in SNAP-25a and SNAP-25b messenger RNA isoforms in the brains of adult colchicine-administered animals. In addition, colchicine administration in five-day-old rat pups induced a notable increase in both SNAP-25 transcript isoforms. The present results indicate that in vivo colchicine administration, under conditions known to inhibit axoplasmic transport, upregulates SNAP-25 expression in the rat brain.

Mechanism of colchicine impairment on learning and memory, and protective effect of CGP36742 in mice

Fourteen days after hippocampal microinfusion with colchicine (COL), learning and memory ability of mice was significantly impaired, while glutamate (Glu), gamma-aminobutyric acid (GABA), Glu/GABAB and GABAB receptor levels in the cortex and/or the hippocampus were significantly changed. After treatment with a GABAB receptor antagonist, CGP36742, learning and memory impairment caused by COL could be significantly improved, and the above indices in brain regions reversed. These results suggest GABAB antagonists may have therapeutic value in the treatment of Alzheimer's disease.

Comparison of neurodegenerative pathology in transgenic mice overexpressing V717F beta-amyloid precursor protein and Alzheimer's disease

Overexpression of mutated human amyloid precursor protein (hAPP717V-->F) under control of platelet-derived growth factor promoter (PDAPP minigene) in transgenic (tg) mice results in neurodegenerative changes similar to Alzheimer's disease (AD). To clarify the pathology of these mice, we studied images derived from laser scanning confocal and electron microscopy and performed comparisons between PDAPP tg mice and AD. Similar to AD, neuritic plaques in PDAPP tg mouse contained a dense amyloid core surrounded by anti-hAPP- and antineurofilament-immunoreactive dystrophic neurites and astroglial cells. Neurons were found in close proximity to plaques in PDAPP tg mice and, to a lesser extent, in AD. In PDAPP tg mice, and occasionally in AD, neuronal processes contained fine intracellular amyloid fibrils in close proximity to the rough endoplasmic reticulum, coated vesicles, and electron-dense material. Extracellular amyloid fibrils (9-11 nm in diameter) were abundant in PDAPP tg and were strikingly similar to those observed in AD. Dystrophic neurites in plaques of PDAPP tg mouse and AD formed synapses and contained many dense multilaminar bodies and neurofilaments (10 nm). Apoptotic-like figures were present in the tg mice. No paired helical filaments have yet been observed in the heterozygote PDAPP tg mice. In summary, this study shows that PDAPP tg mice develop massive neuritic plaque formation and neuronal degeneration similar to AD. These findings show that overproduction of hAPP717V-->F in tg mice is sufficient to cause not only amyloid deposition, but also many of the complex subcellular degenerative changes associated with AD.

Entorhinal cortex lesion or intrahippocampal colchicine injection increases peripheral type benzodiazepine binding sites in rat hippocampus

The peripheral type benzodiazepine binding site (PTBBS) has been proposed to be a good marker for reactive glial cells following brain insults. In the present study, homogenate binding of 3H-Ro5-4864 and quantitative autoradiography of 3H-PK-11195 binding (two ligands for the PTBBS) were used to assess the distribution, time-course and extent of reactive gliosis in the hippocampus following deafferentation by unilateral entorhinal cortex lesion or neuronal death produced by intrahippocampal colchicine injection. Intrahippocampal colchicine injections produced a 3-fold increase in 3H-Ro5-4864 binding in the dentate gyrus within 2 days. This effect was doubled in animals pretreated with the lysosomal inhibitor chloroquine. Quantitative autoradiography of 3H-PK-11195 binding 1 or 2 weeks after colchicine injection indicated that the increase in binding was restricted to the dorsal hippocampus both rostrally and caudally and was present in the dentate gyrus and CA1. Following a unilateral electrolytic lesion of the entorhinal cortex, the binding of 3H-Ro5-4864 to homogenates of the dentate gyrus was doubled 18 h after the lesion, reached a maximum at 4 days post-lesion, and returned to control values by 2 months after the lesion. A transient increase in binding was also observed 2 and 4 days post-lesion in the dentate gyrus contralateral to the lesion side. Autoradiography of 3H-PK-11195 binding indicated that the increase in PTBBS following entorhinal cortex lesion was restricted to the molecular layer of the dentate gyrus.(ABSTRACT TRUNCATED AT 250 WORDS)

Microtubule disruption and cognitive defects: effect of colchicine on learning behavior in rats

Neuropathological findings in Alzheimer's disease (AD) suggest a possible involvement of microtubule dysfunction in neurodegenerative process pathogenesis. Because microtubules have a major role in neuronal plasticity, microtubule disruption could be also directly responsible for cognitive defects in AD. We report that in rats, continuous microtubule disruption induced by chronic colchicine administration results in a dose-dependent learning deficit. In addition, retention is also impaired. These cognitive defects are specific, as chronic colchicine induces no other behavioral toxicity within the study dose range. Colchicine-induced cognitive defects resemble those of AD, which are characterised by amnesia of recent learning and loss of formerly established memories. This new procedure of pharmacologically induced cognitive impairment may prove useful, both towards understanding AD pathogenesis and towards drug screening.

Task-dependent memory loss and recovery following unilateral nucleus basalis lesion: behavioral and neurochemical correlation

We found that rats with unilateral AF64A lesions of the nucleus basalis of Meynert (nbM) showed significant impairment of active avoidance and Morris water maze learning. Impairment of active avoidance learning almost subsided within one month but impairment of Morris water maze learning persisted 5 months later. Two weeks after production of the lesion, choline acetyltransferase (ChAT) activity was reduced by 45% in the frontal cortex (FC), but not in the hippocampus or corpus striatum. The decreased ChAT activity in the FC gradually recovered, but it was still reduced by 20% even after 20 weeks. In contrast, ChAT activity on the contralateral side of the FC began to increase from 5 weeks onwards. Histological examination also indicated that loss of cholinergic fibers in the FC gradually recovered with time after induction of the lesion. The results from the present study suggest that specific learning (Morris water maze) tasks involve the cholinergic system and that recovery of cholinergic function (ChAT) may be related to plasticity of the contralateral FC.

Differential effects of colchicine lesions of dentate granule cells on wet dog shakes and seizures elicited by direct hippocampal stimulation

Direct electrical stimulation of either the dorsal or ventral hippocampal formation elicits wet dog shakes and overt seizures. Destruction of dentate granule cells in the dorsal hippocampal formation does not significantly reduce the number of wet dog shakes elicited by ventral hippocampal stimulation. However, destruction of dentate granule cells in the ventral hippocampus virtually eliminates wet dog shaking elicited by dorsal hippocampal stimulation. Destruction of either dorsal or ventral dentate granule cells lowers the threshold for eliciting forelimb clonus with rearing. These results suggest that dentate granule cells in the ventral hippocampus are essential for wet dog shakes elicited by intrahippocampal stimulation. However, dentate granule cells throughout the hippocampal formation appear to play an important inhibitory role in the spread of seizure activity within the hippocampus.

Differential effects of intracerebroventricular colchicine administration on the expression of mRNAs for neuropeptides and neurotransmitter enzymes, with special emphasis on galanin: an in situ hybridization study

The axonal transport blocker colchicine has been extensively used in immunohistochemical studies to induce accumulation of neuroactive compounds, especially neuropeptides, in neuronal somata and thus improve their visualization. To assess whether colchicine might, in addition, influence the synthesis of such compounds, we have now used in situ hybridization to examine the levels of mRNAs encoding for several neuropeptides (galanin [GAL], cholecystokinin [CCK], somatostatin [SOM], neuropeptide Y [NPY]) and neurotransmitter-synthesizing enzymes (choline acetyltransferase [ChAT], tyrosine hydroxylase [TH], amino acid decarboxylase [AADC], and glutamic acid decarboxylase [GAD]) after intraventricular administration of the drug. The results show that colchicine differentially modifies the levels of several mRNA species in different brain areas. Thus GAL mRNA levels increase in virtually all regions examined, including the basal forebrain, hypothalamus, dorsal raphe nucleus, locus coeruleus, and nucleus tractus solitarii. In addition, after colchicine treatment, GAL mRNA appears to be induced in the ipsilateral hemisphere in regions such as the cortex, hippocampus, striatum, lateral septum, and some nuclei of the thalamus as well as within white matter, where it cannot be detected in control animals. Although GAL mRNA in the vast majority of cases is neuronal, some findings indicate a possible glial localization. In parallel, colchicine depletes ChAT mRNA and increases GAD mRNA in the basal forebrain and striatum and decreases AADC mRNA in the dorsal raphe nucleus and locus coeruleus. In the latter nucleus, NPY and TH mRNA levels are increased by colchicine. In contrast, TH mRNA and also CCK mRNA levels decrease in the substantia nigra. In the cortex, hippocampus, and thalamus ipsilateral to colchicine injection CCK mRNA levels are markedly decreased, whereas SOM mRNA is decreased and NPY mRNA increased in the hippocampus but unchanged in the cortex. The results are discussed with reference to the possible artifacts that the use of colchicine might induce in immunohistochemical mapping studies and in relation to possible neurotoxic actions of colchicine, in some cases perhaps related to impaired retrograde transport of growth factor(s).

Hypothesis: microtubules, a key to Alzheimer disease

Alzheimer disease (AD) is a clinicopathologic syndrome of unknown etiology with numerous abnormalities in neuronal and nonneuronal cells. A review of the literature suggests that a common basic intracellular defect may underlie many of the reported abnormalities. We hypothesize impairment of the microtubule (MT) system as one explanation for the pathogenesis of AD. Evidence in support of the hypothesis includes the following: MTs are ubiquitous and vital cell components, unequally distributed, with the highest concentration in the brain; various abnormalities, including the key neuropathologic lesions, can be explained by impairments of the MT system; and experiments utilizing pharmacologic agents known to disrupt MTs have reproduced certain abnormalities observed in AD. The hypothesis provides a framework for systematic investigations of MTs at the cellular and molecular levels as well as the basis for in vivo diagnostic tests for AD.

Selective destruction of mossy fibers and granule cells with preservation of the GABAergic network in the inferior region of the rat hippocampus after colchicine treatment

Lesions induced by colchicine injection into the rat hippocampus were investigated by means of electron microscopy and GABA immunocytochemistry. Granule cells were nearly completely destroyed 3 days after colchicine injection; since the necrosis of their axonal endings was delayed, an anterograde degeneration of the mossy fibers had probably taken place. The selectivity of the lesions was not limited to granule cells, for some pyramidal neurons in CA1 pyramidal layer were damaged. It was, however, striking to observe that throughout the hippocampal structure GABAergic neurons were spared from the effects of colchicine. For instance, GABAergic neurons were found in the vicinity of the completely destroyed granule cell layer. GABAergic neurons and terminals were also present in the CA3 region where the GABA-containing terminals formed a dense network of synapses with somata and dendrites of pyramidal cells. It was interesting to note that, consistent with previous studies, the GABAergic neurons in CA3 are innervated by mossy fibers. We conclude that after colchicine treatment the destruction of the granule cells was not associated with a lesion of the GABAergic network. This selective lesion provides a useful model with which to study the properties of CA3 neurons deprived of their major excitatory input but with an intact inhibitory network.

Dissociation between changes in glutamate receptor binding sites and their coupling to phosphatidylinositol metabolism following intrahippocampal colchicine injection

Intrahippocampal colchicine injection produces a rapid death of granule cells and pyramidal neurons in the hippocampus in the rat. Under the appropriate assay conditions, [3H]glutamate labels the N-methyl-D-aspartate type of glutamate receptors while [3H]alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate labels the quisqualate type. Unilateral injection of colchicine (15 micrograms) in the dorsal hippocampus did not produce any change in [3H]glutamate and [3H]alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate binding in membrane fractions from the dentate gyrus or CA1 field contralateral to the injection side, at least up to 12 days after the injection. However, it produced a progressive decrease in the binding of both ligands in dentate gyrus and CA1 of the injected hippocampus. In the dentate gyrus the changes in binding as a function of time after the injection were biphasic with a rapid exponential decrease (t1/2 about 8 days for both [3H]glutamate and [3H]alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate) until 12 days after the injection followed by a much slower decrease afterwards. A similar pattern was observed in CA1 although the changes in binding were smaller and delayed by about three days as compared to the dentate gyrus. Kinetic analyses of the binding at equilibrium were performed seven days after the injection and indicated that the changes in [3H]glutamate binding were due to a change in the maximum number of sites but not in affinity for the ligand.(ABSTRACT TRUNCATED AT 250 WORDS)

Intrahippocampal colchicine injection results in spectrin proteolysis

Neurons in the hippocampal formation vary markedly in their susceptibility to colchicine toxicity. The present study was directed at evaluating the effects of colchicine on the proteolytic breakdown of the cytoskeletal protein spectrin within the hippocampus in the rat. Quantified by immunoblot analysis of spectrin breakdown products, the extent of proteolysis was found to correlate with the relative vulnerability of different hippocampal subfields to colchicine toxicity. Levels of breakdown products increased dramatically between 1 and 2 days after colchicine injection, peaked between 2 and 4 days, and remained detectably elevated for at least 35 days. Two days after colchicine injection, the spectrin breakdown products were significantly more concentrated in the molecular layer than in the granule cell/hilar region of the dentate gyrus. The colchicine-induced increase in spectrin breakdown products was significantly reduced by pretreatment with the protease inhibitor leupeptin and was significantly elevated by pretreatment with the lysosomal inhibitor chloroquine. Immunohistochemical analyses of the hippocampus at various times after colchicine injection revealed changes in the distribution of spectrin-like immunoreactivity that paralleled the changes observed by Western blot analysis. Thus increased staining was observed in the molecular layer of the dentate gyrus at 2 and 4 days after the injection, while staining in CA3 was only slightly increased. In addition, abnormal staining of reactive astrocytes was prominent at 2 days. The mechanism whereby colchicine results in neuronal death is as yet unknown. However, the results presented here demonstrate that extensive proteolysis of a cytoskeletal protein occurs in response to the drug, suggesting a plausible mechanism for its neurotoxicity. The protease responsible for the effect is likely to be calpain since the process is non-lysosomal, leupeptin-sensitive and produces spectrin breakdown products indistinguishable from those generated by calpain treatment in vitro. These data support the hypothesis that calpain-mediated degradation of cytoskeletal elements is a common and early response to neurodegenerative events and serves as a trigger in the development of various neuropathologies.

AF64A(ethylcholine aziridinium ion)-induced basal forebrain lesion impairs maze performance

Rats were given bilateral injections of ethylcholine aziridinium ion, AF64A (1 nmol/side) into the basal forebrain (BF). One month later, choline acetyltransferase activity was reduced by 25% in the frontal cortex (FC). There was a marked decrease in cortical uptake of [3H]choline, but [3H]GABA and [3H]dopamine uptake was not affected by the injection. Histological analysis confirmed that this dose of AF64A caused acetylcholinesterase staining in the FC to disappear. Acquisition and retention of a T-maze task were impaired in the rats with BF lesions one month after the injection. Acquisition of the water-filled multiple T-maze task was also impaired by AF64A. These observations suggest that the cholinergic component in the BF is involved in spatial memory.

Enhancement of neurotrophic activity in cholinergic cells by hippocampal extract prepared from colchicine-lesioned rats

The effect of hippocampal extract on neurotrophic activity for cultured cholinergic cells was determined. Extract prepared from lesioned hippocampus caused by intrahippocampal infusion of colchicine promoted neuron survival of chick ciliary ganglion cells. The maximal level of survival-promoting activity was reached at 12 days postlesion. The biochemical differentiation of NG108-15 cells was assessed by measuring the activity of choline acetyltransferase (ChAT). After 3 days in culture, hippocampal extract was found to stimulate ChAT activity in a concentration-dependent manner. Hippocampal extract prepared after colchicine lesions elicited a large increase in ChAT-enhancing activity. The effect of hippocampal extract was additive to that of dibutyryl cyclic AMP (db-cAMP). The neurite outgrowth from NG108-15 cells was also potentiated when cells were cultured with hippocampal extract plus db-cAMP. The results suggest that one or several factors in colchicine-lesioned hippocampus promote neurotrophic activity, and the enhancing effect of hippocampal extract on cellular differentiation may act, at least in part, through a mechanism distinct from that for db-cAMP.