Icariin, a major constituent from Epimedium brevicornum, attenuates ibotenic acid-induced excitotoxicity in rat hippocampus.

Excitotoxicity is one of the most extensively studied causes of neuronal death and plays an important role in Alzheimer's disease (AD). Icariin is a flavonoid component of a traditional Chinese medicine reported to possess a broad spectrum of pharmacological effects. The present study was designed to investigate the effects of icariin against learning and memory impairment induced by excitotoxicity. Here, we demonstrated that rats receiving intracerebroventricular injection of excitatory neurotoxin ibotenic acid exhibited impaired learning and memory. Oral administration of icariin at doses of 20 and 40mg/kg rescued behavioral performance and protected against neurotoxicity in rat hippocampus by suppressing ibotenic acid induced pro-apoptosis. Furthermore, Western blott of hippocampal specimens revealed that icariin up-regulated the expression of calbindin-D28k protein following ibotenic acid administration. Additionally, icariin inhibited mitogen-activated protein kinase (MAPK) family phosphorylation and nuclear factor kappa B (NF-κB) signaling, implicating the MAPK signaling and NF-κB signaling pathways were involved in the mechanism underlying icariin-mediated neuroprotection against ibotenic acid-induced excitotoxicity. These data suggested that icariin could be a potential agent for treatment of excitotoxicity-related diseases, including AD.

Intranasal nanoparticles of basic fibroblast growth factor for brain delivery to treat Alzheimer's disease.

Disabilities caused by neurodegeneration have become one of the main causes of mortality in elderly population, with drug distribution to the brain remaining one of the most difficult challenges in the treatment of the central nervous system (CNS) diseases due to the existence of blood-brain barrier. Lectins modified polyethylene glycol-polylactide-polyglycolide (PEG-PLGA) nanoparticles could enhance the drug delivery to the brain following intranasal administration. In this study, basic fibroblast growth factor (bFGF) was entrapped in nanoparticles conjugated with Solanum tuberosum lectin (STL), which selectively binds to N-acetylglucosamine on the nasal epithelial membrane for its brain delivery. The resulting nanoparticles had uniform particle size and negative zeta potential. The brain distribution of the formulations following intranasal administration was assessed using radioisotopic tracing method. The areas under the concentration-time curve of (125)I-bFGF in the olfactory bulb, cerebrum, and cerebellum of rats following nasal application of STL modified nanoparticles (STL-bFGF-NP) were 1.79-5.17 folds of that of rats with intravenous administration, and 0.61-2.21 and 0.19-1.07 folds higher compared with intranasal solution and unmodified nanoparticles, respectively. Neuroprotective effect was evaluated using Mirror water maze task in rats with intracerebroventricular injection of ß-amyloid25-35 and ibotenic acid. The spatial learning and memory of Alzheimer's disease (AD) rats in STL-bFGF-NP group were significantly improved compared with AD model group, and were also better than other preparations. The results were consistent with the value of choline acetyltransferase activity of rat hippocampus as well as the histological observations of rat hippocampal region. The histopathology assays also confirmed the in vivo safety of STL-bFGF-NP. These results clearly indicated that STL-NP was a promising drug delivery system for peptide and protein drugs such as bFGF to enter the CNS and play the therapeutic role.

Cerebral protective and cognition-improving effects of sinapic acid in rodents.

We previously demonstrated that tenuifoliside B and 3,6'-disinapoylsucrose in Polygalae Radix, the root of Polygala tenuifolia WILLDENOW, inhibited potassium cyanide (KCN)-induced hypoxia and scopolamine-induced memory impairment in mice. Because both ingredients have a common sinapoyl moiety in their structure, we inferred that the sinapoyl moiety could inhibit hypoxia and memory impairment. In the present study to clarify the hypothesis, sinapic acid inhibited KCN-induced hypoxia and scopolamine-induced memory impairment as well as tenuifoliside B and 3,6'-disinapoylsucrose did. In addition, sinapic acid inhibited decompression- or bilateral carotid artery ligation-induced hypoxia (or mortality) and CO2-induced impairment in mice, and basal forebrain lesion-induced cerebral cholinergic dysfunction (decreases in acetylcholine concentration and choline acetyltransferase activity) in rats. These results, taken together, suggest the possibilities that sinapic acid is not only a very important moiety in the pharmacological activities of tenuifoliside B and 3,6'-disinapoylsucrose but also a candidate for a cerebral protective and cognition-improving medicine.

Cholinergic receptor blockade in prefrontal cortex and lesions of the nucleus basalis: implications for allocentric and egocentric spatial memory in rats.

In this study we have examined the involvement of the prefrontal cortex (PFC) along with the Nucleus basalis magnocellularis (NBM) in two types of spatial navigation tasks. We evaluated the effects of excitotoxic (ibotenate-induced) lesions of the NBM in an allocentric and an egocentric task in the Morris water maze, using sham operations for a comparison. In both cases we also assessed the effects of local cholinergic receptor blockade in the PFC by infusing the muscarinic receptor antagonist scopolamine (4 or 20 microg). Anatomically, the results obtained showed that this lesion produced a profound loss of acetylcholinesterase (AChE) positive cells in the NBM, and a loss of AChE positive fibres in most of the neocortex, but hardly in the medial PFC. Behaviourally, such lesions led to a severe impairment in the allocentric task. Intraprefrontal infusions of scopolamine led to a short-lasting impairment in task performance when the high dose was used. In the second experiment, using the same surgical manipulations, we examined the performance in the egocentric task. Like in the allocentric task animals with NBM lesions were also impaired, but with continued training they acquired a level of performance similar to the sham-operated ones. This time, infusions of scopolamine in the medial PFC led to a severe disruption of performance in both groups of animals. We conclude that acetylcholine in the medial PFC is important for egocentric but not allocentric spatial memory, whereas the NBM is involved in the learning of both tasks, be it to a different degree.

Low levels of estrogen significantly diminish axonal sprouting after entorhinal cortex lesions in the mouse.

This study tested the hypothesis that estrogen enhances axonal sprouting in the hippocampal formation in the female mouse. The entorhinal cortex was unilaterally lesioned with ibotenic acid in control mice and in ovariectomized mice that were treated with a high dose of, a moderate dose of, or zero estrogen supplementation pellets. Four weeks later the density of staining for synaptophysin immunoreactivity and acetylcholinesterase (AChE) histochemistry was measured in the molecular layer of the dentate gyrus. In control mice, lesions of the lateral part of the entorhinal cortex increased synaptophysin and acetylcholinesterase staining (i.e., indicative of axonal sprouting) in the outer one-third of the molecular layer of the dentate gyrus. Mice receiving high and moderate estrogen supplementation displayed the same sprouting response; however, in ovariectomized mice the sprouting response was significantly reduced (to nearly nothing). Thus, in ovariectomized compared with control mice the lesion-induced sprouting response is severely blunted, and this effect is reversed by estrogen supplementation. Together, these findings suggest that estrogen plays a prominent role in promoting neuronal plasticity and remodeling in the dentate gyrus.

Influence of the ventral hippocampal formation on plasma vasopressin, hypothalamic-pituitary-adrenal axis, and behavioral responses to novel acoustic stress.

The ventral hippocampal formation (vHF) seems to constrain diverse responses to psychological stimuli, and disruption of this function may underlie severe neuropsychiatric diseases. In particular, the ventral subiculum inhibits hypothalamic-pituitary-adrenal axis (HPA) activity following psychological, but not systemic, stressors. Despite the difficulty in interpreting such HPA responses, they have been relied upon to further characterize vHF function, because increased HPA axis activity is implicated in neuropsychiatric disturbances, and reliance on behavioral and cognitive data is even more problematic. Plasma arginine vasopressin (pAVP), which is inhibited by psychological stimuli and is also implicated in diverse neuropsychiatric diseases, provides a less ambiguous measure of CNS function. To test if its inhibition by psychological stress is also mediated by the vHF, we conducted two studies. In the first, pAVP and behavioral responses to novel acoustic stress were assessed in rats with bilateral excitotoxic lesions of the ventral subiculum and the ventral hippocampus. The subiculum lesions blocked the fall in pAVP and enhanced escape behaviors, whereas the hippocampal lesions produced responses intermediate to those in the subiculum-lesioned and control rats. In the second study, the pAVP response was similarly blocked by small lesions restricted to those vHF subfields which project to the neuroendocrine hypothalamus, compared to the response in animals with lesions in other vHF subfields. These results indicate that discrete projections from the vHF inhibit the pAVP response to psychological stimuli, and suggest that pAVP may provide a reliable probe of vHF activity.

Descending facilitatory influences from the rostral medial medulla mediate secondary, but not primary hyperalgesia in the rat.

Prolonged nociceptive input following peripheral injury results in hyperalgesia (enhanced response to a noxious stimulus), which is thought to occur as a consequence of sensitization of primary afferent nociceptors and enhanced excitability of spinal dorsal horn nociceptive neurons (central sensitization). Since there is often an expansion of hyperalgesia to tissue adjacent, and even distant from the site of injury (secondary hyperalgesia), it is thought that this phenomenon primarily involves mechanisms of central modulation/plasticity. In contrast, hyperalgesia observed at the site of tissue injury (primary hyperalgesia) involves peripheral mechanisms. In the current study, we examined the relative contribution of descending nociceptive facilitatory systems from the rostral medial medulla to enhanced behavioral nociceptive responses in models of primary and secondary hyperalgesia in awake rats. The effect of bilateral rostral medial medulla lesions produced by the soma-selective neurotoxin ibotenic acid was determined in three different models of cutaneous thermal hyperalgesia following peripheral inflammation: (i) intraplantar injection of carrageenan into the hindpaw (model of primary hyperalgesia); (ii) intra-articular injection of carrageenan/kaolin into the knee of the hind leg (model of secondary hyperalgesia); and (iii) topical application of mustard oil to the hind leg (model of secondary hyperalgesia). Compared with sham lesion animals, a bilateral lesion of the rostral medial medulla completely blocked thermal hyperalgesia in the two models of secondary hyperalgesia (intra-articular carrageenan/kaolin injection into the knee and topical mustard oil application to the hind leg), but was ineffective in blocking facilitation of the thermal paw withdrawal response in the model of primary hyperalgesia (intraplantar carrageenan injection into the hindpaw). These results suggest that primary and secondary hyperalgesia are differentially modulated in the CNS, and support the notion that descending nociceptive facilitatory influences from the rostral medial medulla significantly contribute to secondary, but not primary, hyperalgesia.

The function of the pedunculopontine nucleus in the preparation and execution of an externally-cued bar pressing task in the rat.

In the present study the role of the pedunculopontine nucleus (PPN) in the preparation and execution of an externally-cued rewarded motor act was investigated. Animals were instructed to press down a lever at the presentation of a combined visual and acoustic signal and were required to hold down the lever until a trigger stimulus occurred after an unpredictable delay ranging from 2 to 4 s. The trigger stimulus required animals to release the lever and to press a second lever for food reinforcement. The time between instruction and trigger signals represented the preparation phase preceding movement. Unilateral ibotenic acid-induced focal degeneration of pedunculopontine neurons did not influence either reaction and movement times, or capacity of the animals to correctly respond to presentation of stimuli of behavioral significance. On the contrary, bilateral lesions increased both reaction and movement times, and dramatically reduced the percentage of correct responses. The analysis of incorrect responses suggested that the most striking deficit exhibited by the animals following the bilateral lesion was a lack of conditioned response to the signal initiating each trial. However, the animals retained the capability to respond correctly in some trials, and were able to collect the reward when delivered outside the behavioral context. Histological analysis of lesions showed that in addition to loss of neurons within the pedunculopontine region, reduction of tyrosine-hydroxylase positive neurons had occurred in the pars compacta of the substantia nigra. The data suggest that the PPN is involved in the preparation and execution of externally-cued movements, and demonstrate that its destruction mimics the main effects produced by the dopaminergic denervation of the dorsal striatum.

Differential alterations of cortical cholinergic and neurotensin markers following ibotenic acid lesions of the nucleus basalis magnocellularis.

The present study determined whether cortical cholinergic neurons recover functionally following the loss of afferent projections from the nucleus basalis magnocellularis (nbm). At various time points following ibotenic acid lesions of the nbm, choline acetyltransferase (ChAT) activity or the capacity of cortical cholinergic neurons to synthesize [3H]acetylcholine (ACh) from the precursor molecule [3H]choline were measured in the frontoparietal cortex. First, cortical ChAT activity was decreased by 21% and 35% on the side ipsilateral to the lesion at 1 and 2 weeks following the nbm lesion, respectively. By 6 weeks following nbm lesions, cortical ChAT activity returned to control levels and remained at control levels at 10 weeks following nbm lesions. However, by 13 weeks following nbm lesions, we observed a 21% increase in ChAT activity on the side ipsilateral to the lesion. ChAT activity in the nbm remained unchanged over the time course studied. Secondly, there was a parallel reduction (by 43%) in the capacity of frontoparietal cortex slices from the side ipsilateral to the lesion to synthesize [3H]ACh by 2 weeks following nbm lesions. By 13 weeks following the lesion there was a significant increase (29%) in the synthetic capacity of cortical cholinergic neurons compared to the 2 week time point. Third, the content of neurotensin in the frontoparietal cortex was significantly decreased by 25% and 36%, at 2 weeks and 13 weeks following nbm lesions, respectively. Neurotensin levels in the nbm were not affected by ibotenic acid lesions. In contrast, [125I]neurotensin binding sites in the frontal or parietal cortex were not altered at 2 weeks following nbm lesions.(ABSTRACT TRUNCATED AT 250 WORDS)

Enhancement of tonic and phasic events of rapid eye movement sleep following bilateral ibotenic acid injections into centralis lateralis thalamic nucleus of cats.

The excitotoxin ibotenic acid (1.2-2.6 microliters of 50 micrograms/microliters) was injected bilaterally into the thalamic centralis lateralis nucleus of chronically implanted cats in order to study the effects of tonic excitation followed by destruction of perikarya on the sleep-waking cycle and its electrographic correlates. Ibotenate injections were performed under mild ketamine anaesthesia. Immediately afterwards, the animals showed behavioural arousal accompanied first by ocular nystagmiform movements and then by pontogeniculooccipital waves. By 6-10 h post-injection, the numbers of rapid eye movement sleep episodes, but not their duration, increased compared to the preinjection control period. The injection sites were histologically confirmed using conventional Thionin stains. Additional control was provided by retrograde transport of wheat-germ agglutinin conjugated with horseradish peroxidase. The present results suggest that a population of neurons important for ocular saccades, pontogeniculooccipital waves, and the state of desynchronized sleep is present in the internal medullary lamina, in particular in the centralis lateralis nuclei.

The neurotoxic actions of ibotenic acid on cholinergic and opioid peptidergic systems in the central nervous system of the rat.

The neurotoxic effects produced by ibotenic acid (IA) induced chemical lesions of the central nervous system (CNS) cholinergic system were examined on the opioid peptidergic system in adult rats. Forebrain cholinergic systems were bilaterally lesioned by the infusion of IA (1 or 5 micrograms/site) into the nucleus basalis magnocellularis (NBM). One week after the injections, the animals were sacrificed, and activities of acetylcholinesterase (AChE), choline acetyltransferase (ChAT) and concentrations of beta-endorphin (beta-End) and Met-enkephalin (Met-Enk) were measured in different brain regions. Animals treated with IA showed a decrease in the activity of ChAT (-24%), AChE (-36%) and beta-End level (-33%) in the frontoparietal cortex (FC). For the first time we report that these changes were associated with a compensatory increase in the activity of ChAT (+27%), AChE (+25%), beta-End level (+66%) in the remaining part of the cortex, i.e. cortex devoid of frontal cortex (C-FC). Met-enkephalin level increased by 59% in the frontoparietal cortex and did not change in the cortex devoid of frontal cortex upon IA treatment. These results suggest that IA treatment results in changes in the activity of cortical ChAT and AChE, and beta-End level in the same direction. Injection of IA in the NBM did not cause a change in the activity of ChAT or AChE in other brain regions such as hippocampus, striatum or midbrain. In addition to cortex devoid of frontal cortex, midbrain also showed a significant increase in the beta-End level in the IA treated animals. However, pituitary beta-End decreased in the neurotoxin treated animals.(ABSTRACT TRUNCATED AT 250 WORDS)