An Angiotensin-Responsive Connection from the Lamina Terminalis to the Paraventricular Nucleus of the Hypothalamus Evokes Vasopressin Secretion to Increase Blood Pressure in Mice.

Blood pressure is controlled by endocrine, autonomic, and behavioral responses that maintain blood volume and perfusion pressure at levels optimal for survival. Although it is clear that central angiotensin type 1a receptors (AT1aR; encoded by the Agtr1a gene) influence these processes, the neuronal circuits mediating these effects are incompletely understood. The present studies characterize the structure and function of AT1aR neurons in the lamina terminalis (containing the median preoptic nucleus and organum vasculosum of the lamina terminalis), thereby evaluating their roles in blood pressure control. Using male Agtr1a-Cre mice, neuroanatomical studies reveal that AT1aR neurons in the area are largely glutamatergic and send projections to the paraventricular nucleus of the hypothalamus (PVN) that appear to synapse onto vasopressin-synthesizing neurons. To evaluate the functionality of these lamina terminalis AT1aR neurons, we virally delivered light-sensitive opsins and then optogenetically excited or inhibited the neurons while evaluating cardiovascular parameters or fluid intake. Optogenetic excitation robustly elevated blood pressure, water intake, and sodium intake, while optogenetic inhibition produced the opposite effects. Intriguingly, optogenetic excitation of these AT1aR neurons of the lamina terminalis also resulted in Fos induction in vasopressin neurons within the PVN and supraoptic nucleus. Further, within the PVN, selective optogenetic stimulation of afferents that arise from these lamina terminalis AT1aR neurons induced glutamate release onto magnocellular neurons and was sufficient to increase blood pressure. These cardiovascular effects were attenuated by systemic pretreatment with a vasopressin-1a-receptor antagonist. Collectively, these data indicate that excitation of lamina terminalis AT1aR neurons induces neuroendocrine and behavioral responses that increase blood pressure.SIGNIFICANCE STATEMENT Hypertension is a widespread health problem and risk factor for cardiovascular disease. Although treatments exist, a substantial percentage of patients suffer from "drug-resistant" hypertension, a condition associated with increased activation of brain angiotensin receptors, enhanced sympathetic nervous system activity, and elevated vasopressin levels. The present study highlights a role for angiotensin Type 1a receptor expressing neurons located within the lamina terminalis in regulating endocrine and behavioral responses that are involved in maintaining cardiovascular homeostasis. More specifically, data presented here reveal functional excitatory connections between angiotensin-sensitive neurons in the lamina terminals and vasopressin neurons in the paraventricular nucleus of the hypothalamus, and further indicate that activation of this circuit raises blood pressure. These neurons may be a promising target for antihypertensive therapeutics.

Effects of Delphinidin on Pathophysiological Signs of Nucleus Basalis of Meynert Lesioned Rats as Animal Model of Alzheimer Disease.

Alzheimer's disease (AD) is an advanced neurodegenerative disorder greatly accompanied by cognitive deficits, oxidative stress, inflammation, amyloid plaques deposition, and acetylcholinesterase (AChE) hyper-activation. Growing evidence suggests natural compounds with antioxidant and anti-inflammatory features improve pathophysiological signs of AD. The present study was designed to investigate the effects of Delphinidin (25, 50 mg/kg) as an anthocyanidin on spatial memory impairment and AD hallmarks such as hippocampal AChE activity, amyloid plaques deposition, oxidative stress and expression of amyloid precursor protein (APP), AChE, and amyloid beta (Aß) proteins in nucleus basalis of Meynert (NBM) lesioned rats as the most prevalent animal model of AD. Interestingly, Delphinidin-treated animals showed a significant decrease in escape latency and distance moved. Furthermore, in probe test, NBM lesioned rats treated with both doses of Delphinidin spent more time in the target quadrant zone in Morris water maze task. It could also interact with catalytic site of AChE enzyme and inhibits acetylcholine hydrolysis in in vitro and in vivo conditions. In addition, Delphinidin could scavenge additional produced reactive oxygen molecules dose dependently. Our immunoblotting analysis confirmed high dose of Delphinidin reduced AChE, APP and Aß contents in AD model. Staining of hippocampus tissue revealed that Delphinidin treatment decreased amyloid plaques formation in NBM lesion rats. It seems that Delphinidin is a plate-like molecule intercalated between ß-plated sheets related to Aß molecules and inhibited amyloid fibril formation. Altogether, Delphinidin and Delphinidin-rich fruits could be suggested as a therapeutic adjuvant in AD and other related cognitive disorders.

Activation of GSK-3 disrupts cholinergic homoeostasis in nucleus basalis of Meynert and frontal cortex of rats.

The cholinergic impairment is an early marker in Alzheimer's disease (AD), while the mechanisms are not fully understood. We investigated here the effects of glycogen synthase kinse-3 (GSK-3) activation on the cholinergic homoeostasis in nucleus basalis of Meynert (NBM) and frontal cortex, the cholinergic enriched regions. We activated GSK-3 by lateral ventricular infusion of wortmannin (WT) and GF-109203X (GFX), the inhibitors of phosphoinositol-3 kinase (PI3-K) and protein kinase C (PKC), respectively, and significantly decreased the acetylcholine (ACh) level via inhibiting choline acetyl transferase (ChAT) rather than regulating acetylcholinesterase (AChE). Neuronal axonal transport was disrupted and ChAT accumulation occurred in NBM and frontal cortex accompanied with hyperphosphorylation of tau and neurofilaments. Moreover, ChAT expression decreased in NBM attributing to cleavage of nuclear factor-κB/p100 into p52 for translocation into nucleus to lower ChAT mRNA level. The cholinergic dysfunction could be mimicked by overexpression of GSK-3 and rescued by simultaneous administration of LiCl or SB216763, inhibitors of GSK-3. Our data reveal the molecular mechanism that may underlie the cholinergic impairments in AD patients.

Neuroprotective activity of hydroponic Teucrium polium following bilateral ovariectomy.

Ovariectomy is known as "surgical menopause" with decreased levels of estrogen in female rodents. Its reported risks and adverse effects include cognitive impairment. The action of hydroponic Teucrium polium on nucleus basalis of Meynert (bnM) neurons following 6 weeks of ovariectomy was carried out. The analysis of spike activity was observed by on-line selection and the use of a software package. Early and late tetanic, - posttetanic potentiation and depression of neurons to high frequency stimulation of hippocampus were studied. The complex averaged peri-event time and frequency histograms were constructed. The histochemical study of the activity of Са(2+)-dependent acid phosphatase was observed. In conditions of hydroponic Teucrium polium administration, positive changes in neurons and gain of metabolism leading to cellular survival were revealed. The administration of Teucrium polium elicited neurodegenerative changes in bnM.

Effects of Zizyphus jujube extract on memory and learning impairment induced by bilateral electric lesions of the nucleus Basalis of Meynert in rat.

Alzheimer's disease (AD) is a common neurodegenerative condition that affects the elderly population. Its primary symptom is memory loss. The memory dysfunction in AD has been associated with cortical cholinergic deficiency and loss of cholinergic neurons of the nucleus basalis of Meynert (NBM). Zizyphus jujube (ZJ) activates choline acetyltransferase and may have beneficial effects in AD patients. This study investigates the effect of ZJ extract in intact rats and in rat model of AD. 49 male Wistar rats were divided into seven equal groups (1-control, without surgery, received water), 2-AD (bilateral NBM lesion, received water), 3 and 4-AD + ZJ (NBM bilateral lesion, received ZJ extract 500 and 1,000 mg/kg b.w. per day for 15 days), 5-sham (surgery: electrode introduced into NBM without lesion, received water), 6 and 7-without surgery and lesion, received ZJ extract-the same as groups 3 and 4). The learning and memory performance were assessed using passive avoidance paradigm, and the memory cognition for spatial learning and memory was evaluated by Morris water maze. In shuttle box test ZJ extract (500 and 1,000 mg) significantly increased step-through latency in AD + ZJ groups compared with AD group. In Morris water maze test (in probe day), both AD + ZJ groups receiving extract (500 and 1,000 mg) demonstrated significant preference for the quadrant in which the platform was located on the preceding day as compared with AD group. Our results suggested that ZJ has repairing effects on memory and behavioral disorders produced by NBM lesion in rats and may have beneficial effects in treatment of AD patients.

[Repressional effects of the glutamate antibodies on expression of Dffb gene in the brain of rats with experimental Alzheimer's disease].

The intranasal administration of glutamate antibodies in the dose of 300 microg/kg one hour after damage on the level of mRNA expression of Dffb gene which codes caspase-activated DNase which participates in intranucleosome fragmentation of genome DNA in apoptosis was investigated in experimental Alzheimer's disease induced by injection of neurotoxic fragment of beta-amyloid protein Abeta25-35 in Meynert basal magnocellular nuclei on rats. On the Day 3 after Abeta25-35 injection is observed significant decrease of the level of mRNA expression of Dffb gene in prefrontal cortex in 37%, and in hippocampus in 62% in the experiment group versus the control group. These differences were not found in the hypothalamus when comparing the experimental and control animals. It was suggested that repressive effect of glutamate antibodies on the level of mRNA expression of Dffb gene reflects stabilization of processes taking place in brain cells in experimental Alzheimer's disease, and in its turn the intensiveness of nerve and glial cells apoptotic death is decreased.

Specific auditory memory induced by nucleus basalis stimulation depends on intrinsic acetylcholine.

Although the cholinergic system has long been implicated in the formation of memory, there had been no direct demonstration that activation of this system can actually induce specific behavioral memory. We have evaluated the "cholinergic-memory" hypothesis by pairing a tone with stimulation of the nucleus basalis (NB), which provides acetylcholine to the cerebral cortex. We found that such pairing induces behaviorally-validated auditory memory. NB-induced memory has the key features of natural memory: it is associative, highly-specific and rapidly induced. Moreover, the level of NB stimulation controls the amount of detail in memory about the tonal conditioned stimulus. While consistent with the hypothesis that properly-timed release of acetylcholine (ACh) during natural learning is sufficient to induce memory, pharmacological evidence has been lacking. This study asked whether scopolamine, a muscarinic antagonist, impairs or prevents the formation of NB-induced memory. Adult male rats were first tested for responses (disruption of ongoing respiration) to tones (1-15 kHz), constituting a pre-training behavioral frequency generalization gradient (BFGG). Then, they received a single session of 200 trials of a tone (8.00 kHz, 70 dB, 2 s) paired with electrical stimulation of the NB (100 Hz, 0.2 s). Immediately after training, they received either scopolamine (1.0 mg/kg, i.p.) or saline. Twenty-four hours later, they were tested for specific memory by obtaining post-training BFGGs. The saline group developed CS-specific memory, manifested by maximum increase in response specific to the CS frequency band. In contrast, the scopolamine group exhibited no such memory. These findings indicate that NB-induced specific associative behavioral memory requires the action of intrinsic acetylcholine at muscarinic receptors, and supports the hypothesis that natural memory formation engages the nucleus basalis and muscarinic receptors.

Estrogen enhances expression of the complement C5a receptor and the C5a-agonist evoked calcium influx in hormone secreting neurons of the hypothalamus.

In the present study we examined presence of the complement C5a receptor (C5aR) in hypothalamic neurosecretory neurons of the rodent brain and effect of estrogen on C5aR expression. Whole cell patch clamp measurements revealed that magnocellular neurons in the supraoptic and paraventricular nuclei of hypothalamic slices of the rats responded to the C5aR-agonist PL37-MAP peptide with calcium ion current pulses. Gonadotropin-releasing hormone (GnRH) producing neurons in slices of the preoptic area of the mice also reacted to the peptide treatment with inward calcium current. PL37-MAP was able to evoke the inward ion current of GnRH neurons in slices from ovariectomized animals. The amplitude of the inward pulses became higher in slices obtained from 17beta-estradiol (E2) substituted mice. Calcium imaging experiments demonstrated that PL37-MAP increased the intracellular calcium content in the culture of the GnRH-producing GT1-7 cell line in a concentration-dependent manner. Calcium imaging also showed that E2 pretreatment elevated the PL37-MAP evoked increase of the intracellular calcium content in the GT1-7 cells. The estrogen receptor blocker Faslodex in the medium prevented the E2-evoked increase of the PL37-MAP-triggered elevation of the intracellular calcium content in the GT1-7 cells demonstrating that the effect of E2 might be related to the presence of estrogen receptor. Real-time PCR experiments revealed that E2 increased the expression of C5aR mRNA in GT1-7 neurons, suggesting that an increased C5aR synthesis could be involved in the estrogenic modulation of calcium response. These data indicate that hypothalamic neuroendocrine neurons can integrate immune and neuroendocrine functions. Our results may serve a better understanding of the inflammatory and neurodegeneratory diseases of the hypothalamus and the related neuroendocrine and autonomic compensatory responses.

The role of the nucleus basalis magnocellularis in fear conditioning consolidation in the rat.

The nucleus basalis magnocellularis (NBM) is known to be involved in the memorization of several conditioned responses. To investigate the role of the NBM in fear conditioning memorization, this neural site was subjected to fully reversible tetrodotoxin (TTX) inactivation during consolidation in adult male Wistar rats that had undergone fear training to acoustic conditioned stimulus (CS) and context. TTX was stereotaxically administered to different groups of rats at increasing intervals after the acquisition session. Memory was assessed as the conditioned freezing duration measured during retention testing, always performed 72 and 96 h after TTX administration. In this way, there was no interference with normal NBM function during either acquisition or retrieval phases, allowing any amnesic effect to be due only to consolidation disruption. The results show that for contextual fear response memory consolidation, NBM functional integrity is necessary up to 24 h post-acquisition. On the other hand, NBM functional integrity was shown to be necessary for memory consolidation of the acoustic CS fear response only immediately after acquisition and not 24-h post-acquisition. The present findings help to elucidate the role of the NBM in memory consolidation and better define the neural circuits involved in fear memories.

Neurochemical correlates of differential neuroprotection by long-term dietary creatine supplementation.

Dietary supplementation with creatine has proven to be beneficial in models of acute and chronic neurodegeneration. We report here data on the neurochemical correlates of differential protection of long-term creatine supplementation in two models of excitotoxicity in rats, as well as in the mouse model for ALS (G93A mice). In rats, the fall in cholinergic and GABAergic markers due to the excitotoxic death of intrinsic neurons caused by intrastriatal infusion of the neurotoxin, ibotenic acid, was significantly prevented by long-term dietary supplementation with creatine. On the contrary, creatine was unable to recover a cholinergic marker in the cortex of rats subjected to the excitotoxic death of the cholinergic basal forebrain neurons. In G93A mice, long-term creatine supplementation marginally but significantly increased mean lifespan, as previously observed by others, and reverted the cholinergic deficit present in some forebrain areas at an intermediate stage of the disease. In both rats and mice, creatine supplementation increased the activity of the GABAergic enzyme, glutamate decarboxylase, in the striatum but not in other brain regions. The present data point at alterations of neurochemical parameters marking specific neuronal populations, as a useful way to evaluate neuroprotective effects of long-term creatine supplementation in animal models of neurodegeneration.

[Effects of the Panax notoginseng saponins on the level of synaptophysin protein in brain in rat model with lesion of Meynert].

OBJECTIVE: To observe the protective effect of Panax notoginseng saponins (PNS) on the level of synaptophysin ptotein in brain in rat model with Alzheimer's disease (AD). METHOD: The AD rat models were established by intra-peritoneal injection of D-galactose combined with excitatory neurotoxin ibotenic acid injection into bilateral nbM. The activity and content of synaptophysin protein in brain were determined by immunohistochemistry analysis. RESULT: PNS could reduce the lesion of level of synaptophysin protein in brain, as compared with those of model group's rats. CONCLUSION: PNS plays a protective role by reducing down of the level of synaptophysin protein in brain in lesion of AD animal model.

Direct, complex effects of estrogens on basal forebrain cholinergic neurons.

Although controversial, estrogens remain one of the few agents purported to influence the incidence of Alzheimer's disease and one of their postulated mechanisms of action is their effects on basal forebrain cholinergic neurons. However, it is unclear whether the responses of cholinergic neurons to estrogens are direct or mediated via the retrograde influences of neurotrophins, known to be induced by estrogens in the hippocampus and neocortex. In the present study, we explore the issue of the primary site of action of estrogens by studying the regulation of expression of genes that characterize mature cholinergic neurons, i.e., choline acetyltransferase, trkA, and p75(NTR) in the medial septum and the nucleus basalis complex. In parallel, we study the hippocampal expression of NGF, BDNF, and NT-3, i.e., neurotrophins with known trophic roles on cholinergic neurons. Gene expression is studied by RT-PCR in ovariectomized female rats with and without estrogen supplementation within the physiological estradiol range and in rats with complete fimbria-fornix transactions treated with estrogen or vehicle. To clarify mechanisms of estrogen transduction in cholinergic neurons, we study the effects of estrogen treatment on fimbria-fornix-lesioned mice with genetic ablations of ER subtypes alpha and beta. The results of the present study suggest that, while estrogens do regulate BDNF expression in the hippocampus and neocortex, they also exert stimulatory non-trophic effects on basal forebrain cholinergic neurons, primarily on ChAT expression. Cholinergic neurons retain their ability to respond to estrogens after their complete separation from the hippocampus. The elimination of ERalpha alters significantly the phenotypic responsiveness of cholinergic neurons to estrogens, whereas elimination of ERbeta appears to have no effect. Our findings support the idea that estrogens directly enhance cholinergic neuron function and that ERalpha plays a significant role in transducing these regulatory effects.

Aging and cholinergic deafferentation alter GluR1 expression in rat frontal cortex.

Previously, we demonstrated that plasticity of frontal cortex is altered in aging rats: lesions of the nucleus basalis magnocellularis (NBM) produce larger declines in dendritic morphology in frontal cortex of aged rats compared to young adults. Cholinergic afferents from the NBM modulate glutamatergic transmission in neocortex, and glutamate is known to be involved in dendritic plasticity. To begin to identify possible mechanisms underlying age-related differences in plasticity after NBM lesion, we assessed the effect of cholinergic deafferentation on expression of the AMPA receptor subunit GluR1 in frontal cortex of young adult and aging rats. Young adult, middle-aged, and aged rats received sham or 192 IgG-saporin lesions of the NBM, and an unbiased stereological technique was used to estimate the total number of intensely GluR1-immunopositive neurons in layer II-III of frontal cortex. While the number of GluR1-positive neurons was increased in both middle-aged and aged rats, lesions markedly increased the number of intensely GluR1-immunopositive neurons in frontal cortex of young adult rats only. This age-related difference in lesion-induced expression of AMPA receptor subunit protein could underlie the age-related differences in dendritic plasticity after NBM lesions.

Stimulation of cortical acetylcholine release by orexin A.

The basal forebrain cholinergic system is a critical component of the neurobiological substrates underlying attentional function. Orexin neurons are important for arousal and maintenance of wakefulness and are found in the area of the hypothalamus previously shown to project to the basal forebrain. We used dual-probe in vivo microdialysis in rats to test the hypothesis that orexin A (OxA) increases cortical acetylcholine (ACh) release. Intrabasalis administration of OxA (0, 0.1, 10.0 microM via reverse dialysis) dose-dependently increased ACh release within the prefrontal cortex (PFC). In a separate group of animals, local (intra-PFC) administration of OxA via reverse dialysis was found to have no significant effect on ACh release. In order to obtain anatomical corroboration of the basal forebrain as a site of orexin modulation of corticopetal cholinergic activity, we used immunohistochemistry to examine the relationship between orexin fibers and cholinergic neurons in the basal forebrain. We observed widespread distribution of orexin-immunoreactive fibers in cholinergic regions of the basal forebrain, particularly in more rostral areas where frequent instances of apparent appositional contact were observed between orexin fibers and choline acetyltransferase-positive cell bodies. Collectively, these data suggest that orexin projections to the basal forebrain form an important link between hypothalamic arousal and forebrain attentional systems.

Effect of Polygala tenuifolia root on behavioral disorders by lesioning nucleus basalis magnocellularis in rat.

UNLABELLED: We investigated whether an aqueous extract of Polygala tenuifolia Willd (PTW) could improve the rats' memory and behavioral disorders produced by lesioning nucleus basalis magnocellularis (NBM) in rats. The animals were divided into four groups for surgery, and following that they were orally administered PTW extract for 7 and 21 days. Each group consisted of eight male Sprague-Dawley rats and were treated as follows: CONTROL: no surgery (n = 8), PBS: 1M (mol/L) phosphate buffered saline (n = 8), IBO: 0.12 M (n = 8), QUIS: 0.12 M (n = 8). Two 0.5 microL injections were made in the vicinity of the bilateral side of the nucleus basalis magnocellularis (NBM). All rats were tested in the neurological tests and the step-through passive avoidance memory test during pre-surgery, surgery and post-surgery drug treatment. The results suggest that PTW extract has some repairing effects on the memory and behavioral disorders produced by lesioning of the NBM in rats.

Neuroprotective effect of developmental docosahexaenoic acid supplement against excitotoxic brain damage in infant rats.

Long-chain polyunsaturated fatty acid (LC-PUFA) composition of neural membranes is a key factor for brain development, in chemical communication of neurons and probably also their survival in response to injury. Viability of cholinergic neurons was tested during brain development following dietary supplementation of fish oil LC-PUFAs (docosahexaenoic acid [DHA], eicosapentaenoic acid, arachidonic acid) in the food of mother rats. Excitotoxic injury was introduced by N-methyl-D,L-aspartate (NMDA) injection into the cholinergic nucleus basalis magnocellularis of 14-day-old rats. The degree of loss of cholinergic cell bodies, and the extend of axonal and dendritic disintegration were measured following immunocytochemical staining of cell bodies and dendrites for choline acetyltransferase and p75 low-affinity neurotrophin receptor and by histochemical staining of acetylcholinesterase-positive fibres in the parietal neocortex. The impact of different feeding regimens on fatty acid composition of neural membrane phospholipids was also assayed at 12 days of age. Supplementation of LC-PUFAs resulted in a resistance against NMDA-induced excitotoxic degeneration of cholinergic neurones in the infant rats. More cholinergic cells survived, the dendritic involution of surviving neurons in the penumbra region decreased, and the degeneration of axons at the superficial layers of parietal neocortex also attenuated after supplementing LC-PUFAs. A marked increment in DHA content in all types of phospholipids was obtained in the forebrain neuronal membrane fraction of supplemented rats. It is concluded that fish oil LC-PUFAs, first of all DHA, is responsible for the neuroprotective action on developing cholinergic neurons against glutamate cytotoxicity.

Cholinergic modulation of experience-dependent plasticity in human auditory cortex.

The factors that influence experience-dependent plasticity in the human brain are unknown. We used event-related functional magnetic resonance imaging (fMRI) and a pharmacological manipulation to measure cholinergic modulation of experience-dependent plasticity in human auditory cortex. In a differential aversive conditioning paradigm, subjects were presented with high (1600 Hz) and low tones (400 Hz), one of which was conditioned by pairing with an electrical shock. Prior to presentation, subjects were given either a placebo or an anticholinergic drug (0.4 mg iv scopolamine). Experience-dependent plasticity, expressed as a conditioning-specific enhanced BOLD response, was evident in auditory cortex in the placebo group, but not with scopolamine. This study provides in vivo evidence that experience-dependent plasticity, evident in hemodynamic changes in human auditory cortex, is modulated by acetylcholine.

Selective behavioral and neurochemical effects of cholinergic lesions produced by intrabasalis infusions of 192 IgG-saporin on attentional performance in a five-choice serial reaction time task.

The effects of the cholinergic immunotoxin 192 IgG-saporin (SAP) (0.0, 0.15, or 0.45 microg/microl; 0.5 microl/hemisphere) infused into the area of the nucleus basalis magnocellularis (NBM) of rats were tested in a five-choice serial reaction time task (5CSRTT) designed to assess visual attention. The effects of this manipulation on acetylcholine efflux in the medial frontal cortex were determined using in vivo microdialysis during the 5CSRTT. Rats with extensive lesions of the NBM (SAP HIGH) showed an array of behavioral deficits in the 5CSRTT hypothesized to represent deficits in central executive function that were associated with severe deficits in accuracy. Lengthening the stimulus duration ameliorated these deficits. Rats with restricted lesions of the NBM (SAP LOW) showed impairments over time on task when tested under standard conditions that were exacerbated by increases in the event rate. The number of choline acetyltransferase-immunoreactive cells in the area of the NBM but not the vertical limb of the diagonal band correlated significantly with accuracy in the task. SAP HIGH rats had significantly lower levels of cortical acetylcholine (ACh) efflux relative to SHAM both before and during the 5CSRTT. SAP LOW rats showed significantly higher levels of cortical ACh efflux before but not during the 5CSRTT. Cortical ACh efflux increased in all rats with the onset of the attentional task. These data provide the first direct evidence for a relationship between selective damage in the basal forebrain with decreased cortical ACh efflux and impaired attentional function.

Differential changes in rat cholinergic parameters subsequent to immunotoxic lesion of the basal forebrain nuclei.

The degree of lesion produced by 192 IgG-saporin relative to controls was compared using three independent methods. Microdialyzed acetylcholine (ACh), choline acetyltransferase (ChAT) activity, and the rate of ACh synthesis were compared in the frontal cortex and hippocampus. Microdialysis of rats was performed 1 and 15 weeks post-lesion. In week 16, the rats were sacrificed after an injection of deuterated choline (Ch) for determination of the rate of ACh synthesis. ChAT activity was determined at the same timepoints in a separate set of rats. At 1 week, ChAT activity and microdialyzed ACh showed similar degrees of depletion. At 15 weeks, microdialyzed ACh was significantly lower than the synthesis rate in cortex, but not in hippocampus. A small increase in ChAT activity between 1 and 15 weeks was found in the cortex, but not hippocampus. In the hippocampus, however, the rate of ACh synthesis was significantly greater than ChAT activity. This was true for two doses of immunotoxin; the greater compensation occurring with the lesser lesion. Microdialyzed ACh levels were not different from the other measures in hippocampus. Residual cholinergic terminals in the hippocampus, but not frontal cortex, compensate for a selective cholinergic lesion by increasing the rate of synthesis and may thereby alleviate hippocampus-dependent behavioral deficits.

Postnatal treatment with ACTH-(4-9) analog ORG 2766 attenuates N-methyl-D-aspartate-induced excitotoxicity in rat nucleus basalis in adulthood.

It has been reported that the ACTH-(4-9) analog H-Met(O(2))-Glu-His-Phe-D-Lys-Phe-OH (ORG 2766) administered in adulthood has trophic effects on neuronal tissue and when given postnatally, it can induce long-lasting changes in brain development. In the present study, we investigated whether early postnatal treatment with ORG 2766 affects adult neuronal vulnerability, i.e. the sensitivity of cholinergic neurons against excitotoxic damage. Wistar rat pups received injections of ORG 2766 or saline on postnatal days 1, 3 and 5 and were then left undisturbed until adulthood. At the age of 6 months, the animals were subjected to unilateral lesion of magnocellular basal nucleus by infusion of high dose of N-methyl-D-aspartate (NMDA). The effects of the excitotoxic insult were studied 28 hours and 12 days after the lesion by measuring both the acute cholinergic and glial responses, and the final outcome of the degeneration process. Twenty eight hours after NMDA infusion, postnatally ACTH-(4-9)-treated animals showed stronger suppression of choline-acetyltransferase immunoreactivity and increased reaction of glial fibrillary acidic protein -immunopositive astrocytes in the lesioned nucleus compared to control animals. However, 12 days post-surgery, the NMDA-induced loss of cholinergic neurons, as well as the decrease of their acetylcholinesterase -positive fibre projections in the cortex, were less in ACTH-(4-9) animals. Our data indicate that the early developmental effects of ACTH-(4-9) influence intrinsic neuroprotective mechanisms and reactivity of neuronal and glial cells, thereby resulting in a facilitated rescuing mechanism following excitotoxic injury.