Involvement of neuronal nitric oxide synthase in cognitive impairment in isoflurane-treated rats

Laparotomy-Induced Peripheral Inflammation Activates NR2B Receptors on the Brain Mast Cells and Results in Neuroinflammation in a Vagus Nerve-Dependent Manner

Background: The pathophysiological mechanisms underlying postoperative cognitive dysfunction (POCD) remain unclear over the years. Neuroinflammation caused by surgery has been recognized as an important element in the development of POCD. Many studies also suggest that the vagus nerve plays an important role in transmitting peripheral injury signals to the central nervous system (CNS) and the resultant neuroinflammation. Previously, we have demonstrated that brain mast cells (BMCs), as the “first responders”, play a vital role in neuroinflammation and POCD. However, how the vagus nerve communicates with BMCs in POCD has not yet been clarified.

Methods: In the current study, we highlighted the role of the vagus nerve as a conduction highway in surgery-induced neuroinflammation for the first time. In our model, we tested if mice underwent unilateral cervical vagotomy (VGX) had less neuroinflammation compared to the shams after laparotomy (LP) at an early stage. To further investigate the roles of mast cells and glutamate in the process, we employed Kit^W-sh mice and primary bone marrow-derived MCs to verify the glutamate-NR2B axis on MCs once again.

Results: Our results demonstrated that there were higher levels of glutamate and BMCs activation as early as 4 h after LP. Meanwhile, vagotomy could partially block the increases and reduce neuroinflammation caused by peripheral inflammation during the acute phase. Excitingly, inhibition of NR2B receptor and knockout of mast cells can attenuateneuroinflammation induced by glutamate.

Conclusion: Taken together, our findings indicate that the vagus is a high-speed pathway in the transmission of peripheral inflammation to the CNS. Activation of BMCs triggered a neuroinflammatory cascade. Inhibition of NR2B receptor on BMCs can reduce glutamate-induced BMCs activation, neuroinflammation, and memory impairment, suggesting a novel treatment strategy for POCD.

Dexmedetomidine facilitates the expression of nNOS in the hippocampus to alleviate surgery-induced neuroinflammation and cognitive dysfunction in aged rats

Postoperative cognitive dysfunction (POCD) is a common complication in the postoperative nervous system of elderly patients. Surgery-induced hippocampal neuroinflammation is closely associated with POCD. Dexmedetomidine (DEX) is an effective α2-adrenergic receptor agonist, which can reduce inflammation and has neuroprotective effects, thereby improving postoperative cognitive dysfunction. However, the mechanism by which DEX improves POCD is currently unclear. The purpose of the present study was therefore to identify how DEX acted on POCD. Male Sprague Dawley rats with exposed carotid arteries were used to mimic POCD. Locomotor activity was accessed by the open field test and the Morris water maze was performed to estimate spatial learning, memory and cognitive flexibility. Following animal sacrifice, the hippocampus was collected and cell apoptosis was determined by terminal dexynucleotidyl transferase (TdT)-mediated dUTP nick end labeling staining. Subsequently, the expression of apoptosis-related proteins Bax, Bcl-2, cleaved caspase-3 and cleaved caspase-9 was determined by western blotting and the concentrations of TNF-α, IL-6, IL-1β and IL-10 were measured in serum using ELISA. Nitric oxide synthase and neuronal nitric oxide synthase activities in the hippocampus were also measured. The T lymphocyte subsets were analyzed by flow cytometry to evaluate the immune function in each group. Compared with the surgery group, DEX ameliorated POCD by improving cognitive dysfunctions and immune function loss, and attenuated neuroinflammation and neuronal apoptosis.

Isoflurane triggers the acute cognitive impairment of aged rats by damaging hippocampal neurons via the NR2B/CaMKII/CREB pathway

Isoflurane was responsible for acute neuronal impairment, but its potential molecular mechanisms in damaging hippocampal neurons had not been clearly understood. This study aimed to explore the underlying mechanism of how isoflurane affected the cognitive function of aged rats by damaging the hippocampal neurons. Acute cognitive impairment was found in aged Wistar rats via Morris water maze test and Y-maze test after isoflurane anesthesia in a dose-dependent manner compared with the control group in vivo. Isoflurane also decreased the viabilities and strengthened the apoptotic potential of hippocampal neurons by damaging the mitochondria in a time-dependent manner compared with the control group which was reported by MTT, immunofluorescent assay, flow cytometry and western blot assay in vitro. Isoflurane jeopardized hippocampal neurons by directly inactivating the NR2B/CaMKII/CREB pathway and its harmful effects could be ameliorated by adding CaMKII activator CdCl₂. These findings provided evidence that the cognitive ability of aged rats was injured by isoflurane exposure and isoflurane also inhibited the viability and enhanced the apoptosis of hippocampal neurons by damaging the mitochondria through inhibition of the NR2B/CaMKII/CREB pathway and its harmful roles could be partially ameliorated by CdCl₂. Our study demonstrated that isoflurane could cause acute neuronal damage and we provided fresh insights that contributed to the safe use of anesthetic agents and the prevention of PND in elderly people.

Sevoflurane-induced inflammation development: involvement of cholinergic anti-inflammatory pathway

Chronic inflammation plays an important role in the mechanisms underpinning the development of anesthesia-induced cognitive dysfunction. However, less is known about how anesthesia causes inflammation. One possibility is that the inflammation is related to alteration of the activity of the alpha 7 nicotinic acetylcholine receptor cholinergic anti-inflammatory pathway. This study analyzed the effect of sevoflurane administration on the cognitive function by using a novel object recognition test and Y-maze test, and on acetylcholinesterase activity and expression in hippocampal tissue by using an acetylcholinesterase assay kit and quantitative real-time PCR. This study also evaluated the effect of alpha 7 nicotinic acetylcholine receptor agonist PNU-282987 and antagonist methyllycaconitine on cognitive function and the level of hippocampal tumor necrosis factor-α in aged rats exposed to sevoflurane anesthesia. We found that 3% sevoflurane significantly impaired cognitive function and increased acetylcholinesterase activity by upregulating its expression in hippocampal tissue. Sevoflurane-induced impairment of cognitive function was significantly rescued by PNU-282987 but aggravated by methyllycaconitine. In addition to impairment of cognitive function, sevoflurane also significantly increased tumor necrosis factor-α level in plasma and hippocampal tissue. Similarly, this sevoflurane-induced change of tumor necrosis factor-α level in rats was antagonized by PNU-282987 but amplified by methyllycaconitine. In conclusion, our data show that the development of inflammation in sevoflurane-induced cognitive decline is associated with the downregulation of alpha 7 nicotinic acetylcholine receptor cholinergic anti-inflammatory pathway in aged rats.

Absence of Neuropathology With Prolonged Isoflurane Sedation in Healthy Adult Rats

BACKGROUND

The use of isoflurane sedation for prolonged periods in the critical care environment is increasing. However, isoflurane-mediated neurotoxicity has been widely reported. The goal of the present study was to determine whether long-term exposure to low-dose isoflurane in mechanically ventilated rodents is associated with evidence of neurodegeneration or neuroinflammation.

METHODS

Adult female Sprague-Dawley rats were used in this study. Experimental animals (n=11) were induced with 1.5% isoflurane, intubated, and given a neuromuscular blockade with α-cobratoxin. EEG electrodes were surgically implanted, subcutaneous precordial EKG Ag wire electrodes, and bladder, femoral artery, and femoral vein cannulas permanently placed. After these procedures, the isoflurane concentration was reduced to 0.5% and, in conjunction with the neuromuscular blockade, continued for 7 days. Arterial blood gases and chemistry were measured at 3 time points and core body temperature servoregulated and maintenance IV fluids were given during the 7 days. Experimental animals and untreated controls (n=9) were euthanized on day 7.

RESULTS

Immunohistochemical and cytochemical assays did not detect evidence of microgliosis, astrocytosis, neuronal apoptosis or necrosis, amyloidosis, or phosphorylated-tau accumulation. Blood glucose levels were significantly reduced on days 3/4 and 6/7 and partial pressure of oxygen was significantly reduced, but still within the normal range, on day 6/7. All other blood measurements were unchanged.

CONCLUSIONS

No neuropathologic changes consistent with neurotoxicity were detected in the brain after 1 week of continuous exposure to 0.5% isoflurane in healthy rats. These data suggest that even long exposures to low concentrations of isoflurane have no overt consequences on neuropathology.

Isoflurane Use in the Treatment of Super-Refractory Status Epilepticus is Associated with Hippocampal Changes on MRI

BACKGROUND

Refractory status epilepticus (RSE) is associated with high morbidity and mortality. Experts recommend aggressive management with continuous intravenous infusions or inhaled anesthetics such as isoflurane. However, there is concern that MRI changes in RSE reflect isoflurane neurotoxicity. We performed a case-control study to determine whether isoflurane is neurotoxic, based on MRI signal changes.

METHODS

We performed a retrospective case-control study of the incidence of MRI changes in RSE treated with and without isoflurane. Charts were reviewed for demographic and treatment information. T1, T2, and FLAIR sequences of MRIs were reviewed independently by two neuroradiologists blinded to treatment group for presence or absence of signal change or atrophy in the meninges, cortex, white matter, basal ganglia, thalamus, hippocampus, brainstem, and cerebellum.

RESULTS

Eight cases of RSE receiving treatment with isoflurane were identified and double-matched with 15 controls who received only intravenous anesthetics. Baseline characteristics were similar. Hippocampal signal change was observed more frequently in cases receiving isoflurane (p = 0.026).

CONCLUSIONS

Hippocampal signal changes were associated with isoflurane use in patients with RSE. They were also associated with number of seizure days prior to MRI and the use of multiple anesthetic agents. Similar changes have been seen as a result of RSE itself, and one cannot rule out the possibility these changes represent seizure-related effects. If isoflurane-related, these hippocampal signal changes may be the result of a direct neurotoxic effect of prolonged isoflurane use or failure of isoflurane to protect the hippocampus from seizure-induced injury despite achieving electrographic burst-suppression.

Protective effects of salidroside against isoflurane-induced cognitive impairment in rats

Postoperative cognitive dysfunction, which is associated with a wide range of cognitive functions including working memory, long-term memory, information processing, attention, and cognitive flexibility, is a major clinical issue in geriatric surgical patients. The aim of the current study was to determine the protective role and possible mechanisms of salidroside against isoflurane-induced cognitive impairment. Sprague Dawley rats were randomly assigned to five groups and were treated with or without salidroside before isoflurane exposure. Open-field and fear conditioning tests were conducted to evaluate the cognitive function of the rats. Moreover, the hippocampus tissues were obtained for biochemical analysis. The results showed that the isoflurane anesthesia decreased the freezing time to context significantly at 48 h after the isoflurane exposure in the fear conditioning test. Salidroside could ameliorate isoflurane-induced cognitive dysfunction. Further analysis demonstrated salidroside markedly suppressed the release of tumor necrosis factor-α and interleukin-1β. Moreover, salidroside reversed the decreased activity of choline acetyltransferase, superoxide dismutase, glutathione peroxidase, and content of acetylcholine, as well as the increased activity of acetylcholine esterase and content of malondialdehyde in hippocampal tissue of isoflurane-exposed rats. According to the results, we concluded that that salidroside has a protective effect against isoflurane-induced cognitive dysfunction by inhibiting excessive inflammatory responses, decreasing oxidative stress, and regulating the cholinergic system.

Neuroprotective Effects Against POCD by Photobiomodulation: Evidence from Assembly/Disassembly of the Cytoskeleton

Postoperative cognitive dysfunction (POCD) is a decline in memory following anaesthesia and surgery in elderly patients. While often reversible, it consumes medical resources, compromises patient well-being, and possibly accelerates progression into Alzheimer's disease. Anesthetics have been implicated in POCD, as has neuroinflammation, as indicated by cytokine inflammatory markers. Photobiomodulation (PBM) is an effective treatment for a number of conditions, including inflammation. PBM also has a direct effect on microtubule disassembly in neurons with the formation of small, reversible varicosities, which cause neural blockade and alleviation of pain symptoms. This mimics endogenously formed varicosities that are neuroprotective against damage, toxins, and the formation of larger, destructive varicosities and focal swellings. It is proposed that PBM may be effective as a preconditioning treatment against POCD; similar to the PBM treatment, protective and abscopal effects that have been demonstrated in experimental models of macular degeneration, neurological, and cardiac conditions.

Differential hippocampal protein expression between normal aged rats and aged rats with postoperative cognitive dysfunction: A proteomic analysis

The aim of the present study was to investigate the differences in the expression of hippocampal proteins between normal control aged rats and aged rats with postoperative cognitive dysfunction (POCD). A total of 24 aged rats were randomly divided into a surgery group (n=12) and a control group (n=12). The rats in the surgery group were treated with 2 h isoflurane anesthesia and splenectomy, while the rats in the control group received 40% oxygen for 2 h without surgery. The cognitive functions of the two groups were examined using a Y-maze test. The protein expression profiles of the hippocampus of six aged rats (three rats with POCD and three from the normal control group) were assessed using two-dimensional gel electrophoresis and matrix-assisted laser desorption/ionization time of flight mass spectrometry. A total of three differential proteins were further confirmed between the POCD rats and normal rats using reverse transcription quantitative polymerase chain reaction (RT-qPCR). The expression levels of 21 proteins in the rats with POCD were significantly different compared with the normal control rats. These proteins were functionally clustered to synaptic plasticity (three proteins), oxidative stress (four proteins), energy production (six proteins), neuroinflammation (three proteins) and glutamate metabolism (two proteins). In addition, three proteins (fatty acid binding protein 7, brain, glutamate dehydrogenase 1 and glutamine synthetase), associated with astrocytic function, were significantly different in the rats with POCD compared with those in the normal control (P<0.05). Similar changes in the mRNA expression levels of the three proteins in the hippocampi of POCD rats were also detected using RT-qPCR. Neuroinflammation, glutamate toxicity and oxidative stress were possibly involved in the pathological mechanism underlying POCD in aged rats. In addition, astrocytes may also be important in POCD in aged rats.

Inhibiting Rho kinase 2 reduces memory dysfunction in adult rats exposed to sevoflurane at postnatal days 7-9

The aim of the present study was to investigate the roles of Rho protein A (RhoA) and Rho kinases 2 (ROCK2) in the memory dysfunction of adult rats exposed to sevoflurane at postnatal days 7-9 (P7-9). One-week-old Sprague-Dawley rats were divided into four groups known as C, S1, S3 and F. Rats in the S1 (2 h at P7) and S3 groups (2 h/day at P7-9) were exposed to sevoflurane. The rats in the F group were treated with the ROCK2 inhibitor and subsequent sevoflurane exposure (2 h/day at P7-9). The rats in the C group received no sevoflurane. The protein levels of RhoA, ROCK2 and cleaved caspase-3 (Cl-Csp3) in the adult hippocampus were assessed by western blot analysis. Learning and memory of rats at postnatal 45-50 days (P45-50) were detected by the Morris water maze (MWM) test. During the training of MWM, the latency and distance of rats in the S3 group were significantly longer than that of the C group (P<0.05, respectively). In the probe test, the percentages of time and distance in the target quadrant for the S3 group were evidently less than that of the C group (P<0.05). There was no significant difference in the behaviors between the C and S1 groups (P>0.05, respectively). Corresponding to the behavioral changes, the levels of RhoA, ROCK2 and Cl-Csp3 in the hippocampus of the S3 group significantly increased, compared to that of the C and S1 groups (P<0.05). Additionally, the ROCK2 inhibitor clearly decreased ROCK2 and Cl-Csp3 expression and shortened the latency during the training (P<0.05, P46-49 respectively) and probe test (P<0.05) in the F group, compared to that of the S3 group. Compared to the C group, the expression of RhoA, ROCK2 and Cl-Csp3 in the hippocampus of the S1 group had no significant difference (P>0.05). Multiple inhalation of sevoflurane can induce neurotoxicity and memory dysfunction. RhoA and ROCK2 played important roles in the impairment of learning and memory of adults rats exposed to sevoflurane at the postnatal early stage.

Aspartic acid in the hippocampus: a biomarker for postoperative cognitive dysfunction

This study established an aged rat model of cognitive dysfunction using anesthesia with 2% isoflurane and 80% oxygen for 2 hours. Twenty-four hours later, Y-maze test results showed that isoflurane significantly impaired cognitive function in aged rats. Gas chromatography-mass spectrometry results showed that isoflurane also significantly increased the levels of N,N-diethylacetamide, n-ethylacetamide, aspartic acid, malic acid and arabinonic acid in the hippocampus of isoflurane-treated rats. Moreover, aspartic acid, N,N-diethylacetamide, n-ethylacetamide and malic acid concentration was positively correlated with the degree of cognitive dysfunction in the isoflurane-treated rats. It is evident that hippocampal metabolite changes are involved in the formation of cognitive dysfunction after isoflurane anesthesia. To further verify these results, this study cultured hippocampal neurons in vitro, which were then treated with aspartic acid (100 μmol/L). Results suggested that aspartic acid concentration in the hippocampus may be a biomarker for predicting the occurrence and disease progress of cognitive dysfunction.

Aging differentially affects the loss of neuronal dendritic spine, neuroinflammation and memory impairment at rats after surgery

It is known that age is an important factor for postoperative cognitive dysfunction (POCD) and the patients with POCD suffer from the impairment of multiple brain regions and multiple brain functions. However currently animal studies of POCD mainly focus on hippocampus region, therefore in this study we performed partial hepatectomy in young adult and aged rats to test the questions (1) whether POCD in animals involves other brain areas besides hippocampus; (2) how age influences POCD of young adult and aged animals. We found that (1) in young adult rats, the memory was not significantly affected (P>0.05) 1d, 3d and 7d after partial hepatectomy, but was significantly impaired (p<0.001) in aged rats 1d and 3d post-surgery; (2) in young adult rats, the surgery did not significantly affect the densities of dendritic spines of neurons at CA1, dentate gyrus (DG) and cingulate cortex (P>0.05, respectively) 1d and 3d post-surgery, but the spine densities at CA1 and DG of aged rats were significant reduced 1d and 3d post-surgery (p<0.001, respectively), however this didn't happen at cingulate cortex (P>0.05); (3) In young adult rats, surgery didn't affect the activation of microglia and levels of TNF-α and IL-1β at hippocampus (P>0.05), but significantly activated microglia and increased levels of TNF-α and IL-1β at hippocampus of aged rats (P<0.05). Our data suggest that (1) partial hepatectomy-induced POCD mainly involves hippocampus impairments, and (2) differential loss of neuronal dendritic spines and neuroinflammation at hippocampus are most likely the mechanism for the formation of POCD in aged rats.

Tau hyperphosphorylation: a downstream effector of isoflurane-induced neuroinflammation in aged rodents

Postoperative cognitive dysfunction (POCD) is a severe neurological sequela after anesthesia and surgery. Multiple risk factors, such as advanced age and anesthesia duration, relevant to POCD have been made out, although the pathophysiological mechanisms of this complication need to be further elucidated. To date, there is a substantial body of evidence implicating that neuroinflammatory cytokines and the subsequent neuroinflammatory response contribute to the cognitive impairment in aged rodents exposed to isoflurane, a commonly used general anesthetic. Interestingly, this cognitive disorder is mitigated by anti-inflammatory agents even 14 days after isoflurane exposure. In addition, isoflurane-induced upregulation of neuroinflammatory cytokines is only limited within 48 h. So a first possibility to consider is a downstream effector of isoflurane-induced neuroinflammatory cytokines which contributes to the long-lasting cognitive dysfunction. In Alzheimer's disease (AD) models, proinflammatory cytokines can induce tau hyperphosphorylation which is associated with synaptic abnormality and further cognitive impairment. It is unknown whether isoflurane-induced neuroinflammatory cytokines can trigger tau hyperphosphorylation. Taken together, we hypothesize that tau hyperphosphorylation is a downstream target of isoflurane-induced neuroinflammatory response and thus bridges the isoflurane-induced relatively transient neuroinflammatory process to the long-term cognitive impairment.

Resveratrol pretreatment attenuates the isoflurane-induced cognitive impairment through its anti-inflammation and -apoptosis actions in aged mice

Although the underlying mechanisms of isoflurane-induced cognitive impairments remain largely to be determined, neuronal inflammation and apoptosis are thought to be major contributors. Resveratrol is a naturally available herbal compound for the treatment of inflammatory and neurodegenerative diseases. We therefore aimed to investigate the effects of resveratrol on the isoflurane-induced cognitive impairments and the associated hippocampal inflammation responses and neuronal apoptosis in the aged mice. Fifteen-month-old male C57BL/6 mice received 2 h of 1.5 % isoflurane or oxygen exposure 24 h after the intraperitoneal injection of resveratrol or saline daily for 7 consecutive days. Here, we showed that the isoflurane anesthesia decreased the freezing time to context significantly at 48 h after the isoflurane exposure in the fear conditioning test. The hippocampal levels of IL-1β, TNF-α, NLRP3, cleaved caspase-3, and Bax increased significantly while the hippocampal levels of IkBα and Bcl-2 decreased significantly at 6 and/or 48 h after the isoflurane anesthesia. All these effects induced by isoflurane were attenuated by resveratrol pretreatment. However, the isoflurane anesthesia had no significant effect on the hippocampal Sirt1. In conclusion, our results suggest that resveratrol attenuates the hippocampus-dependent cognitive impairment induced by isoflurane anesthesia through its anti-inflammation and anti-apoptosis effects in aged mice.

Up-regulation of Alzheimer's disease-associated proteins may cause enflurane anesthesia induced cognitive decline in aged rats

Isoflurane anesthesia can cause post-operative cognitive dysfunction in elderly patients. As an isomer of isoflurane, enflurane may also account for cognitive dysfunction. However, the mechanism of enflurane-induced cognitive dysfunction remains obscure. In this study, we investigated the effects of enflurane anesthesia on cognitive function and the possible roles of β-amyloid protein and phosphorylated tau protein in response to enflurane anesthesia in aged rats. After intraperitoneal injection of enflurane, the Morris water maze and the step-down passive avoidance tests were conducted to test the cognitive ability and memory. The enflurane group showed prolonged escape latency, extended space exploration time and increased number of errors at early stage after enflurane anesthesia, suggesting that enflurane should be responsible for the impairment of cognition in aged rats. In addition, we analyzed the expression level of β-amyloid and phosphorylation level of tau in the hippocampus by immunoblotting. Interestingly, the levels of β-amyloid and phosphorylated tau in the hippocampus increased significantly at early stage and then restored to pre-anesthetic levels. Taken together, our results suggest that increasing of β-amyloid and phosphorylation of tau are important to cause cognitive decline in aged rats during initial stage after enflurane anesthesia.

The analog of Ginkgo biloba extract 761 is a protective factor of cognitive impairment induced by chronic fluorosis

Ginkgo biloba extract EGb761 is widely used to treat patients with learning and memory impairment in Alzheimer's disease and Parkinson's disease in China. However, it is not yet clear whether the analog of EGb761 (EGb) has a protective effect on the learning and memory damage induced by chronic fluorosis. In this study, 30 Wistar rats were randomly divided into three groups: a control group, a sodium fluoride (NaF) + EGb group, and a NaF group. The rats were administered 0.5 ml water containing NaF (100 mg/l) and EGb (120 mg/kg) per day via gavage. After 3 months, the rats' capacity for learning and memory was tested using a Y-maze. Damage to hippocampal neurons was evaluated by histological examination of the CA3 area. Superoxide dismutase (SOD) activity and the levels of glutathione peroxidase (GSH-Px) and malondialdehyde (MDA) were measured. Furthermore, the expression levels of Bcl-2 and Bax and the levels of cleaved Caspase3 in the hippocampus were evaluated by RT-PCR and Western blotting. The results showed that EGb could improve learning and memory abilities, enhance the activities of SOD and GSH-Px, attenuate the level of MDA, upregulate the ratio of Bcl-2/Bax, and downregulate the level of cleaved Caspase3.

Alterations in nitric oxide synthase-expressing neurons in the forebrain regions of rats after developmental exposure to organophosphates

Several mechanisms have been addressed as contributors to the long lasting behavioral deficits after developmental exposure to organophosphate (OP) compounds. Here, the effects of developmental exposure to two common OP insecticides, chlorpyrifos (CPF) and diazinon (DZN), on nitric oxide synthase (NOS)-expressing neurons in the rat forebrain are reported. A daily dose of 1mg/kg of either CPF or DZN was administered to rats during gestational days 15-18 or postnatal days (PND) 1-4. We then assessed NADPH-diaphorase and neuronal NOS (nNOS) immunohistochemistry in forebrain sections on different postnatal days. Prenatal exposure to CPF and DZN induced a transient reduction of NADPH-d(+)/nNOS-immunoreactive (IR) neurons in most cortical regions on PND 4 but exceptionally increased them in the entorhinal/piriform cortex. On PND 15, NADPH-d(+)/nNOS-IR neurons showed morphological abnormalities within entorhinal/piriform cortex of the rats that gestationally exposed to CPF. Postnatal exposure to CPF and DZN did not induce widespread effects on the number of NADPH-d(+)/nNOS-IR neurons on PNDs 7 and 15 but significantly reduced them in most cortical regions and hippocampal subfields on PND 60. The OPs affected NADPH-d(+)/nNOS-IR neurons in a sex independent manner and apparently spared them in the striatum. While the NADPH-d reactivity of microvessels was normally diminished by age, OP treated rats evidently preserved the NADPH-d reactivity of microvessels in the cerebral cortex and hippocampus. The effects of OPs on NADPH-d(+)/nNOS-IR neurons may contribute to the long-lasting behavioral outcomes and expand the neurotransmitter system that need to be considered in OP neurotoxicity evaluations.

Developmental exposure to chlorpyrifos and diazinon differentially affect passive avoidance performance and nitric oxide synthase-containing neurons in the basolateral complex of the amygdala

Chronic exposure to low doses of organophosphates during brain development can induce persistent neurochemical and behavioral effects. This study sought to determine the long-lasting effects of developmental exposure to chlorpyrifos (CPF) and diazinon (DZN) on passive avoidance (PA) performance and neuronal nitric oxide synthase (nNOS)-containing neurons in the subnuclei within basolateral complex of amygdala (BLC). Developing rats were exposed to daily dose (1mg/kg) of CPF or DZN during gestational days 15-18 and postnatal days (PND) 1-4. PA performance was assessed in young adulthood (PND 60). Brain sections were also processed by NADPH-diaphorase (NADPH-d) and nNOS immunohistochemistry. Gestational exposure to CPF increased NADPH-d(+)/nNOS-immunoreactive (IR) neurons within the basolateral nucleus (BL) and medial paracapsular intercalated cluster, which was along with PA retention impairment in both male and female rats. Prenatal exposure to DZN did not significantly change the number of NADPH-d(+)/nNOS-IR neurons in the BLC while impaired PA retention in females. Postnatal exposure to CPF decreased NADPH-d(+)/NOS-IR neurons in the BL without affecting PA performance. Exposure to DZN during early postnatal period impaired PA retention in both sexes, albeit to a lesser extent in females, and was along with a considerable sex independent reduction of NADPH-d(+)/NOS-IR neurons in all BLC subnuclei. Our data suggest that developmental exposure to apparently subtoxic dose of CPF and DZN elicit long-lasting impairment in PA retention that are associated, but not necessarily correlated with effects on NADPH-d(+)/NOS-IR neurons in BLC of the amygdala.