Dopamine in the hippocampal dentate gyrus modulates spatial learning via D1-like receptors

Enhanced NMDA receptor pathway and glutamate transmission in the hippocampal dentate gyrus mediate the spatial learning and memory impairment of obese rats

Obesity has been linked with the impairment of spatial memory and synaptic plasticity but the molecular mechanisms remained unidentified. Since glutamatergic transmission and NMDA receptor neural pathways in hippocampal dentate gyrus (DG) are essential in the learning and memory, we aimed to investigate glutamate (Glu) and NMDA receptor signaling of DG in spatial learning and memory in diet-induced obesity (DIO) rats. Spatial learning and memory were assessed via Morris water maze (MWM) test on control (Ctr) and DIO rats. Extracellular concentration of Glu in the DG was determined using in vivo microdialysis and HPLC. The protein expressions of NMDA receptor subunit 2B (NR2B), brain-derived neurotrophic factor (BDNF), the activation of calcium/calmodulin-dependent kinase II (CaMKII) and cAMP-response-element-binding protein (CREB) in the DG were observed by western blot. Spatial learning and memory were impaired in DIO rats compared to those of Ctr. NR2B expression was increased, while BDNF expression and CaMKII and CREB activation were decreased in DG of DIO rats. Extracellular concentration of Glu was increased in Ctr on the 3rd and 4th days of the MWM test, but significant further increment was observed in DIO rats. Microinjection of an NMDA antagonist (MK-801) into the DG reversed spatial learning and memory impairment. Such effects were accompanied by greater BDNF expression and CaMKII/CREB activation in the DG of DIO rats. In conclusion, the enhancement of Glu-NMDA receptor transmission in the hippocampal DG contributes to the impairment of spatial learning and memory in DIO rats, maybe via the modulation of CaMKII-CREB-BDNF signaling pathway.

Blocking the dopaminergic receptors within the hippocampal dentate gyrus reduced analgesic responses induced by restraint stress in the formalin test

Previous studies have shown that various receptors, including dopamine receptors, are expressed in the hippocampal dentate gyrus (DG). Besides, indicatively, dopamine receptors play an essential role in the modulation of pain perception. On the other hand, stressful experiences can produce analgesia, termed stress-induced analgesia (SIA). The current study examined the probable role of dopamine receptors within the DG in antinociception induced by restraint stress (RS). Ninety-seven male albino Wistar rats were unilaterally implanted with a cannula in the DG. Animals received intra-DG microinjections of SCH23390 or Sulpiride (0.25, 1, and 4 μg/rat) as D1-and D2-like dopamine receptor antagonists, respectively, five minutes before RS. Ten minutes after the end of the induction of RS for three hours, 50 μl 2.5% formalin was injected subcutaneously into the plantar surface of the hind paw to induce persistent inflammatory pain. Pain scores were evaluated at 5-minute intervals for 60 minutes. These findings showed that; exposure to RS for three hours produced SIA in both phases of the formalin test, while this RS-induced analgesia was attenuated in the early and late phases of the formalin test by intra-DG microinjection of SCH23390 and Sulpiride. The results of the present study suggested that both D1- and D2-like dopamine receptors in the DG have a considerable role in the induced analgesia by RS.

An enriched environment improves long-term functional outcomes in mice after intracerebral hemorrhage by mechanisms that involve the Nrf2/BDNF/glutaminase pathway

Post-stroke depression exacerbates neurologic deficits and quality of life. Depression after ischemic stroke is known to some extent. However, depression after intracerebral hemorrhage (ICH) is relatively unknown. Increasing evidence shows that exposure to an enriched environment (EE) after cerebral ischemia/reperfusion injury has neuroprotective effects in animal models, but its impact after ICH is unknown. In this study, we investigated the effect of EE on long-term functional outcomes in mice subjected to collagenase-induced striatal ICH. Mice were subjected to ICH with the standard environment (SE) or ICH with EE for 6 h/day (8:00 am-2:00 pm). Depressive, anxiety-like behaviors and cognitive tests were evaluated on day 28 with the sucrose preference test, tail suspension test, forced swim test, light-dark transition experiment, morris water maze, and novel object recognition test. Exposure to EE improved neurologic function, attenuated depressive and anxiety-like behaviors, and promoted spatial learning and memory. These changes were associated with increased expression of transcription factor Nrf2 and brain-derived neurotrophic factor (BDNF) and inhibited glutaminase activity in the perihematomal tissue. However, EE did not change the above behavioral outcomes in Nrf2-/- mice on day 28. Furthermore, exposure to EE did not increase BDNF expression compared to exposure to SE in Nrf2-/- mice on day 28 after ICH. These findings indicate that EE improves long-term outcomes in sensorimotor, emotional, and cognitive behavior after ICH and that the underlying mechanism involves the Nrf2/BDNF/glutaminase pathway.

The inhibitory effect of cannabidiol on the rewarding properties of methamphetamine in part mediates by interacting with the hippocampal D1-like dopamine receptors

Cannabidiol (CBD) is a potential treatment to decrease the rewarding properties of psychostimulants. However, the exact mechanism and distinct neuroanatomical areas responsible for the CBD's effects remain unclear. Indicatively, the D1-like dopamine receptors (D1R) in the hippocampus (HIP) are essential for expressing and acquiring drug-associated conditioned place preference (CPP). Therefore, given that involving D1Rs in reward-related behaviors and the encouraging results of CBD in attenuating the psychostimulant's rewarding effects, the present study sought to investigate the role of D1Rs of the hippocampal dentate gyrus (DG) in the inhibitory effects of CBD on the acquisition and expression of METH-induced CPP. To this end, over a 5-day conditioning period by METH (1 mg/kg; sc), different groups of rats were given intra-DG SCH23390 (0.25, 1, or 4 μg/0.5 μl, saline) as a D1Rs antagonist before ICV administration of CBD (10 μg/5 μl, DMSO12%). In addition, a different set of animals, after the conditioning period, received a single dose of SCH23390 (0.25, 1, or 4 μg/0.5 μl) before CBD (50 μg/5 μl) administration on the expression day. The results showed that SCH23390 (1 and 4 μg) significantly reduced the suppressive effects of CBD on the acquisition of METH place preference (P < 0.05 and P < 0.001, respectively). Furthermore, the highest dose of SCH23390 (4 μg) in the expression phase remarkably abolished the preventive effects of CBD on the expression of METH-seeking behavior (P < 0.001). In conclusion, the current study revealed that CBD's inhibitory effect on rewarding properties of METH partially acts through D1Rs in the DG area of the HIP.

Dopaminergic regulation of hippocampal plasticity, learning, and memory

The hippocampus is responsible for encoding behavioral episodes into short-term and long-term memory. The circuits that mediate these processes are subject to neuromodulation, which involves regulation of synaptic plasticity and local neuronal excitability. In this review, we present evidence to demonstrate the influence of dopaminergic neuromodulation on hippocampus-dependent memory, and we address the controversy surrounding the source of dopamine innervation. First, we summarize historical and recent retrograde and anterograde anatomical tracing studies of direct dopaminergic projections from the ventral tegmental area and discuss dopamine release from the adrenergic locus coeruleus. Then, we present evidence of dopaminergic modulation of synaptic plasticity in the hippocampus. Plasticity mechanisms are examined in brain slices and in recordings from in vivo neuronal populations in freely moving rodents. Finally, we review pharmacological, genetic, and circuitry research that demonstrates the importance of dopamine release for learning and memory tasks while dissociating anatomically distinct populations of direct dopaminergic inputs.

Electroacupuncture at Zusanli ameliorates the autistic-like behaviors of rats through activating the Nrf2-mediated antioxidant responses

OBJECTIVE

Emerging evidence suggests that acupuncture plays a neuroprotective role in autism. This study aimed to explore the effect of electroacupuncture at Zusanli (ST36) on autistic-like behaviors and the underlying mechanism.

METHOD

Pregnant rats were administered with valproic acid (VPA) on gestational day 12.5 to induce an autism spectrum disorder (ASD) model. The pups were given electroacupuncture at ST36 daily from postnatal day (PND) 28-48. On PND28, the adenoviral vector containing small interfering RNA Nrf2 (Ad-siRNA-Nrf2) was injected into the prefrontal cortex of rats. The behavioral analysis was performed on PND 44-48. On PND48, the animals were euthanized and the brains were collected for further detection. Nissl staining was performed to detect neuronal viability. The biochemical markers of oxidative stress were subsequently measured.

RESULT

Electroacupuncture at ST36 ameliorated the locomotor activity, social behavior, spatial learning and memory and repetitive behavior compared with ASD rats. It was notable that the electroacupuncture decreased oxidative stress markers in the tissues of prefrontal cortex, enhanced translocation of nuclear factor erythroid2-related factor2 (Nrf2) from cytoplasm to nucleus, and up-regulated the levels of NADP(H) quinone oxidoreductase (NQO1) and heme oxygenase (HO-1). However, these effects induced by electroacupuncture at ST36 were abolished after injection of Ad-siRNA-Nrf2.

CONCLUSION

These data suggested that electroacupuncture at ST36 protected nerve function in ASD rats through Nrf2 activation and the antioxidant response.

The Role of NMDAR and BDNF in Cognitive Dysfunction Induced by Different Microwave Radiation Conditions in Rats

Background: To investigate the effects of different levels of microwave radiation on learning and memory in Wistar rats and explore the underlying mechanisms of N-methyl-D-aspartate receptor (NMDAR/NR) and Brain-derived neurotropic factor (BDNF); Methods: A total of 140 Wistar rats were exposed to microwave radiation levels of 0, 10, 30 or 50 mW/cm2 for 6 min. Morris Water Maze Test, high-performance liquid chromatography, Transmission Electron Microscope and Western blotting were used; Results: The 30 and 50 mW/cm2 groups exhibited longer average escape latencies and fewer platform crossings than the 0 mW/cm2 group from 6 h to 3 d after microwave radiation. Alterations in the amino acid neurotransmitters of the hippocampi were shown at 6 h, 3 d and 7 d after exposure to 10, 30 or 50 mW/cm2 microwave radiation. The length and width of the Postsynaptic density were increased. The expression of NR1, NR2A and NR2B increased from day 1 to day 7; Postsynaptic density protein-95 and cortactin expression increased from day 3 to day 7; BDNF and Tyrosine kinase receptor B (TrkB) expression increased between 6 h and 1 d after 30 mW/cm2 microwave radiation exposure, but they decreased after 50mW/cm2 exposure. Conclusions: Microwave exposure (30 or 50 mW/cm2, for 6 min) may cause abnormalities in neurotransmitter release and synaptic structures, resulting in impaired learning and memory; BDNF and NMDAR-related signaling molecules might contribute differently to these alterations.

The influence of syringic acid treatment on total dopamine levels of the hippocampus and on cognitive behavioral skills

BACKGROUND

Natural polyphenols have been investigated and are claimed to be mediators of the relationship between dopamine (DA) and memory. Therefore, we aimed to measure and evaluate the effect of syringic acid (SA) on DA expression by behavioral tests related to short-term and recognition memory in Wistar rats.

METHODS

Rats were randomly assigned to control (0.5 cc corn oil, n = 10), SA (25 mg/kg/day, o.g, n = 10), Deltamethrin (DTM) (1.28 mg/kg/day o.g, n = 10) and DTM (1.28 mg/kg/day o.g, n = 10) + SA (25 mg/kg/day) groups. The Y-maze and Novel Object Recognition (NOR) tests were performed to assess cognitive and behavioral functions in the rats. Dopamine levels in the hippocampus were measured by mass spectrometry.

RESULTS

Syringic acid significantly increased DA (5.45 ± 1.06 ng/ml, p = 0.0026, p < 0.05) compared with the other groups. SA increased the percent alternation (34.85 ± 0.72%, p < 0.05), time spent in the novel arm (2.88 ± 0.18 min, p < 0.05), and frequency of novel arm entries (44.91 ± 2.28%, p < 0.05), of the rats after the Y-maze test. The SA elevated the discrimination index (70.42 ± 3.59%, p < 0.001), and exploration time (30.44 ± 1.8 sec, p < 0.05) in the NOR test, and increased the short term and recognition memory in behavioral tests.

CONCLUSION

Our findings support the hypothesis that SA-induced DA levels of the hippocampus may facilitate recognition and short-term memory in Wistar rats through the activation of dopaminergic receptors or pathways during the learning process, and that this can be seen in the cognitive behavior of SA-treated rats.

The effects of exercise treatment on learning and memory ability, and cognitive performance in diet-induced prediabetes animals

Changes associated with cognitive function in the high-fat high-carbohydrate diet-induced prediabetes animal model and effect of exercise remain unclear. Rats were randomly assigned to the following groups (n = 6): non-diabetic (ND), prediabetic (PD), intermittent exercising PD (PD + IE) and regular exercising PD (PD + RE). After exercise cessation, oral glucose tolerance (OGT), Novel Object Recognition Test (NORT) and Morris-Water Maze (MWM) tests were performed to assess cognitive function. After sacrifice, malonaldehyde, glutathione peroxidase, interleukin-1β and dopamine concentration in the prefrontal cortex (PFC) and hippocampus were measured. Impaired OGT response in PD animals was accompanied by poor performance on behavioural tasks. This was associated with increased oxidative stress markers and impaired dopamine neurotransmission as evidence by elevated dopamine concentration in the PFC and hippocampal tissue. Improved OGT response by exercise was coupled with improved performance on behavioural tasks, oxidative stress markers and increased interleukin-1β concentration. In regular exercise, this was further coupled with improved dopamine neurotransmission. Cognitive function was affected during prediabetes in animals. This was partly due to oxidative stress and impaired dopamine neurotransmission. Both intermittent and regular exercise improved cognitive function. This was partly mediated by improved glucose tolerance and oxidative stress as well as a subclinical increase in interleukin-1β concentration. In regular exercise, this was further mediated by improved dopamine neurotransmission.

The Lacto-Tetrapeptide Gly-Thr-Trp-Tyr, β-Lactolin, Improves Spatial Memory Functions via Dopamine Release and D1 Receptor Activation in the Hippocampus

Scope: Peptides containing tryptophan–tyrosine sequences, including the lacto-tetrapeptide glycine–threonine–tryptophan–tyrosine (GTWY) and β-lactolin, from β-lactoglobulin in whey enzymatic digestion, enhance hippocampus-dependent memory functions, which are blocked by the systemic administration of dopamine D1-like antagonist. In this study, we investigated the role of the hippocampal dopaminergic system in the memory-enhancing effect of β-lactolin. Methods and Results: The results of in vivo microdialysis revealed that oral administration of β-lactolin increased the extracellular concentration of dopamine in the hippocampus and enhanced both spatial working memory, as measured in the Y-maze test, and spatial reference memory, as measured in the novel object location test. These memory-enhancing effects of β-lactolin, but not the baseline memory functions, were impaired by the knockdown of the dopamine D1 receptor subtype in the hippocampus. β-Lactolin also enhanced object memory, as measured by the novel object recognition test. However, D1 knockdown in the hippocampus spared this memory function either with or without the administration of β-lactolin. Conclusions: The present results indicate that oral administration of β-lactolin increases dopamine release and D1 receptor signaling in the hippocampus, thereby enhancing spatial memory, but it may improve object memory via a separate mechanism.