OBJECTIVE: To investigate the effects of removing microglia from spinal cord on nerve repair and functional recovery after spinal cord injury (SCI) in mice. METHODS: Thirty-nine 6-week-old female C57BL/6 mice were randomly divided into control group ( n=12), SCI group ( n=12), and PLX3397+SCI group ( n=15). The PLX3397+SCI group received continuous feeding of PLX3397, a colony-stimulating factor 1 receptor inhibitor, while the other two groups were fed a standard diet. After 14 days, both the SCI group and the PLX3397+SCI group were tested for ionized calcium binding adapter molecule 1 (Iba1) to confirm that the PLX3397+SCI group had completely depleted the spinal cord microglia. The SCI model was then prepared by clamping the spinal cord in both the SCI group and the PLX3397+SCI group, while the control group underwent laminectomy. Preoperatively and at 1, 3, 7, 14, 21, and 28 days postoperatively, the Basso Mouse Scale (BMS) was used to assess the hind limb function of mice in each group. At 28 days, a footprint test was conducted to observe the gait of the mice. After SCI, spinal cord tissue from the injury site was taken, and Iba1 immunofluorescence staining was performed at 7 days to observe the aggregation and proliferation of microglia in the spinal cord. HE staining was used to observe the formation of glial scars at the injury site at 28 days; glial fibrillary acidic protein (GFAP) immunofluorescence staining was applied to astrocytes to assess the extent of the injured area; neuronal nuclei antigen (NeuN) immunofluorescence staining was used to evaluate neuronal survival. And 5-hydroxytryptamine (5-HT) immunofluorescence staining was performed to assess axonal survival at 60 days. RESULTS: All mice survived until the end of the experiment. Immunofluorescence staining revealed that the microglia in the spinal cord of the PLX3397+SCI group decreased by more than 95% compared to the control group after 14 days of continuous feeding with PLX3397 ( P<0.05). Compared to the control group, the BMS scores in the PLX3397+SCI group and the SCI group significantly decreased at different time points after SCI ( P<0.05). Moreover, the PLX3397+SCI group showed a further decrease in BMS scores compared to the SCI group, and exhibited a dragging gait. The differences between the two groups were significant at 14, 21, and 28 days ( P<0.05). HE staining at 28 days revealed that the SCI group had formed a well-defined and dense gliotic scar, while the PLX3397+SCI group also developed a gliotic scar, but with a more blurred and loose boundary. Immunofluorescence staining revealed that the number of microglia near the injury center at 7 days increased in the SCI group than in the control group, but the difference between groups was not significant ( P>0.05). In contrast, the PLX3397+SCI group showed a significant reduction in microglia compared to both the control and SCI groups ( P<0.05). At 28 days after SCI, the area of spinal cord injury in the PLX3397+SCI group was significantly larger than that in SCI group ( P<0.05); the surviving neurons significantly reduced compared with the control group and SCI group ( P<0.05). The axonal necrosis and retraction at 60 days after SCI were more obvious. CONCLUSION The removal of microglia in the spinal cord aggravate the tissue damage after SCI and affecte the recovery of motor function in mice, suggesting that microglia played a neuroprotective role in SCI.
Animals ; Spinal Cord Injuries/surgery* ; Microglia/pathology* ; Female ; Mice ; Mice, Inbred C57BL ; Nerve Regeneration/drug effects* ; Spinal Cord/pathology* ; Pyrroles/administration & dosage* ; Aminopyridines/administration & dosage* ; Recovery of Function ; Disease Models, Animal ; Calcium-Binding Proteins/metabolism* ; Receptors, Granulocyte-Macrophage Colony-Stimulating Factor/antagonists & inhibitors* ; Microfilament Proteins/metabolism* ; Glial Fibrillary Acidic Protein/metabolism*

Objective To explore the effects of Shuanglu Tongnao Formula on neuroinflammation in ischemic stroke (IS) rats via the P2X purinoceptor 7 receptor (P2X7R)/NLR family pyrin domain-containing 3 (NLRP3) pathway. Methods The rats were divided into five groups: the IS group, control group, Shuanglu Tongnao Formula group, P2X7R inhibitor brilliant blue G (BBG) group, and Shuanglu Tongnao Formula combined with P2X7R activator adenosine triphosphate (ATP) group, with 18 rats in each group. Except for the control group, rats in all other groups were used to construct an IS model using the suture method. After successful modeling, the drug was given once a day for 2 weeks. Neurological function scores and cerebral infarction volume ratios were measured in rats. Pathological examination of the ischemic penumbra brain tissue was performed. Immunofluorescence staining was used to quantify the proportions of microglia co-expressing both inducible nitric oxide synthase (iNOS) and ionized calcium-binding adapter molecule 1 (Iba1), as well as arginase 1 (Arg1) and Iba1, in the ischemic penumbra brain tissue. ELISA was used to detect tumor necrosis factor-alpha (TNF-α), transforming growth factor-beta (TGF-β), interleukin 6 (IL-6) and IL-10 in the ischemic penumbra brain tissue. Western blotting was used to measure P2X7R, NLRP3, and IL-1β proteins in the ischemic penumbra brain tissue. Results Compared with the control group, the IS group showed disordered neuronal arrangement, nuclear condensation, and obvious infiltration of inflammatory cells in the ischemic penumbra; significantly elevated neurological function scores, cerebral infarction volume ratios, proportions of microglia co-expressing iNOS and Iba1, and levels of TNF-α, IL-6, and P2X7R, NLRP3, IL-1β proteins; along with reduced proportions of microglia co-expressing Arg1 and Iba1 and levels of TGF-β and IL-10. Compared with the IS group, the Zhuang medicine Shuanglu Tongnao Formula and BBG groups demonstrated alleviated brain tissue damage; reduced neurological function scores, cerebral infarction volume ratios, proportions of microglia co-expressing iNOS and Iba1, and levels of TNF-α, IL-6, and P2X7R, NLRP3, IL-1β proteins; along with increased proportions of microglia co-expressing Arg1 and Iba1 and levels of TGF-β and IL-10. ATP reversed the effects of Zhuang medicine Shuanglu Tongnao Formula on microglial polarization and neuroinflammation in IS rats. Conclusion Zhuang medicine Shuanglu Tongnao Formula may promote the transformation of microglia from M1 type to M2 type by inhibiting the P2X7R/NLRP3 pathway, thereby improving neuroinflammation in IS rats.
Animals ; NLR Family, Pyrin Domain-Containing 3 Protein/metabolism* ; Receptors, Purinergic P2X7/metabolism* ; Male ; Drugs, Chinese Herbal/pharmacology* ; Rats ; Ischemic Stroke/pathology* ; Rats, Sprague-Dawley ; Disease Models, Animal ; Signal Transduction/drug effects* ; Neuroinflammatory Diseases/metabolism* ; Tumor Necrosis Factor-alpha/metabolism* ; Nitric Oxide Synthase Type II/metabolism* ; Interleukin-10/metabolism* ; Brain Ischemia/drug therapy* ; Microglia/metabolism*

OBJECTIVE: To investigate the therapeutic effect of Xiangshao Granules (XSG) on post-stroke depression (PSD) and explore the underlying mechanisms. METHODS: Forty-three C57BL/6J mice were divided into 3 groups: sham (n=15), PSD+vehicle (n=14), and PSD+XSG (n=14) groups according to a random number table. The PSD models were constructed using chronic unpredictable mild stress (CUMS) after middle cerebral artery occlusion (MCAO). The sham group only experienced the same surgical operation, but without MACO and CUMS stimulation. The XSG group received XSG (60 mg/kg per day) by gavage for 4 weeks. The mice in the sham and vehicle groups were given the same volume of 0.9% saline at the same time. The body weight and behavior tests including open field test, sucrose preference test, tail suspension test, and elevated plus-maze test, were used to validate the PSD mouse model. Real-time fluorescence quantitative polymerase chain reaction (RT-qPCR), enzyme-linked immunosorbent assay (ELISA), and immunofluorescence staining were used to evaluate the anti-inflammatory effects of XSG. The potential molecular mechanisms were explored and verified through network pharmacology analysis, Nissl staining, Western blot, ELISA, and RT-qPCR, respectively. RESULTS: The body weight and behavior tests showed that MCAO combined with CUMS successfully established the PSD models. XSG alleviated neuronal damage, reduced the expressions of pro-apoptotic proteins Caspase-3 and B-cell lymphoma-2 (BCL-2)-associated X (BAX), and increased the expression of anti-apoptotic protein BCL-2 in PSD mice (P<0.05 or P<0.01). XSG inhibited microglial activation and the expressions of pro-inflammatory cytokines including tumor necrosis factor-α, interleukin (IL)-1 β, and IL-6 via the toll-like receptor 4/nuclear factor kappa-B signaling pathway in PSD mice (P<0.05 or P<0.01). Furthermore, XSG decreased the expression of indoleamine 2,3-dioxygenase1 (IDO1) and increased the concentration of 5-hydroxytryptamine in PSD mice (P<0.05 or P<0.01). CONCLUSION XSG could reverse the anxiety/depressionlike behaviors and reduce the neuronal injury in the hippocampus and prefrontal cortex of PSD mice, which may be a potential therapeutic agent for PSD.
Animals ; Indoleamine-Pyrrole 2,3,-Dioxygenase/metabolism* ; Depression/etiology* ; Drugs, Chinese Herbal/therapeutic use* ; Hippocampus/metabolism* ; Male ; Mice, Inbred C57BL ; Prefrontal Cortex/pathology* ; Microglia/metabolism* ; Stroke/drug therapy* ; Disease Models, Animal ; Mice ; Behavior, Animal/drug effects*

OBJECTIVE: To illustrate the role of dehydrocorydaline (DHC) in chronic constriction injury (CCI)-induced neuropathic pain and the underlying mechanism. METHODS: C57BL/6J mice were randomly divided into 3 groups by using a random number table, including sham group (sham operation), CCI group [intrathecal injection of 10% dimethyl sulfoxide (DMSO)], and CCI+DHC group (intrathecal injection of DHC), 8 mice in each group. A CCI mouse model was conducted to induce neuropathic pain through ligating the right common sciatic nerve. On day 14 after CCI modeling or sham operation, mice were intrathecal injected with 5 µL of 10% DMSO or 10 mg/kg DHC (5 µL) into the 5th to 6th lumbar intervertebral space (L5-L6). Pregnant ICR mice were sacrificed for isolating primary spinal neurons on day 14 of embryo development for in vitro experiment. Pain behaviors were evaluated by measuring the paw withdrawal mechanical threshold (PWMT) of mice. Immunofluorescence was used to observe the activation of astrocytes and microglia in mouse spinal cord. Protein expressions of inducible nitric oxide synthase (iNOS), tumor necrosis factor alpha (TNF-α), interleukin 6 (IL-6), phosphorylation of N-methyl-D-aspartate receptor subunit 2B (p-NR2B), and NR2B in the spinal cord or primary spinal neurons were detected by Western blot. RESULTS: In CCI-induced neuropathic pain model, mice presented significantly decreased PWMT, activation of glial cells, overexpressions of iNOS, TNF-α, IL-6, and higher p-NR2B/NR2B ratio in the spinal cord (P<0.05 or P<0.01), which were all reversed by a single intrathecal injection of DHC (P<0.05 or P<0.01). The p-NR2B/NR2B ratio in primary spinal neurons were also inhibited after DHC treatment (P<0.05). CONCLUSION An intrathecal injection of DHC relieved CCI-induced neuropathic pain in mice by inhibiting the neuroinflammation and neuron hyperactivity.
Animals ; Neuralgia/etiology* ; Mice, Inbred C57BL ; Analgesics/pharmacology* ; Neuroinflammatory Diseases/pathology* ; Constriction ; Male ; Receptors, N-Methyl-D-Aspartate/metabolism* ; Nitric Oxide Synthase Type II/metabolism* ; Mice, Inbred ICR ; Microglia/pathology* ; Spinal Cord/drug effects* ; Female ; Mice ; Tumor Necrosis Factor-alpha/metabolism* ; Disease Models, Animal ; Constriction, Pathologic/complications* ; Interleukin-6/metabolism* ; Astrocytes/metabolism* ; Chronic Disease ; Neurons/metabolism*

Microglial functions are linked to Ca²⁺ signaling, with endoplasmic reticulum (ER) calcium stores playing a crucial role. Microglial abnormality is a hallmark of Alzheimer's disease (AD), but how ER Ca²⁺ receptors regulate microglial functions under physiological and AD conditions remains unclear. We found reduced ryanodine receptor 2 (Ryr2) expression in microglia from an AD mouse model. Modulation of RyR2 using S107, a RyR-Calstabin stabilizer, blunted spontaneous Ca²⁺ transients in controls and normalized Ca²⁺ transients in AD mice. S107 enhanced ATP-induced migration and phagocytosis while reducing ramification in control microglia; however, these effects were absent in AD microglia. Our findings indicate that RyR2 stabilization promotes an activation state shift in control microglia, a mechanism impaired in AD. These results highlight the role of ER Ca²⁺ receptors in both homeostatic and AD microglia, providing insights into microglial Ca²⁺ malfunctions in AD.
Animals ; Microglia/pathology* ; Alzheimer Disease/pathology* ; Phagocytosis/drug effects* ; Ryanodine Receptor Calcium Release Channel/metabolism* ; Disease Models, Animal ; Mice ; Cell Movement/drug effects* ; Mice, Transgenic ; Calcium Signaling/physiology* ; Calcium/metabolism* ; Mice, Inbred C57BL ; Male ; Endoplasmic Reticulum/metabolism*

Astrocytes in the spinal dorsal horn (SDH) exhibit diverse reactive phenotypes under neuropathic conditions, yet the mechanisms driving this diversity and its implications in chronic pain remain unclear. Here, we report that spared nerve injury (SNI) induces marked upregulation of both complement component 3 (C3⁺, A1-like) and S100 calcium-binding protein A10 (S100A10⁺, A2-like) astrocyte subpopulations in the SDH, with elevated microglial cytokines including interleukin-1α, tumor necrosis factor-α, and complement component 1q. Transcriptomic, immunohistochemical, and Western blot analyses reveal co-activation of multiple reactive astrocyte states over a unidirectional shift toward an A1-like phenotype. Fibroblast growth factor 8 (FGF8), a neuroprotective factor via FGFR3, mitigated microglia-induced C3⁺ astrocyte reactivity in vitro and suppressed spinal C3 expression and mechanical allodynia following intrathecal administration in SNI mice. These findings reveal a microglia-astrocyte signaling axis that promotes A1 reactivity and position FGF8 as a promising therapeutic candidate for neuropathic pain by modulating astrocyte heterogeneity.
Animals ; Astrocytes/drug effects* ; Neuralgia/pathology* ; Receptor, Fibroblast Growth Factor, Type 3/metabolism* ; Signal Transduction/physiology* ; Male ; Mice ; Microglia/drug effects* ; Fibroblast Growth Factor 8/pharmacology* ; Mice, Inbred C57BL ; Hyperalgesia/drug therapy* ; Spinal Cord/drug effects* ; Complement C3/metabolism* ; Spinal Cord Dorsal Horn/metabolism*

Objective To investigate the effects of sakuranetin (SK) on motor functions in the mouse model of spinal cord injury (SCI) and decipher the mechanism. Methods Fifty-four C57BL/6J mice were randomized into sham,SCI,and SK groups.The mice in the sham group underwent only laminectomy at T9,while those in the SCI and SK groups were subjected to spinal cord contusion injury at T9.Behavioral tests were conducted at different time points after surgery to evaluate the motor functions of mice in each group.The pathological changes in the tissue were observed to assess the extent of SCI in each group.The role and mechanism of SK in SCI were predicted by gene ontology (GO) and Kyoto encyclopedia of genes and genomes (KEGG) enrichment analyses.Reverse transcription real-time fluorescence quantitative PCR,ELISA,and immunofluorescence were employed to evaluate the inflammation and activation of microglia in SCI mice.BV2 cells in vitro were classified into control (Con),lipopolysaccharide (LPS),and LPS+SK groups.The effects of SK intervention on the release of inflammatory cytokines and the activation of BV2 cells were evaluated.Furthermore,the phosphatidylinositol-3-kinase(PI3K)/protein kinase B (AKT) signaling pathway activator insulin-like growth factor-1 (IGF-1) was used to treat the SK-induced BV2 cells in vitro (SK+IGF-1 group),and SK was used to treat the IGF-1-induced BV2 cells in vitro (IGF-1+SK group).Western blotting was conducted for molecular mechanism validation. Results Behavioral tests and histological staining results showed that compared with the SCI group,the SK group exhibited improved motor abilities and reduced area of damage in the spinal cord tissue (all P<0.001).The GO enrichment analysis predicted that SK may be involved in the inflammation following SCI.The KEGG enrichment analysis predicted that SK regulated the PI3K/Akt pathway to exert the neuroprotective effect.The results from in vitro and in vivo experiments showed that SK lowered the levels of tumor necrosis factor-α,interleukin-6,and interleukin-1β and inhibited the activation of microglia (all P<0.05).The results of Western blotting showed that SK down-regulated the phosphorylation levels of PI3K and Akt (all P<0.001) and inhibited the IGF-1-induced elevation of PI3K and Akt phosphorylation levels (all P<0.001).Conversely,IGF-1 had the opposite effects (P=0.001,P<0.001).The results of reverse transcription real-time fluorescence quantitative PCR,ELISA,and immunofluorescence showed that the SK+IGF-1 group had higher levels of inflammatory cytokines and more activated microglia than the SK group(all P<0.05). Conclusion SK may suppress the activation of the PI3K/Akt pathway to inhibit the inflammation mediated by SCI-induced activation of microglia,ameliorate the pathological damage of the spinal cord tissue,and promote the recovery of motor functions in SCI mice.
Animals ; Spinal Cord Injuries/pathology* ; Mice ; Microglia/metabolism* ; Mice, Inbred C57BL ; Neuroinflammatory Diseases/pathology* ; Signal Transduction/drug effects* ; Phosphatidylinositol 3-Kinases/metabolism* ; Proto-Oncogene Proteins c-akt/metabolism* ; Male ; Inflammation ; Lipopolysaccharides ; Insulin-Like Growth Factor I/metabolism* ; Disease Models, Animal

Occupational exposure to 1-bromopropane (1-BP) induces learning and memory deficits. However, no therapeutic strategies are currently available. Accumulating evidence has suggested that N-methyl-D-aspartate receptors (NMDARs) and neuroinflammation are involved in the cognitive impairments in neurodegenerative diseases. In this study we aimed to investigate whether the noncompetitive NMDAR antagonist MK801 protects against 1-BP-induced cognitive dysfunction. Male Wistar rats were administered with MK801 (0.1 mg/kg) prior to 1-BP intoxication (800 mg/kg). Their cognitive performance was evaluated by the Morris water maze test. The brains of rats were dissected for biochemical, neuropathological, and immunological analyses. We found that the spatial learning and memory were significantly impaired in the 1-BP group, and this was associated with neurodegeneration in both the hippocampus (especially CA1 and CA3) and cortex. Besides, the protein levels of phosphorylated NMDARs were increased after 1-BP exposure. MK801 ameliorated the 1-BP-induced cognitive impairments and degeneration of neurons in the hippocampus and cortex. Mechanistically, MK801 abrogated the 1-BP-induced disruption of excitatory and inhibitory amino-acid balance and NMDAR abnormalities. Subsequently, MK801 inhibited the microglial activation and release of pro-inflammatory cytokines in 1-BP-treated rats. Our findings, for the first time, revealed that MK801 protected against 1-BP-induced cognitive dysfunction by ameliorating NMDAR function and blocking microglial activation, which might provide a potential target for the treatment of 1-BP poisoning.
Animals ; Brain ; drug effects ; metabolism ; pathology ; Cognitive Dysfunction ; drug therapy ; metabolism ; pathology ; Disease Models, Animal ; Dizocilpine Maleate ; pharmacology ; Excitatory Amino Acid Antagonists ; pharmacology ; Hydrocarbons, Brominated ; Inflammasomes ; drug effects ; metabolism ; Male ; Maze Learning ; drug effects ; physiology ; Microglia ; drug effects ; metabolism ; pathology ; NLR Family, Pyrin Domain-Containing 3 Protein ; metabolism ; Neurons ; drug effects ; metabolism ; pathology ; Nootropic Agents ; pharmacology ; Random Allocation ; Rats, Wistar ; Receptors, N-Methyl-D-Aspartate ; antagonists & inhibitors ; metabolism ; Spatial Memory ; drug effects ; physiology ; Specific Pathogen-Free Organisms

OBJECTIVE: To investigate the anti-neuroinflammation effect of extract of Fructus Schisandrae chinensis (EFSC) on lipopolysaccharide (LPS)-induced BV-2 cells and the possible involved mechanisms. METHODS: Primary cortical neurons were isolated from embryonic (E17-18) cortices of Institute of Cancer Research (ICR) mouse fetuses. Primary microglia and astroglia were isolated from the frontal cortices of newborn ICR mouse. Different cells were cultured in specific culture medium. Cells were divided into 5 groups: control group, LPS group (treated with 1 μg/mL LPS only) and EFSC groups (treated with 1 μg/mL LPS and 100, 200 or 400 mg/mL EFSC, respectively). The effect of EFSC on cells viability was tested by methylthiazolyldiphenyltetrazolium bromide (MTT) colorimetric assay. EFSC-mediated inhibition of LPS-induced production of pro-inflammatory mediators, such as nitrite oxide (NO) and interleukin-6 (IL-6) were quantified and neuron-protection effect against microglia-mediated inflammation injury was tested by hoechst 33258 apoptosis assay and crystal violet staining assay. The expression of pro-inflammatory marker proteins was evaluated by Western blot analysis or immunofluorescence. RESULTS: EFSC (200 and 400 mg/mL) reduced NO, IL-6, inducible nitric oxide synthase (iNOS) and cyclooxygenase 2 (COX-2) expression in LPS-induced BV-2 cells (P<0.01 or P<0.05). EFSC (200 and 400 mg/mL) reduced the expression of NO in LPS-induced primary microglia and astroglia (P<0.01). In addition, EFSC alleviated cell apoptosis and inflammation injury in neurons exposed to microglia-conditioned medium (P<0.01). The mechanistic studies indicated EFSC could suppress nuclear factor (NF)-?B phosphorylation and its nuclear translocation (P<0.01). The anti-inflammatory effect of EFSC occurred through suppressed activation of mitogen-activated protein kinase (MAPK) pathway (P<0.01 or P<0.05). CONCLUSION EFSC acted as an anti-inflammatory agent in LPS-induced glia cells. These effects might be realized through blocking of NF-κB activity and inhibition of MAPK signaling pathways.
Animals ; Astrocytes ; drug effects ; metabolism ; pathology ; Cell Line ; Cell Nucleus ; drug effects ; metabolism ; Chromatography, High Pressure Liquid ; Down-Regulation ; drug effects ; Inflammation ; pathology ; Inflammation Mediators ; metabolism ; Lipopolysaccharides ; MAP Kinase Signaling System ; drug effects ; Mice, Inbred ICR ; Microglia ; drug effects ; metabolism ; pathology ; NF-kappa B ; metabolism ; Nervous System ; pathology ; Neurons ; drug effects ; metabolism ; pathology ; Neuroprotective Agents ; pharmacology ; Plant Extracts ; pharmacology ; Schisandra ; chemistry ; Spectrometry, Mass, Electrospray Ionization

PURPOSETo investigate the effects of estrogen G protein-coupled receptor 30 (GPR30) agonist G1 on hippocampal neuronal apoptosis and microglial polarization in rat traumatic brain injury (TBI).

METHODSMale SD rats were randomly divided into sham group, TBI + vehicle group, TBI + G1 group. Experimental moderate TBI was induced using Feeney's weigh-drop method. G1 (100μg/kg) or vehicle was intravenously injected from femoral vein at 30 min post-injury. Rats were sacrificed at 24 h after injury for detection of neuronal apoptosis and microglia polarization. Neuronal apoptosis was assayed by immunofluorescent staining of active caspase-3. M1 type microglia markers (iNOS and IL-1β) and M2 type markers (Arg1 and IL-4) were examined by immunoblotting or ELISA. Total protein level of Akt and phosphorylated Akt were assayed by immunoblotting.

RESULTSG1 significantly reduced active caspase-3 positive neurons in hippocampus. Meanwhile G1 increased the ratio of Arg1/iNOS. IL-1β production was decreased but IL-4 was increased after G1 treatment. G1 treatment also increased the active form of Akt.

CONCLUSIONSGPR30 agonist G1 inhibited neuronal apoptosis and favored microglia polarization to M2 type.

Animals ; Apoptosis ; drug effects ; Brain Injuries, Traumatic ; drug therapy ; pathology ; Cell Polarity ; Hippocampus ; drug effects ; Interleukin-1beta ; biosynthesis ; Male ; Microglia ; drug effects ; Neurons ; drug effects ; Proto-Oncogene Proteins c-akt ; metabolism ; Rats ; Rats, Sprague-Dawley ; Receptors, G-Protein-Coupled ; agonists