Malcolm Prior

Progesterone suppresses the inflammatory response and nitric oxide synthase-2 expression following cerebral ischemia.

Gender differences in outcome following cerebral ischemia have frequently been observed and attributed to the actions of steroid hormones. Progesterone has been shown to possess neuroprotective properties following transient ischemia, with respect to decreasing lesion volume and improving functional recovery. The present study was designed to determine the mechanisms of progesterone neuroprotection, and whether these relate to the inflammatory response. Male mice underwent either 60 min or permanent middle cerebral artery occlusion (MCAO) and received progesterone (8 mg/kg ip) or vehicle 1 h, 6 h and 24 h post-MCAO. Forty-eight hours following transient MCAO, structural magnetic resonance imaging revealed a significant decrease in the amount of edematous tissue present in progesterone-treated mice as compared with vehicle. Using real-time PCR we found that progesterone treatment significantly suppressed the injury-induced upregulation of interleukin (IL)-1beta, transforming growth factor (TGF)beta2, and nitric oxide synthase (NOS)-2 mRNAs in the ipsilateral hemisphere while having no effect on tumor necrosis factor (TNF)-alpha mRNA expression. Progesterone treatment following permanent MCAO also resulted in a significant decrease in lesion volume. This was not apparent in mice lacking a functional NOS-2 gene. Thus, progesterone is neuroprotective in both permanent and transient ischemia, and this effect is related to the suppression of specific aspects of the inflammatory response.

Focal astrocyte loss is followed by microvascular damage, with subsequent repair of the blood-brain barrier in the apparent absence of direct astrocytic contact.

Blood‐brain barrier (BBB) breakdown is a feature of cerebral ischaemia, multiple sclerosis, and other neurodegenerative diseases, yet the relationship between astrocytes and the BBB integrity remains unclear. We present a simple in vivo model in which primary astrocyte loss is followed by microvascular damage, using the metabolic toxin 3‐chloropropanediol (S‐α‐chlorohydrin). This model is uncomplicated by trauma, ischaemia, or primary immune involvement, permitting the study of the role of astrocytes in vascular endothelium integrity, maintenance of the BBB, and neuronal function. Male Fisher F344 rats given 3‐chloropropanediol show astrocytic damage and death at 4–24 h in symmetrical brainstem and midbrain nuclear lesions, while neurons show morphological changes at 24–48 h. Fluorescent 10 kDa dextran tracers show the BBB leaking from 24 h, progressing to petechial haemorrhage after 48–72 h, with apparent repair after 6 days. BBB breakdown, but not the earlier astrocytic death, is accompanied by a delayed increase in blood flow in the inferior colliculus. An ED1 inflammatory response develops well after astrocyte loss, suggesting that inflammation may not be a factor in starting BBB breakdown. This model demonstrates that the BBB can self‐repair despite the apparent absence of direct astrocytic‐endothelial contact. The temporal separation of pathological events allows pharmacological intervention, and the mild reversible ataxia permits long‐term survival studies of repair mechanisms.

G-CSF suppresses edema formation and reduces interleukin-1β expression after cerebral ischemia in mice

Granulocyte-colony stimulating factor (G-CSF) is reported to be neuroprotective after transient cerebral ischemia with respect to decreasing lesion volume and enhancing functional recovery. We investigated whether G-CSF is neuroprotective after permanent ischemia and the possible mechanisms underlying this neuroprotection. Mice underwent permanent or 60-minute middle cerebral artery occlusion (MCAO) and received G-CSF (50 μg/kg) or vehicle at the onset or 1 hour post-MCAO. Forty-eight hours after transient MCAO, structural magnetic resonance imaging revealed a significant reduction (50%) in the amount of edematous tissue present in G-CSF-treated mice (p < 0.05). G-CSF treatment also prevented a significant increase in ipsilateral brain water content that was present in vehicle-treated mice after transient (p < 0.05) and permanent (p < 0.001) MCAO. Forty-eight hours after permanent MCAO, G-CSF decreased (50%) the cortical lesion volume (p < 0.05). Using real-time polymerase chain reaction, we found that G-CSF treatment significantly suppressed (p < 0.05) the injury-induced upregulation of IL-1β mRNA while having no effect on TNFα and NOS-2 mRNA expression. This suggests that part of the neuroprotection may be attributed to the ability of G-CSF to reduce the inflammatory response.

Dopamine antagonist modulation of amphetamine response as detected using pharmacological MRI

Functional magnetic resonance imaging (fMRI), employing BOLD-contrast, was used to measure changes in regional brain activation following amphetamine administration, either alone or after pre-treatment with the dopamine D1 receptor antagonist SCH23390, or the dopamine D2 receptor antagonist, sulpiride, in anaesthetised rat. After obtaining baseline data, rats (n=8) were given amphetamine (3 g/kg i.v) and volume data sets collected for 90 mins. Acute amphetamine challenge caused widespread increases in BOLD signal intensity in many subcortical structures with rich dopaminergic innervation, with decreases in BOLD contrast observed in the superficial layers of the cortex. Pretreatment with SCH23390 (n=8, 0.5 mg/kg, i.v) substantially attenuated the increases in BOLD activity in response to amphetamine, with lesser effects on the amphetamine-evoked decreases in BOLD signal. In contrast, sulpiride (n=8, 50 mg/kg, i.v) predominantly blocked the decrease in BOLD signal, having a smaller effect on the increases in BOLD signal. In summary, these data are supportive of the notion that different dopamine receptor types are responsible for separate components of the full amphetamine response. Furthermore the utility of BOLD contrast fMRI as a means of characterising the mechanisms of drug action in the whole brain has been demonstrated. Such studies may be of particular use for investigation of localised action and interaction of different dopaminergic agents.

Methodological considerations in rat brain BOLD contrast pharmacological MRI

Rationale and objectivesBlood oxygen level dependent (BOLD) contrast pharmacological magnetic resonance imaging (phMRI) is an increasingly popular technique that allows the non-invasive investigation of spatial and temporal changes in rat brain function in response to pharmacological stimulation in vivo. Rat brain BOLD contrast phMRI is, at present, established in few neuropharmacological laboratories, and various issues associated with the technique require attention. The present review is primarily aimed at psychopharmacologists with no previous experience of phMRI, who are interested in the practical aspects that phMRI studies entail.Results and discussionExperimental and analytical considerations, including anaesthesia, physiological monitoring, drug dose and delivery, scanning protocols, statistical approaches and the interpretation of phMRI data, are discussed.

Antagonism of the interleukin-1 receptor following traumatic brain injury in the mouse reduces the number of nitric oxide synthase-2-positive cells and improves anatomical and functional outcomes

Interleukin (IL)‐1β plays an important role in the inflammatory response that results from traumatic brain injury and antagonism of the actions of this cytokine can affect outcome. We subjected male mice to aseptic cryogenic injury and assessed recovery through anatomical, histological and functional measures following treatment with recombinant mouse IL‐1 receptor antagonist (IL‐1ra). A single dose (1 µg, i.c.v.) at the time of injury reduced lesion volume 3 days later, as assessed by Nissl staining, and also the number (30%) of FluoroJade‐positive degenerating neurones. Mice treated with IL‐1ra performed better on the beam balance and in the grid test as compared with vehicle‐treated animals. Furthermore, IL‐1ra‐treated animals showed fewer (40%) nitric oxide synthase‐2‐positive cells in and around the lesion. These data suggest that activation of the IL‐1 receptor following trauma contributes to the pathology and that antagonism can reduce both anatomical and functional consequences of neuroinflammation.

The neuroprotective effect of progesterone after traumatic brain injury in male mice is independent of both the inflammatory response and growth factor expression

Previous studies suggest that progesterone may possess neuroprotective properties after traumatic insult but, with the exception of reduced formation of cerebral oedema, limited experimental evidence has been presented to support this claim. In the present study we focused on the effect of progesterone treatment on structural and functional deficits in an experimental model of traumatic brain injury. Female mice exhibited significantly (P = 0.0445) reduced lesion volumes compared with males after aseptic cryogenic cerebral injury (ACI), suggesting that female sex steroids provide protection against this injury. In male mice, progesterone treatment after injury (three intraperitoneal doses of 8 mg/kg) reduced lesion volume (P = 0.0429) and improved performance in a spatial cognitive task (Morris water maze; P = 0.0014). However, progesterone had no demonstrable effect on the formation of oedema as measured using T2‐weighted magnetic resonance imaging, nor did it affect brain water content. The pro‐inflammatory cytokines TNF‐α and IL‐1β, and growth factors BDNF and G‐CSF, were all strongly transcriptionally activated after ACI. However, progesterone administration did not affect expression of these genes. This study provides strong evidence that progesterone possesses neuroprotective properties in a mouse model of traumatic brain injury, but suggests that the steroid achieves this effect through mechanism(s) independent of the inflammatory response or growth factor up‐regulation.

Detection of cannabinoid agonist evoked increase in BOLD contrast in rats using functional magnetic resonance imaging.

BOLD-contrast functional magnetic resonance imaging (fMRI) was used to investigate the effects of the synthetic cannabinoid agonist HU210 on the rat brain in order to determine potential CNS sites of action for the functional effects of cannabinoids. After obtaining basal data, rats (n=8) were given the cannabinoid agonist HU210 (10 microg/kg i.v.) and volume data sets collected for 85 mins. Significant increases in functional BOLD activity were observed in specific brain regions including those important in pain (PAG), reward (VTA and accumbens) and motor function (striatum). In order to confirm cannabinoid receptor involvement in the HU210 evoked functional BOLD activity, rats (n=8) were pre-treated with the CB1 cannabinoid receptor antagonist SR141716A (100 microg/kg i.v.) prior to HU210. Pretreatment with SR141716A abolished all significant evoked HU210 functional BOLD activity. To exclude the involvement of potential systemic effects induced by the cannabinoid agonist administration on the observed evoked functional BOLD activity a separate experiment investigated the effect of HU210 (10 microg/kg i.v.) on mean arterial pressure and showed that HU210 had no significant effect on pressure under chloral hydrate anaesthesia. In summary, this study demonstrates that the cannabinoid agonist HU210 evokes a significant increase in BOLD functional activity in specific regions and that this was cannabinoid receptor mediated. Furthermore the study indicates the potential value of fMRI in rodents to delineate pharmacologically induced changes in regional brain function.

Capsaicin-evoked brain activation and central sensitization in anaesthetised rats: A functional magnetic resonance imaging study

&NA; Functional magnetic resonance imaging (fMRI) of blood oxygen level dependent (BOLD) haemodynamic responses was used to study the effects of the noxious substance capsaicin on whole brain activation in isofluorane anaesthetised rats. Rats (n = 8) received intradermal injection of capsaicin (30 &mgr;g/5 &mgr;l), or topical cream (0.1%) capsaicin and BOLD responses were acquired for up to 120 min. Effects of capsaicin versus placebo cream treatment on the BOLD response to a 15 g mechanical stimulus applied adjacent to the site of cream application were also studied. Both injection and cream application of capsaicin activated brain areas involved in pain processing, including the thalamus and periaqueductal grey (PAG) (p < 0.05, corrected for multiple comparisons). Capsaicin also produced increases in BOLD signal intensity in other regions that contribute to pain processing, such as the parabrachial nucleus and superior colliculus. Mechanical stimulation in capsaicin‐treated rats, but not placebo‐treated rats, induced a significant decrease in BOLD signal intensity in the PAG (p < 0.001). These data demonstrate that the noxious substance capsaicin produces brain activation in the midbrain regions and reveals the importance of the PAG in central sensitization.

Dependence of blood R2 relaxivity on CPMG echo‐spacing at 2.35 and 7 T

The transverse relaxation rate (R2) of fresh human blood has been investigated at high and ultrahigh field, to characterize the R2 dependency on blood sample oxygenation, hematocrit, and Carr‐Purcell Meiboom‐Gill sequence inter‐echo spacing. Data were fitted to chemical exchange and diffusion models to assess their performance at different field strengths. The diffusion model gave a slightly superior fit at both field strengths, but the difference is unlikely to be relevant for the signal to noise ratio achieved in most in vivo experiments. Fitted model parameters were similar to those found in literature. Magn Reson Med, 2010.