Time‐of‐day‐dependent sensitivity of the reproductive axis to RFamide‐related peptide‐3 inhibition in female Syrian hamsters

In spontaneously ovulating rodent species, the timing of the luteinising hormone (LH) surge is controlled by the master circadian pacemaker in the suprachiasmatic nucleus (SCN). The SCN initiates the LH surge via the coordinated control of two opposing neuropeptidergic systems that lie upstream of the gonadotrophin‐releasing hormone (GnRH) neuronal system: the stimulatory peptide, kisspeptin, and the inhibitory peptide, RFamide‐related peptide‐3 (RFRP‐3; the mammalian orthologue of avian gonadotrophin‐inhibitory hormone [GnIH]). We have previously shown that the GnRH system exhibits time‐dependent sensitivity to kisspeptin stimulation, further contributing to the precise timing of the LH surge. To examine whether this time‐dependent sensitivity of the GnRH system is unique to kisspeptin or a more common mechanism of regulatory control, we explored daily changes in the response of the GnRH system to RFRP‐3 inhibition. Female Syrian hamsters were ovariectomised to eliminate oestradiol (E₂)‐negative‐feedback and RFRP‐3 or saline was centrally administered in the morning or late afternoon. LH concentrations and Lhβ mRNA expression did not differ between morning RFRP‐3‐and saline‐treated groups, although they were markedly suppressed by RFRP‐3 administration in the afternoon. However, RFRP‐3 inhibition of circulating LH at the time of the surge does not appear to act via the GnRH system because no differences in medial preoptic area Gnrh or RFRP‐3 receptor Gpr147 mRNA expression were observed. Rather, RFRP‐3 suppressed arcuate nucleus Kiss1 mRNA expression and potentially impacted pituitary gonadotrophs directly. Taken together, these findings reveal time‐dependent responsiveness of the reproductive axis to RFRP‐3 inhibition, possibly via variation in the sensitivity of arcuate nucleus kisspeptin neurones to this neuropeptide.     

Caffeine treatment prevents rapid eye movement sleep deprivation‐induced impairment of late‐phase long‐term potentiation in the dentate gyrus

The CA1 and dentate gyrus (DG) are physically and functionally closely related areas of the hippocampus, but they differ in various respects, including their reactions to different insults. The purpose of this study was to determine the protective effects of chronic caffeine treatment on late‐phase long‐term potentiation (L‐LTP) and its signalling cascade in the DG area of the hippocampus of rapid eye movement sleep‐deprived rats. Rats were chronically treated with caffeine (300 mg/L drinking water) for 4 weeks, after which they were sleep‐deprived for 24 h. L‐LTP was induced in in anaesthetized rats, and extracellular field potentials from the DG area were recorded in vivo. The levels of L‐LTP‐related signalling proteins were assessed by western blot analysis. Sleep deprivation markedly reduced L‐LTP magnitude, and basal levels of total cAMP response element‐binding protein (CREB), phosphorylated CREB (P‐CREB), and calcium/calmodulin kinase IV (CaMKIV). Chronic caffeine treatment prevented the reductions in the basal levels of P‐CREB, total CREB and CaMKIV in sleep‐deprived rats. Furthermore, caffeine prevented post‐L‐LTP sleep deprivation‐induced downregulation of P‐CREB and brain‐derived neurotrophic factor in the DG. The current findings show that caffeine treatment prevents acute sleep deprivation‐induced deficits in brain function.     

Tired and stressed: Examining the need for sleep

A key feature of circadian rhythms is the sleep/wake cycle. Sleep causes reduced responsiveness to the environment, which puts animals in a particularly vulnerable state; yet sleep has been conserved throughout evolution, indicating that it fulfils a vital purpose. A core function of sleep across species has not been identified, but substantial advances in sleep research have been made in recent years using the genetically tractable model organism, Drosophila melanogaster. This review describes the universality of sleep, the regulation of sleep, and current theories on the function of sleep, highlighting a historical and often overlooked theory called the Free Radical Flux Theory of Sleep. Additionally, we summarize our recent work with short‐sleeping Drosophila mutants and other genetic and pharmacological tools for manipulating sleep which supports an antioxidant theory of sleep and demonstrates a bi‐directional relationship between sleep and oxidative stress.     

Site‐specific effects of gastrin‐releasing peptide in the suprachiasmatic nucleus

The effects of gastrin‐releasing peptide (GRP) on the circadian clock in the suprachiasmatic nucleus (SCN) are dependent on the activation of N‐methyl‐d ‐aspartate (NMDA) receptors in the SCN. In this study, the interaction between GRP, glutamate and serotonin in the regulation of circadian phase in Syrian hamsters was evaluated. Microinjection of GRP into the third ventricle induced c‐fos and p‐ERK expression throughout the SCN. Coadministration of an NMDA antagonist or 8‐hydroxy‐2‐di‐n‐propylamino‐tetralin [a serotonin (5‐HT)_1A,7 agonist, DPAT] with GRP limited c‐fos expression in the SCN to a region dorsal to GRP cell bodies. Similar to the effects of NMDA antagonists, DPAT attenuated GRP‐induced phase shifts in the early night, suggesting that the actions of serotonin on the photic phase shifting mechanism occur downstream from retinorecipient cells. c‐fos and p‐ERK immunoreactivity in the supraoptic (SON) and paraventricular hypothalamic nuclei also increased following ventricular microinjection of GRP. Because of this finding, a second set of experiments was designed to test a potential role for the SON in the regulation of clock function. Syrian hamsters were given microinjections of GRP into the peri‐SON during the early night. GRP‐induced c‐fos activity in the SCN was similar to that following ventricular administration of GRP. GRP or bicuculline (a γ‐aminobutyric acid_A antagonist) administered near the SON during the early night elicited phase delays of circadian activity rhythms. These data suggest that GRP‐induced phase‐resetting is dependent on levels of glutamatergic and serotonergic neurotransmission in the SCN and implicate activity in the SON as a potential regulator of photic signaling in the SCN.     

The complex relationship between the light‐entrainable and methamphetamine‐sensitive circadian oscillators: evidence from behavioral studies of Period‐mutant mice

The methamphetamine‐sensitive circadian oscillator (MASCO) is an enigmatic circadian clock whose output is observed during continuous consumption of low‐dose methamphetamine. The MASCO rhythm persists when the light‐entrainable pacemaker in the suprachiasmatic nucleus (SCN) is lesioned, but the anatomical location of MASCO is unknown. We recently found that the period of the MASCO rhythm is unusually short (21 h) in mice with disruption of all three paralogs of the canonical clock gene, Period. In this study, we investigated the contribution of each Period paralog to timekeeping in MASCO. We measured wheel‐running activity rhythms in intact and SCN‐lesioned Per1‐, 2‐ and 3‐mutant mice administered methamphetamine, and found that none of the mice displayed a short (21‐h) period, demonstrating that no single Period gene is responsible for the short‐period MASCO rhythm of Per1^?/?/Per2^?/?/Per3^?/? mice. We also found that the periods of activity rhythms in constant darkness were lengthened by methamphetamine treatment in intact wild‐type, Per1^?/? and Per3^?/? mice but not Per2^?/? mice, and Per2^?/? mice had two distinct activity rhythms upon release to constant light. These data suggest that the SCN and MASCO are not coupled in Per2^?/? mice. The MASCO rhythm in Per1^?/?/Per2^?/? mice in constant darkness alternated between a short (22‐h) and a long (27‐h) period. This pattern could result from two coupled oscillators that are not synchronised to each other, or from a single oscillator displaying birhythmicity. Finally, we propose a working model of the in vivo relationship between MASCO and the SCN that poses testable hypotheses for future studies.     

Inhibitory effects of heterotopic noxious counter‐stimulation on perception and brain activity related to Aβ‐fibre activation

Heterotopic noxious counter‐stimulation (HNCS) inhibits pain and pain processes through cerebral and cerebrospinal mechanisms. However, it is unclear whether HNCS inhibits non‐nociceptive processes, which needs to be clarified for a better understanding of HNCS analgesia. The aim of this study was to examine the effects of HNCS on perception and scalp somatosensory evoked potentials (SEPs). Seventeen healthy volunteers participated in two counter‐balanced sessions, including non‐nociceptive (selective Aβ‐fibre activation) or nociceptive electrical stimulation, combined with HNCS. HNCS was produced by a 20‐min cold pressor test (left hand) adjusted individually to produce moderate pain (mean ± SEM: 42.5 ± 5.3 on a 0–100 scale, where 0 is no pain and 100 the worst pain imaginable). Non‐nociceptive electrical stimulation was adjusted individually at 80% of pain threshold and produced a tactile sensation in every subject. Nociceptive electrical stimulation was adjusted individually at 120% of RIII‐reflex threshold and produced moderate pain (45.3 ± 4.5). Shock sensation was significantly decreased by HNCS compared with baseline for non‐nociceptive (P < 0.001) and nociceptive (P < 0.001) stimulation. SEP peak‐to‐peak amplitude at Cz was significantly decreased by HNCS for non‐nociceptive (P < 0.01) and nociceptive (P < 0.05) stimulation. These results indicate that perception and brain activity related to Aβ‐fibre activation are inhibited by HNCS. The mechanisms of this effect remain to be investigated to clarify whether it involves inhibition of spinal wide‐dynamic‐range neurons by diffuse noxious inhibitory controls, supraspinal processes or both.     

Modulation of task‐related cortical connectivity in the acute and subacute phase after stroke

The functional relevance of cortical reorganization post‐stroke is still not well understood. In this study, we investigated task‐specific modulation of cortical connectivity between neural oscillations in key motor regions during the early phase after stroke. EEG and EMG recordings were examined from 15 patients and 18 controls during a precision grip task using the affected hand. Each patient attended two sessions in the acute and subacute phase (median of 3 and 34 days) post‐stroke. Dynamic causal modelling (DCM) for induced responses was used to investigate task‐specific modulations of oscillatory couplings in a bilateral network comprising supplementary motor area (SMA), dorsal premotor cortex (PMd) and primary motor cortex (M1). Fourteen models were constructed for each subject, and the input induced by the experimental manipulation (task) was set to inferior parietal lobule (IPL). Bayesian model selection favoured a fully connected model. A reduced coupling from SMA and intact M1 in the γ‐band (31–48 Hz) to lesioned M1 in the β‐band (15–30 Hz) was observed in patients in the acute phase compared to controls. Behavioural performance improved significantly in the subacute phase, while an increased positive coupling from intact PMd to lesioned M1 and a less negative modulation from lesioned M1 to intact M1 were observed for patients compared to controls both from the γ‐band to the β‐band. We infer that the observed differences in cross‐frequency cortical interactions are important for functional recovery.     

Prognostic significance of genetic biomarkers in isocitrate dehydrogenase‐wild‐type lower‐grade glioma: the need to further stratify this tumor entity – a meta‐analysis

The clinical outcomes of isocitrate dehydrogenase‐wild‐type (IDH‐wt) lower‐grade glioma (LGG) have been the subject of debate for some time. In this meta‐analysis, we aimed to assess the prognostic values of several known genetic markers (e.g. TERT promoter mutation, H3F3A mutation, CDKN2A loss) in this tumor group. Four electronic databases, including PubMed, Scopus, Web of Science and Virtual Health Library, were searched for relevant articles. Pooled hazard ratio (HR) and corresponding 95% confidence interval (CI) for overall survival were calculated using a random‐effect model weighted by an inverse variance method. A total of 11 studies were finally selected from 2274 articles for meta‐analyses. Several genetic alterations were demonstrated to have a negative impact on prognosis of IDH‐wt LGGs, specifically TERT promoter mutation (HR, 1.96; 95% CI, 1.42–2.70), H3F3A mutation (HR, 3.21; 95% CI, 1.86–5.55) and EGFR amplification (HR, 1.67; 95% CI, 1.02–2.74). However, CDKN loss, ATRX mutation and coexisting gain of chromosome 7/loss of chromosome 10 showed no clinical significance in this glioma entity. Our study results demonstrated that IDH‐wt LGGs are heterogeneous in clinical outcome and not all tumors have a poor prognosis. The presence of TERT promoter mutation, H3F3A mutation and EGFR amplification showed negative prognostic impacts in this tumor entity. These genetic events can be used to better stratify patient outcomes.     

A role for the ventral pallidum in context‐induced and primed reinstatement of alcohol seeking

The ventral pallidum (VP) is a major target of projections from the nucleus accumbens, and has been implicated in the reinstatement of psychostimulant seeking as part of a cortical–striatal–pallidal ‘final common pathway’ for relapse. Here, we studied the role of the VP in context‐induced and primed reinstatement of alcoholic beer seeking, using a combination of microinjections and tract tracing studies. In experiment 1, rats were trained to respond to alcoholic beer in one context (A), and then extinguished in a second context (B), prior to testing for reinstatement (ABA renewal) and extinction (ABB). VP microinjection of the μ‐opioid receptor (MOR) antagonist CTAP prevented reinstatement. In experiment 2, VP microinjection of CTAP also prevented the primed reinstatement of alcoholic beer seeking after rats were trained, extinguished, and tested in the same context. In experiment 3, we employed retrograde neural tract tracing together with c‐Fos immunohistochemistry to identify the VP afferents recruited during context‐induced reinstatement of alcoholic beer seeking. There was evidence for the recruitment of accumbens core→VP, basolateral amygdala→VP and paraventricular thalamus→VP pathways during context‐induced reinstatement. These results indicate that the VP MORs are critical for context‐induced reinstatement, and that the VP receives inputs from a number of regions known to be important in reinstatement of drug seeking.     

Rostro‐caudal maturation of glial cells in the accessory olfactory system during development: involvement in outgrowth of GnRH neurites

During mammalian embryonic development, GnRH neurones differentiate from the nasal placode and migrate through the nasal septum towards the forebrain. We previously showed that a category of glial cells, the olfactory ensheathing cells (OEC), forms the microenvironment of migrating GnRH neurones. Here, to characterize the quantitative and qualitative importance of this glial, we investigated the spatiotemporal maturation of glial cells in situ and the role of maturing glia in GnRH neurones development ex vivo. More than 90% of migrating GnRH neurones were found to be associated with glial cells. There was no change in the cellular microenvironment of GnRH neurones in the regions crossed during embryonic development as glial cells formed the main microenvironment of these neurones (53.4%). However, the phenotype of OEC associated with GnRH neurones changed across regions. The OEC progenitors immunoreactive to brain lipid binding protein formed the microenvironment of migrating GnRH neurones from the vomeronasal organ to the telencephalon and were also present in the diencephalon. However, during GnRH neurone migration, maturation of OEC to [GFAP+] state (glial fibrillary acid protein) was only observed in the nasal septum. Inducing depletion of OEC in maturation, using transgenic mice expressing herpes simplex virus thymidine kinase driven by the GFAP promoter, had no impact on neurogenesis or on triggering GnRH neurones migration in nasal explant culture. Nevertheless, depletion of [GFAP+] cells decreased GnRH neurites outgrowth by 57.4%. This study suggests that specific maturation of OEC in the nasal septum plays a role in morphological differentiation of GnRH neurones.     

Involvement of PKA and ERK pathways in ghrelin‐induced long‐lasting potentiation of excitatory synaptic transmission in the CA1 area of rat hippocampus

Acute effects of ghrelin on excitatory synaptic transmission were evaluated on hippocampal CA1 synapses. Ghrelin triggered an enduring enhancement of synaptic transmission independently of NMDA receptor activation and probably via postsynaptic modifications. This ghrelin‐mediated potentiation resulted from the activation of GHS‐R1a receptors as it was mimicked by the selective agonist JMV1843 and blocked by the selective antagonist JMV2959. This potentiation also required the activation of PKA and ERK pathways to occur as it was inhibited by KT5720 and U0126, respectively. Moreover it most probably involved Ca²⁺ influxes as both ghrelin and JMV1843 elicited intracellular Ca²⁺ increases, which were dependent on the presence of extracellular Ca²⁺ and mediated by L‐type Ca²⁺ channels opening. In addition, ghrelin potentiated AMPA receptor‐mediated [Ca²⁺]i increases while decreasing NMDA receptor‐mediated ones. Thus the potentiation of synaptic transmission by GHS‐R1a at hippocampal CA1 excitatory synapses probably results from postsynaptic mechanisms involving PKA and ERK activation, which are producing long‐lasting enhancement of AMPA receptor‐mediated responses.     

Selectivity for mid‐level properties of faces and places in the fusiform face area and parahippocampal place area

Regions in the ventral visual pathway, such as the fusiform face area (FFA) and parahippocampal place area (PPA) are selective for images from specific object categories. Yet images from different object categories differ in their image properties. To investigate how these image properties are represented in the FFA and PPA, we compared neural responses to locally‐SCRAMBLED images (in which mid‐level, spatial properties are preserved) and globally‐SCRAMBLED images (in which mid‐level, spatial properties are not preserved). There was a greater response in the FFA and PPA to images from the preferred CATEGORY relative to their non‐preferred category for the scrambled conditions. However, there was a greater selectivity for locally‐scrambled compared to globally‐scrambled images. Next, we compared the magnitude of fMR‐adaptation to intact and scrambled images. fMR‐adaptation was evident to locally‐scrambled images from the preferred category. However, there was no adaptation to globally‐scrambled images from the preferred category. These results show that the selectivity to faces and places in the FFA and PPA is dependent on mid‐level properties of the image that are preserved by local‐scrambling.