Biology subjects

Hunt, M. J.

Publications and source records attributed to Hunt, M. J..

4 recordsLinked to original sources

bioRxiv2025

Spatial profiling of central nervous system cellular markers in murine breast cancer to brain metastases

BackgroundBrain metastasis occurs in approximately 16% of metastatic breast cancer patients, and incidence is increasing. Patients with breast cancer brain metastases frequently develop neurological problems including cognitive impairments and seizures. We previously demonstrated accumulation of activated microglia around the tumour site in a breast cancer brain metastasis model, which co-localised with spontaneously occurring local field potential events that resembled interictal epileptic discharges. However, the mechanisms underlying these spatially restricted effects on neuronal excitability are poorly understood. MethodsTo better understand the underlying cellular changes and potential mechanisms, we used digital spatial profiling of brain cell subtype-specific markers to chart the spatial organisation of neurons, oligodendrocytes, astrocytes, and microglia in relation to metastatic lesion site. We developed a novel chordline-based approach to analyse these spatial changes in biomarker distribution. ResultsSeveral protein markers associated with proliferation (Ki67), astrocytes (GFAP) and microglia (CD11b, IBA1, CD45, MSR1) were upregulated in the tumour compared to healthy contralateral brain parenchyma. In contrast, some neuroglial markers (MAP2, Neurofilament light, NeuN, S100B and TMEM119) were lower in the lesion compared to normal tissue. ConclusionsOverall, the protein marker changes in the lesion are indicative of neuronal cell loss and changes in the immune microenvironment of the metastatic lesion involving activated microglia, astrocytes and recruitment of peripheral immune cells. Such cellular changes may contribute to the changes in electrical activity resulting from brain metastases observed in mice and patients.

neuroscience↗

bioRxiv2023

Cortical high-frequency oscillations ({approx} 110 Hz) in cats are state-dependent and enhanced by a subanesthetic dose of ketamine

Ketamine is an NMDA receptor antagonist that has both antidepressant and anesthetic properties. At subanesthetic doses, ketamine can cause transient psychosis in humans, and is used to model psychosis in experimental animals. In rodents, subanesthetic doses of ketamine increase the power of high-frequency oscillations (HFO, 100-180 Hz) in the electroencephalogram and field potentials, a frequency band linked to cognitive functions. However, the effects of ketamine in higher mammals, with more translatable relevance, are poorly investigated. Here, we have examined cortical HFO during wakefulness, sleep, and after administering a sub-anesthetic dose of ketamine (15 mg/kg), utilizing the cat as an animal model. Four cats were implanted with cortical electrodes for chronic polysomnographic recordings. HFO power, connectivity, information flow directionality, and their relationships with respiratory activity were analyzed. During wakefulness, but not during sleep, we found that HFO were coupled with the inspiratory phase of the respiration. After ketamine administration, HFO were enhanced significantly and remained associated with the inspiratory phase. The analysis of the information flow after ketamine suggest that HFO originate from the olfactory bulb and stream towards the prefrontal cortex. Accordingly, occluding the nostrils significantly reduced HFO power in both the olfactory bulb and prefrontal cortex. In contrast, auditory stimulation did not affect HFO. In conclusion, spontaneous cortical HFO show certain state-dependent features in cats, and enhancement of this rhythm by ketamine may disrupt cortical information processing, which could contribute to some of the neuropsychiatric manifestations associated with ketamine. HighlightsO_LIKetamine is used to model psychosis in humans and experimental animals C_LIO_LISubanesthetic doses of ketamine increase the power of high-frequency oscillations C_LIO_LIHigh-frequency oscillations are coupled with the inspiratory phase of respiration C_LIO_LIThese oscillations originate in the olfactory bulb and stream to the neocortex C_LIO_LINostril occlusion lowers high-frequency activity in the olfactory bulb and neocortex C_LI Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=69 SRC="FIGDIR/small/543142v1_ufig1.gif" ALT="Figure 1"> View larger version (34K): org.highwire.dtl.DTLVardef@e386feorg.highwire.dtl.DTLVardef@1b3c06aorg.highwire.dtl.DTLVardef@1d93ecorg.highwire.dtl.DTLVardef@1daa161_HPS_FORMAT_FIGEXP M_FIG C_FIG

neuroscience↗

bioRxiv2020

Nasal respiration is necessary for the emergence of ketamine-induced high frequency network oscillations and behavioral hyperactivity in freely moving rats.

Changes in oscillatory activity are widely reported after subanesthetic ketamine, however their mechanisms of generation are unclear. Here, we tested the hypothesis that nasal respiration underlies the emergence of high-frequency oscillations (130-180 Hz, HFO) and behavioral activation after ketamine in freely moving rats. We found ketamine 20 mg/kg provoked "fast" theta sniffing in rodents which correlated with increased locomotor activity and HFO power in the OB. Bursts of ketamine-dependent HFO were coupled to "fast" theta frequency sniffing. Theta coupling of HFO bursts were also found in the prefrontal cortex and ventral striatum which, although of smaller amplitude, were in phase with OB activity. Haloperidol 1 mg/kg pretreatment prevented ketamine-dependent increases in fast sniffing and instead HFO coupling to slower basal respiration. Consistent with ketamine-dependent HFO being driven by nasal respiration, unilateral naris blockade led to an ipsilateral reduction in ketamine-dependent HFO power compared to the control side. Bilateral nares blockade reduced ketamine-induced hyperactivity and HFO power and frequency. In conclusion, nasal entrainment of ketamine-dependent HFO across cortical and subcortical regions at theta frequencies represents a mechanism of orchestrated neural activity across distinct brain regions. The dense divergent connectivity of the olfactory system serves to broadcast this HFO to limbic areas.

neuroscience↗

bioRxiv2020

Network and synaptic mechanisms underlying high frequency oscillations in the rat and cat olfactory bulb under ketamine-xylazine anesthesia.

High frequency oscillations (HFO) are receiving increased attention for their role in health and disease. Ketamine-dependent HFO have been identified in cortical and subcortical regions in rodents, however, the mechanisms underlying their generation and whether they occur in higher mammals is unclear. Here, we show under ketamine-xylazine anesthesia, classical gamma oscillations diminish and a prominent > 80 Hz oscillation emerges in the olfactory bulb of rats and cats. In cats negligible HFO was observed in the thamalus and visual cortex indicating the OB was a suitable site for further investigation. Simultaneous local field potential and thermocouple recordings demonstrated HFO was dependent on nasal airflow. Silicon probe mapping studies spanning almost the entire dorsal ventral aspect of the OB revealed this rhythm was strongest in ventral areas of the bulb and associated with microcurrent sources about the mitral layer. Pharmacological microinfusion studies revealed HFO was dependent on excitatory-inhibitory synaptic activity, but not gap junctions. Finally, we showed HFO was preserved despite surgical removal of the piriform cortex. We conclude that ketamine-dependent HFO in the OB are driven by nasal airflow and local dendrodendritic interactions. The relevance of our findings to ketamines model of psychosis in awake state are also discussed.

neuroscience↗