Gata2, Nkx2-2 and Skor2 form a transcription factor network regulating development of a midbrain GABAergic neuron subtype with characteristics of REM sleep regulatory neurons

The midbrain reticular formation is a mosaic of diverse GABAergic and glutamatergic neurons that have been associated with a variety of functions, including the regulation of sleep. However the molecular characteristics and development of the midbrain reticular formation neurons are poorly understood. As the transcription factor Gata2 is required for the development of all GABAergic neurons derived from the embryonic mouse midbrain, we hypothesized that the genes expressed downstream of Gata2 could contribute to the diversification of GABAergic neuron subtypes in this brain region. Here, we show that Gata2 is indeed required for the expression of several lineage-specific transcription factors in post-mitotic midbrain GABAergic neuron precursors. These include a homeodomain transcription factor Nkx2-2 and a SKI family transcriptional repressor Skor2, which are co-expressed in a restricted group of GABAergic precursors in the midbrain reticular formation. Both Gata2, and Nkx2-2 function is required for the expression of Skor2 in GABAergic precursors. In the adult mouse as well as rat midbrain, the Nkx2-2 and Skor2 expressing GABAergic neurons locate at the boundary of the ventrolateral periaqueductal gray and the midbrain reticular formation, an area shown to contain REM-off neurons regulating REM sleep. In addition to the characteristic localization, the Skor2 positive cells increase their activity upon REM sleep inhibition, send projections to a pontine region associated with sleep control and are responsive to orexins, consistent with the known properties of the midbrain REM-off neurons.

Brainstem and Cranial Nerves: Longitudinal Pathways of the Brainstem

This chapter reviews pathways that are not at a single level of the brainstem but rather involve multiple areas with supratentorial input. The chapter highlights autonomic pathways, the reticular formation and chemically defined groups, and coordination of eye movements. Sympathetic fibers travel from the hypothalamus to the intermediolateral column in the spinal cord through the lateral brainstem. Patients with a unilateral lesion of the lateral brainstem may have ipsilateral Horner syndrome. The ventrolateral medulla, also a sympathetic region of the brainstem, projects to the spinal cord and is involved in the innervation of blood vessels in the limbs.

Expression of Urocortin 3 mRNA in the Central Nervous System of the Sea Lamprey Petromyzon marinus

In this study, we analyzed the organization of urocortin 3 (Ucn3)-expressing neuronal populations in the brain of the adult sea lamprey by means of in situ hybridization. We also studied the brain of larval sea lampreys to establish whether this prosocial neuropeptide is expressed differentially in two widely different phases of the sea lamprey life cycle. In adult sea lampreys, Ucn3 transcript expression was observed in neurons of the striatum, prethalamus, nucleus of the medial longitudinal fascicle, torus semicircularis, isthmic reticular formation, interpeduncular nucleus, posterior rhombencephalic reticular formation and nucleus of the solitary tract. Interestingly, in larval sea lampreys, only three regions showed Ucn3 expression, namely the prethalamus, the nucleus of the medial longitudinal fascicle and the posterior rhombencephalic reticular formation. A comparison with distributions of Ucn3 in other vertebrates revealed poor conservation of Ucn3 expression during vertebrate evolution. The large qualitative differences in Ucn3 expression observed between larval and adult phases suggest that the maturation of neuroregulatory circuits in the striatum, torus semicircularis and hindbrain chemosensory systems is closely related to profound life-style changes occurring after the transformation from larval to adult life.

Mapping the human corticoreticular pathway with multimodal delineation of the gigantocellular reticular nucleus and high-resolution diffusion tractography

ABSTRACTThe corticoreticular pathway (CRP) is a major motor tract that provides volitional input to the reticular formation motor nuclei and may be an important mediator of motor recovery after central nervous system damage. However, its cortical origins, trajectory and laterality are incompletely understood in humans. This study aimed to map the human CRP and generate an average CRP template in standard MRI space. Following recently established guidelines, we manually delineated the primary reticular formation motor nucleus (gigantocellular reticular nucleus [GRN]) using several group-mean MRI contrasts from the Human Connectome Project (HCP). CRP tractography was then performed with HCP diffusion-weighted MRI data (N=1,065) by selecting diffusion streamlines that reached both the frontal cortex and GRN. Corticospinal tract (CST) tractography was also performed for comparison. Results suggest that the human CRP has widespread origins, which overlap with the CST across most of the motor cortex and include additional exclusive inputs from the medial and anterior prefrontal cortices. The estimated CRP projected through the anterior and posterior limbs of the internal capsule before partially decussating in the midbrain tegmentum and converging bilaterally on the pontomedullary reticular formation. Thus, the CRP trajectory appears to partially overlap the CST, while being more distributed and anteromedial to the CST in the cerebrum before moving posterior to the CST in the brainstem. These findings have important implications for neurophysiologic testing, cortical stimulation and movement recovery after brain lesions. We expect that our GRN and tract maps will also facilitate future CRP research.HIGHLIGHTSThe corticoreticular pathway (CRP) is a major tract with poorly known human anatomyWe mapped the human CRP with diffusion tractography led by postmortem & animal dataThe CRP appears to originate from most of the motor cortices and further anteriorThe estimated CRP had distributed and bilateral projections to the brainstemThese findings have important implications for motor recovery after brain lesions

Distinct fastigial output channels and their impact on temporal lobe seizures

Despite being canonically considered a motor control structure, the cerebellum is increasingly recognized for important roles in processes beyond this traditional framework, including seizure suppression. Excitatory fastigial neurons project to a large number of downstream targets, and it is unclear if this broad targeting underlies seizure suppression, or if a specific output may be sufficient. To address this question, we used the intrahippocampal kainic acid mouse model of temporal lobe epilepsy, male and female animals, and a dual-virus approach to selectively label and manipulate fastigial outputs. We examined fastigial neurons projecting to the superior colliculus, medullary reticular formation, and central lateral nucleus of the thalamus, and found that these comprise largely non-overlapping populations of neurons which send collaterals to unique sets of additional thalamic and brainstem regions, creating distinct, somewhat overlapping, output channels. We found that neither optogenetic stimulation of superior colliculus nor reticular formation output channels attenuated hippocampal seizures. In contrast, on-demand stimulation of fastigial neurons targeting the central lateral nucleus robustly inhibited seizures. Our results indicate that fastigial control of hippocampal seizures does not require simultaneous modulation of many fastigial output channels. Rather, selective modulation of the fastigial output channel to the central lateral thalamus, specifically, is sufficient for seizure control. This may provide a means for more selective therapeutic interventions, which provide seizure control while minimizing unwanted side effects. More broadly, our data highlight the concept of specific cerebellar output channels, whereby discrete cerebellar nucleus neurons project to specific aggregates of downstream targets, with distinct functional outcomes.

Efferent and Afferent Connections of the Supratrigeminal Neurons Conveying Orofacial Muscle Proprioception in Rats

The supratrigeminal nucleus (Su5) is a key structure for controlling jaw-movements since it receives proprioceptive sensation from jaw-closing muscle spindles (JCMSs) and sends projection to the trigeminal motor nucleus (Mo5). However, the central projection and regulation of JCMS proprioceptive sensation have not been fully understood. Therefore, we aimed to reveal the efferents and afferents of the Su5 by means of neuronal tract tracings. Anterograde tracer injections into the Su5 revealed that the Su5 sent contralateral projections (or bilateral projections with a contralateral predominance) to the Su5, basilar pontine nuclei, pontine reticular nucleus, deep mesencephalic nucleus, superior colliculus, caudo-ventromedial edge of ventral posteromedial thalamic nucleus, parafascicular thalamic nucleus, zona incerta, and lateral hypothalamus, and ipsilateral projections (or bilateral projections with an ipsilateral predominance) to the intertrigeminal region, trigeminal oral subnucleus, dorsal medullary reticular formation, and hypoglossal nucleus as well as the Mo5. Retrograde tracer injections into the Su5 demonstrated that the Su5 received bilateral projections with a contralateral predominance (or contralateral projections) from the primary and secondary somatosensory cortices, granular insular cortex and Su5, and ipsilateral projections (or bilateral projections with an ipsilateral predominance) from the dorsal peduncular cortex, bed nuclei of stria terminalis, central amygdaloid nucleus, lateral hypothalamus, parasubthalamic nucleus, trigeminal mesencephalic nucleus, parabrachial nucleus, juxtatrigeminal region, trigeminal oral and caudal subnuclei, and dorsal medullary reticular formation. These findings suggest that the Su5 receiving JCMS proprioceptive sensation has efferent and afferent connections with multiple brain regions, which are involved in emotional and autonomic functions as well as orofacial motor functions.

COVID-19 related leukoencephalopathy with bilateral reticular formation involvement

We are presenting the imaging findings of COVID-19-related leukoencephalopathy associated with bilateral reticular formation diffusion restriction in brain magnetic resonance imaging. To the best of our knowledge, this is the first reported case of bilateral reticular formation affection in a COVID-19 patient.

A Confocal Microscopic Study of Gene Transfer into the Mesencephalic Tegmentum of Juvenile Chum Salmon, Oncorhynchus keta, Using Mouse Adeno-Associated Viral Vectors

To date, data on the presence of adenoviral receptors in fish are very limited. In the present work, we used mouse recombinant adeno-associated viral vectors (rAAV) with a calcium indicator of the latest generation GCaMP6m that are usually applied for the dorsal hippocampus of mice but were not previously used for gene delivery into fish brain. The aim of our work was to study the feasibility of transduction of rAAV in the mouse hippocampus into brain cells of juvenile chum salmon and subsequent determination of the phenotype of rAAV-labeled cells by confocal laser scanning microscopy (CLSM). Delivery of the gene in vivo was carried out by intracranial injection of a GCaMP6m-GFP-containing vector directly into the mesencephalic tegmentum region of juvenile (one-year-old) chum salmon, Oncorhynchus keta. AAV incorporation into brain cells of the juvenile chum salmon was assessed at 1 week after a single injection of the vector. AAV expression in various areas of the thalamus, pretectum, posterior-tuberal region, postcommissural region, medial and lateral regions of the tegmentum, and mesencephalic reticular formation of juvenile O. keta was evaluated using CLSM followed by immunohistochemical analysis of the localization of the neuron-specific calcium binding protein HuCD in combination with nuclear staining with DAPI. The results of the analysis showed partial colocalization of cells expressing GCaMP6m-GFP with red fluorescent HuCD protein. Thus, cells of the thalamus, posterior tuberal region, mesencephalic tegmentum, cells of the accessory visual system, mesencephalic reticular formation, hypothalamus, and postcommissural region of the mesencephalon of juvenile chum salmon expressing GCaMP6m-GFP were attributed to the neuron-specific line of chum salmon brain cells, which indicates the ability of hippocampal mammal rAAV to integrate into neurons of the central nervous system of fish with subsequent expression of viral proteins, which obviously indicates the neuronal expression of a mammalian adenoviral receptor homolog by juvenile chum salmon neurons.