Plasticity of fin command system function following spinal transection in larval sea lamprey

Radiation-activated secretory proteins of Scgb1a1 + club cells increase the efficacy of immune checkpoint blockade in lung cancer

Radiation therapy (RT) in combination with immune checkpoint inhibitor (ICI) represents a promising regimen for non-small cell lung cancer (NSCLC), however, the underlying mechanisms are poorly characterized. We identified a specific dose of RT that conferred tumor regression and improved survival in NSCLC models when combined with ICI. The immune-modulating functions of RT was ascribed to activated lung-resident Scgb1a1+ club cells. Importantly, mice with club cell-specific knockout of synaptosome-associated protein 23 failed to benefit from the combination treatment, indicating a pivotal role of club cell secretome. We identified 8 club cells secretory proteins, which inhibited immunosuppressive myeloid cells, reduced pro-tumor inflammation, and enhanced anti-tumor immunity. Notably, CC10, a member of club cell secretome was increased in plasma of NSCLC patients responding to the combination therapy. By revealing an immune-regulatory role of club cells, our studies have the potential to guide future clinical trials of ICI in NSCLC.

Contributions of identifiable neurons and neuron classes to lamprey vertebrate neurobiology

Among the advantages offered by the lamprey brainstem and spinal cord for studies of the structure and function of the nervous system is the unique identifiability of several pairs of reticulospinal neurons in the brainstem. These neurons have been exploited in investigations of the patterns of sensory input to these cells and the patterns of their outputs to spinal neurons, but no doubt these cells could be used much more effectively in exploring their roles in descending control of the spinal cord. The variability of cell positions of neurons in the spinal cord has precluded the recognition of unique spinal neurons. However, classes of nerve cells can be readily defined and characterized within the lamprey spinal cord and this has led to progress in understanding the cellular and synaptic mechanisms of locomotor activity. In addition, both the identifiable reticulospinal cells and the various spinal nerve cell classes and their known synaptic interactions have been used to demonstrate the degree and specificity of regeneration within the lamprey nervous system. The lack of uniquely identifiable cells within the lamprey spinal cord has hampered progress in these areas, especially in gaining a full understanding of the locomotor network and how neuromodulation of the network is accomplished.

The responses of mammalian spinal axons to an applied DC voltage gradient

We have imposed a steady, rostrally negative, weak (ca 0.4 mV/mm) voltage gradient across transections of ascending white matter tracts in the adult guinea pig using an implanted stimulator and electrodes for about 1 month. We have evaluated the projections of these axons relative to the transection approximately 2 months postinjury by anterograde transport of injected tetramethylrhodamine-conjugated dextran and the use of an indwelling marker device which locates the plane of the original transection. Tract tracing was accomplished with conventional epifluorescence microscopy and confocal laser microscopy. Sham-treated control spinal cords contained well-filled lateral and dorsal column ascending tracts terminating caudal to the lesion which formed at the level of the hemisection. Electric field-treated spinal cords contained similarly labeled columns of axons that penetrated the lesion within the caudal segment of the spinal cord, branched within it, and in some cases such branches projected across the plane of transection. Ascending axons also passed around the lesion through undamaged parenchyma, branched repeatedly at the plane of the hemisection, and passed into the rostral segment of the spinal cord. Spear-shaped endings typical of growth cones were found at the terminals of these processes which often branched again within the rostral segment. Centrally projecting fibers, their processes, and the overall level of branching in these projections was not observed in our previous studies using high molecular weight horseradish peroxidase tracers.

Effects of stimulating the reticular formation during fictive locomotion in lampreys

The effects of stimulating the reticular formation were studied during fictive locomotion in lampreys (Ichthyomyzon unicuspis). The in vitro isolated preparation of the brainstem and spinal cord was used and fictive locomotion was induced by bath application of N-methyl-D-aspartate (NMDA; 50-100 microM). During different phases of the locomotor cycle, short trains of stimuli (10 pulses at 80-100 Hz; 10 microA) were delivered through glass-coated tungsten microelectrodes positioned within the middle rhombencephalic reticular nucleus (MRRN) and their effects were studied on ipsi- and contralateral ventral root locomotor discharges. Irrespective of the locomotor phase during which the stimulation train was delivered, a resetting effect occurred. It was characterized by a re-synchronization of the locomotor discharges with a constant latency for each ventral root on the ipsilateral side. The latency increased as the recorded root was located further caudally. This increase in latency was in the range of the phase lag observed between roots during control bouts of locomotion. These results suggest that reticulospinal neurones exert strong resetting effects on spinal locomotor networks. These effects may play a significant role with respect to changes of direction during swimming.

Preferential regeneration of spinal axons through the scar in hemisected lamprey spinal cord

Axons of lamprey spinal cord can regenerate across a complete spinal transection. Thus, unlike the scar of injured mammalian spinal cords, the scar in the lamprey is not an absolute impediment to regeneration. However, it is still not known whether the scar is a relative impediment or whether it provides a favorable environment for regeneration compared to the spinal cord parenchyma. In order to answer this question, the cords of 12 large larval sea lampreys (4-5 years old) were hemisected at the level of the third gill and the animals allowed to recover for 10 weeks. The large reticulospinal neurons (Müller and Mauthner cells) or their giant axons were injected intracellularly with HRP and their regenerating neurites visualized in central nervous system (CNS) wholemounts. Forty-five of seventy-one regenerating neurites (64%) grew beyond the level of the hemisection. Of these, 36 (82%) regenerated through the scar and remained on the same side of the cord as their parent axons, while only 8 (18%) crossed the midline and grew around the scar. Thus, regenerating neurites of giant reticulospinal axons tended to grow through the hemisection scar rather than around it. Once they passed the level of injury, they continued to elongate in their appropriate paths. It is possible that this tendency for axons to regenerate through the scar reflects the greater amount of empty spaces on the hemisected side. In order to rule this out, 13 animals received contralateral simultaneous hemisections at the level of the 3rd and 7th gills. This procedure created large numbers of degenerating axons and potential empty spaces both rostral and caudal to the scars within both hemicords; 92 of 158 neurites (58%) regenerated beyond the level of their respective hemisections. All of these grew through the scar and none crossed to the contralateral side. Distal to either hemisection, neurites remained on their correct side regardless of whether the contralateral cord contained normal CNS parenchyma or axonal debris and empty spaces produced by Wallerian degeneration. Moreover, in hemisected and double hemisected animals, as well as in completely transected control animals, neurites regenerating in their correct direction grew further than those that were misrouted. Because lamprey spinal axons grow preferentially through a scar rather than around it, the scar may play a positive role in supporting axonal regeneration.

The need for cellular elements during axonal regeneration in the sea lamprey spinal cord

Spinal axons in the larval sea lamprey regenerate following a complete spinal transection. It is not known whether regenerating growth cones require contact with cellular elements or whether the basement membrane and collagenous meninx primitiva which surround the spinal cord are sufficient for neurite out-growth. To determine this, a freeze lesion was made which severed axons, destroyed neuronal perikarya, and greatly reduced the number of glial cells. After at least 10 weeks of recovery, 50 neurites from 31 Müller and Mauthner axons were labeled by intracellular injection of HRP. Eighty-six percent of these neurites did not regenerate into the lesion site. No neurites grew through the lesion. No animals recovered coordinated swimming. These results suggest that glial and/or neuronal surfaces are required for axonal regeneration. Moreover, a monolayer of glial cells appears to be suboptimal and a three-dimensional matrix of cells may be necessary to promote regeneration in the lamprey spinal cord.

Functional regeneration of descending brainstem command pathways for locomotion demonstrated in the in vitro lamprey CNS

Lower vertebrates can recover locomotor function after spinal transections, and several classes of neurons in these animals can regenerate. However, no studies have directly tested for functional regeneration of descending command pathways for the initiation of locomotion in the absence of complications from sensory feedback. In the present study, the contribution of regeneration of descending command pathways to the reacquisition of locomotion was examined in behaviorally recovered, spinal-transected larval lampreys using in vitro brain/spinal cord preparations, in which mechanosensory feedback was eliminated. Activation of brainstem command centers produced locomotor activity below a healed transection site and this burst activity was coupled 1:1 with locomotor activity above the transection site. Furthermore, the parameters characterizing locomotor patterns in in vitro preparations were similar to those recorded during locomotion in normal, whole-animals. Additional experiments indicated that descending pathways from the brainstem had regenerated across the healed transection site and could directly activate spinal locomotor networks below the lesion area. These data appear to be the first direct demonstration in a vertebrate of functional regeneration of descending command pathways for the initiation of locomotion.