Journal of Comparative Neurology最新文献

The amniote inner ear contains an unusual type of hair cell and a unique postsynaptic calyx terminal with specialized ion channel expression and afferent transmission mechanisms. The calyceal afferent terminal enwraps the hair cell and leads to a heminode. It has morphological and functional microdomains with distinct complements of potassium channels and scaffolding proteins. Stimulation of hair cells gives rise to postsynaptic potentials in the membrane facing the hair cell that propagate along the outer face of the calyx and parent axon to the heminode, giving rise to spikes with timing and response properties that vary with location (epithelial zone) and afferent morphology (calyx-only vs. dimorphic with additional bouton terminals). Heminodes of calyx-only afferents lie within the epithelium, placing the calyces themselves closer to the heminode. We report that diverse voltage-gated sodium (Na_V) channel proteins (including Na_V1.1-1.3, 1.5. 1.6, 1.8, and 1.9), HCN (hyperpolarization-activated cyclic nucleotide-gated) channels, and associated scaffolding proteins (ankyrins, βIV-spectrin, and ezrin) are differentially deployed across calyx microdomains, and specific complements of proteins also vary with innervation zone in vestibular epithelia. Our results suggest the calyx outer surface plays a role analogous to an axon initial segment in central neurons, and that systematic variation in Na_V pore-forming subunits underlies differences in firing properties of vestibular afferents in different epithelial zones.

We examined the distribution of axons throughout the spinal cord of the rat that were either immunoreactive for the adrenaline-synthesizing enzyme, phenylethanolamine N-methyltransferase (PNMT), or derived from medullary C1 neurons, one of the three groups of neurons in the brain that synthesize PNMT. We observed that PMNT-immunoreactive axons, as well as C1 axons labelled with GFP from viral transduction, innervate most, but not all, sympathetic preganglionic neurons in the thoracolumbar spinal cord. GFP-positive C1 axons provided innervation to sympathetic preganglionic neurons that expressed cocaine and amphetamine regulated transcript, an accepted marker of sympathetic vasomotor neurons. In addition, we observed axons from PNMT-containing and C1 neurons caudal to the distribution of sympathetic preganglionic neurons in the sacral spinal cord where they closely apposed parasympathetic preganglionic neurons retrogradely labelled from the major pelvic ganglion. We also found close appositions from PNMT-immunoreactive or GFP-labelled C1 axons on choline acetyltransferase-stained parasympathetic preganglionic neurons activated by the micturition reflex, thus providing clear evidence of a non-cardiovascular target for RVLM C1 neurons. Furthermore, we observed a few PNMT-positive and GFP-positive C1 axons making close appositions with somatic motor neurons in Onuf's nucleus in the sacral cord and in the ventral horn at more rostral levels. These data provide a comprehensive map of the distribution of adrenergic inputs to the spinal cord and identify parasympathetic preganglionic neurons, including those involved in the micturition reflex, as well as sympathetic preganglionic neurons as the major targets for these inputs.

The efficient processing of visual information relies on a mature visual cortex, characterized by hierarchically organized areas and a broad diversity of inhibitory and excitatory neurons. A tightly regulated excitation-inhibition (E/I) balance is essential for the optimal processing of visual inputs. A known regulator of the cortical E/I balance is the endocannabinoid (ECB) system, which relies on the cannabinoid type-1 receptor (CB1R) to perform its functions. To better understand the embedding of the CB1R in the neuronal networks of the visual cortex in adolescence and adulthood, we characterized the distribution of the receptor protein and its mRNA (cnr1) across layers, areas, and interneuron subtypes. We describe a specific laminar distribution of CB1R in the mature visual cortex along the full extent of the rostrocaudal brain axis. Moreover, cnr1 is expressed in the three main nonoverlapping subtypes of interneurons and is predominantly enriched in the 5ht3ar subtypes. Comparison of adolescent and adult visual cortex revealed a higher number of cnr1+ reelin interneurons in layer 1 and a lower number of cnr1+ somatostatin interneurons in layer 4 of the primary visual cortex (V1) in adolescence compared with adulthood. Overall, our findings confirm a distinct distribution of the receptor in V1 compared with higher-order visual areas based on a lower CB1R expression in layer 4, a broad cnr1 expression across cortical interneurons in key locations of top-down modulation, and a still immature ECB system in adolescence, making it potentially vulnerable to exogenous cannabinoids during this life period.

Given the rapidly expanding clinical use of glucagon-like peptide-1 receptor (GLP1R) agonists-well-known for their antidiabetic and antiobesity effects-it is increasingly important to understand the precise distribution of GLP1R expression in the human body, as this knowledge is crucial for elucidating both their therapeutic effects and side effects. In this study, we investigated Glp1r mRNA expression in the human nodose ganglion, a key sensory relay between the periphery and the brain. We analyzed postmortem paraffin-embedded nodose ganglia sections from 10 human donors, using RNAscope analysis. We found that optimal tissue required fixation times under 48 h and postmortem intervals of approximately 10 h or less. Ultimately, nine nodose ganglia from six donors met quality standards for analysis. Using multiplex RNAscope, we detected moderate to high levels of Glp1r expression in approximately 7% of all nodose neurons, with no clear differences between sides, sex, or age. The proportion of neurons with low Glp1r expression rose to nearly 28%. Notably, Glp1r expression was also observed in nonneuronal cells within the perineurium, epineurium, and fascicles of the human vagus nerve. As a point of comparison, we also examined Glp1r expression in mice, where 17.9%-29.1% of nodose neurons were positive, with slightly higher expression on the right side. In mice, Glp1r expression was strictly neuronal. Overall, our findings demonstrate that the human nodose ganglion is a potential target for GLP1R-based therapeutics and reveal species similarities and differences in Glp1r expression between humans and mice.

The lateral line system is an essential sensory modality used by fishes and aquatic amphibians to sense hydrodynamic information. The system comprises distributed sense organs called neuromasts and their afferent nerves, organized into anterior lateral lines around the eye and jaw and posterior lateral lines (LL) on the trunk. At postembryonic stages, early forming neuromasts expand in size and sink into bony canals, while late-forming superficial neuromasts are added as the fish grows. Unlike the well-studied zebrafish posterior LL, details of anterior LL postembryonic development remain unknown. Here, we have characterized developmental mechanisms and innervation patterns driving expansion of the zebrafish anterior LL. Using tissue-clearing to observe neuromast and nerve markers through ontogeny, we demonstrate continuous neuromast addition in the anterior LL, with peak rates at larval stages of 7–10 mm standard length (SL). Lines of superficial neuromasts form parallel to existing lines of presumptive canal neuromasts as late as 7 mm SL, with new neuromasts added through migration of new primordia, budding, intercalation, and a novel “hybrid-origin” mechanism. Despite some canal lines being innervated by the anterodorsal ganglion, all superficial lines are innervated by the anteroventral ganglion. Anterior LL ganglion ablation reveals that denervation abrogates superficial neuromast formation—including via the hybrid-origin mechanism—and reduces growth of canal neuromasts. While the anterior and posterior LL use disparate developmental mechanisms, innervation is critical to the expansion of both. Our findings reveal a “developmental switch” at 7 mm SL, when innervation becomes necessary for a secondary phase of anterior LL development.

The perirhinal and parahippocampal cortices are two prominent structures of the medial temporal lobe that play essential roles in memory and perceptual processes. In humans, major changes in memory capacities occur within the first 7 years of life, but the neurobiological substrates underlying these changes have long been hypothetical. Previous studies have shown that distinct regions, layers, and cells of the hippocampal formation, including the entorhinal cortex, exhibit different profiles of structural and molecular development. Here, to further understand the postnatal maturation of the medial temporal lobe, we implemented stereological techniques to characterize the structural development of the perirhinal and parahippocampal cortices in macaque monkeys. We found distinct, age-related differences in volume, neuronal soma size, and neuron number in different layers and subdivisions. Volumetric data indicated a late maturation of areas 36r and 36c compared to areas 35, TF, and TH. There was also an earlier maturation of the superficial layers compared to the deep layers in areas 36r and 36c. We observed a transient increase in neuronal soma size at 6 months of age in several subdivisions. Additionally, we found a decrease in neuron numbers in both the perirhinal and parahippocampal cortices, but particularly in area 35 and layer III of area TF between birth and 6 months. These findings are consistent with the differential maturation of the rostral and caudal entorhinal cortex, which are interconnected with the perirhinal and parahippocampal cortices, respectively. Altogether, they support the theory that the differential maturation of distinct hippocampal circuits underlies the emergence of specific “hippocampus-dependent” memory processes.

The subgenual organ complex is an elaborate mechanosensory complex in the insect leg containing chordotonal organs. In stick and leaf insects (Phasmatodea), it includes the subgenual organ and the distal organ. This study documents the neuroanatomy and functional morphology of the subgenual organ complex in the stick insect Bacillus rossius (Bacillidae: Bacillinae) by axonal tracing and micro-computed tomography. It also considers the first report on the subgenual organ complex in stick insects that reported a relatively simple organization of the sensory organ and its nerves on the basis of histological sections. Our findings show the neuroanatomy and nerve pattern of the subgenual organ complex in B. rossius with a subgenual organ and a distal organ. The subgenual organ is placed in the hemolymph channel. The distal organ is also located in the hemolymph channel, and it has several attachment elements, linking it to the cuticle of the tibia, the tibial tracheae, and the subgenual organ. The connections to the tibia may form an input pathway for vibrations transmitted over the cuticle, whereas the position in the hemolymph channel and the connection to the subgenual organ indicate a mechanical activation by vibrations transmitted via the hemolymph. Overall, the axonal tracing preparations document neuroanatomical details for B. rossius and resolve the numbers of sensilla in the sensory organs, the length of the distal organ, and confirm a single nerve branch for the subgenual organ. The data provide support for a consistent organization of the subgenual organ complex within stick insects.