ABSTRACTNeurons that express Nps send output to brain regions implicated in circadian function and threat responses, but less is known about the afferent control of these neurons. In this study, we used a sensitive retrograde tracer, cholera toxin beta subunit (CTb), to identify afferents to the rostral–lateral parabrachial region that contains the main concentration of Nps‐expressing neurons. We then used Cre‐dependent rabies retrograde tracing in Nps‐2A‐Cre mice to identify inputs to Nps‐expressing neurons within this region. These neurons receive heavy input from auditory brainstem structures, including the inferior colliculus, ventral nucleus of the lateral lemniscus, superior olivary complex, and cochlear nucleus. Due to a discrepancy between sparse rabies and prominent CTb labeling extending from the ipsilateral insular to auditory areas of the cerebral cortex, we also performed anterograde labeling and found many close contacts between cortical boutons and Nps‐expressing neurons. These findings suggest an unexpected role for auditory information in controlling the activity of Nps‐expressing neurons and add to existing evidence suggesting that rabies is relatively insensitive to retrograde labeling of cortical afferents.

The trigeminal nerve consists of three major branches or rami (r) in jawed vertebrates: the ophthalmic (rV1), maxillary (rV2), and mandibular (rV3), with rV2 and rV3 innervating the upper and lower jaws, respectively. This three-branch configuration is conserved in the lamprey, a representative of the cyclostomes, the sole survivor of jawless vertebrates. While the first branch is widely accepted to be homologous to that of jawed vertebrate rV1, the homology of the other two remains unclear, so they are called rV1, rV2/3A, and rV2/3B. In this study, we investigate evolutionary modifications of the trigeminal nerve by comparing its organization in lamprey and jawed vertebrate embryos. By detailed neuronal tracing analysis of rV2/3B, which innervates the velum, we demonstrate that it consists solely of motor components. Conversely, we identify both sensory and motor fibers in rV2/3A. These results make a striking contrast to the trigeminal nerve of the jawed vertebrates, as their rV2 is purely sensory, but rV3 is a mixed nerve. Furthermore, through comparative analyses of sensory projection inside the brain, we clarify that the principal sensory nucleus of the trigeminal nerve (PrV) of anamniotes (shark, catfish, and Xenopus) lacks a somatotopic organization, suggesting that somatotopy evolved in at least the last common ancestor of amniotes. Last, by gene expression analysis of Drg11, a marker for the PrV and the spinal trigeminal nucleus (SpV), we show that a PrV-equivalent region is not present in the lamprey. These findings indicate significant structural changes in the trigeminal nerve associated with jaw acquisition, including shifts in innervation territories, the disappearance of the branch innervating the velum, and the emergence of novel brain nuclei.

Puncta adherentia junctions (PAJs) have been observed at glutamatergic excitatory synapses on glutamatergic excitatory neurons (E→E synapses) in the mouse hippocampus and are considered to be the mechanical adhesion sites between axon terminals and dendritic shafts. However, it remains unclear whether they are present at other types of synapses, such as glutamatergic synapses on GABAergic inhibitory neurons (E→I synapses) and GABAergic synapses on excitatory neurons (I→E synapses) and inhibitory neurons (I→I synapses). We showed here that the PAJ components, such as nectin-1, nectin-3, l-afadin, N-cadherin, β-catenin, and αN-catenin, were observed at all four types of synapses in cultured mouse hippocampal neurons. In the adult mouse hippocampus, these PAJ components were observed at a subset of I→I synapses on parvalbumin-positive GABAergic inhibitory neurons, similarly to their presence at E→E synapses in the CA1 and CA3 regions. In contrast, several PAJ components, including nectin-3, l-afadin, N-cadherin, β-catenin, and αN-catenin, were observed at E→I and I→E synapses, whereas nectin-1 was absent. These results indicate that the PAJs are formed at a subset of I→I synapses in addition to E→E synapses, where all examined PAJ components are present, whereas E→I and I→E synapses exhibit only partial localization of these components, reflecting molecular diversity among different synapses in the adult mouse hippocampus.

ABSTRACTWe 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 ascending sensory projections from the dorsal thalamus to the pallium are one of the most distinctive features of the amniote brain. In mammals, these projections can be broadly classified into two main types: (1) those arising from "core" neurons, mostly located in the central region of sensory nuclei, which relay topographic inputs to the intermediate layers of primary sensory cortices, forming a reciprocal circuit with the reticular thalamic nucleus (RTN); and (2) those originating from "matrix" neurons, located in the periphery of sensory nuclei, which project to superficial layers of primary and higher order cortices. To date, both the reciprocal core-RTN circuitry and the matrix projections have only been described in mammals. In this study, we re-examined the organization of thalamic projections to the visual dorsal ventricular ridge (DVR) in pigeons using neural tracing techniques. In addition to the well-known projection from the thalamic nucleus rotundus (Rt) to the ventral layer of the visual DVR (entopallium), we described a reciprocal projection pattern between the Rt and the RTN. Moreover, we identified a second ascending thalamopallial projection, arising from neurons surrounding the Rt and terminating primarily in the intermediate layer of the visual DVR. These neurons form a continuous "matrix" of cells within the dorsal thalamus, which as a group also give rise to axons targeting several associative pallial areas. Furthermore, we found that this "matrix" region receives descending inputs from the motor arcopallium. Collectively, these findings indicate that the avian thalamopallial system is more complex than previously recognized and thus more comparable to its mammalian counterpart.

ABSTRACTThe 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.

For centuries, anatomists have charted the folding patterns of the sulci of the cerebral cortex in primates. Improvements in neuroimaging technologies over the past decades have led to advancements in the understanding of the sulcal organization of the human cerebral cortex, yet comparisons to chimpanzees, one of humans' closest extant phylogenetic relatives, remain to be performed in many regions, such as the caudal temporoparietal region (cTPR). For example, while several posterior branches, or rami, of the superior temporal sulcus (STS) have been identified within the cTPR in great apes since the late 1800s, no study has yet comprehensively identified and quantitatively compared these rami across species. To fill this gap in knowledge, in the present study, we defined the three caudal branches of the STS (cSTS) in 72 human and 29 chimpanzee brains (202 total hemispheres) and then extracted and compared the morphological (depth and surface area) properties of these sulci. We report three main findings. First, modern methods replicate classic findings that three rami of the posterior STS are unique to the hominid lineage (i.e., humans and great apes). Second, normalizing for brain size, the cSTS rami were relatively deeper in chimpanzees compared to humans. Third, the cSTS branches were relatively larger in surface area in humans compared to chimpanzees. Finally, we share probabilistic predictions of the cSTS to guide the identification of these sulci in future studies. Altogether, these findings bridge the gap between historic qualitative observations and modern quantitative measurements in a part of the brain that has expanded substantially throughout evolution and that is involved in human-specific aspects of cognition.

ABSTRACTHoloprosencephaly (HPE) is the most frequent developmental disorder of the forebrain. In this condition, the separation of the early precursor domains is hampered. A spectrum of clinical manifestations can be observed, for example, severe forms like alobar HPE and less severe forms like lobar HPE. Ophthalmologic findings that accompany HPE also occur as a spectrum that ranges from ocular hypotelorism and synophthalmia to cyclopia and anophthalmia. In this brief analysis, we made use of a recently established zebrafish model of HPE. This model is based on experimental BMP ligand induction that resulted in anophthalmia. We attenuated the induction protocol to investigate whether the ophthalmologic phenotype can also be attenuated. We found a spectrum of ocular phenotypes: ocular hypotelorism, cases of synophthalmia, and cyclopia.

ABSTRACTAdult neurogenesis describes the formation of new neurons in the adult brain, a process that is fundamental to related functions, particularly in the hippocampus. Although studies reported adult striatal neurogenesis in humans, the phenomenon is still understudied in those regions. Thus, to gain a deeper understanding in different species, the expression of neurogenic markers was quantitatively analyzed in striatal subregions of pigeons and mice. Further, in macaques and human a detailed analysis of the subventricular zone (SVZ) was performed and the human caudate nucleus was qualitatively examined. The results show higher neuronal plasticity in striatal subregions of pigeons compared to mice, as reflected by higher numbers of Bromodeoxyuridine (BrdU)+, BrdU+/Doublecortin+, Doublecortin+, and BrdU+/Neuronal nuclei marker+ cells. Analysis of BrdU+/glial fibrillary acidic protein (GFAP)+ signals indicated further higher gliogenesis/potential stem cell division in pigeons. As newborn striatal neurons may arise from stem cell niches in the SVZ, active proliferation was analyzed with (sex determining region Y)‐box 2, GFAP, and Ki‐67 in macaques and humans. Specific subdivisions of the SVZ were identified, with GFAP and Ki‐67 differentially distributed. Additionally, signs of persistent neuronal plasticity were observed with Doublecortin+ cells in the human caudate nucleus but not in the macaque. The higher levels of striatal adult neurogenesis in pigeons and perspectives of useful methods may encourage the use of birds to investigate the functional role of this phenomenon and may facilitate our understanding of neuronal plasticity even in the human striatum in the future.