Journal of Comparative Neurology最新文献

Feedforward (FF) and feedback (FB) cortico-cortical neurons are distinct yet spatially intermingled subtypes distributed across cortical layers, playing specialized roles in sensory and cognitive processing. However, whether their presynaptic inputs differ to support these functions remains unknown. Using projection- and layer-specific monosynaptic rabies tracing, we mapped brain-wide long-distance inputs to multiple FF and FB neuron types in VISl (also known as LM), the mouse secondary visual cortex. Overall, long-distance input patterns for these FF and FB neurons were largely similar, as all received the majority of their inputs from VISp, the primary visual cortex, along with substantial inputs from various other cortical and visual thalamic regions. Despite their similarities, these FF and FB types differed in the proportion of long-distance cortical inputs originating from specific visual, retrosplenial, and auditory cortices. These findings reveal the input connectivity patterns of cortico-cortical neurons based on FF and FB projections, providing an anatomical framework for future studies on their functions and circuit integration.

Breathing is inherently variable due to the nonlinear dynamics of its brainstem neural control. In amphibians, a gill and a lung oscillator interact to produce breathing but the lung oscillator is necessary and sufficient to produce a mathematically complex behavior. In mammals, where the preBötzinger complex (preBötC) is considered homologous to the amphibian lung oscillator and the retrotrapezoid nucleus/parafacial respiratory group (RTN/pFRG) homologous to the amphibian gill oscillator, the origin of ventilatory complexity is not known. We address this question by characterizing ventilation variability in Phox2b mutant mice lacking the RTN/pFRG and human patients with Phox2b mutation-confirmed congenital central hypoventilation syndrome (CCHS). Ventilatory recordings were obtained from Phox2b^27ala/+—dying within hours after birth—and Egr2^cre/+; Phox2b^27ala/+ mice—generally surviving until adulthood—and their wild-type (WT) littermates, during behavioral quiescence at various developmental stages. Human data were collected from CCHS patients and healthy controls during quiet wakefulness. Variability was assessed using the coefficient of variation, complexity using noise titration (noise limit, NL), and sensitivity to initial conditions using the largest Lyapunov exponent (LLE). Mice from both mutant lineages exhibited greater variability at early developmental stages, which decreased with maturation in Egr2^cre/+; Phox2b^27ala/+ mice. NL was consistently higher in mutant mice than in WT, indicating preserved or even enhanced ventilatory complexity despite RTN/pFRG dysfunction. CO₂ reduced variability but did not affect complexity. In humans, no differences were observed between patients and controls for variability, NL, or LLE. Ventilatory complexity persists in mice lacking a functional RTN/pFRG and despite Phox2b mutations in humans, suggesting that the pontomedullary rhythm and pattern generators that include the preBötC may be its principal source. This supports the analogy between mammalian and amphibian rhythm generators.

The acoustic startle reaction is a rapid behavioral response to an unexpected auditory stimulus. In mammals, this reaction is based on an archaic reflex arch connecting auditory inputs via the sensor-motor interface in the caudal pontine reticular nucleus (PnC) of the reticular formation with motor output. The neuronal population in the PnC is heterogeneous, containing an interspersed set of giant neurons that represent the cellular substrate of the sensorimotor interface. To probe whether the heterogeneous cell population can be divided into distinct subpopulations based on somatic morphometry or potassium channel expression, we quantitatively analyzed immunofluorescence labeling in the PnC and compared this between three mammals. In gerbil, mouse, and Etruscan shrew, soma size and roundness showed a continuum over all analyzed cells. Somatic Kv1.1 labeling intensity continuously increased with increasing soma size. Overall, no subpopulations based on somatic morphometric parameters and Kv1.1 expression were observed, suggesting that the PnC is composed of neurons displaying a continuum of soma sizes. Moreover, in mice, neurons of the MNTB but not PnC showed a postnatal developmentally regulated Kv1.1 expression, contrasting this sensorimotor interface with the sensory nuclei of the auditory brainstem.

Numerous studies support a mechanistic link between hearing loss and increased risks of cognitive decline and dementia. Hearing loss is widely viewed as a modifiable risk factor for Alzheimer's disease (AD). During normal aging the inferior colliculus (IC), a large auditory midbrain nucleus, undergoes numerous changes to neurotransmission, and these changes contribute to the development of central gain and presbycusis. Recent reports also implicate the IC as a nucleus that undergoes processing changes during AD. We used transmission electron microscopy (EM) to examine the synaptic ultrastructure of the central IC (ICc) in 3xTG mice during presymptomatic, emerging, and established disease stages. Synapses were identified by a collection of presynaptic vesicles, a clear synaptic cleft, and a postsynaptic density. Symmetric synapses had pre and postsynaptic membranes of similar thickness, whereas asymmetric synapses had postsynaptic densities were conspicuously thicker than the presynaptic densities. We also quantified the presynaptic profile areas, active zone lengths, and presynaptic mitochondria. The data demonstrate a significant loss of symmetric and asymmetric synapses in the emerging disease stage. In particular, the density of symmetric synapses in the ICc was reduced by ∼50%. As inhibitory neurotransmitters gamma-aminobutyric acid (GABA), glycine, and neuropeptide Y are released from neurons that form symmetric synapses in the IC, the robust loss of these synapses may contribute to central gain and presbycusis during AD. Furthermore, as these synapses were lost well before the established disease stages, perhaps alterations in ICc represent an early biomarker for Alzheimer's progression.

Neuroplasticity is a core property of animal nervous systems, enabling structural changes in the brain in response to environmental stimuli or internal processes such as learning. Among spiders—a diverse group of predators—neuroanatomy varies with hunting strategy: stationary species that build capture webs differ from cursorial species that hunt without webs, reflecting reliance on distinct sensory modalities. While neuroplasticity has been documented in cursorial jumping spiders, its direct drivers remain unclear. In this study, we tested how sensory input influences the central nervous system (CNS) and whether stationary and cursorial hunters differ in their plastic responses. Using sensory deprivation and enrichment, we reared spiders under four treatments: control (CON), vibratory enrichment (VIB), visual enrichment (VIS), and combined enrichment (VISVIB). We examined the stationary hunter Parasteatoda tepidariorum and the cursorial hunter Marpissa muscosa. We predicted that enrichment would enlarge neuropil volumes in modality-specific brain regions, with stronger vibratory effects in P. tepidariorum and stronger visual effects in M. muscosa. Contrary to our expectations, sensory enrichment did not increase the volume of the corresponding CNS neuropils in either species. Although certain neuropils showed significant differences in specific groups, no clear causal link to sensory input emerged. Instead, a substantial proportion of the variation in neuropil volume was explained by family effects (shared maternal origin). We discuss these findings in the context of potential mechanisms underlying environmental plasticity in the spider brain.

The sexually dimorphic genitourinary organs and specialized striated muscles in the pelvis are controlled by a spinal cord motor neuron (MN) subsystem that produces reflexogenic and psychogenic (conscious) visceral and somatic motor activity during urinary continence and voiding, scent marking (in some species), defecation, reproduction, and sexual activity. To produce a three-dimensional (3D) atlas of the pelvic MN system, we performed whole-mount immunostaining and advanced 3D microscopy on the caudal spinal cord of adult female and male rats. We used choline acetyltransferase immunolabeling to study the macroscopic topology of visceral (autonomic preganglionic; VMN) and somatic MN (SMN) subcolumns and retrograde neural tracing from major pelvic ganglia to locate preganglionic neurons required for pelvic organ regulation. This identified parasympathetic VMNs in the sacral intermediolateral nucleus of segments L6–S1 and pelvic sympathetic preganglionic neurons that were mostly found in the medial dorsal commissural nucleus of segments L1–L2. Retrogradely labeled SMNs were also identified in lumbosacral nuclei containing the urinary rhabdosphincter, cremaster, and levator ani motor pools, suggesting that pelvic MNs project through both the pelvic and pudendal nerves. Evidence of sexual dimorphism was provided by VMN counts and measurements of their dendritic arborizations, and the volume of the dorsolateral and dorsomedial SMN columns. Three-dimensional visualization also revealed areas of overlap between pelvic VMNs and rhabdosphincter SMNs in dendritic bundles, suggesting a possible functional role in coordinating urinary activity. The datasets are available as an open resource (sparc.science) to support 3D visualization of the pelvic motor system in the intact rat spinal cord.

The interpeduncular nucleus (IPN) is an evolutionarily conserved brain nucleus that receives direct input from the habenula (Hb). In zebrafish (Danio rerio), it is involved in decision-making dependent on the idiothetic perception of the status of the body, such as head direction and posture. It is also known that the potentiation of the Hb–IPN–griseum centrale (GC) circuit makes fish resilient to stress in coping with fear and social conflict. To address why the same neural circuit controls these two distinctive physiological aspects, we performed anterograde and retrograde trans-synaptic viral tracing, retrograde mono-synaptic viral tracing, and lipophilic dye tracing to map the connectivity from the dorsal and intermediate IPN. We revealed reciprocal connections of d/iIPN and GC neurons with multiple brain regions for sensory inputs, including interoceptive systems that receive proprioception and the perception of balance and water flow, autonomic nervous systems for visceral control, and exteroceptive systems that receive vision and olfaction through the Hb. The positively labeled signals also cover the emotional regulatory system (i.e., serotonin, noradrenaline, and dopamine neurons) and the motor control system that administers the presentation of behaviors. Our anatomical results imply that multimodal sensorimotor information may converge in the Hb–IPN–GC circuit, hinting at its possible involvement in integrating inner states for responses to upcoming external challenges and in regulating allostasis through anticipatory biological reactions.

Understanding how animals perceive environmental stimuli is essential for reconstructing the evolution of their sensory systems. Nematodes provide a useful model for studying sensory adaptation due to their relatively simple nervous systems and broad ecological diversity. The amphid, the primary sensory organ in nematodes, has been well characterized in Caenorhabditis elegans and other bacterivorous species. However, comparatively little is known about amphid structures in nematodes with different ecological niches.​ In this study, we performed serial section transmission electron microscopy and three-dimensional reconstruction of amphid neurons in Bursaphelenchus xylophilus, a fungal-feeding, plant-parasitic nematode. We identified 13 amphid neurons, five of which showed a distinct morphology and are designated as type V neurons.These neurons were previously described as outer accessory cilia in other stylet-bearing nematodes, and had not been observed in bacterivorous species. Type V neurons exhibited trifurcated cilia that extended toward each lip and were structurally reminiscent of mechanosensory neurons.​ The presence of type V neurons only in stylet-bearing nematodes is consistent with the hypothesis that these neurons may have evolved in association with the stylet. Their trifurcated cilia suggest a potential role in detecting mechanical cues during lip contact with substrates, which could trigger stylet ejection. Alternatively, they may also contribute to other sensory modalities. Our findings reveal that fungal-feeding plant-parasitic nematodes possess amphid sensory architectures that differ markedly from those of bacterivorous species.