The insular areas of the cerebral cortex in carnivores remain vaguely defined and fragmentarily characterized. We have examined the cortical microarchitecture and thalamic connections of the insular region in cats, as a part of a broader study aimed to clarify their subdivisions, functional affiliations, and eventual similarities with other mammals. We report that cortical areas, which resemble the insular fields of other mammals, are located in the cat's orbital gyrus and anterior rhinal sulcus. Our data suggest four such areas: (a) a "ventral agranular insular area" in the lower bank of the anterior rhinal sulcus, architectonically transitional between iso- and allocortex and sparsely connected to the thalamus, mainly with midline nuclei; (b) a "dorsal agranular insular area" in the upper bank of the anterior rhinal sulcus, linked to the mediodorsal, ventromedial, parafascicular and midline nuclei; (c) a "dysgranular insular area" in the anteroventral half of the orbital gyrus, characterized by its connections with gustatory and viscerosensory portions of the ventroposterior complex and with the ventrolateral nucleus; and (d) a "granular insular area", dorsocaudal in the orbital gyrus, which is chiefly bound to spinothalamic-recipient thalamic nuclei such as the posterior medial and the ventroposterior inferior. Three further fields are situated caudally to the insular areas. The anterior sylvian gyrus and dorsal lip of the pseudosylvian sulcus, which we designate "anterior sylvian area", is connected to the ventromedial, suprageniculate, and lateralis medialis nuclei. The fundus and ventral bank of the pseudosylvian sulcus, or "parainsular area", is associated with caudal portions of the medial geniculate complex. The rostral part of the ventral bank of the anterior ectosylvian sulcus, referred to as "ventral anterior ectosylvian area", is heavily interconnected with the lateral posterior-pulvinar complex and the ventromedial nucleus. Present results reveal that these areas interact with a wide array of sensory, motor, and limbic thalamic nuclei. In addition, these data provide a consistent basis for comparisons with cortical fields in other mammals.
The brainstem mechanisms for the generation of paradoxical sleep are under considerable debate. Previous experiments in cats have demonstrated that injections of the cholinergic agonist carbachol into the oral pontine tegmentum elicit paradoxical sleep behaviour and its polygraphic correlates. The different results on the pontine structures that mediate this effect do not agree. We report here that limited microinjections of a carbachol solution into the ventral part of the oral pontine reticular nucleus in the cat induce, with a short latency, a dramatic, long-lasting increase in paradoxical sleep. Moreover, neuronal tracing experiments show that this pontine site is connected with brain structures responsible for the different bioelectric events of paradoxical sleep. These two facts suggest that the ventral part of the oral pontine reticular nucleus is a nodal link in the neuronal network underlying paradoxical sleep mechanisms.
The state of non-REM sleep (NREM), or slow wave sleep, is associated with a synchronized EEG pattern in which sleep spindles and/or K complexes and high-voltage slow wave activity (SWA) can be recorded over the entire cortical surface. In humans, NREM is subdivided into stages 2 and 3–4 (presently named N3) depending on the proportions of each of these polygraphic events. NREM is necessary for normal physical and intellectual performance and behavior. An overview of the brain structures involved in NREM generation shows that the thalamus and the cerebral cortex are absolutely necessary for the most significant bioelectric and behavioral events of NREM to be expressed; other structures like the basal forebrain, anterior hypothalamus, cerebellum, caudal brain stem, spinal cord and peripheral nerves contribute to NREM regulation and modulation. In NREM stage 2, sustained hyperpolarized membrane potential levels resulting from interaction between thalamic reticular and projection neurons gives rise to spindle oscillations in the membrane potential; the initiation and termination of individual spindle sequences depends on corticothalamic activities. Cortical and thalamic mechanisms are also involved in the generation of EEG delta SWA that appears in deep stage 3–4 (N3) NREM; the cortex has classically been considered to be the structure that generates this activity, but delta oscillations can also be generated in thalamocortical neurons. NREM is probably necessary to normalize synapses to a sustainable basal condition that can ensure cellular homeostasis. Sleep homeostasis depends not only on the duration of prior wakefulness but also on its intensity, and sleep need increases when wakefulness is associated with learning. NREM seems to ensure cell homeostasis by reducing the number of synaptic connections to a basic level; based on simple energy demands, cerebral energy economizing during NREM sleep is one of the prevalent hypotheses to explain NREM homeostasis.
The large Spanish wildcat, Felis silvestris tartessia, has retained features of the Pleistocene ancestor of the modern domestic cat, F. catus. To gauge the direction and magnitude of short-term evolutionary change in this lineage, we have compared the retina, the optic nerve, and the dorsal lateral geniculate nucleus (LGN) of Spanish wildcats and their domestic relatives. Retinas of the two species have the same area. However, densities of cone photoreceptors are higher in wildcat--over 100% higher in the area centralis--whereas rod densities are as high, or higher, in the domestic lineage. Densities of retinal ganglion cells are typically 20-100% higher across the wildcat retina, and the total ganglion cell population is nearly 70% higher than in the domestic cat. These differences are confined to the populations of beta and gamma retinal ganglion cells. In contrast, the population of alpha cells is almost precisely the same in both species. The wildcat LGN is much larger than that of the domestic cat and contains approximately 50% more neurons. However, cell size does not differ appreciably in either the retina or LGN of these species. The differences in total numbers of ganglion cells and LGN neurons correspond neatly to the overall decline in brain size in the domestic lineage and to allometric predictions based on average species differences in body size. We suggest that an increase in the severity of naturally occurring cell death is the most plausible mechanism that can account for the rapid evolutionary reduction in cell populations in this feline lineage.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
customersupport@researchsolutions.com
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply.
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.