Anatomical Markers of Activity in Hypothalamic Neurons

Abstract

The scientific community has searched for years for ways of examining neuronal tissue to track neural activity with reliable anatomical markers for stimulated neuronal activity. Existing studies that focused on hypothalamic systems offer a few options but do not always compare approaches or validate them for dependence on cell firing, leaving the reader uncertain of the benefits and limitations of each method. Thus, in this article, potential markers will be presented and, where possible, placed into perspective in terms of when and how these methods pertain to hypothalamic function. An example of each approach is included. In reviewing the approaches, one is guided through how neurons work, the consequences of their stimulation, and then the potential markers that could be applied to hypothalamic systems are discussed. Approaches will use features of neuronal glucose utilization, water/oxygen movement, changes in neuron-glial interactions, receptor translocation, cytoskeletal changes, stimulus-synthesis coupling that includes expression of the heteronuclear or mature mRNA for transmitters or the enzymes that make them, and changes in transcription factors (immediate early gene products, precursor buildup, use of promoter-driven surrogate proteins, and induced expression of added transmitters. This article includes discussion of methodological limitations and the power of combining approaches to understand neuronal function.

Highlights of neuroanatomical discoveries of the mammalian gonadotropin‐releasing hormone system

“…Examples of dendritic associations in a primate and a rat is presented in Figure 1. 33 The advent of genetic animal models expressing reporter proteins under the control of the GnRH promoter has since richly contributed to our understanding of the connectedness of GnRH neurons. As discussed in detail below, the absence of electrical coupling between GnRH neurons was initially reported in mice expressing GFP in GnRH neurons, 34 and later confirmed in other reports.…”

“…The interaction of cellular processes in GnRH neurons is seen in both primates and rat and could be the result of dendron or dendritic interactions in mice. Examples of dendritic associations in a primate and a rat is presented in Figure 1 33 . The advent of genetic animal models expressing reporter proteins under the control of the GnRH promoter has since richly contributed to our understanding of the connectedness of GnRH neurons.…”

“…(B) Example of two intercellular bridges across GnRH neurons in a rat brain (red circle). Figure reproduced from Hoffman 33 …”

Fluorescent transgenic mouse models for whole-brain imaging in health and disease

“…The tight control over the expression time window of the fluorescent protein is also essential for enabling correlations between transitional physiological states of neurons at different temporal scales and the events that triggered them. For instance, the activity of neurons can be interrogated with many anatomical markers (Hoffman, 2020) such as IEGs to precisely tag only those cells that were active during a particular event. Therefore, the expression of the fluorescent protein driven by an IEG (e.g., cFos or Arc) should ideally be switched on at the start and switched off at the end of the event of interest to avoid tagging neurons associated with past or future events.…”

Implantação De Neurônios Artificiais No Córtex Pré-Frontal

“…Chamados de células nervosas, atuam no sistema nervoso sendo responsáveis pela propagação do impulso nervoso e consideradas as unidades básicas desse sistema (FRIED, 2022;HOFFMAN, 2020).…”