| Description |
The brain flows and functions through the action of excitatory neurons, yet for the brain to function properly that excitation must be regulated by inhibitory cells. Many brain disorders are a result of imbalance between excitation and inhibition, including seizures, schizophrenia, and autism. (O'Donnell, Goncalves, Portera-Cailliau, Sejnowki, 2017). This is why inhibitory neurons are so essential, this special class of neurons regulates/modulates this excitation when necessary. Inhibitory neurons make up approximately 20-25% of the neuronal populations of the brain, yet their function is incredibly important for maintenance of proper brain function (Travaglio & Jones, 2017). Information flow in the brain propagates via the electrical discharge of neurons. In sensory cortices, such as the primary visual cortex (V1), excitatory signals from the eye carry information about the visual world. Under normal circumstances, the excitatory electrical information in the visual cortex is fine-tuned by a special class of inhibitory neurons that regulate the information flow from excitatory neurons. My honors thesis focuses specifically on the novel quantification of specific classes of inhibitory neurons in V1 of non-human primate. V1 is the subject of study because the excitatory cells in the primary sensory cortices are well understood. Yet, it is the modulation and inhibition of these excitatory cells, through inhibitory neurons, that allow us to see the world around us. Inhibitory cells are subdivided into three main classes based on morphology, function and molecular markers. The three main classes include Somatostatin (SOM), Parvalbumin (PV), and Vasoactive Intestinal Polypeptide (VIP). What little is known about the laminar distribution and cellular function of these inhibitory interneuron subclasses (in the cortex) is based on rodent studies. To bridge the gap from understanding the role of inhibition in mice to human vision, we used standard immuno-histochemical (IHC) techniques to identify the laminar distribution of inhibitory neurons in the V1 of the marmoset monkey (Callithrix jacchus). In this project, I explored the distribution of inhibitory neurons across the layers of the marmoset cortex in area V1. The inhibitory neurons in the marmoset are being studied due to the marmoset's similarity to the human brain, which is much more so than mice or rats. The distribution of inhibitory neurons has already been discovered, quantified, and is known in mice (Tremblay et al, 2016). Yet, this information is yet to be discovered in the primate model which will be helpful knowledge to apply to human models. By probing each subclass of neurons using IHC, these neurons can be counted and quantified. An antibody against Gamma-Amino Butyric Acid(GABA) was used to identify all inhibitory interneurons, and antibodies against PV and SOM were used to identify the distribution of these PV+ and SOM+ cells. The boundaries between cortical laminae (Layers 1, 2/3, 4a. 4b. 4c, 5, 6 from pia to white matter) were identified using a fluorescent Nissl stain. The distribution of these inhibitory neuron cells through these layers was manually counted and the density of each subclass in each layer was quantified (cells/mm 2 in each layer). The results from this study will help create a reference for the standard laminar distribution of inhibitory neurons in the non-human primate brain that will contribute to understanding neural circuits that underlie visual function and dysfunction in future studies. |
