Textbook - BIOLOGICAL CHEMISTRY - Y.I. Gubsky - 2000

Chapter VI. BIOCHEMISTRY OF PHYSIOLOGICAL FUNCTIONS AND SPECIALIZED TISSUES

CHAPTER 33. BIOCHEMISTRY OF THE NERVOUS SYSTEM. MOLECULAR PSYCHOBIOLOGY

The human Brain is the most complex information system existing in living and non-living nature.

Neurochemistry, as a branch of science that studies the Chemical Composition and biochemical processes occurring in neural structures of varying degrees of complexity, has a history of about a century, starting with the classical works of J. Thudichum (Germany) and O.Ya. Danilevsky (Russia). A significant contribution to The Study of the Chemical composition of the Brain and the metabolic features of neural tissue was made by the prominent Ukrainian scientist O.V. Palladin (1885-1972) and his scientific school.

At the same time, the first real breakthroughs in understanding the molecular mechanisms governing The Nervous system, and the brain in particular, have been achieved only over the past 10-20 years thanks to research from leading biochemical and neurophysiological laboratories worldwide. These advancements primarily concern the biochemistry and molecular biology of Neurotransmitters, the Structure and biophysical properties of Ion Channels and ion pumps—processes that form The basis of electrical potential generation and information transmission within neural networks. Nevertheless, a whole range of fundamental problems in molecular psychobiology, specifically the NEUROCHEMICAL MECHANISMS OF thought, memory, and emotion, remains largely a terra incognita.

A fundamental challenge in studying the BIOCHEMICAL FOUNDATIONS OF the nervous system in general, and the brain of higher organisms in particular, is the remarkable Water/126.html">Diversity of the cellular composition within the morphofunctional structures of the nervous system.

According to estimates in scientific literature, the human brain contains about 10¹⁰-10¹¹ Neurons, which roughly corresponds to the number of stars in our Galaxy. Furthermore, individual neurons and groups of neurons differ significantly both in morphological characteristics and in the profile of the neurotransmitters they produce. Considering the number of contacts each neuron makes via axons and dendrites, the total number of interneuronal synapses in the human brain reaches 10¹³-10¹⁴. Besides neurons, neural tissue contains Connective Tissue-derived elements that perform trophic and supportive Functions—neuroglia and microglia. Neurons are predominantly clustered in the Gray matter of the brain (making up 60-65% of its cellular composition), whereas the White matter consists of neuroglia elements and myelin, a specialized Membrane Structure derived from Schwann Cells wrapped around neuronal axons.

33.1. FEATURES OF THE CHEMICAL COMPOSITION AND METABOLISM OF THE NERVOUS SYSTEM

Class="center">Chemical COMPOSITION OF THE Brain

The general chemical composition of the brain is characterized by the presence of Proteins (about 8% of total tissue mass), a significant amount of Lipids (10-12%), CARBOHYDRATES (about 1%), other low-molecular-weight Biomolecules, inorganic salts, and water (77-78%).

Lipids of Neural Tissue

The unique chemical composition of neural tissue and the brain is defined by an exceptionally high content of lipids with diverse chemical structures. Total lipids across various classes average about half of the dry mass of brain tissue.

KEY FEATURES OF brain Lipid Composition include the predominance of complex polar lipids (phosphoglycerides, Sphingolipids, Glycolipids) and Cholesterol, alongside minor amounts of neutral fats (triacylglycerols). Moreover, lipid content in the WHITE MATTER OF the brain is significantly higher than in the gray matter, which is attributed to the Abundance of nerve myelin sheaths in the latter structure — Table 33.1:

Table 33.1. Content of various lipid classes in the brain (mean values, % of dry tissue mass)

The predominance of polar lipids in various Regions of the brain is due to the abundance of membrane structures that perform specialized functions related to neuronal potential generation, Nerve Impulse Conduction, and synaptic transmission—namely, the Plasma Membranes of neuronal Cell bodies and axons, as well as specialized membranes of nerve terminals and synaptic vesicles.

Brain Proteins

The protein composition of the brain features a diverse spectrum comprising proteins with various biochemical and functional properties, including enzymatic, regulatory, and structural proteins. Brain proteins are categorized into neuroalbumins, neuroglobulins, and neuroscleroproteins, which differ in their physicochemical properties and represent fractions consisting of dozens of individual proteins and Polypeptides. Neural tissue Peptides that perform mediator functions (Neuropeptides) are discussed below.

Another distinctive biochemical feature of the brain is the presence of high concentrations of free Amino Acids, the vast majority of which (up to 75% of the total amount) are dicarboxylic Amino Acids and their derivatives: aspartate, glutamate, glutamine, 4-aminobutyrate, and N-acetylaspartate.

Brain METABOLISM

Energy Metabolism in the Brain

Brain Bioenergetics is characterized by a strong dependence on oxygen supply, which is utilized primarily for the aerobic oxidation of glucose. Although the brain accounts for about 2% of body mass, O₂ consumption by brain tissue in a resting adult constitutes 20-25% of the body's total demand, and up to 50% in children under four years of age. Thus, Gas Exchange in the brain is significantly higher than in other Tissues, exceeding that in Muscle tissue by 20 times.

The primary consumer of metabolic energy in the brain—utilized in the form of ATP—is the generation of neuronal membrane potentials, which requires the continuous operation of the sodium pump: the membrane-bound Na⁺, K⁺-ATPase.

A key feature of brain energy metabolism is the significant predominance of glucose utilization over other energy substrates. Unlike cells of other tissues capable of utilizing diverse metabolic fuels, neurons under normal physiological conditions rely predominantly on Blood-borne glucose as an energy substrate. A shift in brain cells toward The oxidation of acetoacetate is observed only under conditions of starvation or exhausting physical labor.

Glycogen reserves in the body are limited (Chapter 13), and impaired glucose and O₂ consumption by the brain under hypoglycemic conditions leads to profound Metabolic Disorders and the onset of coma within just a few minutes.

In brain tissue, free ammonia is constantly produced via the hydrolytic deamination of AMP. It is detoxified by reacting with glutamate to form glutamine, which then enters the bloodstream.