• Comprehensive CNS neurochemical atlas emerges from immunohistochemical mapping of peptides (enkephalin, substance P, dynorphin) and monoamines (serotonin, catecholamines), revealing widespread co-localization and organization of peptide and enzymatic systems in rat brain and beyond [2], [3], [5], [6], [7], [9], [11], [17].

• Psychoneuroimmunology-oriented lines treat CNS peptide networks as interfaces with immune-related circuits, using immunohistochemistry to probe how enkephalin, adrenaline, and related neuropeptides may participate in brain-immune communication and regulatory pathways [4], [8], [11].

• Evidence for segregated and co-localized peptide populations underpins functional circuit logic, showing separate beta-endorphin vs enkephalin populations and instances of co-localization (alpha-neo-endorphin/dynorphin) across rat brain structures, shaping divergent signaling roles [9], [16], [19].

• Methodological consolidation highlights antibody-based mapping and technique development for serotonin and other neurotransmitters, including specific, sensitive immunohistochemical approaches and regional mapping protocols that enabled broader CNS neurochemical inference [7], [8], [17].