Organization of enkephalinergic neuronal system in the central nervous system of the gecko Hemidactylus frenatus

• Published in: Brain Structure and Function Vol. 229; no. 6; pp. 1365 - 1395
• Main Authors: Ganeyan, Ananya, Ganesh, C. B.
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer Berlin Heidelberg 01.07.2024; Springer Nature B.V
• Subjects: Animals; Biomedical and Life Sciences; Biomedicine; Brain - metabolism; Cell Biology; Central nervous system; Central Nervous System - metabolism; Enkephalin (methionine); Enkephalin, Leucine - metabolism; Enkephalin, Methionine - metabolism; Enkephalins; Enkephalins - metabolism; Female; Fibers; Hemidactylus frenatus; Hindbrain; Hypothalamus (lateral); Immunofluorescence; Innervation; Lizards - metabolism; Male; Mesencephalon; Methionine; Nervous system; Neurology; Neuromodulation; Neurons; Neurons - metabolism; Neurosciences; Neurotransmission; Olfactory bulb; Original Article; Pentapeptides; Periventricular nucleus; Pituitary; Thalamic nuclei; Thalamus; Opioid peptides; Methionine-enkephalin; Gecko; Lizard brain; Enkephalins; Leucine-enkephalin
• ISSN: 1863-2661; 1863-2653; 1863-2661; 0340-2061
• DOI: 10.1007/s00429-024-02805-4

Enkephalins are endogenous opioid pentapeptides that play a role in neurotransmission and pain modulation in vertebrates. However, the distribution pattern of enkephalinergic neurons in the brains of reptiles has been understudied. This study reports the organization of the methionine-enkephalin (M-ENK) and leucine-enkephalin (L-ENK) neuronal systems in the central nervous system of the gecko Hemidactylus frenatus using an immunofluorescence labeling method. Although M-ENK and L-ENK-immunoreactive (ir) fibers extended throughout the pallial and subpallial subdivisions, including the olfactory bulbs, M-ENK and L-ENK-ir cells were found only in the dorsal septal nucleus. Enkephalinergic perikarya and fibers were highly concentrated in the periventricular and lateral preoptic areas, as well as in the anterior and lateral subdivisions of the hypothalamus, while enkephalinergic innervation was observed in the hypothalamic periventricular nucleus, infundibular recess nucleus and median eminence. The dense accumulation of enkephalinergic content was noticed in the pars distalis of the hypophysis. In the thalamus, the nucleus rotundus and the dorsolateral, medial, and medial posterior thalamic nuclei contained M-ENK and L-ENK-ir fibers, whereas clusters of M-ENK and L-ENK-ir neurons were observed in the pretectum, mesencephalon, and rhombencephalon. The enkephalinergic fibers were also seen in the area X around the central canal, as well as the dorsal and ventral horns. The widespread distribution of enkephalin-containing neurons within the central nervous system implies that enkephalins regulate a variety of functions in the gecko, including sensory, behavioral, hypophysiotropic, and neuroendocrine functions.