Abstract
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.
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Abbreviations
- ACC:
-
Nucleus accumbens
- AM:
-
Amygdala
- AMC:
-
nucleus centralis amygdalae
- AME:
-
nucleus externus amygdalae
- AX:
-
Area X of central canal
- BSA:
-
Bovine serum albumin
- CA:
-
Anterior commissure
- CB:
-
Cerebellum
- CC:
-
Central canal
- CNS:
-
Central nervous system
- CP:
-
Posterior commissure
- CTX:
-
Cortex
- DCTX:
-
Dorsal cortex
- DF:
-
Dorsal funiculus
- DH:
-
Dorsal horn of the spinal cord
- DLH:
-
Dorsolateral hypothalamic nucleus
- DLT:
-
Dorsolateral thalamic nucleus
- DMT:
-
Dorsomedial thalamic nucleus
- DVR:
-
Dorsoventricular ridge
- EPL:
-
External plexiform layer
- FLM:
-
Fasciculus longitudinalis medialis
- GC:
-
Griseum centrale
- GCL:
-
Granular layer of the cerebellum
- GL:
-
Glomerular layer
- GP:
-
Globus pallidus
- IGL:
-
Inner granular layer
- IPN:
-
Interpeduncular nucleus
- IR:
-
Infundibular recess
- ir:
-
immunoreactive
- IRN:
-
Infundibular recess nucleus
- IS:
-
Isthmus
- L-ENK:
-
Leucine-enkephalin
- LA:
-
Lateral amygdala
- LCO:
-
Locus coeruleus
- LDT:
-
Laterodorsal tegmental nucleus
- LCTX:
-
Lateral cortex
- LF:
-
Lateral funiculus
- LFB:
-
Lateral forebrain bundle
- LHA:
-
Lateral hypothalamic area
- LM:
-
pretectal lentiform mesencephalic nucleus
- lPOA:
-
Lateral preoptic area
- M-ENK:
-
Methionine-enkephalin
- MCL:
-
Molecular layer of the cerebellum
- MCTX:
-
Medial cortex
- ME:
-
Median eminence
- ML:
-
Mitral cell layer
- MP:
-
Medial posterior thalamic nucleus
- MT:
-
Medial thalamic nucleus
- MV:
-
Motor nucleus of trigeminal nerve
- NCP:
-
Nucleus of the posterior commissure
- NdB:
-
Nucleus of the diagonal band of Broca
- OC:
-
Optic chiasma
- OLF:
-
Olfactory bulb
- ON:
-
Optic nerve
- OT:
-
Optic tectum
- PB:
-
Parabrachial nucleus
- PD:
-
Pars distalis
- PDN:
-
Posterodorsal nucleus
- PH:
-
Periventricular nucleus of hypothalamus
- PIT:
-
Pituitary gland
- POA:
-
Preoptic area
- pPOA:
-
Periventricular preoptic area
- PRD:
-
Dorsal pretectal nucleus
- PVN:
-
Paraventricular nucleus
- RAS:
-
Superior raphe nucleus
- RF:
-
Reticular formation
- ROT:
-
Nucleus rotundus
- RS:
-
Superior reticular nucleus
- SP:
-
Septum
- SA:
-
Anterior septal nucleus
- SAC:
-
Stratum album centrale
- SC:
-
Spinal cord
- SCN:
-
Suprachiasmatic nucleus
- SCO:
-
Subcommissural organ
- SD:
-
Dorsal septal nucleus
- SGC:
-
Stratum griseum centrale
- SGFP:
-
Stratum griseum et fibrosum periventriculare
- SGFS:
-
Stratum griseum et fibrosum superficiale
- SL:
-
Lateral septal nucleus
- SM:
-
Medial septal nucleus
- SN:
-
Substantia nigra
- SO:
-
Stratum opticum
- SON:
-
Supraoptic nucleus
- ST:
-
Striatum
- TEGM:
-
Tegmentum
- TH:
-
Thalamus
- TS:
-
Torus semicircularis
- TSC:
-
Torus semicircularis pars centralis
- TSL:
-
Torus semicircularis pars lateralis
- V:
-
Ventricle
- VF:
-
Ventral funiculus
- VH:
-
Ventral horn of the spinal cord
- VTA:
-
Ventral tegmental area
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This research was supported by a grant (No. CRG/2020/4764) from Science and Engineering Research Board–Department of Science and Technology (SERB-DST), New Delhi, Government of India.
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Ganeyan, A., Ganesh, C.B. Organization of enkephalinergic neuronal system in the central nervous system of the gecko Hemidactylus frenatus. Brain Struct Funct (2024). https://doi.org/10.1007/s00429-024-02805-4
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DOI: https://doi.org/10.1007/s00429-024-02805-4