The distribution of orexin receptor mRNA (OX₁R and OX₂R) in the rat brain was investigated. OX₁R mRNA is most abundant in the ventromedial hypothalamic nucleus (VMH), while OX₂R is predominantly expressed in the paraventricular nucleus (PVN). High levels of OX₁R mRNA were also found in the tenia tecta, hippocampal formation, dorsal raphe, and locus coeruleus. OX₂R mRNA is mainly expressed in the cerebral cortex, nucleus accumbens, subthalamic and paraventricular thalamic nuclei, and anterior pretectal nucleus. These findings support the role of orexin receptors in feeding regulation and suggest additional functions for orexins. The study used in situ hybridization with specific oligonucleotide probes to detect OX₁R and OX₂R mRNA. Adjacent coronal sections from the same brain were used for hybridization with specific probes against either OX₁R or OX₂R mRNA. The signals were considered specific if they could be displaced by the addition of 100-fold molar excess of the corresponding non-labeled oligonucleotides. The results showed that OX₁R and OX₂R have strikingly different expression patterns in the rat brain. The hypothalamus is the primary brain center for regulating feeding behavior and energy metabolism. Within this region, OX₁R mRNA is most abundant in the VMH, while OX₂R mRNA is predominantly expressed in the PVN. The expression of OX₁R and OX₂R in various brain regions suggests that orexins may be involved in multiple functional pathways. The wide CNS distribution of OX₁R and OX₂R mRNA indicates that orexins may play a role in various physiological functions, including feeding regulation, neuroendocrine functions, and memory storage. The study also found that OX₁R and OX₂R are heavily expressed in the hippocampus and associated structures, suggesting a role in learning and memory. The paraventricular thalamic nucleus (PVT) is believed to be part of the circadian timing system and relay information to regions involved in motivational components of behaviors and visceral functions. The results indicate that orexin receptors may mediate distinct functions for orexins, with OX₁R and OX₂R having divergent distributions in the brain. The findings support the proposed role of orexin receptors in feeding regulation and suggest additional physiological functions for the orexin family.The distribution of orexin receptor mRNA (OX₁R and OX₂R) in the rat brain was investigated. OX₁R mRNA is most abundant in the ventromedial hypothalamic nucleus (VMH), while OX₂R is predominantly expressed in the paraventricular nucleus (PVN). High levels of OX₁R mRNA were also found in the tenia tecta, hippocampal formation, dorsal raphe, and locus coeruleus. OX₂R mRNA is mainly expressed in the cerebral cortex, nucleus accumbens, subthalamic and paraventricular thalamic nuclei, and anterior pretectal nucleus. These findings support the role of orexin receptors in feeding regulation and suggest additional functions for orexins. The study used in situ hybridization with specific oligonucleotide probes to detect OX₁R and OX₂R mRNA. Adjacent coronal sections from the same brain were used for hybridization with specific probes against either OX₁R or OX₂R mRNA. The signals were considered specific if they could be displaced by the addition of 100-fold molar excess of the corresponding non-labeled oligonucleotides. The results showed that OX₁R and OX₂R have strikingly different expression patterns in the rat brain. The hypothalamus is the primary brain center for regulating feeding behavior and energy metabolism. Within this region, OX₁R mRNA is most abundant in the VMH, while OX₂R mRNA is predominantly expressed in the PVN. The expression of OX₁R and OX₂R in various brain regions suggests that orexins may be involved in multiple functional pathways. The wide CNS distribution of OX₁R and OX₂R mRNA indicates that orexins may play a role in various physiological functions, including feeding regulation, neuroendocrine functions, and memory storage. The study also found that OX₁R and OX₂R are heavily expressed in the hippocampus and associated structures, suggesting a role in learning and memory. The paraventricular thalamic nucleus (PVT) is believed to be part of the circadian timing system and relay information to regions involved in motivational components of behaviors and visceral functions. The results indicate that orexin receptors may mediate distinct functions for orexins, with OX₁R and OX₂R having divergent distributions in the brain. The findings support the proposed role of orexin receptors in feeding regulation and suggest additional physiological functions for the orexin family.