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Qi, Meizhu; Fadool, Debra Ann; Storace, Douglas A.
doi: 10.1002/cne.25518pmid: 37434469
Olfactory cues play a key role in natural behaviors such as finding food, finding mates, and avoiding predators. In principle, the ability of the olfactory system to carry out these perceptual functions would be facilitated by signaling related to an organism's physiological state. One candidate pathway includes a direct projection from the hypothalamus to the main olfactory bulb, the first stage of olfactory sensory processing. The pathway from the hypothalamus to the main olfactory bulb is thought to include neurons that express the neuropeptide orexin, although the proportion that is orexinergic remains unknown. A current model proposes that the orexin population is heterogeneous, yet it remains unknown whether the proportion that innervates the main olfactory bulb reflects a distinct subpopulation of the orexin population. Herein, we carried out combined retrograde tract tracing with immunohistochemistry for orexin‐A in the mouse to define the proportion of hypothalamic input to the main olfactory bulb that is orexinergic and to determine what fraction of the orexin‐A population innervates the bulb. The numbers and spatial positions of all retrogradely labeled neurons and all the orexin‐A‐expressing neurons were quantified in sequential sections through the hypothalamus. Retrogradely labeled neurons were found in the ipsilateral hypothalamus, of which 22% expressed orexin‐A. The retrogradely labeled neurons that did and did not express orexin‐A could be anatomically distinguished based on their spatial position and cell body area. Remarkably, only 7% of all the orexin‐A neurons were retrogradely labeled, suggesting that only a small fraction of the orexin‐A population directly innervate the main olfactory bulb. These neurons spatially overlapped with the orexin‐A neurons that did not innervate the bulb, although the two cell populations were differentiated based on cell body area. Overall, these results support a model in which olfactory sensory processing is influenced by orexinergic feedback at the first synapse in the olfactory processing pathway.
Manoli, Giulia; Zandawala, Meet; Yoshii, Taishi; Helfrich‐Förster, Charlotte
doi: 10.1002/cne.25522pmid: 37493077
Insects from high latitudes spend the winter in a state of overwintering diapause, which is characterized by arrested reproduction, reduced food intake and metabolism, and increased life span. The main trigger to enter diapause is the decreasing day length in summer–autumn. It is thus assumed that the circadian clock acts as an internal sensor for measuring photoperiod and orchestrates appropriate seasonal changes in physiology and metabolism through various neurohormones. However, little is known about the neuronal organization of the circadian clock network and the neurosecretory system that controls diapause in high‐latitude insects. We addressed this here by mapping the expression of clock proteins and neuropeptides/neurohormones in the high‐latitude fly Drosophila littoralis. We found that the principal organization of both systems is similar to that in Drosophila melanogaster, but with some striking differences in neuropeptide expression levels and patterns. The small ventrolateral clock neurons that express pigment‐dispersing factor (PDF) and short neuropeptide F (sNPF) and are most important for robust circadian rhythmicity in D. melanogaster virtually lack PDF and sNPF expression in D. littoralis. In contrast, dorsolateral clock neurons that express ion transport peptide in D. melanogaster additionally express allatostatin‐C and appear suited to transfer day‐length information to the neurosecretory system of D. littoralis. The lateral neurosecretory cells of D. littoralis contain more neuropeptides than D. melanogaster. Among them, the cells that coexpress corazonin, PDF, and diuretic hormone 44 appear most suited to control diapause. Our work sets the stage to investigate the roles of these diverse neuropeptides in regulating insect diapause.
Pfau, Daniel R.; Baribeau, Sarah; Brown, Felix; Khetarpal, Niki; Marc Breedlove, S.; Jordan, Cynthia L.
doi: 10.1002/cne.25528pmid: 37496437
The transient receptor potential cation channel 2 (TRPC2) conveys pheromonal information from the vomeronasal organ (VNO) to the brain. Both male and female mice lacking this gene show altered sex‐typical behavior as adults. We asked whether TRPC2, highly expressed in the VNO, normally participates in the development of VNO‐recipient brain regions controlling mounting and aggression, two behaviors affected by TRPC2 loss. We now report significant effects of TRPC2 loss in both the posterodorsal aspect of the medial amygdala (MePD) and ventromedial nucleus of the hypothalamus (VMH) of male and female mice. In the MePD, a sex difference in neuron number was eliminated by the TRPC2 knockout (KO), but the effect was complex, with fewer neurons in the right MePD of females, and fewer neurons in the left MePD of males. In contrast, MePD astrocytes were unaffected by the KO. In the ventrolateral (vl) aspect of the VMH, KO females were like wildtype (WT) females, but TRPC2 loss had a dramatic effect in males, with fewer neurons than WT males and a smaller VMHvl overall. We also discovered a glial sex difference in VMHvl of WTs, with females having more astrocytes than males. Interestingly, TRPC2 loss increased astrocyte number in males in this region. We conclude that TRPC2 normally participates in the sexual differentiation of the mouse MePD and VMHvl. These changes in two key VNO‐recipient regions may underlie the effects of the TRPC2 KO on behavior.
Richardson, Janell; Dezfuli, Ghazaul; Mangel, Allen W.; Gillis, Richard A.; Vicini, Stefano; Sahibzada, Niaz
doi: 10.1002/cne.25530pmid: 37507853
The pyloric sphincter receives parasympathetic vagal innervation from the dorsal motor nucleus of the vagus (DMV). However, little is known about its higher‐order neurons and the nuclei that engage the DMV neurons controlling the pylorus. The purpose of the present study was twofold. First, to identify neuroanatomical connections between higher‐order neurons and the DMV. This was carried out by using the transneuronal pseudorabies virus PRV‐152 injected into rat pylorus torus and examining the brains of these animals for PRV labeling. Second, to identify the specific sites within the DMV that functionally control the motility and tone of the pyloric sphincter. For these studies, experiments were performed to assess the effect of DMV stimulation on pylorus activity in urethane‐anesthetized male rats. A strain gauge force transducer was sutured onto the pyloric tonus to monitor tone and motility. L‐glutamate (500 pmol/30 nL) was microinjected unilaterally into the rostral and caudal areas of the DMV. Data from the first study indicated that neurons labeled with PRV occurred in the DMV, hindbrain raphe nuclei, midbrain Edinger–Westphal nucleus, ventral tegmental area, lateral habenula, and arcuate nucleus. Data from the second study indicated that microinjected L‐glutamate into the rostral DMV results in contraction of the pylorus blocked by intravenously administered atropine and ipsilateral vagotomy. L‐glutamate injected into the caudal DMV relaxed the pylorus. This response was abolished by ipsilateral vagotomy but not by intravenously administered atropine or L‐NG‐nitroarginine methyl ester (L‐NAME). These findings identify the anatomical and functional brain neurocircuitry involved in controlling the pyloric sphincter. Our results also show that site‐specific stimulation of the DMV can differentially influence the activity of the pyloric sphincter by separate vagal nerve pathways.
doi: 10.1002/cne.25531pmid: 37507852
The epithalamus, an area of the dorsal diencephalon found in all vertebrates, consists of the habenula, the subhabenular nuclei, and associated tracts. The habenula is itself divisible into two parts—a medial and a lateral nucleus differing in their inputs, outputs, and cellular morphology. The medial component is related to the limbic system and serotonergic raphe, while the lateral nucleus is more interconnected with the basal ganglia and midbrain dopamine systems. These findings, which come from experiments mainly done on mammals, serve as a basis for comparison with other vertebrates. However, similar studies in other amniotes, such as reptiles, are few. To fill this gap in knowledge, two species of crocodiles were examined utilizing a variety of histological methods in various planes of section. The following results were obtained. First, the habenula was divided into medial and lateral parts based on its cytoarchitecture. Neurons in the medial habenula were small, were closely packed, and had a limited dendritic arbor characterized by unusual distal dendritic appendages, whereas neurons in the lateral habenula were larger, were more loosely packed, and had longer dendritic processes that were commonly beaded. Second, the stria medullaris, the major input to the habenula, was identified by its immunoreactivity to parvalbumin. Third, the fasciculus retroflexus (habenulointerpeduncular tract), the primary output of the habenula, was visualized by staining with acetylcholinesterase. Fourth, nuclei associated with the habenula, the subhabenular nuclei, have been identified and characterized. These features provide a means to recognize the major nuclei and tracts in the epithalamus in crocodiles and are likely applicable to other reptiles.
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