Population bursts in a modular neural network as a mechanism for synchronized activity in KNDy neurons.

The pulsatile activity of gonadotropin-releasing hormone neurons (GnRH neurons) is a key factor in the regulation of reproductive hormones. This pulsatility is orchestrated by a network of neurons that release the neurotransmitters kisspeptin, neurokinin B, and dynorphin (KNDy neurons), and produce episodic bursts of activity driving the GnRH neurons. We show in this computational study that the features of coordinated KNDy neuron activity can be explained by a neural network in which connectivity among neurons is modular. That is, a network structure consisting of clusters of highly-connected neurons with sparse coupling among the clusters. This modular structure, with distinct parameters for intracluster and intercluster coupling, also yields predictions for the differential effects on synchronization of changes in the coupling strength within clusters versus between clusters.

The Origin of GnRH Pulse Generation: An Integrative Mathematical-Experimental Approach.

Fertility critically depends on the gonadotropin-releasing hormone (GnRH) pulse generator, a neural construct comprised of hypothalamic neurons coexpressing kisspeptin, neurokoinin-B and dynorphin. Here, using mathematical modeling and in vivo optogenetics we reveal for the first time how this neural construct initiates and sustains the appropriate ultradian frequency essential for reproduction. Prompted by mathematical modeling, we show experimentally using female estrous mice that robust pulsatile release of luteinizing hormone, a proxy for GnRH, emerges abruptly as we increase the basal activity of the neuronal network using continuous low-frequency optogenetic stimulation. Further increase in basal activity markedly increases pulse frequency and eventually leads to pulse termination. Additional model predictions that pulsatile dynamics emerge from nonlinear positive and negative feedback interactions mediated through neurokinin-B and dynorphin signaling respectively are confirmed neuropharmacologically. Our results shed light on the long-elusive GnRH pulse generator offering new horizons for reproductive health and wellbeing.SIGNIFICANCE STATEMENT The gonadotropin-releasing hormone (GnRH) pulse generator controls the pulsatile secretion of the gonadotropic hormones LH and FSH and is critical for fertility. The hypothalamic arcuate kisspeptin neurons are thought to represent the GnRH pulse generator, since their oscillatory activity is coincident with LH pulses in the blood; a proxy for GnRH pulses. However, the mechanisms underlying GnRH pulse generation remain elusive. We developed a mathematical model of the kisspeptin neuronal network and confirmed its predictions experimentally, showing how LH secretion is frequency-modulated as we increase the basal activity of the arcuate kisspeptin neurons in vivo using continuous optogenetic stimulation. Our model provides a quantitative framework for understanding the reproductive neuroendocrine system and opens new horizons for fertility regulation.

Roles of copper in neurokinin B and gonadotropin-releasing hormone structure and function and the endocrinology of reproduction.

Copper is a metal ion present in all organisms, where it has well-known roles in association with proteins and enzymes essential for cellular processes. In the early decades of the twentieth century copper was shown to influence mammalian reproductive biology, and it was subsequently shown to exert effects primarily at the level of the pituitary gland and/or hypothalamic regions of the brain. Furthermore, it has been reported that copper can interact with key neuropeptides in the hypothalamic-pituitary-gonadal axis, notably gonadotropin-releasing hormone (GnRH) and neurokinin B. Interestingly, recent phylogenetic analysis of the sequences of GnRH-related peptides indicates that copper binding is an evolutionarily ancient property of this neuropeptide family, which has been variously retained, modified or lost in the different taxa. In this mini-review the metal-binding properties of neuropeptides in the vertebrate reproductive pathway are reviewed and the evolutionary and functional significance of copper binding by GnRH-related neuropeptides in vertebrates and invertebrates are discussed.

Regulation of GnRH pulsatility in ewes.

Early work in ewes provided a wealth of information on the physiological regulation of pulsatile gonadotropin-releasing hormone (GnRH) secretion by internal and external inputs. Identification of the neural systems involved, however, was limited by the lack of information on neural mechanisms underlying generation of GnRH pulses. Over the last decade, considerable evidence supported the hypothesis that a group of neurons in the arcuate nucleus that contain kisspeptin, neurokinin B and dynorphin (KNDy neurons) are responsible for synchronizing secretion of GnRH during each pulse in ewes. In this review, we describe our current understanding of the neural systems mediating the actions of ovarian steroids and three external inputs on GnRH pulsatility in light of the hypothesis that KNDy neurons play a key role in GnRH pulse generation. In breeding season adults, estradiol (E2) and progesterone decrease GnRH pulse amplitude and frequency, respectively, by actions on KNDy neurons, with E2 decreasing kisspeptin and progesterone increasing dynorphin release onto GnRH neurons. In pre-pubertal lambs, E2 inhibits GnRH pulse frequency by decreasing kisspeptin and increasing dynorphin release, actions that wane as the lamb matures to allow increased pulsatile GnRH secretion at puberty. Less is known about mediators of undernutrition and stress, although some evidence implicates kisspeptin and dynorphin, respectively, in the inhibition of GnRH pulse frequency by these factors. During the anoestrus, inhibitory photoperiod acting via melatonin activates A15 dopaminergic neurons that innervate KNDy neurons; E2 increases dopamine release from these neurons to inhibit KNDy neurons and suppress the frequency of kisspeptin and GnRH release.

The role of kisspeptin/neurokinin B/dynorphin neurons in pathomechanism of vasomotor symptoms in postmenopausal women: from physiology to potential therapeutic applications.

Women during perimenopausal period experience a range of symptoms, which interfere with physical, sexual, and social life. About 65-75% of symptoms connected with postmenopausal period are vasomotor symptoms (VMS), such as hot flushes and night sweats. Hot flushes are subjective sensation of heat associated with cutaneous vasodilatation and drop in core temperature. It is suspected that VMS are strongly correlated with pulsatile oversecretion of gonadotropin-releasing hormone (GnRH) and subsequently luteinizing hormone (LH). Evidence has accumulated in parallel showing that lack of negative feedback of steroid hormones synthesized in ovary causes overactivation of hypertrophied kisspeptin/neurokinin B/dynorphin (KNDy) neurons, located in infundibular nucleus. Oversecretion of both kisspeptin (KISS1) and neurokinin B (NKB), as well as downregulation of dynorphin, plays dominant role in creation of GnRH pulses. This in turn causes VMS. Administration of senktide, highly potent and selective NK3R agonist, resulted in increase of serum LH concentration, induction of VMS, increase in heart rate, and skin temperature in postmenopausal women. These finding suggest that modulation of KNDy neurons may become new therapeutic approach in the treatment of VMS.

Role for kisspeptin/neurokinin B/dynorphin (KNDy) neurons in cutaneous vasodilatation and the estrogen modulation of body temperature.

Estrogen withdrawal in menopausal women leads to hot flushes, a syndrome characterized by the episodic activation of heat dissipation effectors. Despite the extraordinary number of individuals affected, the etiology of flushes remains an enigma. Because menopause is accompanied by marked alterations in hypothalamic kisspeptin/neurokinin B/dynorphin (KNDy) neurons, we hypothesized that these neurons could contribute to the generation of flushes. To determine if KNDy neurons participate in the regulation of body temperature, we evaluated the thermoregulatory effects of ablating KNDy neurons by injecting a selective toxin for neurokinin-3 expressing neurons [NK(3)-saporin (SAP)] into the rat arcuate nucleus. Remarkably, KNDy neuron ablation consistently reduced tail-skin temperature (T(SKIN)), indicating that KNDy neurons facilitate cutaneous vasodilatation, an important heat dissipation effector. Moreover, KNDy ablation blocked the reduction of T(SKIN) by 17ß-estradiol (E(2)), which occurred in the environmental chamber during the light phase, but did not affect the E(2) suppression of T(SKIN) during the dark phase. At the high ambient temperature of 33 °C, the average core temperature (T(CORE)) of ovariectomized (OVX) control rats was significantly elevated, and this value was reduced by E(2) replacement. In contrast, the average T(CORE) of OVX, KNDy-ablated rats was lower than OVX control rats at 33 °C, and not altered by E(2) replacement. These data provide unique evidence that KNDy neurons promote cutaneous vasodilatation and participate in the E(2) modulation of body temperature. Because cutaneous vasodilatation is a cardinal sign of a hot flush, these results support the hypothesis that KNDy neurons could play a role in the generation of flushes.

Neurokinin Bs and neurokinin B receptors in zebrafish-potential role in controlling fish reproduction.

The endocrine regulation of vertebrate reproduction is achieved by the coordinated actions of several peptide neurohormones, tachykinin among them. To study the evolutionary conservation and physiological functions of neurokinin B (NKB), we identified tachykinin (tac) and tac receptor (NKBR) genes from many fish species, and cloned two cDNA forms from zebrafish. Phylogenetic analysis showed that piscine Tac3s and mammalian neurokinin genes arise from one lineage. High identity was found among different fish species in the region encoding the NKB; all shared the common C-terminal sequence. Although the piscine Tac3 gene encodes for two putative tachykinin peptides, the mammalian ortholog encodes for only one. The second fish putative peptide, referred to as neurokinin F (NKF), is unique and found to be conserved among the fish species when tested in silico. tac3a was expressed asymmetrically in the habenula of embryos, whereas in adults zebrafish tac3a-expressing neurons were localized in specific brain nuclei that are known to be involved in reproduction. Zebrafish tac3a mRNA levels gradually increased during the first few weeks of life and peaked at pubescence. Estrogen treatment of prepubertal fish elicited increases in tac3a, kiss1, kiss2, and kiss1ra expression. The synthetic zebrafish peptides (NKBa, NKBb, and NKF) activated Tac3 receptors via both PKC/Ca(2+) and PKA/cAMP signal-transduction pathways in vitro. Moreover, a single intraperitoneal injection of NKBa and NKF significantly increased leuteinizing hormone levels in mature female zebrafish. These results suggest that the NKB/NKBR system may participate in neuroendocrine control of fish reproduction.

Modulation of body temperature and LH secretion by hypothalamic KNDy (kisspeptin, neurokinin B and dynorphin) neurons: a novel hypothesis on the mechanism of hot flushes.

Despite affecting millions of individuals, the etiology of hot flushes remains unknown. Here we review the physiology of hot flushes, CNS pathways regulating heat-dissipation effectors, and effects of estrogen on thermoregulation in animal models. Based on the marked changes in hypothalamic kisspeptin, neurokinin B and dynorphin (KNDy) neurons in postmenopausal women, we hypothesize that KNDy neurons play a role in the mechanism of flushes. In the rat, KNDy neurons project to preoptic thermoregulatory areas that express the neurokinin 3 receptor (NK3R), the primary receptor for NKB. Furthermore, activation of NK3R in the median preoptic nucleus, part of the heat-defense pathway, reduces body temperature. Finally, ablation of KNDy neurons reduces cutaneous vasodilatation and partially blocks the effects of estrogen on thermoregulation. These data suggest that arcuate KNDy neurons relay estrogen signals to preoptic structures regulating heat-dissipation effectors, supporting the hypothesis that KNDy neurons participate in the generation of flushes.

Kisspeptin and neurokinin B neuroendocrine pathways in the control of human ovulation.

The roles of initially kisspeptin and subsequently neurokinin B pathways in the regulation of human reproduction through the control of GnRH secretion were first identified 20 years ago, as essential for the onset of puberty in both boys and girls. Within that short time we already now have the first licence for clinical use for a neurokinin antagonist in a related indication, for menopausal vasomotor symptoms. Between these two markers of the start and end of the reproductive lifespan, it is clear that these pathways underlie many of the aspects of the hypothalamic regulation of reproduction which had hitherto been enigmatic. In this review, we describe the data currently available from studies designed to elucidate the roles of kisspeptin and neurokinin B in human ovarian function, specifically the regulation of follicle development leading up to ovulation, and in the control of the mid-cycle GnRH/LH surge that triggers ovulation. These studies, undertaken with only very limited pharmacological tools, provide evidence that the neurokinin B pathway is important in controlling the hypothalamic contribution to the precise gonadotropic drive to the ovary that is necessary for mono-ovulation, whereas the switch from negative to positive estrogenic feedback results in kisspeptin-mediated increased GnRH secretion. Potential therapeutic opportunities in conditions characterised by disordered hypothalamic/pituitary function, polycystic ovary syndrome, and functional hypothalamic amenorrhoea, and in the induced LH surge that is a necessary part of IVF treatment are discussed.

Role of neurokinin B in the control of female puberty and its modulation by metabolic status.

Human genetic studies have revealed that neurokinin B (NKB) and its receptor, neurokinin-3 receptor (NK3R), are essential elements for normal reproduction; however, the precise role of NKB-NK3R signaling in the initiation of puberty remains unknown. We investigated here the regulation of Tac2 and Tacr3 mRNAs (encoding NKB and NK3R, respectively) in female rats and demonstrated that their hypothalamic expression is increased along postnatal maturation. At puberty, both genes were widely expressed throughout the brain, including the lateral hypothalamic area and the arcuate nucleus (ARC)/medial basal hypothalamus, where the expression of Tacr3 increased across pubertal transition. We showed that central administration of senktide (NK3R agonist) induced luteinizing hormone (LH) secretion in prepubertal and peripubertal females. Conversely, chronic infusion of an NK3R antagonist during puberty moderately delayed the timing of vaginal opening (VO) and tended to decrease LH levels. The expression of NKB and its receptor was sensitive to changes in metabolic status during puberty, as reflected by a reduction in Tacr3 (and, to a lesser extent, Tac2) expression in the ARC after a 48 h fast. Yet, acute LH responses to senktide in pubertal females were preserved, if not augmented, under fasting conditions, suggesting sensitization of the NKB-NK3R-gonadotropin-releasing hormone signaling pathway under metabolic distress. Moreover, repeated administration of senktide to female rats with pubertal arrest due to chronic undernutrition rescued VO (in ∼50% of animals) and potently elicited LH release. Altogether, our observations suggest that NKB-NK3R signaling plays a role in pubertal maturation and that its alterations may contribute to pubertal disorders linked to metabolic stress and negative energy balance.

A nociceptive signaling role for neuromedin B.

Here we used an array-based differential screen to uncover the expression of the neuropeptide neuromedin B (NMB) in the trigeminal ganglia of mice. Double-labeling experiments reveal NMB is expressed in a subset of sensory neurons that colabel with calcitonin gene-related peptide and TRPV1 suggestive of a role for NMB in nociception. Indeed, administration of NMB antagonist greatly attenuates edema and nerve sensitization following stimulation of peripheral nerves with mustard oil, demonstrating that NMB contributes to neurogenic inflammation. Moreover, direct injection of NMB causes local swelling and nociceptive sensitization. Interestingly, we also find that the receptor for NMB is expressed in interneurons in the superficial layers of the dorsal horn. We used NMB-saporin to specifically eliminate NMBR-expressing neurons and determined they are required in responses to noxious heat, but not for reaction to mechanical and pruritic stimuli. Thus, NMB may be a neurotransmitter that is selectively involved in the perception of thermal stimuli.

Use of genetic models of idiopathic hypogonadotrophic hypogonadism in mice and men to understand the mechanisms of disease.

Mutations in the genes encoding the neuropeptides kisspeptin and neurokinin B, as well as their receptors, are associated with gonadotrophin-releasing hormone (GnRH) deficiency and a failure to initiate and/or progress through puberty. Although the total number of patients studied to date is small, mutations in the kisspeptin pathway appear to result in lifelong GnRH deficiency. Mice with mutations in kisspeptin and the kisspeptin receptor, Kiss1(-/-) and Kiss1r(-/-), respectively, appear to be phenocopies of the human with abnormal sexual maturation and infertility. In contrast, mutations in the neurokinin B pathway lead to a more variable adult reproductive phenotype, with a subset of hypogonadotrophic individuals demonstrating paradoxical recovery of reproductive function later in life. While 'reversal' remains poorly understood, the ability to recover reproductive function indicates that neurokinin B may play different roles in the initiation of sexual maturation compared with the maintenance of adult reproductive function. Mice with mutations in the gene encoding the neurokinin B receptor, Tacr3, have abnormal oestrous cycles and subfertility but, similar to their human counterparts, appear less severely affected than mice with kisspeptin deficiency. Further investigations into the interaction between the kisspeptin and neurokinin B pathways will reveal key insights into how GnRH neuronal modulation occurs at puberty and throughout reproductive life.

Neuromedin B and its receptor influence the activity of myometrial primary cells in vitro through regulation of Il6 expression via the Rela/p65 pathway in mice.

The neuromedin B receptor (Nmbr) is an important physiological regulator of spontaneous activities and stress responses through different cascades as well as its autocrine and paracrine effects. Previous studies have revealed that neuromedin B (Nmb) and its receptor signal via the Rela (also known as p65)/Il6 pathway in a mouse model of pregnancy. This study investigated the mechanism of Nmbr signaling via the Rela/p65-Il6 pathway and regulation of the concentration of intracellular free calcium ([Ca(2+)](i)) during the onset of labor in primary mouse myometrial cell cultures isolated from mice in term labor. Data demonstrated Nmbr agonist-mediated upregulation of the DNA binding activity of Rela/p65, Il6 expression, and [Ca(2+)](i) in a concentration-dependent manner. Furthermore, a significant correlation was observed between DNA binding activity of Rela/p65 and Il6 expression. Moreover, this up-regulation was blocked by Nmbr and Rela/p65 knockdown, achieved by RNA interference (RNAi) technology. No significant differences were identified in the inhibition of Il6 expression as a result of Nmbr or Rela/p65 knockdown. However, significant differences were observed between the [Ca(2+)](i) in Rela/p65-specific group and that in the Nmbr-specific small interfering RNA (siRNA)-treated groups. These data demonstrated that the Nmb/Nmbr interaction in pregnant myometrial primary cells in vitro predominantly influenced uterine activity through regulation of Il6 expression via the Rela/p65 pathway, although the effects of Nmbr on [Ca(2+)](i) involved several pathways that remain to be elucidated.

Role of Neurokinin B and Dynorphin A in pituitary gonadotroph and somatolactotroph cell lines.

The role of Neurokinin B (NKB) and Dynorphin A (Dyn) in the regulation of the hypothalamic pituitary axis is an important area of recent investigation. These peptides are critical for the rhythmic release of GnRH, which subsequently stimulates the secretion of the gonadotropins, luteinizing hormone (LH) and follicle-stimulating hormone (FSH). The present study utilized the gonadotroph cell line LßT2 and the somatolactotroph GH3 cell line to examine the possible role of these peptides in pituitary hormone secretion. The NKB receptor (NK3R) and the Dyn receptor (the κ-opiate receptor (KOR)) were both detected in LßT2 cells and GH3 cells. NKB, by itself, failed to increase gonadotropin LHß and FSHß promoter activities and did not modulate the effects of GnRH on gonadotropin promoter activity. In GH3 cells, NKB significantly increased TRH-induced PRL promoter activity although NKB alone did not have an effect on basal PRL promoter activity. Dyn had no effect on gonadotropin promoters alone or in combination with GnRH stimulation. PRL promoters stimulated by TRH were not significantly changed by Dyn. TRH-induced PRL promoter activity was further increased in the presence of higher concentrations of NKB, whereas Dyn did not have a significant effect on the PRL promoter even at a high concentration. In addition, TRH-induced ERK (Extracelluar signal-regulated kinase) activation was enhanced in the presence of NKB. Our current study demonstrated that NKB had a stimulatory effect on PRL expression in a PRL-producing cell, but had no effect on gonadotropin secretion from a gonadotroph cell line.

[Neurokinkin B and it's function on reproductive endocrine].

Neurokinkin B (NKB) is a member of tachykinin family and plays a role mainly through its receptor NK3R. NKB and NK3R are wide spread through the neural system. Studies revealed that NKB has kinds of biological functions such as constringing the smooth muscle of hollow viscus, relaxing blood vessels, reducing mean arterial pressure, slowing heart rate, exciting in vitro spinal cord neurons of rats and astringing sphincter pupillae. For the past few years, people pay more and more attentions to the regulating action of NKB on reproductive endocrine and a lot of research are made to discuss the function of NKB in HPGA. This article summarizes the distribution and physiological function of NKB and NK3R, discusses their functions in reproductive endocrine. Future studies will be needed to determine the precise mechanism of NKB.

Invited review: Translating kisspeptin and neurokinin B biology into new therapies for reproductive health.

The reproductive neuropeptide kisspeptin has emerged as the master regulator of mammalian reproduction due to its key roles in the initiation of puberty and the control of fertility. Alongside the tachykinin neurokinin B and the endogenous opioid dynorphin, these peptides are central to the hormonal control of reproduction. Building on the expanding body of experimental animal models, interest has flourished with human studies revealing that kisspeptin administration stimulates physiological reproductive hormone secretion in both healthy men and women, as well as patients with common reproductive disorders. In addition, emerging therapeutic roles based on neurokinin B for the management of menopausal flushing, endometriosis and uterine fibroids are increasingly recognised. In this review, we focus on kisspeptin and neurokinin B and their potential application as novel clinical strategies for the management of reproductive disorders.

The mechanism underlying the pubertal increase in pulsatile GnRH release in primates.

In primates, the gonatotropin-releasing hormone (GnRH) neurosecretory system, consisting of GnRH, kisspeptin, and neurokinin B neurons, is active during the neonatal/early infantile period. During the late infantile period, however, activity of the GnRH neurosecretory system becomes minimal as a result of gonadal steroid independent central inhibition, and this suppressed GnRH neurosecretory state continues throughout the prepubertal period. At the initiation of puberty, the GnRH neurosecretory system becomes active again because of the decrease in central inhibition. During the progress of puberty, kisspeptin and neurokinin B signaling to GnRH neurons further increases, resulting in the release of gonadotropins and subsequent gonadal maturation, and hence puberty. This review further discusses potential substrates of central inhibition and subsequent pubertal modification of the GnRH neurosecretory system by the pubertal increase in steroid hormones, which ensures the regulation of adult reproductive function.

An antiangiogenic neurokinin-B/thromboxane A2 regulatory axis.

Establishment of angiogenic circuits that orchestrate blood vessel development and remodeling requires an exquisite balance between the activities of pro- and antiangiogenic factors. However, the logic that permits complex signal integration by vascular endothelium is poorly understood. We demonstrate that a "neuropeptide," neurokinin-B (NK-B), reversibly inhibits endothelial cell vascular network assembly and opposes angiogenesis in the chicken chorioallantoic membrane. Disruption of endogenous NK-B signaling promoted angiogenesis. Mechanistic analyses defined a multicomponent pathway in which NK-B signaling converges upon cellular processes essential for angiogenesis. NK-B-mediated ablation of Ca2+ oscillations and elevation of 3'-5' [corrected] cyclic adenosine monophosphate (cAMP) reduced cellular proliferation, migration, and vascular endothelial growth factor receptor expression and induced the antiangiogenic protein calreticulin. Whereas NK-B initiated certain responses, other activities required additional stimuli that increase cAMP. Although NK-B is a neurotransmitter/ neuromodulator and NK-B overexpression characterizes the pregnancy-associated disorder preeclampsia, NK-B had not been linked to vascular remodeling. These results establish a conserved mechanism in which NK-B instigates multiple activities that collectively oppose vascular remodeling.

Evidence from the agonadal juvenile male rhesus monkey (Macaca mulatta) for the view that the action of neurokinin B to trigger gonadotropin-releasing hormone release is upstream from the kisspeptin receptor.

Human genetics have revealed that kisspeptin signaling and neurokinin B (NKB) signaling are both required for robust pulsatile gonadotropin-releasing hormone (GnRH) release, and therefore for puberty and maintenance of adult gonadal function. How these two peptides interact to affect GnRH pulse generation remains a mystery. To address the hierarchy of the NKB and kisspeptin signaling pathways that are essential for GnRH release, two experiments were conducted using agonadal, juvenile male monkeys. Pituitary responsiveness to GnRH was first heightened by a pulsatile GnRH infusion to use the in situ pituitary as a bioassay for GnRH release. In the first experiment (n = 3), the kisspeptin receptor (KISS1R) was desensitized by a continuous 99-hour i.v. infusion of kisspeptin-10 (100 µg/h). During the last 4 h of continuous kisspeptin-10 infusion, desensitization of KISS1R was confirmed by failure of an i.v. bolus of kisspeptin-10 to elicit GnRH release. Desensitization of KISS1R was associated with a markedly blunted GnRH response to senktide. The response to senktide was progressively restored during the 72 h following termination of continuous kisspeptin-10. An analogous design was employed in the second experiment (n = 2) to desensitize the NKB receptor (neurokinin 3 receptor, NK3R) by administration of a continuous 48-hour i.v. infusion of senktide (200 µg/h). While a bolus of senktide during the last 3 h of continuous senktide administration failed to elicit GnRH release, thus confirming desensitization of NK3R, the ability of kisspeptin to stimulate GnRH was unimpaired. The foregoing findings support the view that NKB stimulation of GnRH release is upstream from KISS1R.

Biochemical specificity of von Economo neurons in hominoids.

OBJECTIVES: Von Economo neurons (VENs) are defined by their thin, elongated cell body and long dendrites projecting from apical and basal ends. These distinctive neurons are mostly present in anterior cingulate (ACC) and fronto-insular (FI) cortex, with particularly high densities in cetaceans, elephants, and hominoid primates (i.e., humans and apes). This distribution suggests that VENs contribute to specializations of neural circuits in species that share both large brain size and complex social cognition, possibly representing an adaptation to rapidly relay socially-relevant information over long distances across the brain. Recent evidence indicates that unique patterns of protein expression may also characterize VENs, particularly involving molecules that are known to regulate gut and immune function. METHODS: In this study, we used quantitative stereologic methods to examine the expression of three such proteins that are localized in VENs-activating-transcription factor 3 (ATF3), interleukin 4 receptor (IL4Rα), and neuromedin B (NMB). We quantified immunoreactivity against these proteins in different morphological classes of ACC layer V neurons of hominoids. RESULTS: Among the different neuron types analyzed (pyramidal, VEN, fork, enveloping, and other multipolar), VENs showed the greatest percentage that displayed immunostaining. Additionally, a higher proportion of VENs in humans were immunoreactive to ATF3, IL4Rα, and NMB than in other apes. No other ACC layer V neuron type displayed a significant species difference in the percentage of immunoreactive neurons. CONCLUSIONS: These findings demonstrate that phylogenetic variation exists in the protein expression profile of VENs, suggesting that humans might have evolved biochemical specializations for enhanced interoceptive sensitivity.