Molecular Biology of Mini-Puberty, LH-RH and Cognition

Vincent Prévot

Univ. Lille, Inserm, CHU Lille, Laboratory of Development and Plasticity of the Neuroendorine Brain, UMR_S1172, Lille, France

Correspondence: Dr. Vincent Prévot, Ph.D. UMR_S1172, Lille, France

Table of contents

Abstract
Résumé
Paper
References
Author

Abstract

Mini-puberty—the brief, physiological re-activation of the hypothalamic–pituitary–gonadal (HPG) axis in early infancy—is a process critical for adult male and female reproduction. Work led by Prévot and colleagues defines mini-puberty as a neurodevelopmental program that determines both reproductive and cognitive functions. At its core is a molecular switch in infant GnRH (LH-RH) neurons in which microRNAs (notably the miR-200 family and miR-155) repress transcriptional repressors (e.g., ZEB1 and C/EBPβ), enabling the postnatal upregulation of GNRH1 transcription. Nitric-oxide (NO) signaling via NOS1 modulates this switch and therefore influences GnRH signaling. Perturbations—including DICER loss in GnRH neurons, trisomy-driven microRNA disequilibria in Down syndrome models, or NOS1 deficiency—distort pulsatility, a critical feature of the GnRH signal, with downstream reproductive and cognitive consequences. Strikingly, pulsatile (but not continuous) GnRH delivery improves cognition and strengthens basal network connectivity in adults with Down syndrome, extending GnRH’s role from a purely reproductive hormone to a systems-level neuromodulator of cortical networks. These mechanistic insights intersect directly with andrology: mini-puberty determines androgen/INSL3 function during normal testicular descent, while absent or distorted infantile HPG dynamics are linked to abnormal genital development (micropenis) and cryptorchidism in congenital GnRH deficiency. Here, I describe the development of GnRH neurons, molecular biological insights into the infantile GNRH1 transcriptional switch, evidence for extra-hypothalamic GnRH actions on cognition, and clinical implications for cryptorchidism and pediatric endocrinology.

Key words: Mini-puberty, GnRH neuron, Down syndrome, memory

Résumé

La mini-puberté—réactivation physiologique transitoire de l’axe hypothalamo–hypophyso–gonadique (HPG) en début de vie—est essentielle à la reproduction ultérieure chez l’homme et la femme. Les travaux de Prévot et collaborateurs en font un programme neurodéveloppemental déterminant les fonctions reproductives et cognitives. Au cœur de ce processus se trouve un commutateur moléculaire dans les neurones GnRH du nourrisson : des microARN (notamment la famille miR-200 et miR-155) répriment des répresseurs transcriptionnels (ZEB1, C/EBPβ), permettant l’activation postnatale de la transcription de GNRH1. La signalisation du monoxyde d’azote (NO), via NOS1, module ce commutateur et donc l’activité GnRH.

Toute perturbation—perte de DICER dans les neurones GnRH, déséquilibres microARN induits par la trisomie dans les modèles de syndrome de Down, ou déficit en NOS1—altère la pulsatilité du signal GnRH, caractéristique indispensable à ses effets reproductifs et cognitifs. De manière remarquable, une administration pulsatile, mais non continue, de GnRH améliore la cognition et la connectivité corticale de base chez l’adulte trisomique, étendant le rôle de GnRH d’une hormone strictement reproductive à celui de neuromodulateur des réseaux corticaux.

Ces avancées éclairent directement l’andrologie : la mini-puberté régule la fonction androgène/INSL3 dans la descente testiculaire, tandis que l’absence ou la distorsion de l’activation HPG infantile est liée au micropénis et à la cryptorchidie dans les déficits congénitaux en GnRH. Cette revue décrit le développement des neurones GnRH, les mécanismes moléculaires du commutateur transcriptionnel infantile de GNRH1, les actions extra-hypothalamiques de GnRH sur la cognition et leurs implications cliniques pour la cryptorchidie et l’endocrinologie pédiatrique.

Mots-clés: Mini-puberté, neurone GnRH, syndrome de Down, mémoire

Open slides

Developmental background

GnRH neuron differentiation. A few thousand GnRH (LH-RH) neurons originate in the olfactory placode, migrate into the forebrain, then project to the median eminence where pulsatile GnRH release drives pituitary LH/FSH secretion in a process conserved across mammals [1,2,3,4]. Beyond the canonical hypothalamic population, an extra-hypothalamic type of GNRH1-expressing neurons has been identified in adult human basal ganglia and the basal forebrain, many with a cholinergic phenotype, expanding plausible brain targets of GnRH signaling [4, 5]. The GnRH signal profile is comprised of fetal activation, mini-puberty (occurring several weeks after birth in humans), juvenile quiescence, pubertal re-activation, and senescent decline. Importantly, the biological effect depends on the frequency and amplitude of signal pulses to pituitary and brain targets rather than transmitter levels [6].    

Mini-puberty: timing, sex differences, and significance

In term human infants, LH/FSH rise in the first weeks, peak between 1–3 months, and decline from around six months onward in boys; FSH can remain comparatively elevated for longer periods of time in girls [2]. This period promotes Sertoli cell proliferation, Leydig cell steroidogenesis, ovarian signaling and determines penile growth and anogenital distance, thereby likely establishing adult reproductive capacity [2]. In rodents, these processes occur during the second–third postnatal weeks, scaling with lifespan.

Mini-puberty represents with the last developmental step where spontaneous testicular descent occurs; endocrinological data obtained during this period can inform prognosis in cryptorchid boys[3].

The infant GNRH1 transcriptional switch: microRNAs and NO

microRNA control of GNRH1 expression. In infant GnRH neurons, microRNAs contribute to the regulation of GNRH1 expression after birth. Genetic disruption of microRNA biogenesis (e.g., conditional DICER mutation in GnRH neurons) leads to progressive loss of GnRH peptide despite neuronal survival and culminates in infertility—evidence that postnatal gene-regulatory control is essential for maintaining the GnRH phenotype (summarized from the provided transcript and supported by microRNA-puberty reviews) [7].

NO/NOS1 as a permissive modulator. NO signaling contributes to this switch’s kinetics. Rare NOS1 variants in humans cause congenital hypogonadotropic hypogonadism (CHH) with sensory and cognitive features. In mice, loss of NOS1 exaggerates mini-puberty hormone profiles and impairs sensory–cognitive behaviors in adults, which can be rescued in mice by transient NO-pathway stimulation (inhaled NO or sildenafil) during the infantile period [8].  These data reveal NO as a modulator of infant GnRH activation.

Trisomy-21-dependent disequilibria (Down syndrome). In the Ts65Dn mouse model of Down syndrome, GnRH transcripts fall at the peak of rodent mini-puberty, with up-regulation of ZEB1 (consistent with reduced miR-200 levels); in adulthood, GnRH peptide diminishes and LH pulsatility shifts to higher baseline with blunted peaks without change in testosterone—an endocrine signature also observed in adult men with Down syndrome [1]. Together with human imaging and cognitive data (Section 5), these findings support a link between early molecular tuning of GnRH neurons during the infantile period and altered brain and endocrine network function in adulthood.

Pulsatility is the message— and it reaches the cortex

Anatomy to mechanism. Tissue-clearing and tract-tracing work (as presented in the transcript) and human histological mapping indicate GnRH-responsive elements outside the hypothalamus, including cortex, hippocampus, and basal ganglia [1,4,8]. This provides a substrate for GnRH as a neuromodulator of attention, memory, and network synchrony.

Continuous vs pulsatile delivery. In adult wild-type mice, continuous GnRH delivery suppresses the HPG axis by desensitizing the GnRH receptor (GnRH-R) on pituitary gonadotrophs, but also impairs cognition by producing the same receptor desensitization in GnRH-R-expressing neocortical neurons in the brain [1].  However, pulsatile GnRH delivery restores olfaction and cognition in trisomic mice [1]. Clinically, neurocognitive complaints during long-term GnRH-agonist therapy for sex-steroid-dependent conditions are consistent with the hazards of desensitizing, non-physiologic stimulation. However, this remains hypothesis-generating rather than proof of causality and would require further clinical studies in humans to be confirmed. Conversely, pulsatile GnRH has decades of safety/efficacy in CHH/functional hypothalamic amenorrhea and now shows cognitive benefits in Down syndrome (next section).

Human translation: pulsatile GnRH enhances cognition in Down syndrome

In a pilot open-label study, seven adults with Down syndrome received pulsatile GnRH (1 pulse/2 h) for six months via a portable pump. All improved on composite cognitive measures (~20% mean), and resting-state functional magnetic resonance imaging (fMRI) showed stronger default-mode network connectivity—an objective network shift in a system typically hypoactive in Down syndrome [1].  Commentaries highlight the novelty and call for controlled trials [9,10]. While preliminary, these results suggest GnRH to be not only critical for reproduction but also systems-level neuromodulation with therapeutic implications.

Cryptorchidism and the critical role of mini-puberty

Two-phase model and molecular drivers. The transabdominal phase of descent is driven largely by INSL3 acting via RXFP2, whereas the inguinoscrotal phase requires androgens (testosterone/DHT) and neural inputs [11-13]. Human genetics work identified biallelic loss-of-function variants in INSL3 or RXFP2 that cause bilateral cryptorchidism and infertility, with heterozygous carriers often unaffected—underscoring the pathway’s central role in the process [11].

Essential functions of mini-puberty. Mini-puberty supplies the androgen/INSL3 environment in the first six months to enable spontaneous descent. Prospective observations suggest some undescended testes descend during this period; persistence beyond approximately six months indicates the need for surgery [3]. Hormone ratios (e.g., LH/testosterone or LH/INSL3) during mini-puberty may be more informative for Leydig cell efficiency than absolute values and the prognosis of ultimate testicular descent [3,1,13].

CHH and absent mini-puberty. In congenital GnRH deficiency, the infant LH/FSH surge is attenuated or absent, predisposing patients to micropenis, cryptorchidism, and impaired testicular maturation—mirrored by mouse models where selective impairment of GnRH release (with preserved migration) yields cryptorchidism, micropenis, reduced anogenital distance, and absent LH pulsatility (from the transcript; clinical analogs summarized in [2,3].

Prematurity, exaggerated mini-puberty, and NO-pathway therapeutics

Preterm infants often display abnormally high gonadotropin profiles in mini-puberty, and they carry higher risks for later neurocognitive and metabolic issues. Experimental NOS1 loss exaggerates mini-puberty in mice and impairs cognition, but short-term inhaled NO or sildenafil treatment of infantile mice normalizes endocrine signatures and rescues adult behaviors [8]. Since these agents are already used in neonatal pulmonary care and show no adverse effects on later cognitive outcomes [14].  pursuing a translational program with time-specific NO supplementation is a plausible path (with careful ethics and endpoints).

Therapeutic implications

Respect pulsatility. Where GnRH therapy is indicated, pulsatile delivery preserves physiological signaling. In CHH/functional hypothalamic amenorrhea, pulsatile GnRH remains a gold-standard option; in Down syndrome and possibly other neurodevelopmental contexts, pulsatile GnRH emerges as a candidate neurotherapeutic under clinical trials [1,2].

Mini-puberty replacement in CHH infants. Early gonadotropin therapy to mimic mini-puberty (rhLH/FSH via pump or injections) promotes penile growth, Sertoli cell proliferation, and testicular descent in CHH boys, strengthening the case for time-sensitive endocrine replacement alongside surgical intervention [2,15-17].

Pathway-specific adjuncts. In the case of cryptorchidism caused by INSL3/RXFP2 defects, endocrine therapies will not restore a dysfunctional receptor–ligand axis, underscoring the priority of timely orchiopexy; however, understanding whether an individual’s clinical state is androgenic vs INSL3-centric may influence prognosis of fertility and follow-up care [11,13]. In prematurity-associated dysregulation, NO-pathway modulation in infants is an attractive research avenue [8].

Practical checklist for clinicians (0–6 months)

  1. Profile dynamics, not just levels. Consider LH, testosterone, INSL3, and ratios (LH/testosterone, LH/INSL3) when evaluating cryptorchid infants; integrate with gestational age and clinical exam [3,12,13].
  2. Consider CHH when mini-puberty is absent. Micropenis ± cryptorchidism with low/flat LH/FSH/testosterone suggests CHH and justifies early endocrine and surgical coordination [2,3].
  3. Use pulsatile patterns when treating with GnRH. Avoid flattening the axis unless clinically necessary; anticipate potential neurocognitive consequences of long-term continuous GnRH-agonist therapy (hypothesis based on animal and clinical observation) [1,6].
  4. Discuss trials. For selected contexts (e.g., Down syndrome cognition, prematurity-related dysregulation), consider referral to research studies exploring pulsatile GnRH or NO-pathway interventions [1,8].

Conclusions

Mini-puberty is a developmental process that affects both reproductive and cognitive systems. A microRNA–transcription factor program, responding to NO signaling, operates a transcriptional switch in GNRH1 expression in infants and sets pulsatile dynamics of GnRH signaling. Disruptions (microRNA imbalance, NOS1 variants, trisomy-driven disequilibria, or non-physiologic therapies) can simultaneously skew reproductive outcomes (micropenis, cryptorchidism, later infertility risks) and degrade cognition. The demonstration that pulsatile GnRH improves cognition and network connectivity in adults with Down syndrome reveals GnRH as a brain-wide neuromodulator and opens a translational path for developmental stage-specific interventions. Combining endocrinological exams and timely surgery during mini-puberty is a promising approach to treating cryptorchidism and adult infertility it entails.

Declaration Section

a) Ethics Approval and Consent to Participate Investigations were carried out in accordance 326 with the Declaration of Helsinki of 1975, revised in 2008.

b) Consent for publication Not applicable

c) Availability of data and supporting material Not applicable

d) Competing interests Author/s declare that they have no competing interests

e) Funding: Gratitude to funding bodies: European Union ERC-2023-PoC UPGRADE (No 101123221) and H2020 miniNO (No 847941), and AXA mécènat France No 2024SANTE0152.

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Vincent Prévot

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