Overexpression of PACAP in the pancreas failed to rescue early postnatal mortality in PACAP-null mice

Pituitary Adenylate Cyclase-Activating Polypeptide (PACAP) and Sudden Infant Death Syndrome: A Potential Model for Investigation

Sudden infant death syndrome (SIDS) represents a significant cause of post-neonatal mortality, yet its underlying mechanisms remain unclear. The triple-risk model of SIDS proposes that intrinsic vulnerability, exogenous triggers, and a critical developmental period are required for SIDS to occur. Although case-control studies have identified potential risk factors, no in vivo model fully reflects the complexities observed in human studies. Pituitary adenylate cyclase-activating polypeptide (PACAP), a highly conserved neuropeptide with diverse physiological functions, including metabolic and thermal regulation, cardiovascular adaptation, breathing control, stress responses, sleep-wake regulation and immunohomeostasis, has been subject to early animal studies, which revealed that the absence of PACAP or its specific receptor (PAC1 receptor: PAC1R) correlates with increased neonatal mortality similar to the susceptible period for SIDS in humans. Recent human investigations have further implicated PACAP and PAC1R genes as plausible contributors to the pathomechanism of SIDS. This mini-review comprehensively synthesizes all PACAP-related research from the perspective of SIDS and proposes that PACAP deficiency might offer a promising avenue for studying SIDS.

Pituitary adenylate cyclase-activating polypeptide drives cardiorespiratory responses to heat stress in neonatal mice

The neuropeptide pituitary adenylate cyclase-activating polypeptide (PACAP) has emerged as a principal and rate-limiting regulator of physiological stress responses in adult rodents and has been implicated in sudden infant death syndrome (SIDS). Recent studies show that PACAP plays a role in neonatal cardiorespiratory responses to hypoxia, hypercapnia, and hypothermia, but not hyperthermia, which is often associated with SIDS. Here we tested the hypothesis that, consistent with a role in SIDS, PACAP is involved in regulating the neonatal cardiorespiratory responses to severe heat. To address this, we used head-out plethysmography and surface ECG electrodes to study the cardiorespiratory physiology of conscious neonatal PACAP-null and wild-type mice at ambient temperatures of 32°C (baseline) and 40°C (heat stress). We also assessed body surface temperature as an indicator of cutaneous heat loss. Our results show that wild-type neonatal mice respond to heat stress by increasing ventilation ( P = 0.007) and associated expired CO2 ( P = 0.041), heart rate ( P < 0.001), and cutaneous heat loss ( P < 0.001). In PACAP-null neonates, this heat response is impaired, as indicated by a decrease in ventilation ( P = 0.04) and associated expired CO2 ( P = 0.006) and a blunted increase in heart rate ( P = 0.001) and cutaneous heat loss ( P = 0.0002). In addition, heart rate variability at baseline was lower in PACAP-null neonates than wild-type controls ( P < 0.01). These results suggest that, during heat stress, PACAP is important for neonatal cardiorespiratory responses that help regulate body temperature. Abnormal PACAP regulation could, therefore, contribute to neonatal disorders in which the autonomic response to stress is impaired, such as SIDS.

Developmental changes in pituitary adenylate cyclase activating polypeptide expression during the perinatal period: possible role in fetal gonadotroph regulation

Normal reproductive functioning may require secretion of LH independently of FSH. Variation in GnRH pulse frequency and inhibin negative feedback are mechanisms for differential gonadotropin regulation; however, the first instance of differential regulation in rats is during fetal development, prior to the establishment of GnRH connections, when LH accumulates appreciably 2-4 d prior to FSH. Pituitary adenylate cyclase activating polypeptide (PACAP) can differentially regulate the gonadotropins in vitro by stimulating alpha-subunit transcription, lengthening LHbeta transcripts and decreasing FSHbeta mRNA levels, probably through stimulation of follistatin transcription. These experiments are the first to examine whether PACAP influences gonadotroph function in perinatal pituitaries. In vivo, pituitary PACAP mRNA and peptide levels were high at embryonic d 19 and declined by 94 and 85%, respectively, after parturition. This was accompanied by a decrease of 65 and 96% in total follistatin and follistatin-288 mRNAs. These changes were temporally associated with a 20- and 6.5-fold rise in FSHbeta and GnRH receptor mRNAs, respectively, with no significant increase in LHbeta mRNA. In pituitary cell cultures from fetal and postnatal male rats, PACAP mRNA levels were likewise highest in fetal cultures in which the PACAP 6-38 antagonist decreased alpha-subunit and increased FSHbeta mRNA. PACAP 6-38 also reduced basal and GnRH-stimulated LH secretion with little effect on FSH. These data support the hypothesis that PACAP expressed at high levels in the fetal pituitary stimulates alpha-subunit expression and LH secretion and restrains FSH synthesis relative to LH and that a decline in PACAP allows for the neonatal rise in FSH and GnRH receptor because follistatin is decreased.