Dora Reglodi

Pituitary adenylate cyclase activating polypeptide: A potential neuroprotective peptide

Pituitary adenylate cyclase activating polypeptide (PACAP) was first isolated from hypothalamic extracts on the basis of its ability to stimulate cAMP formation in pituitary cells. PACAP is widely distributed in the central and peripheral nervous systems and exerts numerous effects. Currently available data indicate that PACAP is a promising neuroprotective peptide. PACAP plays an important role during the development of the nervous system and in regeneration following nervous injuries. It has strong anti-apoptotic effects in several neuronal cultures and in vivo. PACAP protects neurons against various toxic insults in vitro, has anti-inflammatory actions and stimulates the release of neuroprotective substances from astrocytes. In vivo, the protective effects of PACAP have been shown in various models of brain injuries, including cerebral ischemia, Parkinsons disease, trauma and nerve transections. The upregulation of PACAP following several types of nerve injuries indicates that endogenous PACAP plays a role in the post-traumatic recovery of the nervous system. The present report reviews the current knowledge on the neurotrophic and neuroprotective effects of PACAP.

Neurological reflexes and early motor behavior in rats subjected to neonatal hypoxic-ischemic injury.

Severe perinatal hypoxia-ischemia is an important cause of brain injury in both full-term and premature newborns, with a high risk of future behavioral and neurological deficits. The most commonly used animal model of neonatal hypoxia-ischemia is the unilateral ligation of the common carotid artery followed by exposure to hypoxia in 7-day-old rats. In spite of the wide use of this model, lot of contradictions and discrepancies exist between the results obtained by different laboratories regarding behavioral deficits and there are no data regarding the possible delay of the appearance of neurological reflexes and the time-course of reflex performances following neonatal hypoxic-ischemic injury in rats. In the present study we showed that neonatal hypoxia-ischemia retarded the development of somatic growth and several neurological reflexes (ear twitch, grasping, gait and negative geotaxis). Hypoxic animals also displayed retarded performance in righting, geotaxis and gait reflexes. Although hypoxic pups performed worse in most tests for motor coordination, they reached normal levels by 5 weeks of age except in the footfault test. In the open-field, hypoxic animals were generally more active, except at 3 weeks, when activity of normal pups increased enormously as well. Brain areas were significantly reduced in hypoxic animals, but no close correlation was found with behavioral deficits.

Review on the protective effects of PACAP in models of neurodegenerative diseases in vitro and in vivo.

Pituitary adenylate cyclase activating polypeptide (PACAP) is a pleiotropic and multifunctional peptide exerting its effects via 3 main receptors (PAC1, VPAC1 and VPAC2). PACAP is now considered to be a potent neurotrophic and neuroprotective peptide. It plays an important role during the embryonic development of the nervous system. PACAP also protects neurons against various toxic insults in neuronal cultures of diverse origins. In vivo, PACAP shows neuroprotection in models of ischemic and traumatic brain injuries, and those of neurodegenerative diseases. The present review summarizes the findings on the neuroprotective potential of PACAP in models of neurodegenerative diseases, with special focus on in vitro and in vivo models of Parkinson`s disease, Huntington chorea and Alzheimer`s disease. Based on these observations, both endogenous and exogenously administered PACAP or its novel analogs, fragments offer a novel therapeutic approach in treatment of neurodegenerative diseases.

Examination of sensorimotor performance following middle cerebral artery occlusion in rats

Middle cerebral artery occlusion (MCAO) in rats is the most commonly used stroke model. Besides the infarct size, assessment of sensorimotor performance has become increasingly important in neuroprotective drug research. However, contradictions exist about procedures for testing functional outcome following MCAO. The aim of the present study was to evaluate a relatively simple set of neurological tests based on the most commonly used scoring systems, and to describe the functional recovery and correlation with the infarct size in rats sacrificed 2 or 14 days after permanent or transient MCAO. The smaller infarct size of rats with transient occlusion was reflected in the neurological scores only during the first 6h. By day 14, no recovery occurred in postural signs, lateral resistance and spontaneous activity, other signs showed different degrees of recovery. Correlation with the infarct size was found only on certain days in gait disturbance, placing reactions, daily body weight and spontaneous activity. According to our observations, the most commonly used sensorimotor tests provide a useful initial screening of functional deficits, but these tests most probably measure deficits caused by infarction of the core area. It is suggested that these tests should be completed by more refined tests when testing a neuroprotective drug which reduces the infarct size in penumbral areas.

PACAP is an endogenous protective factor-insights from PACAP-deficient mice.

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a widespread neuropeptide with a diverse array of biological functions. Not surprisingly, the lack of endogenous PACAP therefore results in a variety of abnormalities. One of the important effects of PACAP is its neuroprotective and general cytoprotective role. PACAP protects neurons and other tissues against ischemic, toxic, and traumatic lesions. Data obtained from PACAP-deficient mice provide evidence that endogenous PACAP also has protective functions. Mice lacking PACAP are more vulnerable to different in vitro and in vivo insults. The present review summarizes data on the increased sensitivity of PACAP-deficient mice against harmful stimuli. Mice lacking PACAP respond with a higher degree of injury in cerebral ischemia, autoimmune encephalomyelitis, and axonal lesion. Retinal ischemic and excitotoxic injuries also produce increased cell loss in PACAP-deficient mice. In peripheral organs, kidney cell cultures from PACAP-deficient mice are more sensitive to oxidative stress and in vitro hypoxia. In vivo, PACAP-deficient mice have a negative histological outcome and altered cytokine response in kidney and small intestine ischemia/reperfusion injury. Large intestinal inflammation, toxic lesion of the pancreas, and doxorubicin-induced cardiomyopathy are also more severe with a lack of endogenous PACAP. Finally, an increased inflammatory response has been described in subacute endotoxin-induced airway inflammation and in an oxazolone-induced allergic contact dermatitis model. In summary, lack of endogenous PACAP leads to higher vulnerability in a number of injuries in the nervous system and peripheral organs, supporting the hypothesis that PACAP is part of the endogenous cytoprotective machinery.

Pituitary adenylate cyclase-activating polypeptide plays a key role in nitroglycerol-induced trigeminovascular activation in mice

Pituitary adenylate cyclase-activating polypeptide (PACAP) and its receptors (PAC1, VPAC) are present in sensory neurons and vascular smooth muscle. PACAP infusion was found to trigger migraine-like headache in humans and we showed its central pro-nociceptive function in several mouse pain models. Nitroglycerol (NTG)-induced pathophysiological changes were investigated in this study in PACAP gene-deleted (PACAP(-/-)) and wildtype (PACAP(+/+)) mice. Chemical activation of the trigeminovascular system was induced by 10 mg/kg i.p. NTG. Light-aversive behavior was determined in a light-dark box, meningeal microcirculation by laser Doppler blood perfusion scanning and the early neuronal activation marker c-Fos with immunohistochemistry. NTG-induced photophobia both in the early (0-30 min) and late phases (90-120 min) due to direct vasodilation and trigeminal sensitization, respectively, was significantly reduced in PACAP(-/-) mice. Meningeal blood flow increased by 30-35% during 4 h in PACAP(+/+) mice, but only a 5-10% elevation occurred from the second hour in PACAP(-/-) ones. The number of c-Fos expressing cells referring to neuronal activation in the trigeminal ganglia and nucleus caudalis significantly increased 4h after NTG in PACAP(+/+), but not in PACAP(-/-) animals. Similar PAC1 receptor immunostaining was detected in both groups, which did not change 4 h after NTG treatment. PACAP-38 (300 μg/kg, i.p.) produced photophobia similarly to NTG and 30% meningeal vasodilatation for 30 min in PACAP(+/+), but not in PACAP(-/-) mice. It significantly increased neural activation 4h later in the trigeminal ganglia of both groups, but in the nucleus caudalis of only the PACAP(+/+) mice. We provide the first experimental results that PACAP is a pivotal mediator of trigeminovascular activation/sensitization and meningeal vasodilation related to migraine.

Pituitary adenylate cyclase activating polypeptide protects dopaminergic neurons and improves behavioral deficits in a rat model of Parkinson's disease.

Pituitary adenylate cyclase activating polypeptide (PACAP) is a pleiotropic neuropeptide, exerting different actions in the central and peripheral nervous systems. Among others, it has neurotrophic and neuroprotective effects. In the present study, we investigated the effects of PACAP in a rat model of Parkinsons disease. Rats were given unilateral injections of 6-hydroxydopamine (6-OHDA) into the substantia nigra. PACAP-treated animals received 0.1 microg PACAP as a pretreatment. Control animals without PACAP treatment displayed severe hypokinesia at 1 and 10 days postlesion when compared to animals receiving saline only. In only 1 day postlesion, by contrast, PACAP-treated rats showed no hypokinesia. Asymmetrical signs, such as turning, rearing and biased thigmotaxic scanning were observed in all lesioned animals 1 day postlesion. PACAP-treated animals, however, showed better recovery as they ceased to display asymmetrical signs 10 days later and showed markedly less apomorphine-induced rotations. Tyrosine-hydroxylase immunohistochemistry revealed that control animals had more than 95% loss of the dopaminergic cells in the ipsilateral substantia nigra, while PACAP-treated animals had only approximately 50% loss of dopaminergic cells. In summary, the present results show the neuroprotective effect of PACAP in 6-OHDA-induced lesion of substantia nigra, with less severe acute neurological symptoms and a more rapid amelioration of behavioral deficits.

Pituitary adenylate cyclase activating polypeptide protects cardiomyocytes against oxidative stress-induced apoptosis

Pituitary adenylate cyclase activating polypeptide (PACAP) has well-known neuroprotective effects, and one of the main factors leading to neuroprotection seems to be its anti-apoptotic effects. The peptide and its receptors are present also in the heart, but whether PACAP can be protective in cardiomyocytes, is not known. Therefore, the aim of the present study was to investigate the effects of PACAP on oxidative stress-induced apoptosis in cardiomyocytes. Our results show that PACAP increased cell viability by attenuating H2O2-induced apoptosis in a cardiac myocyte culture. PACAP also decreased caspase-3 activity and increased the expression of the anti-apoptotic markers Bcl-2 and phospho-Bad. These effects of PACAP were counteracted by the PACAP antagonist PACAP6-38. In summary, our results show that PACAP is able to attenuate oxidative stress-induced cardiomyocyte apoptosis.

The neuroprotective effects of PACAP in monosodium glutamate-induced retinal lesion involve inhibition of proapoptotic signaling pathways

Pituitary adenylate cyclase activating polypeptide (PACAP) and its receptors are present in the retina and exert several distinct functions. PACAP has well-known neuroprotective effects in neuronal cultures in vitro and against different insults in vivo. Recently we have shown that PACAP is neuroprotective against monosodium glutamate (MSG)-induced retinal degeneration. In the present study we investigated the possible signal transduction pathways involved in the protective effect of intravitreal PACAP administration against apoptotic retinal degeneration induced by neonatal MSG treatment. MSG induced activation of proapoptotic signaling proteins and reduced the levels of antiapoptotic molecules in neonatal retinas. Co-treatment with PACAP attenuated the MSG-induced activation of caspase-3 and JNK, inhibited the MSG-induced cytosolic translocation of apoptosis inducing factor (AIF) and cytochrome c, and increased the level of phospho-Bad. Furthermore, PACAP treatment alone decreased cytosolic AIF and cytochrome c levels, while PACAP6-38 increased cytochrome c release, caspase-3 and JNK activity and decreased phospho-Bad activity. In summary, our results show that PACAP treatment attenuated the MSG-induced changes in apoptotic signaling molecules in vivo and suggest that also endogenously present PACAP has neuroprotective effects. These results may have further clinical implications in reducing glutamate-induced excitotoxicity in several ophthalmic diseases.

Pituitary adenylate cyclase activating polypeptide in the retina: focus on the retinoprotective effects.

Pituitary adenylate cyclase activating polypeptide (PACAP) is a neurotrophic and neuroprotective peptide that has been shown to exert protective effects against different neuronal injuries, such as traumatic brain and spinal cord injury, models of neurodegenerative diseases, and cerebral ischemia. PACAP and its receptors are present in the retina. In this study, we summarize the current knowledge on retinal PACAP with focus on the retinoprotective effects. Results of histological, immunohistochemical, and molecular biological analysis are reviewed. In vitro, PACAP shows protection against glutamate, thapsigargin, anisomycin, and anoxia. In vivo, the protective effects of intravitreal PACAP treatment have been shown in the following models of retinal degeneration in rats: excitotoxic injury induced by glutamate and kainate, ischemic injury, degeneration caused by UV‐A light, optic nerve transection, and streptozotocin‐induced diabetic retinopathy. Studying the molecular mechanism has revealed that PACAP acts by activating antiapoptotic and inhibiting proapoptotic signaling pathways in the retina in vivo. These studies strongly suggest that PACAP is an excellent candidate retinoprotective agent that could be a potential therapeutic substance in various retinal diseases.