vasoactive-intestinal-peptide and Retinal-Degeneration

Vasoactive intestinal peptide (VIP) and pituitary adenylate cyclase activating polypeptide (PACAP) belong to the same peptide family and exert a variety of biological functions. Both PACAP and VIP have protective effects in several tissues. While PACAP is known to be a stronger retinoprotective peptide, VIP has very potent anti-inflammatory effects. The need for a non-invasive therapeutic approach has emerged and PACAP has been shown to be retinoprotective when administered in the form of eye drops as well. The cell penetrating peptide TAT is composed of 11 amino acids and tagging of TAT at the C-terminus of neuropeptides PACAP/VIP can enhance the traversing ability of the peptides through the biological barriers. We hypothesized that TAT-bound PACAP and VIP could be more effective in exerting retinoprotective effects when given in eye drops, by increasing the traversing efficacy and enhancing the activation of the PAC1 receptor. Rats were subjected to bilateral carotid artery occlusion (BCCAO), and retinas were processed for histological analysis 14 days later. The efficiency of the TAT-bound peptides to reach the retina was assessed as well as their cAMP increasing ability. Our present study provides evidence, for the first time, that topically administered PACAP and VIP derivatives (PACAP-TAT and VIP-TAT) attenuate ischemic retinal degeneration via the PAC1 receptor presumably due to a multifactorial protective mechanism.

Topics: Animals; Anti-Inflammatory Agents; CHO Cells; Cricetinae; Cricetulus; Male; Neuroprotective Agents; Ophthalmic Solutions; Pituitary Adenylate Cyclase-Activating Polypeptide; Rats; Recombinant Proteins; Retina; Retinal Degeneration; tat Gene Products, Human Immunodeficiency Virus; Vasoactive Intestinal Peptide

Vasoactive intestinal peptide (VIP) is a pleiotropic neuropeptide, acting as a neuromodulator and neuroprotective peptide in the CNS after injuries. We have previously described that pituitary adenylate cyclase-activating polypeptide (PACAP), another member of the same peptide family, is retinoprotective in ischemic lesions. The aim of this study was to investigate the protective potential of VIP in bilateral common carotid artery occlusion (BCCAO)-induced ischemic retinal lesion. Two-month-old rats were subjected to BCCAO and treated with intravitreal VIP injection. Their retinas were processed for histology after 2 weeks of survival. We measured the number of the cells/100 μm of the ganglion cell layer and the thickness of each layer such as the outer nuclear, outer plexiform, inner nuclear, and inner plexiform layers as well as that of the whole retina. We found that treatment with 1,000 pmol VIP, but not 100 pmol VIP, had significant protective effects in BCCAO-injured retina, as shown by the morphometric analysis. Comparing the neuroprotective effects of VIP and PACAP in BCCAO-operated retinas, PACAP was more effective, already protective at 100-pmol doses. Similar to other studies, we found that VIP must be given at least in 10 times more concentration than PACAP to achieve a similar degree of neuroprotection in the retina.

Topics: Animals; Apoptosis; Carotid Artery, Common; Carotid Stenosis; Dose-Response Relationship, Drug; Drug Evaluation, Preclinical; Intravitreal Injections; Ischemia; Male; Models, Neurological; Neuroprotective Agents; Pituitary Adenylate Cyclase-Activating Polypeptide; Rats; Rats, Wistar; Retinal Degeneration; Retinal Neurons; Retinal Vessels; Retinitis; Time Factors; Vasoactive Intestinal Peptide

In mammals, the brain clock responsible for generating circadian rhythms is located in the suprachiasmatic nucleus (SCN) of the hypothalamus. Light entrainment of the clock occurs through intrinsically photosensitive retinal ganglion cells (ipRGCs) whose axons project to the SCN via the retinohypothalamic tract. Although ipRGCs are sufficient for photoentrainment, rod and cone photoreceptors also contribute. Adult CBA/J mice, which exhibit loss of rod and cone photoreceptors during early postnatal development, have greater numbers of ipRGCs compared to CBA/N control mice. A greater number of photosensitive cells might argue for enhanced light responses, however, these mice exhibit attenuated phase shifting behaviors. To reconcile these findings, we looked for potential differences in SCN neurons of CBA/J mice that might underly the altered circadian behaviors. We hypothesized that CBA/J mice have differences in the expression of neuropeptides in the SCN, where ipRGCs synapse. The neuropeptides vasoactive intestinal peptide (VIP) and vasopressin (VP) are expressed by many SCN neurons and play an important role in the generation of circadian rhythms and photic entrainment.. Using immunohistochemistry, we looked for differences in the expression of VIP and VP in the SCN of CBA/J mice, and using a light-induced FOS assay, we also examined the degree of retinal innervation of the SCN by ipRGCs.. Our data demonstrate greater numbers of VIP-and VP-positive cells in the SCN of CBA/J mice and a greater degree of light-induced FOS expression.. These results implicate changes in neuropeptide expression in the SCN which may underlie the altered circadian responses to light in these animals.

Topics: Age Factors; Animals; Cell Count; Cyclic Nucleotide Phosphodiesterases, Type 6; Immunohistochemistry; Male; Mice; Mice, Inbred CBA; Mice, Mutant Strains; Photic Stimulation; Proto-Oncogene Proteins c-fos; Retina; Retinal Degeneration; Retinal Ganglion Cells; Suprachiasmatic Nucleus; Vasoactive Intestinal Peptide; Vasopressins; Visual Pathways

The impact of photoreceptor loss on the circadian system was examined by utilizing a transgenic mouse model (rdta) in which rod photoreceptors were specifically ablated. These mice were able to phase-shift their circadian locomotor behaviour in response to light, but features of this circadian behaviour were markedly altered. The amplitude of circadian responses to light were approximately 2.5 greater, the circadian period (tau) was reduced (c. 20 min) and the total duration of activity (alpha) was increased (c. 50 min) when compared to wild type (+/+) and rd/rd mice (retinal degeneration, mice which also lack rod photoreceptors) of the same genetic background. The pattern of Fos expression in the suprachiasmatic nuclei (the site of the primary circadian clock in mammals) was indistinguishable between +/+ and rdta mice. However, Fos expression in the retina suggested that rod loss in rdta mice resulted in a functional reorganization of the retina and the constitutive activation of a population of retinal ganglion cells. Although it has been known for several years that the entraining photoreceptors of mammals are ocular, and that rod photoreceptors are not required for light regulation of the clock, these are the first data to show that features of the circadian phenotype (amplitude of the phase response curve, alpha, tau) can be influenced by photoreceptor ablation. These data support the hypothesis that the circadian phenotype of mammals is the product of an interaction between the suprachiasmatic nuclei and the retina. Thus, mammals which show an altered circadian behaviour can no longer be assumed to have defects associated only with specific clock genes; genes that affect photoreceptor survival may also modify circadian behaviour.

Topics: Animals; Circadian Rhythm; Geniculate Bodies; Immunohistochemistry; Light; Mice; Mice, Inbred C57BL; Mice, Transgenic; Motor Activity; Phenotype; Proto-Oncogene Proteins c-fos; Reference Values; Retinal Degeneration; Retinal Ganglion Cells; Retinal Rod Photoreceptor Cells; Suprachiasmatic Nucleus; Vasoactive Intestinal Peptide

In the Royal College of Surgeons (RCS) rat, characterized by inherited retinal dystrophy, retinal projections to the brain were studied using anterograde neuronal transport of cholera toxin B subunit upon injection into one eye. The respective immunoreactivity was found predominantly contralateral to the injection site in the lateral geniculate nucleus, superior colliculus, nucleus of the optic tract, medial terminal nucleus of the accessory optic tract, and bilateral hypothalamic suprachiasmatic nuclei. Although terminal density was somewhat reduced in dystrophic rats, the projection patterns in these animals appeared similar to those seen in their congenic controls and were comparable to the visual pathways described for the rat previously. In dystrophic rats, the number of cell bodies exhibiting immunoreactivity to vasoactive intestinal polypeptide, viz. a population of suprachiasmatic neurons receiving major retinohypothalamic input, was reduced by one-third, and some differences were observed in the termination pattern of the geniculohypothalamic tract, as revealed by immunoreactivity to neuropeptide Y in the suprachiasmatic nucleus.

Topics: Afferent Pathways; Animals; Cholera Toxin; Female; Geniculate Bodies; Hypothalamus; Male; Neuropeptide Y; Rats; Rats, Inbred Strains; Retina; Retinal Degeneration; Suprachiasmatic Nucleus; Vasoactive Intestinal Peptide

As photoreceptor degeneration progresses in Royal College of Surgeons (RCS) rats, a variety of morphological and physiological alterations occur in the outer retina. Since the choriocapillaris responds to changes in the outer retina in other retinopathies, we examined the possibility that changes in the choroidal vasculature also occur in RCS rats. The choroidal and choriocapillary vessels in RCS and control (RCS-rdy+) rats were examined during the period after which photoreceptor loss and retinal vascular changes had occurred (7-mos to 28-mos). Light microscopic (LM) morphometry and electron microscopic (EM) examination showed no significant differences between these groups in the number, size or morphology of these vessels. However, EM image analysis revealed that nerve fibers and bundles were twice as abundant in the RCS choroid than in the control. Using immunohistochemical techniques at the LM level combined with image analysis we found that vasoactive intestinal polypeptide positive (VIP+) fibers were significantly increased in the RCS choroid compared with control choroid. In contrast, the abundance of immunoreactive fibers labelled for substance P and dopamine beta hydroxylase appeared similar in both the control and RCS choroid. Since VIP is a potent vasodilator, the increased abundance of nerve fibers in the RCS choroid in conjunction with the unaltered number and size of these vessels suggests that choroidal blood flow may be increased. It is uncertain whether this increase is a response to the outer retinal pathology or contributes to it.

Topics: Animals; Choroid; Dopamine beta-Hydroxylase; Fluorescent Antibody Technique; Image Processing, Computer-Assisted; Nerve Fibers; Rats; Rats, Mutant Strains; Retinal Degeneration; Retinal Vessels; Substance P; Vasoactive Intestinal Peptide