PACAP-containing intrapineal nerve fibers originate predominantly in the trigeminal ganglion: a combined retrograde tracing- and immunohistochemical study of the rat

Vasopressin and oxytocin beyond the pituitary in the human brain

Vasopressin and oxytocin are primarily synthesized in the magnocellular supraoptic and paraventricular nuclei of the hypothalamus and transported to the posterior pituitary. In the human, an extensive accessory magnocellular neuroendocrine system is present with contact to the posterior pituitary and blood vessels in the hypothalamus itself. Vasopressin and oxytocin are involved in social and behavioral functions. However, only few neocortical areas are targeted by vasopressinergic and oxytocinergic nerve fibers, which mostly project to limbic areas in the forebrain, where also their receptors are located. Vasopressinergic/oxytocinergic perikarya in the forebrain project to the brain stem and spinal cord targeting nuclei and areas involved in autonomic functions. Parvocellular neurons containing vasopressin are located in the suprachiasmatic nucleus and synchronize the activity of the pacemaker in this nucleus. From the suprachiasmatic nucleus fibers project to the parvocellular part of the paraventricular nucleus, where preautonomic neurons project to the intermediolateral nucleus in the thoracic spinal cord, from where the superior cervical ganglion is reached whose noradrenergic fibers terminate in the pineal gland to stimulate melatonin secretion at night. The pineal gland is also innervated by vasopressin- and oxytocin-containing fibers reaching the gland via the "central innervation" in the pineal stalk, which might be involve in an annual regulation of melatonin secretion.

PACAP-38 but not VIP induces release of CGRP from trigeminal nucleus caudalis via a receptor distinct from the PAC1 receptor

OBJECTIVE

To investigate if PACAP and VIP have an effect on CGRP release or NOS activity in the trigeminal ganglion and trigeminal nucleus caudalis and if there can be a difference in effect between PACAP and VIP on these two systems. Furthermore, we investigate if PACAP co-localize with CGRP and/or nNOS in the two tissues.

BACKGROUND

The structurally related neuropeptides vasoactive intestinal peptide (VIP) and pituitary adenylate cyclase activating peptide-38 (PACAP-38) partially share receptors and are both potent vasodilators. However, PACAP-38 but not VIP is an efficient inducer of migraine attacks in migraineurs. Calcitonin gene-related peptide (CGRP) and nitric oxide (NO) are two signaling molecules known to be involved in migraine.

METHODS

Rat tissue was used for all experiments. Release of CGRP induced by VIP and PACAP in dura mater, trigeminal ganglion (TG) and trigeminal nucleus caudalis (TNC) was quantified by EIA. Regulation of NOS-enzymes caused by VIP and PACAP was investigated in dura mater, TG and TNC by measuring the conversion of L-[3H]arginine to L-[3H]citrulline. Co-expression of PACAP, neuronal nitric oxide synthase (nNOS) and CGRP was explored by immunohistochemistry in TG and TNC. mRNA expression studies of VPAC1, VPAC2 and PAC1-receptors were performed by qRT-PCR.

RESULTS

PACAP-38 administered in increasing concentrations caused a concentration-dependent CGRP-release in the TNC, but not in TG. VIP was without effect in both tissues examined. The PAC1 receptor agonist maxadilan had no effect on CGRP release and the PAC1 antagonist M65 did not inhibit PACAP-38 induced CGRP release. PACAP-38 or VIP did not affect NOS activity in homogenates of TG and TNC. Quantitative PCR demonstrated the presence of VPAC1, VPAC2 and PAC1 receptors in TG and TNC. Immunohistochemistry of PACAP and CGRP showed co-expression in TG and TNC. PACAP and nNOS were co-localized in TG, but not in TNC. PACAP was found to co-localize with glutamine synthetase in TG satellite glial cells.

CONCLUSION

PACAP-38 cause release of CGRP from TNC but not from TG. We suggest that the release is not caused via activation of PAC1, VPAC1 or VPAC2 receptors. PACAP has no effect on NOS activity in TG or TNC. In TG PACAP was found in neuronal cells and in satellite glial cells. It co-localized with CGRP and nNOS in the neuronal cells. In TNC PACAP was co-localized with CGRP but not with nNOS.

Peptidergic and Nitrergic Innervation of the Pineal Gland in the Domestic Pig: An Immunohistochemical Study

The presence and co-localization of vasoactive intestinal polypeptide (VIP), peptide N-terminal histidine C-terminal isoleucine (PHI), pituitary adenylate cyclase-activating peptide (PACAP), somatostatin (SOM), calcitonin gene-related peptide (CGRP), substance P (SP) and the neuronal isoform of nitric oxide synthase (NOS) were studied in neuronal structures of the pig pineal gland. Paraformaldehyde-fixed pineals of 3-month-old gilts were sliced into serial cryostat sections, which were subjected to a set of double immunofluorescence stainings. Based on the co-existence patterns of neuropeptides, five populations of nerve fibres supplying the pig pineal were distinguished: (1) PHI-positive, (2) PACAP-positive, (3) SOM-positive, (4) SP/CGRP-positive and (5) SP-positive/CGRP-negative. Only a subpopulation of PHI-positive fibres contained VIP at the level detectable by immunofluorescence. NOS was found in some intrapineal PHI- and VIP-positive fibres. PHI-, VIP- and NOS-positive nerve fibres were more numerous in the peripheral than in the central part of the pineal. PACAP-positive fibres were equally distributed within the gland. The density of SOM-positive fibres was higher in the ventro-proximal than in the dorso-distal part of the pineal. SOM was also detected in some neuronal-like cells or specialized pinealocytes situated in the central region of the gland. Two populations of fibres containing SP were found: CGRP-positive, present in the distal and central parts of the pineal as well as CGRP-negative, localized in the proximal compartment of the gland.

Influence of sympathectomy in humans on the rhythmicity of 6-sulphatoxymelatonin urinary excretion

The amount of 6-sulphatoxymelatonin, the chief metabolite of melatonin, in the urine was measured in nine patients, who were subjected to bilateral sympathectomy at the second thoracic ganglionic level for treatment of hyperhidrosis of the palms. All patients showed before surgery a normal 6-sulphatoxymelatonin excretion with a peak in the excretion during the night time. After the sympathectomy, the high night time excretion was clearly abolished in five patients but remained high in four patients. This indicates that the segmental locations of the preganglionic sympathetic perikarya in the spinal cord, stimulating the melatonin secretion in the pineal gland in humans, vary between individuals. An increase in daytime melatonin excretion was observed in the patients responding to the sympathectomy with an abolished 6-sulphatoxymelatonin rhythm. This increase could indicate that the final sympathetic neurons innervating the pineal gland might have a both stimulatory and inhibitory function.

Demonstration of PACAP-immunoreactive intrapineal nerve fibers in the golden hamster (Mesocricetus auratus) originating from the trigeminal ganglion

By using immunohistochemistry, a network of nerve fibers containing pituitary adenylate-cyclase activating polypeptide (PACAP) was demonstrated in the pineal gland of the golden hamster, a photoperiodic species often used in pineal and circadian rhythm research. The nerve fibers are present in the capsule from where they permeate into the pineal perivascular spaces and parenchyma. Immuno-electron microscopy showed the PACAPergic nerve terminals, with clear transmitter vesicles, to terminate in the interstitial spaces between the pinealocytes or in the perivascular spaces. Some of the PACAPergic nerve terminals made synapse-like contacts with the pinealocytes. The origin of the PACAP-containing nerve fibers innervating the pineal gland of the hamster was investigated by combined retrograde tracing with fluorogold and immunohistochemistry for PACAP. A 2% fluorogold solution was injected iontophoretically into the superficial pineal gland and the animals were allowed to survive for 1 wk. After perfusion fixation of the rats, the location of the tracer was investigated in the brain, the parasympathetic sphenopalatine, and otic ganglia, as well as in the sensory trigeminal ganglia. The tracer was found in perikarya of all the investigated ganglia. However, co-localization with PACAP was found only in the trigeminal ganglion.

Origin of PACAP-immunoreactive nerve fibers innervating the subarachnoidal blood vessels of the rat brain

The subarachnoidal cerebral blood vessels of the rat are innervated by nerve fibers containing different neuropeptides, e.g. pituitary adenylatecyclase activating polypeptide (PACAP). PACAP dilates brain arterioles and immunohistochemical studies of the rat have indicated that PACAP binds to a VPAC1-receptor in the cerebral vasculature of this species. We have investigated the perikaryal origin of the nerve fibers innervating the subarachnoidal blood vessels of the rat by combined retrograde tracing with Fluorogold and immunohistochemistry. The in vivo neuronal retrograde tracings were done by injection of 2% Fluorogold in water into the subarachnoidal space in the area of the middle cerebral artery. The retrograde transported tracer was detected by use of an antibody against Fluorogold. One week after the injections, the animals were vascularly perfused with Stephanini's fixative and labeled perikarya were found bilaterally in the trigeminal, sphenopalatine, and otic ganglia. The retrograde Fluorogold tracings were combined with immunohistochemistry for PACAP using a mouse monoclonal antibody and the biotinylated tyramide amplification system. Double labeled perikarya containing both Fluoro-gold and PACAP were found predominantly in the trigeminal ganglion, and only rarely in the otic and sphenopalatine ganglion. Summarizing, our retrograde tracings combined with immunohistochemistry indicate that the perikarya in the trigeminal ganglion are the main origin of PACAPergic nerve fibers projecting to the cerebral vasculature of the rat.