Age-related changes in rat optic nerve: morphological studies

Age-related changes of the optic nerve were studied in 3-month-old (young), 12-month-old (adult) and 24-month-old (aged) male Sprague-Dawley rats. Cross sections of the intracranial portion of the optic nerves of animals of different age groups were stained with haematoxylin-eosin and examined under a light microscope at low and high magnification. Other sections were stained with crystal violet for demonstration of glial cells. A third group of sections were stained immunohistochemically to detect glial fibrillary acidic protein (GFAP) which is a marker for localizing and characterizing astrocytes. All morphological results were subjected to the quantitative analysis of images and to statistical analysis to identify significant morphometrical data. Tissue protein concentrations were determined on homogenized fragments of optic nerve. Our results demonstrate the following age-related changes: (1) increase of the optic nerve sheaths (meningeal membranes); (2) increased number of astrocytes; (3) increase of areal density of GFAP immunoreactivity; (4) increased diameter and area of the optic nerve; (5) decreased number of nerve fibres; (6) decreased-size of nerve fibres and (7) decrease of the nerve fibres/meningeal membrane ratio from 3:1 to 1:1. Moreover, the protein amount does not change with age. The rat optic nerve, therefore, appears sensitive to ageing processes and can be considered as a useful model for the studies on neuronal ageing.     

Immunohistochemical characterization of neurons in the porcine ciliary ganglion

The present study was aimed at disclosing the chemical coding of nerve structures in the porcine ciliary ganglion (CG) using immunohistochemical methods. The substances under investigation included markers of "classical" neurotransmitters, choline acetyltransferase (ChAT), vesicular acetylcholine transporter (VAChT), tyrosine hydroxylase (TH) and dopamine beta-hydroxylase (DbetaH) as well as neuropeptides, somatostatin (SOM), galanin (GAL), substance P (SP), calcitonin gene-related peptide (CGRP), vasoactive intestinal polypeptide (VIP) and neuropeptide Y (NPY). Immunoreactivity to ChAT and VAChT was found virtually in all the neuronal somata and in numerous intraganglionic, varicose nerve fibres which often formed basket-like formations around the nerve cell bodies. Many CG neurons contained immunoreactivity for SOM (46%) or GAL (29%). Interestingly, a small number (approx. 1%) of the cholinergic somata stained for TH but not for DbetaH; nevertheless, some extra- and intraganglionic nerve fibres displayed immunoreactivity for DbetaH or TH. The CG perikarya stained neither for vasoactive intestinal polypeptide (VIP) nor for neuropeptide Y (NPY), but some NPY- or VIP-positive nerve terminals were observed within nerve bundles distributed outside the ganglion. SP- and CGRP-immunoreactivity was found in some intraganglionic nerve fibres only. The present study revealed that the porcine CG consists of cholinergic neurons many of which contain SOM and GAL. Thus, it can be assumed that in the pig, these neuropeptides are involved, complementary to acetylocholine, in the parasympathetic postganglionic nerve pathway to structures of the eye including the ciliary and iris sphincter muscles.     

牛眼球石蜡切片制作方法的探索

为探索一种牛眼球的石蜡切片制作方法,本试验比较了常规石蜡切片制作方法和改良的石蜡切片制作方法．结果表明,试验组标本固定后肉眼可见视网膜与脉络膜紧密相连,仅有小部分视网膜出现脱离的现象;切片显示小梁网连续性未被破坏;眼球壁全层组织连续性未破坏,各层未出现分离现象;视网膜无脱离,各层组织细胞无收缩现象。说明试验组大大改进了眼球固定、脱水、透明技术方法,解决了较大眼球无法制作石蜡切片的难题,为眼球基础研究和相应病理研究提供了基础：     

Morphologic features of the aqueous humor drainage pathways in horses

The iridocorneal angle of the horse was anteriorly lined by a pectinate ligament, consisting of several layers of vertically oriented collagenous beams, that were interrupted by a network of extracellular spaces. The anterior chamber angle consisted mostly of a large uveal trabecular meshwork that was composed of widely-spaced, thick trabeculae. These trabeculae were attached in part posteriorly to extensions of the ciliary body musculature and anteriorly inserted into the prominent pectinate ligament. The corneoscleral trabecular meshwork was shaped hemiobovately and formed the external boundary of the iridocorneal angle. The extracellular spaces were smaller and more evenly spaced than those in the uveal trabecular meshwork. Uveal and corneoscleral trabecular meshwork beams were mostly composed of cores of collagen and elastin surrounded by several layers of basement membrane-like material and, in turn, were entirely enveloped by trabecular cells. An anterior narrow zone of broad corneoscleral trabeculae was composed of elastin-collagen cores surrounded by circular bundles of long-spacing collagen. The angular aqueous plexus was extensive, forming much of the external border of the outer corneoscleral trabecular meshwork. A dense zone was associated with the angular aqueous plexus, completely encompassing these aqueous outflow vessels. Posteriorly, the iridocorneal angle was confluent with a well-defined band of trabeculae that was situated between the ciliary body musculature and subjacent sclera and extended posteriorly to the anterior-most region of the choroid where these trabeculae tapered and ended. This region is referred to as the supraciliary trabecular meshwork and indicates a potentially extensive route for outflow of aqueous humor in the equine eye.     

Glandular structures in the major interlobular and extrapancreatic ducts in the guinea pig

The morphology of the pancreatic duct system did not receive much attention as compared to the microanatomy of the exocrine and endocrine pancreas. The histological peculiarities of the excretory duct system are of major importance especially in laboratory animals like guinea pigs. The paper describes the histological peculiarities of the major interlobular and extrapancreatic ducts in guinea pigs. The pancreatic tissue samples were collected from five guinea pigs. For histological investigation, several pancreatic fragments underwent fixation in 10% buffered formalin and were later processed by the standard paraffin technique. Subsequentially, tissue sections were stained by Goldner's trichrome staining. The mucous substances were assessed by Alcian blue and Periodic acid–Schiff staining methods. The interlobular and main pancreatic ducts in the guinea pig present a simple columnar epithelium surrounded by a thick layer of dense connective tissue. The aforementioned epithelium of the main pancreatic ducts includes principal cells, goblet cells and basal cells. Additionally, the ductal epithelium presents occasional unicellular multiloculated intraepithelial mucous glands and prominent extraepithelial glands. The latter adopts a simple or compound tubular feature. The mucus elaborated by the three glandular types is mostly neutral in goblet cells, predominantly acidic in extraepithelial ductal glands, and a similar amount of acidic and neutral mucin in intraepithelial glands. In conclusion, the epithelium-associated mucous glands in the interlobular and main pancreatic ducts in the guinea pig are restricted not only to goblet cells. A substantial mucous discharge probably with a protecting role against irritative pancreatic juice derives from the main ductal intraepithelial and extraepithelial glands.     

Study of retinal microvessels in a Rhesus monkey model of chronic high intraocular pressure

Objective  To investigate the changes in retinal vessels, especially macular capillaries, under high IOP using the Rhesus monkey high IOP model.
Methods  The trabecular meshwork of the adult Rhesus monkey was cauterized by laser to induce increased IOPs with different degrees of damage. The eyeballs were enucleated, and the optic nerves were stained with toluidine blue in semithick slices. Part of the retina was observed under electron microscope, and the rest was stained by the ADPase method. The damage levels of the optic nerve were evaluated by axon count, and the pathological appearance of the macular capillaries were observed.
Results  Five mildly damaged eyes, three moderately damaged eyes and three severely damaged eyes were evaluated. Dense and intact perifoveal vascular rings were observed in all the eyes. The vessels' area percentages, as well as area, perimeter and diameter of the foveal avascular zones, were measured, and no statistically differences were found among different groups ( P -values were 0.269, 0.500, 0.951, and 0.555 separately). The ultra structures of the normal capillaries showed regular tubes and intact basement membranes, while lipoid substances in capillary tubes, swollen mitochondria in endothelial cell bodies, and uneven basement membranes were found in the high IOP-damaged eyes.
Conclusions  Compared with normal eyes, no obvious differences were found in macular microvessels and foveal avascular zones in the Rhesus monkey model of high IOP. However, presence of swollen mitochondria in endothelial cells and lipoid substances in capillary tubes might suggest that high IOP could damage the capillary endothelial cells.     

Anatomy of the California sea lion globe

Objective This study analyzed the morphology of the California sea lion globe to determine what features may contribute to their characteristic visual abilities. Procedure Globes from the Comparative Ocular Pathology Laboratory of Wisconsin (COPLOW) collection were examined from gross photographs and microscopic sections stained with hematoxylin and eosin, trichrome, smooth muscle actin, and alcian blue periodic acid–Schiff (PAS). Transmission electron microscopy of the cornea and iris was also performed. Clinical results There was a round, flattened area ventromedial to the axial cornea. The pupil was tear‐drop shaped. Pectinate ligaments were visible without magnification. The retina was holangiotic, containing numerous spoke‐like venules and arterioles. The tapetum was green encompassing the entire fundus. The optic nerve was unmyelinated. Histological results The sclera was thinnest equatorially and thickest at the limbus and posterior pole. Bowman’s layer was difficult to see by light microscopy but clear with transmission electron microscopy. The cornea had a thick epithelium, thin endothelium and Descemet’s membrane, and the stroma thinned axially. The dilator muscle was absent near the pupil, but enlarged and mingled with the sphincter muscle near the iris base. A large, wide ciliary cleft with prominent trabeculae and a single continuous pectinate ligament was present. The corneoscleral trabecular meshwork was discontinuous. A round lens attached to the ciliary body via direct attachment to ciliary processes and delicate zonular ligaments. There was a circumferential muscle at the base of the ciliary processes. A thick tapetum covered the entire fundus except peripherally. The retina was characterized by sparse, large ganglion cells.     

Axonal and neuronal amyloid precursor protein immunoreactivity in the brains of guinea pigs given tunicamycin

Amyloid precursor protein (APP) immunocytochemistry was used to study axonal and neuronal changes in guinea pig brains exposed to tunicamycin. Substantial axonal injury was found in ischemic-hypoxic foci and more generally, but this injury was not readily appreciable in conventionally stained sections. Neuronal perikaryal APP expression was also widely distributed, possibly as an acute phase response to this neurotoxin.     

Osteodystrophia fibrosa in two guinea pigs.

Two adult guinea pigs were examined because they were lethargic and reluctant to walk. Additionally, I guinea pig had otitis media, and the other had dental malocclusion. Both guinea pigs had been fed a commercially available diet of cereals and pellets enriched with vitamin C and formulated for this species. Radiographically, the guinea pigs had coarse trabecular bone patterns, skeletal deformations, pathologic fractures, and polyarthritic degenerative joint disease. A double cortical line was also evident on several long bones, the pelvis, and the vertebrae. A diagnosis of osteopenia was confirmed by use of dual-energy x-ray absorptiometry. Analysis of a food sample fed to 1 guinea pig revealed calcium and phosphorus contents of 0.524 and 0.425%, respectively (Ca:P ratio, 1.23:1). Microscopic examination of bone tissue from both guinea pigs revealed severe fibrous osteodystrophy. Nutritional secondary hyperparathyroidism caused by calcium-phosphorus imbalance was considered to be the underlying cause of osteodystrophia fibrosa in both guinea pigs.     

The distribution of nerve fibres immunoreactive for vasoactive intestinal peptide, calcitonin gene-related peptide, substance P and dopamine beta-hydroxylase in the normal equine larynx

The autonomic innervation of the mammalian respiratory system is complex, and involves a wide variety of peptide and non-peptide neurotransmitters which will have an important role in normal laryngeal function and the response to disease. This innervation has been partially described in the horse airway and lung, but there is no information on the equine larynx. This paper describes the expression and distribution of nerve fibres immunoreactive for vasoactive intestinal peptide (VIP), calcitonin gene-related peptide (CGRP), substance P (SP) and the adrenergic enzymatic marker dopamine beta-hydroxylase (DBetaH) in the mucosa of the equine larynx. The overall relative density of nerve fibres immunoreactive for the different antigens was VIP>CGRP>SP>DBetaH. There were differences in the distribution of nerve fibre types, although each antigen was found in nerve fibres adjacent to blood vessels and mucous glands. VIP -like immunoreactivity (VIP -Li) was particularly extensive in association with mucous glands. SP - and CGRP -like immunoreactivity (SP -Li, CGRP -Li) were also seen close to the epithelium, with occasional nerve fibres coursing beneath and between the epithelial cells. Fragments of SP -Li and CGRP -Li fibres were also present in large nerve fibre bundles and ganglionic cell clusters, but not in the neurons themselves. The density of nerve fibres immunoreactive for DBetaH was very low and restricted to blood vessels and mucous glands. There was marked variation in the density of nerve fibres at the different sites, with the greatest density, particularly for VIP, over the arytenoid cartilage. Immunoreactive nerve fibres were less plentiful over the epiglottis, and the density of all types of nerve fibres was low over the cricoid cartilage. Overall VIP -Li nerve fibres were the most plentiful.     

Intraocular ALλ amyloidoma with plasma cell neoplasia in a cat

An 11-year-old, neutered male domestic short-hair cat was presented with buphthalmos of the right eye and diagnosed with advanced glaucoma. Sonographic examination revealed an iridial thickening. Neoplasia was suspected and an enucleation was performed. Histopathology of the enucleated eye revealed abundant amyloid deposition predominantly in the anterior uveal tract accompanied by few to moderate numbers of well-differentiated plasma cells. The amyloid deposits were identified by staining with Congo red and showing green birefringence under polarized light. Immunohistochemically, amyloid and plasma cells stained intensely only with anti-ALλ antibody, supporting the amyloid tumor being an immunoglobulin-λ-light chain origin. Additional abnormalities included narrowing of the filtration angle and collapse of the ciliary cleft, and trabecular meshwork. One year post-enucleation, the cat was still healthy without signs of systemic amyloidosis or apparent metastatic disease. This is the first report of a cat with noncutaneous extramedullary plasmacytoma originating in the anterior uveal tract with resulting local amyloid.     

Investigations on the conjunctival goblet cells and on the characteristics of glands associated with the eye in the guinea pig

Objective To investigate the distribution and density of conjunctival goblet cells (GC) and to study the anatomy and microscopic characteristics of glands associated with the eye in the guinea pig. Procedures Twenty‐five guinea pigs were used. Meibomian gland openings were counted using biomicroscopy. Conjunctiva, eyelids and glands were embedded in glycol methacrylate and paraffin. Sections were stained with hematoxylin and eosin (H&E), periodic acid Schiff’s reaction (PAS) and Alcian blue (AB). Results Highest GC densities were found in the bulbar and palpebral region of the nasal conjunctiva (GC index: 13.7–16.4%). Lowest GC densities (GC index: 0.0–1.0%) were found in 3/4 limbal regions (nasal and temporal upper eyelid, temporal lower eyelid). Guinea pigs have 27.1 ± 3.0 (mean ± SD) meibomian gland openings in the upper lid and 25.7 ± 2.3 in the lower lid. Difference between upper and lower lid was significant (P = 0.037). Two subconjunctival sebaceous glands occur temporal to each eye. The Harderian gland is very large. In the lacrimal gland three different cell types were distinguished both according to the cell structure and histochemical staining. Conclusions Goblet cell densities are lower in guinea pigs than in dogs and horses. Positive staining with PAS and AB could be an indication that mucins are produced in the lacrimal gland. If so, they may contribute to the mucin layer of the tear film. Both the extraordinarily large Harderian gland and the subconjunctival sebaceous glands produce lipids and may contribute to the lipid layer of the tear film.     

Distribution of Galanin and Galanin Receptor 2 in the Pre‐optic Area of the Female Guinea Pig

This study describes the distribution of galanin (Gal) and galanin receptor 2 (GalR2) in the pre‐optic area (POA) of the female guinea pig. Frozen sections were undergone for a routine immunofluorescence labelling. Gal and GalR2 display immunoreactivity in all parts of the pre‐optic area. Gal shows reactivity both in perikarya and fibres, whereas GalR2 was observed only in perikarya. Gal‐ and GalR2‐immunoreactive (‐ir) perikarya were the most numerous in the medial pre‐optic area (MPA) with the highest reactivity in its dorsal part. In the median pre‐optic nucleus (MPN) and periventricular pre‐optic nucleus (PPN), only single Gal‐ and GalR2‐ir neurons were observed. The highest density of Gal‐ir fibres was revealed in the PPN and the lowest in the lateral pre‐optic area (LPA). The results of this study indicate that the distribution pattern of Gal containing neurons overlaps well with the distribution pattern of GalR2‐positive neurons, especially in the MPA. This may suggest GalR2‐dependent activity in this brain region.     

Distribution of serotonin immunoreactivity in the main olfactory bulb of the Mongolian gerbil

The distribution of serotonin immunoreactivity in the main olfactory bulb (MOB) of the Mongolian gerbil (Meriones unguiculatus) was examined by immunohistochemistry. Seven distinct layers of the Mongolian gerbil MOB-stained with cresyl violet were identified. Serotonin-immunoreactive (IR) cell bodies were not found in the MOB. The serotonin-IR nerve fibres had a specific laminar distribution and morphology in the gerbil MOB. Serotonin-IR nerve fibres were observed in the glomerular, external plexiform and granule cell layers of the MOB. These serotonin-IR nerve fibres showed varicosities that were larger than the thickness of the axon. The highest density of serotonin-IR nerve fibres was in glomeruli of the glomerular layer. The average fibre density in the glomerular layer was more than three to four times the density in the infraglomerular layers. Glomerular serotonin-IR fibres were much more intensively stained than infraglomerular serotonin-IR fibres. This result suggests that serotonin-IR nerve fibres of Mongolian gerbil MOB are extrinsic and may act to modulate the olfactory transmission.     

Comparison of chicken plasma and guinea pig serum in a quantitative microtiter method of determining microbial complement resistance.

A quantitative microtiter method using chicken plasma is described for determining the degree of complement resistance or sensitivity of avian Escherichia coli isolates. Results obtained with the microtiter method using chicken plasma were compred with results obtained using commercially available standardized guinea pig serum as the source of complement. The test organisms consisted of five isolates of E. coli isolated from chickens. Three isolates were from flocks with colisepticemia; one was from a flock with omphalitis; and one isolate was a non-pathogenic control. Data were accumulated from the five avian E. coli isolates incubated at 35 C with either chicken plasma or guinea pig serum and with heat-inactivated chicken plasma or guinea pig serum. The microtiter results of the chicken plasma and guinea pig serum had a statistically positive correlation. The use of commercially available guinea pig serum in the test system will allow for standardization of this method.     

Immunocytochemical localisation of carbonic anhydrase isozyme III in equine skeletal muscle

The location of carbonic anhydrase III (CA-III) in frozen sections of biopsies of Thoroughbred horse skeletal muscle was studied. Fibre types were determined by ATP-ase and succinate dehydrogenase staining. CA-III isozyme was detected using a peroxidase conjugated anti-CA-III antibody. CA-III was found to be localised in slow twitch oxidative fibres (ST), but was also present in fast twitch oxidative (FTH) fibres in small amounts. Fast twitch glycolytic (FT) fibres were stained lightly compared with control sections. The concentrations of CA-III in muscle and liver were 70 micrograms/mg protein and 4 micrograms/mg protein, respectively. CA-I and CA-II were not found in muscle extracts by the double immunodiffusion method.     

Histochemical and morphometrical characterization and distribution of fibre types in four muscles of ostrich (Struthio camelus)

A staining procedure used for simultaneously determining three different fibre types in single sections bovine, porcine or ovine skeletal muscle was modified for use with ostrich skeletal muscle. The muscle fibres of gastrocnemius pars externa, tibialis cranialis caput tibiale, tibialis cranialis caput femorale and fibularis longus tendo caudalis were studied. The histochemical results revealed the presence of three types of fibre only in the gastrocnemius pars externa muscle: fast-twitch glycolytic fibres (FG), fast-twitch oxidative glycolytic fibres (FOG) and slow-twitch oxidative fibres (SO), while in the other muscles the FG fibres were absent. The percentage distribution of fibres types showed a higher incidence of SO fibres compared to FOG fibres in tibialis cranialis caput femorale and tibialis cranialis caput tibiale muscles, while it was opposite in the case of the fibularis longus tendo caudalis muscle. In the gastrocnemius pars externa muscle the FG fibres outnumber the other fibres, followed by the SO and FOG fibres. The results of the analysis of variance show significant interaction between muscle x fibre type for every morphometric parameter evaluated. Differences about value of fibres area exists between tibialis cranialis caput femorale and fibularis longus tendo caudalis muscles. Both fibre types in tibialis cranialis caput tibiale muscle have mean values of transversal section area smaller than tibialis cranialis caput femorale. The other morphometric parameters show a similar trend. The gastrocnemius pars externa muscle presents similar dimensions of muscle fibres for the FG and FOG types, and significantly smaller for the SO type.     

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.     

Early dexamethasone treatment after implantation of a sciatic-nerve cuff decreases the concentration of substance P in the lumbar spinal cord of rats with neuropathic pain

The main purpose of this study was to evaluate the effects of early dexamethasone treatment on pain-related peptides at an early stage in the development of neuropathic pain induced by implantation of a sciatic nerve cuff in Sprague Dawley rats (body weight 250 to 350 g). The rats were tested for touch sensitivity with the use of von Frey filaments before and 3 d after cuff implantation (n = 12) or sham surgery (n = 6). Half of the cuff-implanted rats received dexamethasone, 1 mg/kg intraperitoneally, 1 h after surgery. Spinal cords were collected on the 3rd day after surgery, and the lumbar enlargement was processed for the detection of selected peptides (neurotensin, substance P, cholecystokinin [CCK], vasoactive intestinal peptide, and calcitonin gene-related peptide) by means of liquid chromatography and tandem mass spectrometry. The right sciatic nerve of each rat was collected, fixed, and stained for histopathological evaluation. Except for neurotensin, all the peptides showed an increased concentration with neuropathic pain; however, the differences were significant (P < 0.05) only for substance P and CCK. In the animals treated with dexamethasone, mechanical allodynia was less pronounced (P < 0.01), and only the concentration of substance P was decreased significantly (P < 0.05). Sciatic nerve sections showed a decrease in C (P < 0.01) and Adelta (P < 0.03) fibres with neuropathic pain and a nearly normal percentage of C fibres after dexamethasone treatment. The dexamethasone-treated animals also had less inflammation detectable microscopically at the nerve constriction site compared with cuff-implanted animals that were not treated with dexamethasone. Our results suggest that in the early stages of neuropathic pain induced by an inflammatory process, dexamethasone may be a useful treatment and that substance P plays an important role in pain perception.     

Expression of the PACAP‐immunoreactivity in the Lymphoid Organs of the Duck

Introduction: The interactions occurring between nervous and immune systems are well documented. These interactions involve several types of chemical messengers including hormones, cytokines, classic neurotransmitters and neuropeptides. It has been observed that the lymphoid organs receive a dense peptidergic innervation and immune cells produce neuropeptides. Neuropeptides, in turn, are involved in the regulation of the inflammatory processes and in the maturation of the lymphoid organs. Several studies have demonstrated that the immunomodulatory neuropeptides and their receptors are expressed in the thymus and bursa of fabricius. PACAP is a glucagon/VIP/secretin family peptide. It was originally isolated from the ovine hypothalamus and then it was found in the autonomic nervous system. PACAP is involved in the regulation of the hypothalamic‐pituitary function, neurotransmission and neuromodulation. In the immune system, PACAP is expressed in lymphoid tissues of the rat and in the lymphocytes of the duck GALT. PACAP, therefore, could be a messenger of the dialogue between nervous and immune system. It may have a role in the regulation of the inflammatory processes by stimulating histamine and serotonin and modulating the production of the cytokines in immune cells. Methods: Immunohistochemistry on paraffin‐embedded sections of thymus and bursa of fabricius of the duck of different ages by using an antibody anti‐PACAP38. Results and Discussion: In the thymus, PACAP‐immunoreactivity was found in lymphoid cells and, with a lesser extent, in epithelial reticular cells. The immunoreactive lymphocytes were primarily observed in the interlobular septa in close vicinity to the interlobular veins. The number of positive lymphocytes increased with ageing. In the bursa of fabricius, PACAP‐IR was found in nerve fibres and in a few lymphoid cells. These results suggest that PACAP could play a role in the maturation and involution of these organs and in the immune functions.