Neurochemical properties of the middle cervical ganglion in the sheep

The neurochemical properties of the ovine middle cervical ganglion (MCG) were studied using antibodies raised against tyrosine hydroxylase (TH), dopamine beta-hydroxylase (DbetaH), neuropeptide Y (NPY), substance P (SP), calcitonin gene-related peptide (CGRP), vasoactive intestinal polypeptide (VIP) and galanin (GAL). Double-labelling immunocytochemistry revealed that the vast majority (95.5 +/- 0.8%) of postganglionic sympathetic MCG neurons expressed simultaneously both catecholamine-synthesizing enzymes (neurons were TH/DbetaH-positive). A large population of noradrenergic neurons exhibited immunoreactivity (IR) to NPY (62.2 +/- 2.2%), but single NPY-positive perikarya-lacking noradrenergic markers were also observed (2.0 +/- 0.3%). None of the examined MCG neuronal somata contained SP, CGRP, GAL or VIP. A moderate number of noradrenergic nerve fibres located amongst neuronal cell bodies was also found. In small number of these terminals the presence of NPYor GAL (but not CGRP or VIP) was detected. The ovine MCG was numerously innervated with SP-immunoreactive nerve fibres which sometimes formed basket-like formations around postganglionic neurons. The MCG exhibited a sparse CGRP-immunoreactive innervation and lacked VIP-positive nerve terminals. In many aspects the chemical coding of MCG postganglionic neurons and nerve terminals resembles that found in other mammalian cervico-thoracic paravertebral ganglia, but some important species-dependent differences exist. The functional implications of these differences remain to be elucidated.     

The innervation of the synovium of the knee joint in the guinea pig: an immunohistochemical and ultrastructural study

 The innervation of the knee joint synovial membrane of the guinea pig, i.e., the synoviocyte layer, the subjacent connective tissue and the connective tissue region beneath, was analyzed with immunohistofluorescence and electron microscopy. A screening of the innervation with antibodies against the general axon marker – protein gene product (PGP) 9,5 – revealed the presence of nerve fibers distributed in various regions of the knee joint synovial membrane. Confirmating previous studies, some of these nerve fibers stained with antibodies to tyrosine hydroxylase (TH), neuropeptide Y (NPY), substance P (SP), calcitonin gene-related peptide (CGRP), and vasoactive intestinal polypeptide (VIP). In addition, dynorphin (DYN)-containing fibers were detected, which have not been reported previously in normal joints. In general, the immunoreactive fibers were observed close to the synoviocytes and at blood vessels. Fibers with colocalization of NPY- and TH-like immunoreactivities (LIs), as well as of DYN- and TH-LIs were demonstrated. In the electron microscope, bundles of unmyelinated fibers as well as single fibers were found in the connective tissue region below the synoviocytes. Varicose parts of the nerve fibers contained mainly small, clear vesicles. Small and large dense-cored vesicles were also seen, but less frequently. Denser portions of the plasma membranes of some axons were observed in these regions, facing the extracellular space. Myelinated fibers were also observed in some nerve bundles. These findings emphasize the complex innervation of the synovial membrane, with nerve fibers containing a host of neuroactive substances. Altogether, these fibers are probably involved in many functions such as vasoregulation and control of synovial secretion in addition to being a source of mediators in joint inflammation. Accepted: 22 November 1997     

Localisation and quantitation of autonomic innervation in the porcine heart II: endocardium, myocardium and epicardium

The immunological problems of pig hearts supporting life in human recipients have potentially been solved by transgenic technology. Nevertheless, other problems still remain. Autonomic innervation is important for the control of cardiac dynamics and there is evidence suggesting that some neurons remain intact after transplantation. Previous studies in the human heart have established regional differences in both general autonomic innervation and in its component neural subpopulations. Such studies are lacking in the pig heart. Quantitative immunohistochemical and histochemical techniques were used to demonstrate the pattern of innervation in pig hearts (Sus scrofa). Gradients of immunoreactivity for the general neural marker protein gene product 9.5 were observed both within and between the endocardial, myocardial and epicardial plexuses throughout the 4 cardiac chambers. An extensive ganglionated plexus was observed in the epicardial tissues and, to a lesser extent, in the myocardial tissues. The predominant neural subpopulation displayed acetylcholinesterase activity, throughout the endocardium, myocardium and epicardium. These nerves showed a right to left gradient in density in the endocardial plexus, which was not observed in either the myocardial or epicardial plexuses. A large proportion of nerves in the ganglionated plexus of the atrial epicardial tissues displayed AChE activity, together with their cell bodies. Tyrosine hydroxylase (TH)-immunoreactive nerves were the next most prominent subpopulation throughout the heart. TH-immunoreactive cell bodies were observed in the atrial ganglionated plexuses. Endocardial TH- and NPY-immunoreactive nerves also displayed a right to left gradient in density, whereas in the epicardial tissues they showed a ventricular to atrial gradient. Calcitonin gene-related peptide (CGRP)-immunoreactive nerves were the most abundant peptide-containing subpopulation after those possessing NPY immunoreactivity. They were most abundant in the epicardial tissues of the ventricles. Several important differences were observed between the innervation of the pig heart compared with the human heart. These differences may have implications for the function of donor transgenic pig hearts within human recipients.     

A systematic study of the vascularisation of the pancreas

Summary The anatomy of the vessels of the pancreas is well known. However, some refinement is necessary in response to new requirements. In this study 40 specimens of pancreas plus duodenum were dissected after injecting the vessels with latex. Arteries and veins were measured and drawn. The origin and course of the vessels and their anastomoses were studied. If the vessels less than 0,5 mm in diameter are disregarded, it is seen that the vascularisation of the head of the pancreas can be systematised. Since the development of very selective arteriography and phlebography, two main types of artery and of vein have been discerned. Charts of the vessels for such an identification have been suggested. The two types of vessel are either terminal or anastomotic. Determination of the type of vessel can be useful: for the localisation of endocrine tumors of the pancreas by selective catheterisation; in making the decision for a limited operative intervention when immediate effective blood supply of the remaining tissue is important.This work was carried out in the Anatomy Laboratory of Université René-Descartes (Paris V) in collaboration with the Service d'Anatomo-Pathologie of the Hôpital du Kremlin-Bicêtre     

Age-associated plasticity in the intrinsic innervation of the ovine rumen

The rumen of adult sheep functions as a large fermentation chamber. In the newborn suckling ruminant, the rumen is bypassed and milk enters the abomasum directly. It was the aim of our study to investigate whether the transmitter content of intrinsic nerves changes with the developmental stage. The neurochemical code of myenteric neurons in the rumen from suckling lambs, fattened lambs and adult sheep was determined by using quadruple immunohistochemistry against choline-acetyltransferase (ChAT), nitric oxide synthase (NOS), substance P (SP) and vasoactive intestinal peptide (VIP). Three neurochemically distinct subpopulations were identified within the rumen. They expressed the code ChAT/-, ChAT/SP and NOS/VIP. The number of ChAT/SP neurons did not change during development. It was 62% in the newborn lamb and remained stable in fattened lambs (63%) and adult sheep (63%). By contrast, the number of ChAT/- neurons decreased significantly from 20% in suckling lambs to 11% and 7% in fattened lambs and adult sheep, respectively. Simultaneously, the proportion of NOS/VIP neurons increased from 16% in suckling lambs to 29% in adult sheep. The increase in the proportion of NOS/VIP immunoreactive neurons indicates an adaptation to large volumes of ingesta at the beginning of roughage intake and rumination. We conclude that the age-associated changes in neurochemical code of myenteric neurons in the forestomach are related to the adaption of the rumen to different functional properties during development.     

Expression profile of some neuronal and glial cell markers in the ovine ileal enteric nervous system during prenatal development

The enteric nervous system (ENS) is a network of neurons and glia found in the gut wall and governs this gastrointestinal function independently from the central nervous system (CNS). ENS comprises the myenteric plexus (MP) and the submucous plexus (SP). In this study, we examined the expression profile of neurofilament heavy chain (NF-H), neuron-specific enolase (NSE), calcyclin (S100A6), vimentin and glial fibril acidic protein (GFAP) in ovine ileal enteric neurons and enteric glia cells (EGCs) during prenatal development using an immunohistochemical method. The material of the study consisted of 15 different fetal ileum tissues obtained between days 60 and 150 of pregnancy. NF-H was observed in the majority of ganglion cells in SP and MP throughout the fetal period. It was determined that there was no NF-H reaction in some ganglion cells in Peyer’s patches of internal submucosal plexus (ISPF). In the early stage of pregnancy (60–90 days), there was no expression of NSE and S1006 in ileum. After this period, NSE and S1006 were expressed in the ganglion cells of the plexus, indicating an increase in the amount of expression towards the end of pregnancy. In the early period, vimentin expression was only detected in intramuscular interstitial cells (ICs) (60–90 days), but later (90–150 days) it was also seen in the cells around the ganglion cells in the plexus. On days 60–90 of gestation, GFAP expression only occurred in MP, but in later stages, staining was also detected in SP. In the plexus, an immunoreactivity was present in EGCs forming a network around the ganglion cell. During the last period of gestation (120–150 days), the number of GFAP-positive plexus increased, with the majority of these stained cells being observed in MP. Interestingly, weak staining or reaction did not occur in ISPF, unlike other plexuses. In conclusion, this is the first study that demonstrated the expression of NF-H, vimentin, S100A6, NSE and glial fibril acidic protein (GFAP) in ovine ileal ENS in the prenatal period. In the last period of gestation (120–150 days), the expression profile of ENS was similar to that of adult animals. The expression of the used markers increased toward the end of pregnancy. Our results suggest that neurons and EGCs show heterogeneity, and GFAP and NF-H cannot be used as panenteric glial or panneuronal markers, respectively. We also demonstrated, for the first time, the prenatal expression of S100A6 in enteric neurons and the possibility of using this protein for the identification of enteric neurons.     

Co-expression of tyrosine hydroxylase, dopamine beta-hydroxylase and neuropeptide Y in the sympathetic neurons projecting to the submandibular gland in the sheep

Sympathetic neurons projecting to the ovine submandibular gland (SMG) from the superior cervical ganglion (SCG) and middle cervical ganglion (MCG) were identified using retrograde tracing with fluorescent dye (Fast Blue). Antibodies to tyrosine hydroxylase (TH), dopamine beta-hydroxylase (DH) and neuropeptide Y (NPY) were used to determine the immunochemical characteristics of SMG-innervating sympathetic neurons. Immunohistochemistry combined with the retrograde tracing revealed that the population of SMG-projecting neurons consist of four distinct sub-populations, but taking into account their possible different physiological properties only three major sub-populations can be distinguished. The vast majority of neurons in both ganglia are noradrenergic in nature (co-express TH and DH). All examined TH-immunoreactive (IR) neurons also show immunoreactivity to DH. Sub-population of noradrenergic neurons can be divided into NPY-IR and non-NPY-IR. Noradrenergic neurons expressing NPY may act as vasoconstrictors. The second sub-population of SMG projecting neurons in the ganglia studied consists of non-noradrenergic neurons (containing NPY, but not TH). It is known that these kinds of neurons may play a vasodilatory role. In both examined ganglia the third sub-population consists of non-TH-IR and non-NPY-IR neurons of unknown physiological function. Since no DH immunoreactivity was found in any of TH– neurons these nerve cells can also be regarded as non-noradrenergic. It is possible that some neurons of the second as well as the third sub-population are cholinergic and some of them are non-noradrenergic/non-cholinergic in character.     

Osteoclast-like giant cell tumor of the pancreas: an immunohistochemical and ultrastructural study

We report a rare case of osteoclast-like giant cell tumor of the pancreas in a 70-year-old Japanese woman. The tumor was composed of a proliferation of ovoid to spindle-shaped mononuclear cells admixed with osteoclast-like giant cells. The tumor cells were immunore-active for vimentin, ±₁-antitrypsin, and CD68. In ultrastructural examination, the giant cells resembled osteoclasts, and the mononuclear stromal cells had fibroblastic and histiocytic features. No elements of epithelial differentiation were found in this tumor. These findings suggest that this tumor had a derivation similar to giant cell tumor of bone.This study was presented at the 28th Annual Meeting of the Clinical Electron Microscopy Society of Japan, Osaka, October 17–19, 1996.     

The emerging role of the sympathetic nervous system in skeletal muscle motor innervation and sarcopenia

Examining neural etiologic factors’role in the decline of neuromuscular function with aging is essential to our understanding of the mechanisms underlying sarcopenia, the age-dependent decline in muscle mass, force and power. Innervation of the skeletal muscle by both motor and sympathetic axons has been established, igniting interest in determining how the sympathetic nervous system (SNS) affect skeletal muscle composition and function throughout the lifetime. Selective expression of the heart and neural crest derivative 2 gene in peripheral SNs increases muscle mass and force regulating skeletal muscle sympathetic and motor innervation; improving acetylcholine receptor stability and NMJ transmission; preventing inflammation and myofibrillar protein degradation; increasing autophagy; and probably enhancing protein synthesis. Elucidating the role of central SNs will help to define the coordinated response of the visceral and neuromuscular system to physiological and pathological challenges across ages.This review discusses the following questions: (1) Does the SNS regulate skeletal muscle motor innervation? (2) Does the SNS regulate presynaptic and postsynaptic neuromuscular junction (NMJ) structure and function? (3) Does sympathetic neuron (SN) regulation of NMJ transmission decline with aging? (4) Does maintenance of SNs attenuate aging sarcopenia? and (5) Do central SN group relays influence sympathetic and motor muscle innervation?     

胎儿胰腺的显微形态学观察

目的观察胎儿胰腺的结构特点,为胎胰临床应用提供资料.方法取30例21～41W胎儿胰腺,利用超薄切片及透射电镜观察和石蜡包埋切片HE染色、SP免疫组化方法进行染色.结果胎儿胰腺内分泌部随胎龄增加而相对减少;外分泌部逐渐增加.A、B细胞超微结构在21～41W无明显变化.结论 25～35w胎儿更适合临床应用.     

Nitric oxide synthase, choline acetyltransferase, catecholamine enzymes and neuropeptides and their colocalization in the anterior pelvic ganglion, the inferior mesenteric ganglion and the hypogastric nerve of the male guinea pig

By the indirect immunofluorescence method, the distribution of nitric oxide synthase (NOS)-like immunoreactivity (LI) and its possible colocalization with neuropeptide immunoreactivities, with two enzymes for the catecholamine synthesis pathway, tyrosine hydroxylase (TH) and dopamine β-hydroxylase (DBH), as well as the enzyme for the acetylcholine synthesis pathway, choline acetyltransferase (ChAT) were studied in the anterior pelvic ganglion (APG), the inferior mesenteric ganglion (IMG) and the hypogastric nerve in the male guinea pig. The analyses were performed on tissues from intact animals, as well as after compression/ligation or cut of the hypogastric nerve. In some cases the colonic nerves were also cut. Analysis of the APG showed two main neuronal cell populations, one group containing NOS localized in the caudal part of the APG and one TH-positive group lacking NOS in its cranial part. The majority of the NOS-positive neurons contained ChAT-LI. Some NOS-positive cells did not contain detectable ChAT, but all ChAT-positive cells contained NOS. NOS neurons often contained peptides, including vasoactive intestinal peptide (VIP), neuropeptide tyrosine (NPY), somatostatin (SOM) and/or calcitonin gene-related peptide (CGRP). Some NOS cells expressed DBH, but never TH. The second cell group, characterized by absence of NOS, contained TH, mostly DBH and NPY and occasionally SOM and CGRP. Some TH-positive neurons lacked DBH. In the IMG, the NOS-LI was principally in nerve fibers, which were of two types, one consisting of strongly immunoreactive, coarse, varicose fibers with a patchy distribution, the other one forming fine, varicose, weakly immunoreactive fibers with a more general distribution. In the coarse networks, NOS-LI coexisted with VIP- and DYN-LI and the fibers surrounded mainly the SOM-containing noradrenergic principal ganglion cells. A network of ChAT-positive, often NOS-containing nerve fibers, surrounded the principal neurons. Occasional neuronal cell bodies in the IMG contained both NOS- and ChAT-LI. Accumulation of NOS was observed, both caudal and cranial, to a crush of the hypogastric nerve. VIP accumulated mainly on the caudal side and often coexisted with NOS. NPY accumulated on both sides of the crush, but mainly on the cranial side, and ENK was exclusively on the cranial side. Neither peptide coexisted with NOS. Both substance P (SP) and CGRP showed the strongest accumulation on the cranial side, possibly partly colocalized with NOS. It is concluded that the APG in the male guinea-pig consists of two major complementary neuron populations, the cholinergic neurons always containing NOS and the noradrenergic neurons containing TH and DBH. Some NOS neurons lacked ChAT and could represent truly non-adrenergic, non-cholinergic neurons. In addition, there may be a small dopaminergic neuron population, that is containing TH but lacking DBH. The cholinergic NOS neurons contain varying combinations of peptides. The noradrenergic population often contained NPY and occasionally SOM and CGRP. It is suggested that NO may interact with a number of other messenger molecules to play a role both within the APG and IMG and also in the projection areas of the APG.     

The innervation of rainbow trout (Oncorhynchus mykiss) liver: protein gene product 9.5 and neuronal nitric oxide synthase immunoreactivities

We have explored the innervation of the rainbow trout ( O. mykiss ) liver using immunohistochemical procedures and light microscopy to detect in situ protein gene product 9.5 and neuronal nitric oxide synthase immunoreactivities (PGP-IR and NOS-IR). The results showed PGP-IR nerve fibres running with the extralobular biliary duct (EBD), hepatic artery (EHA) and portal vein (EPV) that form the hepatic hilum, as well as following the spatial distribution of the intrahepatic blood vessel and biliary channels. These nerve fibres appear as single varicose processes, thin bundles, or thick bundles depending on their diameter and location in the wall of the blood vessel or biliary duct. No PGP-IR fibres were detected in the liver parenchyma. NOS-IR nerve fibres were located only in the vessels and ducts that form the hepatic hilum (EBD, EHA, EPV); in addition, NOS-IR nerve cell bodies were found isolated or forming ganglionated plexuses in the peribiliary fibromuscular tissue of the EBD. No PGP-IR ganglionated plexuses were detected in the EBD. The location of the general (PGP-IR) and nitrergic (nNOS-IR) intrinsic nerves of the trout liver suggest a conserved evolutionary role of the nervous control of hepatic blood flow and hepatobiliary activity.     

Differential galanin upregulation in dorsal root ganglia and spinal cord after graded single ligature nerve constriction of the rat sciatic nerve

Single ligature nerve constriction (SLNC) is a newly developed animal model for the study of neuropathic pain. SLNC of the rat sciatic nerve induces pain-related behaviors, as well as changes in the expression of neuropeptide tyrosine and the Y(1) receptor in lumbar dorsal root ganglia (DRGs) and spinal cord. In the present study, we have analyzed the expression of another neuropeptide, galanin, in lumbar DRGs and spinal cord after different degrees of constriction of the rat sciatic nerve. The nerve was ligated and reduced to 10-30, 40-80 or 90% of its original diameter (light, medium or strong SLNCs). At different times after injury (7, 14, 30, 60 days), lumbar 4 and 5 DRGs and the corresponding levels of the spinal cord were dissected out and processed for galanin-immunohistochemistry. In DRGs, SLNC induced a gradual increase in the number of galanin-immunoreactive (IR) neurons, in direct correlation with the degree of constriction. Thus, after light SLNC, a modest upregulation of galanin was observed, mainly in small-sized neurons. However, following medium or strong SLNCs, there was a more drastic increase in the number of galanin-IR neurons, involving also medium and large-sized cells. The highest numbers of galanin-IR neurons were detected 14 days after injury. In the dorsal horn of the spinal cord, medium and strong SLNCs induced a marked ipsilateral increase in galanin-like immunoreactivity in laminae I-II. These results show that galanin expression in DRGs and spinal cord is differentially regulated by different degrees of nerve constriction and further support its modulatory role on neuropathic pain.     

Immunohistochemical evidence from co-localization and denervation studies for four types of substance P-containing nervous structures in the rat superior cervical ganglion

Four types of substance P-immunoreactive structures have been distinguished in the rat superior cervical ganglion by double-immunofluorescence microscopy: (1) A major population of mainly varicose fibres enmeshed singly-scattered neuronal perikarya, some of which contained vasoactive intestinal polypeptide-immunoreactivity. These substance P-immunoreactive fibres did not contain colocalized calcitonin gene-related peptide (CGRP) and were absent after transection of the cervical sympathetic trunk. (2) A rather small substance P-immunoreactive fibre population with colocalized calcitonin gene-related peptide-immunoreactivity was distributed in a patchy manner and disappeared after cutting the postganglionic branches. (3) Most of the intraganglionic small intensely fluorescent (SIF) cell clusters were intensely substance P-immunoreactive. SIF cells were not visibly changed in number and fluorescence intensity by either surgical procedure. (4) Immunoreactivity was not visible in principal ganglionic neurons of control ganglia, but occurred in cell bodies after pre- as well as after postganglionic nerve transection. Some of the substance P-immunolabelled perikarya in addition revealed immunostaining to antisera against the catecholamine-synthesizin enyzme tyrosine hydroxylase or against the neuropeptides leu-enkephalin and vasoactive intestinal polypeptide, respectively. The results strongly suggest that, in addition to a substance P-containing preganglionic input (1), and a supply by substance P-containing sensory axon collaterals (2), the superior cervical ganglion of the rat gives origin to a paraganglionic (3) and a postganglionic (4) substance P-immunoreactive intrinsic system, the latter becoming visible only after disconnection of the sympathetic pathway.     

Immunoassay of lymphocyte subsets in ovine palatine tonsils

By means of immunohistochemistry (IHC) and triple color flow cytometry (FCM), five commercial antibodies (anti-CD2, CD4, CD8, CD21, and CD45) were evaluated to quantify and localize the B- and T-lymphocytes in the ovine palatine tonsil. The results of both techniques were compared and evaluated. For the immunohistochemical analysis, three fixation methods were evaluated for their suitability to localize the different lymphocyte populations: 3.5% formaldehyde, zinc salts-based fixative and cryopreservation. The anti-CD45 antibody showed a positive reaction after all three fixation methods. The four other antibodies tested (anti-CD2, CD4, CD8 and CD21) were compatible with zinc salts-based fixation and cryopreservation. The CD21+ B-lymphocytes were localized in the tonsillar lymphoid follicles, while the CD2+ T-lymphocytes were abundant in the interfollicular regions and rare within the lymphoid follicles. The CD8+ T-cells were concentrated adjacent to the follicles, while the CD4+ T-cells were localized in the interfollicular zones as well as in the follicles. Both by immunohistochemistry and flow cytometry, a quantification of the different lymphocyte subsets was made. When comparing the results, a reversed B/T cell ratio was noticed. Possible explanations for this observation are discussed.     

Functional neuroanatomical correlates of electrodermal activity: A positron emission tomographic study

To reveal areas in the central nervous system of importance for electrodermal control, regional cerebral blood flow (rCBF) was correlated to nonspecific skin conductance fluctuations (NSF) during aversive and nonaversive conditions. Participants viewed a TV screen displaying white noise or snake videotapes presented both with and without electric shocks given to the right hand. H₂¹⁵O positron emission tomography was used to measure rCBF, and the constant voltage technique was used to measure NSF from the left hand. Electrodermal activity was positively related to rCBF in the left primary motor cortex (MI, Brodmann's Area 4) and bilaterally in the anterior (Areas 24 and 32) and posterior cingulate cortex (Area 23). Negative relations were observed bilaterally in the secondary visual cortex (Areas 18 and 19) and the right inferior parietal cortex (Area 39), with a tendency also for the right insular cortex (Areas 13, 15, and 16). Because results from lesion and stimulation studies in humans converge with the present imaging results, we conclude that the cingulum and the motor cortex, in addition to the parietal and possibly the insular cortex, form part of one or several distributed neural network(s) involved in electrodermal control. Because these areas also support anticipation, affect, and locomotion, electrodermal responses seem to reflect cognitively or emotionally mediated motor preparation.     

Effects of chronic oestrogen treatment are not selective for uterine noradrenaline-containing sympathetic nerves: a transplantation study

Previous studies have shown that chronic administration of oestrogen during postnatal rat development dramatically reduces the total content of noradrenaline in the uterine horn, abolishes myometrial noradrenergic innervation and reduces noradrenaline‐fluorescence intensity of intrauterine perivascular nerve fibres. In the present study we analysed if this response is due to a direct and selective effect of oestrogen on the uterine noradrenaline‐containing sympathetic nerves, using the in oculo transplantation method. Small pieces of myometrium from prepubertal rats were transplanted into the anterior eye chamber of adult ovariectomised host rats. The effect of systemic chronic oestrogen treatment on the reinnervation of the transplants by noradrenaline‐containing sympathetic fibres from the superior cervical ganglion was analysed on cryostat tissue sections processed by the glyoxylic acid technique. In addition, the innervation of the host iris was assessed histochemically and biochemically. The histology of the transplants and irises was examined in toluidine blue‐stained semithin sections. These studies showed that after 5 wk in oculo, the overall size of the oestrogen‐treated transplants was substantially larger than controls, and histology showed that this change was related to an increase in the size and number of smooth muscle cells within the transplant. Chronic oestrogen treatment did not provoke trophic changes in the irideal muscle. Histochemistry showed that control transplants had a rich noradrenergic innervation, associated with both myometrium and blood vessels. Conversely, in oestrogen‐treated transplants only occasional fibres were recognised, showing a reduced NA fluorescence intensity. No changes in the pattern and density of innervation or in the total content of noradrenaline of the host irises were detected after chronic exposure to oestrogen. We interpreted these results to indicate that the effects of oestrogen on uterine noradrenaline‐containing sympathetic nerves are neither selective or direct, but result from an interaction between sympathetic nerve fibres with the oestradiol‐primed uterine tissue. A potential effect of oestrogen on the neurotrophic capacity of the uterus is discussed.