Deciphering biased-agonism complexity reveals a new active AT1 receptor entity

Functional selectivity of G protein-coupled receptor (GPCR) ligands toward different downstream signals has recently emerged as a general hallmark of this receptor class. However, pleiotropic and crosstalk signaling of GPCRs makes functional selectivity difficult to decode. To look from the initial active receptor point of view, we developed new, highly sensitive and direct bioluminescence resonance energy transfer-based G protein activation probes specific for all G protein isoforms, and we used them to evaluate the G protein-coupling activity of [(1)Sar(4)Ile(8)Ile]-angiotensin II (SII), previously described as an angiotensin II type 1 (AT(1)) receptor-biased agonist that is G protein independent but β-arrestin selective. By multiplexing assays sensing sequential signaling events, from receptor conformations to downstream signaling, we decoded SII as an agonist stabilizing a G protein-dependent AT(1A) receptor signaling module different from that of the physiological agonist angiotensin II, both in recombinant and primary cells. Thus, a biased agonist does not necessarily select effects from the physiological agonist but may instead stabilize and create a new distinct active pharmacological receptor entity.

beta-Arrestin 1 and 2 stabilize the angiotensin II type I receptor in distinct high-affinity conformations

BACKGROUND AND PURPOSE

The angiotensin II type 1 (AT(1)) receptor belongs to family A of 7 transmembrane (7TM) receptors. The receptor has important roles in the cardiovascular system and is commonly used as a drug target in cardiovascular diseases. Interaction of 7TM receptors with G proteins or beta-arrestins often induces higher binding affinity for agonists. Here, we examined interactions between AT(1A) receptors and beta-arrestins to look for differences between the AT(1A) receptor interaction with beta-arrestin1 and beta-arrestin2.

EXPERIMENTAL APPROACH

Ligand-induced interaction between AT(1A) receptors and beta-arrestins was measured by Bioluminescence Resonance Energy Transfer 2. AT(1A)-beta-arrestin1 and AT(1A)-beta-arrestin2 fusion proteins were cloned and tested for differences using immunocytochemistry, inositol phosphate hydrolysis and competition radioligand binding.

KEY RESULTS

Bioluminescence Resonance Energy Transfer 2 analysis showed that beta-arrestin1 and 2 were recruited to AT(1A) receptors with similar ligand potencies and efficacies. The AT(1A)-beta-arrestin fusion proteins showed attenuated G protein signalling and increased agonist binding affinity, while antagonist affinity was unchanged. Importantly, larger agonist affinity shifts were observed for AT(1A)-beta-arrestin2 than for AT(1A)-beta-arrestin1.

CONCLUSION AND IMPLICATIONS

beta-Arrestin1 and 2 are recruited to AT(1A) receptors with similar ligand pharmacology and stabilize AT(1A) receptors in distinct high-affinity conformations. However, beta-arrestin2 induces a receptor conformation with a higher agonist-binding affinity than beta-arrestin1. Thus, this study demonstrates that beta-arrestins interact with AT(1A) receptors in different ways and suggest that AT(1) receptor biased agonists with the ability to recruit either of the beta-arrestins selectively, would be possible to design.

Alanine metabolism, transport, and cycling in the brain

Brain glutamate/glutamine cycling is incomplete without return of ammonia to glial cells. Previous studies suggest that alanine is an important carrier for ammonia transfer. In this study, we investigated alanine transport and metabolism in Guinea pig brain cortical tissue slices and prisms, in primary cultures of neurons and astrocytes, and in synaptosomes. Alanine uptake into astrocytes was largely mediated by system L isoform LAT2, whereas alanine uptake into neurons was mediated by Na(+)-dependent transporters with properties similar to system B(0) isoform B(0)AT2. To investigate the role of alanine transport in metabolism, its uptake was inhibited in cortical tissue slices under depolarizing conditions using the system L transport inhibitors 2-aminobicyclo[2.2.1]heptane-2-carboxylic acid and cycloleucine (1-aminocyclopentanecarboxylic acid; cLeu). The results indicated that alanine cycling occurs subsequent to glutamate/glutamine cycling and that a significant proportion of cycling occurs via amino acid transport system L. Our results show that system L isoform LAT2 is critical for alanine uptake into astrocytes. However, alanine does not provide any significant carbon for energy or neurotransmitter metabolism under the conditions studied.

Human responses in assessing object relations subscales of the Psychoanalytic Rorschach Profile

The Rorschach test is often used to assess object relations. This research examined whether human responses are necessary for a valid assessment.

Clinical anatomy in the oncology patient: a preclinical elective that reinforces cross-sectional anatomy using examples of cancer spread patterns

A preclinical elective entitled Oncologic Anatomy is described which emphasizes the study of anatomy from a three-dimensional approach using examples of cancer spread patterns. Features of this elective course include patient presentations, a review of the anatomy, a diagnostic presentation and overview of radiologic imaging techniques, and "hands on" experience where students are introduced to aspects of the physical examination. This course format encourages active learning, facilitates basic and clinical science integration, offers early exposure to patients, and validates the importance of the psychosocial aspects of the medical profession.

TNF alpha and IL-1beta mediate intercellular adhesion molecule-1 induction via microglia-astrocyte interaction in CNS radiation injury

Radiation injury to the central nervous system (CNS) results in glial activation accompanied by expression of pro-inflammatory cytokines and adhesion molecules. In this study we demonstrate intercellular adhesion molecule-1 (ICAM-1) induction in the irradiated mouse brain at the mRNA and protein levels. Immunocytochemical analysis revealed that ICAM-1 protein was primarily expressed in endothelial cells and microglia. In vitro, ionizing radiation significantly induces TNF alpha, IL-1beta and ICAM-1 mRNA in primary microglia cultures. Interestingly, although ionizing radiation activated primary astrocyte cultures, it did not induce ICAM-1 expression. However, exposure of astrocytes to conditioned medium collected from irradiated microglia resulted in ICAM-1 induction, which was abrogated when the conditioned medium was pre-incubated with neutralizing antibodies raised against murine TNF alpha and IL-1beta. These results indicate that pro-inflammatory cytokines may be necessary for ICAM-1 expression in astrocytes in CNS radiation injury.

ICAM-1 induction in the mouse CNS following irradiation

Injury to the central nervous system (CNS) results in inflammation, increased trafficking of leukocytes into the CNS, induction of cytokines, and exacerbation of the primary injury. The increased trafficking of neutrophils into the CNS has been described following a number of injury models including stab, stroke, and excitotoxin-induced injury. This enhanced trafficking has largely been ascribed to the adhesion molecule intercellular adhesion molecule-1 (ICAM-1, CD54). In the current study, we wished to determine if the inflammation caused by irradiation of the CNS resulted in a similar induction of ICAM-1. C3H/HeJ mice were irradiated using gamma irradiation aimed over the right cerebral hemisphere. The relative induction of ICAM-1 mRNA levels was determined using quantitative RT-PCR 6 hours following irradiation with either 0, 5, 15, 25 or 35 Gy. ICAM-1 message was seen to exhibit a normal dose response curve with increasing mRNA levels seen at 15 Gy and higher. To determine the cellular distribution of the ICAM-1 protein following irradiation, mice were sacrificed at 4 hrs, 24 hrs, 48 hrs and 7 days following 25 Gy irradiation and the tissue was processed for ICAM-1 immunocytochemistry. ICAM-1 staining was seen to increase in both endothelial cells and astrocytes beginning as early as 4 hrs. The staining intensity continued to increase throughout the 7 day period observed. Together, these results suggest that irradiation of the CNS causes a rapid induction of both ICAM-1 mRNA and protein. This suggests that increased leukocyte trafficking into the CNS may exacerbate the inflammation induced by radiation injury.

The implementation of therapeutic community principles in acute care psychiatric hospital settings: an empirical analysis and recommendations to clinicians

We applied therapeutic community principles to a contemporary acute care psychiatric treatment program and investigated the effects upon milieu treatment variables using the Ward Atmosphere Scale (WAS) as a measure. Significant differences were found between experimental and control units on several scales of the WAS following the introduction of program changes. These differences indicated that the introduction of therapeutic community principles in treatment programming enhanced milieu factors that are conducive to patient recovery.

Sprouting of dopaminergic fibers from spared mesencephalic dopamine neurons in the unilateral partial lesioned rat

A unilateral partially lesioned rat model of Parkinson's disease was developed following selective lesioning of the dopamine neurons of the substantia nigra pars compacta by stereotactic injection of the neurotoxin 6-hydroxydopamine. In this animal model the dopamine neurons of the ventral tegmental area and medial substantia nigra are spared. The neuronal loss in such partial lesioned models mimics more closely that seen in human mid-stage parkinsonism. Cografts of adrenal medullary cells and sciatic nerve to the partially lesioned striatum induced a sprouting response in grafted animals that was confirmed by immunocytochemical staining with antibodies to tyrosine hydroxylase (TH) and by quantification of the high affinity dopamine uptake complex using [3H]GBR 12935 binding. Enhanced TH fiber immunostaining was evident even in the presence of poor cograft survival. The origin of the TH-like immunostained fibers in the striatum was determined using Lucifer yellow retrograde axonal transport. Following discrete tracer injections into the striatum adjacent to a cograft, neurons in the medial substantia nigra and ventral tegmental area (areas A9 and A10, respectively) were labeled with Lucifer yellow. These labelled neurons displayed a morphology characteristic of dopamine neurons and, in double-labelling experiments, also immunostained for TH. These results support the utility of unilateral partially lesioned rat models of Parkinson's disease for studies investigating a host sprouting or upregulation response and confirm that the immunostained striatal fibers originate from spared dopamine neurons in the ventromedial midbrain.

Adrenal medulla in neural grafting and neural plasticity

The recent history of neural transplantation using the adrenal medulla parallels an evolution in our thinking about neural grafting as a therapeutic approach to treat neurodegenerative diseases such as Parkinson's disease. Initially, neural grafting was an approach to study development and regeneration. With the discovery that adrenal chromaffin cell grafts would ameliorate some of the motor deficits associated with the loss of striatal dopamine, adrenal grafts were used to provide dopamine to the dopamine-depleted striatum. However, subsequent studies showed poor chromaffin cell survival unless trophic factors were present at the site of transplantation. These experiments lead to the appreciation of the complex interactions between neurotrophic factors, inflammatory cytokines, the grafted tissue, and the host brain's response. Thus, we find ourselves again using neural transplantation as an approach to help us better understand central nervous system plasticity and the features this plasticity shares in common with development and regeneration.

Disruption of the blood-brain barrier as the primary effect of CNS irradiation

The blood-brain barrier (BBB) is believed to be unique in organ microcirculation due to the 'tight junctions' which exist between endothelial cells and, some argue, the additional functional components represented by the perivascular boundary of neuroglial cells; these selectively exclude proteins and drugs from the brain parenchyma. This study was designed to examine the effects of irradiation on the BBB and determine the impact of the altered pathophysiology on the production of central nervous system (CNS) late effects such as demyelination, gliosis and necrosis. Rats, irradiated at 60 Gy, were serially sacrificed at 2, 6, 12 and 24 weeks. Magnetic resonance image analysis (MRI) was obtained prior to sacrifice with selected animals from each group. The remaining animals underwent horse-radish peroxidase (HRP) perfusion at the time of sacrifice. The serial studies showed a detectable disruption of the BBB at 2 weeks post-irradiation and this was manifested as discrete leakage; late injury seen at 24 weeks indicated diffuse vasculature leakage, severe loss of the capillary network, cortical atrophy and white matter necrosis. Reversal or repair of radiation injury was seen between 6 and 12 weeks, indicating a bimodal peak in events. Blood-brain barrier disruption is an early, readily recognizable pathophysiological event occurring after radiation injury, is detectable in vivo/in vitro by MRI and HRP studies, and appears to precede white matter necrosis. Dose response studies over a wide range of doses, utilizing both external and interstitial irradiation, are in progress along with correlative histopathologic and ultrastructural studies.

The use of genetically altered astrocytes to provide nerve growth factor to adrenal chromaffin cells grafted into the striatum

Transplantation of adrenal chromaffin cells into the striatum of Parkinson's disease patients is unlikely to become a reliable therapy unless techniques are devised to improve cell survival. To address this issue, we investigated the use of genetically altered astrocytes that constitutively secrete beta-nerve growth factor (NGF) to provide trophic support for adrenal chromaffin cells grafted into the dopamine-denervated striatum of the rat. Primary rat astrocytes were altered genetically in vitro by infection with a retroviral vector harboring a mouse beta-NGF transgene under constitutive long terminal repeat transcriptional control. Confluent cultures of these genetically altered astrocytes secrete NGF into their culture medium at a rate of approximately 9 pg/10(5) cells/h. This rate of NGF secretion is at least 10-fold higher than that of confluent sister cultures of uninfected astrocytes. The effects of the NGF-secreting astrocytes on the survival and neuronal transformation of dissociated adrenal chromaffin cells were assessed in vitro and following transplantation into the dopamine-denervated striatum of the adult rat. In vitro experiments demonstrated that neuritic outgrowth is stimulated when postnatal day 12 chromaffin cells are grown on a monolayer of the genetically altered astrocytes. When co-grafted with genetically altered astrocytes, young postnatal chromaffin cells displayed extensive neuritic outgrowth within the host brain 2 weeks postimplantation, whereas chromaffin cells grafted alone or with normal astrocytes retain an endocrine-like morphology. Survival of the chromaffin cells is also enhanced 3-6-fold when co-grafted with the genetically altered astrocytes. In addition, the neuronally transformed chromaffin cells appear to lose adrenergic properties as assessed by diminished immunoreactivity to the adrenergic marker, phenylethanolamine-N-methyltransferase. Although their survival is also enhanced approximately 4-fold relative to controls, adult chromaffin cells do not convert to a neuronal morphology when co-grafted with the genetically altered astrocytes. These studies demonstrate that rat astrocytes carrying a mouse NGF transgene provide trophic support for intrastriatal chromaffin cell grafts.

NGF-like trophic support from peripheral nerve for grafted rhesus adrenal chromaffin cells

Autopsy results on patients and corresponding studies in nonhuman primates have revealed that autografts of adrenal medulla into the striatum, used as a treatment for Parkinson's disease, do not survive well. Because adrenal chromaffin cell viability may be limited by the low levels of available nerve growth factor (NGF) in the striatum, the present study was conducted to determine if transected peripheral nerve segments could provide sufficient levels of NGF to enhance chromaffin cell survival in vitro and in vivo. Aged female rhesus monkeys, rendered hemiparkinsonian by the drug MPTP (n-methyl-4-phenyl-1,2,3,6 tetrahydropyridine), received autografts into the striatum using a stereotactic approach, of either sural nerve or adrenal medulla, or cografts of adrenal medulla and sural nerve (three animals in each group). Cell cultures were established from tissue not used in the grafts. Adrenal chromaffin cells either cocultured with sural nerve segments or exposed to exogenous NGF differentiated into a neuronal phenotype. Chromaffin cell survival, when cografted with sural nerve into the striatum, was enhanced four- to eightfold from between 8000 and 18,000 surviving cells in grafts of adrenal tissue only up to 67,000 surviving chromaffin cells in cografts. In grafts of adrenal tissue only, the implant site consisted of an inflammatory focus. Surviving chromaffin cells, which could be identified by both chromogranin A and tyrosine hydroxylase staining, retained their endocrine phenotype. Cografted chromaffin cells exhibited multipolar neuritic processes and numerous chromaffin granules, and were also immunoreactive for tyrosine hydroxylase and chromogranin A. Blood vessels within the graft were fenestrated, indicating that the blood-brain barrier was not intact. Additionally, cografted chromaffin cells were observed in a postsynaptic relationship with axon terminals from an undetermined but presumably a host origin.

Cografts of adrenal medulla with C6 glioma cells in rats with 6-hydroxydopamine-induced lesions

Amitotic [3H]thymidine-labeled C6 glioma cells, which are known to produce neurotrophic factor(s), were grafted alone and with adrenal chromaffin cells in an attempt to improve chromaffin cell survival and phenotypic differentiation. Long-Evans rats with unilateral 6-hydroxydopamine-induced lesions of the nigrostriatal pathway were divided into four groups: (1) those receiving adrenal medullary cells co-transplanted with C6 glioma cells; (2) those receiving adrenal medullary graft alone; (3) those receiving C6 glioma grafts alone; and (4) those serving as a vehicle control group. All rats were killed one month after transplantation. Immunohistochemical, neurochemical, and autoradiographic methods were used to identify and characterize the grafted cells. Tyrosine hydroxylase-immunoreactive cells were found in all animals that received grafts of the adrenal medulla alone or of adrenal medulla co-transplanted with C6 glioma cells. The cograft recipients had more tyrosine hydroxylase-immunoreactive cells than the hosts receiving just adrenal chromaffin cells (P less than 0.05). Additionally, more grafted chromaffin cells formed processes in the former group. All three tissue recipient groups (adrenal medullary, C6 glioma cell, and cografted animals) had a significant reduction (P less than 0.05) in ipsilateral rotations after amphetamine (0.5 mg/kg i.p.) injections as compared to the control vehicle recipient group. Moreover, the reduction in rotation was more marked in the cografted hosts than in the other two implanted groups (P less than 0.05). Significantly higher dopamine levels were found in the transplant sites of both cograft and adrenal medullary graft recipients than in sham grafted control animals.

Effects of NGF and dibutyryl cAMP on neuronal differentiation of embryonal carcinoma cells

The P19S18O1A1 embryonal carcinoma cell line is capable of neuronal differentiation and is therefore useful in studying neuronal development and the influence of growth modulators on neuronal differentiation. We report here on the effects of nerve growth factor (NGF) and dibutyryl cyclic adenosine monophosphate (db cAMP), individually and combined, on differentiation of P19S18O1A1 cells. NGF alone did not induce any significant neuron-like changes in cultures exposed to NGF for as long as 12 days. Treatment with db cAMP resulted in changes in a significant population of the cells, including development of a neuron-like morphology, seen at both the light and electron microscopic level, loss of stage-specific embryonic antigen expression and the appearance of two neuronal markers, neurofilament protein and neuron-specific enolase. These changes were similar to changes seen when embryonal carcinoma (EC) cells are treated with retinoic acid. NGF in combination with dibutyryl cyclic adenosine monophosphate brought about similar changes as dibutyryl cyclic adenosine monophosphate alone, and was therefore not synergistic for induction of neuronal properties. In retinoic acid-treated cultures, the neuron-like cells had ultrastructural features very similar to neurons in non-tumorous, normal tissue, with typical organelles, such as one nucleolus, neurotubules and neurofilaments, while db cAMP-treated EC cells showed similar findings at the electronmicroscopic level. The results suggest that db cAMP can induce the neuronal phenotype in EC cells alone without pre-treatment with retinoic acid.

Fetal research

This article reviews some of the significant contributions of fetal research and fetal tissue research over the past 20 years. The benefits of fetal research include the development of vaccines, advances in prenatal diagnosis, detection of malformations, assessment of safe and effective medications, and the development of in utero surgical therapies. Fetal tissue research benefits vaccine development, assessment of risk factors and toxicity levels in drug production, development of cell lines, and provides a source of fetal cells for ongoing transplantation trials. Together, fetal research and fetal tissue research offer tremendous potential for the treatment of the fetus, neonate, and adult.

Adrenal chromaffin cells as transplants in animal models of Parkinson's disease

The field of neural transplantation has moved rapidly forward in the last decade. Initially, fetal cells were used as implants to investigate their potential to ameliorate deficits in animal models of Parkinson's disease. However, because of the moral and legal problems associated with the use of fetal tissues in humans, alternative sources of donor tissue were sought which possessed the structural and functional characteristics needed to improve motor function in Parkinsonian patients. To date, one of the most promising tissues being investigated is the adrenal medulla, whose chromaffin cells possess an inherent plasticity of form and function. Transplanted chromaffin cells currently are being studied by a variety of approaches, including electron microscopy, in mouse, rat, and primate models of Parkinson's disease. An overview of the role of the chromaffin cell in this exciting and clinically important arena is briefly reviewed, with an emphasis on the fine structure of implanted chromaffin cells.

Rodent and primate adrenal medullary cells in vitro: phenotypic plasticity in response to coculture with C6 glioma cells or NGF

In order to maintain a chronic supply of growth factor for medulla cells in vitro, chromaffin cells from rat, African green monkeys and man were co-cultured with C6 glioma cells, which secrete growth factors that sustain sympathetic neurons in vitro. The response of chromaffin cells to coculture was compared to treatment of medullary cells with nerve growth factor (NGF) alone. Dispersed chromaffin cell preparations were obtained by a trypsin-collagenase procedure, and subjected to differential plating on collagen-coated surfaces. With both human and monkey tissue, non-chromaffin cells did attach to the culture plates and an enriched chromaffin cell population could be replated. Rat adrenal medulla cells survived very poorly in vitro and were not enriched in this procedure. Cultured human and monkey chromaffin cells survived as epithelial cells (50%) and showed neuritic outgrowth on 55 to 66% of the cells after eight days when treated with nerve growth factor (NGF). These cells showed strong catecholamine histofluorescence, tyrosine hydroxylase (TH) and dopamine beta hydroxylase (DBH) immunoreactivity. In contrast, only ten percent of adult rat chromaffin cells survived in culture, although NGF treatment rescued an additional 20% of the cells and induced neuritic outgrowth after one week in vitro. C6 glioma cells were treated with mitomycin C bromodeoxyuridine to inhibit mitosis and were plated with the various medulla cells in a one to one ratio. Both human and monkey chromaffin cells expressed extensive and enhanced neuritic arborization within eight days of co-culture, (64-82% respectively) and exhibited intimate contact with the glioma cells as seen at the ultrastructural level. Importantly, survival of adult rat adrenal medulla cells was enhanced to 50% or more with 40% of the cells extending neurites when co-cultured with glioma cells for seven days. Chromaffin cells from all three species reacted for TH, DBH and PNMT in co-culture and were histo-fluorescent. The majority of these cells were also immunoreactive for serotonin and enkephalin, while only 37% of chromaffin cells indicated the presence of NPY. These data indicate that adrenal medulla can be maintained in vitro as the neuronal phenotype when co-cultured with growth factor producing cells and that this strategy may be useful for in vivo transplantation studies.

Organization, fine structure, and viability of the human adrenal medulla: considerations for neural transplantation

Recent reports of adrenal medullary autografts in patients with Parkinson's disease raise several important questions with respect to the cell types actually being transplanted as well as the potential for chromaffin cell banking prior to neural transplantation. In this study, we determined the general morphological characteristics of the human adrenal medulla and assessed factors important for the maintenance of cultured chromaffin cells for later use as transplants. The human adrenal medulla contained islands of cortical cells scattered throughout the gland as well as Schwann cells, nerve endings, endothelial cells, pericytes, isolated ganglionic neurons, and connective tissue elements such as fibroblasts and smooth muscle cells. Because many of these cell types are mitotically active, transplantation of medullary fragments that contain these cells could have far-reaching consequences. One approach that could circumvent the problems arising from multiple cell types in the medulla is differential plating of chromaffin cells prior to transplantation. Differential plating yielded relatively pure populations of chromaffin cells that demonstrated excellent viability if processed within 2 hours after cessation of the gland's circulation. Chromaffin cells cultured in the presence of nerve growth factor exhibited a neuronal phenotype, possessed catecholamine histofluorescence, and displayed tyrosine hydroxylase- and dopamine beta-hydroxylase-like immunoreactivity. The sex and age of the donor did not affect cell viability or morphological characteristics.

Adrenal medullary autografts into the basal ganglia of Cebus monkeys: graft viability and fine structure

Based largely upon studies done in rats, a number of medical centers are now performing autografts of adrenal medullary tissue in consenting patients with Parkinson's disease. However, a systematic experimental evaluation of adrenal medullary autografts in nonhuman primates is necessary. This study provides a detailed analysis of the implant site at the fine structural level 30 days post-transplantation in the Cebus monkey. Five normal and two 1-methyl-4-phenyl-1,2,5,6-tetrahydropyridine (MPTP)-treated Cebus monkeys received adrenal medullary autografts using an open microsurgical approach (n = 3) or via stereotactic placement with a tissue carrier (n = 4). Analysis of preimplant samples of the adrenal medulla confirmed that viable chromaffin cells were implanted into the basal ganglia. However, 30 days later, the implant site resembled a chronic inflammatory focus, with grafted chromaffin cells identified ultrastructurally in only two of the seven transplanted monkeys. The grafted cells showed overt signs of cellular degeneration and were surrounded by phagocytic macrophages. All of the implant sites, regardless of the surgical approach, were filled with macrophages, cells of hematogenous origin, and fibrous astrocytes. The vasculature of the implant site was of the nonfenestrated type, characteristic of the host striatum. Despite the poor survival of implanted chromaffin cells, robust sprouting of tyrosine hydroxylase-like immunoreactive fibers was evident in the striatum adjacent to the implant site (see accompanying manuscript, M.S. Fiandaca, J. H. Kordower, J.T. Hansen, S.-S. Jiao, and D.M. Gash, 1988, Exp. Neurol. 102: 76-91), suggesting that implantation may have precipitated a host response that was beneficial to the transplanted animal. Additional studies that provide a better understanding of the cellular elements residing in the implant site and their potential for trophic influence seem warranted.

Adrenal medullary autografts into the basal ganglia of Cebus monkeys: injury-induced regeneration

Questions arising from recent clinical neural transplantation trials in Parkinson's disease have under-scored the necessity for a thorough experimental evaluation of the structural and functional consequences of this procedure. The present study investigated the neuroanatomical host reaction to intrastriatal implants in normal and 1-methyl-4-phenyl-1,2,5,6-tetrahydropyridine (MPTP)-treated nonhuman primates. Nine monkeys (Cebus apella) received intrastriatal implants using either a stereotactic approach with a silver tissue carrier or an open microsurgical procedure. Seven of these animals received intrastriatal adrenal medullary autografts, while two received control implants consisting of the tissue carrier alone. One month following transplantation, the hosts' brains were evaluated via immunohistochemical and routine histologic methods. In both MPTP-treated and normal monkeys, enhanced ipsilateral expression of tyrosine hydroxylase-like immunoreactive (TH-IR) fibers in the caudate nucleus was observed, despite minimal survival of adrenal chromaffin cells in the implants. The intensity of this response was greatest adjacent to the implant site, but a clearly increased degree of ipsilateral striatal fiber staining also could be seen several millimeters from the graft. TH-IR fibers also were more dense and of thicker caliber throughout the nigrostriatal and mesolimbic pathways ipsilateral to the implant. Control stereotactic implants, consisting of a silver tissue carrier alone, produced a similar enhancement of immunoreactive fibers, suggesting an induction of TH-IR fibers by the parenchymal injury produced during surgical implantation. There are two major hypotheses proposed to explain why adrenal medullary grafts may promote functional recovery in human parkinsonism: (1) replacement of lost striatal neurotransmitter (dopamine) by the viable grafted tissue, or (2) induction of recovery of remaining host dopaminergic systems by the implantation procedure. Our current data appear to support the latter.

Comparison of adrenal medullary, carotid body and PC12 cell grafts in 6-OHDA lesioned rats

The survival and functional properties of dispersed cell implants of catecholaminergic cells obtained from the peripheral nervous system of adult rats (adrenal medulla and carotid body glomus cells) and PC12 cells from a rat pheochromocytoma cell line were examined following transplantation into the striatum of the adult rat. The host animals, all with unilateral 6-hydroxydopamine (6-OHDA) nigrostriatal lesions, were divided into 5 groups: (1) PC12 cells transplanted into Cyclosporin-A treated hosts; (2) PC12 cell grafts into hosts without Cyclosporin-A treatment; (3) grafts of adrenal medullary cells; (4) grafts of glomus cells; and (5) vehicle controls. All animals were sacrificed one month after transplantation. Immunocytochemical staining for tyrosine hydroxylase, the rate-limiting enzyme for catecholamine synthesis, was used to identify and characterize the grafted cells. PC12 cells were detected in four of six Cyclosporin-A treated rats, and two of these grafts developed into tumors. However, only one of the six non-Cyclosporin-A treated hosts was found to have surviving PC12 cells, and none of these rats developed tumors. No significant differences in rotational behavior were seen in either of the PC12 cell recipient groups. Grafted cells could be identified in all of the adrenal medullary and glomus cell recipients. However, the number of surviving cells was quite limited, with not more than 100 tyrosine hydroxylase-positive grafted cells found in any one recipient. Tyrosine hydroxylase-positive fibers were present adjacent to the transplants in these latter graft recipients, but the fibers appeared to be of host origin rather than from the grafts.(ABSTRACT TRUNCATED AT 250 WORDS)

Morphology of the carotid sinus wall in normotensive and spontaneously hypertensive rats

The morphology of the carotid sinus region of the internal carotid artery was studied in spontaneously hypertensive rats (SHR) at 5, 8, 16, and 24 weeks of age. The carotid sinus region occupied the proximal millimeter of the internal carotid artery, and was easily recognizable by the presence of an extensive adventitial capillary plexus, which was absent on adjacent arteries (e.g., common and external carotid arteries). Methylene blue-stained whole-mount preparations showed the extent of baroreceptor nerves over the sinus. Baroreceptor fibers terminated in distinctive bulbous-like endings, which, at the ultrastructural level, were filled with mitochondria. No differences were noted in the sinus adventitial capillary network or baroreceptor distribution between SHR and age-matched Wistar-Kyoto (WKY) normotensive control animals. With the onset of a significant rise in SHR blood pressure, the carotid sinus wall increased in thickness and total vessel size. The wall/lumen ratios were significantly larger in the SHR than in age-matched WKY ratios in all age groups. SHR carotid sinus vessel enlargement was uniform throughout the vessel tunics, with no significant change in the proportion of the tunica media occupied by smooth muscle cells. The increase in the carotid sinus wall thickness associated with increasing hypertension could affect the ability of the sinus to distend and may play a secondary role in the maintenance of hypertension by compromising baroreceptor nerve ending sensitivity.

Effects of salt loading on the fractional volume of atria-specific granules in Dahl salt-sensitive and salt-resistant rats

The cardiac atria are known to play a role in blood volume homeostasis, secreting a peptide that induces a potent natriuresis and diuresis. This peptide is atrial natriuretic factor (ANF), and its primary site of storage is within atria-specific granules found in atrial cardiocytes. Since salt loading results in an increase in circulating levels of ANF, our aim was to determine if the atria-specific granule population in the cardiocytes of Dahl rats would decrease accordingly. To this end, the fractional volume of the atria-specific granules was determined by ultrastructural morphometric analysis in the Dahl salt model of hypertension. This analysis was performed on the right atria of Dahl Salt-resistant (DR) and salt-sensitive (DS) rats fed either a low-salt (0.4%) or high-salt (8%) diet for 12 weeks prior to sacrifice. DR and DS rats fed a low-salt diet had significantly reduced plasma sodium levels and osmolalities, and a significantly lower mean arterial blood pressure than did rats fed a high-salt diet. The fractional volume of atria-specific granules was significantly lower in salt-loaded DR (P less than 0.01) and DS (P less than 0.025) rats than in their respective low-salt controls. This significant decrease in atrial granules corresponds to the reported decrease in the storage of atrial ANF in salt-loaded rats, and provides a morphological verification of the biochemical studies. Moreover, these results, in combination with a growing body of physiological data, lend support to the hypothesized role of ANF in the regulation of water-electrolyte balance, which may play an important role in cardiovascular pathophysiological states related to hypertension.

Evidence that dopamine regulates norepinephrine synthesis in the rat superior cervical ganglion during hypoxic stress

Electrical stimulation of preganglionic nerves is known to increase norepinephrine synthesis in the rat superior cervical ganglion in vitro, an effect which appears to be partially regulated by a non-cholinergic transmitter. In the present study, we sought to determine whether sympathetic stimulation also increases norepinephrine synthesis in the rat ganglion in vivo, and whether dopamine released from ganglionic interneurons might regulate this response. To tackle these questions, rats were pretreated with spiroperidol, a selective dopamine-receptor blocker, and then were sympathetically stimulated by exposure to severe hypoxic stress. Other rats were pretreated with vehicle alone before the hypoxic exposure. Norepinephrine synthesis in ganglia was assessed by measuring endogenous tyrosine hydroxylase activity and norepinephrine turnover. We found that hypoxic stress increased both of these indices of norepinephrine synthesis, but only in rats pretreated with spiroperidol. No such response was detected in rats pretreated with vehicle. These results indicate that sympathetic stimulation increases norepinephrine synthesis in the rat superior cervical ganglion in vivo, and that dopamine released from interneurons might regulate this response.

Substance P-like immunoreactivity in rat and cat carotid bodies: light and electron microscopic studies

Substance P-immunoreactive (SP-1) structures in the carotid bodies of rats and cats were examined with the light and electron microscopes. In both species SP-I varicose nerve fibers were located singly in the interstitial connective tissue in close association with blood vessels. They were small unmyelinated fibers enveloped in a common Schwann cell sheath with other SP-negative fibers. Some of SP-I fibers contained large dense-cored granules and small clear vesicles in addition to microtubules and mitochondria and probably represented nerve fiber varicosities. The latter often were found incompletely invested by Schwann cell sheaths. SP-fibers were found occasionally in the envelopes of supporting cells at the periphery of parenchymal cell groups. However, none of the nerve terminals making synaptic contacts with glomus cells exhibited SP-like immunoreactivity. In cat carotid bodies some glomus cells showed moderate to intense SP-like immunoreactivity. The intense SP-I glomus cells displayed numerous dense-cored vesicles of 85 to 140 nm in diameter and frequently showed synaptic contacts with SP-negative nerve terminals. In rat carotid bodies we were unable to detect consistent SP-immunoreactivity in glomus cells. Our results do not favor the hypothesis that SP is a neurotransmitter/modulator in the chemoreceptor afferents synapsing on glomus cells in either the cat or rat carotid body. However our results support the hypothesis that SP in cat glomus cells may play a role in the modulation of chemoreceptor activity.

Immunocytochemical staining of Histoplasma capsulatum at the electron microscopic level

Rabbits were immunized with histoplasmin emulsified in Freund's complete adjuvant. Antibody raised in these rabbits was exposed to Histoplasma capsulatum yeast cells, either in tissue culture medium, or after in vitro or in vivo phagocytosis by mouse macrophages. The sites of antibody binding were identified using an immunoperoxidase technique. At least two sites of antibody binding were identified, one to the fungal cell wall and the other to the outer cell membrane. Within 6 h after phagocytosis by macrophages, fungal cell walls appeared roughened, with what appeared to be cell wall antigen released into the phagolysosome, appearing associated with the phagolysosome membrane, and possibly adjacent macrophage cytoplasm. Similar staining of fungal antigen was noted in alveolar macrophages which had ingested Histoplasma capsulatum after a respiratory challenge. This method may be useful in detailing the host/pathogen interactions which occur in human pulmonary histoplasmosis.

Elemental concentration gradients between subcellular compartments

To gain information on the mechanisms involved in the establishment and maintenance of subcellular gradients of Na, K, Cl and other elements in the flagellate, Euglena gracilis, we turned to the technique of ultracentrifugal stratification of its intracellular contents, which is achieved without loss of viability or cell rupture. Stratified and non-stratified Euglena were cryofixed for energy-dispersive X-ray microanalysis of Na, K, Cl and other elements in thin freeze-dried cryosections. A number of significant elemental concentration differences (expressed as mmol kg-1 dry weight) were found between chloroplast, nucleus, paramylon granules and open cytoplasm (which contained ribosomes, membranes and macromolecules associated with the cytomatrix) in the non-stratified cells. Stratification caused several ions to be redistributed. For example, we observed a significant increase in K and Cl in the nucleus, which was correlated with the condensation of chromatin. Also Cl, but not Na, decreased significantly in the region of cytoplasm that was cleared of observable ribosomes, membranes and macromolecules associated with the cytomatrix, as well as of observable cytochemical enzyme activity. We conclude from the data that more than half of the Cl in open cytoplasm was adsorbed to or entrapped in material that was removed by ultracentrifugation. Thus, it appears that a close association of at least one ion, Cl, with ultracentrifugable material is involved in maintenance of the measured Cl concentration in the open cytoplasm of the non-stratified cell.

The effects of hypoxia on catecholamine dynamics in the rat carotid body

The catecholamine content of the rat carotid body was assayed using high performance liquid chromatography with electrochemical detection. The concentration of dopamine (DA) was found to predominate over that of norepinephrine (NE) by a small margin (31 pmol/carotid body pair DA; 23 pmol/carotid body pair NE). The turnover rates of carotid body DA and NE were determined from the time-dependent decline in their concentrations following the blockade of synthesis with alpha-methyl-p-tyrosine. Values were obtained (DA t 1/2 = 1.9 h; NE t 1/2 = 2.3 h) which suggested a rapid turnover of carotid body catecholamines. Exposure of rats to conditions of severe hypoxia (5% O2-95% N2) failed to significantly alter either the content or turnover of carotid body catecholamines. By contrast, the concentration of carotid body DOPAC, a reflection of DA utilization, was significantly elevated following hypoxic conditions. Further, in vivo tyrosine hydroxylase activity was assessed by measuring the accumulation of carotid body DOPA after inhibiting L-aromatic amino acid decarboxylase with NSD-1015. Basal tyrosine hydroxylase activity (approximately 14-16 pmol/carotid body pair/h) also was significantly increased by acute hypoxic exposure. These results, in part, suggest that rat carotid body DA may act as a neurotransmitter whose synthesis and release are coupled to stimulus demand.

Ultrastructure of the primate carotid body: a morphometric study of the glomus cells and nerve endings in the monkey (Macaca fascicularis)

The carotid body of the monkey (Macaca fascicularis) was studied at both the light and electron microscopic levels in an effort to provide a detailed quantitative characterization of this chemoreceptor organ in the primate. Structurally, the monkey carotid body was organized into lobules of from three to eight glomus cells (in section) and their ensheathing supporting cells. Interspersed among the lobules was abundant connective tissue stroma, fibroblasts and mast cells. Fenestrated capillaries, small arterioles and venules also permeated the organ. Each supporting cell partially ensheathed about three glomus cells and could be easily differentiated from glomus cells by their darker cytoplasmic staining, lack of dense-core vesicles and angular nuclear profile. Glomus cells exhibited an intense catecholamine histofluorescence and contained abundant dense-core vesicles. On the basis of dense-core vesicle size, shape and numerical density, four types of glomus cells were identified. The most common type (62% of all glomus cells) contained vesicles with an average diameter of 219 nm and a density of 8 vesicles per micron 2 of cytoplasm. The second type possessed larger vesicles (264 nm in diameter) and accounted for about 14% of all glomus cells. A third type of glomus cell contained smaller (167 nm) and fewer (5 vesicles per micron2) dense-core vesicles. The fourth type of glomus cell contained pleomorphic-shaped vesicles with a maximal diameter of 232 nm. Each of these last two types accounted for about 12% of all glomus cells. All four types of glomus cells were innervated, averaging 1.43 nerve endings per glomus cell (in sections). Nerve endings were primarily of the bouton-like variety averaging 2 micron2 in sectional area and containing 34.3 clear-core synaptic vesicles (average size 73.5 nm in diameter) per micron2 of cytoplasm. Of the 57 nerve endings examined in single sections, 16% displayed junctions typical of synaptic specializations and most of these were presynaptic to glomus cells. Glomus cell-glomus cell synapses were not observed. Based on these quantitative observations and on previous studies of carotid body cytoarchitecture in other laboratory species, it appears that the primate organ most closely resembles the cat carotid body, although several differences exist.

Dopamine beta-hydroxylase-like immunoreactivity in the rat and cat carotid body: a light and electron microscopic study

Immunocytochemical localization of dopamine beta-hydroxylase (DBH) was used to study the synthesis and storage sites of norepinephrine (noradrenaline) in the rat and cat carotid bodies. In the rat carotid body some parenchymal cells exhibited strong DBH-like immunoreactivity (DBH-I), while others displayed only faint DBH-I. In a typical parenchymal cell cluster, most cells with strong DBH-I were irregular in shape and appeared to partially surround those with weak DBH-I which usually were rounded in contour. In the cat carotid body most parenchymal cells showed a strong to moderate DBH-I. In both the rat and cat carotid bodies varicose nerve fibres with DBH-I were associated primarily with blood vessels. All autonomic ganglion cells examined, which were associated with the rat carotid body, showed DBH-I. Electron microscopy revealed that most DBH-I in the strongly positive cells of the rat carotid body was associated with dense granules (possibly corresponding to dense-cored vesicles of various sizes), although some was found in other sites. In oval cells with less DBH-I, reactivity resided in some of the large granules. In the cat carotid body the glomus cells contained more granules of various sizes and shapes than did those of the rat carotid body. Most of the cat glomus cell granules exhibited DBH-I activity. Our results indicate that some of glomus cells in the rat and most of the glomus cells in the cat contain DBH and therefore may be sites of norepinephrine synthesis.

Cytochemical evidence for the existence of norepinephrine-containing glomus cells in the rat carotid body

Some investigators have postulated that glomus cells of the rat carotid body contain only dopamine (DA), and that the norepinephrine (NE) measured in the carotid body resides only in sympathetic nerve endings and ganglion cells. To investigate this hypothesis, we employed a pharmacologic drug sequence which depleted all carotid body catecholamines and then selectively restored DA levels while keeping NE levels significantly lowered. Analysis of carotid body catecholamines by high performance liquid chromatography (HPLC) validated this drug regimen. Employing this drug treatment, we examined glomus cells after potassium dichromate cytochemical staining in an effort to distinguish those glomus cell vesicles which still contained appreciable amounts of catecholamine, presumably DA. Glomus cells from rats receiving vehicle or L-dopa (100 mg kg-1 ip) alone had 83 and 97% of their cells stained, respectively. However, glomus cells from reserpinized (5 mg kg-1 ip) animals were largely unstained (89%). Carotid bodies from animals treated with reserpine and then, 24 h later, with L-dopa 90 min prior to sacrifice had about 46% of their glomus cells stained while 54% of the cells were unstained. The results of this last group, coupled with our biochemical data which demonstrated that DA levels were comparable to control values but that NE was 80% depleted, suggest that a significant number of glomus cells did not contain enough catecholamine to react with the dichromate. We believe that these unstained cells may normally contain NE and that glomus cells may be of several types, some containing predominantly DA and others NE.

Ultrastructure of the pineal gland of the brush mouse (Peromyscus boylei): influence of long and short photoperiod

The ultrastructure of the pineal gland of wild-captured brush mice (Peromyscus boylei) was examined. A homogeneous population of pinealocytes was present in the pineal gland of this species. The Golgi apparatus, granular endoplasmic reticulum, mitochondria, lysosomes, dense-core vesicles, vacuoles containing fluocculent material, clear vesicles, microtubules and glycogen particles were consistent components of the pinealocyte cytoplasm; infrequently-observed organelles included centrioles, "synaptic" ribbons, subsurface cisternae, multivesicular bodies, lipid droplets and annulate lamellae-like structures. Quantitative comparison of pinealocyte ultrastructure revealed larger cross-sectional areas of cytoplasma, nucleus, Golgi apparatus, granular endoplasmic reticulum, mitochondria and vacuoles containing flocculent material as well as higher number of dense-core vesicles in the animals kept in short photoperiod (LD 8 : 16) as compared to those in animals kept in long photoperiod (LD 16 : 8). These observations suggest that restricting the amount of light to which animals are exposed activated the pinealocytes of brush mice.

Inclusion bodies in pinealocytes of the cotton rat (Sigmodon hispidus). An ultrastructural study and X-ray microanalysis

Pinealocytes of the cotton rat (Sigmodon hispidus) often contain large (2-6 micron diameter) intracytoplasmic inclusions, the function of which is not known. These inclusions may represent nucleolus-like bodies, mineral deposits, secretory products or viral inclusions. In this study these inclusions were classified as type A, B or C inclusions based on the amount of electron-dense material interspersed within the finely granular material comprising the bulk of these inclusions. Each type of inclusion was analyzed by X-ray microanalysis and enzymatic proteinaceous digestion. X-ray microanalysis of these inclusions differed both quantitatively and semiquantitatively from that of human or gerbil pineal concretions, the latter two of which are extracellular deposits. Pronase, a proteolytic enzyme, digested the electron-dense material only after longer times of tissue exposure to this enzyme in contrast to the easily digested, finely granular matrix-like material of these inclusions. Such intrapinealocytic inclusions have only been observed in the cotton rat. Their functional significance remains unknown.

Effect of superior cervical ganglionectomy on the ultrastructure of the pinealocyte in the cotton rat (Sigmodon hispidus)

The ultrastructure of pinealocytes was examined morphometrically in superior cervical ganglionectomized and sham-operated cotton rats. Following denervation, the pinealocytes decreased in size. Reduced areas of the nucleoli, Golgi apparatus, granular endoplasmic reticulum, mitochondria, and vacuoles containing a flocculent material as well as a decreased number of dense-core vesicles were noted. In contrast, the numbers of "synaptic" ribbons and ribbon fields increased. The nature of ultrastructural changes observed in the cotton rat pinealocyte after sympathectomy may indicate a diminution of the presumptive secretory processes of this cell. The presence of a small number of myelinated and unmyelinated axons in the pineal gland of the cotton rat following superior cervical ganglionectomy suggests that the sympathetic nerve fibers from the superior cervical ganglia do not comprise the only source of innervation to the pineal. Additionally, the presence of striated muscle fibers has been observed in the present study in the pineal gland of the cotton rat which heretofore has not been reported in this species.

Inverse correlation between "synaptic" ribbon number and the density of adrenergic nerve endings in the pineal gland of various mammals

The number of "synaptic" ribbons was inversely correlated with the density of the adrenergic nerve endings of the pineal gland compared among a diverse group of species including the fox, cat, rat, cotton rat, white-footed mouse, Djungarian hamster, ground squirrel, and chipmunk. The concentration of norepinephrine paralleled the number of adrenergic nerve terminals in the pineal glands of the cotton rat, rat, and ground squirrel, the only species in which norepinephrine concentrations were measured. The number of ribbon fields paralleled numbers of "synaptic" ribbons in all species examined. Adrenergic nerve endings were observed primarily within the perivascular spaces, although some endings also were found among parenchymal cells. Adrenergic nerve endings forming synaptic junctions with pinealocytes were not observed in any of these species, nor was there any physical association between these nerve endings and "synaptic" ribbons.

Effects of advancing age on the ultrastructure of pinealocytes in the male white-footed mouse (Peromyscus leucopus)

Quantitative comparison of pinealocyte ultrastructure in 3-month-old and 28-month-old male white-footed mice (Peromyscus leucopus) revealed decreases both in the area of the Golgi apparatus and in the number of dense-core vesicles. In contrast, no differences between these two age groups were noted in the areas of granular endoplasmic reticulum, vacuoles with flocculent content, lysosome-like bodies, or mitochondria. Nor were any changes between groups of mice apparent in pinealocyte nuclear or cytoplasmic areas, nuclear: cytoplasmic ratios, or the number of pinealocyte nuclei per unit area. Areas of unusual, annulate lamellae-like structures were increased in the pinealocytes of a group of 28-month-old mice. These observations suggest a possible age-associated decrease in the neurosecretory-like (but not ependymal-like) secretory process in the pinealocyte of white-footed mice.

Ultrastructure of pinealocytes of the kangaroo rat (Dipodomys ordi)

The ultrastructure of the pinealocytes of the wild-captured ord kangaroo rat (Dipodomys ordi) was examined. A homogeneous population of pinealocytes was present in the pineal gland of the kangaroo rat. The Golgi apparatus, granular endoplasmic reticulum, mitochondria, lysosomes, dense-core vesicles, vacuoles containing a flocculent material and lipid droplets were consistent components of the pinealocyte cytoplasm, whereas infrequently-observed organelles included centrioles, multivesicular bodies, subsurface cisternae, "synaptic" ribbons and cilia. The number of dense-core vesicles was relatively high and dense-core vesicles and vacuoles containing a flocculent material were present in the same cell. Although it has been recently suggested that two different secretory processes, i.e., neurosecretory-like (Golgi apparatus - dense-core vesicles) and ependymal-like (granular endoplasmic reticulum - vacuoles containing a flocculent material) may be involved in different regulatory mechanisms in the pinealocytes, the definitive answer to this is still far from clear. Therefore, the pineal gland of the kangaroo rat appears to be a good model for the study of the potential relationship between these two secretory processes, especially in respect to seasonal changes.

Localization of enkephalin-like immunoreactivity in the cat carotid and aortic body chemoreceptors

The purpose of this study was to determine if enkephalin-like immunoreactivity was present in the glomus cells of the carotid and aortic body peripheral arterial chemoreceptors. Cat carotid and aortic bodies were reacted with antisera to met- and leu-enkephalin using the indirect peroxidase-antiperoxidase immunocytochemical method of Sternberger (1979). Both the carotid and aortic bodies demonstrated clusters of immunoreactive cells for both met- and leu-enkephalin. Additionally, met-enkephalin-like immunoreactivity was observed in many of the dense-core vesicles of the glomus cells of the carotid body. The glomus cells of these chemoreceptors are known to contain catecholamines which may modulate chemoreceptor activity. The presence of opioid peptide-like substances co-existing with the glomus cell catecholamines, perhaps in the same vesicles, may have important implications for a trophic influence of these peptides on glomus cell chemoreceptor modulation.

Ultrastructure of the pineal gland of the eastern chipmunk (Tamias striatus)

The ultrastructure of the pineal gland of the wild-captured eastern chipmunk (Tamias striatus) was examined. A homogenous population of pinealocytes was the characteristic cellular element of the chipmunk pineal gland. Often, pinealocytes showed a folliclelike arrangement. Mitochondria, Golgi apparatus, granular endoplasmic reticulum, lysosomes, centrioles, dense-core vesicles, clear vesicles, glycogen particles, and microtubules were consistent components of the pinealocyte cytoplasm. The extraordinary ultrastructural feature of the chipmunk pinealocyte was the presence of extremely large numbers of "synaptic" ribbons. The number of "synaptic" ribbons in this species exceeded by a factor of five to 30 times that found in any species previously reported. In addition to pinealocytes, the pineal parenchyma contained glial cells (oligodendrocytes and fibrous astrocytes). Capillaries of the pineal gland of the chipmunk consisted of a fenestrated endothelium. Adrenergic nerve terminals were relatively sparse.

Effects of hereditary hypopituitarism and ectopic pituitary transplants on pinealocytes of the mouse: a quantitative ultrastructural study

The ultrastructure of the pinealocytes of Snell dwarf mice (dw/dw) was examined morphometrically and compared with that of both phenotypically normal (dw/+ or +/+) animals of the same strain and dwarf mice with ectopic pituitary grafts. Ultrastructural features characteristic of diminished activity of the pinealocytes were observed in dwarf mice as compared with controls. Ectopic pituitary grafts induced morphological signs of activation of the pinealocytes in this mutant. The results of the present study demonstrate the influence of the adenohypophysis on the pineal gland and these data, together with the known influence of the pineal gland on the adenohypophysis, support the existence of a reciprocal relationship between these two glands.