Catecholamine-containing neurons and lymphoid cells in a lacrimal gland of the pigeon

The symbiotic magnetic-sensing hypothesis: do Magnetotactic Bacteria underlie the magnetic sensing capability of animals?

The ability to sense Earth's magnetic field has evolved in various taxa. However, despite great efforts to find the 'magnetic-sensor' in vertebrates, the results of these scientific efforts remain inconclusive. A few decades ago, it was found that bacteria, known as magnetotactic bacteria (MTB), can move along a magnetic field using nanometric chain-like structures. Still, it is not fully clear why these bacteria evolved to have this capacity. Thus, while for MTB the 'magnetic-sensor' is known but the adaptive value is still under debate, for metazoa it is the other way around. In the absence of convincing evidence for any 'magnetic-sensor' in metazoan species sensitive to Earth's magnetic field, we hypothesize that a mutualism between these species and MTB provides one. In this relationship the host benefits from a magnetotactic capacity, while the bacteria benefit a hosting environment and dispersal. We provide support for this hypothesis using existing literature, demonstrating that by placing the MTB as the 'magnetic-sensor', previously contradictory results are now in agreement. We also propose plausible mechanisms and ways to test the hypothesis. If proven correct, this hypothesis would shed light on the forces driving both animal and bacteria magnetotactic abilities.

Cholinergic modulation of immunoglobulin secretion from avian plasma cells: the role of calcium

The existence of a functional connection between the nervous and immune systems has long been argued. To determine if such a link exists in the secretory immune system, we have examined the avian lacrimal gland (Harderian gland) which contains large numbers of plasma cells. We have shown that these plasma cells bind an antibody to muscarinic acetylcholine receptor and that carbachol, an acetylcholine agonist, increases the secretion rate of IgG by these cells above a constitutive baseline level. This neurotransmitter-dependent increase of immunoglobulin secretion requires an influx of Ca2+, whereas the constitutive baseline secretion is apparently less dependent on such a flux. Furthermore, the Ca2+ flux appears to be mediated by voltage-dependent calcium channels. These data support the hypothesis that plasma cells can respond to neurotransmitters and, in the case of acetylcholine, increase immunoglobulin secretion.

The Harderian gland of the rodent Octodon degus: a structural and ultrastructural study

Harderian glands from male and female Octodon degus were examined by light and transmission electron microscopy. Two types of secretory units, designated as type I and type II, were observed. Type I secretory units comprise three types of epithelial cells: Cells packed with numerous lipid droplets (Type a), cells with few lipid droplets (Type b), and cells with numerous mitochondria and a very well developed Golgi complex (Type c). Type II secretory units were found exclusively in female Octodon degus and comprised a type of secretory cells which contained numerous basophilic granules in their apical cytoplasm. In addition, in female Octodon degus, clusters of lymphocyte-like cells and plasmatic cells were also observed. The vascularization of the gland appeared very well developed. The most unique feature of the blood supply was the existence of large sinusoidal vessels extremely variable in shape. In the medullar region, the sinsoidal wall adapts its contour to that of the tubuloalveolar surface. Unmyelinated and myelinated nerve fibers were found in the connective stroma of the gland.

The effects of stress on splenic immune function are mediated by the splenic nerve

Intermittent footshock (FS) suppresses immune function of spleen cells. To determine if the autonomic nervous system mediates this immunosuppression in spleen cells, we tested whether cutting the splenic nerve, which depletes splenic norepinephrine levels by 98-100% and eliminates catecholamine fibers, blocks the effects of stress. Splenic nerve sections, sham operations, or no surgery were performed on male Sprague-Dawley rats. Ten days later, rats were injected with sheep red blood cells (SRBC). Three days later, rats were placed in a chamber equipped with a shock grid. Foot shock (1.6 mA) was administered for 5 s on a VI 3.5 min schedule for 60 min. Each FS was preceded by a 15-s warning tone. Controls were treated identically except for the FS. The next day spleen cells were harvested and the number of IgM plaque-forming cells (PFCs) determined. For the sham and unoperated control animals, the number of PFCs was reduced for the stressed animals relative to the nonstressed controls, and there was no effect of the sham surgeries. In contrast, there was no difference between the stressed and nonstressed groups in which the splenic nerve had been sectioned, and their PFC response was comparable to the controls. Next we examined the effects of FS on the proliferative response to mitogens (PHA and ConA) following splenic nerve sections or sham operations. One week following surgery, animals were given a 60-min session of FS or exposed to the chamber/tone without FS. Rats were then killed, spleens harvested, and the proliferative response to mitogens determined.(ABSTRACT TRUNCATED AT 250 WORDS)

Lymphoid cells in the harderian gland of the rodent Octodon degus

The Harderian gland of the degu (Octodon degus) is composed of tubulo-alveolar secretory units that share most of morphological features found in the Harderian glands of other rodents. However, a peculiar characteristic observed in the glands of female degus is the existence of lymphoid cell clusters within the connective tissue surrounding the secretory adenomeres. Lymphocytes and lymphoblasts are found associated with blood vessels and especially with nerve bundles in the medullary region of the gland. Occasionally, macrophages and plasma cells are also observed. Although the Golgi apparatus appears well developed, the ultrastructural characteristics of most of these lymphoid elements correspond to those of inactive lymphocytes. Unmyelinated fibers containing clear and dense-core vesicles are found closely related to lymphocytes. On some occasions, lymphocytes present extensive areas of apposition with structures resembling intercellular junctions. The analogy of the lymphoid clusters reported in this study with those described in the avian Harderian gland is discussed.

Absence of neural responses following suppression of the immune response by cyclophosphamide

Injection of sheep red blood cells (SRBC) as an antigenic stimulus, causes significant increases (up to 300%) in multiunit neural activity in the preoptic area/anterior hypothalamus of conscious rats. This increase occurs on the fifth or sixth day after immunization, at the time of first appearance of circulating antibodies at a serum titer of 1:32, increasing to 1:128 by day 10 following sensitization. Treatment with the immunosuppressive drug cyclophoshamide was able to prevent both antibody production and the expected increases in electrical activity in 5 of 6 rats; the one remaining animal showed a low level of circulating anti-SRBC antibodies on day 10 (1:32) and also, a small increase (36%) in neural activity at the expected time. These results provide further evidence that activation of the immune system is able to alter neuronal activity in an area of the brain important in the regulation of both neuroendocrine and neuroimmunomodulatory mechanisms, and that such activity is probably due to soluble secretory products released from components of the immune system.

Origin of noradrenergic innervation of the spleen in rats

Noradrenergic (NA) sympathetic innervation of the spleen was examined in young adult Sprague-Dawley rats (200-250 g) following surgical removal of the superior mesenteric-celiac ganglia (SM-CG) and/or bilateral transection of the subdiaphragmatic vagus nerve. Sham-operated and unoperated rats served as controls. NA sympathetic innervation of spleens from sham-operated and unoperated controls, and from vagotomized rats, was qualitatively similar, with fibers distributing to the capsule, trabeculae, vasculature, and parenchyma of the white pulp. Complete ganglionic extirpation resulted in almost total denervation of NA fibers in all compartments of the spleen. High-performance liquid chromatography with electrochemical detection (LCEC) for catecholamines (CA) and quantitative morphometry of the density of NA varicosities confirmed these observations. LCEC revealed a greater than 85% depletion of norepinephrine (NE) in the spleen following superior mesenteric-celiac ganglionectomy. Stereological evaluation of NA varicosities with a point counting method revealed a decline of 99% in the volume density of NA terminals that occurred uniformly in all compartments of spleens from ganglionectomized rats. In addition, stereological analysis revealed a loss of total NA varicosities (approximately 31% decrease) in spleens from sham-operated rats. This loss in volume density occurred largely due to a loss in parenchymal fibers (approximately 45% decrease). Bilateral subdiaphragmatic vagotomy blocked the effect on NA innervation produced by the surgical stress of sham operation. Retrograde tracing following injection of either fluorogold or true blue into the spleen, coupled with immunocytochemical localization of tyrosine hydroxylase (TH), demonstrated abundant fluorogold (true blue)-labeled neurons in the SM-CG; many, but not all, of these neurons also were TH-positive. These findings indicate that the SM-CG neurons supply NA innervation to the spleen, providing sympathetic innervation as the second neuron in the classical two-neuron sympathetic chain, and suggest additional non-NA innervation of the spleen as well. This study also suggests that surgical stress of sham operation may alter directly the NA innervation of the spleen, possibly by inducing temporary retraction of NA fibers of the parenchymal compartment, which is likely to reduce the availability of NE for interaction with cells of the immune system that possess adrenoceptors and are present adjacent to NA varicosities in this region.4+ Bilateral vagotomy ameliorated the effects of sham operation on NA innervation; since the vagal nerve does not distribute fibers to the spleen, this effect is likely to occur through altered feedback circuits effecting sympathetic outflow, or through altered neuroendocrine outflow.(ABSTRACT TRUNCATED AT 400 WORDS)

Neurophysiological and endocrine consequences of immune activity

The studies presented herein demonstrate the potency with which activity of the immune system is able to influence the central nervous system. Electrophysiological recordings have demonstrated significant changes in preoptic area/anterior hypothalamic (PO/AH) multiunit electrical activity (MUA) following sensitization with sheep red blood cells. The peak of activity occurred on the fifth day after immunization, the same day that serum antibodies were first detected. A significant increase in paraventricular nucleus MUA was also demonstrated, but this appeared to be delayed with respect to that in the PO/AH, occurring on the sixth day. Further changes thought to be associated with the immune response also were found: Serum corticosterone levels were elevated on the eighth day of the response, and PO/AH tissue levels of norepinephrine were reduced between the sixth and tenth days. During induction of a secondary response, PO/AH MUA showed a different profile of activity from that recorded during the first response. Chronic administration of the immunosuppressive drug, cyclophosphamide, prevented the recorded changes in PO/AH MUA. These results suggest that some secretory product(s) of the activated immune system may be able to exert effects on the central nervous system. Various immunoactive substances therefore were administered intra-cerebroventricularly in order to examine their effects upon PO/AH MUA, cortical EEG and adrenocortical hormone secretory activity. alpha-Interferon and thymic humoral factor were both found to decrease PO/AH MUA, increase EEG synchronization, and decrease basal levels of circulating corticosterone. In contrast, histamine and interleukin-1 did not alter PO/AH MUA but did cause decreased EEG synchronization and increased serum corticosterone levels. With another preparation, a specific activating effect of interleukin-1 upon putative corticotropin-releasing factor-secreting neurones has also been found, identified vasopressinergic neurones not being affected.

Alterations of monoamines in specific central autonomic nuclei following immunization in mice

At the peak of an immune response (Day 4 following immunization) in mice, norepinephrine (NE) was selectively decreased in the paraventricular nucleus (PVN) of the hypothalamus. At times before (Day 2) and after (Day 8) the peak immune response, no changes in NE were found in this nucleus. Decreases in NE were not seen in other hypothalamic sites or in the A1 cell group of the medulla, which sends noradrenergic projections to the hypothalamus, suggesting that the effect is selective and regional. Morphometric evaluation of varicosities revealed no alterations in density of catecholamine-containing varicosities in the PVN, further suggesting that the decrease in NE is a metabolic effect and not a loss or redistribution of fibers. NE also was decreased in the hippocampus on Day 2 at the rising phase of the immune response. In addition, alterations in serotonin levels were found in the brain during an immune response. Serotonin was decreased in the hippocampus on Day 2, was decreased in the PVN and supraoptic nucleus on Day 4, and was increased in the nucleus tractus solitarius (NTS) on Day 2. These results support the presence of a functional link from the activated immune system to central autonomic nuclei interconnecting the hypothalamus, the limbic system, and the autonomic nervous system. In view of the role of the PVN in corticotropin-releasing factor secretion and regulation of autonomic outflow, evidence from lesion studies for hippocampal involvement in immune regulation, and a key role for NTS in regulation of autonomic outflow, the present findings reinforce the potential importance of these brain regions in reciprocal communication between the nervous and immune systems.

Decreased sympathetic innervation of spleen in aged Fischer 344 rats

Splenic noradrenergic innervation in young adult and aged Fischer 344 rats was examined using fluorescence histochemistry for catecholamines and high performance liquid chromatography with electrochemical detection (LCEC) for the quantitation of norepinephrine (NE). In young adult rats, abundant noradrenergic plexuses followed the vasculature and trabeculae into splenic white pulp. In aged rats, noradrenergic innervation was reduced in density and in overall intensity of fluorescence, and splenic NE levels were significantly lower. The relationship between diminished noradrenergic innervation and diminished immune responsiveness in aging mammals, while not clear on a causal level, is presented as a hypothesis for further testing.

Noradrenergic sympathetic innervation of the spleen: IV. Morphometric analysis in adult and aged F344 rats

Noradrenergic postganglionic sympathetic innervation of the spleen in 8-month-old (adult) and 27-month-old (aged) Fischer 344 (F344) rats was examined using fluorescence histochemistry for catecholamines coupled with stereologic point-counting analysis for quantitation of noradrenergic varicosities. Noradrenergic varicosities in the spleen were evaluated in four compartments: (1) vascular-, (2) trabecular-, (3) capsular-, and (4) parenchymal-associated fibers. The 27-month-old rats were subdivided further into two groups based upon behavioral testing for gustatory neophobia, a condition reported to be associated with acute locus coeruleus lesions in young rats and with diminished norepinephrine (NE) levels in central noradrenergic neurons in aged rats. In the 8-month-old rats, spleens displayed abundant innervation. Noradrenergic plexuses entered the spleen with the splenic artery and its branches, distributed into capsular and trabecular compartments, and followed the vasculature and trabeculae into splenic white pulp. Noradrenergic fibers entered the white pulp mainly in association with the central artery and its branches; liner and punctate varicosities branched mainly from vascular plexuses into the large, well-defined parenchyma of the white pulp, ending primarily among fields of T lymphocytes. Some fibers extended along the inner edge of the marginal zone and the parafollicular zone. Few noradrenergic varicosities were found in the red pulp. In both groups of aged rats, sympathetic noradrenergic innervation was diminished markedly.(ABSTRACT TRUNCATED AT 250 WORDS)

Noradrenergic sympathetic innervation of the spleen: I. Nerve fibers associate with lymphocytes and macrophages in specific compartments of the splenic white pulp

Sympathetic noradrenergic nerve fibers, stained with antiserum for tyrosine hydroxylase (TH), richly innervate the splenic white pulp. These fibers distribute with the vascular and trabecular systems, and associate mainly with the central artery and its branches, the periarteriolar lymphatic sheath (PALS), the marginal sinus, and the parafollicular zone, with occasional delicate fibers also present in the follicles. Simultaneous staining of TH-positive nerve fibers and markers for specific lymphoid cells has shown several regions of contact between nerves and lymphocytes or macrophages. The TH-positive nerve fibers in the plexuses around the central arterial system and in the PALS are present among T lymphocytes (OX-19-positive cells) including both T helper and T suppressor cells, and interdigitating cells. At the marginal sinus, TH-positive fibers run adjacent to macrophages (ED3-positive cells), B lymphocytes (IgM-positive), and intensely fluorescent IgM-positive cells. Along the parafollicular zone, TH-positive nerve fibers run adjacent to T lymphocytes, peripheral follicular B lymphocytes, and intensely fluorescent IgM-positive cells. Within some follicles, delicate fibers end adjacent to both T and B lymphocytes. These relationships suggest a direct interaction between norepinephrine release from the TH-positive nerve terminals and the lymphocytes and macrophages closely associated with them, and focuses attention on the potential neural modulation of related functions such as T and B lymphocyte entry into the spleen and antigen capture (marginal zone), antigen presentation and T cell activation (PALS), B cell activation (parafollicular zone and marginal zone), and lymphocyte egress (outer marginal zone).

Involvement of peripheral and central catecholamine systems in neural-immune interactions

In this review, we have attempted to delineate the current state of knowledge of the relationships between the immune system and one chemically specific component of the nervous system, the noradrenergic system, both in the brain and the periphery. We have discussed recent work describing the presence of noradrenergic innervation in lymphoid tissues in the major lymphatic organs. Our findings demonstrate clearly that the regions in which lymphocytes (mainly T cells) reside, and through which they recirculate, receive direct sympathetic neural input. The immune system can, therefore, be considered 'hard-wired' to the brain. The evidence for receptors on cells of the immune system capable of receiving signals from the brain is discussed. The significance of this 'hard-wiring' to the function of the immune system is considered, both with regard to the effect of its disruption on immune responses, and to the direct and indirect effects of sympathetic neurotransmitter substances on lymphocytes and their behavior in vitro and in vivo. Finally, our detailed analysis of changes occurring in central noradrenergic pathways as a result of stimulation of the immune system leads to an emerging picture of feedback loops from the immune system to the brain. Such circuits employ endocrine, and probably autonomic, outflow to modulate and regulate immune responses.