Localization of choline acetyltransferase and NADPH diaphorase activities in the submucous ganglia of the guinea-pig colon

A combined immunohistochemical and histochemical demonstration of choline acetyltransferase (ChAT) and nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d) was carried out, respectively, to determine the localization of the neurotransmitters, acetylcholine and nitric oxide (NO) in the submucous neurons of guinea-pig colon. Almost half of the submucous neurons in the guinea-pig colon exhibited ChAT-immunoreactivity. Some of the ChAT-immunoreactive neurons were also stained for NADPH-d, although most of them showed only weak to moderate diaphorase activity. Many of the submucous neurons displayed exclusively either ChAT or NADPH-d activity. A close spatial relationship was observed between the cholinergic and nitrergic submucous neurons. Thus, in light microscopy, some ChAT-immunoreactive fibres were closely associated with the NADPH-d-positive nerve cell bodies. Ultrastructural study extended the fact that many of the ChAT-immunoreactive terminals made synaptic contacts with the soma of the NADPH-d-positive submucous neurons. A remarkable feature was the demonstration of ChAT and NADPH-d in some of the neurons and their presynaptic axon terminals, suggesting the co-localization of acetylcholine and NO as neurotransmitters in the submucous neurons and their presynaptic axon terminals. It is suggested that the submucous neurons with their specific neurochemical codings would subserve different functions.

Ultrastructural study of external cuneothalamic neurons and their synaptic relationships with primary afferents in the gerbil

The present study examined the synaptic organization of external cuneothalamic neurons and their relationships with primary afferents in the gerbil external cuneate nucleus (ECN) following an injection of horseradish peroxidase (HRP) into the anterodorsal cap of the ventrobasal thalamus in conjunction with a simultaneous injection of HRP into the contralateral brachial and cervical nerve plexuses. The thalamus-projecting neurons have been shown to be confined to the intermediate portion of the caudal half of the ECN at the light microscopic level (Lan et al., 1994c). In this study, HRP-labelled external cuneothalamic neurons were ultrastructurally characterized by their relatively small-sized soma bearing a variable number of somal spines. Their nucleus had a slightly indented contour with an eccentric nucleolus. The HRP-labelled somata were postsynaptic to many axon terminals, which were classified into round (Rs type; 53.0%), pleomorphic (Ps type; 32.7%), and flattened (Fs type; 14.3%) vesicle-containing boutons. The HRP-labelled dendritic elements were postsynaptic to a greater number of axon terminals, which were also classified into the round (Rd; 64.7%), pleomorphic (Pd; 25.2%), and flattened (Fd; 10.1%) type boutons. These presynaptic axonal boutons tended to synapse on distal and secondary dendrites of external cuneothalamic neurons. In the present simultaneous HRP labelling study, some of the primary afferent terminals made direct synaptic contacts with the dendrites of the external cuneothalamic neurons. In view of the multiple inputs onto the external cuneothalamic neurons, impinging particularly on their somata and secondary dendrites, it is suggested that the proprioceptive information reaching these neurons is intensively modulated and integrated before transmission ultimately to the cerebral sensorimotor cortex.

Ultrastructural study of phenylethanolamine-N-methyltransferase, corticotropin-releasing factor and neurotensin immunoreactive neurons in the external cuneate nucleus of the gerbil

The present study examined the existence of catecholamine-, corticotropin-releasing factor (CRF)- and neurotensin (NT)-containing neurons in the external cuneate nucleus (ECN) of the gerbil using single label pre-embedding immunocytochemistry in an attempt to shed light on the increasing evidence for autonomic involvement of the ECN. Peroxidase immunoreactivity of phenylethanolamine-N-methyl-transferase (PNMT), CRF or NT was identified in the heterogeneous population of the ECN neurons characterized by a deeply infolded nucleus. The label was localized in their somata, dendrites, myelinated axons and axon terminals. The immunolabelled dendrites were contacted by spherical (S) and flattened (F) types of presynaptic boutons containing spherical and flattened synaptic vesicles, respectively. The PNMT-labelled dendrites, however, were postsynaptic to an additional type of axon terminals containing pleomorphic (P) synaptic vesicles. Among the immunoreactive axon terminals, the PNMT-labelled boutons consisted of two types: S and F; in the CRF- and NT-labelled axon terminals, only the S type was observed. The catecholamine-containing ECN neurons differed from the CRF- and NT-immunoreactive neurons in their synaptic organization. The latter two were considered to be of the same cell population because of their similarities in ultrastructural features and synaptic relations. In view of a high frequency (48% for PNMT, 50% for CRF and 46% for NT) of the F-typed boutons associated with the three categories of immunolabelled neurons in the ECN, it is possible that they are under considerable inhibitory control. The presence of catecholamine, CRF and NT in the ECN suggests that the nucleus may be involved in the integration of proprioception-, exercise- or stress-evoked autonomic responses.

Expression and upregulation of transferrin receptors and iron uptake in the epiplexus cells of different aged rats injected with lipopolysaccharide and interferon-gamma

The expression of transferrin receptors marked by the monoclonal antibody OX-26 and localisation of iron was studied in epiplexus cells in the lateral ventricles of different aged rats subjected to the challenge of the bacterial toxin, lipopolysaccharide, and treatment with interferon-gamma. Transferrin receptor expression in epiplexus cells was extremely low in normal rats, but was vigorously elevated in rats receiving intraperitoneal injections of lipopolysaccharide (LPS); other antigens such as complement type 3 receptors immunostained with OX-42 and macrophage antigen marked by ED-1 were also notably augmented. After 6 successive intraperitoneal injections of interferon-gamma, the expression of transferrin receptors showed only a moderate increase. Using Perls' staining method, some iron-containing epiplexus cells were observed in early normal postnatal rats, but their number was markedly decreased with age. After LPS administration, a moderate increase in the number of iron-containing epiplexus cells was observed in different aged rats. The significance of the upregulation and vigorous expression of transferrin receptors on epiplexus cells is speculative. One possible explanation would be that they facilitate an increase in the acquisition of iron by these cells for storage, oxidative killing and/or immunological activation. The localisation of iron in the choroid plexus in the lateral ventricles suggests that the latter may function as an important storage organ for iron. Present results also suggest the presence of an efficient transport system for the transfer of iron across the interface of the blood and cerebrospinal fluid.

An ultrastructural study of the submucous plexus of guinea pig intestine after unilateral vagotomy

This study describes the degenerative changes of the axon terminals making synaptic contacts with the neurons in the submucous ganglia of guinea pig small and large intestines following left or right cervical vagotomy. There were no noticeable ultrastructural changes 1 d after the operation. Beginning at the 3rd postoperative day for the small intestines and the 5th day for the large intestines, some of the axon terminals presynaptic to the submucous neurons displayed different stages of degeneration. The most obvious feature of the degenerating terminals was the swelling and vacuolation of mitochondria with disrupted cristae; another change was the clumping of synaptic vesicles. In the animals killed 7 d after vagotomy, besides the above changes, the degenerating axon terminals also showed an accumulation of a variable amount of glycogen-like particles. The changes were most severe in the guinea pigs killed on the 10th postoperative day. The synaptic vesicles in some degenerating terminals were depleted. There were occasional degenerating nerve cell bodies in the submucous ganglia in the period studied. A variable number of lamellated bodies were found in some of the submucous neurons of 10 and 15 d postoperative animals. By 30 d after vagotomy, all the terminals presynaptic to the submucous neurons appeared normal. There was no significant difference in the total number of axon terminals between 10 d and 30 d after operation (P > 0.05). This suggests that either there had been successful reinnervation or new synaptic contacts had been established by sprouting from the unoperated vagus or other intrinsic neurons. The present quantitative studies also showed that the number of degenerating axon terminals in the submucous ganglia of duodenum after left vagotomy was higher than right vagotomy (P < 0.05). This feature was particularly evident in animals killed 10 d after the operation. The larger number of degenerating terminals in the submucous ganglia of duodenum after left vagotomy suggests that the presynaptic axon terminals in the submucous ganglia of different gut regions are not evenly distributed. Finally, the present study showed that the degenerative changes in the small intestine preceded the large intestine.

Light and electron microscopic studies of the distribution of NADPH-diaphorase in the rat upper thoracic spinal cord with special reference to the spinal autonomic region

The distribution of nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d) was examined in the upper thoracic segment of the spinal cord in rat. Under the light microscope, NADPH-d positive cell bodies and fibers were readily detected in the following areas: 1) the dorsal horn; 2) the dorsolateral funiculus and lateral spinal neurons; 3) spinal autonomic region, consisting of the nucl. intermediolaterialis pars funicularis, nucl. intermediolateralis pars principalis, nucl. intercalatus spinalis and nucl. intercalatus pars paraependymalis; and 4) in the white matter lateral to the nucl. intermediolateralis pars funicularis. In the nucl. intermediolateralis pars principalis, the positive dendrites, running in bundles, were directed medially in the gray matter towards the central canal as well as laterally in the white matter towards the pia mater. The medially-directed positive dendrites fomed a subependymal plexus around the central canal. A dense bundle of NADPH-d positive fibers were also observed running longitudinally. Combined retrograde tracing with fluorogold and NADPH-d histochemistry study revealed that some of the NADPH-d positive neurons, due to their fluorescence labelling, were sympathetic preganglionic neurons that innervated the superior cervical ganglion. Under the electron microscope, the reaction products in the neurons of the nucl. intermediolateralis pars principalis were deposited in their nuclear envelope, rough endoplasmic reticulum, mitochondria and Golgi apparatus. In the neuropil, three types of synaptic configurations were observed: between NADPH-d negative axon terminals and NADPH-d positive dendrites, between NADPH-d positive axon terminals and NADPH-d negative dendrites, and between NADPH-d positive axons terminals and NADPH-d positive dendrites. These synaptic configurations suggest that the neurons are regulated by nitric oxide released from both pre- and post-synaptic elements. The sources of the NADPH-d positive axon terminals associated with the neurons remain unclear although the possibility of their being derived from supraspinal origins has to be considered. The ultrastructural demonstration of NADPH-d reaction product in the three major types of glial cells suggests that nitric oxide might be produced by these cells, but its functional significance awaits further investigation.

Glial reaction after pyramidotomy in mice and rats

Adult mice and rats were sacrificed by perfusion between 2 and 90 days after right pyramidotomy to study the microglial and astroglial response in the brain and spinal cord. The microglia were detected immunohistochemically with OX-42, OX-18 and OX-6 to assess respectively the expression of complement type 3 receptor, and major histocompatibility class I and class II antigens. Cell counting was also carried out in some animals to determine the possible proliferation of glial cells in the corticospinal tract and around layer V neurons in the cerebral cortex. Some operated animals were given rhodamine B isothiocyanate injection to investigate whether macrophages/monocytes could have migrated from the blood stream to the reactive area. The glial response around the cell bodies of layer V neurons in the ipsilateral cerebral cortex did not display any noticeable difference compared with that of the contralateral side and of the cerebral cortex of the sham-operated and normal control animals. In the cervical and lumbar cord segments of the operated animals, reactive microglial cells in the contralateral corticospinal tract appeared as early as 2 days post pyramidotomy (PP) in rats and 4 days PP in mice. Activation of microglial cells lasted up till 35 days PP, showing gradual increase in immunoreactive staining and hypertrophy. After that, the microglial immunoreactivity subsided and the cells assumed normal appearance by 90 days PP. Quantitative analysis showed a marked increase in the number of microglial cells in the contralateral CST up till 60 days PP. In mice, at 6 days PP, astroglial cells were hypertrophic and more intensely stained but showed no increase in number. No noticeable changes were noted in the astroglia of the rats throughout the period studied. Rhodamine-labelled cells were found at the lesion site, but not in layer V of the cerebral cortex, nor in the corticospinal tract. Though different glial reactions in the degenerating corticospinal tract were noted in mice and rats, there was the same apparent lack of glial reaction around the cell bodies of layer V neurons in the two animal species. Such lack of significant glial response is different from the vigorous glial response around the cell bodies of peripherally projecting neurons demonstrated in previous work. The possible mechanisms for such difference and the implication of the difference in axonal regeneration were discussed.

Histochemical demonstration of nitric oxide synthase-like immunoreactivity in epiplexus cells and choroid epithelia in the lateral ventricles of postnatal rat brain induced by an intracerebral injection of lipopolysaccharide

The present in vivo study showed the expression of nitric oxide synthase-like immunoreactivity in epiplexus cells in the lateral ventricles induced by intracerebral injection of lipopolysaccharide into postnatal rats. Nitric oxide synthase-like immunoreactivity was vigorously expressed in epiplexus cells 1 and 3 days after the lipopolysaccharide injection, but by 7 days post-injection, it became undetectable. The expression of nitric oxide synthase-like immunoreactivity was also observed in some of the choroid epithelial cells. The nitric oxide synthase-like immunoreactivity in these cells appeared to be more intense in the ventricle ipsilateral to the LPS injection than that on the contralateral side. The immunostaining patterns of OX-42 and OX-6 for the detection of complement type 3 receptors and major histocompatibility complex class II antigens respectively paralleled that of anti-nitric oxide synthase, indicating that lipopolysaccharide-induced nitric oxide synthase-like immunoreactivity was primarily in epiplexus cells. Immunoelectron microscopy revealed that the nitric oxide synthase-like immunoprecipitate in epiplexus cells and choroid epithelial cells filled the entire cytoplasm and in some areas associated with the membranes of some of the organelles especially the mitochondria, suggesting that the enzyme is mainly cytosolic. It is speculated that nitric oxide synthase in these cells is involved in the synthesis of nitric oxide. The nitric oxide production, if any, through the enzymatic activity of nitric oxide synthase in epiplexus cells as well as the choroid epithelial cells may be involved in host defense against bacterial endotoxin in the ventricular system of postnatal rat brain.

Ultrastructural identification of cholinergic neurons in the external cuneate nucleus of the gerbil: acetylcholinesterase histochemistry and choline acetyltransferase immunocytochemistry

Using acetylcholinesterase histochemical and choline acetyltransferase immunocytochemical localization methods, this study has provided conclusive evidence for the existence of cholinergic neurons in the external cuneate nucleus of gerbils. By light microscopy, both acetylcholinesterase and choline acetyltransferase labelling was confined to the rostral portion of the external cuneate nucleus. Ultrastructurally, acetylcholinesterase reaction products were found in the nuclear envelope, cisternae of rough endoplasmic reticulum and Golgi saccules of some somata and large dendrites as well as in the membranes of small dendrites, myelinated axons and axon terminals. These neuronal elements were also stained for choline acetyltransferase; immunoreactivity was associated with nuclear pores, nuclear envelope, perikaryal membrane and all the membranous structures within the cytoplasm. Of the total choline acetyltransferase-labelled neuronal profiles analysed, 79% were myelinated axons, 15% dendrites, 4% somata and 2% axon terminals. The immunostained axon terminals consisted of two types containing either round (Rd type; 62.5%) or pleomorphic (Pd type; 37.5%) vesicles. Both were associated directly with choline acetyltransferase-positive dendrites. In contrast to the paucity of choline acetyltransferase-labelled axon terminals, numerous choline acetyltransferase-positive myelinated axons were present. It may thus be hypothesized that most, if not all, of the external cuneate nucleus cholinergic neurons are projection cells; such cells may give rise to axonal collaterals which synapse onto their own dendrites for possible feedback control. Choline acetyltransferase-positive dendrites were contacted by numerous unlabelled presynaptic boutons, 60% of which contained round or spherical synaptic vesicles (Rd boutons) and 40% flattened vesicles (Fd boutons), suggesting that these neurons are under strong inhibitory control. The preferential concentration of cholinergic components in the rostral external cuneate nucleus may be significant in the light of the highly organized somatotopy in the external cuneate nucleus and its extensive efferent projections to medullary autonomic-related nuclei. Our results suggest that the cholinergic neurons may be involved in somatoautonomic integration.

A study of the structure and functions of the submandibular ganglion

The submandibular ganglion (SMG) of both the rat and monkey is composed of a collection of small ganglia distributed mainly at the hilum of the submandibular gland. Ultrastructurally, its constituent neurons have a prominent nucleus and numerous randomly distributed cytoplasmic organelles. In the rat SMG a variable number of its neurons are immunoreactivities for [Met5]enkephalin-Arg6-Gly7-Leu8, neuropeptide Y (NPY), substance P (SP), tyrosine hydroxylase (TH) and vasoactive intestinal polypeptide (VIP). In the monkey, however, the SMG neurons only react for NPY and SP. Following sectioning of the lingual nerve, SMG neurons of both the rat and monkey showed structural alterations; a marked change was also observed in the immunoreactivities of the rat neurons. There were signs of recovery in the structural features and immunoreactivities in the SMG neurons in animals with longer survival periods of up to 2 months. This suggests that the changes in the neurons after denervation are acute but reversible in nature. After fluorogold injections into the submandibular and sublingual glands of the rat, a variable number of neurons in the superior salivatory nucleus (SSN), superior cervical ganglion (SCG) and trigeminal ganglion (TG) were labelled. A hypothetical model depicting the possible interactions between the parasympathetic SMG and the preganglionic nucleus, that is, the SSN, as well as the sympathetic SCG and the sensory TG is presented. It is proposed that the SMG functions as a relay as well as a modulatory centre for salivatory activity.

The response of neurons and microglia to blast injury in the rat brain

Rats subjected to a single non-penetrative blast were examined for possible neuronal damage and glial reaction by immunohistochemistry and electron microscopy. The most dramatic feature in rats killed between 1 and 14 days after the blast was the widespread response of microglial cells in various parts of the brain in which the cells were hypertrophied and their surface antigens, like complement type three receptors (CR3), were upregulated. The blast wave also induced the vigorous expression of major histocompatibility complex (MHC) class I and II (Ia) antigen. In rats killed 21 days after the blast, the elevated immunoreactivity of microglia had subsided and at 28 days both the microglial external morphology and immunoreactivity were comparable to those of normal animals. In rats killed 4-7 days after the blast, the neurons in the cerebral and cerebellar cortex appeared normal except for the occurrence of some 'darkened' dendrites. The incidence of 'darkened' dendrites was most common in rats killed at day 14 but they were absent at 21 and 28 days. Microglial cells were closely associated with some of the 'darkened' dendrites. Results in this study show that a non-penetrative blast in rats provokes a widespread microglial activation suggesting increased endocytosis and immunological responses. However, it remains uncertain whether such a drastic response was a direct activation of the cells by the blast wave or elicited indirectly by some chemical factors released from the damaged brain tissues.

The distribution of NADPH-d in the central grey region (lamina X) of rat upper thoracic spinal cord

The distribution of nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d) in the central grey region (lamina X of Rexed) of the rat upper thoracic cord was examined by LM and EM. Numerous NADPH-d positive neuronal somata and fibres were present in the subependymal areas of the central grey region at levels T1-T3. Most of the neurons were located dorsal to the central canal in horizontal sections through this region. Many medially-directed NADPH-d positive fibres arising from neurons in n. intermediolateralis pars principalis, n. intercalatus spinalis and longitudinally-directed NADPH-d positive fibres arising from neurons in n. intercalatus pars paraependymalis formed a subependymal plexus. In horizontal sections through the central canal, some NADPH-d positive nerve fibres appeared to traverse the ependyma to enter and run along the central canal. By EM, NADPH-d reaction products were localized on the nuclear membrane, outer mitochondrial membrane and Golgi apparatus of both neurons and ependymal cells and in some axon terminals containing pleomorphic and round agranular synaptic vesicles. Present results suggest that besides the traditional monoamine-, amino acid- and peptide-containing axon terminals, the central grey region also contains fibres in which nitric oxide is utilized as a neurotransmitter or neuromodulator. The finding of NADPH-d positive fibres in the central canal suggests that nitric oxide may be released into DPH-cerebrospinal fluid. Since some of the ependymal cells were NADPH-d positive, it is suggested that they may be involved in the modulation of nitric oxide levels in the cerebrospinal fluid.

A comparative study of NADPH-diaphorase in the sympathetic preganglionic neurons of the upper thoracic cord between spontaneously hypertensive rats and Wistar-Kyoto rats

With retrograde tracing using fluorogold injection into the superior cervical ganglion and nicotinamide adenine dinucleotide phosphate diaphorase (NADPH-d) histochemistry, the present comparative study revealed that the retrogradely labelled neurons in n. intermediolateralis pars funicularis (ILf) and n. intermediolateralis pars principalis (ILp) of the autonomic region in the upper thoracic cord exhibited a much stronger reactivity for NADPH-diaphorase in Wistar-Kyoto (WKY) rats than those in spontaneously hypertensive rats (SHR). It was found that in ILf in WKY rats, 77.62% of the fluorogold-labelled neurons were NADPH-d positive, while in SHR, only 56.43% of the labelled neurons were NADPH-d positive. The frequency distribution of NADPH-d positive retrogradely labelled neurons was significantly reduced in ILf of the spinal cord of SHR (U-test: P < 0.01). In ILp in WKY rats, 65.25% of fluorogold-labelled neurons were NADPH-d positive in WKY rats, while in SHR, only 56.28% of the labelled neurons were NADPH-d positive. Although the difference (P > 0.05) in the frequency of NADPH-d positive neurons in ILp between the two strains of rats was not significant, the reductions in SHR seemed considerable. Examination of the preganglionic sympathetic trunk and the superior cervical ganglion between SHR and WKY rats revealed that virtually all the NADPH-d positive fibers were derived from the sympathetic preganglionic neurons. In SHR, the NADPH-d positive fibers were not as intensely stained as those of WKY rats. This preliminary results suggest that nitric oxide, as an inhibitory neurotransmitter, may be implicated in the onset of hypertension.

A qualitative and quantitative study of the glial cells in normal and athymic mice

A qualitative and quantitative light and electron microscopic analysis of the glial cells in the supraventricular part of the corpus callosum of the neonatal and adult homozygous athymic nude (nu/nu) and normal BALB/c (+/+) mice was carried out to determine the possible contribution of nude gene mutation to glial cell development. Quantitative cell counts using toluidine blue stained serial callosal sections of 0.5 micron thickness showed that the overall glial cell population was significantly reduced in both neonatal and adult athymic mice. The number of glioblasts, astrocytes and microglia of 5-day-old athymic mouse was reduced by 10%, 27%, and 39%, respectively, when compared to the 5-day-old normal mouse. The frequency of necrotic cells in the neonatal athymic mouse increased by 70% when compared with the normal mouse. In the 13-week-old adult athymic mouse, the number of oligodendrocytes, astrocytes, and microglia decreased by 19%, 31%, and 33%, respectively, when compared to normal mouse. There was no significant difference in the area covered by the corpus callosum in 5-day-old and adult nude mice versus the normal ones of corresponding ages. Except for microglia and astrocytes, the ultrastructural features of the other glial cell types in both strains were comparable. Most of the microglial cells of the neonatal normal mouse were round and were selectively marked by Mac-1 monoclonal antibody at their plasma membrane. The immunoreactivity appeared to be more intense in the normal than the athymic mouse, suggesting a down regulation of CR3 receptors and reduced phagocytic activity of this cell type in the athymic mouse. It is proposed that the increased number of necrotic cells in the neonatal athymic mouse may be attributed to the delay in the removal of dead cells normally phagocytosed by microglia. The microglia in both strains of mouse showed comparable lectin staining intensity at the plasma membrane, indicating that their glycoprotein binding receptors to lectin remained unchanged. Some astrocytes in the adult athymic mice showed hypertrophy. The reduced number of glial cells may be the direct result of genetic mutation or consequential to the lack of certain trophic factors arising from the genetic mutation. Thus, the reduction of microglial cells in both neonatal and adult athymic mice may be due to the lack of thymic hormones which, together with lymphokines have been shown to affect the maturation of bone marrow-derived cells including monocytes, the putative precursor cells of microglia. The reduction in the number of glioblasts and astrocytes may be attributed to the diminution of T lymphocytes or consequential to the reduction of microglia which are known to secrete interleukin-1 that would influence gliogenesis and produce specific growth factors for promoting astrocyte proliferation. Last, as interaction exists between astrocytes and oligodendrocytes, the products of astrocytes may affect the development of oligodendrocytes and vice vasa. The present findings point to a relation between glial cell development and immune network system.

Effects of dexamethasone on the epiplexus cells in postnatal rats

The epiplexus cells in postnatal rats were markedly reduced in number and immunoreactivity for OX-42, OX-18 and ED1 following subcutaneous injections of dexamethasone. This was especially evident in rats receiving two or three successive injections of dexamethasone and killed at the age of 4 or 7 days. At 14 and 21 days, the cells did not exhibit any striking difference from their corresponding controls in terms of cell number and immunoreactivity for the above antibodies. Occasional epiplexus cells were labelled with the antibody OX-6 in both groups of rats sacrificed at different time points. In rats receiving dexamethasone coupled with rhodamine isothiocyanate (RhIc), the epiplexus cells, though fewer in number than the corresponding controls, emitted bright fluorescence. It is concluded that the reduction of epiplexus cells following dexamethasone injections is due to the suppression of their precursor cells, i.e. monocytes. The phagocytic activity of the persisting epiplexus cells did not appear to be abolished by dexamethasone as evidenced by their uptake of RhIc. Our results suggest that the effects of dexamethasone are reversible.

A comparative ultrastructural study of primary afferents from the brachial and cervical plexuses to the external cuneate nucleus of gerbils

The synaptic organisation of the primary afferents from the brachial and cervical plexuses to the external cuneate nucleus of gerbils was compared following an intraneural injection of horseradish peroxidase into the musculocutaneous, median, ulnar and radial nerves of the brachial plexus or the main branches of the cervical plexus; 407 labelled primary afferent terminals from the brachial and 459 from the cervical plexus were studied. These boutons made synaptic contacts with 586 and 633 dendritic profiles, respectively. 99.0% of the primary afferent boutons from the brachial plexus contained clear round synaptic vesicles (R boutons); the remaining 1% of boutons contained pleomorphic synaptic vesicles (P boutons). For boutons from the cervical plexus, 95% were R boutons and 5% were P boutons. The labelled R bouton profiles had a wide range of cross-sectional area from 0.4 to 13.1 microns 2, while the P boutonal profiles were of a small variety (range, 0.4-2.3 microns 2; mean, 1.5; S.D., 0.6 micron 2). The R boutons from the brachial plexus (mean, 3.9 microns; S.D., 2.1 microns 2) were generally larger than those from the cervical plexus (mean, 3.3 microns 2; S.D., 1.9 microns 2). On close analysis, 72.4% of R boutons from the brachial plexus were found to synapse on distal dendrites, 15.9% on secondary dendrites, 9.5% on dendritic spines and 2.2% on proximal dendrites. For R boutons from the cervical plexus, 81.1% synapsed on distal dendrites, 12.1% on dendritic spines and 6.8% on secondary dendrites; none was observed on proximal dendrites. Such a different synaptic organisation between the two nerve plexuses may be related to their different perceptuomotor executions.

Multiple origins of cerebellar cholinergic afferents from the lower brainstem in the gerbil

The possible origins of cerebellar cholinergic afferents from the lower brainstem of the gerbil were examined using immunohistochemistry combined with retrograde neuronal labelling techniques. Choline acetyltransferase (ChAT) monoclonal antibody was used in conjunction with a retrogradely transported tracer, horseradish peroxidase (HRP). The use of this technique allowed an unequivocal localisation of cholinergic neurons in different parts of the lower brainstem projecting to the cerebellum. In addition, single labelling of acetylcholinesterase (AChE), ChAT and HRP was carried out to elucidate the efferent projection from the lower brainstem to the cerebellum as well as the cholinergic distribution in these two areas. Our results showed the presence of HRP/ChAT double-labelled neurons in (1) the midline medulla: the periventricular gray beneath the 4th ventricle, C3 adrenergic area, raphe obscurus nucleus and medial longitudinal fasciculus, (2) the reticular formation: the medullary, lateral, intermediate, gigantocellular, lateral paragigantocellular and dorsal paragigantocellular reticular nuclei and gigantocellular reticular nucleus ventralis, and (3) sensory nuclei: the gracile nucleus, cuneate nucleus, external cuneate nucleus, spinal trigeminal nucleus interpolaris, prepositus hypoglossal nucleus and medial vestibular nucleus. In the cerebellum, AChE-positive mossy fibres were chiefly localised in the vermian lobules VIb,c, VII and X, paramedian lobule, crura I and II, paraflocculus and flocculus, and they were distributed in the white matter and granular layer of the cortex. The 3 above-mentioned cerebellar cholinergic afferent systems associated with the unique AChE distribution pattern in the cerebellum may be of important functional significance.

An ultrastructural study of cuneocerebellar neurons and primary afferent terminals in the external cuneate nucleus of gerbils as revealed by retrograde and transganglionic transport of horseradish peroxidase

The present study examined the synaptic organization of cuneocerebellar neurons and their relationships with the primary afferents in the gerbil external cuneate nucleus following multiple injections of horseradish peroxidase over a widespread area in the cerebellum in conjunction with a simultaneous injection of horseradish peroxidase into the cervical or brachial nerve plexus. The external cuneate nucleus is topographically organized: the rostral portion receiving the primary afferents from the cervical plexus and the caudal portion primary afferents from the brachial plexus. This study attempted to correlate the synaptology with the topography and different cytoarchitecture in these two specific regions in the external cuneate nucleus. Ultrastructurally, the profiles of horseradish peroxidase-labelled cuneocerebellar neurons could be divided into three types, namely, small, medium and large on the basis of their cross-sectional areas. Axon terminals which formed axosomatic synapses could be classified into: round (Rs type; 22.2%), pleomorphic (Ps type; 55.6%) and flattened (Fs type; 22.2%) vesicle boutons. The horseradish peroxidase-labelled dendritic elements of the cuneocerebellar neurons were postsynaptic to a greater number of axon terminals which were also classified into Rd (77.5%), Pd (18.8%) and Fd (3.7%) type boutons. Some of the Rd boutons making direct synaptic contacts with the cuneocerebellar neurons originated from primary afferents since they were simultaneously labelled by transganglionic transport of horseradish peroxidase. In the rostral external cuneate nucleus, synapses on cuneocerebellar neurons were more frequent on their primary dendrites as compared with those on the primary dendrites of the caudal cuneocerebellar neurons. The latter, on the other hand, showed more synapses on their distal dendrites. This may have functional implications with regard to the afferent inputs to cuneocerebellar neurons in the rostral and caudal external cuneate nucleus.

Semen extenders to salvage ejaculate in a retrograde ejaculate environment: a potential use in spinal cord-injured men

Infertility is a well-recognized complication in spinal cord-injured men. Vibratory stimulation and electroejaculation are being used to overcome the inability to ejaculate, but poor sperm quality remains a significant problem. Retrograde ejaculation is known to occur with both sperm retrieval techniques, and may contribute to the poor semen quality. In addition, the amount of retrograde ejaculate produced is generally of sufficient quantity worthy of salvaging. We investigated the effectiveness of various semen media in maintaining the viability of healthy sperm placed in a retrograde ejaculate environment. Six semen extenders, media used to process spermatozoa for artificial insemination and to maintain viability during cryopreservation, were studied. We found that Ham's F-10 with 3.5gm % bovine serum albumin seems to be an effective medium to maintain sperm viability over a wide range of urine concentrations (up to 60% to 80% urine), and potentially, may be useful by its infusion into the bladder before vibratory or electrostimulation to enhance the recovery of greater numbers of viable sperm from the retrograde environment.

Induction of major histocompatibility complex class II antigen on amoeboid microglial cells in early postnatal rats following intraperitoneal injections of lipopolysaccharide or interferon-gamma

The induction of major histocompatibility complex (MHC) class II antigen on amoeboid microglia cells (AMC) by lipopolysaccharide (LPS) and interferon-gamma (INF-gamma) in early postnatal rat brain was studied by immunohistochemistry. In newborn rats given successive intraperitoneal injections of LPS or INF-gamma and killed at the age of 7 days, MHC class II antigen expressing AMC were consistently present in specific areas throughout the entire brain, notably in the subcortical white matter and circumventricular region. It is concluded from this study that the induction of MHC class II antigen on AMC by LPS or INF-gamma is a widespread phenomenon in the developing brain. Since MHC class II antigen is essential for the initiation of immune response, it is suggested that besides their phagocytic nature, AMC may also be involved in immunological processes in the developing brain.

Localization of NADPH-diaphorase activity in the submucous plexus of the guinea-pig intestine: light and electron microscopic studies

The localization of reduced nicotinamide adenine dinucleotide phosphate diaphorase in the submucous plexus of duodenum, jejunum, ileum, proximal colon, distal colon and rectum in the guinea-pig was examined histochemically by light and electron microscopy. The majority of reactive submucous neurons displayed features common to either Dogiel type I or type II neurons; some were closely adherent to the outer walls of lymphatic vessels. The use of 2-(2'-benzothiazolyl)-5-styryl-3-(4'-phthalhydrazidyl) tetrazolium chloride (BSPT) at the ultrastructural level showed that nicotinamide adenine dinucleotide phosphate diaphorase is a membrane-associated protein widely distributed in the cells, including the rough endoplasmic reticulum, Golgi apparatus and synaptic vesicles in the axon terminals associated with submucous neurons. On the basis of their diaphorase reactivity or the lack of it, the submucous neuronal somata and their associated terminals were observed to form several different kinds of synaptic configurations. The present quantitative analysis showed that the frequency of reactive submucous neurons in the large intestine was significantly higher than in the small intestine. Based on the ultrastructural localization of the diaphorase reaction product in positive cells, it is speculated that nitric oxide might be synthesized within the neurons. The demonstration of different synaptic configurations in the submucous ganglia suggests that the functional interaction between submucous neurons is extremely complex. Finally, the higher frequency of diaphorase reactive submucous neurons in the large intestine than in the small intestine indicates that submucous neurons in these two gut regions may not play equivalent roles.

A comparative study by retrograde neuronal tracing and substance P immunohistochemistry of sympathetic preganglionic neurons in spontaneously hypertensive rats and Wistar-Kyoto rats

A comparative morphological study of the sympathetic preganglionic neurons that innervate the superior cervical ganglion (SPN-scg) was made in spontaneously hypertensive rats (SHR) and age-matched normotensive Wistar-Kyoto (WKY) rats. The cytoarchitectonics and dendroarchitectonics of the SPN-scg were studied following retrograde transport of choleragen subunit B horseradish peroxidase conjugate (CB-HRP) and Fluorogold. Significant differences were observed in the maximum and minimum diameters of neurons of the nucleus intermediolateralis pars principalis (ILp) and in the minimum diameter of neurons in the nucleus intermediolateralis pars funicularis (ILf) between SHR and WKY rats (P < 0.01). These diameters were decreased in neurons of SHR. The distribution patterns of dendrites of SPN-scg also showed differences between SHR and WKY rats. The dendritic distribution patterns showed the following changes in SH rats: (1) the mediolaterally oriented dendrites were reduced in number, (2) the ladder-like configuration of the medially oriented grey-matter dendrites was less prominent, (3) the medially oriented dendrites formed a triangular or dome-like configuration, and (4) the white matter dendritic plexuses and subependymal plexuses were reduced. Similar differences between SHR and WKY rats were also observed in our immunohistochemical study of substance P-like fibres. In addition, the SP study has also shown a close association of SP fibres with the central canal both in SHR and WKY rats; some of the SP fibres penetrated the ependymal lining to run longitudinally up or down the central canal. This finding suggests the presence of substance P-positive neurons contacting the cerebrospinal fluid.

Transient expression of transferrin receptors and localisation of iron in amoeboid microglia in postnatal rats

The expression of transferrin receptors marked by the monoclonal antibody OX-26 and the localisation of iron were studied in amoeboid microglial cells in postnatal rats. Transferrin receptors were vigorously expressed in amoeboid microglia in rats ranging from 1 to 10 d of age but were undetectable in older rats. Thin serial sections showed that the OX-26 positive amoeboid microglial cells were also immunoreactive for OX-42 and ED1. Using Perls' medium, this study showed the presence of a considerable amount of iron in amoeboid microglial cells in 1-10 d rats. Most iron-containing cells were round but their number had diminished by 2 and 3 wk of age, when the iron was localised instead in some branched cells which were identified as either oligodendrocytes or ramified microglia cells. There has been much speculation on the functional significance of transferrin receptors on amoeboid microglia in postnatal rats. It is suggested that the receptors facilitate the acquisition of iron necessitated for various functions of amoeboid microglia in the developing brain. The presence of iron in some oligodendrocytes suggests their involvement in mediating iron mobilisation and storage. Its localisation in some ramified microglia in older rats indicates the possible role of these cells in sequestration and detoxification of iron in the central nervous system.

Ultrastructural localisation of substance P, vasoactive intestinal peptide and somatostatin immunoreactivities in the submucous plexus of guinea pig ileum

The submucous neurons, especially those related to the lymphatic vessels, together with their associated synapses, were studied ultrastructurally with respect to their immunoreactivities for 3 types of neuropeptides, namely substance P (SP), vasoactive intestinal peptide (VIP) and somatostatin (SOM). With the antibodies directed against the 3 types of neuropeptides, a variable number of submucous neurons including those contacting the lymphatic vessels were immunostained. Based on the immunoreactivities and synaptic relations with the submucous neurons contacting the lymphatic vessels, at least 4 types of synaptic relations with the submucous neurons contacting the lymphatic vessels, at least 4 types of synaptic configurations were observed: immunopositive terminals with positive neurons, immunopositive terminals with negative neurons, immunonegative terminals with positive neurons and immunonegative terminals with negative neurons. All 4 types of synaptic configurations were observed in SP and VIP-immunostained specimens, with the exception of type 3 which was not encountered in samples immunoreacted for SOM. When the proportions of all 4 types of peptidergic immunopositive terminals contacting the lymphatic vessel-associated neurons were totalled, the value exceeded 100%, suggesting the coexistence of 2 or more neuropeptides in the same terminals. Furthermore, some immunoreactive axon terminals made direct synaptic contacts with positive neurons suggesting the formation of the so-called 'peptide neuron chain'. It is speculated from this study that the submucous neurons receive multiple peptidergic inputs. The various synaptic contacts would imply a complicated reflex pathway in the submucous plexus.

A light-microscopic study of the intermediolateral nucleus following injection of CB-HRP and fluorogold into the superior cervical ganglion of the rat

Sympathetic preganglionic neurons in the intermediolateral nucleus of the thoracic spinal cord of the adult rat which innervate the superior cervical ganglion (SPN-scg) were identified by means of retrograde transport of cholera subunit B-conjugated horseradish peroxidase and fluorogold. In horizontal sections of the spinal cord, the SPN-scg were observed to be arranged in clusters which displayed a characteristic triangular configuration. Within this triangle, the cells showed no preferential orientation for their long axes were oriented obliquely, transversely or longitudinally. The dendrites arising from these clusters were oriented either longitudinally, medially, or laterally. The medially-oriented dendrites formed a subependymal plexus and some have been observed to cross the midline to the opposite side. The most significant finding was the presence of the white matter dendritic plexus which was formed by the laterally-directed bundles of dendrites. The present findings thus suggested that SPN-scg may be regulated by means of two circuits: the classical (medial) core circuit and a paralateral circuit which may convey supraspinal afferent inputs to the SPN-scg.

Efferent connections from the external cuneate nucleus to the medulla oblongata in the gerbil

The present study revealed the efferent projections from the external cuneate nucleus (ECN) to various medullary nuclei in the gerbil as demonstrated in fresh living brainstem slices by using in vitro anterogradely tracing with the dextran-tetramethyl-rhodamine-biotin. The tracer-labelled ECN axon terminals were observed (1) in most of the vital autonomic-related nuclei: the nucleus solitary tractus, nucleus ambiguus, rostroventrolateral reticular nucleus and C2 adrenergic area, (2) in the reticular formation: the medullary, parvocellular, intermediate, gigantocellular, dorsal paragigantocellular and lateral paragigantocellular reticular nuclei and medullary linear nucleus, and (3) in sensory nuclei: the cuneate nucleus, spinal trigeminal nuclei caudalis and interpolaris, paratrigeminal nucleus, medial and spinal vestibular nuclei, inferior olive and prepositus hypoglossal nucleus. These new findings are discussed in relation to possible roles of the ECN in cardiovascular, respiratory and sensorimotor controls.

The effects of subcutaneous injections of glucocorticoids on amoeboid microglia in postnatal rats

Subcutaneous injections of glucocorticoids into postnatal rats resulted in a drastic reduction in the number of amoeboid microglial cells in the corpus callosum as shown by their labelling with the monoclonal antibodies of the OX-series, ED1, lectin and rhodamine isothiocynate (RhIc). In rats receiving 2 or 3 injections of glucocorticoids and killed at the age of 4 or 7 days, between 40 to 60% of the callosal amoeboid microglial cells were depleted when compared with the corresponding control animals. The cells that survived the glucocorticoid treatments became ramified, while those in the controls of the same age group remained round or amoeboidic. In rats killed at 2 or 3 weeks of age, the microglia became extremely ramified with a concomitant diminution in their immunostaining, particularly in the glucocorticoid-injected rats. In rats receiving glucocorticoid injections along with RhIc, the RhIc-laden amoeboid microglia appeared round and amoeboidic and were intensely stained with OX-42, suggesting their activation and upregulation of complement type 3 receptors when compared with rats receiving only glucocorticoids. Compared with the control, cellular proliferation continued in rats given glucocorticoid injection as indicated by the occurrence of many bromodeoxyuridine-labelled cells in the corpus callosum at the age of 6 days. Ultrastructural studies confirmed the presence of mitotic cells identified as amoeboid microglia because of their labelling with isolectin. A striking ultrastructural feature in glucocorticoids-injected rats was the wide occurrence of amoeboid microglial cells that had ingested a variable number of lectin-labelled cells. It is concluded from this study that the drastic reduction of amoeboid microglia after glucocorticoid injections can be attributed to the suppression of their precursor cells, monocytes. Another possible explanation is the acceleration of their degeneration process, probably greatly enhanced by glucocorticoids; the degenerating amoeboid microglia were readily eliminated by the surviving amoeboid microglial cells through endocytosis. Glucocorticoids also accelerated the maturation process of the persisting amoeboid microglia to become ramified in form.

Up-regulation of surface antigens on epiplexus cells in postnatal rats following intraperitoneal injections of lipopolysaccharide

Epiplexus cells in postnatal rats exhibited a remarkable up-regulation of major histocompatibility complex class I and II antigen expression after intraperitoneal administration of bacterial lipopolysaccharide; other surface antigens, i.e. complement type 3 receptors and leukocyte common antigens, were also vigorously elevated when compared with those of the corresponding control rats. The immunostaining of epiplexus cells with OX-42, OX-18 and OX-1 for the detection of complement type 3 receptors, major histocompatibility class I and leukocyte common antigens, respectively, was noticeably enhanced with a drastic increase in their numbers. The most significant finding was the upsurge of OX-6-positive epiplexus cells exhibiting major histocompatibility class II antigens, especially in rats receiving two intraperitoneal injections of lipopolysaccharide and killed at the age of 14 days. Immunoelectron microscopy confirmed the above findings and added the fact that the immunoreactive site was confined to the plasma membrane. An interesting feature was the occurrence of OX-6-positive macrophage-like cells in transit across the choroid epithelium. It is concluded from this study that the upsurge of immunopositive epiplexus cells after lipopolysaccharide injections was partly attributed to the infiltration of stromal macrophages which migrated across the epithelium. The up-regulation of major histocompatibility complex class I and II antigen expression on epiplexus cells by lipopolysaccharide would enable them to carry out self-recognizing and antigen-presenting function in the ventricular system.

A comparative Mac-1 immunocytochemical and lectin histochemical study of microglial cells in the normal and athymic mice

The number of microglial cells in the supraventricular part of the corpus callosum stained with Mac-1 antibody (against CR3 antigens) and the intensity of staining were studied in both the homozygous athymic nude mouse (nu/nu) and normal BALB/c mouse (+/+). For quantitative analysis, the mean microglial cell counts (expressed in terms of packing density) from 40 microns thick immunostained sections were obtained and tested by analysis of variance. The Mac-1 positive cells in neonatal nude mice were slightly less intensely stained than those of their normal littermates. Such was not noticeable in the 13-week- and 1-year-old animals. The mean number of immunopositive microglial cells per 0.0324 mm2 was significantly less in the 5-day-old (P < 0.001) and 13-week-old (P < 0.05) nude mice when compared to normal mice of corresponding ages. The difference was insignificant in the 1-year-old nude and normal mice. The distribution of Mac-1 labelled microglia in different areas of the brain of the postnatal nude and normal mouse was also examined. In the brain areas examined, e.g., the olfactory bulb, cerebral and cerebellar cortex, the number of microglia in the nude mouse was considerably reduced. The study of lectin labelled sections also showed a much smaller number of labelled microglial cells in the athymic mouse. This was especially obvious in the 5-day-old nude mouse when compared to the normal BALB/c mouse (P < 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Immunophenotypic features of epiplexus cells and their response to interferon gamma injected intraperitoneally in postnatal rats

The expression of major histocompatibility complex (MHC) antigens (class I and II), type 3 complement receptor (CR3) and leucocyte common antigen (LCA) was examined in epiplexus cells in rats of different ages. The cells exhibited intense immunoreactivity with the monoclonal antibody OX-42 which recognizes CR3 receptors. In early postnatal rats (1 d), the immunolabelled cells were mostly round but with increasing age (7 wk), they assumed a ramified or elongated form. The expression of LCA marked by the monoclonal antibody OX-1 followed a similar staining pattern. Class I MHC antigen expression was also demonstrated in some epiplexus cells using the monoclonal antibody OX-18 but they were less numerous than the OX-42 or OX-1 positive cells. Only sporadic OX-6 positive cells were observed in postnatal rats but they showed a marked increase in number in adult rats, suggesting an upregulation of class II MHC antigens with age. The expression of MHC class II antigens was vigorously elevated in postnatal rats receiving 6 successive intraperitoneal (i.p.) injections of interferon gamma (IFN-gamma). In these animals, a large number of intensely stained OX-6 positive epiplexus cells were observed. These were mostly elongated or ramified with long processes. The immunostaining of epiplexus cells with OX-18 was also enhanced after IFN-gamma injections but the expression of CR3 and LCA appeared to be unaffected. It is concluded that the expression of MHC class I and II antigens on epiplexus cells is upregulated and induced respectively after successive i.p. injections of IFN-gamma into postnatal rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Alzheimer's disease cerebrospinal fluid antibodies display selectivity for microglia. Investigations with cell cultures and human cortical biopsies

Previous investigations demonstrated that the cerebrospinal fluid (CSF) from Alzheimer's disease (AD) patients contains antibodies that recognize specific neuronal populations in the adult rat central nervous system (CNS). These findings suggest a pathogenic role for immunological aberrations in this disorder. To determine if antibodies may provide a means to differentially diagnose the dementias, CSF from a diversified dementia population was screened against the developing rat CNS and a cell culture system. Markings produced by AD CSF were distinctly different from those of vascular dementias (VAD) against the developing rat CNS. More importantly, some AD CSF recognized amoeboid microglia. The recognition of amoeboid microglia by antibodies in AD CSF is particularly interesting since these cells proliferate in response to nervous system disease and also engulf debris. A cell culture technique was developed to allow the rapid screening of CSF antibodies. Patient CSF produced five different types of markings in the cell culture: microglia, glioblasts, fibers, nonspecific, or negative. Correlations with these structures and the diagnosis of four different dementia populations revealed that, in comparison to the other groups, AD CSF displayed remarkable selectivity toward microglial cells. Cortical biopsies from patients suspected to have AD were incubated with the patient's own CSF and that of confirmed AD patients. Both CSF samples recognized microglial cells in the patient's cortical biopsy. The same CSF samples incubated against normal human cortical autopsy or a biopsy from a 3-mo-old child displayed negative immunoreactivity. These three approaches suggest that the presence of CSF microglial antibodies may be a means to distinguish AD patients from other dementias. The results add further support to the widely growing concept that inflammation and similar immune mechanisms may contribute to AD pathogenesis.

Catecholamine-containing biodegradable microsphere implants as a novel approach in the treatment of CNS neurodegenerative disease. A review of experimental studies in DA-lesioned rats

Biodegradable controlled-release microsphere systems made with the biocompatible biodegradable polyester excipient poly(DL-lactide-co-glycolide) constitute an exciting new technology for drug delivery to the central nervous system (CNS). Implantable controlled-release microspheres containing dopamine (DA) or norepinephrine (NE) provide a novel means to compare DA- or NE -induced restitution of function in unilateral 6-hydroxydopamine lesioned rats. A suspension of 3 microL of DA- or NE-containing microspheres or empty microspheres was implanted in 2 sites of the DA denervated striatum of rats previously unilaterally lesioned with 6-hydroxydopamine. Contralateral-rotational behavior induced by apomorphine was used as an index of lesion success and, following implantation of the microspheres, also as an index of functional recovery. Interestingly, both DA- and NE-microsphere-implanted rats displayed a 30-50% reduction in the number of apomorphine-induced rotations up to 8 wk postimplantation. Rats implanted with empty microspheres did not demonstrate significant changes in contralateral rotational behavior. Behavioral studies following implantation of a mixture of DA and NE microspheres revealed an 80% decrease in the number of apomorphine induced rotations up to 4 wk. On conclusion of the studies, immunocytochemical examination revealed growth of DA and tyrosine hydroxylase immunoreactive fibers in the striatum of DA and NE microsphere-implanted rats. Functional behavior appeared to correlate with the degree of fiber growth. Preliminary electron microscopic studies showed signs of axonal sprouting in the vicinity of the implanted microspheres. No growth was noted in rats implanted with empty microspheres. This report reviews the abilities of both microencapsulated NE and DA to assure functional recovery and to promote DA fiber (re)growth in parkinsonian rats. This novel means to deliver these substances to the central nervous system could be of therapeutic usefulness in Parkinson's disease.

Studies of the lymphatic vessel-associated neurons in the intestine of the guinea pig

A unique group of neurons in the submucous plexus of the gastrointestinal tract in guinea pigs was studied using (1) Nissl staining and an enzyme histochemical technique for acetylcholinesterase (AChE), (2) immunohistochemical methods for the localisation of neuron specific enolase (NSE) and neuropeptides, including vasoactive intestinal peptide (VIP), substance P (SP), somatostatin (SOM), calcitonin gene-related peptide (CGRP), leu-enkephalin (leu-ENK), neuropeptide (NPY) and cholecystokinin (CCK), (3) a fluorescence tracer technique involving the intraperitoneal (i.p.) injection of fluorogold, and (4) normal electron microscopy. The results showed that these neurons were distributed singly or in groups in the submucosa. They were closely adherent to the outer walls of lymphatic vessels, some appearing to protrude into the lumen. Ultrastructurally, only a thin layer of basal lamina and some collagen fibrils intervened between the endothelia of the lymphatic vessels and these neurons. Based on their synaptic contacts and the features of their content of synaptic vesicles, at least 4 types of axon terminal forming synaptic contacts with the 'lymphatic vessel-associated neurons' (LV-AN) were identified. The sources of origin of these terminals remains uncertain although it is speculated that they may be derived from vagal efferents or of intrinsic origin from the neighbouring neurons. All the LV-AN showed AChE and NSE positive reactions, but only a varying number were positive for VIP, SP, SOM, ENK, CGRP, CCK or NPY. The LV-AN were labelled with fluorogold injected i.p.(ABSTRACT TRUNCATED AT 250 WORDS)

Expression of major histocompatibility complex class II antigen on amoeboid microglial cells in early postnatal rat brain following intraperitoneal injections of lipopolysaccharide

In rats given two single intraperitoneal injections of lipopolysaccharide (LPS) at 1 and 4 days of age and killed at 7 days of age, 11.5--12% of amoeboid microglial cells (AMC) in the supraventricular corpus callosum were induced to express major histocompatibility complex (MHC) class II antigen, as detected with monoclonal antibody OX-6. The MHC class II antigen induced was colocalized with MHC class I antigen and type 3 complement receptors on the same cells. The expression of MHC class II antigen on the plasma membrane of AMC was confirmed in immunoelectron microscopy. Although OX-6-positive AMC often assumed a perivascular position, the majority of them, however, were far removed from the blood vessels. The cytoplasmic processes of the perivascular OX-6-positive AMC appeared to rest directly on the vascular lamina, and in some section profiles they were in contact with a large surface area of the outer wall of small blood vessels. It is concluded from this study that although MHC class II antigen is not constitutively present on AMC, it is, however, inducible under stimulation with LPS. It is, therefore, suggested that the OX-6-positive AMC, especially the perivascular AMC, may have the potentiality to function as antigen-presenting cells in the developing brain when challenged by LPS.

Upregulation and induction of major histocompatibility complex class I and II antigens on microglial cells in early postnatal rat brain following intraperitoneal injections of recombinant interferon-gamma

Interferon-gamma when given intraperitoneally by single daily injection into one-day-old rats upregulated the expression of major histocompatibility complex class I antigen on ramified microglial cells in cerebral cortex and induced the expression of major histocompatibility complex class II antigen both on amoeboid and ramified microglial cells present in corpus callosum and cerebral cortex, respectively. In rats receiving single daily injections of interferon-gamma over a period of three consecutive days and killed at the age of seven days, the endothelium exhibited a moderate to weak immunoreaction for major histocompatibility complex class I antigen as detected with the monoclonal antibody OX-18. The immunoreactivity of major histocompatibility complex class I antigen on amoeboid microglial cells was comparable to that of control rats. On the other hand, it was remarkably enhanced on ramified microglial cells and was further intensified with four or six injections of interferon-gamma. In the latter, the endothelial cells also showed a stronger immunoreactivity with OX-18. In rats given three successive injections of interferon-gamma and killed at the age of seven days, 7.5% of amoeboid microglial cells in corpus callosum were induced to exhibit major histocompatibility complex class II antigen as detected with OX-6. An upsurge of the amoeboid microglial cells with major histocompatibility complex class II antigen amounting to about 40% was observed following four and six injections of interferon-gamma. A minimum of four successive injections of interferon-gamma were needed to elicit the expression of major histocompatibility complex class II antigen on ramified microglial cells in cerebral cortex.(ABSTRACT TRUNCATED AT 250 WORDS)

Down-regulation of membrane glycoprotein in amoeboid microglia transforming into ramified microglia in postnatal rat brain

The present study describes the ultrastructural localization and labelling pattern of lectin in different microglial cell phenotypes in the postnatal rat brain using the isolectin, GSA I-B4. The nascent round and amoeboid microglial cells (round cells and cells displaying short processes) were labelled at their cytoplasmic membrane and the membrane of the subplasmalemmal vacuoles. In the course of their transformation into ramified forms with age, dense lectin labelling was observed successively at different sites in the differentiating cells. The most striking feature was the staining of the Golgi saccules on the trans face, the trans tubular network and associated vesicles and vacuoles in the 'intermediate' ramified microglia (ramified cells bearing thick and long processes and those with thin and long processes). The vacuoles with accumulated reaction products were closely associated with many microtubules extending into the cytoplasmic processes. At the surface, the lectin-labelled vacuoles and vesicles appeared to fuse with the membrane and their contents communicated with the exterior. In the advanced or most differentiated ramified microglial cells (cells bearing attenuated processes), the lectin staining at all the above mentioned sites became diminished. In conclusion, in the transformation of the round microglia into their ramified derivatives, the glycoconjugates at the cytoplasmic membrane are progressively reduced. It is postulated from this study that the down-regulation of the glycoconjugates of the microglial plasma membrane is due primarily to their internalization during endocytosis. This process would trigger a de novo galactosyl protein synthesis and/or modification at the trans Golgi saccules and trans tubular network probably in an attempt to degrade the internalized membrane glycoproteins or to replenish the consumption of the membrane glycoconjugates.

Upregulation and induction of surface antigens with special reference to MHC class II expression in microglia in postnatal rat brain following intravenous or intraperitoneal injections of lipopolysaccharide

The effects of bacterial lipopolysaccharide (LPS) on the expression of surface antigens including major histocompatibility complex (MHC) and complement type 3 (CR3) receptors on microglial cells in the corpus callosum in postnatal rat brain were investigated. When LPS was injected intravenously (i.v.) in 1-d-old rats, the immunostaining of callosal amoeboid microglial cells with OX-18 directed against MHC class I antigen was enhanced 24 h after the injection in comparison with the controls. The expression of MHC class II (Ia) antigen on the same cell type as shown by its immunoreactivity with OX-6 was also elicited especially after 2 intraperitoneal (i.p.) injections of LPS. Thus 7 d after a single i.p. injection of LPS into 1-d-old rats, only a few OX-6 positive cells showing a moderate staining reaction were observed in the corpus callosum. The immunoreactivity diminished 14 d after the injection. However, in rats receiving 2 successive i.p. injections of LPS at 1 and 4 d of age and killed 7 d after the 1st injection, a significant number of intensely stained OX-6 positive amoeboid microglial cells were observed in the corpus callosum. The expression of MHC class II antigens induced by 2 injections of LPS was sustained at least until d 14 when the callosal ramified microglial cells, known to be derived from gradual metamorphic transformation of amoeboid microglia, still exhibited intense immunoreactivity with OX-6. The effect of LPS on the expression of CR3 on amoeboid microglial cells was not obvious after a single injection, but the immunoreactivity with OX-42 was also augmented in rats given 2 i.p. administration of LPS into rats at 1 an 4 d of age. It is concluded from this study that the expression of MHC class I and class II antigens on amoeboid microglial cells in corpus callosum was upregulated and induced respectively after i.v. or i.p. injection of LPS into early postnatal rats. Although relatively fewer in number when compared with OX-18 and OX-42 positive cells, it is suggested that the OX-6 positive cells would have the potentiality to function in antigen presentation in the postnatal rat brain when challenged by the endotoxin.

Studies of the ultrastructure and permeability of the blood-brain barrier in the developing corpus callosum in postnatal rat brain using electron dense tracers

The ultrastructure of the capillaries and their permeability to lanthanum ions and ferritin in the corpus callosum was examined in postnatal rat brain. In 1 and 7-d-old rats, numerous pinocytotic vesicles were observed in the endothelial cytoplasm of the callosal capillaries. Tight junctions were present between adjacent endothelial cells which were surrounded by an ill defined layer of basal lamina. The latter was almost devoid of astrocytic association in 1 d rats and partially covered by astrocytic end-feet in 7 d rats. Pericytes were a common feature. Amoeboid microglial cells were in direct contact with some parts of the vascular wall. Large extracellular spaces were present around the capillaries. In 14 d rats, the walls of the callosal capillaries became more well developed and were surrounded by a continuous sheath of astrocytic end-feet. The basal lamina became denser and well defined. The pericapillary spaces had diminished. Immunostaining for GFAP confirmed that, with age, the walls of the callosal capillaries became increasingly covered by the astrocytic end-feet. After perfusion with lanthanum, the tracer was deposited on the luminal surface but not in the abluminal side of the endothelial cells; the passage of the tracer was apparently obstructed in the intercellular space by the tight junctions in both the 1 and 14 d rats. When injected intravenously in 1-7 d rats, ferritin was transported across the endothelial cells by transcytosis and consequently taken up by the pericytes and amoeboid microglial cells contacting the basal lamina. In 14 d rats, the injected ferritin was only found in the endothelial cytoplasm. It was concluded that the difference in the capillary permeability to exogenous material in 1-7 and 14 d rats is due to the difference in the activities of the transendothelial transport. The pericytes and amoeboid microglial cells associated with the capillary probably play a role as phagocytes in maintaining the function of the blood-brain barrier by trapping any serum-derived foreign substances with astrocytes having a regulatory role in the formation of the barrier.

Studies of the distribution and functional roles of transitory amoeboid microglial cells in developing rat brain using exogenous horseradish peroxidase as a marker

When HRP was injected intraperitoneally (i. p.), labelled amoeboid microglial cells (AMC) were consistently localized in the subcortical white matter and circumventricular zones in early postnatal (1 and 7 days old) but absent in late postnatal (14-day-old) rats. The ingested HRP disappeared from the labelled cells 5 days after IP injection. Subcutaneous injection of HRP had also resulted in the labelling of amoeboid microglial cells in the corpus callosum of early postnatal rats. When the injected HRP was followed ultrastructurally over a time course sequence in intravenously (i. v.) injected rats, it was first detected in the invaginations on the luminal side of endothelium and in the endothelial cytoplasm 30 min after injection. HRP was present both in the endothelium and amoeboid microglial cells 3 hours later. With time, the tracer was progressively accumulated in the cytoplasm of AMC and it was sequestered in the vacuoles and lysosomes. It is concluded from this study that when injected i. p., i. v. or subcutaneously in the early postnatal rats, HRP is circulated to the blood vessels in the subcortical white matter and circumventricular zones where it gains access into the nervous tissues by transendothelial transport. The extravasated tracer is then phagocytosed by the residential AMC and subsequently degraded. The absence of labelling of AMC is attributed to the maturation of BBB which impedes the entry of exogenous tracer by the 14th postnatal day.

Uptake of tracer by the epiplexus cells via the choroid plexus epithelium following an intravenous or intraperitoneal injection of horseradish peroxidase in rats

Rapid passage of horseradish peroxidase (HRP) from the blood circulation to the cerebrospinal fluid was demonstrated in postnatal rats. At 30 min-1 h after an intravenous (i.v.) injection of HRP, the extravasated tracer from the blood vessels entered the connective tissue of the choroid plexus to reach the epithelial intercellular spaces where it was retarded by the apical tight junctions. The HRP which accumulated in widened intercellular spaces was readily endocytosed by the epithelial cells, notably at their lateral surfaces. This was especially pronounced 3 h after the injection. The endocytosed HRP was either routed to lysosomes or discharged apically by exocytosis into the CSF via membrane-bound vesicles by the epithelial cells. After longer survival periods, i.e. 6 h after injection, the intercellular spaces were relatively clear of tracer. HRP-labelled vacuoles or vesicles had diminished with a concomitant increase in the number of lysosomes containing HRP reaction product. In the course of HRP injection, the epiplexus cells residing on the choroid epithelium progressively accumulated HRP by endocytosis so that in rats killed 6 h after injection, the cells were heavily loaded with HRP incorporated into massive lysosomes. The labelling pattern of epithelial and epiplexus cells in rats injected intraperitoneally followed that observed in those receiving i.v. injections. These results suggest that the epiplexus cells together with lysosomal activity by the choroid epithelial cells serve as a protective line of defence for the blood-CSF barrier which appears to be inefficient.

Immunohistochemical and lectin-labelling studies of the distribution and development of microglia in the spinal cord of postnatal rats

The present study describes the development and differentiation of microglial cells in the spinal cord of postnatal rats ranging from 1 day to 3 weeks of age. Using the monoclonal antibody OX-42, three different morphological forms of immunoreactive cells (SP, TLP, and AP) were identified based on their staining intensities, cell shapes and configurations of their cytoplasmic processes. Round or oval cells with short thick processes (SP) and cells with thick or thin long processes (TLP) were common in younger rats (1 day-1 week), while cells with attenuated processes (AP) preponderated in older animals (2-3 weeks). The immunoreactivity of microglial cells was gradually reduced as the cells differentiated progressively from the SP through the TLP type into the AP form. Similar results were obtained using the monoclonal antibody OX-18 and the isolectin Griffonia simplicifolia. None of the cells were stained with the antibody OX-6. A quantitative study showed a rapid increase in the cell density of OX-42 positive cells in both the gray and white matter from 1 day to 2 weeks of age, but this appeared to decrease thereafter. The increase in the cell density was attributed to the active proliferation of the cells as shown by the detection of many bromodeoxyuridine-labelled cells in the same region. Its reduction in 3-week-old rats was most probably due to the apparent expansion of the spinal cord as a result of the growth of its fibre size and other structural elements.

Cerebrospinal fluid microglial antibodies: potential diagnostic markers for immune mechanisms in Alzheimer's disease

Hallmark lesions of Alzheimer's disease (AD) are filled with reactive immunocompetent microglia, suggesting that immunological aberrations may participate in the pathophysiology of this disorder. Microglia may participate in the initial stages of neurodegeneration before the onset of dementia. If immune mediated processes are closely linked to neuronal breakdown it would be of importance to have a reliable means to detect these processes. Serum and cerebrospinal fluid (CSF) antibodies are discussed as such potential sources. The serendipitous use of the developing rat central nervous system (CNS) to screen CSF antibrain antibodies produced some unexpected findings. Firstly, CSF antibodies of AD and other dementia patients recognized distinctly different neuronal structures in the developing rat brain. Secondly, some AD CSF recognized fiber networks whereas others recognized amoeboid microglial cells. The same AD CSF which recognized amoeboid microglia cells also specifically marked activated microglia and neural macrophages in experimentally induced lesions. AD CSF microglial antibodies appear to be significant in view of the increasing association between microglia and neurogenerative processes in AD. In addition, CSF microglial antibodies are present in numerous at-risk descendants of familial AD patients. Some have subsequently developed the disorder. These findings together with the fact that microglial antibodies are usually found in the early stages of AD suggest that AD CSF microglial antibodies could be of value in detecting neurodegenerative processes before the onset of dementia. These findings add further support to the concept that inflammation and similar immune mechanisms may contribute to AD pathogenesis.

A study on the submandibular ganglion of the monkey with special reference to ultrastructural changes after lingual nerve sectioning

This study describes normal light and electron microscopic features of the monkey submandibular ganglion. The intraglandular ganglion is composed of a collection of smaller ganglia distributed mainly at the hilum of the submandibular gland: one or two large ganglia were often found along with the main duct, while the smaller ones were located at the periphery. All ganglion cells were covered by satellite cells. Ultrastructurally, the ganglion cells showed the usual features of autonomic neurons, being round to oval with a prominent nucleus and nucleolus. Their cytoplasm contained numerous randomly distributed organelles. Occasional ganglion cells showed darkened dendrites. The majority of the synapses observed were of the axo-dendritic type, although the axo-somatic type was not uncommon. In the latter, the axon terminals were sometimes seen to deeply invaginate the soma of the ganglion cells forming synaptic contacts. Non-synaptic desmosome-like junctional complexes were common between the ganglion cells. Following the severance of the lingual nerve, the ganglion showed structural alterations beginning 1 day after the operation. The earliest sign of change was the increase in the number of macrophages surrounding the ganglion. Three and five days after the lingual nerve sectioning, the number of darkened dendrites considerably increased. Associated with this change were neuronal nuclei displaying irregular outlines. Other changes involved the disintegration of the preganglionic fibres and their axon terminals. The latter were observed to be engulfed by the infiltrated macrophages and Schwann cells. By 7 days after the preganglionic parasympathectomy, the ganglion cells resumed normal features, suggesting the acute and reversible nature of the transneuronal degeneration of the monkey submandibular ganglion cells. This is further supported by the absence of cell death during the period examined.

Studies of activated microglia and macrophages in lumbosacral spinal cord following an intraperitoneal injection of 6-aminonicotinamide into adult rats

The anterior horns of the lumbosacral segment of the spinal cord in rats showed an extensive lesion following an intraperitoneal administration of 6-amino-nicotinamide (6-AN). Neuronal chromatolysis was observed in some of the large efferent neurons 1-7 days after the injection of 6-AN. The capability in their uptake of fluorogold and its retrograde transport was comparable to those in the normal rats. Small neurons presumably internuncial cells underwent degeneration. 8 weeks after 6-AN injection, all the surviving neurons appeared normal. 1 day after 6-AN injection microglial cells appeared activated as evidenced by the hypertrophy and expansion of their processes. A large number of macrophages were observed in the lesioned site 7 days after the administration of 6-AN. The activated microglia and macrophages showed intense immunoreactivity with the monoclonal antibody OX-42. The immunoreactivity declined with time so that by 4 weeks after the injection of 6-AN very weak immunoreactivity was seen on some very branched cells. A similar pattern of immunoreactivity was observed with the monoclonal antibodies OX-18 and OX-6. It was concluded from this study that neuronal chromatolysis and neuronal degeneration induced the expression of CR3 receptors (marked by OX-42) and MHC encoded antigens (marked by OX-18 and OX-6) in activated microglia and macrophages. With time the immunoreactivity decreased so that by 4 weeks after the administration of 6-AN only faint immunoreactivity was observed on some branched cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Intraventricular macrophages in the lateral ventricles with special reference to epiplexus cells: a quantitative analysis and their uptake of fluorescent tracer injected intraperitoneally in rats of different ages

The labelling of epiplexus cells associated with the choroid plexus in the lateral ventricles was examined in rats of different ages with the fluorescent dye, rhodamine isothiocyanate (RhIc). A quantitative study was also attempted; this showed that the number of epiplexus cells and their related cells, namely supraependymal and free-floating cells, increased with age. The mean absolute number of epiplexus cells ranged from approximately 700 in the newborn to approximately 2200 in rats of 17 d of age; thereafter it remained unchanged. The number of free-floating cells also increased substantially but showed considerable individual variation. Following i.p. injection, the tracer was rapidly taken up by the epiplexus cells. This provided strong support for their phagocytic nature. In the newborn (1 d) and developing (13 d, 17 d) rats, RhIc-labelled epiplexus cells were first observed 3 h after the injection. In adult rats, labelled cells were not observed until 12 h after injection. In either case, the fluorescence in the epiplexus cells gradually increased with time. It is suggested from this study that the blood-CSF barrier in the choroid plexus in postnatal rats is incomplete, thereby allowing a rapid transvascular diffusion of the injected RhIc into the blood circulation. The fluorescent dye which enters the ventricle by way of the choroid epithelium is subsequently taken up by the epiplexus cells. Such an unimpeded passage, however, is reduced in the adult rats, probably due to the maturation of the blood capillaries as well as the choroid epithelium.

A qualitative and quantitative study of substance P immuno-cytochemistry of the trigeminal ganglion in the monkey

The immunoreactivity of substance P(SP) in the monkey trigeminal ganglion was examined and the distribution of immunoreactive cells determined. The monkey trigeminal ganglion is composed of clusters of sensory cells arranged in cords parallel to the long axis of the nerve fibres. The cells have prominent nuclei and are surrounded by satellite cells. Abundant organelles are randomly distributed throughout the cytoplasm. A striking feature of the ganglion was the presence of some axon-like prolifes containing mainly dense-cored vesicles and some agranular vesicles. Between 16 and 32% of the ganglion cells displayed SP-immunoreactivity. Most of the SP-IR cells were unipolar, small to medium-sized ganglion cells and they had no specific pattern of distribution. The staining of the SP-IR cells varied considerably, ranging from weak or moderate to heavy staining, although the majority of them were moderately stained. Immuno-electron microscopy showed that the SP-IR products were distributed throughout the soma of ganglion cells and not associated with any particular organelles or inclusions. The reaction products were also found in both myelinated and unmyelinated fibres between the ganglion cells. Another remarkable feature of the trigeminal ganglion was the occurrence of some SP-IR nerve fibres forming a rich "glomerular" network of pericellular arborizations around some of the SP-negative cells. Ultrastructural study showed the presence of some SP-IR nerve terminals in close approximation to some SP-negative cells, but there were no synaptic contacts. The relative frequency of the SP-IR pericellular arborizations paralleled the frequency of all the SP-IR cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparison of semen quality obtained by vibratory stimulation and masturbation

Six normal males underwent both penile vibratory stimulation and masturbation in order to compare the quantity and quality of semen produced by each method. There was no significant difference in the quantity and quality of the ejaculates produced by vibratory stimulation of the penis and masturbation. In addition, biochemical analysis of the seminal fluid collected by both procedures revealed similar values between all specimens for nine organic constituents, seven inorganic constituents and seven metabolic enzymes. None of the subjects demonstrated retrograde flow of semen. These findings indicate that vibratory stimulation is a 'physiological' means of inducing ejaculation, and can produce semen of normal quality.

A quantitative study of the differentiation of microglial cells in the developing cerebral cortex in rats

The distribution of various morphological forms of microglia stained with lectin in different regions of postnatal rat brain was examined in 2 planes of section, coronal and sagittal. In the coronal sections (mediolateral plane) taken at the level of the optic chiasma, the lectin-labelled cells were examined in the gustatory (GU), lateral somatosensory (LSS), medial somatosensory (MSS), motor (MO) and cingulate (CI) cortex. In the sagittal sections (rostrocaudal plane), the lectin-labelled cells in the medial orbital (MOA), motor (MO) and primary visual area (PVA) were studied. The cells in the motor area in coronal plane were further analysed with reference to their distribution in each of the laminae (layers). Based on the variation of their external morphology which represents different degrees of differentiation, all lectin-labelled microglial cells of the above-mentioned regions in newborn (P0) and rats aged 4 d (P4) and 8 d (P8) postnatum were classified and quantified. In the mediolateral plane of any given age group, the most differentiated ramified cells were located in GU except in P8 rats where the cells were also concentrated in CI. Of the 3 regions in the rostrocaudal plane the majority of the more differentiated ramified cells at P0 were found in the PVA but were the major cell type in MO in P4 and P8 rats. For the distribution of cells in MO, the most differentiated cells were located in the intermediate zones. It was concluded from this study that microglial cells in the developing cerebrum showed a gradient of differentiation in relation to different regions of the cerebral cortex but this appeared to vary with age. Thus in the mediolateral plane in P0 and P4 rats, the gradient extended from GU to CI in a lateromedial fashion but in P8, in the direction towards MSS from GU and CI. In the sagittal section, the gradient was directed caudorostrally in P0 rats. In P4 and P8 rats, however, the gradient was from MO to both poles (MOA, PVA). In the motor cortex, the gradient was from the intermediate zone towards the superficial and deep laminae. The gradient of differentiation of microglia may be related to the growth of the respective regions in the cerebral hemisphere but inherent genetic factors were also considered.

Variation with age in the labelling of amoeboid microglial cells in rats following intraperitoneal or intravenous injection of a fluorescent dye

Amoeboid microglial cells (AMC) in the corpus callosum were selectively labelled following a single intraperitoneal (i.p.) injection of the fluorescent dye, rhodamine isothiocyanate (RhIc) into postnatal rats. The frequency of RhIc-labelled cells varied with age, with the largest number occurring in 7-d-old animals. Thereafter, the labelled cells declined drastically in number and fluorescence and were barely detectable in 12-d-old injected rats. Labelled cells were absent in 13-d or older rats given an RhIc injection. When the injected RhIc was followed over a time course sequence, it was first detected in the cerebral blood vessels and their lining endothelia within 5 min after the injection. A variable number of AMC emitting a weaker fluorescence were closely adherent to the outer walls of the blood vessels. With time, the fluorescence in the AMC was progressively enhanced, but that in the blood vessels showed a concomitant reduction. In the rats that received an intravenous (i.v.) injection of RhIc, the labelling pattern of AMC, both in terms of its variation with age and in temporal sequence, paralleled that in rats given i.p. injections. In 12-d-old rats subjected to a stab wound coupled with an i.p. injection of RhIc, a considerable number of AMC not normally labelled at this age were activated. The cells exhibited an intense fluorescence and expressed MHC surface antigen immunoreactivity. It is concluded from this study that when injected i.p. or i.v., RhIc is readily circulated to the cerebral vessels, where it enters brain tissue by transendothelial transport.(ABSTRACT TRUNCATED AT 250 WORDS)