A histochemical study on the innervation of the cerebral blood vessels in bats

Vasomotor effects of noradrenaline, 5-hydroxytryptamine, angiotensin II, bradykinin, histamine, and acetylcholine on the bat (Rhinolophus ferrumequinum) basilar artery

The responsiveness of the basilar artery to intrinsic vasoactive substances is species-specific and can be a unique characteristic. We investigated the responsiveness of the bat (Rhinolophus ferrumequinum) basilar artery to noradrenaline (NA), 5-hydroxytryptamine (5-HT), angiotensin (Ang) II, bradykinin (BK), histamine (His), and acetylcholine (ACh). NA, 5-HT, Ang II, and BK induced contraction, whereas His and ACh induced relaxation, in a concentration-dependent manner. The NA cumulative concentration-response curve was shifted to the right in parallel with phentolamine (an α-antagonist). However, propranolol, a β-antagonist, had no significant effect. The 5-HT curve was shifted to the right in parallel by ketanserin (a 5-HT₂ antagonist) and methiothepin (a 5-HT₁ and 5-HT₂ antagonist). Losartan (an AT₁ antagonist) shifted the Ang II curve to the right, whereas PD123319 (an AT₂ antagonist) had no significant effect. L-NA, indomethacin, and des-Arg⁹-[Leu⁸]-BK (a B₁ antagonist) did not significantly affect BK-induced contractions. HOE140 (a B₂ antagonist) shifted the BK concentration-response curve to the right. The His curve was shifted to the right weakly by diphenhydramine (an H₁ antagonist) and strongly by cimetidine (a H₂ antagonist). ACh-induced relaxation was significantly inhibited by L-NA, atropine, and pFHHSiD (a muscarinic M₃ antagonist), whereas pirenzepine and methoctramine (muscarinic M₁ and M₂ antagonists, respectively) showed no significant effects. At a resting vascular tone, L-NA-induced contraction and indomethacin induced relaxation. These results suggest that α-adrenergic, 5-HT₁, 5-HT₂, AT₁, and B₂ receptors might be important in arterial contraction, whereas M₃ and H₂ (>H₁) receptors might modify these contractions, inducing relaxation.

Different Patterns of Vasoactive Intestinal Polypeptide (VIP)-Immunoreactive and Acetylcholinesterase (AChE)-Positive Innervation in the Internal Carotid Artery and Cerebral Arterial Tree of the Quail

The innervation pattern of vasoactive intestinal polypeptide-immunoreactive (VIP-IR) nerves in the quail internal carotid artery (ICA) and cerebral arterial tree was investigated and compared with that of acetylcholinesterase-positive (AChE-P) nerves. The supply of VIP-IR nerves to the two arterial systems was distinctly richer than that of AChE-P nerves. It was focused mainly on the walls from the distal ICA to the caudal half of the anterior ramus (AR) through the cerebral carotid artery (CCA). Indeed, double staining clearly showed that numerous VIP+/AChE-axons were distributed over these arterial regions where VIP+/AChE+ or AChE+/VIP- axons were sporadic or often lacking. The finding that nerve bundles accompanying the ICA within the carotid canal contained abundant VIP+/AChE- nerve cells suggests that cerebrovascular VIP-IR nerves in the quail have their major source at these neurons and enter the cranial cavity through the CCA. Another significant finding was that a small number of nerve cells, which were mostly stained for AChE alone and occasionally for VIP alone or both, occurred in the major arteries located more rostral than the middle AR. Thus, the quail cerebral arterial tree, at least the rostral segment of the anterior circulation, is multiply innervated by these three distinct categories of the extracranial and intracranial VIP-IR and AChE-P neurons.

Noradrenergic and cholinergic nerves in the uterus of the Japanese long-fingered bat, Miniopterus schreibersii fuliginosus, change with reproductive cycle

The pattern of uterine innervation by noradrenergic (NA) and acetylcholinesterase-positive (AChE) nerves in different reproductive stages of the adult Japanese long-fingered bats were investigated histochemically and immunohistochemically. In the non-pregnant bat, the uterine horn was supplied with abundant NA and AChE nerves. These two types of nerves were closely associated with the uterine arteries and myometrial smooth muscles. In the pregnant bat, NA and AChE nerves supplying the uterus did not degenerate much during hibernating period, but reduced markedly after arousal. In the postpartum bat, the density of nerves recovered progressively. The significant change in the innervation pattern of uterine NA and AChE nerves in the pregnant bats under and after hibernation, and in the postpartum bat must be considered in relation to the adrenergic and cholinergic controlling mechanisms on the uterine function that is matched for the unique reproductive cycle of this bat.

Innervation of cerebral blood vessels: morphology, plasticity, age-related, and Alzheimer's disease-related neurodegeneration

The light microscopical and ultrastructural morphology of the innervation of the major cerebral arteries and pial vessels is described, including the origins of the different groups of nerve fibres and their characteristic neurotransmitter phenotype. Species and region specific variations are described and novel data regarding the parasympathetic innervation of cerebral vessels are presented. The dynamic nature, or plasticity, of cerebrovascular innervation is emphasized in describing changes affecting particular subpopulations of neurons during normal ageing and in Alzheimer's disease. The molecular controls on plasticity are discussed with particular reference to target-associated factors such as the neurotrophins and their neuronal receptors, as well as extracellular matrix related factors such as laminin. Hypotheses are presented regarding the principal extrinsic and intrinsic influences on plasticity of the cerebrovascular innervation.

Nitrergic innervation of the cerebral arterial tree in the bent-winged bat (mammalia: Microchiroptera)

The distribution and origin of cerebrovascular nitrergic nerves were studied immunohistochemically and histochemically in the bent-winged bat. The supply of nitric oxide synthase (NOS)-immunoreactive (IR) and nicotinamide adenine dinucleotide phosphate diaphorase (NADPHd)-positive nerves to the bat major cerebral arteries differs from the general mammalian pattern in that it is preferential for the vertebrobasilar system (VBS) as opposed to the internal carotid system. Interestingly, a few nerve cells with bright NOS immunofluorescence and intense NADPHd activity were localized in the walls of the vertebral artery (VA) and basilar artery (BA) from many individual bats. Cerebral perivascular NOS-IR nerves were generally immunoreactive for vasoactive intestinal polypeptide (VIP). NOS-IR neurons intrinsic to the BA and VA expressed variable degrees of VIP immunoreactivity and showed no acetylcholinesterase (AChE) activity. Most cell bodies of the microganglia (MG) in the carotid canal and tympanic cavity, and those of the cranial and cervical facial ganglia, showed both NOS and VIP immunoreactivities and were stained intensely for NADPHd. From these and other findings, it is suggested that, in the bent-winged bat at least, the BA and VA of the cerebral arterial tree are frequently dually innervated by two neurochemically defined nitrergic neurons, the cranial parasympathetic VIP-IR and AChE-positive neurons, which are derived mainly from the MG via the internal carotid artery, and the intrinsic neurons, either IR or immunonegative for VIP but negative for AChE, which form an outflow tract from some caudally located ganglia projecting to the VBS via the VA.

Cholinergic and vasoactive intestinal polypeptidergic innervation of the cerebral arteries

Acetylcholine and vasoactive intestinal polypeptide are not only two vasoactive agonists that predominantly induce a vasodilatation of the cerebral arteries, but also correspond to neurotransmitters that innervate the various anatomical segments of the cerebral vasculature. The distinct patterns of the cerebrovascular cholinergic and vasoactive intestinal polypeptidergic innervation, their neurochemistry, in vitro and in vivo pharmacology, as well as the putative pathophysiological implications of these neurotransmission systems are critically summarized on the basis of the most recently published literature.

Nature and origin of cerebrovascular nerves with substance P immunoreactivity in bats (Mammalia: Microchiroptera), with special reference to species differences

Double staining immunohistochemistry was used to investigate the origin and projection of nerves with substance P (SP) immunoreactivity (-IR) in the walls of the major cerebral arteries in two microchiropteran species. In the greater horseshoe bat, most of the cerebral perivascular nerves with SP-IR did not exhibit calcitonin gene-related peptide (CGRP)-IR, but emitted bright immunofluorescence for vasoactive intestinal polypeptide (VIP). In this species, a large number of cell bodies with both SP- and VIP-IR were observed in many cranial ganglia along various branches of the facial and glossopharyngeal nerves. There were no cell bodies immunoreactive for either SP and VIP in the two sensory (trigeminal and upper cervical dorsal root), two sympathetic (superior cervical and stellate), or two vagal (superior and jugular) ganglia. In addition, several thick fiber bundles with both SP- and VIP-IR were present in the wall of the cerebral carotid artery, and descended progressively reaching as far as the middle part of the basilar artery (BA). These and other findings suggest that SP-immunoreactive nerves with VIP-IR but not CGRP-IR, which contribute to the rich innervation of the vertebrobasilar system in the greater horseshoe bat, originate from neurons with the same combination of peptide-IR in the major or local facial or glossopharyngeal parasympathetic ganglia, and enter the cranial cavity along the internal carotid artery. In the bent-winged bat, however, cerebral perivascular SP-immunoreactive nerves, as well as SP-immunoreactive neurons within the trigeminal and upper cervical dorsal root ganglia (uCDRG), showed neither CGRP-IR nor VIP-IR, and were mostly confined to the caudal BA and the vertebral artery (VA). These observations, in addition to the projection of this nerve type to the BA via the VA as fiber bundles, or through the meninges, indicate that the principal source of the cerebrovascular SP-immunoreactive innervation in this species is the uCDRG.

Effects of locus ceruleus lesions on the pericapillary nerve terminals in the feline brain

The effects of bilateral locus ceruleus (LC) lesions on the pericapillary nerve terminals were investigated in the feline brain parenchyma using electron microscopy. LC lesions were induced stereotaxically and the animals were sacrificed after intravenous administration of 5-hydroxydopamine (5-OHDA). The diameter and number of dense-cored vesicles (DCVs) and clear vesicles (CVs) in the pericapillary nerve terminals were measured. The number of DCVs in the nerve terminal was significantly decreased by bilateral LC lesions. The diameters of the DCVs and CVs decreased significantly as compared with those in the non-operated control group. These data suggest that the LC is closely related to the pericapillary nerve terminals in the brain parenchyma and that not only nerve terminals with DCVs but also those with CVs are affected by LC lesions.

Development of AChE-positive, NA-containing and VIP- and NPY-immunoreactive nerves in the major cerebral arteries of the rat

The development of cerebrovascular nerves containing noradrenaline (NA), acetylcholinesterase (AChE), neuropeptide Y (NPY), and vasoactive intestinal polypeptide (VIP) was studied in rats from before birth to adulthood. All these nerves entered the cranial cavity along the cerebral carotid, internal ethmoidal, and vertebral arteries during the early stages of development, but the subsequent growth and distribution of NA-containing and NPY-immunoreactive (IR) nerves differed greatly from that of AChE-positive and VIP-IR nerves. NA-containing and NPY-IR nerves extended rapidly from the cerebral carotid artery and spread over all the major arteries of the internal carotid system by postnatal day 3, as well as descending the posterior ramus of the cerebral carotid to mingle with nerves from the vertebral artery around the mid-basilar artery by day 5. AChE-positive and VIP-IR nerves from the internal ethmoidal artery covered the whole internal carotid system during the first postnatal week, and projected to the upper basilar artery after the second week, while those from the cerebral carotid artery remained limited to the middle cerebral artery throughout development. By day 21, all major arteries of the internal carotid system had dense plexuses of the four nerve types that were similar to those observed in adult rats. The vertebrobasilar system also had a well-organized network of NA-containing and NPY-IR nerves, but only a poor supply of AChE-positive and VIP-IR nerves. Even on day 30, the latter two nerve types were sometimes absent from the middle to caudal basilar artery, owing to a lack of interdigitation by nerves from the internal ethmoidal and vertebral arteries.

Vascular cholinesterases and choline uptake in isolated rat forebrain microvessels: a possible link

The two parameters of the active [methyl-3H]choline uptake into isolated rat forebrain microvessels, Km and Vmax, were determined for 1-, 3-, 10-, and 24-month-old Charles River male rats and compared with the activities of the enzymes choline acetyltransferase (ChAT), acetylcholinesterase (AChE), and butyrylcholinesterase (BuChE) in these microvessels over the same time course. The value of Km remained constant over the entire period, but that of Vmax increased from 8.5 +/- 1.0 to 80.6 +/- 16.4 nmol g-1 (mean +/- SEM) over the first 3 months of life. Over the same period, the increase in ChAT activity, from an initial value of 7.1 +/- 1.6 to 10.2 +/- 0.3 nmol g-1 min-1, was not proportional to that of choline uptake. Levels of BuChE activity (0.9-1.3 mumol g-1 min-1) were almost unchanged throughout the entire 24-month period, but those of AChE showed a steady and significant increase from 1 to 24 months, remaining relatively high at senescence (4.7 mumol g-1 min-1), when choline uptake had decreased to one-third of its optimal value. Selective inhibition of AChE with 1,5-bis(4-allyldimethylammonium-phenyl)pentan-3-one dibromide (0.5 microM) in unruptured capillaries from 3-month-old rats resulted in a decrease in Vmax of choline uptake from approximately 81 to 59 nmol g-1 min-1 or with 9-amino-1,2,3,4-tetrahydroacridine (10 microM) in capillaries from 2-month-old rats from approximately 30 to 15 nmol g-1 min-1. Selective inhibition of BuChE with tetraisopropyl pyrophosphoramide (100 microM) resulted in an increase in Vmax from approximately 81 to 96 nmol g-1 min-1. It is possible that the two vascular enzyme systems are coupled to a hypothetical endothelial choline transporter, but with an action opposite to each other.

Comparison of the muscarinic receptors in the coronary artery, cerebral artery and atrium of the pig

The affinity of various muscarinic antagonists for the muscarinic receptors mediating contraction (induced by acetyl-beta-methylcholine) of the isolated pig coronary and basilar artery was determined in order to compare the muscarinic receptor subtype involved in the contractile response of these arteries. In order to identify the muscarinic receptor subtype(s) involved, the affinity of the antagonists for the M2 receptor present in the pig atria was also investigated. The following muscarinic antagonists were used: atropine, pirenzepine, AF-DX 116 (11-2[[2-[(diethylamino)methyl]-1- piperidinyl]acetyl]-5,11-dihydro-6H- pyrido[2,3-b][1,4]benzodiazepin-6-one),4-DAMP(4-diphenylacetoxy-N- methylpiperidine methiodide), HHSiD (hexahydrosiladifenidol), methoctramine (N,N'-bis[6-[(2- methoxybenzyl)amino]hexyl]-1,8-octane-diamine tetrahydrochloride) and ipratropium. The order of affinity of the antagonists with respect to the muscarinic receptor in the coronary artery was clearly different from that for the muscarinic receptor in the basilar artery. The order of affinity established on the basilar artery closely resembled that for the M2 receptor in the atria. It is concluded that the muscarinic receptors on smooth muscle of the coronary and basilar arteries are not identical. The muscarinic receptor involved in the contraction of the basilar artery adheres to the M2 receptor subtype. A comparison of the selectivity of the antagonists suggests that the muscarinic receptor involved in the contraction of the coronary artery belongs to the M3 (like in exocrine glands) or M4 (as found in ileal smooth muscle) receptor subtype.

An immunohistochemical study on the innervation of SP-IR nerves in the cerebral arteries of the bent-winged bat

The overall distribution of substance P (SP) immunoreactive (IR) nerves surrounding the cerebral arteries of the bent-winged bat were investigated immunohistochemically. In this microchiropteran species, the walls from the vertebral artery to the caudal part of the basilar artery have considerably well-developed plexuses of SP-IR nerves, whereas no demonstrable SP-IR fibers were found in the rostral part of the basilar artery, and in more rostrally located arteries the nerve supply was very sparse or occasionally lacking. This innervation pattern has not yet been established for the cerebral arterial systems of other mammals that have been studied under normal conditions, but it is very similar to the pattern of SP-IR innervation observed in the guinea pig and cat of which the trigeminal ganglia have been destroyed. From the combination of this and other immunohistochemical findings, it is suggested that SP-IR nerves innervating the vertebral and basilar arteries of the bent-winged bat originate from the upper cervical dorsal root ganglia (DRG) and enter the cranial cavity along the vertebral artery and through the meninges.

Acetylcholinesterase-containing fibers and choline acetyltransferase activity in isolated cerebral microvessels from goats

Microvessels have been isolated from goat cerebral cortex and caudate nucleus. The purity of the preparations was assessed by light microscopy and by the high enrichment in the marker enzymes alkaline phosphatase and gamma-glutamyltransferase. Choline acetyltransferase activity was detected in the vascular fractions, being significantly higher in capillaries than in larger vessels. Acetylcholinesterase (AChE)-containing fibers were visualized in vessels of different caliber. Vessels with diameters larger than 70-90 microns showed a network pattern of fibers similar to that of pial arteries. In small vessels (10-70 microns) longitudinal or helical fibers were observed with occasional side-branches that surround the vessel. No AChE staining was visualized in isolated capillaries under light microscopy. This study shows that isolated intracerebral microvessels are suitable preparations for histochemical studies of perivascular nerves. Taken together, the biochemical and histological results are in accordance with a cholinergic innervation of the goat intracerebral vasculature.

Distribution and origin of vasoactive intestinal polypeptide (VIP)-immunoreactive, acetylcholinesterase-positive and adrenergic nerves of the cerebral arteries in the bent-winged bat (Mammalia: Chiroptera)

The overall distribution and origins of vasoactive intestinal polypeptide (VIP)-immunoreactive (IR), acetylcholinesterase (AChE)-positive and adrenergic nerves in the walls of the cerebral arteries were investigated in the bent-winged bat. VIP-IR and AChE-positive nerves innervating the bat cerebral vasculature appear to arise mainly from VIP-IR and AChE-positive cell bodies within microganglia found in the nerve bundle accompanying the sympathetic nerve bundle within the tympanic cavity. These microganglia, as well as the nerve bundle containing them, do not emit catecholamine fluorescence, suggesting that they are of the cranial parasympathetic outflow, probably the facial or glossopharyngeal one. The axons from VIP-IR and AChE-positive microganglia run intermingled with sympathetic adrenergic nerves in the same thick fiber bundles, and reach the cranial cavity through the carotid canal. In addition, some of the VIP-IR fibers innervating the vertebro-basilar system, at least the basilar artery, originate from VIP-IR nerve cells located in the wall of this artery. The supply of VIP-IR fibers to the bat major cerebral arteries is the richest among mammals in that it is much greater in the vertebro-basilar system than in the internal carotid system: plexuses of VIP-IR nerves are particularly dense along the walls from the posterior ramus to posterior cerebral and basilar arteries. Small pial and intracerebral arteries of the vertebro-basilar system, especially those of the posterior cerebral artery which supply most parts of the diencephalon and cerebrum, are also richly innervated by peripheral VIP-IR fibers. This pattern corresponds well with the innervation pattern of adrenergic and AChE-positive nerves.

Ultrastructural characterization of choline acetyltransferase-containing neurons in the basal forebrain of rat: evidence for a cholinergic innervation of intracerebral blood vessels

The ultrastructural morphology and vascular associations of cholinergic neurons in the horizontal limb of the nucleus of the diagonal band of Broca (nDBBhl) and amygdala of rat were determined by the immunocytochemical localization of choline acetyltransferase (ChAT), the acetylcholine biosynthetic enzyme. Within the nDBBhl peroxidase reaction product was distributed throughout the cytoplasm of selectively labeled neuronal perikarya and dendrites. Labeled perikarya were characterized by an oval cell body (7-10 microns X 17-26 microns in diameter) in which was located a large nucleus and often a prominent nucleolus. Dendrites were by far the most numerous immuno-labeled profiles in the nDBBhl. The labeled dendrites had a cross-sectional diameter of 0.4-4.6 microns and contained numerous mitochondria and microtubules. Approximately 10% of all immunolabeled dendrites received synaptic contacts from unlabeled presynaptic boutons. In contrast to the relatively large number of ChAT-labeled dendrites within the nDBBhl, ChAT-positive axons were less frequently observed and immunolabeled axon terminals were never detected. The labeled axons had an outside diameter of 0.4-1.4 micron and were myelinated. The absence or relative paucity of immunolabeled terminals in the nDBBhl indicates that most if not all of the cholinergic perikarya within this nucleus are efferent projection neurons. The nDBB is known to have widespread projections to many areas of the neocortex, hippocampus, and amygdala. In the present study we examined the amygdala and observed many ChAT-labeled axon boutons. The immunolabeled varicosities contained numerous agranular vesicles and although ChAT-positive terminals were in direct contact with unlabeled neuronal elements within the amygdala, few if any synaptic densities were detected in a single plane of section. With respect to the vasculature, immunolabeled perikarya and dendrites within the nDBBhl and axon terminals in the amygdala were often in direct apposition to blood vessels. In many instances the labeled profile was observed lying directly on the basal lamina of a capillary endothelial cell. In no instance, however, were membrane densities observed. The presence of cholinergic neuronal elements contacting the vessel wall provides morphologic evidence suggesting that the neurogenic control of cerebral vasculature is in part mediated via a cholinergic mechanism.

A comparative study of the innervation of the choroid plexus in amphibia

The aminergic and cholinergic innervation of choroid plexuses in three species of amphibia was investigated. Plexuses of the Japanese toad and the bullfrog had poor innervation by adrenergic nerves of sympathetic origin, but in the clawed toad, these plexuses were heavily innervated by adrenergic axons from ganglion cells located in the plexus stroma. Nerve fibers positive for acetylcholinesterase were not found in the plexuses, except for a few fibers with very weak enzyme activity in the clawed toad.

Neuronal control of brain microvessel function

Cerebral capillary endothelium forms a barrier limiting and controlling the movement of ions and solutes between blood and brain. Recent anatomical, physiological and biochemical studies have suggested the possibility that capillary function may be directly controlled by neuronal structures. Alterations in neuronal systems involved in the regulation of microcirculation may account for microvascular dysfunctions which occur in different pathologic conditions.

Biochemical evidence for cholinergic innervation of intracerebral blood vessels

Muscarinic cholinergic receptor sites were detected with [3H]quinuclidinylbenzilate (QNB) binding techniques in two fractions of bovine intracerebral vessels; one of the fractions contained primarily small arteries and veins with some attached capillaries, and the other one was highly enriched in capillaries. The amounts of binding were similar in equivalent vascular fractions isolated from cerebral cortex, caudate nucleus and cerebellar cortex in spite of large differences among the 3 regions in [3H]QNB binding to brain tissue. The different distribution of muscarinic receptors in brain tissue and blood vessels argues against the possibility that the receptors represent a contamination of the vascular fractions by brain parenchyma. Cerebral endothelial cells, which were isolated by treating capillaries with collagenase, bound [3H]QNB to the same extent as did cerebral capillaries. This is consistent with an endothelial localization of capillary muscarinic receptors. Choline acetyltransferase (ChAT) activity, a marker for cholinergic neurons, also was present in the vascular preparations. Within each brain region, ChAT activities in capillaries and larger vessels were similar, but significant regional differences were found for vascular ChAT activity, with the highest values in the caudate. Isolated endothelial cells contained significantly lower levels of ChAT activity than intact capillaries, suggesting a periendothelial location of the enzyme, as would also be the case for attached nerve terminals. The presence of [3H]QNB binding sites and ChAT activity in intracerebral blood vessels is consistent with an innervation of the cerebral vasculature by a cholinergic system that may regulate cerebral blood flow and capillary permeability.