Intracranial trajectories of sympathetic nerve fibers originating in the superior cervical ganglion in the rat: WGA-HRP anterograde labeling study

Sympathetic reinnervation of peripheral targets following bilateral axotomy of the adult superior cervical ganglion

The ability of adult injured postganglionic axons to reinnervate cerebrovascular targets is unknown, yet these axons can influence cerebral blood flow, particularly during REM sleep. The objective of the present study was to assess quantitatively the sympathetic reinnervation of vascular as well as non-vascular targets following bilateral axotomy of the superior cervical ganglion (SCG) at short term (1 day, 7 day) and long term (8 weeks, 12 weeks) survival time points. The sympathetic innervation of representative extracerebral blood vessels [internal carotid artery (ICA), basilar artery (BA), middle cerebral artery (MCA)], the submandibular gland (SMG), and pineal gland was quantified following injury using an antibody to tyrosine hydroxylase (TH). Changes in TH innervation were related to TH protein content in the SCG. At 7 day following bilateral SCG axotomy, all targets were significantly depleted of TH innervation, and the exact site on the BA where SCG input was lost could be discerned. Complete sympathetic reinnervation of the ICA was observed at long term survival times, yet TH innervation of other vascular targets showed significant decreases even at 12 weeks following axotomy. The SMG was fully reinnervated by 12 weeks, yet TH innervation of the pineal gland remained significantly decreased. TH protein in the SCG was significantly decreased at both short term and long term time points and showed little evidence of recovery. Our data demonstrate a slow reinnervation of most vascular targets following axotomy of the SCG with only minimal recovery of TH protein in the SCG at 12 weeks following injury.

On the presence of neurotrophin p75 receptor on rat sympathetic cerebrovascular nerves

Although the presence of neurotrophin p75 receptor on sympathetic nerves is a well-recognised feature, there is still a scarcity of details of the distribution of the receptor on cerebrovascular nerves. This study examined the distribution of p75 receptor on perivascular sympathetic nerves of the middle cerebral artery and the basilar artery of healthy young rats using immunohistochemical methods at the laser confocal microscope and transmission electron microscope levels. Immunofluorescence methods of detection of tyrosine hydroxylase (TH) in sympathetic nerves, p75 receptor associated with the nerves, and also S-100 protein in Schwann cells were applied in conjunction with confocal microscopy, while the pre-embedding single and double immunolabelling methods (ExtrAvidin and immuno-gold-silver) were applied for the electron microscopic examination. Immunofluorescence studies revealed "punctuate" distribution of the p75 receptor on sympathetic nerves including accompanying Schwann cells. Image analysis of the nerves showed that the level of co-localization of p75 receptor and TH was low. Immunolabelling applied at the electron microscope level also showed scarce co-localization of TH (which was intra-axonal) and p75. Immunoreactivity for p75 receptor was present on the cell membrane of perivascular axons and to a greater extent on the processes of accompanying Schwann cells. Some Schwann cell processes were adjacent to each other displaying strong immunoreactivity for p75 receptor; immunoreactivity was located on the extracellular sites of the adjacent cell membranes suggesting that the receptor was involved in cross talk between these. It is likely that variability of locations of p75 receptor detected in the study reflects diverse interactions of p75 receptor with axons and Schwann cells. It might also imply a diverse role for the receptor and/or the plasticity of sympathetic cerebrovascular nerves to neurotrophin signalling.

The circumventricular organs: an atlas of comparative anatomy and vascularization

The circumventricular organs are small sized structures lining the cavity of the third ventricle (neurohypophysis, vascular organ of the lamina terminalis, subfornical organ, pineal gland and subcommissural organ) and of the fourth ventricle (area postrema). Their particular location in relation to the ventricular cavities is to be noted: the subfornical organ, the subcommissural organ and the area postrema are situated at the confluence between ventricles while the neurohypophysis, the vascular organ of the lamina terminalis and the pineal gland line ventricular recesses. The main object of this work is to study the specific characteristics of the vascular architecture of these organs: their capillaries have a wall devoid of blood-brain barrier, as opposed to central capillaries. This particular arrangement allows direct exchange between the blood and the nervous tissue of these organs. This work is based on a unique set of histological preparations from 12 species of mammals and 5 species of birds, and is taking the form of an atlas.

Estrogen regulation of neurotrophin expression in sympathetic neurons and vascular targets

We hypothesize that estrogen exerts a modulatory effect on sympathetic neurons to reduce neural cardiovascular tone and that these effects are modulated by nerve growth factor (NGF), a neurotrophin that regulates sympathetic neuron survival and maintenance. We examined the effects of estrogen on NGF and tyrosine hydroxylase (TH) protein content in specific vascular targets. Ovariectomized, adult Sprague-Dawley rats were implanted with placebo or 17beta-estradiol (release rate, 0.05 mg/day). Fourteen days later, NGF levels in the superior cervical ganglia (SCG) and its targets, the heart, external carotid artery, and the extracerebral blood vessels, as well as estrogen receptor alpha (ERalpha) content levels in the heart, were determined using semi-quantitative Western blot analysis. TH levels in the SCG and extracerebral blood vessels were determined by Western blotting and immunocytochemistry, respectively. Circulating levels of 17beta-estradiol and prolactin (PRL) were quantified by RIA. Estrogen replacement significantly decreased NGF protein in the SCG and its targets, the external carotid artery, heart and extracerebral blood vessels. TH protein associated with the extracerebral blood vessels was also significantly decreased, but ERalpha levels were significantly increased in the heart following estrogen replacement. These results indicate that estrogen reduces NGF protein content in sympathetic vascular targets, which may lead to decreased sympathetic innervations to these targets, and therefore reduced sympathetic regulation. In addition, the estrogen-induced increase in ERalpha levels in the heart, a target tissue of the SCG, suggests that estrogen may sensitize the heart to further estrogen modulation, and possibly increase vasodilation of the coronary vasculature.

Cortical cooling induces conditioned consumption reduction in male rats

Previous studies have shown that male rats acquire a conditioned reduction in consumption of a sucrose solution when consumption of that taste solution is followed by cooling the caudate putamen. Because the shaft of the cold probe was not insulated, this cooling also included the cortex and meninges overlying the caudate putamen. When cooling the meninges was eliminated as a factor, the conditioned consumption reduction was weaker but it was not abolished. This suggests that meninges cooling contribute to the conditioned consumption reduction induced when all three structures are cooled, but it is not sufficient. Five experiments were designed to determine whether cooling the cortex also contributes. In the first experiment, the temperature of the cortex and meninges overlying the caudate putamen was measured during cooling. In the following three experiments the ability of male rats to acquire a conditioned consumption reduction was determined after pairing a sucrose solution with cooling the cortex and meninges overlying the caudate putamen, cooling the cortex with and without cooling the dura meninges membrane, and cooling the cortex with and without cooling the entire meninges. When the cortex was cooled without cooling the caudate putamen, dura, or entire meninges, a conditioned consumption reduction was acquired. The last experiment demonstrated that contingent pairing of sucrose and cortical cooling was required to obtain consumption reduction. These results clearly indicate that cortical cooling contributes to the acquisition of conditioned consumption reduction induced when the caudate putamen and overlying cortex and meninges are cooled. Two hypotheses are suggested to account for the ability of neural cooling to act as an unconditioned stimulus in the conditioned consumption reduction paradigm: (1) neuronal inactivation produces physiological changes that can serve as unconditioned stimuli and (2) cooling itself produces physiological changes that can serve as unconditioned stimuli.

On the atrophy of the internal carotid artery in capybara

Capybara might be a useful model for studying changes in cerebral circulation as the natural atrophy of the internal carotid artery (ICA) occurs in this animal at maturation. In this study, confocal and electron microscopy combined with immunohistochemical techniques were applied in order to reveal the changes in morphology and innervation to the proximal part of ICA in young (6-month-old) and mature (12-month-old) capybaras. Some features of the basilar artery (BA) were also revealed. The ICA of young animals degenerated to a ligamentous cord in mature animals. Immunolabelling positive for pan-neuronal marker protein gene product 9.5 but negative for tyrosine hydroxylase was observed in the proximal part of ICA at both ages examined. Axon varicosities positive for synaptophysin were present in the adventitia of ICA of young animals but were absent in the ligamentous cord of mature animals. In the ICA of young animals, adventitial connective tissue invaded the media suggesting that the process of regression of this artery began within the first 6 months of life. An increase in size of the BA was found in mature animals indicating increased blood flow in the vertebro-basilar system, possibly making capybara susceptible to cerebrovascular pathology (e.g. stroke). Capybara may therefore provide a natural model for studying adaptive responses to ICA regression/occlusion.

Ultrastructural Identification of a Sympathetic Component in the Hypoglossal Nerve of Hamsters Using Experimental Degeneration and Horseradish Peroxidase Methods

We employed experimental degeneration, tract-tracing with wheatgerm agglutinin conjugated with horseradish peroxidase (WGA-HRP) and electron microscopy to explore the postganglionic sympathetic fibers in the hypoglossal nerve of hamsters. Quantitative results of normal untreated animals at the electron microscopic level showed the existence of unmyelinated fibers, which made up about 20% of the total fibers in the nerve, being more numerous on the left side. The nerve fibers were preferentially distributed at the periphery of the nerve. Following superior cervical ganglionectomy, most of the unmyelinated fibers underwent degenerative changes. Tract-tracing studies showed that some of the unmyelinated fibers were labeled by WGA-HRP injected into the superior cervical ganglion (SCG). It is suggested that the unmyelinated fibers represent the postganglionic sympathetic fibers originated from the SCG.

Evidence for a central pathway in the cerebrovascular effects of spinal cord stimulation

OBJECTIVE

Cervical spinal cord stimulation (SCS) augments cerebral blood flow (CBF) in a number of animal models. The mechanisms underlying the cerebrovascular effects of SCS are not yet well delineated. In this study, we analyzed two alternative pathways in CBF alterations induced by SCS in rats, one involving direct modulation of sympathetic outflow and the other through central vasomotor influence.

METHODS

Resection of the superior cervical ganglion (SCG), SCS alone, or SCS after SCG removal was performed in adult male Sprague-Dawley rats. CBF was measured with (14)C-inosine monophosphate radiotracer studies. In another set of experiments, SCS was performed after spinalization at the cervicomedullary junction or after laminectomy alone.

RESULTS

Baseline CBF in the SCG removal group was 71 +/- 8 ml/100 g/min, similar to controls. SCS alone significantly increased blood flow to 100 +/- 10 ml/100 g/min (P < 0.05). Animals that underwent SCS after SCG removal demonstrated a similar robust augmentation in CBF. SCS-induced changes in CBF were completely attenuated by spinalization.

CONCLUSION

The profound effects of spinal cord transection on SCS-induced CBF augmentation, together with the lack of effect of surgical sympathectomy, suggest that the mechanisms underlying the effects of SCS involve central influences rather than cervical sympathetic outflow. These findings suggest a possible role for brainstem vasomotor centers in the cerebrovascular effects of SCS.

Basilar artery of the capybara (Hydrochaeris hydrochaeris): an ultrastructural study

The present study investigated the ultrastructural features of the basilar artery of the largest rodent species, the capybara. The study suggests that the general ultrastructural morphological organization of the basilar artery of the capybara is similar to that of small rodents. However, there are some exceptions. The basilar artery of the capybara contains a subpopulation of 'granular' vascular smooth muscle cells resembling monocytes and/or macrophages. The possibility cannot be excluded that the presence of these cells reflects the remodelling processes of the artery due to animal maturation and the regression of the internal carotid artery. To clarify this issue, more systemic studies are required involving capybaras of various ages.

Immobilization stress elevates tryptophan hydroxylase mRNA and protein in the rat raphe nuclei

BACKGROUND

Stress triggers adaptive and maladaptive changes in the central nervous system, including activation of the hypothalamic-pituitary-adrenal axis, and can trigger mood disorders and posttraumatic stress disorder. We examined the effect of immobilization stress (IMO) on gene expression of tryptophan hydroxylase (TPH), the rate-limiting enzyme in serotonin biosynthesis, and the role of cortisol in that response.

METHODS

Regular and adrenalectomized Sprague-Dawley rats were exposed to various repetitions of IMO. Tryptophan hydroxylase messenger ribonucleic acid (mRNA) was determined by competitive reverse transcriptase polymerase chain reaction, and TPH protein was examined by immunoblot and immunocytochemistry.

RESULTS

Elevation of TPH mRNA by IMO was tissue-specific and dose-dependent. A single IMO elicited a threefold rise in TPH mRNA in median raphe nucleus (MRN), but repeated (3x) IMOs were needed for similar response in dorsal raphe nucleus (DRN). Repeated daily IMO, up to 7 days, triggered a robust induction (6-10-fold) in TPH mRNA, accompanied by corresponding rise in TPH protein levels in raphe nuclei but not in the pineal gland. The rise in TPH immunoreactivity was widespread throughout the DRN and MRN. Bilateral adrenalectomy did not prevent the IMO-triggered increase in TPH immunoreactive protein in the raphe nuclei.

CONCLUSIONS

This study reveals adrenal glucocorticoid-independent induction of TPH gene expression in raphe nuclei in response to immobilization stress.

Anatomy of the tonsillar bed: topographical relationship between the palatine tonsil and the lingual branch of the glossopharyngeal nerve

Taste disturbance may result from injury to the lingual branch of the glossopharyngeal nerve (LBGN) during tonsillectomy. Because an understanding of the anatomy of this nerve is required in order to avoid injuring it, a gross, histologic anatomic study was undertaken of the topographical relationship between the LBGN and the muscle layer of the palatine tonsillar bed. Evaluation of 107 sides of 83 Japanese adult cadavers (aged 27-88 years) confirmed that the muscular composition and lamination of the tonsillar bed do not change with age or pathological conditions such as inflammation. In about a quarter (23.4%) of cases, the LBGN traveled inferior to the styloglossus muscle and lateral to the superior constrictor pharyngeal muscle over its whole course to the base of the tongue, so that the palatine tonsil was clearly separated from the LBGN. In 55.1% of cases, however, the muscle lining of the tonsillar bed was discontinuous and thin muscle bundles, derived from the stylopharyngeus, palatopharyngeus or superior constrictor pharyngeal muscle, partially covered the tonsillar capsule externally. Moreover, in 21.5% of cases the LBGN was firmly adherent to the tonsillar capsule, due to the complete absence of muscles lining the tonsillar bed. In these cases, and also probably in a similar percentage of patients undergoing tonsillectomy, taste disturbance may occur on removal of the hypertrophic tonsillar capsule. Therefore, minimal disturbance of the tonsillar bed is recommended in all cases of tonsillectomy.

The meninges contribute to the conditioned taste avoidance induced by neural cooling in male rats

After consumption of a novel sucrose solution, temporary cooling of neural areas that mediate conditioned taste avoidance can itself induce conditioned avoidance to the sucrose. It has been suggested that this effect is either a result of inactivation of neurons in these areas or of cooling the meninges. In a series of studies, we demonstrated that cooling the outer layer of the meninges, the dura mater, does not contribute to the conditioned taste avoidance induced by cooling any of these areas. The present experiments were designed to determine whether the inner layers of the meninges are involved. If they are involved, then one would expect that cooling locations in the brain that do not mediate conditioned taste avoidance, such as the caudate putamen (CP), would induce conditioned taste avoidance as long as the meninges were cooled as well. One also would expect that cooling neural tissue without cooling the meninges would reduce the strength of the conditioned taste avoidance. Experiment 1 established that the temperature of the neural tissue and meninges around the cold probes implanted in the CP were cooled to temperatures that have been shown to block synaptic transmission. Experiment 2 demonstrated that cooling the caudate putamen and overlying cortex and meninges induced conditioned taste avoidance. In experiment 3, a circle of meninges was cut away so that the caudate putamen and overlying cortex could be cooled without cooling the meninges. The strength of the conditioned taste avoidance was substantially reduced, but it was not entirely eliminated. These data support the hypothesis that cooling the meninges contributes to the conditioned taste avoidance induced by neural cooling. They also allow the possibility that neural inactivation produces physiological changes that can induce conditioned taste avoidance.

The role of the dura in conditioned taste avoidance induced by cooling the area postrema of male rats

Experiments were designed to assess the contribution of the dura mater to the formation of conditioned taste avoidance induced by cooling the area postrema. The results of the first experiment verified that the temperature of the dura showed a temperature gradient at various distances from the tip of the cold probe. In the second and third experiments, a circle of dura was cut away so that different amounts of the area postrema could be cooled without cooling the overlying dura. Cooling the dura plus the area postrema did not produce a stronger avoidance than just cooling the area postrema. In the fourth experiment, the cerebellar cortex was cooled with and without cooling the dura. Cooling the cerebellar cortex produced conditioned taste avoidance, and cooling the dura plus the cerebellar cortex did not produce a stronger avoidance. Taken together, these results suggest that cooling the dura mater does not contribute to the conditioned taste avoidance induced by cooling the area postrema. The results of the fifth experiment showed that cooling the area postrema produced a stronger conditioned taste avoidance than cooling the cerebellar cortex. It is suggested that the avoidance induced by cooling both of these structures is the result of physiological changes occurring when neurons in these structures are inactivated and when the subdural meninges are cooled. Furthermore, these changes are more severe when the area postrema is cooled.

The lateral sellar nerve plexus and its connections in humans

OBJECT

The aim of the present study was to elucidate the systematic topography of the lateral sellar (cavernous sinus [CS]) nerve plexus and its connections in humans.

METHODS

Seven specimens of human CS and adjacent regions were dissected in steps and stained as whole-mount preparations by using a sensitive acetylcholinesterase method. Another specimen was frozen, cut on a frontal plane, and stained for acetylcholinesterase. The human CS contains an extensive nerve plexus with small ganglia. The plexus is composed of a main part, the lateral sellar plexus proper, which is located around the abducent nerve and medial to the ophthalmic nerve, and a lateral extension just underneath the outermost layer of the lateral CS wall, which is located lateral to the trochlear and ophthalmic nerves. The lateral sellar plexus is connected to the internal carotid nerve, the pterygopalatine ganglion, and the trigeminal ganglion. From the lateral sellar plexus, nerve branches run along the oculomotor, trochlear, ophthalmic, and abducent nerves into the orbit. In addition, the lateral sellar plexus has multiple connections with nerves located around the internal carotid artery. The presence of connections between the lateral sellar plexus and functionally defined neural structures suggests that the plexus receives sympathetic, parasympathetic, and sensory contributions.

CONCLUSIONS

The plexus may distribute nerve subpopulations to several targets, including cerebral arteries and orbital structures. The presence of a mixed nerve plexus that projects to a variety of targets indicates that injury or disease in the CS may result in a variety of symptoms.

Ultrastructure of NADPH diaphorase-positive nerve fibers and their terminals in the rat cerebral arterial system

To investigate how perivascular NO synthase (NOS)-containing nerves in the cerebral arterial system are involved in controlling the cerebral circulation, we observed the ultrastructure of NOS-containing nerve fibers and their terminals by means of nicotinamide adenine dinucleotide hydrogen phosphate-diaphorase (NADPH-d) histochemistry. We also observed the correlation between NADPH-d stained perivascular nerves and the perivascular sympathetic nerves, by means of double staining with NADPH-d histochemistry and tyrosine hydroxylase (TH) immunohistochemistry at the light microscopic level. NADPH-d-positive nerve fibers showed dense distribution mainly in the rostral portion of the circle of Willis and proximal portions of its main branches, where some of the NADPH-d-positive fibers coexisted with TH-positive fibers in a single nerve bundle. NADPH-d-positive nerve fibers were unmyelinated and had close contact with NADPH-d-negative myelinated and unmyelinated nerve fibers in a single nerve bundle, and NADPH-d-positive nerve terminals also existed closely with NADPH-d-negative nerve terminals. The number of NADPH-d-positive nerve terminals and their ratio to all other terminals were significantly higher in the rostral portion of the circle of Willis and the proximal portion of its branches, than the caudal portion of the circle of Willis and the distal portion of its branches. Nerve terminals were observed to locate within 250 nm from the basal lamina of arterial smooth muscle cells in the rostral portion of the circle of Willis and proximal portion of its branching arteries. The present observation confirmed that NOS-containing nerve fibers truly innervate the smooth muscle cells of the arterial wall in the circle of Willis and its main branches. Close contact between NADPH-d-positive and -negative nerve fibers and terminals in these arterial portions may indicate that NOS-containing perivascular nerves may work to modulate the rest of the other perivascular nervous system, such as the sympathetic nerves, to regulate the homeostasis of the arterial tonus.

Intracranial distribution of the sympathetic system in mice: DiI tracing and immunocytochemical labeling

The intracranial distribution of the cephalic branches of the superior cervical ganglion (scg) was studied in mice using indocarbocyanine dye (DiI) anterograde tracing. Two main branches were traced from the scg. The first branch joined the nerve of the pterygoid canal (the vidian nerve), npc, from which several intracranial sympathetic branches passed to the branches of the trigeminal nerve (tgn), abducent nerve (abn), trochlear nerve (trn), and oculomotor nerve (ocn). Most of the second branch joined the abn, from which sympathetic fibers dispersed in the distal region of the trigeminal ganglion (tgg) to form a plexus close to the ganglion's branches. Branches from this plexus joined the branches of the tgn, trn, and ocn. Several minor branches arising from the second branch of the scg were also observed. One formed a sympathetic plexus around the internal carotid artery (ica); a second formed a sympathetic plexus in the proximal region of tgg, close to its root; and a third branch coursed laterally to reach the ear by passing along the greater petrosal nerve (gpn). All of the intracranial trajectories traced from scg were found to be catecholaminergic, and likely sympathetic, using tyrosine hydroxylase (TH) immunocytochemistry.

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.

Evidence of neuroanatomical connection between the superior cervical ganglion and hypoglossal nerve in the hamster as revealed by tract-tracing and degeneration methods

Previous studies have shown the existence of a sympathetic component in some cranial nerves including the hypoglossal nerve. In this study, the horseradish peroxidase (HRP) tract-tracing retrograde technique and experimental degeneration method were used to elucidate the possible neuroanatomical relationship between the superior cervical ganglion (SCG) and the hypoglossal nerve of hamsters. About 10% of the SCG principal neurons were HRP positive following the tracer application to the trunk of hypoglossal nerve. Most of the HRP-labelled neurons were multipolar and were randomly distributed in the ganglion. When HRP was injected into the medial branch of the hypoglossal nerve, some of the SCG neurons were labelled, but they were not detected when HRP was injected into the lateral branch. The present findings suggest that postganglionic sympathetic fibres from the SCG may travel along the hypoglossal nerve trunk via its medial branch to terminate in visceral targets such as the intralingual glands. By electron microscopy, the HRP reaction product was localised in the neuronal somata and numerous unmyelinated fibres in the SCG. In addition, HRP-labelled axon profiles considered to be the collateral branches of the principal neurons contained numerous clear round and a few dense core vesicles. Besides the above, some HRP-labelled small myelinated fibres, considered to be visceral afferents, were also present. Results of experimental degeneration following the severance of the hypoglossal nerve showed the presence of degenerating neuronal elements both in the hypoglossal nucleus and the SCG. This confirms that the hypoglossal nerve contains sympathetic component from the SCG which may be involved in regulation of the autonomic function of the tongue.

Cavernous sinus ganglia are sources for parasympathetic innervation of cerebral arteries in rat

Retrograde tracing and immunohistochemistry was used in rats to investigate whether the ganglia in the cavernous sinus contribute to cerebrovascular innervation. The cavernous sinus ganglia in rat include the cavernous part of the pterygopalatine ganglion (PGC) and small cavernous ganglia (CG). The tracers, fluorogold and fast blue, were applied to the middle cerebral artery in eight rats. After 1 to 4 days, the cavernous sinuses were dissected out and studied as whole mount preparations and sections. A moderate number of labeled neurons were visible in the ipsilateral PGC and CG. Furthermore, fibers in the cavernous nerve plexus and abducens nerve were labeled, suggesting that the pathway from the cavernous sinus ganglia to the cerebral arteries runs through the cavernous plexus and then retrogradely along the abducens nerve to the internal carotid artery. Selected sections were immunohistochemically stained for the cholinergic marker, vesicular acetylcholine transporter (VAChT). Most cells in the PGC and CG were VAChT-immunoreactive, some of which also contained tracer. It is concluded that in rat, the cavernous sinus ganglia, consisting of the PGC and small CG, contribute to parasympathetic cerebrovascular innervation and that the cavernous nerve plexus and abducens nerve are involved in the pathway from these ganglia to the cerebral arteries.

Carotid bifurcation pressure modulation of spontaneous activity in external and internal carotid nerves can occur in the superior cervical ganglion

Previous reports have suggested that a peripheral pressure-modulated reflex operates at the level of the superior cervical ganglion to alter evoked activity in the postganglionic nerves of the ganglion in both the cat and rabbit. In the present study we have examined if spontaneous activity of the external and internal carotid nerves of the rabbit superior cervical ganglion can be modulated during changes of the carotid bifurcation pressure (CBP), independent of central nervous system (CNS) integration. For external carotid nerve recordings increases in CBP resulted in a reduction in spontaneous activity while decreases in CBP were associated with an increase in spontaneous activity. For internal carotid nerve recordings similar effects were observed in the majority of recordings although a subset of recordings showed opposite effects or were not responsive to changes in pressure. To determine if vagus nerve afferents contribute to the observed pressure-modulated spontaneous activity effects, the influence of CBP on external carotid nerve recordings was examined before and after section of the vagus nerve rostral to the nodose ganglion. We found that even following section of the vagus nerve the external carotid nerve response to an increase in pressure remained intact. These results demonstrate that, after section of centrally-projecting afferent pathways from the carotid bifurcation to the CNS, changes in CBP can still modify spontaneous sympathetic activity of the rabbit superior cervical ganglion. The data reinforce previous findings related to evoked responses in the postganglionic nerves and also suggest that a pressure-modulated reflex, integrated at the level of the superior cervical ganglion, can influence ongoing sympathetic nervous outflow from the superior cervical ganglion in the rabbit.

Histochemical detection of age- and injury-related changes in signal transduction in the superior cervical ganglion

The superior cervical ganglion (SCG) is thought to be a good model for correlation studies of morphology, function and metabolism of neurons. The SCG has a relatively simple organization, it can be easily manipulated in situ, and it maintains synaptic transmission and a high metabolic rate during in vitro incubations. The histology and structure of SCG neurons have been characterized in detail, and physiologic stimuli, injury and aging have all been found to induce changes in the SCG morphology. During the last decade, research in the field of signal transduction has greatly expanded. Several signal transduction pathways have been identified that participate in the regulation of neurotransmitter synthesis, gene expression, neuronal excitability and growth factor responses of sympathetic neurons. We have been interested in using the SCG to study some of the second and third messengers involved in converting external stimuli received by sympathetic neurons into cellular short- and long-term events. Using immunohistochemistry, we have investigated protein kinase C-subtypes and the immediate early gene product Fos in the SCG, and characterized some of the changes induced by injury and aging in these messenger molecules. We will review the results and discuss the advantages and disadvantages of using histological methods in the study of signal transduction in sympathetic neurons.

Modification of superior cervical ganglion transmission, by changes of carotid bifurcation pressure

We investigated the effect of alterations in carotid bifurcation pressure on transmission in the superior cervical ganglion of pentobarbital-anaesthetized rabbits. Compound action potentials were evoked in the internal and external carotid nerves (post-ganglionic fibres) by electrical stimulation of the decentralized cervical sympathetic trunk. Pressure in the ipsilateral isolated carotid bifurcation (CBP) was maintained at a control value of 100 mmHg. Increases of CBP to between 125 and 200 mmHg caused graded reductions in the height and increases in the time to peak (TTP) of the S2 wave of the compound action potential recorded from the external carotid nerve (mean +/- SEM: -5.8 +/- 0.9% and +3.0 +/- 0.5%, respectively, at 200 mmHg, P < 0.05). In the same nerve, reductions in CBP to between 25 and 75 mmHg caused graduated increases in the height and decreases in TTP of the S2 wave (+6.3 +/- 0.8% and -2.8 +/- 0.4% at 25 mmHg, P < 0.05). Similar responses were obtained from the internal carotid nerve. The response of the S2 wave in the external carotid nerve to a step increase of CBP from 100 to 175 mmHg was examined before and after section of either the ganglioglomerular or carotid sinus nerve. Section of the ganglioglomerular nerve abolished the response (height and TTP of the S2 wave: before -10.7 +/- 0.8% and +5.9 +/- 0.9%; after -0.6 +/- 0.6% and +0.2 +/- 0.5%, P < 0.05). Section of the carotid sinus nerve had no effect on the S2 wave response. It appears that a population of ganglioglomerular nerve fibres, with pressure-sensitive endings located in the wall of the carotid bifurcation, form the afferent limb of a reflex integrated in the superior cervical ganglion of the rabbit. The efferent limb includes postganglionic fibres in the internal and external carotid nerves.

Neural connections in and around the cavernous sinus in rat, with special reference to cerebrovascular innervation

There is a confluence in and around the cavernous sinus of neural pathways innervating the intracranial structures. To determine the patterns of innervation, particularly of the cerebral arteries, we stained whole-mount preparations of the cavernous sinus and adjacent regions of the rat for acetylcholinesterase. The cavernous nerve plexus, with several small ganglia, mainly occupied the lateral wall of the sinus and extended laterally above the ophthalmic and maxillary divisions of the trigeminal nerve, in relation to the oculomotor and trochlear nerves. The cavernous plexus was connected to the pterygopalatine ganglion, the trigeminal ganglion, and the abducens nerve. The elongated pterygopalatine ganglion consisted of an orbital part, from which parasympathetic fibers ran to the cerebral arteries, and a cavernous part. Nerves from the lateral extension of the cavernous plexus ran rostrally into the orbit along the oculomotor, trochlear, and ophthalmic nerves, and caudally to the pineal gland along the trochlear nerve. Several branches also ran over the dura mater. Caudal to the cavernous sinus, we found two large nerves and a number of small nerves that ran between the nerves surrounding the internal carotid artery and the abducens nerve. These nerves may represent additional parasympathetic and/or sensory pathways to the cerebral arteries.

Assessment of the CO2 response by means of non diffusible contrast media and angio-CT in patients with cluster headache

We analyzed the possibility of assessing functional vasomotor changes by means of Arm-Brain Circulation Time (rABCT) and Vascular volume images (Vv) obtained with Angio-CT, in basal condition and following CO2 inhalation, in a sample of 48 patients with cluster headache. CO2 inhalation resulted in the appearance of local changes, which were detected in 28 regions. Analysis by indicator images of Vv-dependent rABCT distribution showed two main patterns: abnormal rABCT mostly evident at the smallest Vv pixels and abnormal rABCT dependent on abnormal Vv distribution. The former pattern was linked to abnormality at the circle of Willis; the latter to abnormal local vasomotor responses. Patients with cluster headache showed both patterns, which prompted us to conclude for the presence of low-degree stenosis in carotid arteries and vasomotor instability in peripheral brain vessels.

Sympathetic nerve trajectories to rat orbital targets: role of connective tissue pathways

The trajectories of sympathetic nerves projecting to orbital targets were determined in adult rats with intact innervation and following acute sympathetic denervation, neonatal unilateral superior cervical ganglionectomy, or unilateral ganglionectomy on postnatal day 30. Sympathetic nerves were identified by using immunofluorescence for the noradrenergic transmitter enzyme dopamine beta-hydroxylase and by using catecholamine histofluorescence. In rats with intact innervation, sympathetic fibers travel to the orbit in association with the abducens, trochlear, and Vidian nerves. Within the retroorbital and retroocular connective tissue, the fibers redistribute to become associated with sensory-nerve branches of the trigeminal nerve, the orbital vasculature, and the periorbital sheath. Fibers reach their targets by traversing variable amounts of connective tissue of the periorbitum, the orbital septa, and the striated muscle epimysia. Following neonatal ganglionectomy, intracranial fibers of contralateral origin enter the orbit by traveling through connective tissue of the optic nerve meninges and lining the anterior lacerated foramen. These fibers travel independent of the trochlear, abducens, and Vidian nerves, but, otherwise, they use the same orbital pathways as those employed in the intact animal. In animals ganglionectomized on postnatal day 30, fibers enter the posterior portion of the orbit primarily via the optic foramen; they travel only short distances and end blindly in the periorbital sheath. These findings indicate that fascial structures are a major component of the pathways that guide sympathetic fibers to their appropriate targets both in normal development and during reinnervation following neonatal ganglionectomy. Because orbital connective tissues are termination sites of abortive fiber sprouting in older rats, developmental changes in the properties of these tissues may contribute to the absence of pathway formation in the mature animal.

Origins of nitric oxide synthase-containing nerve fibers in the rat basilar artery with reference to the fine structure of the nerve fibers

The origins of nitric oxide synthase (NOS)-containing nerve fibers in the rat basilar artery were studied by a combination of Fluoro-Gold retrograde tracing and immunohistochemistry. After application of Fluoro-Gold onto the middle part of the basilar artery, the dye accumulated in the sphenopalatine, otic, trigeminal, superior cervical, nodose ganglia and in the spinal ganglia at level C2 and C3. Nerve cells with NOS-like immunoreactivity were detected in the above ganglia, except for the superior cervical ganglion. Neurons that showed both NOS-like immunoreactivity and Fluoro-Gold fluorescence were numerous in the sphenopalatine and otic ganglia, and less numerous in the trigeminal, nodose and spinal ganglia. Under electron microscopy, a number of unmyelinated nerve terminals with neuronal NOS-like immunoreactivity was seen in proximity to smooth muscle cells in the tunica media of the basilar artery. These findings provide morphological evidence that NOS-containing nerve fibers in the rat basilar artery have multiple origins, and suggest that the control of posterior cerebral circulation by the parasympathetic and sensory ganglia are more complex than previously considered.

Influence of cerebrovascular sympathetic, parasympathetic, and sensory nerves on autoregulation and spontaneous vasomotion

The effect of removal of cerebrovascular sympathetic, parasympathetic or sensory nerve on brain cortical blood flow and spontaneous vasomotion during changes in systemic blood pressure was studied by laser-Doppler flowmetry in anaesthetized rats. Selective section of sympathetic fibres along the internal carotid artery markedly affected the ability to autoregulate, as measured in microvessels of the middle cerebral arterial territory. Removal of the parasympathetic nerves tended to reduce the ability to autoregulate, whereas no significant influence was found after sensory denervation. Following the denervations, spontaneous vasomotion was not significantly affected in frequency or amplitude.

Peripheral neural circuits regulating IOP? A review of its anatomical backbone

The peripheral nervous system is classically separated into a somatic division containing both afferent and efferent pathways and an autonomic division composed of efferents only. The somatic afferent division is divided in A- and B-neurons. The B-neurons are supposed to be autonomic afferents as part of a reflex system involved in homeostasis. Recent data obtained by neuronal tracing and immunohistochemical experiments concerning the eye related peripheral nervous system endorse the existence of these peripheral reflex systems. Somatic afferents of trigeminal origin synaptically innervate parasympathetic neurons in the pterygopalatine ganglion. This probably represents a pathway mediating autonomically regulated ocular activity in response to sensory stimulation. In addition, it has been hypothesized that trigeminal sensory nerve fibres have an efferent function in response to noxious stimuli e.g. the ocular injury response. Sympathetic nerve fibres originating in the superior cervical ganglion course through the trigeminal and pterygopalatine ganglion without forming direct synaptic contacts. These fibres, however, contain clusters of vesicles suggesting some kind of interneural communication. Parasympathetic nerve fibres of pterygopalatine origin course through the ciliary ganglion. These nerve fibre terminals also contain clusters of vesicles without direct synaptic contacts. Experimental data concerning the distribution of neuropeptides revealed a more detailed knowledge of the anterior eye segment innervation. These experimental data are subject to some debate. The pros and cons of different techniques are discussed. Neural circuits regulating IOP have long been postulated. The possible role of peripheral reflex systems in the regulation of IOP is discussed.

Distribution and pathway of the cerebrovascular nerve fibers from the otic ganglion in the rat: anterograde tracing study

The distribution and pathway of cerebrovascular nerve fibers from the otic ganglion were studied by an anterograde tracing technique in the rat. Wheat germ agglutinin-horseradish peroxidase was injected as an anterograde axonal tracer into the otic ganglion on one side. Forty-eight hours later, the animals were killed and specimens were reacted with tetramethylbenzidine. Wheat germ agglutinin-horseradish peroxidase positive fine nerve fibers were observed in the circle of Willis and its branches, i.e., anterior cerebral artery, middle cerebral artery, internal ethmoidal artery and posterior cerebral artery, while no positive fiber could be detected in the vertebrobasilar artery. A positive reaction with tetramethylbenzidine was also observed in the lesser superficial petrosal nerve, the greater superficial petrosal nerve, the vidian nerve, the greater deep petrosal nerve, the internal carotid ganglion and the trigeminal ganglion. The sphenopalatine ganglion, however, failed to reveal any positive neurons or nerve fibers. It is concluded that the cerebrovascular nerve fibers originating from the otic ganglion run along the lesser superficial petrosal nerve to join the greater superficial petrosal nerve. They then reach the greater deep petrosal nerve and ascend along the internal carotid artery to distribute themselves to the cerebral blood vessels. This study demonstrated, for the first time, that the otic ganglion innervates the cerebral vessels and elucidated the pathway from the otic ganglion to the cerebral vessels directly by means of an anterograde axonal tracing technique.

Sensory and autonomic innervation of the rat eyelid: neuronal origins and peptide phenotypes

Neuronal origins, peptide phenotypes and target distributions were determined for sensory and autonomic nerves projecting to the eyelid. The retrograde tracer, Fluoro-Ruby, was injected into the superior tarsal muscle and meibomian gland of Sprague-Dawley rats. Labelled neurons were observed within the pterygopalatine (31 +/- 6 of a total of 8238 +/- 1610 ganglion neurons), trigeminal (173 +/- 43 of 62,082 +/- 5869) and superior cervical ganglia (184 +/- 35 of 21,900 +/- 1741). Immunostaining revealed vasoactive intestinal polypeptide immunoreactivity (VIP-ir) in nearly all Fluoro-Ruby-labelled pterygopalatine ganglion neurons (86 +/- 5%) but only rarely in trigeminal (0.3 +/- 0.3%) or superior cervical (1.4 +/- 1.4%) ganglion neurons. Calcitonin gene-related peptide (CGRP)-ir was not observed in pterygopalatine or superior cervical ganglion somata, but was present in 24 +/- 4% of trigeminal neurons. Bright dopamine beta-hydroxylase (DBH) immunofluorescence was observed in the majority of eyelid-projecting neurons within the superior cervical ganglia (65 +/- 5%) and lighter staining was detected in pterygopalatine neurons (63 +/- 3%), but no DBH-ir was observed in trigeminal neurons. Examination of eyelid sections revealed dense VIP-ir innervation of meibomian gland acini and vasculature and modest distribution within tarsal muscle. CGRP-ir fibers surrounded ductal and vascular elements of the meibomian gland and the perimeter of tarsal muscle. DBH-ir fibers were associated with meibomian gland blood vessels and acini, and were more densely distributed within tarsal muscle. This study provides evidence for prominent meibomian gland innervation by parasympathetic pterygopalatine ganglion VIP-ir neurons, with more restricted innervation by sensory trigeminal CGRP-ir and sympathetic neurons. Tarsal muscle receives abundant sympathetic innervation, as well as moderate parasympathetic and sensory CGRP-ir projections. The eyelid contains substantial non-CGRP-ir sensory innervation, the targets of which remain undetermined. The distribution of identified autonomic and sensory fibers is consistent with the idea that meibomian gland function, as well as that of the tarsal muscle, is regulated by peripheral innervation.

The trajectory of the sympathetic nerve fibers to the rat cochlea as revealed by anterograde and retrograde WGA-HRP tracing

Wheat germ agglutinin-horseradish peroxidase conjugate was injected in the unilateral superior cervical ganglion (SCG), and the projection pathways of postganglionic sympathetic nerve fibers innervating the cochlea were traced in the rat. The labeled axons advanced along the internal carotid artery (ICA), and a few advanced caudally in the major petrosal nerve (MPN) and entered the facial nerve, while the majority ran rostral to the pterygopalatine ganglion at the point where they crossed the MPN in the carotid canal. The rest of the labeled fibers remained on the surface of the ICA and advanced to the cranial cavity. Most of the labeled fibers along the facial nerve joined the cochlear nerve and finally reached the osseous spiral lamina through the spiral ganglion. Some of the labeled fibers ran along the anterior inferior cerebellar artery from the basilar artery which was previously thought to have been the only pathway. We could not find any labeled fiber on the modiolar artery from anterior inferior cerebellar artery in the cochlea. These observations are consistent with our hypothesis that the sympathetic fibers innervating the neural tissues or related structures follow nerve fibers and meninges as matrices of projection pathways rather than arteries.

Distribution patterns of sensory innervation from the trigeminal ganglion to cerebral arteries in rabbits studied by wheat germ agglutinin-conjugated horseradish peroxidase anterograde tracing

Distribution patterns of sensory nerves from the trigeminal ganglion to cerebral arteries in rabbits were studied by the wheat germ agglutinin-conjugated horseradish peroxidase anterograde tracing technique along with the 3,3',5,5'-teramethylbenzidine method. Labeled sensory nerves were densely distributed in whole-mount specimens of cerebral arteries after the injection of wheat germ agglutinin-conjugated horseradish peroxidase into the trigeminal ganglion. The characteristics of the innervation in rabbits included: 1) cerebrovascular sensory nerves were more dense in the ipsilateral side than in the contralateral side; 2) the anterior cerebral artery was less densely innervated than the posterior cerebral artery; 3) labeled nerves on the proximal segment of arteries were more prominent than those on the distal segment. The smallest pial branches of the middle cerebral, posterior cerebral, and anterior inferior cerebellar arteries overlying the fine sensory nerves were 50, 75, and 80 microns in diameter, respectively. Two patterns of the sensory innervation were seen. A meshwork pattern was mainly observed in the circle of Willis and the proximal segments of its main branches, as well as in the upper two thirds of the basilar artery; a parallel or slightly twisted pattern was shown in the small pial arterioles. Our results in this study may be useful to understand better the trigeminocerebrovascular system.

Parasympathetic cerebrovascular innervation: an anterograde tracing from the sphenopalatine ganglion in the rat

To elucidate parasympathetic cerebrovascular innervation of the rat sphenopalatine ganglion (SPG), we injected wheat germ agglutinin-conjugated horseradish peroxidase into the SPG of one side and traced anterogradely labeled nerve fibers. Three days after the injection, the animals were killed and tissues including the SPG, major cerebral arteries, and ethmoidal arteries were reacted by the tetramethylbenzidine method. A number of cells and nerve fibers labeled with wheat germ agglutinin-conjugated horseradish peroxidase were observed in the SPG. The nasal mucous membrane, the periorbital soft tissue, and the lacrimal gland of the injected side contained numerous labeled nerve fibers. In cerebral vessels, anterogradely labeled nerve fibers were observed around the internal ethmoidal, anterior cerebral, middle cerebral, internal carotid, and posterior cerebral arteries of both sides. A few labeled nerve fibers were seen on the wall of the basilar arteries of the distal portion, and the vertebral arteries contained no labeled nerve fiber. In animals of which the ethmoidal nerve and the external ethmoidal artery were cut together with the surrounding periorbital soft tissues just before entering the ethmoidal foramen, no labeled nerve fiber was identified on the wall of the major cerebral arteries. Although labeled gangliocytes were found in the trigeminal and superior cervical ganglia after the tracer injection to the ipsilateral SPG, the chronic maxillary neurotomy and superior cervical ganglionectomy did not alter the distribution of the labeled nerve fibers on the wall of the cerebral arteries.(ABSTRACT TRUNCATED AT 250 WORDS)

Sensory and sympathetic nerve sprouting in the rat cornea following neonatal administration of capsaicin

Corneal sensory and sympathetic nerves exert opposing actions on corneal mitogenesis and wound healing. The mechanisms by which these nerves exert their actions are unknown; however, the release of axonally transported neuropeptides has been postulated. In the present study, we investigated changes in innervation densities of calcitonin gene-related peptide (CGRP-) and tyrosine hydroxylase (TH-)immunoreactive (IR) nerves of the rat cornea following neonatal capsaicin administration, and the relationships between these changes and the development of neuroparalytic keratitis. Newborn rats were injected with capsaicin on each of the first 3 days of life. Forty-eight hours after the last injection, corneal CGRP immunostaining had totally disappeared from the cornea, whereas TH immunostaining was relatively unaffected. Over the next several weeks, a dramatic reinnervation of the cornea took place. By 6-8 weeks both the CGRP- and TH-IR corneal innervation density in the capsaicin-treated animals exceeded that of age-matched control or normal animals; that is, the corneas had become "hyper-reinnervated." The pattern of innervation that returned was grossly abnormal and was characterized by the presence of a bizarre subepithelial plexus of fine stromal sprouts; an abundance of myelinated axons; and complex, atypical, epithelial leash morphologies. Retrograde transport of wheatgerm agglutinin conjugated to horseradish peroxidase (WGA:HRP) from the central cornea in control and capsaicin-treated adult animals labeled an average of 143 and 47 trigeminal ganglion cells, respectively (with mean diameters of 25.7 +/- 0.49 microns and 34.3 +/- 0.72 microns), suggesting a 67% decrease in corneal afferent neurons in the capsaicin-treated animals. Transection of the ophthalmomaxillary nerve in adult capsaicin-treated animals completely eliminated corneal CGRP-IR staining, and extirpation of the superior cervical ganglion resulted in the loss of 70-80% of corneal TH-IR nerves, thus demonstrating the sensory and predominantly sympathetic origins, respectively, of these fiber populations. Chronic keratitis and neovascularization developed in the capsaicin-treated animals by approximately 3 weeks of age, achieved a maximum intensity between 4 and 6 weeks, and showed some gradual improvement thereafter. However, the keratitis never completely disappeared, even after 13 months. In conclusion, these data show that corneal sensory (CGRP-IR) and sympathetic (TH-IR) nerve fibers undergo extensive sprouting following partial corneal sensory denervation with the neurotoxin capsaicin. However, the resultant "hyper-reinnervation" is morphologically abnormal and, for reasons unknown, functionally incapable of preventing or totally reversing the keratitis.

Plasticity of the sympathetic nervous system innervating the cerebral arteries in rats

In order to investigate the neuroplasticity of the peripheral sympathetic nervous system innervating the cerebral blood vessels, we observed and traced the sprouting nerve fibers originating in the contralateral superior cervical ganglion (SCG) into the previously denervated cerebral arteries following unilateral excision of the SCG and/or decentralization of the contralateral SCG in young rats (4 weeks old). These nerve fibers were labeled anterogradely with wheat germ agglutinin-horseradish peroxidase or stained immunohistochemically with anti-tyrosine hydroxylase antibody. Eight weeks after the right SCG excision, reinnervating nerve fibers originating in the contralateral ganglion formed a circular pattern of nerve plexus only on the wall of the main cerebral arteries of the circle of Willis in the ganglionectomized side. However, the decentralization of the contralateral SCG, which was performed simultaneously with a unilateral SCG excision, prevented the nerve sprouting into the denervated regions. Unilateral decentralization of SCG itself failed to affect their distribution pattern or their density of nerve fibers originating in the ganglion. It is concluded that in the young rat the outgrowth of the sympathetic nerve fibers into the denervated cerebral arteries was strongly impeded by the disconnection of ganglion cells from the central nervous system, while the decentralization alone could not affect the innervation pattern of the postganglionic fibers which have been already built-up in the cerebral arterial system.

Developmental regulation of parasympathetic nerve density by sympathetic innervation in the tarsal smooth muscle of the rat

The developmental influence of sympathetic innervation on parasympathetic nerve density was investigated in the tarsal smooth muscle of the rat. Specificity of acetylcholinesterase staining as a marker for parasympathetic innervation was first determined by acute selective denervations. Excision of the ipsilateral superior cervical ganglion caused a 39% reduction in the density of acetylcholinesterase-positive nerves seven days later, indicating that sympathetic nerves contribute to cholinesterase-positive tarsal muscle innervation. Excision of the pterygopalatine ganglion concurrent with superior cervical ganglionectomy caused a virtually complete disappearance of acetylcholinesterase-positive innervation within seven days, indicating that non-sympathetic cholinesterase-positive fibers derive from the pterygopalatine ganglion and are presumed to be parasympathetic. Analysis of the control population indicated that parasympathetic nerve density did not vary significantly between males and females, between the superior and inferior muscles, or in rats studied at four and 12 months of age. The influence of sympathetic innervation on parasympathetic nerve density during postnatal development was examined by conducting surgical sympathectomies on postnatal day 5 and quantifying acetylcholinesterase-positive nerve density at four months of age. Neonatal sympathectomy caused a 46% reduction in cholinesterase-positive nerve density beyond that which occurred in acutely sympathectomized adult controls. It is concluded that sympathetic innervation is required for developing parasympathetic nerves to attain their normal density within the rat tarsal muscle. This finding is consistent with the idea that sympathetic nerves can exert positive effects on parasympathetic nerve outgrowth during development.

Nerve growth factor and septal grafts: a study of behavioral recovery following partial damage to the septum in rats

Previous studies have produced conflicting results about the effects of intracerebral injection of NGF after septal damage in rats: in one experiment, behavioral deficits in maze tasks were exacerbated by NGF administration whereas they were alleviated in another one. The present investigation aimed to clarify the effects of NGF and to identify factors liable to induce different behavioral outcomes. Behavioral effects were assessed following a postsurgical delay of five months using various parameters: food consumption in a novel environment, spontaneous activity, locomotion in an open-field, immobility in a tail suspension test, spontaneous alternation in a T-maze and performance in a radial eight-arm maze. Possible influence of intrahippocampal sympathetic fiber ingrowth occurring after septal lesions was ruled out, as the comparison of rats subjected to superior cervical ganglia removal with their lesion-control counterparts showed few behavioral differences, even after NGF administration. All lesioned rats showed reduced adaptability in most of these tests. Grafts partially reversed the lesion-induced deficit in spontaneous alternation. A single intracerebral NGF injection was found to ameliorate radial maze performance, whether rats were grafted or not. However, it appeared that the number of strategies available to NGF-rats in the radial maze task was as limited as for lesion-control rats. These findings suggest that NGF-rats do not recover spatial abilities lost after septal lesions, but are able to make more efficient use of remaining capacities to master the maze task.

Effects of hydrocephalus on the sympathetic nerves of cerebral arteries, investigated with WGA-HRP anterograde tracing in the rat

The effects of hydrocephalus on the plexus of sympathetic nerves of the intracranial vessels were investigated using wheat germ agglutinin combined with horseradish peroxidase (WGA-HRP). Hydrocephalus was induced by injection of kaolin into the cisterna magna of rats. Three weeks later the superior cervical ganglion (SCG) of one side received WGA-HRP. Three days later the circle of Willis and the contralateral superior cervical ganglion were dissected out. The intensity of labelling and density on the cerebral vessels and the number of labelled neurons on the contralateral superior cervical ganglion were calculated. The intensity of labelled nerves and thick bundles were significantly decreased, although tracing the nerve fibers throughout the length of the vessels was possible. The number of labelled neurons in the contralateral superior cervical ganglion indicated that the injection technique of WGA-HRP into the ganglion was correct in all rats. These results are in favour of the assumption, that the hydrocephalus related incomplete adrenergic denervation of the sympathetic perivascular nerve plexus was mainly due to neuropraxia of the nerve fibers rather than anatomical interruption of the axons.

Reorganization of cranial sympathetic pathways following neonatal ganglionectomy in the rat

Postganglionic sympathetic innervation normally is distributed ipsilaterally to lateral cranial targets. However, contralateral outgrowth occurs following unilateral ganglionectomy in neonatal rats. This study was conducted to determine the prevalence, morphological features, ganglionic derivations, and temporal sequence of sympathetic reinnervation of denervated cranial targets. Unilateral superior cervical ganglionectomy of mature rats revealed exclusively ipsilateral distributions of catecholaminergic histofluorescent fibers to orbital targets (Meibomian gland, tarsal muscle, orbital muscle, iris, ciliary body, vasculature) and the circle of Willis, with the exception of the anterior cerebral artery. In mature rats following neonatal unilateral ganglionectomy, all targets were reinnervated by fibers displaying morphologies and target relationships similar to normal innervation, but with lower densities. Acute excision of the remaining superior cervical ganglion eliminated all fibers in 7 of 8 preparations. In adult rats receiving neonatal bilateral superior cervical ganglionectomies, cerebral vasculature was reinnervated consistently, and orbital targets contained fluorescent fibers in 6 of 16 cases, indicating that reinnervation can derive from other sources when superior ganglion outgrowth is prevented. Observations in developing rats revealed fibers along the cranial portion of the contralateral optic nerve sheath at 2-3 days postganglionectomy, and within the orbit at later ages, reaching the most distal targets by 14 days. It is concluded that widespread sympathetic reinnervation of orbital and cerebrovascular targets derives primarily from the contralateral superior ganglion. Orbital ingrowth apparently originates intracranially and enters the orbit by an atypical pathway within the optic foramen.

Local distribution of the effects of sympathetic stimulation on cerebral blood flow in the rat

Although the density of sympathetic fibres on the cerebral vessels varies regionally, the cerebral circulatory effects of electrical stimulation of these fibres on the cerebral circulation have not been mapped in detail. In the present study the effects of sympathetic stimulation on local cerebral blood flow were examined in urethane anaesthetized rats using autoradiographic techniques. Initial experiments determined that unilateral stimulation of the superior cervical ganglion altered cerebral circulatory dynamics to an extent sufficient to reduce cerebral venous pressure by 1.1 +/- 0.2 mm Hg. Local cerebral blood flow was measured with iodo[14C]antipyrine autoradiography in 4 groups: (1) sham; (2) sham + unilateral sympathetic nerve section; (3) unilateral stimulation of the superior cervical ganglion; and (4) unilateral sympathetic stimulation + contralateral sympathetic nerve section. In the sham animals, local cerebral blood flow was equivalent in the innervated and denervated hemispheres. During stimulation plus contralateral nerve section, a regionally heterogeneous response to sympathetic stimulation was observed. Local cerebral blood flow was reduced 11-19% on the stimulated side in over one half (15/28) of the regions examined (e.g. thalamic nuclei and caudate nucleus). In general, ipsilateral reductions in flow occurred in the territory supplied by the middle cerebral, posterior cerebral and posterior communicating arteries and their branches. Cerebral blood flow was symmetrical in regions supplied by the basilar and anterior cerebral arteries and in some midline structures.

Appearance of retrogradely labeled neurons in the rat superior cervical ganglion after injection of wheat-germ agglutinin-horseradish peroxidase conjugate into the contralateral ganglion

Injection of wheat-germ agglutinin-horseradish peroxidase conjugate (WGA-HRP) into the superior cervical ganglion (SCG) of the rat results in accumulation of WGA-HRP in sympathetic postganglionic neurons in the contralateral SCG. The sympathetic pathways involved and the mechanism underlying the labeling were investigated. The labeling in neurons in the contralateral SCG was apparent 6 h after injection and increased in intensity with longer survival times. The number of labeled neurons reached 1300 at 72 h after the injection. Transection of the external (ECN) or internal carotid nerves (ICN) resulted in considerable reduction in the number of labeled neurons. Combined transection of both ECN and ICN virtually eliminated labeling in the contralateral SCG. This provides strong evidence that these two nerves are the major pathways for WGA-HRP transport out of the SCG. No labeling was observed in the contralateral SCG following injection of horseradish peroxidase (HRP). Therefore, it seems unlikely that a direct nerve connection exists between the bilateral ganglia. Instead, the labeling of contralateral SCG neurons appears to depend on the transneuronal transport capacity of WGA-HRP, which conveys the marker in an anterograde direction along the postganglionic fibers to terminals in sympathetic target organs, and then delivers it transneuronally to contralateral SCG neurons. We suggest that the sympathetic nerve fibers originating in the bilateral SCGs run intermingled and are in close contact in their peripheral target organs.

Increased expression of T alpha 1 alpha-tubulin mRNA during collateral and NGF-induced sprouting of sympathetic neurons

We have examined expression of T alpha 1 alpha-tubulin mRNA in the rat superior cervical ganglion (SCG) to determine whether changes in gene expression accompany neuronal sprouting and to investigate factors that regulate growth-associated genes in intact neurons. Northern blot analysis demonstrates that levels of T alpha 1 alpha-tubulin mRNA increase in the uninjured SCG following transection of contralateral neurons that project to bilaterally innervated, but not unilaterally innervated target organs. The observed increase in uninjured neurons is associated with collateral sprouting, as measured by increased tyrosine hydroxylase immunoreactivity within the pineal gland. These data suggest that target-derived factors may regulate T alpha 1 mRNA in sprouting neurons. Consistent with this hypothesis, systemic NGF treatment of neonatal animals over a developmental interval when T alpha 1 alpha-tubulin mRNA normally decreases led to a 5- to 10-fold increase in T alpha 1 mRNA levels in developing sympathetic neurons. In addition, deafferentation of the SCG, which promotes neuronal sprouting in the ganglion, increases T alpha 1 mRNA in ganglia on the ipsilateral and contralateral sides. Together, these data demonstrate that T alpha 1 alpha-tubulin mRNA elevates as a function of neuronal sprouting, and that T alpha 1 mRNA expression in intact neurons can be regulated by extrinsic cues, including NGF and changes in connectivity.

NGF-induced remodeling of mature uninjured axon collaterals

Accumulation of nerve growth factor (NGF) within the rat hippocampus following septal denervation is thought to contribute to sympathetic axon ingrowth. However, intraventricular NGF infusion, which results in elevated hippocampal NGF, fails to elicit such sprouting, although it increases innervation of the extracerebral vasculature. To determine whether or not NGF would stimulate sympathohippocampal sprouting, we infused NGF after sprouting was initiated. Surprisingly, NGF reduced the amount of hippocampal sprouting and, when infused at the time of lesion, delayed its onset while, at the same time, stimulating perivascular sprouting. Since NGF did not prevent ingrowth into the hippocampus from transplanted sympathetic ganglia, the reduction in sympathetic hippocampal fibers from intact ganglia appears to result from the proliferation of vascular fibers. Thus, changes in trophic support (NGF levels) appear to be sufficient to produce remodeling of mature, uninjured sympathetic arbors. Such trophomorphism may underlie collateral elimination during normal development and injury-induced neuronal rearrangements.

Somatostatin-, vasoactive intestinal polypeptide- and neuropeptide Y-like immunoreactivity in eye- and submandibular gland-projecting sympathetic neurons

Studies combine the use of the retrograde tracer, fluorogold, and immunocytochemical staining to determine whether superior cervical ganglion (SCG) neurons projecting to the iris or submandibular gland (SMG) in adult male and female rats show distinctive immunoreactivity to somatostatin (SS), vasoactive intestinal polypeptide (VIP), or neuropeptide Y. Overall, more SMG-projecting neurons than eye-projecting neurons contain VIP-like immunoreactivity (VIP-LI), and more eye-projecting neurons than SMG-projecting neurons contain SS-LI and VIP-LI. Thus, postganglionic neurons of the SCG that project to specific target tissues are heterogeneous in their peptide content, and there are differences in the pattern of peptide-immunoreactivity between neurons projecting to these two target tissues. In addition, the results indicate that there may be gender differences in the expression of these neuropeptides.

The allocation of nerve fibres to the anterior eye segment and peripheral ganglia of rats. II. The sympathetic innervation

The sympathetic innervation of the peripheral ganglia related to the eye, i.e. the trigeminal ganglion, the ciliary ganglion and the pterygopalatine ganglion, and of the anterior eye segment was studied in rats. Selective labelling of sympathetic nerves was obtained by means of injection of [3H]leucine into the superior cervical ganglion. Bundles of sympathetic nerve fibres were found in the trigeminal ganglion and the pterygopalatine ganglion but were absent in the ciliary ganglion. In addition individual sympathetic nerve fibres, which may have contacts with trigeminal ganglion cells, were found between the ganglion cell bodies all over the trigeminal ganglion indicating a sympathetic innervation of this ganglion. In the anterior eye segment, there appeared to be a sympathetic innervation of the ciliary cleft, the ciliary body and the iris. Within the ciliary body sympathetic nerve fibres innervate the central stroma and the stroma of the ciliary processes. Labelled sympathetic nerve fibres were also observed in the stroma of the iris and were most abundant in its periphery. Most sympathetic fibres reach the iris and ciliary body by way of the base of the ciliary body. Only few sympathetic fibres are present in the ciliary cleft. No sympathetic innervation of the cornea was found.

Origins and pathways of cerebrovascular nerves storing substance P and calcitonin gene-related peptide in rat

Origins and pathways of cerebrovascular substance P- and calcitonin gene-related peptide-positive nerves in rat were studied by immunohistochemistry combined with denervation experiments and retrograde axonal tracer technique. The two peptides have been found to coexist in one and the same neuron. After sectioning of the nasociliary nerve bilaterally the substance P/calcitonin gene-related peptide fibers in the rostral half of the circle of Willis and its branches were eliminated, whereas the number decreased in the caudal half of the circle of Willis and rostral two thirds of the basilar artery. Substance P/calcitonin gene-related peptide fibers in the internal carotid arteries, the caudal third of the basilar artery and the vertebral arteries were not affected by the nerve section. After application of the retrograde axonal tracer True Blue onto the proximal segment of the middle cerebral artery the dye accumulated in several Substance P/calcitonin gene-related peptide-containing cells in the ophthalmic division of the ipsilateral trigeminal ganglion and in a few cells in the maxillary trigeminal division and in the internal carotid miniganglion. No other cranial ganglia accumulating the dye contained any substance P/calcitonin gene-related peptide-positive cells. It is concluded that the rostral portion and part of the caudal portion of the cerebral vessels are innervated by substance P/calcitonin gene-related peptide-containing fibers from the trigeminal ganglion and the internal carotid miniganglion. The great majority of trigeminal fibers reach the vessels via the nasociliary nerve of the ophthalmic division, which enters the cranial cavity through the ethmoidal foramen, whereas fibers from the miniganglion project directly to the bypassing internal carotid artery. A probable pathway for the fibers from the maxillary division is suggested. The caudal portion receives, in addition, a supply from other sensory ganglia (lower cranial and/or upper cervical dorsal root ganglia).