The distribution of 5-hydroxytryptamine and norepinephrine in cat spinal cord

5-Hydroxytryptamine, substance P, and thyrotropin-releasing hormone in the adult cat spinal cord segment L7: immunohistochemical and chemical studies

The terminal projections of the descending 5-hydroxytryptamine (5-HT) bulbospinal pathway and the coexistence among 5-HT-, substance P (SP)-, and thyrotropin-releasing hormone (TRH)-like immunoreactivities (LI) in fibers innervating the L7 segment in the cat spinal cord were studied quantitatively and semiquantitatively by use of the indirect double-staining immunofluorescence technique. The content of 5-HT, SP, and TRH in different parts of the spinal cord was determined by use of radioimmunoassay (RIA) (SP and TRH) and high-performance liquid chromatography with electrochemical detection (HPLC-ECD) (5-HT). For all three substances studied, immunoreactive (IR) axon terminals were found in all parts of the gray matter, but with clear regional variation in the density of innervation. Thus, all three substances showed a dense innervation in the motor nucleus, particularly in the ventral part of the nucleus, while the superficial dorsal horn was very densely innervated by SP-IR fibers (laminae I and II) and TRH-IR fibers (laminae II and III). In the motor nucleus, the studied substances coexisted to a very high degree, but some 5-HT-IR fibers (about 10%) lacked peptide-LI and some SP-IR fibers (about 10%) lacked 5-HT-LI while virtually all TRH-IR fibers also contained 5-HT-LI. In the superficial dorsal horn (laminae I-III), no coexistence was detected, while other parts of the gray matter displayed various degrees of coexistence in between those found in the motor nucleus and laminae I-III. The quantitative analysis of IR varicosities in the motor nucleus suggested that the unilateral L7 motor nucleus is innervated by about 55-110 x 10(6) 5-HT-IR nerve terminals, which may indicate as many as 4,000 boutons per descending 5-HT cell body in the brain stem only with this restricted projection. When combing these results with the biochemical data, it could be calculated that the concentration of 5-HT in IR varicosities is about 3-6 x 10(-3) M, while the corresponding figures for SP and TRH was 0.3-0.5 x 10(-3) M and 0.1-0.2 x 10(-3) M, respectively. In cats subjected to spinal cord transection at the lower thoracic level, all 5-HT-IR fibers in the L7 segment had disappeared 44 days after the lesion, indicating a strict suprasegmental origin of 5-HT-IR fibers in this segment.(ABSTRACT TRUNCATED AT 400 WORDS)

Developmental changes in serotonin levels in the chick spinal cord and brain

Developmental changes in 5-hydroxytryptamine (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) in the developing chick spinal cord and brain were examined using high-performance liquid chromatography with electrochemical detection and immunohistochemistry. On embryonic day (E)6 only small amounts of 5-HT (0.086 ng) and 5-HIAA (0.0144 ng) were found in the spinal cord. By contrast, large amounts of 5-HT (x30) and 5-HIAA (x60) were detected in non-neuronal tissue outside the spinal cord; a similar distribution of 5-HT was also detected by immunohistochemistry. Up to E10, the highest concentrations of 5-HT in the spinal cord were found in the cervical region, followed by the thoracic and lumbar regions. In embryos older than E16, as well as in posthatched chicks, however, the highest and lowest concentrations of 5-HT were found in the lumbar and thoracic spinal cord, respectively. The concentration of spinal cord 5-HT reached maximal values on posthatching day (P)7, after which there was a marked decrease. By P120, 5-HT levels in the spinal cord decreased to the same level as on E10-E16. Concentrations in the brain, however, gradually increased with development. The basic pattern of development of 5-HIAA was similar to that of 5-HT.

Developmental changes in density and distribution of serotoninergic fibers in the chick spinal cord

Developmental changes of serotoninergic innervation in the chick spinal cord (third lumbosacral segment) were examined with an immunohistochemical technique using an antiserum to serotonin. In the 1-day-old hatched chick, serotoninergic fibers were located in laminae I, II, VII, IX, and X. A large number of serotonin-positive fibers and terminals were found around somal profiles of large neurons and in the neuropil of the medial and lateral parts of the lateral motor column (LMC). In the 1-week-old chick, the density of serotoninergic fibers was greatly increased in the posterior columns, and serotoninergic fibers were most densely aggregated in the dorsolateral part of the LMC. In the 2-week-old chick, a considerable decrease in the density of serotoninergic fibers was observed in the lateral funiculus and the gray matter (laminae I, II, VII, IX, and X). In the LMC, serotonin-positive fibers and terminals were largely absent from the neuropil, but were found preferentially around the somal profiles of large neurons. Between 1 and 2 weeks after hatching the density of varicosities and terminals in the neuropil of the dorsolateral and medial parts of the LMC decreased by 33% and 56%, respectively. In the 3-month-old chick, the density of serotoninergic fibers in laminae I, II, V, VII, and X had increased compared to younger ages. Serotonin-positive fibers were not evenly distributed in the LMC of the adult chicken; rather, they were densely aggregated around the soma and proximal dendrites of motoneurons in the dorsolateral LMC. Many neuronal soma in the medial and intermediate regions of the LMC lacked serotoninergic fibers.

Norepinephrine depolarizes lateral horn cells of neonatal rat spinal cord in vitro

Superfusion of norepinephrine (NE) (1-50 microM) onto lateral horn cells, including antidromically identified sympathetic preganglionic neurons (SPNs), situated in thin transverse neonatal rat thoracolumbar spinal cord slices caused a membrane depolarization and repetitive cell discharges. The NE depolarization was associated with an increase in membrane resistance, and the response became smaller upon conditioning hyperpolarization; a clear reversal of polarity, however, was not observed. Pretreating the slices with phentolamine and prazosin but not yohimbine or propranolol prevented the depolarizing effect of NE. This finding, in conjunction with the evidence of the presence of noradrenergic fibers in the spinal cord, suggests that NE may serve as an excitatory neurotransmitter to neurons of the lateral horn.

L-dopa-induced locomotor-like activity in ankle flexor and extensor nerves of chronic and acute spinal cats

The ability of L-DOPA and nialamide to produce locomotor-like rhythmic discharges (fictive locomotion) in hind limb nerves of acute and chronically spinalized and paralyzed cats was examined. Ankle flexor and extensor nerves of chronic cats exhibited pharmacologically induced alternate bursts of activity that had significantly shorter cycle times and burst durations than those produced in ankle flexor and extensor nerves of acutely prepared cats. Furthermore, prior to pharmacologic activation, both ankle flexor and extensor nerves of chronic preparations frequently exhibited spontaneous alternate bursts of activity. Neuronal discharges from nerves of chronic preparations, both prior to and after pharmacologic activation, exhibited much greater variability in both cycle time and burst duration compared with those observed in acute preparations.

The development of catecholaminergic nerves in the spinal cord of rat. II. Regional development

The development of noradrenergic and dopaminergic nerves in 5 regions of the developing spinal cord of rat, from fetal day (FD) 16, to the young adult stage was studied. The normal synthetic capacity of adrenergic nerves in the ventral horn of the cervical and lumbar regions developed at the same time, and at the same rate, despite their spatial separation, and before similar development of the noradrenergic nerves in the dorsal horn and zona intermedia. In the ventral horn, the synthesis of NE from injected L-DOPA, as well as the release and metabolism of NE are well-established at 12 h (ND 0.5) after birth. In the dorsal horn these developments occur later at ND 4. Except in the dorsal horn of the cervical region, there was no easily observable, consistent pattern in the development of regional spinal dopaminergic innervation. The capacity of the developing cord to synthesize dopamine (DA) from injected DOPA is significantly developed at FD 16 (the earliest time studied), and peaked in all regions as early as ND 4. Control experiments indicate that 100%, and only 10% respectively of NE and DA synthetized from injected DOPA, occurred in descending monoaminergic fibers. Norepinephrine is synthesized exclusively in noradrenergic nerves. Cells appear transiently in the developing cord at FD 18, that are capable of synthesizing catecholamines (probably mainly DA) from injected DOPA. During postnatal development of the cord, and to a less extent in the adult, the network of catecholaminergic nerves actually present, is more extensive than that normally revealed during routine fluorescence microscopy. The results are discussed in the context of current attempts to understand the functional importance of catecholaminergic nerves in the mammalian spinal cord, and elsewhere in the CNS.

Development of catecholaminergic nerves in the spinal cord of the rat

The development of the noradrenergic and dopaminergic innervations in the spinal cord of rat was studied using fluorescence histochemical and neurochemical methods. From fetal day (FD) 16 to neonatal day (ND) 26, the cord increased in weight by 4-6 mg/day, except for the period between ND 14 and 20, when the increase was 13 mg/day. Norepinephrine was first detectable in the whole cord at ND 18, and then increased rapidly thereafter, peaking at ND 14, then declining at the end of neonatal life to the values found in the young adult spinal cord. The innervation in the intermediolateral cell column of the thoracic cord appeared to be more extensive at ND 14 than in the adult, raising the possibility of the selective destruction of a part of this noradrenergic innervation during later development. The nerve terminals in the ventral horn were first visualized clearly at birth, with a pattern similar to that of the adult. When the fetal locus coeruleus is transplanted into the transected spinal cord of the adult rat, it induces an extensive proliferation of the cut rostral axons in the ventral horn specifically. It is proposed that the transplanted fetal locus coeruleus produces a neurotrophic substance which stimulates the proliferation of the cut rostral axons derived from the locus coeruleus. Dopamine was first detectable in the cord at ND 20. Unlike noradrenergic nerves, dopaminergic nerves developed slowly throughout neonatal life. The adult innervation presumably develops slowly between ND 26 and young adulthood. In the fetus and very young neonate, DA was most concentrated in the thoracic region. Dopamine metabolism in the cord during neonatal life was a fraction of that found in the adult. It is concluded that the spinal dopaminergic and noradrenergic innervations develop with quite different time sequences. The rapid peaking of the noradrenergic innervation of ND 14 may play a significant role in the overall development and functional maturation of the cord.

Drug-induced alterations in the efflux of 5-hydroxytryptamine and of 5-hydroxyindoleacetic acid into superfusates of the rat spinal cord

The effect of dl-p-chloroamphetamine, fluoxetine and probenecid on the efflux of endogenous 5-hydroxytryptamine (5HT) and 5-hydroxyindoleacetic acid (5HIAA) into superfusates of the spinal cord of anesthetized rats was examined. Mean basal efflux of 5HT and 5HIAA was 0.27 and 15.56 ng/ml superfusate, respectively. The addition of dl-p-chloroamphetamine to the superfusate produced a dose-dependent increase in the efflux of 5HT into the superfusate, but did not increase the efflux of 5HIAA. Probenecid (200 mg/kg i.p.) increased the basal efflux of both 5HT and 5HIAA as compared to control values. When administered systemically, fluoxetine (10 mg/kg i.p. or s.c.) decreased the basal efflux of 5HIAA, but did not alter the basal efflux of 5HT as compared to control values. In contrast, when administered in the superfusate, fluoxetine produced a dose-dependent increase in the basal efflux of 5HT, but did not alter the basal efflux of 5HIAA. The release of 5HT produced by the addition of 2.5 X 10(-4) M dl-p-chloroamphetamine to the superfusate was not prevented in rats pretreated systemically with fluoxetine, although when administered in the superfusate fluoxetine inhibited the dl-p-chloroamphetamine-induced release of 5HT.

Inhibition of the activity of sympathetic preganglionic neurones and neurones activated by visceral afferents, by alpha-methylnoradrenaline and endogenous catecholamines

The responses of electrophysiologically identified sympathetic preganglionic neurones (SPGN) and neurones activated by visceral afferents (VA) to iontophoretic application of: (1) the intraneuronal metabolites of alpha-methyl-DOPA (alpha-MD): alpha-methylnoradrenaline (alpha-MNA) and alpha-methyldopamine (alpha-MDA); (2) noradrenaline (NA) and adrenaline (Ad); and (3) N-methyl-beta-hydroxy-phenylethylamine (NMPEA), were tested in the upper and lower segments of the thoracic spinal cord of the cat. alpha-Methylnoradrenaline, NA and Ad had an inhibitory action on the majority of spontaneously firing neurones. Inhibition of the activity of preganglionic neurones and neurones activated by visceral afferents induced by alpha-MNA was usually equal to the effect of NA, but in some neurones alpha-MNA was more potent. The transport numbers of both amines are similar. The alpha adrenoceptor antagonists, thymoxamine, piperoxan and yohimbine, antagonized the inhibitory effects of alpha-MNA in spontaneously-active preganglionic neurones and neurones activated by visceral afferents. Piperoxan antagonized also the inhibitory effects of NA. The inhibitory effect of alpha-MDA was weaker and that of NMPEA was much weaker than that of alpha-MNA and NA. The inhibitory effects of alpha-MNA and NA in the cerveau isolé preparation resembled those observed in anaesthetized animals. In reserpinized cats, with catecholamine levels in brain stem and spinal cord reduced by 98-99%, the inhibitory effects of alpha-MNA were preserved. It is postulated that alpha-MNA modulates the activity of preganglionic neurones and that this action, leading to a decrease in sympathetic output and mediated by alpha 1 and alpha 2 adrenoceptors, could be the most important factor in the antihypertensive effect of alpha-MD. The inhibition of the activity of neurones activated by visceral afferents by alpha-MNA indicates that alpha-MD may also attenuate the response of the central nervous system to the input from the heart and other organs.

Selective inhibition by methysergide of the monosynaptic reflex discharge in the isolated spinal cord of the newborn rat

In the isolated spinal cord of the newborn rat, methysergide and LSD-25 depressed the monosynaptic reflex discharge selectively. Cyproheptadine and dimethothiazine did not inhibit the monosynaptic reflex. The selective inhibitory effect of methysergide on the monosynaptic reflex was not due to a presumptive low safety factor of this reflex. The inhibition was restored under a condition such as the compound action potential in the dorsal root was enhanced by 4-aminopyridine. Methysergide did not decrease the sensitivity of the motoneuron to substance P and L-glutamic acid. It is suggested that methysergide acts at the presynaptic terminal of Ia afferent fibers and depresses evoked transmitter release.

Presence of conjugated 5-hydroxytryptamine in in vivo superfusates of rat spinal cord

The presence of an acid-hydrolyzable conjugate of 5-hydroxytryptamine, presumably 5-hydroxytryptamine-O-sulfate, was demonstrated in in vivo superfusates of rat spinal cord by HPLC with electrochemical detection. In untreated rats, the concentration of the 5-hydroxytryptamine conjugate measured during the basal efflux of 5-hydroxytryptamine did not differ from that measured during the release of 5-hydroxytryptamine evoked by DL-p-chloroamphetamine. Pretreatment of the rats with clorgyline, an inhibitor of the enzyme monoamine oxidase (EC 1.4.3.4), or with probenecid did not alter the concentrations of conjugated 5-hydroxytryptamine measured during the basal efflux of 5-hydroxytryptamine, but did elevate the concentrations of conjugate measured during the evoked release of 5-hydroxytryptamine.

Contribution of noradrenaline-, dopamine- and adrenaline-containing axons to the innervation of different regions of the spinal cord of the cat

The quantitative distributions of noradrenaline (NA), dopamine (DA) and adrenaline (A) were estimated throughout the grey and white matter at various levels of the cat spinal cord (C5, T3, T10 and L2). NA levels were high at all levels of the cord (about 1000 ng/100 mg protein), being more ventrally placed at the cervical level and tending to be more medially placed at lower thoracic and lumbar levels. DA was found at much lower concentrations than NA (less than 100 ng/100 mg protein) and generally decreased in more caudal segments. There was a mediodorsal distribution throughout the cord. A levels were extremely low throughout the cord (less than 17 ng/100 mg protein), but tended to be higher in the rostral-most segments. Up to 5 days after a total transection at T3, there was accumulation of NA in the white matter regions known to contain catecholamine axon tracts. DA, however, showed a much more restricted accumulation in the white matter. The possibility of whether each catecholamine exists separately as a neurotransmitter in the cat spinal cord is discussed.

Contribution of the locus coeruleus to the adrenergic innervation of the rat spinal cord: a biochemical study

The possible existence and magnitude of a noradrenergic innervation from the locus coeruleus (LC) to the spinal cord was investigated in the rat with various techniques. Horseradish peroxidase, injected into the lumbar spinal cord produced heavy labelling of presumably noradrenaline (NA)-containing neurons in the ventral region of the LC, while cells in the dorsal region of the LC were only lightly labelled. The effects of electrothermic destruction and electrical stimulation of the LC on levels of NA in various parts of the spinal cord, the cerebral cortex and the hippocampus were studied. Fourteen days after unilateral destruction of the LC there were decreases in NA levels of about 85% in the cerebral cortex and hippocampus and of about 15% in the cervical and thoracic segments of the spinal cord (ipsilateral versus contralateral). Fourteen days after bilateral lesioning of the LC significant decreases (about 25%) in NA levels were observed in all spinal cord segments. Unilateral stimulation in or near the LC induced decreases of NA levels in all areas of the central nervous system investigated. In this experiment the levels of NA in the spinal cord were significantly lowered in the ipsilateral cervical (16%), thoracic (12%) and lumbar/sacral (15%) segments of the spinal cord. These findings together indicate that a small part (no more than 30%) of the NA levels in the rat spinal cord are dependent upon the integrity and activity of NA-containing neurons of the predominantly ipsilaterally localized LC.

Norepinephrine levels in experimental spinal cord trauma. Part 1: Biochemical study of hemorrhagic necrosis

Levels of norepinephrine (NE) in the spinal cord tissue of nontraumatized cats are highest in the cervical and lumbar enlargements. A rather uniform but slightly increasing concentration gradient from cephalad to caudad is observed in the thoracic segments. A 500 gm-cm trauma at the T-5 or C-7 spinal cord segment did not demonstrate any significant increase in NE levels measured sequentially over a 4-hour period after trauma. Dopamine levels could not be detected in the nontraumatized or traumatized cat spinal cords. Four traumatized cats treated with alpha methyl tyrosine, a tyrosine hydroxylase inhibitor, and followed clinically for 5 months showed no improvement in neurological function when compared to untreated traumatized cats. This study does not support the norepinephrine hypothesis of experimental spinal cord trauma.

The raphe nuclei of the cat brain stem: a topographical atlas of their efferent projections as revealed by autoradiography

Stereotaxic injections of [14C]leucine were made in nulei raphe centralis superior, raphe dorsalis, raphe magnus and raphe pontis of the cat. The organization of the regional connections was outlined in a stereotaxic atlas using the autoradiographic tracing method: the majority of the ascending pathways from the rostral raphe nuclei are directed mainly through a ventrolateral bundle via the ventral tegmental area of Tsai, with some lateral extensions to the substantia nigra, and then through the fields of Forel and the zona incerta. More rostrally the fibers are joined to the medial forebrain bundle through the hypothalamic region up to the preoptic area or the diagonal band of Broca. Multiple divisions leave this tract towards the epithalamic or the intralaminar thalamic nuclei, the stria terminalis, the septum, the capsula interna and the ansa lenticularis. The bulk of the rostral projections terminates in the frontal lobe, while some labeling is scarcely distributed throughout the rest of the neocortex. The projections of nucleus (n.) raphe centralis superior are specifically associated with the n. interpeduncularis, the mammillary bodies and the hippocampal formation while the n. raphe dorsalis innervates selectively the lateral geniculate bodies, striatus, piriform lobes, olfactory bulb and amygdala. The rest of the ascending fibers form the centrolateral or the dorsal ascending tracts radiating either in the reticular mesencephalic formation or in the periventricular gray matter. On the contrary there are heavy descending projections from n. raphe centralis superior which distribute to the main nuclei of the brain stem, the central gray matter and the cerebellum. The ascending projections form the caudal raphe nuclei are much less dense. They disseminate mainly in the colliculus superior, the pretectum, the nucleus of the posterior commissure, the preoculomotor complex and the intralaminar nuclei of the thalamus. From n. raphe pontis, a dense labeling is selectively localized at the n. paraventricularis hypothalami with some rostral extensions to limbic areas. Diffuse caudal and rostral projections from both nuclei are observed in the mesencephalic, pontobulbar reticular formation and the cerebellum. The main differences come from the specific localization of their descending bulbospinal tracts inside the lateroventral funiculus of the spinal cervical cord.

Axonal transport in serotonin neurons of the midbrain raphe

The projections of serotonin-containing neurons of the midbrain raphe nuclei (nucleus raphe dorsalis, nucleus centralis superior) are studied by analysis of axonal transport of labeled amino acids. These results are correlated with regional alterations of serotonin content following midbrain raphe lesions which produce significant serotonin depletion in nearly all regions of the central nervous system. Twenty-four hours following injection of 100 muCi [3H]proline, raphe neurons have taken up labeled material and transported it, presumably as protein, to telencephalon, diencephalon, brain stem, the cerebellum and the spinal cord. This transport appears to take place predominantly in serotonin neurons. After injection of 100 muCi [3H]5-HTP into nucleus raphe dorsalis or nucleus centralis superior, the pattern of regional distribution of transported material is very similar to that obtained with tritiated proline. Selective lesions of serotonin terminals with 5.6-DHT result in greatly diminished axonal transport of proteins to all telencephalic, diencephalic and mesencephalic areas as well as to cerebellum, pons-medulla and spinal cord. Unilateral destruction of the medial forebrain bundle results in significant reduction in axonal transport of labeled material to ipsilateral telencehalon and thalamus. These results provide further support for the view that serotonin neurons of the midbrain raphe nuclei project widely throughout the neuraxis to telencephalon, diencephalon, brain stem, cerebellum and spinal cord.

Quantitative localization of biogenic amines in the spinal cord

Recently developed highly sensitive radiometric assays for biogenic amines have been combined with microdissection techniques to localize and quantify these amines in different structures, and at various levels of rabbit and rat spinal cords. Assays were performed for serotonin, norepinephrine, dopamine and epinephrine. It was generally found that the highest concentrations of those biogenic amines were found in the lateral and ventral horns, slightly lesser concentrations were found around the central canal, and still lower concentrations were found in the dorsal horns. Relatively low amine concentrations were found in the white matter. These biochemical measurements correlate well with localizations indicated by histofluorescence methods but provide precise quantification. Comparisons with previously available, less sensitive biochemical measurements are discussed.

Altered norepinephrine metabolism following experimental spinal cord injury. 1. Relationship to hemorrhagic necrosis and post-wounding neurological deficits

✓ Experimentally injured spinal cord tissues were chemically examined for changes in norepinephrine (NE), serotonin, and dopamine; remarkable NE metabolic alterations were found. The amine doubled in 30 minutes, quadrupled in 1 hour, and thereafter slowly declined to approach control values at 4 hours. Comparisons between injured tissue NE content and the presence of central gray hemorrhages and necrosis were consistently found, and profound increases in NE were universally associated with massive central hemorrhages. Within 2 hours of injection of minute quantities of pure NE into the spinal gray matter, large central hemorrhages appeared that closely resembled the lesions associated with severe spinal cord injury. We have hypothesized that toxic quantities of tissue NE induce intense vasospasm which impedes or arrests cord perfusion and causes the neuronal necrosis, vascular rupture, and parenchymal self-destruction manifest as central hemorrhagic necrosis. Thus, excess NE liberated within traumatized tissue may act to depress or halt electrical activity of adjacent fibers and neurons, producing the neuronal response of transient weakness or paralysis. Permanent loss of function ensues as the electrically depressed spinal cord tissue also undergoes hemorrhagic autodestruction.

Origin of 5-hydroxyindoleacetic acid in the spinl fluid

5-Hydroxyindoleacetic acid applied intracisternally in cats does not appear in spinal fluid. Changes of 5-hydroxyindoleacetic acid concentration in the spinal cord are clearly reflected in the perfusate of the spinal subarachnoid space. Thus, 5-hydroxyindoleacetic acid in the spinal fluid originates from the spinal cord and reflects metabolic changes of 5-hydroxytryptamine in the spinal tissue, but not those in the brain.

The action of para-methoxyphenylethylamine (PMPEA) on monosynaptic reflex transmission in the cat

1. The intravenous injection of para-methoxyphenylethylamine (PMPEA) into cats produces an increase in the size of the spinal cord monosynaptic reflex. The reflex elevation occurs within 30 s of drug administration, reaches a peak within 2 min, and lasts about 20 min.2. The action of PMPEA is similar for extensor (gastrocnemius-soleus) and flexor (posterior biceps-semitendinosus) monosynaptic reflexes.3. Repeated doses of PMPEA give comparable effects. The degree of monosynaptic reflex elevation is dose related.4. The action of PMPEA is antagonized by phenoxybenzamine and by methysergide or cyproheptadine. The combination of phenoxybenzamine with either of the latter is particularly effective in preventing the reflex facilitation by PMPEA.5. It is concluded that PMPEA has a central action on the spinal cord. It seems likely that monoaminergic synapses are involved.