Brain Research, 261 (1983) 151-154 151 Elsevier Biomedical Press

Catecholamine varicosiUes in cat dorsal root ganglion and spinal ventral roots

RICHARD T. STEVENS, CHARLES J. HODGE Jr. and A. VANIA APKARIAN

Weiskotten Hall Upstate Medical Center, 750 East A dams Street, Syracuse, N Y 13210 (U.S.A.)

(Accepted October 26th, 1982)

Key words: catecholamine - dorsal root ganglion - ventral root

Catecholamine (CA) varicosities have been observed within the dorsal root ganglion and spinal ventral roots of the cat at all spinal levels. There was no apparent change in either appearance or numbers of these CA varicosities following spinal tran- section or distal spinal root lesion. It is suggested that the source of CA innervation of these areas is sympathetic accompanying transdural blood vessels.

Catecholamine fibers have been described at all spinal cord levels throughout the dorsal and ventral grey matter t6. The primary source of these catecholamine (CA) fibers has been shown to be suprasegmental brain stem nuclei 6.~H3. Catecholamine fibers have also been described within the ventral roots (VR) and dorsal root ganglia (DRG) 5.16 as well as in cranial gan- glia L°,~7. Both suprasegmentaP and sympathetic sources t6.~7 of CA innervation to these areas have been suggested. The purpose of this investiga- tion was to further study the types of CA varico- sities in the D R G / V R region and their possible sources.

Cats weighing 2.~Y2.5 kg were anesthetized with Nembutal (35 mg/kg). Following a spinal laminectomy dorsal root ganglia were removed and quickly frozen in a metal container cooled by a dry-ice-acetone mixture. Cryostat sections (6-8/~m) were collected onto clean slides and re- acted for CA histofluorescence by a modifica- tion of the de la Torre and Surgeon technique 7 as reported previously tS. Sections were viewed with a Zeiss Epifluor system equipped with a 405/435 nm filter combination for visualizing catechola- mines. To locate the position of blood vessels, a 2% solution of the fluorescent dye, Evans Blue, was injected intravenously 10 min before sacrifi- ce and the tissue was subsequently treated as de-

scribed above for CA histofluorescence. Evans Blue was visualized with a 550/590 nm filter combination.

In non-lesioned animals, CA fibers with typ- ical varicosities were observed in the DRG and VR areas at all spinal levels. Most CA varicosi- ties within the DRG traversed the ganglion area within axon bundles. However, unlike those de- scribed in the rat 5, CA nerve fibers in the DRG of the cat were very often seen in close associa- tion with ganglion cell bodies suggestive of syn- aptic contact (Fig. 1). Fibers in transition be- tween axon bundles and ganglion cell regions were commonly observed as were occasional CA fiber bifurcations.

Catecholamine fibers were also seen in the ventral roots. They were fewer in number than in the DRG and their course paralleled the cour- se of ventral root axons. Only rarely were CA fi- bers seen in the dorsal roots.

The general morphology of the CA fibers in the D R G / V R area, as in the spinal grey matter °, takes two forms. The first type (Fig. 2A) is a single, fine, varicose fiber which is the type most common in the spinal cord grey matter. Within the spinal cord, this form of CA fiber is elimina- ted by a rostral spinal transection indicating a suprasegmental source from brain stem nuclei. The second type (Fig. 2B) is an intertwined

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Fig. 1. Fluorescent catecholamine varicosities (arrows) with- in the dorsal root ganglion in close apposition to ganglion cell bodies which contain autofluorescent lipids (double ar- rowhead). Bar equals 10/~m.

bundle of several fine CA fibers which collecti- vely produce intense fluorescence. Within the spinal cord this type of arrangement of CA fi- bers is generally associated with blood vessels and is presumed to be sympathetic in origin. Following a chronic spinal transection, CA fi- bers have been described within the spinal cord caudal to the transection, located primarily along the ventromedial fissure accompanying blood vessels ~2. The majority of CA fibers in the DRG were of the second type.

To determine the source of the CA varicosities in the D R G and ventral roots, various lesions were performed two weeks prior to sacrifice (Fig, 4). Two weeks is ample time for complete degeneration of lesioned CA fibers*. There are no CA containing cell bodies located within the spinal cord4~~"~: therefore a rostral spinal tran- section is sufficient to eliminate all CA-con-

taining fibers innervating the D R G / V R region which originate from central sources. Following a total transection of the spinal cord at the thora- cic level, there was no visible change in the num- bers of CA varicosities within the lumbar DRG and ventral roots, though the spinal grey matter was nearly devoid of all CA-containing fibers. In separate experiments, the ventral roots were le- sioned proximal to the DRG and following a 3 week survival period, CA varicosities were ob- served not only in the DRG but also among the degeneration ventral root fibers. Since proximal lesions of spinal cord or of the VR did not pro- duce a detectable change in the numbers of CA fibers in the D R G or ventral roots, supraseg- mental CA sources are presumed to contribute only minimally if at all to the CA fibers in this region. The other possible source of CA varico- soties innervating the DRG is from the sympa- thetic system. When a chronic lesion was perfor- med distal to the lumbar D R G again, CA vari- cosities of both types survived in the D R G and ventral roots. This indicated that peripheral nerves were not the primary means of access for sympathetic CA fibers innervating the D R G / V R region. Alternative means of access of these fibers to the D R G region is illustrated in Fig. 3. Catecholamine varicosities are seen en- tering the D R G accompanying blood vessels which vascularize this region transdurally 2. Transdural innervation is likely to be the prima- ry source of CA varicosities in the DRG and ventral roots since neither distal nor proximal neural lesions greatly affect the number of CA fibers remaining there (Fig. 4).

To determine the extent to which CA varicosi- ties are associated with DRG and VR blood ves- sels, intravascular injections of the fluorescent dye, Evans Blue, were made to label blood vessel locations. Within the spinal cord there was a dense pattern of labeled blood vessels through- out the grey matter. The spinal cord blood ves- sels were rarely seen adjacent to CA fibers and their course did not approximate the pattern of CA varicosities in the spinal cord 4,9. Within the spinal ventral root the cours of both CA varicosi- ties and Evans Blue-filled blood vessels paral- leled the course of nerve fibers. The close proxi-

N

Fig. 2. Catecholamine (CA) varicosities in the dorsal root ganglion/ventral root region appear in two forms. A: the first type is a single, fine, varicose fiber. (Photograph from ventral root. Bar equals 10/~m.) B: the second type is an intertwined collection of several CA fibers. (Photograph from dorsal root ganglion. Bar equals l0/tin.) Note difference in magnification.

mity of CA fibers with blood vessels was often observed; however, numerous examples of non- association were also noted. In the DRG the re- lation of CA fibers to blood vessels could not be tested by the Evans Blue technique since there is no blood-brain barrier in the ganglion cell re- gion 13"14'15'j9. Extravasated Evans Blue filled the pericellular region making the localization of blood vessels impossible.

The DRG is highly vascularized and fine cap- illaries have been described as surrounding vir- tually every cell 2.3. Due to the close proximity of the CA fibers to both the ganglion cell bodies and the ganglionic vasculature, the relationship between these structures can only be resolved at the electron microscopic level.

These studies have demonstrated that there are large numbers of CA varicosities within the DRG and ventral roots of the cat and the prima- ry means of access of these fibers to this region is

Fig. 3. Catecholamine fibers entering the dorsal root gang- lion accompanying a blood vessel (BV). Bar equals 100 ~m.

154

(~ ~SUPRASEGMENTAL

S Y M P A T H E ~ ~ ~" ~ J k J' / SOURCES~ ~ ~ . ~ ~ /

Fig. 4. Diagrammatic illustration of the relationships between possible CA sources supplying the DRG/VR region and the neu- ral lesions performed. Lesion A eliminated all direct innervation from the sympathetic system. Lesion B eliminated all supraseg- mental innervation. Since CA varicosities remain following each lesion, the most likely source of CA innervation is transdural ac- companying blood vessels.

most likely transdural, accompanying entering blood vessels. It has not yet been determined to what degree CA-containing axons remain asso- ciated with blood vessels once within the DRG.

This research has been partially supported by Grant R01 NS 12761 from the National Institu- tes of Health.

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