Atrial natriuretic factor in sympathetic ganglia of the rat: dependence on cholinergic innervation

Calretinin-containing preganglionic nerve terminals in the rat superior cervical ganglion surround neurons projecting to the submandibular salivary gland

The distribution and targets of calretinin-immunoreactive preganglionic nerve terminals in the superior cervical ganglion of the rat were examined using immunohistochemistry and retrograde neuronal tracing. Calretinin-immunoreactive nerve terminals were found throughout the ganglion, forming distinct pericellular baskets around a sub-population of postganglionic neurons. The targets of postganglionic neurons surrounded by calretinin-immunoreactive nerve terminals were determined after injection of tracer into the submandibular salivary gland, the extra-orbital lacrimal gland, the thyroid gland, the anterior chamber of the eye or the skin of the forehead. Only when tracer was injected into the submandibular gland were neurons labelled that were surrounded by calretinin-immunoreactive nerve terminals. When immunohistochemistry using antisera to neuropeptide Y was combined with retrograde tracing, only submandibular gland projecting neurons lacking neuropeptide Y were surrounded by calretinin-immunoreactive terminals. When retrograde neuronal tracer was injected into the superior cervical ganglion, a proportion of retrogradely-labelled neurons in the upper thoracic spinal cord showed relatively weak calretinin-immunoreactivity. All calretinin-immunoreactive terminals in the superior cervical ganglion disappeared following section of the sympathetic chain distal to the superior cervical ganglion. Thus, calretinin is present in a population of preganglionic neurons projecting exclusively to neuropeptide Y non-immunoreactive (presumably secretomotor) neurons innervating the submandibular salivary gland of the rat.

Thyroidal ANF: a possible mediator of autocrine regulation in the porcine thyroid gland

Atrial natriuretic factor immunoreactivity (ir-ANF) was examined in thyroid tissue sections and cultured thyroid cells using immunohistochemical staining with a monoclonal anti-ANF antibody. Localization of ir-ANF in perinuclear granules in cultured cells and in the basal region of follicular cells in sectioned tissue suggests that ir-ANF is a basally secreted product. Thyroidal ir-ANF was also characterized using reversed phase high performance liquid chromatography (RP-HPLC) of acidic thyroid extracts. An ir-ANF peak coeluting with synthetic rat ANF(99-126) suggests that thyroidal ir-ANF may be identical in form to circulating atrial ANF. However, the detection of ir-ANF in cultured thyroid cells confirms that the immunoreactivity is locally produced. Saturation analysis revealed high affinity ANF receptors (Kd = 0.1 nM; MBC = 17.2 fmol/mg protein) on these cultured cells, and a competition study demonstrated the ability of extracted thyroidal ir-ANF to inhibit 125I rat ANF binding to the membrane receptors. The evidence presented here suggests that ir-ANF in the thyroid may be secreted locally to exert an autocrine effect on neighboring follicular cells.

Cholinergic innervation of the mouse superior cervical ganglion: light- and electron-microscopic immunocytochemistry for choline acetyltransferase

The cholinergic innervation of the mouse superior cervical ganglion was investigated by means of immunocytochemistry using a well-characterized monoclonal antibody against choline acetyltransferase (ChAT). Immunopositive nerve fibers entered the superior cervical ganglion from the cervical sympathetic trunk. Light-microscopically, these fibers appeared to be heterogeneously distributed among the principal ganglion cells. The rostral part of the ganglion contained more ChAT-positive fibers then the middle or the caudal one. The axons branched several times before forming numerous varicosities. Most of the ChAT-stained fibers and varicosities aggregated in glomerula-like neuropil structures that were surrounded by principal ganglion cell bodies, whereas others were isolated or formed little bundles among principle neurons. None of the neurons or other cell types in the ganglion exhibited ChAT-positivity. ChAT-immunoreactive fibers disappeared from the ganglion 5 or 13 days after transection of the cervical sympathetic trunk. At the ultrastructural level, most axon terminals and synapses showed ChAT-immunoreactivity. An ultrastructural analysis indicated that immunostained synapses occurred directly on the surface of neuronal soma (1.8%) and dendritic shafts (17.6%). Synapses were often seen on soma spines (18.4%) and on dendritic spines (62.2%). All immunoreactive synapses were of the asymmetric type. The results provide immunocytochemical evidence for a heterogeneous cholinergic innervation of the ganglion and the principal neurons.

Atrial natriuretic factor constitutes an intrinsic functional unit within superior cervical ganglia of the rat

The molecular forms of atrial natriuretic factor were studied in the sympathetic ganglia of the rat. The peptide atrial natriuretic factor was also tested for its ability to induce intracellular changes in ganglionic elements. Chromatographic evaluation of extracted ganglionic atrial natriuretic factor revealed the presence of proatrial natriuretic factor together with lower molecular weight peptides. Atrial natriuretic factor induced a maximal six-fold increase of cGMP accumulation within ganglia in vitro, most probably in principal ganglionic cells. Its effect on cGMP was not mediated by acetylcholine or any other neurotransmitter because it persisted after muscarinic receptor blockade and in a calcium-free medium and was not affected by ganglia decentralization. Thus, atrial natriuretic factor appears to be produced by a structural neural component of ganglia (in preganglionic cholinergic neurons or small intensely fluorescent cells?) and has receptors at sites different from its source. It is suggested that atrial natriuretic factor may be locally involved in the process of neurotransmission and may be yet another peptide neurotransmitter and/or neuromodulator.

Atrial natriuretic factor is a new neuromodulatory peptide

In this commentary, we will briefly discuss the potential regulatory role of atrial natriuretic factor in peripheral autonomic nervous system function. The focus will be on atrial natriuretic factor's involvement in cardiovascular homeostasis through its peripheral effect on sympathetic nervous activity, which may complement its humoral role. [Kuchel et al. (1987) Life Sci. 40, 1545-1551; Lang et al. (1985) Nature 314, 264-266]. We will attempt to support the hypothesis of its neuromodulatory action on efferent autonomic outflow. Specifically, the role of atrial natriuretic factor in the regulation of the synthesis and release of neurotransmitters and in synaptic transmission at the level of the sympathetic ganglia will be outlined. Its potential usefulness in neurobiological studies will also be indicated.

Atrial natriuretic factor in the spinal cord of normotensive and hypertensive rats

Atrial natriuretic factor (ANF) was investigated in the rat spinal cord and hypothalamus using two radioimmunoassays. ANF was also quantified in both tissues of Spontaneously Hypertensive Rats and Dahl rats. Spinal cord and hypothalamus were found to be immunoreactive to proANF and its near-NH2- or near-COOH-terminal fragments. A major part of the extracted ANF was a COOH-terminal peptide smaller than or the same as ANF (Ser99-Tyr 126). SHR had higher hypothalamic and spinal cord ANF concentrations than Wistar Kyoto rats, while the Dahl salt-sensitive animals exhibited an increase in spinal cord ANF when compared with the Dahl salt-resistant group. The data suggest that spinal cord may produce ANF locally with processing similar to that in hypothalamus. Changes in ANF concentrations occurring during the course of hypertension remain to be further investigated.