Parasympathetic reflex salivary secretion in the cat parotid gland

Differences in control of parasympathetic vasodilation between submandibular and sublingual glands in the rat

We examined blood flow in the submandibular gland (SMGBF) and sublingual gland (SLGBF) during electrical stimulation of the central cut end of the lingual nerve (LN) in the urethane-anesthetized rats using a laser speckle imaging flow meter. LN stimulation elicited intensity- and frequency-dependent SMGBF and SLGBF increases, and the magnitude of the SMGBF increase was higher than that of the SLGBF increase. The increase in both glands was significantly inhibited by intravenous administration of the autonomic cholinergic ganglion blocker hexamethonium. The antimuscarinic agent atropine markedly inhibited the SMGBF increase and partly inhibited the SLGBF increase. The atropine-resistant SLGBF increase was significantly inhibited by infusion of vasoactive intestinal peptide (VIP) receptor antagonist, although administration of VIP receptor antagonist alone had no effect. The recovery time to the basal blood flow level was shorter after LN stimulation than after administration of VIP. However, the recovery time after LN stimulation was significantly delayed by administration of atropine in a dose-dependent manner to the same level as after administration of VIP. Our results indicate that 1) LN stimulation elicits both a parasympathetic SMGBF increase mainly evoked by cholinergic fibers and a parasympathetic SLGBF increase evoked by cholinergic and noncholinergic fibers, and 2) VIP-ergic mechanisms are involved in the noncholinergic SLGBF increase and are activated when muscarinic mechanisms are deactivated.

Bulbar pathway for contralateral lingual nerve-evoked reflex vasodilatation in cat palate

We investigated the brain-stem pathway(s) by which electrical stimulation of the central cut end of the lingual nerve (LN) evokes parasympathetic reflex vasodilatation in the palate contralateral to the stimulated side. This occurs in artificially ventilated, cervically vagosympathectomized cats deeply anesthetized with alpha-chloralose and urethane. For this purpose, we made microinjections within the brain stem to produce nonselective, reversible local anesthesia (lidocaine) or soma-selective, irreversible neurotoxic damage (kainic acid). Local anesthesia of the trigeminal spinal nucleus (Vsp) ipsilateral to the stimulated side produced by microinjection of lidocaine (2%; 1 microl/site) reversibly and significantly reduced the LN stimulus-evoked palatal blood flow (PBF) increases. PBF increases ipsilateral and contralateral to the stimulated nerve were equally affected. In contrast, microinjection of lidocaine into the Vsp contralateral to the stimulated side did not affect these responses. Microinjection of kainic acid (10 mM/site; 1 microl) into the Vsp ipsilateral to the stimulated side led to a bilateral irreversible reduction in reflex vasodilatation in the palate. Microinjection of lidocaine into either superior salivatory nucleus (SSN) attenuated the PBF increase only on the side ipsilateral to the microinjection site. Hexamethonium (1.0 mg/kg iv) significantly reduced the vasodilator responses to electrical stimulation of Vsp by blocking ganglionic transmission on both sides. The simplest interpretation of these results is that the LN-evoked parasympathetic reflex vasodilatation in the contralateral palate depends on activation of a pathway originating from the Vsp ipsilateral to the stimulated nerve and crossing to the contralateral SSN.

Involvement of trigeminal spinal nucleus in parasympathetic reflex vasodilatation in cat lower lip

We examined whether the trigeminal spinal nucleus (Vsp) forms part of the central mechanism by which electrical stimulation of the central cut end of the lingual nerve (LN) evokes parasympathetic reflex vasodilatation in the lower lip in artificially ventilated, cervically vagosympathectomized cats deeply anesthetized with alpha-chloralose and urethane. For this purpose, we made microinjections within the brain stem to produce nonselective, reversible local anesthesia (lidocaine) or soma-selective, irreversible neurotoxic damage (kainic acid). Local anesthesia of Vsp by microinjection of lidocaine (2%; 1 microl/site) reversibly and significantly reduced the ipsilateral-LN-evoked parasympathetic reflex vasodilatation. Unilateral microinjection of kainic acid (10 mM/site; 1 microl) into Vsp ipsilateral to the stimulated LN led to an irreversible reduction in the reflex vasodilatation but had no effect on the vasodilatation elicited by stimulation of the contralateral LN. Such microinjection of kainic acid into Vsp had no effect on the vasodilatation evoked by electrical stimulation of the ipsilateral inferior salivatory nucleus. Electrical stimulation of Vsp elicited a blood flow increase in the lower lip in an intensity- and frequency-dependent manner, regardless of whether systemic arterial blood pressure rose or fell. Hexamethonium (1.0 mg/kg iv) significantly reduced the vasodilator responses elicited by electrical stimulation of the central cut end of LN or of Vsp, each to a similar degree. After hexamethonium, both vasodilator responses showed time-dependent recovery. These results strongly suggest that Vsp is an important bulbar relay for LN-evoked parasympathetic reflex vasodilatation in the cat lower lip.

Nervous control of blood flow in the orofacial region

The blood vessels of orofacial tissues are innervated by cranial parasympathetic, superior cervical sympathetic, and trigeminal nerves, a situation somewhat different from that seen in body skin. This review summarizes our current knowledge of the nervous control of blood flow in the orofacial region, and focuses on what we know of the respective roles of sympathetic, parasympathetic, and trigeminal sensory nerves in the regulation of blood flow in this region, with particular attention being paid to the mutual interaction between them.

Selective innervation of different target tissues in guinea-pig cranial exocrine glands by sub-populations of parasympathetic and sympathetic neurons

This study has used multiple-labelling immunohistochemistry and quantitative analysis to examine the projections of subpopulations of parasympathetic and sympathetic neurons to different vascular and secretory structures in five cranial exocrine glands of guinea-pigs. Multiple subpopulations of parasympathetic axons, identified by immunoreactivity (IR) for various combinations of peptides, innervated arteries, arterioles, ducts and acini in sublingual, submandibular, parotid, lacrimal and zygomatic glands, although axons were absent from ducts in the parotid gland. Most parasympathetic axons contained IR for vasoactive intestinal peptide (VIP) and neuropeptide Y (NPY), with or without enkephalin (Enk). The proportion of parasympathetic axons that contained Enk-IR varied greatly between target tissues and glands: Enk-IR was more common in axons supplying secretory ducts, acini and arterioles than in axons innervating more proximal arteries; Enk-IR was less common in axons supplying the lacrimal gland than axons supplying the submandibular, lacrimal and zygomatic glands. Sympathetic axons with IR for tyrosine hydroxylase (TH) innervated arterial vessels in all glands, but innervated secretory structures only in the salivary glands. Sympathetic axons supplying proximal arterial segments often contained NPY-IR and sometimes also contained IR for dynorphin. Dynorphin-IR was more common in axons in the parotid, lacrimal and zygomatic glands than in the sublingual and submandibular glands. In contrast, axons supplying arterioles, ducts and acini lacked peptide IR. These results indicate that neuronal pathways regulating proximal arteries in cranial exocrine glands are different from the neuronal pathways regulating arterioles and acini, and may be different from neurons projecting to proximal secretory ducts. Furthermore, the peptides enkephalin, NPY and dynorphin are likely to make variable contributions to autonomic neurotransmission in different arterial segments and in different cranial exocrine glands.