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.

The stopping response of Xenopus laevis embryos: pharmacology and intracellular physiology of rhythmic spinal neurones and hindbrain neurones

1. Xenopus laevis embryos stop swimming in response to pressure on the cement gland. This behaviour and ‘fictive’ stopping are blocked by bicuculline (10 mumol 1(−1)), tubocurarine (110 mumol 1(−1)) and kynurenic acid (0.5 mmol 1(−1)). 2. Intracellular recordings from spinal neurones active during swimming have shown that pressure on the cement gland evokes compound, chloride-dependent inhibitory postsynaptic potentials (IPSPs). These are blocked by bicuculline, tubocurarine and kynurenic acid, but are unaffected by strychnine (2 mumol 1(−1)). 3. When the cement gland is pressed, trigeminal ganglion activity precedes both the IPSPs and the termination of ‘fictive’ swimming activity recorded in rhythmic spinal neurones. The trigeminal discharge is unaffected by the antagonists bicuculline, tubocurarine, kynurenic acid and strychnine. 4. Intracellular recordings from the hindbrain have revealed neurones that are normally silent, but rhythmically inhibited during ‘fictive’ swimming. In these neurones pressure on the cement gland evokes depolarising potentials, often with one or more spikes. 5. We propose that the stopping response depends on the excitation of pressure-sensitive trigeminal receptors which innervate the cement gland. These release an excitatory amino acid to excite brainstem GABAergic reticulospinal neurones, which inhibit spinal neurones to turn off the central pattern generator for swimming. There may also be a less direct pathway.

Vanilloid receptor loss in rat sensory ganglia associated with long term desensitization to resiniferatoxin

A dose-dependent loss of vanilloid receptors (specific [3H]resiniferatoxin binding sites) was found in sensory ganglia of rats 24 h after s.c. administration of resiniferatoxin (RTX), an ultrapotent capsaicin analog. This receptor loss displayed an ED50 of 30 micrograms/kg both in dorsal root and trigeminal ganglia; the ED50 was 6-fold higher than the ED50 for loss of the neurogenic inflammatory response and 30-60-fold higher than the ED50 for desensitization in the standard eye-wiping (chemogenic pain) response. The receptor loss appeared later (24 h) than the loss of the physiological responses (6 h) and showed modest recovery (to 20-30% of control levels) over the following 4 weeks. This vanilloid receptor loss may represent a novel, specific mechanism for vanilloid-induced chronic desensitization.

Nasal mucosa sensitization with toluene diisocyanate (TDI) increases preprotachykinin A (PPTA) and preproCGRP mRNAs in guinea pig trigeminal ganglion neurons

Toluene diisocyanate (TDI) induces respiratory allergy in mammals. Using immunohistochemistry and in situ hybridization histochemistry, the present study examined effects of nasal mucosa sensitization by TDI on the immunoreactivity for substance P (SP) and calcitonin gene-related peptide (CGRP) and on the expression of their mRNAs in guinea pig trigeminal ganglion and their terminals. Single intranasal application of TDI (acute experiment) did not induce nasal allergy-like behaviours and failed to cause changes of SP and CGRP immunoreactivity and in the expression of preprotachykinin A (PPTA) mRNA and preproCGRP mRNA coding for SP and CGRP respectively in the trigeminal ganglion neurons. However, repeated application of TDI (chronic experiment) caused a dramatic increase of SP and CGRP immunoreactivity in peripheral neurites of sensory nerves in the nasal mucosa but a slight increase in the spinal trigeminal nucleus, a decrease of the same immunoreactivities in the cell bodies of the trigeminal ganglion neurons, and an increase of the expression of PPTA and preproCGRP mRNA in the same neurons. These findings suggest that chronic exposure of the nasal mucosa to TDI apparently causes enhancement of both the biosynthesis of SP and CGRP and their axonal transport in the trigeminal system.

Glycerol injection to the rat trigeminal nerve: histological and immunohistochemical studies

The effect of topical glycerol injection into the rat trigeminal nerves was investigated histologically and immunohistochemically. Anhydrous glycerol was injected into the preganglionic portion of the trigeminal nerves via a ventral approach. Extensive myelin swelling and axonolysis were observed in the rats killed 1 and 2 weeks after glycerol injection. Numerous inflammatory cells were seen especially in the animals sacrificed 1 week after surgery. Myelin disintegration continued up to 4 weeks after glycerol injection. In normal and saline injected sham operated nerves, calcitonin gene-related peptide (CGRP)- and substance P(SP)-like immunoreactivities were densely localized in the nerve fibers. A marked decrease in both CGRP- and SP-like immunofluorescence was seen in the nerves after glycerol injection. The remaining nerve fibers often had blunt endings with increased fluorescence. Swollen and winding structures were also found. These immunohistochemical changes were observed in the rats killed 1 and 2 weeks following surgery. A similar change but of lesser degree was seen in the 4-week-animal. The present study suggests that topical glycerol injection into the trigeminal nerve induces degeneration of the nerves immunoreactive to CGRP and SP. These changes emphasize the putative functional implications of the peptides in relieving the pain of trigeminal neuralgia after topical glycerol injection.

Ammonia and proton gated channel populations in trigeminal ganglion neurons

The existence of three distinct types of proton-gated sodium currents classified in accordance with their kinetics of desensitization as fast, medium and slow, has been confirmed in the present study on isolated rat trigeminal ganglion neurons. The emphasis was put on the investigation of a peculiar medium type of a chemically gated channel population, using the concentration jump method. The features of the medium-type mechanism allow to distinguish it from the other already known types: it was insensitive to the Ca antagonist verapamil (in contrast to proton-gated sodium current found in dorsal root ganglion neurons), displayed a strong dependence of the kinetics of desensitization on the membrane potential, and (besides the apparent proton-gating) was activated and desensitized by the application of ammonia containing solution at normal pH values. The effect of ammonia itself appeared to be a good tool for the separation of fast and slow proton-gated responses. The results obtained allow to postulate a nonspecific proton-activation of medium-type receptor-channel complexes and their specificity to ammonia (Kd = 10(-4) mol/l) as an agonist.

Dihydroergotamine and sumatriptan attenuate levels of CGRP in plasma in rat superior sagittal sinus during electrical stimulation of the trigeminal ganglion

Vasoactive neuropeptides, present in unmyelinated C-fibers, can be released from perivascular sensory axons by antidromic stimulation, to mediate vasodilation and extravasation of plasma protein (neurogenic inflammation). In this report, the effects of antidromic trigeminal stimulation on levels of calcitonin gene-related peptide (CGRP) in plasma were examined in the superior sagittal sinus and the effects of drugs that have been shown previously to block extravasation of neurogenic plasma determined. The levels of immunoreactive CGRP in plasma were measured both before and during electrical stimulation of the trigeminal ganglion (0.1-1.0 mA, 5 msec, 5 Hz, 3-5 min), using a highly specific and sensitive immunochemiluminometric assay. Levels of CGRP increased and became maximal within the first minute of stimulation. The increases were detectable at intensities of current as small as 0.1 mA. Peak levels related to the intensity of the stimulus. Samples from femoral arterial blood did not show concomitant increases at 1 min. Pretreatment with dihydroergotamine (DHE) (50 micrograms/kg i.v.) did not change the baseline levels but decreased levels of CGRP during stimulation (0.3 mA), by 55% at 1 min and 50% at 3 min. Sumatriptan (GR43175) (300 micrograms/kg) attenuated the increase by 57% at 3 min (0.1 mA, 5 msec, 5 Hz) but not after 1 min of stimulation, although decreases were observed at the latter time during an individual experiment. Drug-induced attenuation of levels of CGRP in plasma may reflect inhibition of release, to thereby provide evidence to explain blockade of neurogenic extravasation of plasma.

Relation between sensory disturbance and outcome after retrogasserian glycerol rhizotomy

The relation between postoperative sensory deterioration and surgical outcome in 54 patients treated by retrogasserian glycerol rhizotomy for trigeminal neuralgia was studied. The facial sensibility was assessed one day and three months postoperatively. Thresholds for perception and pain were determined quantitatively using transcutaneous electrical stimulation and clinically by light touch and pinprick tests. At a follow-up one year after surgery there was no significant difference in pain relief between patients who did show and patients who did not show sensory deterioration at the one day or three months evaluations. Nevertheless, there was a tendency for higher recurrence rate in patients with mild or no sensory disturbance.

Transoval administration of opiates into trigeminal cistern for cancer pain. Preliminary report

A new method for administration of opiates into the ventriculo-cisternal system for intractable pain due to cancer is presented. Five patients suffering from such pain underwent the permanent implantation of a subcutaneous reservoir connected to a thin catheter inserted into the trigeminal cistern. The indications are those of the intraventricular way. Percutaneous trigeminal opiates administration (PTO) proved to be a valid and simple alternative method to intrathecal and intraventricular morphine.

Glycerol injection into the trigeminal ganglion provokes a selective increase in human cerebral blood flow

Fourteen patients suffering from idiopathic trigeminal neuralgia (refractory to medication) were treated by injection of glycerol into the trigeminal ganglion. The changes in cerebral blood flow (CBF) after glycerol injection were quantified by intravenous 133Xe emission tomography. There was a significant 11% (P less than 0.01) increase in ipsilateral CBF and an 8% (P less than 0.05) increase in contralateral CBF 1 h after glycerol injection. The interhemispheric difference was significant (P less than 0.05). The increase was significantly greater in the ipsilateral internal carotid territory, in the anterior cerebral artery and middle cerebral artery territories (superficial (P less than 0.05), deep territories (P less than 0.001]. We suggest that these changes are due to the release of substance P and/or calcitonin gene-related peptide, from terminals of the trigeminal-vascular system during glycerol injection.

[Effects of allapinin on sodium currents in isolated neurons of the trigeminal ganglia and cardiomyocytes of rats]

Block of sodium currents by allapinin (diterpene alkaloid with strong antiarrhythmic properties) was investigated in isolated, voltage clamped rat trigeminal neurons and cultured neonatal rat single ventricular myocytes. Allapinin produces a decrease in sodium current amplitude without any changes in voltage dependent properties. Possible differences between the mechanisms of antiarrhythmic effect of diterpene alkaloids and classic antiarrhythmic agents have been analysed.

[Relief of intractable post-herpetic neuralgia with gasserian ganglion block using methyl prednisolone acetate and with TENS]

A 58 year old man had been suffering from intractable left ophthalmic post herpetic neuralgia (PHN) for 7 years. He has also been treated for polyarteritis nodosa for 10 years. For pain relief, he was treated initially with frequent (4 times a day) stellate ganglion block (SGB) and peripheral ophthalmic nerve block for a month without relief. Then supraorbital nerve block with neurolytics, TENS and acupuncture were done with a slight relief of his pain. Recently his pain became worse even with imipramine 75 mg and carbamazepine 100 mg a day which relieved effectively the patient from the pain for the last 3 years. The pain was so severe to disturb his usual daily activity. Gasserian ganglion block with methyl prednisolone acetate 10 mg was done. After the block, his ADL improved markedly. Three months after the block, he had no spontaneous pain and slight pain with light touch on the injured skin did not annoy him. Several days before the block, electric stimulation to control his pain was tested. Stimulation with the electricity (4.5 mA, 10 cycle and 400 microseconds) brought him complete relief from the pain during the stimulation. Trigeminal SEP showed no response to the stimulation of injured skin.

Histamine acts directly on calcitonin gene-related peptide- and substance P-containing trigeminal ganglion neurons as assessed by calcium influx and immunocytochemistry

Primary cultures of rat trigeminal ganglion cells were exposed to histamine, and the intracellular free-calcium concentration, [Ca2+]i, was measured by the calcium-sensitive dye fura-2. Histamine increased the [Ca2+]i of the neurons. Pretreatment of the cells with histamine H1-receptor blocker, or removal of extracellular calcium, abolished the response, however, the response was not altered by pretreatment with H2-blocker. Immunocytochemical analysis showed that these cultured cells that responded to histamine identically showed substance P- or calcitonin gene-related peptide-like immunoreactivity.

Calcitonin gene-related peptide containing sensory neurons innervating tooth pulp and buccal mucosa of the rat: an immunohistochemical analysis

Differential peptidergic innervation of the rat buccal mucosa and incisor tooth pulp was demonstrated by experimental immunohistochemistry. In the buccal mucosa, calcitonin gene-related peptide (CGRP)-like immunoreactive (IR) nerve fibres were observed in both the epithelium and submucosal layer. Most of these fibres were also immunoreactive to substance P (SP). On the other hand, SP-IR fibres were less numerous than CGRP-IR fibres in the incisor tooth pulp. Fast blue (FB) was applied to the buccal mucosa and the incisor pulp chamber. Small (less than 20 microns) FB-labelled CGRP-IR neurons were more numerous in the buccal mucosa group, while medium to large neurons (20-50 microns) predominated in the incisor pulp. Following neonatal capsaicin treatment, CGRP- and SP-containing fibres in the buccal mucosa almost totally disappeared, but many CGRP-IR fibres remained in the incisor tooth pulp. The findings suggest that these two oral tissues are innervated by different subgroups of CGRP-IR neurons in the trigeminal ganglia.

Histamine application to the nasal mucosa induces release of calcitonin gene-related peptide and substance P from peripheral terminals of trigeminal ganglion: a morphological study in the guinea pig

Short-term effects of application of histamine to the nasal mucosa on trigeminal ganglion neurons containing calcitonin gene-related peptide (CGRP) and substance P (SP) were examined in guinea pig. Immunoreactivities to CGRP and SP in these neurons were decreased 30 min after the histamine application. The decreases were most marked at 1-3 h after application, after which the immunoreactivities began to increase, reaching the base line by 6 h after the application. The immunoreactivities to CGRP and SP in the nerve endings of nasal mucosa were not decreased. The expression of mRNAs for both peptides in the soma of trigeminal neurons was unchanged. The histamine application to the nasal mucosa may cause release of CGRP and SP from terminals of peripheral processes of trigeminal ganglion neurons, and enhance axonal transport of these peptides, but does not affect their biosynthesis in the soma of trigeminal ganglion neurons.

Ionic dependencies of tetrodotoxin-resistant action potentials in trigeminal root ganglion neurons

Action potentials recorded in vitro from the perikarya of trigeminal root ganglion neurons (guinea-pig) were examined for their sensitivities to blockers of specific ion channels or to removal of certain ionic species in the bathing media. The majority (approximately 65%) of the 137 neurons exhibited action potentials following application of the Na(+)-channel blocker, tetrodotoxin. This group of neurons was selected for further investigation under conditions of extracellular K(+)-channel blockade with tetraethylammonium and 4-aminopyridine. Long-duration action potentials consisting of two distinct components could be evoked under such conditions. The fast component of the spike was abolished in Na(+)-deficient perfusion media and was sensitive to blockade by extracellular lidocaine or intracellular QX-222 applications. It is likely that the slow component was mediated mainly by Ca2+, but in Ca2(+)-deficient media. Mg2(+)-influx may have contributed to the small voltage response. The amplitude and shape of the slow component was unaffected by applications of lidocaine or QX-222. Self-sustained repetitive firing was also observed in 11 neurons in the above conditions. This activity persisted even under conditions of severe deficiencies in extracellular [Ca2+] or [Na+]. Two distinct but overlapping K(+)-conductances that were sensitive to blockade by internal Cs(+)-application and insensitive to applications of tetraethylammonium and 4-aminopyridine, appear to mediate the afterhyperpolarization of the long-duration spike. One portion of the afterhyperpolarization was 60-150 ms in duration and was unaffected by removal of Ca2+ from the extracellular media, while the other had a time-course lasting 150-250 ms and was abolished by removal of external Ca2+. In some neurons, these K(+)-conductances were blocked by high doses of doxorubicin or cisplatin. The results show that at least two ion species (Na+ and Ca2+) contribute to the formation of the tetrodotoxin-resistant, long-duration action potential in trigeminal root ganglion neurons during selective K(+)-conductance blockade and also provide evidence for Mg2+ involvement in the generation of this voltage response.

Retrograde adriamycin sensory ganglionectomy: novel approach for the treatment of intractable pain

Selective sensory ganglionectomy by means of retrograde suicide transport of adriamycin was performed on 3 patients with neuropathic pain in the areas of the trigeminal and intercostal nerves, producing significant pain relief, particularly from hyperalgesic pain. Adriamycin ganglionectomy is considered as a less invasive and highly selective pain treatment, which may possibly become an alternative for surgical ganglionectomy or rhizotomy.

Evidence that the site of action of glycerol in relieving tic douloureux is its actual site of application

Axonal transport of 3H labeled glycerol in the rat trigeminal nerve was investigated as well as the effects of pure glycerol on the infraorbital nerve (IN). 3H activity in the Gasserian Ganglion (GG) was less than 0.1% of that in the nerve stump at the application site. IN showed destructive changes at the injection site restricted mainly to the periphery of the nerve bundles. It was concluded that the site of action of glycerol in relieving trigeminal pain is its site of application irrespective whether applied as a peripheral injection or injected into the cistern of GG.

Consequences and complications of glycerol injection in the cavum of Meckel: a series of 120 consecutive injections

From 1983 to 1989, 120 injections of glycerol into the trigeminal ganglion were performed to treat facialgias of different origin. The subjective and objective consequences and complications are reviewed. Since this operation yielded most often mild, transient and well tolerated consequences and complications for the patient, we now propose this method as first choice for trigeminal neuralgia when there is no anamnestic or clinical evidence of damage to the trigeminal system.

Consequences of 4-aminopyridine applications to trigeminal root ganglion neurons

1. The effects of 4-aminopyridine (4-AP) on the electrical properties of 30 trigeminal root ganglion (TRG) neurons were determined from the membrane voltage responses to step and sinusoidal current injections using intracellular microelectrode techniques in in vitro slice preparations (guinea pigs). 2. Comparisons of results from 4-AP applications (0.05-5 mM) with those from tetraethylammonium (TEA) applications (0.1-10 mM) revealed very different actions of these agents. Both agents produced an increase in input resistance and a decrease in threshold for spike generation. Applications of 4-AP increased subthreshold oscillations of the membrane potential and enhanced the repetitive spike firing evoked by intracellular injections of current pulses. However, TEA applications blocked the potential oscillations and did not exaggerate repetitive spike discharges. Spontaneous spike activity or bursts were observed in four neurons that received 4-AP applications. 3. Membrane properties were determined in 20 of the 30 neurons by fitting impedance data in the frequency domain with a four-parameter membrane model by the use of computer-intensive techniques. In the majority of neurons, the time-invariant and time-dependent membrane conductances decreased during 4-AP application. The time constant for the time-dependent conductance also decreased, suggesting that the closing of K+-channels was facilitated in the membrane. 4. Applications of 4-AP in a dose range of 50 microM-5 mM produced rapid (approximately tens of seconds) responses of the neurons, resulting in a dose-dependent increase of the impedance magnitude functions and in a leftward shift of the resonant "humps" to lower frequencies. This shift indicates that the TRG neuronal membrane is capable of producing large voltage responses to current inputs at low frequencies. Recovery from the effects of 4-AP was slow (usually greater than 30 min). 5. Applications of 4-AP at high doses (greater than or equal to 1 mM) and at various imposed membrane potentials in four neurons resulted in poorly reversible unspecific changes in certain membrane parameters (increased input capacitance and conductance) and an insensitivity of the input conductance to the imposed membrane potential. These effects could be interpreted as membrane breakdown. 6. The tendencies of TRG neurons to fire repetitively and in bursts of spikes during 4-AP application result from the increased oscillatory behavior of their membrane potentials and changes in membrane resonance induced by presumed blockade of K+ channels.(ABSTRACT TRUNCATED AT 400 WORDS)

Transoval trigeminal cisternography and glycerol injection in trigeminal neuralgia

In a series of 25 consecutive patients suffering from essential trigeminal neuralgia, transoval glycerol injection following Håkanson was performed in order to alleviate the pain attacks. This treatment proved to be successful in 76% of the patients. No major side-effects were reported. Authors stress the importance of a precise cisternography of Meckel's cave to ascertain the correct position of the needle, before injecting the glycerol. They discuss their mode of conducting the examination in using a conventional radiologic set-up. Transoval glycerol injection is a valuable interventional radiologic procedure and has to be taken into account as an alternative treatment of essential trigeminal neuralgia, especially when current therapeutic measures have failed.

Bradykinin as a pain mediator: receptors are localized to sensory neurons, and antagonists have analgesic actions

Autoradiographic studies localize [3H]bradykinin receptor binding sites to the substantia gelatinosa, dorsal root, and a subset of small cells in both the dorsal root and trigeminal ganglia of the guinea pig. [3H]Bradykinin labeling is also observed over myocardial/coronary visceral afferent fibers. The localization of [3H]bradykinin receptors to nociceptive pathways supports a role for bradykinin in pain mediation. Several bradykinin antagonists block bradykinin-induced acute vascular pain in the rat. The bradykinin antagonists also relieve bradykinin- and urate-induced hyperalgesia in the rat paw. These results indicate that bradykinin is a physiologic mediator of pain and that bradykinin antagonists have analgesic activity in both acute and chronic pain models.

Electrophysiological responses of trigeminal root ganglion neurons in vitro

The membrane electrical properties of neurons and their responses to endogenous compounds or other neuroactive substances were investigated in vitro with intracellular recording techniques in slices of trigeminal root ganglia of guinea-pigs. The mean resting membrane potential of these neurons was -60 mV. Intracellular injections of hyperpolarizing current pulses evoked time-dependent rectification with varying degrees of dependence on membrane voltage in 107 of 110 neurons. Membrane potential oscillations were observed following the termination of the hyperpolarizing pulses and after similar injections of depolarizing current. This phenomenon appeared to be voltage-dependent at levels that were subthreshold for spike genesis; the more pronounced oscillations were evident at the more depolarized levels and were insensitive to tetrodotoxin applications. Two groups of neurons could be distinguished on the basis of certain characteristics in their action potentials. The majority exhibited short duration (0.6 ms) spikes with mean amplitude of 72 mV in response to intracellular depolarizing current. The brief (3 ms) afterhyperpolarizations that followed such spikes were blocked by intracellular injections of Cs+ or by bath applications of tetraethylammonium. Action potentials in the minority group exhibited a hump in their repolarization phase. The humped spikes had a mean peak amplitude of 78 mV and a longer duration (2 ms). Both the duration (6 ms) and the amplitude (16 mV) of the afterhyperpolarization were significantly greater in this latter group of neurons. Some fast spikes were easily blocked whereas others, including humped spikes, were resistant to tetrodotoxin (10(-6) M). Spikes which were resistant, were also not affected by perfusion with Co2+ (10(-3) M) and were reduced in amplitude during perfusion with Na+-deficient solution. Bath applications of S-glutamate (10(-4)-10(-2) M) depolarized only two of ten neurons by less than 3 mV. Similarly, 5-hydroxytryptamine produced a small depolarization in only two of thirteen neurons. Perfusion of gamma-aminobutyrate (10(-5)-10(-2) M) resulted in an increase in input conductance that waned despite continued application and was associated with a depolarization (2-14 mV) in 44/50 neurons. In some neurons, gamma-aminobutyrate application enhanced their repetitive firing ability, possibly as a result of the increased oscillatory behavior of the membrane at certain depolarized potentials. The effects of gamma-aminobutyrate were blocked by the GABAA-receptor antagonist, bicuculline (10(-4) M) but were unaffected by the GABAB-receptor agonist, baclofen (10(-4) M).(ABSTRACT TRUNCATED AT 400 WORDS)

Axonal transport and tissue contents of substance P in rats with long-term streptozotocin-diabetes. Effects of the aldose reductase inhibitor 'statil'

This study examined the axonal transport of substance P-like immunoreactivity (SPLI) and its content in dorsal root ganglion, trigeminal ganglion, stomach and ileum of non-diabetic rats and two groups of rats with streptozotocin-induced diabetes of 9 months duration. One diabetic group received the aldose reductase inhibitor 'Statil' throughout the period of study. To reduce morbidity all diabetic animals were given twice-weekly injections of a long-acting insulin which restricted weight loss but did not prevent regular and severe hyperglycaemia. Axonal transport of SPLI was studied by measurement of accumulation at 12 h ligatures on the left sciatic nerve. There were no differences between the 3 groups either in the calculated anterograde and retrograde mean rates of accumulation (ranges 6.0 to 7.6 and 0.38 to 0.72 mm/h respectively) or mobile fractions of SPLI (means from 0.54 to 0.58). There were, however, marked reductions in anterograde and retrograde accumulations of SPLI in the constricted nerves of the 'untreated' diabetics (respectively 57 and 33% of controls; P less than 0.01 for both). In the 'Statil'-treated rats these deficits were attenuated (80 and 75% of controls). Diabetes also reduced the SPLI content of unligated sciatic nerve and trigeminal ganglion (65 and 75% of controls). 'Statil' prevented the deficit in the ganglion, but not in the nerve. 'Statil' treatment prevented the myo-inositol depletion and attenuated the sorbitol and fructose accumulation seen in the sciatic nerves of the untreated diabetic animals suggesting effective inhibition of aldose reductase in this tissue. The total SPLI content of the stomach and 1-cm segments of ileum were unaltered in the diabetic animals but due to the increased weights of these tissues the SPLI content per unit weight was reduced. These changes were unaffected by 'Statil'.

Ultrastructure of degenerative changes following ricin application to feline dental pulps

The ultrastructure of degenerative changes within the ipsilateral trigeminal ganglion, and partes caudalis and interpolaris of the spinal trigeminal nucleus in the cat is described following the application of the potent toxin ricin to the tooth pulps of unilateral maxillary and mandibular posterior teeth, including the cuspids. Survival times ranged from 6 to 10 days. Typical changes identified within the ipsilateral trigeminal ganglion included myelin fragmentation and 'compartmentalization' of the axoplasm of medium-sized myelinated axons, while small myelinated and unmyelinated axons underwent a more variable response ranging from electron-lucent to electron-dense changes. The affected cell body was characterized by the presence of swollen, electron-lucent mitochondria, a reduction of cytoplasmic ribosomes and a filamentous hyperplasia. Other changes often included an eccentric nucleus and satellite cell proliferation. Degenerative changes often occurred in isolated elements surrounded by normal profiles, suggesting specificity of ricin within the trigeminal ganglion. Changes within brainstem axons showed both an electron-dense and a lucent, fragmenting type of axonal alteration. Terminal changes ranged from electron-dense to lucent and also included filamentous hyperplasia and 'hyperglycogenesis'. The altered axonal knobs contained round synaptic vesicles that were presynaptic to dendritic profiles and postsynaptic to terminals containing flattened synaptic vesicles. The above brainstem alterations were identified specifically in the following areas: ventrolateral, medial and dorsomedial pars interpolaris; the ventrolateral and mid-dorsal to dorsomedial areas of the marginalis and outer substantia gelatinosa layers of pars caudalis; and in ventral pockets corresponding to lamina V of the medullary dorsal horn. Dense alterations within terminals containing flattened synaptic vesicles that are typically presynaptic to primary afferents in these areas were rare findings, but along with vacuolization of dendritic profiles suggest a trans-synaptic effect possibly due to the exocytosis of ricin. The results are discussed in relation to different reports of dental projections and with regards to patterns of transganglionic degeneration.