Lack of long-term potentiation, non-cholinergic transmission and muscarinic inhibition in cat superior cervical ganglia innervated by nodose ganglion cells.

In anesthetized cats, in which a nodose-superior cervical ganglion (SCG) anastomosis had been performed 6-9 months earlier, the nictitating membrane contraction evoked by electrical stimulation of the cervical vagus nerve ipsilateral to the anastomosis was recorded. The competence of nodose neurons in regulation the multiple synaptic mechanisms of the sympathetic ganglion was tested by comparing this response with the responses to stimulation of (self-reinnervated SCG). The response of the nictitating membrane ipsilateral to the anastomosis was smaller and had a lower EC50 for hexamethonium (C6) than the responses of the nictitating membrane ipsilateral to the intact or sutured CST. A 40 Hz 10s stimulus train to the intact or sutured CST produced potentiation of ganglionic transmission lasting 1 hour or longer, while a similar stimulus train to the anastomosed cervical vagus nerve produced no potentiation. During block of ganglionic nicotinic transmission with C6, CST or vagus nerve stimulation evoked responses which increased in amplitude with increasing stimulus frequency and were blocked by the selective muscarinic receptor antagonist pirenzepine. When the anticholinesterase eserine was added, the responses evoked by preganglionic stimulation decreased in amplitude in the intact SCG, as previously shown [7], and in the self-reinnervated SCG. This effect, which is due to inhibition mediated by muscarinic receptors selectively blocked by AF-DX116, was absent in the anastomosed SCG. During block of ganglionic transmission with C6 and atropine, a 40 Hz stimulus train to the intact or to the sutured CST evoked a slow, small amplitude contraction that was enhanced by naloxone. This response, most likely mediated by peptides [6], was absent in the anastomosed SCG.(ABSTRACT TRUNCATED AT 250 WORDS)

The temporary inactivation of the red nucleus affects performance of both conditioned and unconditioned nictitating membrane responses in the rabbit.

These experiments are part of a series of studies examining the role of the red nucleus in the performance of the conditioned and unconditioned nictitating membrane reflexes in the rabbit. Specifically, the experiments test the hypothesis that the temporary inactivation of the red nucleus selectively affects the performance of the conditioned reflex. The experiments were designed to assess the effects of lidocaine and control saline microinjections on conditioned as well as unconditioned responses in both paired and unpaired trials. Rabbits were chronically implanted with cannulae through which small injecting tubes were passed stereotaxically to the red nucleus. The animals were conditioned using a delay paradigm in which a 1 kHz tone and an air puff applied to the cornea were used as the unconditioned and conditioned stimulus, respectively. Once conditioned, the effects of either lidocaine or saline injection were evaluated while alternating paired trials with unpaired trials in which only the air puff was applied. The principal finding of this study was that the amplitudes of both the conditioned and unconditioned responses were reduced following lidocaine injection into the red nucleus. The effect on the unconditioned response amplitude could not be ascribed to any interaction between the conditioned and unconditioned responses, since it also was present in the unpaired trials. The reduction in amplitude of the conditioned and unconditioned responses was shown to be correlated with changes in other characteristics of the same responses. The data suggest that the red nucleus contributes to the performance of both the conditioned and unconditioned nictitating membrane reflexes and consequently is not likely to be involved only in pathways responsible for mediating and/or storing the engram for the conditioned reflex.

Neurons located in the trigeminal sensory complex and the lateral pontine tegmentum project to the oculomotor nucleus in the rabbit.

Neurons located in the trigeminal sensory complex (TSC) and the lateral pontine tegmentum (LPT) have been reported to project to both the accessory abducens and the facial nuclei, which innervate the retractor bulbi and orbicularis oculi muscles respectively, in order to control the nictitating membrane (NM) and eyelid defensive reflex. Since muscles innervated by the oculomotor nucleus (OCM) also appear to be involved in this reflex, retrograde and anterograde tracers were used in this study to determine whether there are projections from the TSC and LPT to the OCM in the rabbit. Injections of horseradish peroxidase (HRP) in the OCM nucleus labeled neurons in the LPT surrounding the trigeminal motor nucleus dorsally, laterally and ventrally. Only a few scattered neurons were found in the principal and spinal trigeminal nuclei. Injection of biocytin in the LPT area containing most of the HRP-labeled neurons caused anterograde labeling of fibers that crossed the midline and ascended just dorsal to the contralateral medial lemniscus. A proportion of these fibers coursed in a dorsal direction to enter and terminate within the OCM contralateral to the injection site. The location of the motoneuronal groups innervating the different extraocular muscles was studied by retrograde transport of HRP, and compared with the distribution of biocytin-labeled terminals. It was found that the terminals were located in the superior rectus and the levator palpebrae zone of the nucleus. We discuss the functional significance of this projection for the eyelid and NM response.

Activation of histamine H3 receptors produces presynaptic inhibition of neurally evoked cat nictitating membrane responses in vivo.

This study was undertaken in order to determine the potential role of prejunctional histamine H3 receptors in an in vivo adrenergic model system. Frequency-dependent nictitating membrane responses were elicited by sympathetic nerve stimulation in anesthetized cats. Systemic administration of the selective histamine H3 receptor agonist, (R)-alpha-methylhistamine (R alpha MeHA) produced a dose-related depression of amplitude of the evoked nictitating membrane responses with a threshold of about 10 micrograms/kg and maximal effect (50% depression at the lowest frequency; 0.5 Hz) seen at 100-300 micrograms/kg. Responses obtained with low frequency stimulation were more sensitive to depression by R alpha MeHA than were responses evoked with higher frequencies of stimulation. Larger doses of R alpha MeHA given to the same animals, failed to produce additional inhibition. R alpha MeHA depressed the amplitude of nictitating membrane responses evoked by either pre- or postganglionic nerve stimulation to an equivalent degree. This depressant action of R alpha MeHA was antagonized by pretreatment with the specific histamine H3 antagonist, thioperamide (3 mg/kg), but not by combined pretreatment with histamine H1 and H2 blockers chlorpheniramine (300 micrograms/kg) and cimetidine (5 mg/kg). Intravenous administration of adrenaline (1-30 micrograms/kg) also produced graded nictitating membrane responses that were not altered by subsequent administration of R alpha MeHA. These results suggest that histamine H3 receptors are involved in the modulation of neurally evoked noradrenaline release in the cat nictitating membrane by an inhibitory presynaptic action.(ABSTRACT TRUNCATED AT 250 WORDS)

Evidence for verapamil-induced functional inhibition of noradrenergic neurotransmission in vivo.

Contractions of the cat nictitating membrane have been used to explore the effects of calcium channel blockers on neurotransmission in vivo, by comparing the effects of verapamil and nifedipine on contractions of nictitating membrane following either electrical stimulation of the superior cervical ganglion or intravenous injection of the alpha-adrenoceptor agonist phenylephrine. Verapamil (0.3, 0.6 and 1.2 mg/kg, iv) produced a dose related and reversible inhibition of stimulation induced contractions but did not affect phenylephrine responses of nictitating membrane. Intravenous nifedipine (10, 20 and 40 micrograms/kg) produced inconsistent effects on both stimulation- and phenylephrine-induced contractions of the nictitating membrane. Thus only verapamil appears to selectively affect noradrenergic neurotransmission in this model, possibly by altering the neurotransmitter release from the terminals innervating the nictitating membrane in the cat.

Control of rabbit nictitating membrane movements. I. A computer model of the retractor bulbi muscle and the associated orbital mechanics.

Our objective in this study is to synthesize existing experimental data by constructing a realistic neuromechanical control model of rabbit nictitating membrane (NM) movements. We model the retractor bulbi muscle at the motor unit level because this is the level of nervous system control and also facilitates comparison with experimental data. Our motor unit model is derived from an earlier model of muscle activation based on calcium kinetics and includes a post-activation potentiation mechanism. Motor units are combined into a model of whole muscle that includes length-tension and force-velocity effects. Finally, we incorporate the muscle model into a biomechanical model in which the globe and NM are represented as a system of inertial, viscous, and elastic elements. The model takes patterns of neural signals (in the form of impulses) as input and produces movement of the NM as output. Our muscle model quantitatively accounts for data on isometric force development and decay for twitch, double shock, and tetanic stimulation. The complete model may be used for analysis of the relationship of motoneuron activity to behavior or as a realistic response generator in models of NM conditioning. This study also highlights gaps in the experimental data on the rabbit NM effector system.

Control of rabbit nictitating membrane movements. II. Analysis of the relation of motoneuron activity to behavior.

The objective of this study is to understand more precisely the relationship of motoneuron activity to movements of the rabbit nictitating membrane (NM). We use a model of the oculomotor plant to investigate what NM movements are generated by a given pattern of neural input and what inputs are required to generate particular NM movements. Simulated peak NM extensions can occur well over 50 ms after the end of motoneuron activity. The neural input required for the model to generate full amplitude NM extension responses is more consistent with single accessory abducens unit recordings from awake rabbits than recordings from anesthetized rabbits. An initial high frequency burst of neural activity followed by a rapid decay is required for simulations of conditioned responses (CRs) trained at a 125 ms interstimulus interval (ISI). For CRs trained with a 250 ms ISI, a more slowly rising and decaying neural activity is required. Model simulations show that the linear correlation between the shape of histogrammed motoneuron activity and the shape of NM movements can be high for long duration responses (> 400 ms) but is low for short duration responses (< 200 ms). Simulations are also consistent with the hypothesis that NM retraction is generally passive.

[The effect of sympathetic denervation on the structure, contractility and electrical activity of the smooth-muscle cells in the cat nictitating membrane]. / Vliianie simpaticheskoi denervatsii na strukturu, sokratimost' i élektricheskuiu aktivnost' gladkomyshechnykh kletok migatel'noi pereponki koshki.

The nucleus and soma of sympathetically denervated smooth muscle cells (SMCs) of the cat nictitating membrane were found to be enlarged. The number of free ribosomes was dramatically increased and a disintegration of microfilaments was found. The functional changes involved spontaneous or agonist-induced generation of APs. These findings suggest that the denervation destructed the adrenoreceptor control mechanisms of the excitable membrane's potential. The possibility of emergence of new Ca2+ channels in the denervated SMCs is discussed.

Medetomidine-induced alterations of intraocular pressure and contraction of the nictitating membrane.

The alpha-2 adrenoceptor agonist, medotomidine (MED), was examined for effects on: (1) intraocular pressure (IOP) in normal and sympathectomized (SX) rabbits; (2) IOP in normal rabbits pretreated with the alpha-2 antagonist idazoxan; (3) contractions of the cat nictitating membrane (CNM) elicited by nerve stimulation and intra-arterial (IA) norepinephrine. Unilateral topical administration of MED (7.5-75 micrograms) caused dose-dependent, bilateral IOP reduction in normal eyes, but MED (25 micrograms) had no appreciable hypotensive activity in SX eyes. The ocular hypotensive effect of MED (25 micrograms) was antagonized by treatment with idazoxan (100 micrograms, bilaterally), a relatively selective alpha-2 antagonist. MED and dexmedetomidine (DMED) also inhibited frequency-related contractions of CNM induced by electrical stimulation of the cervical sympathetic trunk. Rauwolscine (100 micrograms, IA) shifted the MED dose response in the CNM to the right indicative competitive antagonism, whereas SK&F 104078 (300 micrograms, IA), a relatively dose-selective postjunctional alpha-2 antagonist, had no effect on DMED suppression. These results show that MED lowers IOP in part, by interacting with alpha-2 adrenoceptors located on sympathetic nerve endings. An effect of MED on imidazoline sites may also be possible.

Evidence from lack of decentralization-induced supersensitivity that beta 2-adrenoceptors of the cat nictitating membrane are non-innervated.

The right superior of cervical sympathetic trunk of cats was sectioned preganglionically under anaesthesia. Six days later the blood pressure, heart rate and contractions of the left (control) and right (decentralized) nictitating membranes were recorded under chloralose anaesthesia (80 mg kg-1). The alpha-adrenoceptor-mediated contractile responses of the nictitating membrane to intravenous adrenaline were greater on the decentralized side than the control side, with a significant shift of the dose-response curve to the left. After phentolamine (8 mg kg-1 i.v.), adrenaline administered intra-arterially exerted beta-adrenoceptor-mediated relaxation of the nictitating membranes. However, there was no difference in the sensitivity or magnitude of responses between decentralized and control sides. In a separate series of experiments, the alpha-adrenoceptor-mediated contractile responses of the nictitating membrane to intra-arterial noradrenaline displayed supersensitivity on the decentralized side, the dose-response curve being significantly shifted to the left. In the same animals, the beta-adrenoceptor-mediated relaxation responses to intra-arterial isoprenaline were non-significantly greater on the decentralized side, presumably because of raised tone. However, when expressed as a percentage of the maximum relaxation, there was no difference in sensitivity. This study shows that the alpha-adrenoceptor-mediated contractile response of the nictitating membrane displays supersensitivity after preganglionic section of the sympathetic innervation. This is presumably because of an up-regulation arising from loss of sympathetic traffic onto the receptor. The relaxation response is mediated via adrenoceptors of the beta 2-subtype and shows no supersensitivity. This suggests that these receptors are not under the influence of the sympathetic innervation.

Lesions of the cerebellar interpositus nucleus abolish both nictitating membrane and eyelid EMG conditioned responses.

Both nictitating membrane extension and eyelid EMG activity were measured during classical conditioning of rabbits to tone-airpuff pairings. Both measures were highly correlated. Over trials, learning criterion was met earlier with eyelid EMG activity than with nictitating membrane extension. Within a trial, eyelid EMG preceded and was more robust than nictitating membrane extension. The rabbits were lesioned in the cerebellar interpositus nucleus and then trained for up to 26 days. Detailed analyses of tone alone trials demonstrate that the lesion abolished conditioned responses for both measures. These data confirm that conditioned responses are abolished by lesion of the cerebellar interpositus nucleus.

[Activation of the fast calcium input in the denervated smooth muscle of the cat nictitating membrane]. / Aktivatsiia bystrogo kal'tsievogo vkhoda v denervirovannoi gladkoi myshtse migatel'noi pereponki koshki.

The excitation and contraction features of innervated and sympathetically denervated smooth muscle strips from cat's nictitating membrane have been studied by single sucrose gap arrangement. Increasing of smooth muscle cells sensitivity to drugs were accompanied by elevation of membrane response and the ability to generation of action potentials. Action potentials have been induced by agonists or high potassium concentration in external solution and spontaneously. In innervated muscle action potentials have been evoked as a result of depolarization by high potassium concentration of TEA blockade of potassium conductance. Induced and spontaneously generated action potentials were blocked by organic and inorganic antagonists of potential dependent Ca++ channels. In Ca-free solution action potentials were absent but might be supported by Ba++. Decrease of Na+ had no effect on smooth muscle excitability. It is supposed that activation of potential depended Ca++ channels in smooth muscle cells with pharmaco-mechanical coupling are under influence of sympathetic nerves.

[Regulation of the postsynaptic alpha-1-adrenoreceptors of the smooth muscle of the nictitating membrane in the cat]. / Reguliatsiia postsinapticheskikh al'fa-1-adrenoretseptorov gladkoi myshtsy migatel'noi pereponki koshki.

Radioassay binding of the smooth muscle of the nictitating membrane of cat has revealed the specific binding sites of [3H]prazosin corresponding to alpha-1 adrenoceptors. There was a significant increase in the number of alpha-1 adrenoceptors without any changes in their affinity. Incubation of the culture of the preliminary sympathectomized smooth muscle with noradrenaline decreased the number of alpha-1 adrenoceptors also without altering the affinity of binding. So, it is concluded that sympathetic nervous system regulated the number of postsynaptic alpha-1 adrenoceptors by means of neurotransmitter (noradrenaline).

Aluminum-induced neurofibrillary degeneration disrupts acquisition of the rabbit's classically conditioned nictitating membrane response.

Rabbits received intraventricular injections of aluminum chloride, hydrochloric acid, or served as unoperated controls. On the 6th day postsurgery, they underwent 4 days (100 trials per day) of classical conditioning of the nictitating membrane response (NMR) to a tone conditioned stimulus and an air-puff unconditioned stimulus. Unoperated and hydrochloric acid control animals readily acquired the conditioned response. Aluminum intoxicated rabbits, in contrast, did not acquire the conditioned response over the 4 days of testing. This disruption of conditioning in aluminum-treated rabbits could not be attributed to deficits in sensory or motor processes or to illness. Neuropathological analysis revealed widespread neurofibrillary tangle formation in aluminum-treated animals. Furthermore, the degree of neurofibrillary degeneration was significantly negatively correlated with the degree of conditioning. The results are considered in the context of using the rabbit NMR preparation as a model system for studying age-related conditioning disorders.

Reflex facilitation of the nictitating membrane response remains after cerebellar lesions.

Reflex facilitation and associated properties were investigated during classical conditioning of the nictitating membrane (NM) response in rabbit. In the first experiment, the role of the cerebellum was examined by comparing the unconditioned responses of animals with bilateral lesions of the deep cerebellar nuclei with those of operated controls during counterbalanced tone/light (T/L) discrimination training. Both T and L facilitated unconditioned NM responses when used as the CS+ (conditioned stimulus), but neither facilitated when used as the CS-. There were no significant differences in the amount of reflex facilitation exhibited by animals with lesions compared with control animals. Animals with lesions, however, failed to acquire conditioned responses after 10 days of training, whereas all control animals met acquisition criterion within 4 days. In the second experiment, reflex facilitation was shown to decrement in a stimulus-specific manner when nonreinforced presentations of an auditory stimulus were given. The discussion of results focuses on the relation between reflex facilitation and classical conditioning in terms of behavioral properties and underlying neural systems.

Stimulation of the spinal trigeminal nucleus supports classical conditioning of the rabbit's nictitating membrane response.

Acquisition, extinction, and differential conditioning of the rabbit's nictitating membrane response to a tone conditioned stimulus were supported by electrical stimulation of the spinal trigeminal nucleus. Stimulation of the accessory abducens nucleus, the abducens nucleus, and the reticular formation at the level of the spinal trigeminal nucleus supported lower, transient levels of conditioning. The results are discussed in terms of stimulation of sensory inputs to the brainstem and cerebellum.

Motor innervation of the bursalis muscle (nictitating membrane) in the lizard Callopistes maculatus.

The motor neurones which innervate the bursalis muscle of the lizard Callopistes maculatus were identified by means of intra-axonal retrograde transport of horseradish peroxidase. These neurones were distributed in the oculomotor abducens and accessory abducens nuclei. In the oculomotor nucleus one group of neurones was located in the ventral subnucleus of the contralateral side while the other group was found in the dorsolateral subnucleus of the ipsilateral side. In the abducens and accessory abducens nuclei all the neurones were in the ipsilateral side. The accessory abducens cells, although less numerous, were larger and had a prominent dendritic field in close relationship with the nucleus descendens nervi trigemini.

Mechanism of action of a new prostaglandin antihypertensive, viprostol [CL 115 347; (dl)-15-deoxy-16-hydroxy-16(alpha/beta)-vinyl-prostaglandin E2 methyl ester]: (II). Effects on the adrenergic nervous system.

Viprostol [(dl)-15-deoxy-16-hydroxy-16(alpha/beta)-vinyl-prostaglandin E2 methyl ester; CL 115 347] is a new orally and transdermally active antihypertensive agent that exerts its major antihypertensive action by vasodilation. The present studies were conducted to examine its effects on the adrenergic nervous system. In cats, viprostol did not inhibit renal sympathetic nerve discharge (RSND) monitored at the postganglionic region, indicating that nerve transmission or conduction was not blocked at the ganglion or the pre- or postganglionic fibres. In cat nictitating membrane preparations in situ, viprostol partially blocked the membrane contractile response to exogenous epinephrine and norepinephrine, as well as to electrical stimulation of pre- and postganglionic fibres. In spontaneously hypertensive rats (SHR), viprostol partially blocked the vasopressor response of exogenous norepinephrine and epinephrine specifically without influencing that of angiotensin II. All these suggest that viprostol produced weak alpha-adrenoceptor blockade. Viprostol did not antagonize the tachycardia induced by stimulation of the discrete segments at C7-T1 (cardio-accelerator) of the spinal cord in pithed SHR, suggesting that viprostol did not activate the presynaptic alpha-adrenoceptors. Viprostol significantly inhibited the increase in blood pressure induced by electrical stimulation of the spinal cord at T7-T9 in pithed SHR, probably due to postsynaptic alpha-adrenoceptor blockade. In conclusion, viprostol produced weak, but statistically significant alpha-adrenoceptor blockade which may contribute partially to its antihypertensive action.