Ongoing activity in trigeminal wide-dynamic range neurons is driven from the periphery.

Ongoing activity of spinal trigeminal neurons is observed under various conditions and suggested to be responsible for ongoing headache. It can be spontaneous, i.e. arising intrinsically from the neuron, or the product of descending influences from other central neurons, or maintained by ongoing afferent input. The aim of the present study was to examine if ongoing activity of neurons in different subnuclei of the spinal trigeminal nucleus is driven from peripheral afferent input. Experiments were performed in Wistar rats anesthetized with isoflurane or Nembutal/urethane. Ongoing activity of single wide-dynamic range (WDR) neurons was recorded with carbon fiber glass microelectrodes in two subnuclei of the spinal trigeminal nucleus: oral (Sp5O) and caudal (Sp5C). Peripheral receptive fields were evaluated using von Frey filaments. Sp5O neurons received peripheral input from facial areas innervated by the mandibular branch of the trigeminal nerve. Units in Sp5C had receptive fields in the surgically exposed dura mater and in facial areas innervated by the ophthalmic and maxillary branch of the trigeminal nerve. Saline or the local anesthetic lidocaine was locally applied onto the exposed dura mater or microinjected into V3 (for Sp5O units) or V1/V2 (for Sp5C units) divisions of the trigeminal ganglion via the infraorbital channel. Local application of lidocaine onto the exposed dura caused mechanical insensitivity of dural receptive fields but not significant decrease in ongoing activity. Microinjection of lidocaine but not saline into the trigeminal ganglion was followed by a substantial decrease in both the receptive field size and the activity of the recorded WDR units. Mechanical insensitivity of receptive fields after trigeminal ganglion blockade was accompanied by the disappearance of ongoing activity. We conclude that the ongoing activity of WDR neurons in the spinal trigeminal nucleus, which may be indicative for processes of sensitization, is driven remotely by ongoing afferent input.

Dependence of electrical activity of neurons in rostral parts of spinal trigeminal nucleus on functional state of trigeminal Gasser ganglion.

Unilateral injection of 100 microl 1% lidocaine into the trigeminal Gasser ganglion of narcotized rats produced a long-term moderation of the discharge rate of neurons in the ipsilateral (relative to the side of injection) rostral area of the spinal trigeminal nucleus. Activity of neurons in the contralateral rostral area of the spinal trigeminal nucleus was not blocked. Functional state of neurons in the trigeminal ganglion determines discharge activity of ipsilateral neurons of the spinal trigeminal nucleus. Activity of neurons in the contralateral rostral area of spinal trigeminal nucleus was not inhibited. Functional state of the cells in the trigeminal ganglion determines the character of electrical activity of neurons in the ipsilateral rostral area of spinal trigeminal nucleus.

Capsaicin-sensitive area in the ventral surface of the rat medulla.

In acute experiments on nembutal-urethan-anesthetized rats, structures selectively sensitive to capsaicin were found near the ventral surface of the medulla at the exit of hypoglossal nerve roots. Microinjection of 5-50 nl 0.01% capsaicin to the rostral region of the capsaicin-sensitive area mostly activated respiration, arterial pressure and heart rate (HR) while that to the caudal region inhibited arterial pressure and HR. In chronic experiments on rats, injection of 25 nl 1% capsaicin to the caudal capsaicin-sensitive area led to a decrease in arterial pressure by 35-45% and in HR by 10-15% within a week after operation. Arterial pressure and HR virtually reached the control level and the rostral and caudal ventral medulla showed asymmetric distribution of nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d)-positive cells by the end of the 2nd week. It is suggested that nitric oxide may be involved in the mechanisms of neurochemical rearrangements in the brainstem after application of capsaicin to the caudal ventrolateral medulla (CVLM).

[Function of the hypothalamo-thyroid system after administration of kainate into the ventrolateral portion of the medulla oblongata]. / Funktsiia sistemy gipotalamus--shchitovidnaia zheleza posle vvedeniia kainata v ventrolateral'nyi otdel prodolgovatogo mozga.

Contribution of the bulbar structures to mechanisms of realization of the hypothalamo-thyroid system feedback was studied in experiments on 73 adult male Wistar rats. Histologically confirmed unilateral destruction of neurones in the caudal part of medulla oblongata ventral portions after injection of 0.65 micrograms of kainate as soon as 30 min after injection was paralleled by a trend to increase of the blood serum levels of triiodothyronine and thyroxin-binding globulin, this increase attaining reliable values by day 7 after destruction, when the effects of operation stress levelled. During the same period we observed activation of glucocorticoid-dependent choline-, serotonin-, and noradrenergic-processes in the mediobasal zone of the hypothalamus, this indicating the presence of functional relationships of medulla oblongata ventral portions with the hypothalamo thyroid system realized by disinhibition of this system during destruction of neurones in the caudal part of the ventral portion of medulla oblongata.

[The cardiovascular effects after kainate administration into the caudal ventral sections of the medulla oblongata]. / Kardiovaskuliarnye éffekty posle vvedeniia kainata v kaudal'nuiu chast' ventral'nykh otdelov prodolgovatogo mozga.

Kainate destruction of the caudal ventral medulla's neurons raised by 70-90% the level of arterial pressure within 1 hour in anesthetised rats, the heart rate decreasing by 25-30% at the same time. Presection of the vagus at the neck level prevented the development of bradycardia and accelerated the formation of systemic arterial hypertension after administration of kainic acid to the caudal ventral medulla. The role of the vagal component in transmission of control signals from the ventral medullary structures to the heart and vessels, is discussed.

[Intracerebral connections after administration of kainate into the caudal part of ventral sections of the medulla oblongata]. / Vnutrimozgovye sviazi posle vvedeniia kainata v kaudal'nuiu chast' ventral'nykh otdelov prodolgovatogo mozga.

It was found that 1 day after unilateral destruction with kainate of neurons in the caudal ventral medulla unanesthetized animals showed disorders of arterial pressure control with a prevalence of hypertensive response. In 7 days after operation there was a decrease in the rate of neuronal uptake of serotonin and an increase in choline-, dopamine-, noradrenaline-, and glycinergic mediation in the basal hypothalamus and rostral ventral medulla, which characterize the functional state of synaptic formations in the brain stem structures connected to neurons in the caudal ventral medulla and involved in cardiovascular regulation.