Parallel pathways from motor and somatosensory cortex for controlling whisker movements in mice.

Mice can gather tactile sensory information by actively moving their whiskers to palpate objects in their immediate surroundings. Whisker sensory perception therefore requires integration of sensory and motor information, which occurs prominently in the neocortex. The signalling pathways from the neocortex for controlling whisker movements are currently poorly understood in mice. Here, we delineate two pathways, one originating from primary whisker somatosensory cortex (wS1) and the other from whisker motor cortex (wM1), that control qualitatively distinct movements of contralateral whiskers. Optogenetic stimulation of wS1 drove retraction of contralateral whiskers while stimulation of wM1 drove rhythmic whisker protraction. To map brainstem pathways connecting these cortical areas to whisker motor neurons, we used a combination of anterograde tracing using adenoassociated virus injected into neocortex and retrograde tracing using monosynaptic rabies virus injected into whisker muscles. Our data are consistent with wS1 driving whisker retraction by exciting glutamatergic premotor neurons in the rostral spinal trigeminal interpolaris nucleus, which in turn activate the motor neurons innervating the extrinsic retractor muscle nasolabialis. The rhythmic whisker protraction evoked by wM1 stimulation might be driven by excitation of excitatory and inhibitory premotor neurons in the brainstem reticular formation innervating both intrinsic and extrinsic muscles. Our data therefore begin to unravel the neuronal circuits linking the neocortex to whisker motor neurons.

Terminal field specificity of forebrain efferent axons to the pontine parabrachial nucleus and medullary reticular formation.

The pontine parabrachial nucleus (PBN) and medullary reticular formation (RF) are hindbrain regions that, respectively, process sensory input and coordinate motor output related to ingestive behavior. Neural processing in each hindbrain site is subject to modulation originating from several forebrain structures including the insular gustatory cortex (IC), bed nucleus of the stria terminalis (BNST), central nucleus of the amygdala (CeA), and lateral hypothalamus (LH). The present study combined electrophysiology and retrograde tracing techniques to determine the extent of overlap between neurons within the IC, BNST, CeA and LH that target both the PBN and RF. One fluorescent retrograde tracer, red (RFB) or green (GFB) latex microbeads, was injected into the gustatory PBN under electrophysiological guidance and a different retrograde tracer, GFB or fluorogold (FG), into the ipsilateral RF using the location of gustatory NST as a point of reference. Brain tissue containing each forebrain region was sectioned, scanned using a confocal microscope, and scored for the number of single and double labeled neurons. Neurons innervating the RF only, the PBN only, or both the medullary RF and PBN were observed, largely intermingled, in each forebrain region. The CeA contained the largest number of cells retrogradely labeled after tracer injection into either hindbrain region. For each forebrain area except the IC, the origin of descending input to the RF and PBN was almost entirely ipsilateral. Axons from a small percentage of hindbrain projecting forebrain neurons targeted both the PBN and RF. Target specific and non-specific inputs from a variety of forebrain nuclei to the hindbrain likely reflect functional specialization in the control of ingestive behaviors.

Posterior lateral hypothalamic axon terminals are in contact with trigeminal premotor neurons in the parvicellular reticular formation of the rat medulla oblongata.

This study was performed to understand the anatomical substrates of hypothalamic modulation of jaw movements. After cholera toxin B subunit (CTb) injection into the parvicellular reticular formation (RFp) of the rat medulla oblongata, where many trigeminal premotor neurons have been known to exist, numerous CTb-labeled neurons were found in the posterior lateral hypothalamus (PLH) bilaterally with a clear-cut ipsilateral dominance. After ipsilateral injections of biotinylated dextran amine (BDA) into the PLH and CTb into the motor trigeminal nucleus (Vm), the prominent distribution of BDA-labeled axon terminals around CTb-labeled neurons was found in the RFp region just ventral to the nucleus of the solitary tract and medial to the spinal trigeminal nucleus ipsilateral to the injection sites. Within the neuropil of the RFp, BDA-labeled axon terminals made an asymmetrical synaptic contact predominantly with dendrites and additionally with somata of the RFp neurons, some of which were labeled with CTb. It was further revealed that these BDA-labeled axon terminals were immunoreactive for vesicular glutamate transporter 2. The present data suggest that the PLH plays an important role in the control of jaw movements by exerting its glutamatergic excitatory action upon RFp neurons presynaptic to trigeminal motoneurons.

GABAergic and non-GABAergic thalamic, hypothalamic and basal forebrain projections to the ventral oral pontine reticular nucleus: their implication in REM sleep modulation.

The ventral part of the oral pontine reticular nucleus (vRPO) is a demonstrated site of brainstem REM-sleep generation and maintenance. The vRPO has reciprocal connections with structures that control other states of the sleep-wakefulness cycle, many situated in the basal forebrain and the diencephalon. Some of these connections utilize the inhibitory neurotransmitter GABA. The aim of the present work is to map the local origin of the basal forebrain and diencephalon projections to the vRPO whether GABAergic or non-GABAergic. A double-labelling technique combining vRPO injections of the neuronal tracer, cholera-toxin (CTB), with GAD-immunohistochemistry, was used for this purpose in adult cats. All of the numerous CTB-positive neurons in the reticular thalamic and dorsocaudal hypothalamic nuclei were double-labelled (CTB/GAD-positive) neurons. Approximately 15%, 14% and 16% of the CTB-positive neurons in the zona incerta and the dorsal and lateral hypothalamic areas are, respectively, CTB/GAD-positive neurons. However, only some double-labelled neurons were found in other hypothalamic nuclei with abundant CTB-positive neurons, such as the paraventricular nucleus, perifornical area and H1 Forel field. In addition, CTB-positive neurons were abundant in the central amygdaline nucleus, terminal stria bed nuclei, median preoptic nucleus, medial and lateral preoptic areas, dorsomedial and ventromedial hypothalamic nuclei, posterior hypothalamic area and periventricular thalamic nucleus. The GABAergic and non-GABAergic connections described here may be the morphological pillar through which these prosencephalic structures modulate, either by inhibiting or by exciting, the vRPO REM-sleep inducing neurons during the different sleep-wakefulness cycle states.

The descending motorcortical pathway to the laryngeal motoneurons in the squirrel monkey.

The motor cortex of primates contains an area ("larynx area") which, when stimulated unilaterally, produces bilateral vocal fold adduction. In order to identify the pathway along which the cortical larynx area exerts its control on the laryngeal motoneurons, we have blocked excitatory neurotransmission in each of the main projection fields of the cortical larynx area and tested for the elicitability of vocal fold movements from this area in the squirrel monkey. Blocking was carried out by injection of the glutamate antagonist kynurenic acid. We found that injection into the dorsal reticular nucleus of the caudal medulla ipsilateral to the stimulation site blocked vocal fold movements bilaterally; injections invading major parts of the nucleus ambiguus blocked vocal fold movements exclusively ipsilateral to the injection site; and injections centered on the parvocellular reticular formation bordering the nucleus ambiguus blocked exclusively contralateral vocal fold movements. We conclude from this that the corticobulbar laryngeal control pathway synapses in the ipsilateral dorsal reticular nucleus and then divides into one component running directly to the ipsilateral nucleus ambiguus and a second component crossing to the contralateral nucleus ambiguus after having synapsed in the ipsilateral peri-ambigual reticular formation.

Present concepts of oculomotor organization.

This chapter gives an introduction to the oculomotor system, thus providing a framework for the subsequent chapters. This chapter describes the characteristics, and outlines the structures involved, of the five basic types of eye movements, for gaze holding ("neural integrator") and eye movements in three dimensions (Listing's law, pulleys).

Medial septal modulation of the ascending brainstem hippocampal synchronizing pathways in the anesthetized rat.

Independent and combined electrical stimulation pairings of the medial septum (MS), posterior hypothalamus (PH), and reticular pontine oralis (RPO) of the brainstem were performed in the acute urethane anesthetized rat, while recording field activity from electrodes in either the stratum oriens or stratum moleculare of the hippocampal formation. Theta frequency and power were measured during independent stimulation of each nuclei and during combined stimulation using three pairings: (1) MS-PH (2) MS-RPO and (3) PH-RPO. Each pairing consisted of parameters known to elicit theta of a high frequency for one nucleus, and parameters known to elicit a low frequency for the second nucleus. This methodology allowed us to observe whether one nucleus preferentially modulated theta activity in the hippocampus in terms of frequency and power. The MS was observed to reset theta frequency in both the upward and downward direction when stimulated in combination with either the PH (Experiment 1) or the RPO (Experiment 2). In Experiment 3 (PH-RPO), the structure receiving the higher intensity stimulation had the predominate effect on theta frequency. With MS stimulation combinations, the power of the elicited theta activity was found to increase over the independent stimulation in some cases during Experiment 1. Likewise, in Experiment 2, the combined stimulation produced a power that in most cases was significantly greater than that measured during the independent stimulations. This effect was not observed with PH and RPO stimulation combinations. The combined stimulation of the PH and RPO yielded a power similar to the independent PH stimulations. The findings support the following conclusions: (1) the major theta generating activity of the ascending brainstem synchronizing pathways involves projections from the RPO to the PH, relayed through the MS, to the hippocampal formation; and (2) that the MS directly controls theta amplitude and secondarily translates the level of ascending brainstem activity into the appropriate frequency of hippocampal theta.

The integrative role of the rat medullary subnucleus reticularis dorsalis in nociception.

Neurons within the medullary subnucleus reticularis dorsalis (SRD) of the rat convey selectively nociceptive information from all parts of the body. We have sought to define the neuronal networks that convey information from widespread noxious stimuli to the diffuse thalamocortical system and also modulate spinal outflow. The experiments, which were performed in rats, were designed to determine whether efferents from the SRD issue collaterals to the thalamus and spinal cord. Injections of the tracers fluorogold and tetramethylrhodamine-labelled dextran were centred stereotaxically in two areas that receive dense projections from the SRD: the cervical spinal cord and the lateral ventromedial thalamus (VMl), respectively. In other experimental series, SRD neurons were characterized electrophysiologically and individually labelled in a Golgi-like manner following juxtacellular iontophoresis of biotin-dextran. More than half reticulothalamic neurons within the SRD provided monosynaptic connections to the spinal cord. SRD neurons that responded to Adelta- or Adelta- and C-fibre activation from any area of the body had axons that gave both ascending and descending collaterals. Because the SRD innervates several areas involved in motor processing and receives strong, direct influences from several cortical regions, it could provide a structural basis for the processing of nociceptive and motor activities.

Different roles of alpha 2-adrenoceptors of the medulla versus the spinal cord in modulation of mustard oil-induced central hyperalgesia in rats.

We attempted to determine the roles of spinal versus medullary alpha 2-adrenoceptors in modulation of central hyperalgesia in rats. Central hyperalgesia was produced by applying mustard oil (50%) to the skin of the ankle of one hindpaw. The threshold for eliciting a hindlimb flexion reflex was determined by applying a series of calibrated monofilaments to the glabrous skin of the hindpaw contralaterally (= control) or ipsilaterally to the mustard oil-treated ankle (= outside the area of primary hyperalgesia). Medetomidine (an alpha 2-adrenoceptor agonist; 1 micrograms), atipamezole (an alpha 2-adrenoceptor antagonist; 2.5 micrograms) or saline was microinjected into the lateral reticular nucleus of the medulla, the nucleus raphe magnus, or intrathecally to the lumbar spinal cord 12 min before the mustard oil treatment. Following saline injections, mustard oil produced a significant decrease of the hindlimb withdrawal threshold in the mustard oil-treated limb but not in the contralateral limb. Atipamezole in the lateral reticular nucleus produced a complete reversal of the hyperalgesia but no effect on the threshold of the intact limb. However, atipamezole in the raphe magnus nucleus or in the lumbar spinal cord did not produce a significant attenuation of the hyperalgesia. Medetomidine in the spinal cord, but not in the lateral reticular nucleus, reversed the hyperalgesia. At this dose range (up to 3 micrograms), medetomidine in the spinal cord of nonhyperalgesic control rats did not produce any significant change in the withdrawal response of hindlimbs or in the tail-flick latency. The results indicate that neurogenic inflammation induces significant plastic changes in the function of alpha 2-adrenergic pain regulatory mechanisms. In rats with mustard oil-induced central hyperalgesia, an alpha 2-adrenoceptor antagonist produces an antihyperalgesic effect due to an action on the caudal ventrolateral medulla, whereas an alpha 2-adrenoceptor agonist produces an enhanced antinociceptive effect due to a direct action on the spinal cord.

GABAergic projections from the thalamic reticular nucleus to the anteroventral and anterodorsal thalamic nuclei of the rat.

We have studied GABAergic projections from the thalamic reticular nucleus to the anterior thalamic nuclei of the rat by combining retrograde labelling with horseradish peroxidase and GABA-immunohistochemistry. Small iontophoretic injections of the tracer into subnuclei of the anterior thalamic nuclear complex resulted in retrograde labelling of cells in the rostrodorsal pole of the ipsilateral thalamic reticular nucleus. All of these cells were also GABA-positive. The projections were topographically organized. Neurons located in the most dorsal part of the rostral reticular nucleus projected to the dorsal half of both the posterior sub-division and the medial subdivision of the anteroventral thalamic nucleus, and to the rostral portion of the anterodorsal thalamic nucleus. Immediately ventral to this group of neurons, but still within the dorsal portion of the reticular nucleus, a second group of neurons, extending from the dorsolateral to the dorsomedial edge of the nucleus, projected to the ventral parts of the posterior and medial subdivisions of the anteroventral nucleus. Following injection of tracer into the dorsal part of the rostral anteroventral nucleus, retrograde labelled GABA-containing cell bodies were also found in the ipsilateral anterodorsal nucleus.

Fronto-parietal control of electrodermal activity in the cat.

The aim of this work was to investigate the direct involvement of the fronto-parietal cortex in the control of spinal autonomic centers eliciting electrodermal activity (EDA). This autonomic response, linked with the activity of sweat glands, was recorded as skin potential responses (SPRs) from forepaws in the cat. Animals were paralyzed by gallamine and SPRs were obtained under halothane anaesthesia. For each animal, a transection of the medulla sparing only pyramidal tracts was carried out. SPRs were elicited by direct electrical stimulation of pericruciate and posterior parietal cortical areas before and after such a transection. Results showed that in intact preparations, stimulation of the pericruciate cortex evoked SPRs at lower thresholds than the posterior parietal cortex. After the bulbar transection, only the stimulation of pericruciate areas still elicited SPRs at low intensities. Results are interpreted as indicating that fronto-parietal control of EDA is probably mediated by a double descending system: one involving corticoreticulospinal pathways and a direct corticospinal one. We hypothesized that the somatic motor cortex initiates descending programs to autonomic centers at bulbar and spinal levels, and that these centers are involved in autonomic adjustments to somatomotor movements.

Differentiation of intracranial morphine self-administration behavior among five brain regions in mice.

BALB/c mice were unilaterally implanted with a guide cannula, the tip of which was positioned 1.5 mm above either the lateral hypothalamus (LH) the medial hypothalamus (MH), the mesencephalic central gray area (CG), or either the dorsal (DRF) or ventral parts (VRF) of the reticular formation. On each day of the experimental period a stainless steel injection cannula was inserted into these brain structures to compare the self-administration of two doses of morphine (5 ng or 50 ng), using a spatial discrimination task in a Y-maze. At the dose of 5 ng, LH-, MH-, CG-, and VRF-injected mice all showed a regular self-administration response. At the dose of 50 ng, a discrimination between the reinforced arm and the neutral arm of the Y-maze was observed in LH-, MH-, and VRF-injected mice. Animals of the MH group exhibited the highest level of discrimination performance. At this dose, long injection latencies (> 15 min) were recorded in the CG group, which constrained us to reduce the number of daily trials from 10 to 4. In these modified conditions, CG animals clearly self-injected the dose of 50 ng of morphine. Subcutaneous injections of naloxone (4 mg/kg) reduced the number of self-administrations of morphine at each of the four responding structures. Marked signs of physical dependence (escape attempts) were observed in the four groups but with a higher frequency in CG and MH animals. When the injections of naloxone were suspended, a regular self-administration reappeared.(ABSTRACT TRUNCATED AT 250 WORDS)

Crosstalk between the two sides of the thalamus through the reticular nucleus: a retrograde and anterograde tracing study in the rat.

In order to investigate the possible routes linking the thalamus in the two sides of the brain, the connections of the reticular nucleus (RT), the major component of the ventral thalamus, with contralateral dorsal thalamic nuclei were systematically investigated in the adult rat. This study was performed with several tract-tracing techniques: single and double retrograde labeling with fluorescent tracers, and anterograde tracing with biocytin. Retrograde tracing was also combined with immunocytochemistry to provide additional criteria for the identification of labeled RT neurons. The data obtained with the retrograde transport of one fluorescent tracer showed that RT neurons project to contralateral dorsal thalamic domains. In particular, retrograde labeling findings indicated that the anterior intralaminar nuclei, as well as the ventromedial (VM) nucleus, are preferential targets of the contralateral RT projections. Commissural neurons were concentrated in two portions of RT: its rostral part, including the rostral pole, which projects to the contralateral central lateral (CL) and paracentral (Pc) nuclei, and the ventromedial sector of the middle third of RT, which projects to the contralateral VM and posterior part of CL and Pc. The double retrograde labeling study of the bilateral RT-intralaminar connection indicated that at least part of the commissural RT cells bifurcate bilaterally to symmetrical portions of the anterior intralaminar nuclei. The targets of the RT commissural system inferred from the retrograde labeling data were largely confirmed by anterograde tracing. Moreover, it was shown that RT fibers cross the midline in the intrathalamic commissure. The present data demonstrate that bilateral RT connections with the dorsal thalamus provide a channel for interthalamic crosstalk. Through these bilateral connections with thalamic VM and intralaminar neurons, RT could influence the activity of wide territories of the cerebral cortex and basal ganglia of both hemispheres.

Auditory sensory gating in the rat hippocampus: modulation by brainstem activity.

Auditory stimuli repeated at short intervals result in diminished evoked responses recorded from the skull surface and from the hippocampus in the rat. The rat has been used to model diminished responses to repeated auditory stimuli--a phenomenon seen in normal human subjects, but often absent in schizophrenics. In this study, we examined the neural circuitry involved in the processing and gating of auditory responses recorded from the hippocampus of the rat. Evoked potentials and single neuron activity with diminished responses to the second of paired tones were recorded in the brainstem reticular formation in the paragigantocellular region at the caudal level of the pons, but diminished responses were not observed in the primary auditory relay nuclei. Electrical stimulation of this region of the brainstem reticular formation was able to substitute for the first, or conditioning, auditory tone to produce sensory gating of the response to the second, or test, tone when recording from the hippocampus. Stimulation of the auditory nuclei up to the level of the lateral lemniscus, but not the superior colliculus, was also able to substitute for an auditory stimulus to produce sensory gating in the hippocampus. The gating of hippocampal responses to auditory stimuli may thus involve pathways which branch from the lemniscal auditory pathway at the level of the lateral lemniscus and ascend to the hippocampus via the brainstem reticular formation.

Glutamate antagonists in the reticular formation reduce the acoustic startle response.

A previous study has shown that the acoustic responsiveness of reticulospinal neurones in the caudal pontine reticular nucleus (PnC) is reduced by glutamate antagonists. It was postulated that the acoustic startle response is mediated by glutamate receptors on PnC-neurones. In the present study, we tested this hypothesis by local microinjections of different glutamate antagonists into the PnC of unrestrained awake rats. In order to differentiate the drug effects on the head and body startle responses, we measured the head startle response electromyographically, and the body startle response in a ballistic chamber. Both the AMPA/kainate and the NMDA receptor antagonists reduced both components of the startle response dose-dependently. We conclude that both subtypes of ionotropic glutamate receptors in the PnC are relevant for the acoustic startle response in rats.

Reticular formation influences on primary and non-primary auditory pathways as reflected by the middle latency response.

Ongoing studies are aimed at identifying the neural pathways responsible for the middle latency response (MLR). These studies involve the analysis of surface and intracranial potentials following pharmacologic inactivation (with lidocaine) of discrete regions of the guinea pig brain. Previous investigations have shown that MLR surface waves recorded over the temporal lobe originate from pathways anatomically and functionally distinct from those that generate MLR waves recorded over the midline, and that both primary and non-primary auditory thalamo-cortical pathways contribute to the guinea pig MLR. The present investigation examines the role of the mesencephalic reticular formation (mRF) in the MLR generating system. Inactivation of the mRF was associated with disruption of the midline response. These waves have been shown to reflect activity from non-primary subdivisions of the thalamo-cortical pathway. Components recorded over the temporal lobe were also affected, consisting of amplitude reduction and latency prolongation without changes in response morphology. Changes in temporal MLR components with mRF inactivation were smaller than those associated with direct inactivation of primary and non-primary subdivisions of the medial geniculate body. These findings indicate that mRF input is essential for normal generation of those components of the MLR thought to reflect both primary and non-primary auditory pathway activity.

Descending projections of Forel's field H neurones to the brain stem and the upper cervical spinal cord in the cat.

1. Descending projections from Forel's field H (FFH) to the brain stem and upper cervical spinal cord were studied in cats. 2. Following implantation of HRP pellets into the spinal gray matter (C1-C3) or in the ponto-medullary reticular formation, the nucleus reticularis pontis caudalis (NRPC) or in the nucleus reticularis gigantocellularis (NRG), numerous neurones were retrogradely labelled in FFH on the ipsilateral side. In the former cases, the sizes of labelled neurones were medium-large (20-40 microns in diameter) while both small and medium-large neurones were labelled in the latter cases. 3. The lowest levels of spinal projection of single FFH neurones (n = 70) were assessed by antidromic spikes elicited by stimulating electrodes placed in C1, C3 and C7. The majority (59%) projected to C1 (but not to C3), about 27% to C3 (but not to C7), and only 14% to C7. 4. Axonal trajectories of single FFH neurones in C1-C3 segments were investigated by antidromic threshold mapping methods. The stem axons of spinal-projecting FFH neurones descended in the ventral or in the ventrolateral funiculi and the collaterals were projected to neck motor nuclei (lamina IX, Rexed 1954) and laminae V-VIII. The conduction velocities were estimated as 8-37 m/s from the antidromic latencies. 5. Axonal trajectories of 7 FFH neurones were investigated in the ponto-medullary reticular formation. All were antidromically activated from C1. In six neurones, the stem axons were located in the ventral part of the central tegmental tract and collaterals were projected to the NRPC and/or the NRG. Some of them projected to the inferior olive and the nucleus prepositus hypoglossi as well. The stem axon, in the remaining cell, was in the most dorso-medial part of the medial longitudinal fasciculus and collaterals were projected mainly to the dorsal part of the NRPC and the NRG, and also to the medial vestibular nucleus. 6. Anterograde transport of WGA-HRP injected into FFH revealed that in the upper cervical spinal cord, stem axons were found in the ventral funiculus and ventral part of the lateral funiculus. Collateral projections and presumed bouton-like deposits were observed in the laminae VI-IX, especially in their medial part. In the brain stem, dense bundles of the descending fibres were found in the central and the medial tegmental tracts and in the medial longitudinal fasciculus. FFH neurones projected densely to the caudal half of the NRPC and to the rostral half of the NRG.(ABSTRACT TRUNCATED AT 400 WORDS)

Mono- and disynaptic pathways from Forel's field H to dorsal neck motoneurones in the cat.

1. We analysed the synaptic actions produced by Forel's field H (FFH) neurones on dorsal neck motoneurones and the pathways mediating the effects. 2. Stimulation of ipsilateral FFH induced negative field potentials of several hundred microvolts with the latency of about 1.1 ms in the medial ponto-medullary reticular formation, being largest in the ventral part of the nucleus reticularis pontis caudalis (NRPC), and in the dorsal part of the nucleus reticularis gigantocellularis (NRG). 3. Stimulation of ipsilateral FFH induced excitatory postsynaptic potentials (EPSPs) in 90% (47/52) and inhibitory postsynaptic potentials (IPSPs) in 19% (10/52) of the reticulospinal neurones (RSNs) in the NRPC and the NRG. Latencies of the EPSPs and IPSPs were 0.7-3.0 ms, the majority of which were in the monosynaptic range. The monosynaptic connexions were confirmed by spike triggered averaging technique both in excitatory (n = 4) and inhibitory (n = 2) pathways. 4. Single stimulation of FFH induced EPSPs at the segmental latencies of 0.3-1.0 ms in neck motoneurones, which were clearly in the monosynaptic range. Repetitive stimulation of FFH produced marked temporal facilitation of EPSPs in neck motoneurones. The facilitated components of the EPSPs had a little longer latencies and their amplitude reached several times as large as that evoked by single stimulation in all the tested motoneurones. These facilitated excitations are assumed to be mediated by RSNs in the NRPC and NRG, since RSNs were mono- and polysynaptically fired by stimulation of FFH and they were previously shown to directly project to neck motoneurones. 5. EPSPs were induced in 91% (82/91) of motoneurones supplying m. biventer cervicis and complexus (BCC; head elevator), 10% (3/29) of motoneurones supplying m. splenius (SPL; lateral head flexor). Likewise, stimulation of FFH produced EMG responses in BCC muscles, while not in SPL muscle. Thus FFH neurones produce excitations preferentially in BCC motoneurones. 6. Systematic tracking in and around FFH revealed that the effective sites for evoking above effects were in FFH and extended caudally along their efferent axonal course. 7. These results suggested that FFH neurones connect with neck motoneurones (chiefly BCC, head elevator) mono-, di- and/or polysynaptically and are mainly concerned with the control of vertical head movements.