Supraspinal and segmental input to lumbar epaxial motoneurons in the rat

Inputs to medial longissimus (ML) and lateral longissimus (LL) motoneurons were studied in urethane or urethane-chloralose anesthetized rats by recording from ML and LL nerves while stimulating ipsilateral lumbosacral dorsal roots, medial medullary reticular formation (RF), vestibular nuclei (VN), dorsal midbrain (MDBR), or ventromedial hypothalamus (VMH).Stimulation of appropriate dorsal roots produced short-latency responses (1.5–3.0 ms) in nerves to medial longissimus or lateral longissimus. The connections underlying these responses, which could be monosynaptic, are weak, since generally two or more stimuli were necessary for a response to occur. Short-latency LL nerve responses required more dorsal root stimuli than did ML nerve responses and stable LL responses sometimes could not be obtained, suggesting that segmental reflexes to a back muscle (LL) could be weaker than those to a proximal tail muscle (ML).Trains of conditioning stimuli delivered to the RF, VN, and MDBR facilitated segmental responses in ML nerves or LL nerves. Temporal profiles of facilitation of ML differed for the three regions. On one extreme, the facilitation produced by RF conditioning required few stimuli (median, 3 shocks) and peak facilitation occurred at short condition-test intervals (median, 1.5 ms). On the other extreme, facilitation produced by MDBR conditioning required long trains (median, 14 stimuli) and peak facilitation occurred at longer condition-test intervals (median, 10ms).Stimulation within the VMH never facilitated ML or LL nerve activity.These results demonstrate excitatory connections from reticular formation, vestibular nuclei and the dorsal midbrain to medial longissimus and lateral longissimus. Such connections could be involved in behaviors mediated by midbrain, and in postural regulation through brain stem control of axial musculature.Motoneuron cell bodies for LL, ML and lumbar transversospinalis (TS) muscles were localized by ejecting dye at sites where unitary antidromic responses to muscle nerve stimulation were recorded extracellularly. ML cells were found ventrolaterally in the L₆-S₁ ventral horn. LL and TS cells were found medially in the ventral horn of the lumbar enlargement.     

Integration in descending motor pathways controlling the forelimb in the cat 15. Comparison of the projection from excitatory C3-C4 propriospinal neurones to different species of forelimb motoneurones

Summary In the preceding report (Alstermark and Sasaki 1986) it was shown that a stimulus of 500 A applied in the lateral reticular nucleus (LRN) evokes a maximal or near monosynaptic EPSP (LRN EPSP) in forelimb motoneurones. This EPSP which is assumed to be selectively mediated by C3-C4 propriospinal neurones (PNs), was used to estimate the strength of the excitatory projection from C3-C4 PNs. A systematic comparison was made of the size and time course of the maximal LRN EPSP in various species of forelimb -motoneurones innervating shoulder, elbow, wrist and digit muscles. The LRN EPSP was evoked in all investigated species of forelimb motoneurones. When either the peak amplitude or the underlying area of the LRN EPSP was compared, a three-fold range was found with some tendency for the size to vary in the order of wrist > shoulder elbow > digit > intrinsic paw motor nuclei. Generally, a positive correlation was found in each motor nucleus between the peak amplitude of the LRN EPSP versus the monosynaptic homonymous group Ia EPSP, input resistance and afterhyperpolarization duration respectively (cf. Alstermark and Sasaki 1986). It is therefore postulated, that the LRN EPSP peak amplitude is correlated with motor unit type. Comparison of the time course of the LRN EPSPs was made by measuring the time-to-peak (T-t-p) and half-width (H-w). The finding in the preceding report that the T-t-p and H-w is longer in slow than in fast motoneurones was confirmed and extended to all the investigated motor nuclei. The hypothesis that both fast slow motoneurones receive projection from a group of fast C3-C4 PNs, while slow motoneurones receive an additional projection from a group with lower conduction velocity, can therefore be applied to all forelimb motor nuclei. In addition, it is proposed that some slow shoulder, wrist and digit motoneurones receive projection from a special subpopulation of C3-C4 PNs with very slow conduction velocity.This work was supported by the Swedish Medical Research Council (project no. 94 and 6953)     

Involvement of both cholinergic and catecholaminergic pathways in the central action of methylphenidate: A study utilizing lead-exposed rats

The effects of methylphenidate (MPH) and the cholinergic agonists nicotine and oxotremorine were tested on the spontaneous multiple unit activity in the mesencephalic reticular formation of two groups of rats. In control rats i.v. MPH (1 mg/kg), nicotine (0.125 mg/kg), and oxotremorine (0.5 mg/kg) all attenuated the unit activity with latencies of less than 10 min. In another group of rats, exposed to lead acetate since birth, the extent of attenuation of unit activity induced by MPH and nicotine was reduced and the latency of effect was delayed by 45–50 min. The latency of the oxotremorine effect was not changed but the attenuation of unit activity was more pronounced in the lead-treated group. Pretreatment with spiroperidol, to inhibit the aminergic receptors, diminished the inhibitory effect of MPH in the control group but not in the lead-treated group, whereas the attenuating effect of oxotremorine was not affected in either group. These data support our previous evidence that MPH exerts its action in the central nervous system by a cholinergic pathway in addition to published catecholaminergic pathways. Furthermore, the present findings indicate that chronic leadexposure in rats results in cholinergic hypofunction and supersensitivity at central cholinergic receptor sites. This alteration of central cholinergic function may be partially attributed to the malnutrition observed in the lead-exposed animals.Part of this work was presented in abstract form (Shih et al., 1976b)     

Projections from the pontine reticular formation to the lateral geniculate body: Autoradiographic demonstration of a pathway that could mediate pontine-geniculate-occipital waves

Autoradiographic studies have revealed a pathway that may mediate pontinegeniculate-occipital waves. The projection originates in the rostral pontine tegmentum. Axons course rostrally through the midbrain and zona incerta, and turn ventrally at the level of the optic chiasm. Some axons cross the midline through the supraoptic commissure. The axons then travel caudally, just dorsal-medial to the optic tract, and appear to terminate bilaterally in the dorsal lateral geniculate nucleus.     

Simultaneous electrochemical and unit recording measurements: characterization of the effects of D-amphetamine and ascorbic acid on neostriatal neurons

The distribution of creatine kinase BB-isoenzyme in the human central nervous system (CNS) was investigated immunohistochemically and the findings were compared with the distributions of tubulin and astroprotein. Creatine kinase BB-isoenzyme existed both in neurons and astrocytes, and was universally distributed within the CNS. Tubulin was visualized only in the neuronal elements, namely perikarya, dendrites and axons, while astroprotein was exclusively visualized in astrocytes. A combination of immunohistochemistry for structural and soluble proteins may be a useful tool for the investigation of pathophysiological conditions within the CNS.     

Electrophysiological evidence for branching nigral projections to pontine reticular formation, superior colliculus and thalamus

Neurons of the pars reticulata of the substantia nigra were activated antidromically by stimulating pontine reticular formation, superior colliculus and thalamus. Many nigral neurons (42.6%) were activated antidromically from pontine reticular formation ipsilaterally and about a half of them had branching axons to superior colliculus and/or thalamus.     

Microinjection of neostigmine into the pontine reticular formation of the mouse: further evaluation of a proposed REM sleep enhancement technique

Microinjections of cholinergic agonists into the pontine reticular formation (PRF) powerfully induce rapid eye movement sleep (REMS) in cats but have comparatively weaker effects in rats. Recently, the cholinomimetic neostigmine has been reported to strongly enhance REMS following microinjection into the PRF of the mouse. That study used behavioral assessments of locomotion in lieu of electrophysiological measures of muscle tone to identify REMS. We sought to confirm that the behavioral state induced in mice by PRF injections of neostigmine meets standard electroencephalogram (EEG) and electromyogram (EMG) criteria for defining REMS. Cortical EEG, nuchal muscle EMG, and PGO waves were recorded from male C57BL/6N mice with chronic indwelling cannulae for the delivery of neostigmine to the PRF. Recordings were made during midday following injections of neostigmine (8.8 mM, 50 nl), 2 h after lights on (LD 12:12). Neostigmine induced a behavioral state characterized by low amplitude, highly desynchronized cortical EEG with little theta, no PGO waves, and a sustained high muscle tone. Behavioral states meeting standard criteria for slow-wave sleep (SWS) and REMS were significantly suppressed compared to baseline recordings, and REMS onset was delayed by 3 h. Consistent with earlier reports, neostigmine did strongly suppress locomotor activity in open field tests and in the home cage. Due to the failure to meet criteria for defining REMS, we conclude that neostigmine microinjection into the PRF of the mouse induces an abnormal waking state rather than REMS.