DIFFERENTIAL COURSE AND ORGANIZATION OF UNCROSSED AND CROSSED LONG ASCENDING SPINAL TRACTS

A cryogenic device for reversibly blocking transmission through small regions of the spinal cord white matter

A simple cryogenic device is described. This device is capable of cooling neural tissue in contact with the probe and maintaining the tissue at the desired temperature for extended periods of time. The cold probe can thereby reversibly block neural transmission through small portions of the spinal cord white matter. Interruption of axonal transmission is achieved by placing the tip of the device in contact with the exposed surface of the spinal cord and cooling the tip of the probe to -1 to +2 degrees C. The investigator monitors the tip temperature and adjusts the pump rate to maintain a constant tip temperature. The cross-sectional area under the probe where effective transmission block is achieved is about 1.5 mm2 which approximates the size of a single funiculus in the cat thoracic spinal cord. The cryogenic device was constructed for less than $700. The properties of this device were studied in physiologic experiments in cats. This device reversibly, selectively and repeatedly blocked the ascending mass action potential in the dorsolateral funiculus, transmission through ascending spinal axons in the dorsal columns, transmission through axons of spinal dorsal horn cells, the descending inhibitory input to the dorsal horn and the activity of thalamic nociceptive neurons. The reversible cold block effects on single units were observed for the duration of the experiments (up to 18 h) with no detectable damage to the underlying tissue. The physiologic effects of the cold block were usually reversed a few minutes after rewarming, although in some cases it took up to 40 min for the complete reversal of the cold block. This cryogenic device is useful for studying spinal cord pathways.

The central cervical nucleus in the cat. II. The cerebellar connections studied with retrograde transport of horseradish peroxidase

After HRP injections in kittens and adult cats into parts of the cerebellum known to receive spinal afferents, retrogradely labelled neurones were found in the C1--C4 segments of the spinal cord, primarily in the central cervical nucleus (CCN). A few labelled neurones were also found in laminae IV and VI--IX of Rexed. The results obtained in kittens and adult cats were similar. Control HRP injections were made into the vestibular nuclei and the inferior colliculus. After injections mainly involving the vestibular nuclei a few faintly labelled neurones were found in the C1--C4 segments in, and occasionally also outside the CCN, in laminae VI--VIII. After injections into the inferior colliculus, however, no labelled neurones were observed in these segments. After spinal cord hemisections at C1 and bilateral HRP injections into the anterior lobe, nearly all labelled CCN neurones were found ipsilateral to the hemisections. Labelled axons of such CCN neurones could be traced across the midline to the lateral funiculus. A few neurones were found outside the CCN in laminae VII--IX. Contralaterally labelled neurones were found mainly in lamina VI.

Studies on the human evoked electrospinogram. II. The conduction velocity along the dorsal funiculus

The propagation velocity of the ascending volleys along the dorsal funiculus of the human spinal cord was studied in 31 normal volunteers. Intrathecal recordings from lower cervical and lower thoracic intervertebral levels were made after the supramaximal stimulation of the posterior tibial nerves. When the electrode tip was behind the cord dorsum at the cervical level, it was easily possible to obtain very clear triphasic compound action potential on stimulation of the posterior tibial nerve of one leg or both legs. This "Tractus Potential" was found to originate mainly from the dorsal funiculus fibres, i.e. Fasciculus gracilis. The maximal conduction velocity of the ascending afferent volley from the leg was then calculated to be, on average, 37 meters/sec between lumbar and cervical spinal enlargements. Intrathecal stimulation and recording of the spinal cord gave the distinct triphasic wave with low threshold. This was also found to be related to dorsal funiculus activity. In these intraspinal stimulations and recordings, very early small and some late long-lasting deflections appeared, especially in the lateral position of the intrathecal electrode.

Termination and functional organization of the ventral spino-olivocerebellar path

1. The spino-olivocerebellar path ascending through the ventral funiculus (VF-SOCP) was investigated in decerebrate cats with the cord transected in the third cervical segment except for the left ventral funiculus. The climbing fibre responses evoked in Purkinje cells were studied by recording from single cells and by recording the mass activity at the cerebellar surface or in the molecular layer.2. In the spinal cord the forelimb component of the VF-SOCP occupies a medial part and the hind limb component a lateral part of the ventral funiculus.3. The main projection of the limb nerves through the VF-SOCP is to the lateral two thirds of the vermis of the anterior lobe. The projection area consists of three sagittally arranged bands: a lateral band receiving olivary axons activated exclusively from the ipsilateral hind limb, an intermediate band receiving olivary axons activated bilaterally from the hind limbs, and a medial band receiving olivary axons activated bilaterally from the forelimbs. Some olivary neurones are activated from all four limbs.4. The latency of the climbing fibre responses was about 22 msec on stimulation of ipsilateral hind limb nerves and about 20 msec on stimulation of ipsilateral forelimb nerves. The responses evoked from contralateral nerves had a latency which was about 3 msec longer than the latency of the corresponding ipsilateral responses.5. The olivary neurones were usually activated from all tested muscle and skin nerves in the limb(s) constituting the receptive field. Cutaneous afferents and groups II and III muscle afferents were responsible for the excitation elicited by single shock stimulation of the nerves. Brief repetitive stimulation revealed additional activation from mainly Ib, but also Ia, afferents in ipsilateral hind limb nerves.6. Natural stimulation of receptors evoked responses in about half of the olivary neurones tested. The responses were elicited by strong pressure against deep structures. Inhibitory effects were seldom observed.