Axonal trajectories of single Forel's field H neurones in the mesencephalon, pons and medulla oblongata in the cat.

We studied axonal trajectories of single Forel's field H (FFH) neurones (n = 19) in the mesencephalon, pons and medulla by systematic antidromic threshold mapping in cats and differentiated them into two major types. Type I neurones were characterized by projections to the oculomotor nucleus (IIIn) and type II neurones by lack of projections to the IIIn. 2. Type I neurones (11/19) were further classified into three subtypes by the lowest level of projections; type Ic (n = 3) which projected to the cervical cord and type Ib (n = 7) which terminated at the ponto-medullary level and type Ia (n = 1) at more rostral level. In the mesencephalon, stem axons passed just lateral to the IIIn and projected collaterals to the IIIn and the ventral part of the periaqueductal gray matter. In the lower brain stem, stem axons of type Ib and Ic neurones passed in the dorsal part of the reticular formation or in the medial longitudinal fasciculus and projected collaterals to the dorsal part of the nucleus reticularis pontis caudalis (NRPC) and the nucleus reticularis gigantocellularis (NRG) and the reticular formation underlying the nucleus prepositus hypoglossi (PH) and the raphe region. Projections to the superior colliculus were observed in two cases. 3. Type II neurones (8/19) were classified into 2 type IIb projecting to the ponto-medullary reticular formation and 6 type IIc projecting to the cervical spinal cord. In the mesencephalon, stem axons passed through a more lateral region than those of type I and projected collaterals to the mesencephalic reticular formation and the red nucleus. In the lower brain stem, the stem axons passed in the ventral part of the reticular formation corresponding to the central tegmental tract and projected collaterals to the ventral part of the NRPC and NRG. Projections to the interstitial nucleus of Cajal, the inferior olive and the reticular formation underlying the PH were also observed. 4. The dorsal and ventral location of, respectively, stem axons of type I and type II neurones in the lower brain stem was confirmed in a larger number of neurones in experiments with restricted mapping. 5. There was not much difference in location of cell bodies of type I (totally n = 50) and type II (n = 46) neurones. The proportion of spinal-projecting neurones were larger in type II (21/46, 46%) than in type I (7/50, 14%) neurones.

Excitatory pathways from Forel's field H to head elevator motoneurones in the cat.

Projections of neurones in Forel's field H (FFH) to the upper cervical cord and to the lower brainstem were demonstrated by retrograde labelling of the neurones with horseradish peroxidase (HRP). Systematic threshold mapping for evoking antidromic spikes of FFH neurones revealed that they projected to the neck motor nuclei and to pontomedullary reticular formation (PMRF). Stimulation of FFH evoked large monosynaptic excitatory postsynaptic potentials (EPSPs) in reticulospinal neurones (RSNs) of the PMRF, and mono- and disynaptic EPSPs in the dorsal neck motoneurones. Above EPSPs were evoked from areas confined to FFH, thus indicating that they were elicited by stimulation of FFH neurones. Monosynaptic EPSPs in motoneurones were small but disynaptic EPSPs were markedly facilitated following stimulation with train pulses, becoming several times larger than the monosynaptic EPSPs. Disynaptic EPSPs were supposed to be relayed by RSNs in the PMRF which are known to project to dorsal neck motoneurones. The mono- and disynaptic EPSPs were induced chiefly in motoneurones of the head elevator (m. biventer cervicis and complexus) and rarely of the neck lateral flexor (m. splenius). It was suggested that FFH neurones are involved in the control of vertical head movements.

Subtypes of neurones in Forel's field H as defined by their axonal projection.

Projection of neurones in Forel's field H (FFH) to the mesencephalon, the lower brainstem, and the upper cervical spinal cord (C1) was investigated by threshold mapping for evoking antidromic spikes from these areas. Projections of all FFH neurones tested were ipsilateral. Two main types (Type I and II) and their subtypes were differentiated from the pattern of the trajectories. Type Ia FFH neurones were found to project primarily to the oculomotor nucleus (IIIn) and the periaqueductal gray (PAG) bud did not descend down to the medulla, while Type Ib neurones projected to IIIn, PAG and the nucleus reticularis gigantocellularis (NRG) and Type Ic projected further down to the C1. Type II neurones were characterized by the absence of collaterals to IIIn. Type IIb projected to the cuneiform, subcuneiform and red nuclei in the mesencephalon and to the NRG, while Type IIc projected further down to the spinal cord. Type IIa neurones which terminated rostral to the NRG were found only rarely. These results suggested that Type Ib and Ic neurones are involved in the control of synergic eye and head movements, while Type IIb, IIc and Ia neurones are specified for the independent control of head and eye movement.

Dissecting aneurysms of the anterior circle of Willis arteries. Report of two cases.

Two cases of spontaneous dissecting aneurysm extending from the supraclinoid portion of the internal carotid artery to the middle cerebral artery are reported in two teenaged patients. Both patients collapsed with a headache on the right side, left hemiparesis, and altered consciousness due to cerebral ischemia. One patient became alert in 2 days; however, his condition rapidly deteriorated 4 days later and he died on the 8th day from massive cerebral infarction. The other patient received a right superficial temporal artery (STA)-middle cerebral artery (MCA) anastomosis 50 hours after his initial symptoms. He improved gradually and is able to walk without help. Cerebral angiograms 3 months after the operation disclosed progressive attenuation of the MCA and dilatation of the anastomosed STA. Artificial collateral flow demonstrated in the postoperative angiogram may have been useful in preventing massive cerebral infarction.