Zona Incerta Neurons Research Articles

Zona incerta and lateral hypothalamic afferents to the midbrain reticular core of cat — An HRP and electrophysiological study

The zona incerta (ZI) and lateral hypothalamic afferents to the midbrain reticular formation (MRF) of cat were investigated with the horseradish peroxidase (HRP) technique and by using antidromic identification in experiments on chronically implanted, behaving preparations. Following HRP injections restricted to the MRF territory (nucleus cuneiformis and central tegmental field), the largest number of retrogradely labeled cells appeared in the medial third of the ipsilateral ZI. Labeling extended medially to the adjacent lateral hypothalamus. The number of positive elements gradually diminished towards the lateral extremity of the ZI and continuing reticularis thalamic nucleus. Ventral lateral geniculate neurons were consistently labeled. No positive elements were found in ventrobasal, pulvinar-lateralis posterior and ventralis lateralis thalamic nuclei. The MRF-evoked antidromic invasion of ZI cells occurred with a sharp mode between 0.5 and 0.75 ms (median latency of the whole sample: 0.6 ms). The conduction velocity of the ZI leads to MRF axons is twice as high as the values found in the reciprocal MRF leads to ZI projection. In addition to the antidromically elicited discharges, MRF stimulated resulted in short-latency synaptic excitation, sometimes following the antidromic invasion of the same neuron. The difference between the discharge rates of ZI neurons during EEG-desynchronized and EEG-synchronized behavioral states was not significant. A statistically significant increase in firing rates was found in ZI neurons during waking periods with movements compared to quiet, motionless epochs of waking. The possible involvement of caudally projecting ZI cells in the preparation of postural and/or phasic motor functions is discussed.

A Golgi study on the zona incerta of the mouse.

The zona incerta (ZI) of the mouse was studied by the rapid Golgi method. In the ZI, small and medium-sized neurons were recognized. The former were the main constituents; their soma were fusiform or piriform in shape (15.5×22 μm) and had 4 to 8 primary dendrites. Dendrites of the small neurons in the regions near the ventral and dorsal margins of the ZI ran medially and laterally along the margins of the ZI. The mediumsized neurons were seen in the central ZI portions at the caudal levels of the ZI; they had polygonal or fusiform cell bodies (25×31 μm) which emitted 5 to 9 primary dendrites. Some dendrites of the ZI neurons extended into the ventral lateral geniculate nucleus (LGNv), the nucleus of the field of Forel (FF), the cerebral peduncle and the internal capsule. On the other hand, some dendrites of neurons in the LGNv and FF extended into the ZI. Most axons of the ZI neurons coursed dorsally, and some of them could be traced into the medial lemniscus or the dorsal thalamus. A few neurons in the regions near the ventral margin of the ZI sent axons ventrally into the cerebral peduncle. Afferent fibers to the ZI were traced from the cerebral peduncle, internal capsule, field H1, medial lemniscus and dorsal thalamus. Collaterals of fibers in the Meynert's commissure and field H2 entered the ZI. Fibers passing through the LGNv also entered the ZI. Additionally, terminal collaterals were observed to arise from fibers running mediolaterally in the ZI. Some fibers were found to send terminals commonly to the ZI, FF and LGNv by way of axon collaterals.

Descending and ascending influences on neurons of the zona incerta

Characteristics of responses of single neurons in zona incerta to electrical stimulation of the amygdala and central gray matter of the midbrain were compared in acute experiments on rats. Analysis of the results showed that stimulation of the central gray matter evokes predominantly excitation (86%), where stimulation of the amygdala invokes inhibition (64%). Convergence of impulses from the amygdala and central gray matter was observed on 58 of 174 responding neurons. Most frequently (57%) the responses were opposite in direction. Stimulation of the amygdala invoked inhibitory effects and stimulation of the central gray matter activation effects. Possible functional relation in the amygdala-zona incerta-central gray matter system are discussed and the role of competitive interactions of flows of impulses descending from the amygdala and ascending from the central gray matter of neurons of zona incerta is examined.