Cytokinetic evaluation in human head and neck cancer by autoradiography and DNA cytofluorometry

As part of a comprehensive research program on cell proliferation characteristics of squamous cell carcinoma in humans and the relation of these characteristics to treatment, 4 untreated cases of head and neck cancer and 2 recurrences were studied. Previously, cell kinetics following the percent labelled mitoses method were done and the same carcinomas now studied by measuring microfluorometrically the time distribution of the nuclear DNA content. Two cases were characterized by a homogeneous cell population, whereas in 2 other cases, two cycling subpopulations distinguished by their DNA content were encountered. The clinical response was not related to the occurrence of single- or multiple-cell populations. In all cases, a great variability in the mitotic index (MI) and in the proportion of cells in the different cycle phases was found. The heterogencity in the proliferative structure of these tumors stresses the need for a greater accuracy in performing cell kinetics studies in vivo and could account for the difficulties in devising a therapeutic regimen based on cycle or phase-specific agents.

Loss of striatal neurons after local microinjection of colchicine

Intrastriatal injections of colchicine (4 micrograms) produced irreversible striatal damage characterized 30 days later by loss of intrinsic striatal neurons, gliosis and shrinkage but no apparent damage to myelinated bundles of the internal capsule. This neuronal loss was associated with a dramatic reduction of striatal and nigral glutamate-decarboxylase (GAD), the marker of GABA-ergic synapses and of striatal choline-acetyltransferase (CAT), the marker of cholinergic synapses. The levels of dopamine (DA) and serotonin (5HT) in the striatum as well as those of their metabolites were also reduced, indicating that colchicine exerts toxic effects also on terminals of striatal afferent neurons.

Opposite turning effects of dainic and ibotenic acid injected in the rat substantia nigra

Unilateral intranigral administration of kainic and ibotenic acid, two putative stimulants of glutamatergic mechanisms, elicited turning behaviour starting from doses of 10 ng. While the turning produced by kainic acid was ipsilateral, that produced by ibotenic acid was contralateral to the injected side. Previous destruction of dopaminergic neurons on the side of the intranigral injection failed to reduce the turning behaviour. Peripheral treatment with picrotoxin did not reduce the turning in response to ibotenic acid. The results might suggest the existence of excitatory and inhibitory glutamate receptors which control nigral non-dopaminergic neurons mediating turning-behaviour.

Evidence for a GABAergic projection from the substantia nigra to the ventromedial thalamus and to the superior colliculus of the rat

Unilateral intranigral infusion of kainic acid (1.5 microgram) produced neuronal loss in the lateral two-thirds of the nigra while sparing axons en passage. Fink-Heimer silver impregnation revealed dense terminal degeneration in the nigra itself (both in the compacta and in the reticulata) and in areas of non-dopaminergic nigral projection such as the ventromedial (VM) nucleus of the thalamus, the superior colliculus and the reticular formation; only spare terminal degeneration was found in areas of dopaminergic projection such as the caudate and septum. In order to clarify the nature of the transmitter of the nigrothalamic and nigrocollicular neurons, the activity of glutamic decarboxylase (GAD), the marker of cholinergic neurons, was measured in the VM and ventrobasal (VB) thalamus and in the nigra of each side, 7 days after unilateral intranigral injection of kainic acid. GAD activity was reduced significantly in the VM-thalamus (-33%), in the superior colliculus (-40%) and in the substantia nigra (-18%) but not in the VB-thalamus of the lesioned side. CAT remained unchanged in these areas. Similar results were obtained in the thalamus and in the superior colliculus after electrocoagulative lesions of the nigra. The results indicate the existence of a nigrothalamic and of a nigrocollicular GABAergic pathway. This projection might play an important role in motor coordination and gaze control.

Substantia nigra as an out-put station for striatal dopaminergic responses: role of a GABA-mediated inhibition of pars reticulata neurons

Intranigral administration of kainic acid results in loss of pars reticulata neurons without damage to axons traversing or terminating within the nigra. Unilateral nigral lesions with kainic acid result in an ipsilateral turning upon administration of apomorphine, a dopamine (DA)-receptor agonist and in contralateral turning upon administration of haloperidol, a DA-receptor blocker. Destruction of post-synaptic structures in the striatum of the side contralateral to that injected with kainic acid results in a drastic reduction, abolition or even reversal of the turning effects elicited by apomorphine and haloperidol. Unilateral intranigral microinjection of nanogram amounts of the GABA-receptor antagonists picrotoxin and bicuculline elicits ipsilateral circling upon apomorphine administration. Kainic-induced lesion or microinjection of picrotoxin or bicuculline in the nigra ipsilateral to a 6-OHDA-lesion of nigro-striatal DA-neurons results in reduction, abolition or reversal of the contralateral circling produced by apomorphine. The results indicate that the nigra pars reticulata is a station for dopaminergic impulses originating from the striatum and suggest that the turning behavior in response to striatal DA-receptor stimulation is due to a GABA-mediated inhibition of ipsiversive pars reticulata neurons.

Apparatus for quantitative evaluation of visually guided pecking in the pigeon

An apparatus using a phase-locked loop is described which allows automated, differential counts of correct and incorrectly oriented pecks, elicited by apomorphine in the pigeon. This apparatus provides a unique and precise means for the study of this characteristic, visually guided behavior.