Harold A. Robertson

Activation of c-fos in the brain.

Activation of the proto-oncogene c-fos in the brain was described initially almost a decade ago and represents one of the most studied immediate early genes in the brain. Transient c-fos expression in the central nervous system was first observed after seizure activity and following noxious stimulation in the spinal cord. Since then, multiple studies have shown that different stimuli can induce c-fos expression. Seizure activity induces rapid and transient expression of c-fos in hippocampal structures. Similarly, transient activation of c-fos follows cortical brain injury in a pattern that resembles that of spreading depression. Many other stimuli have been shown to induce the expression of this proto-oncogene in the brain and c-fos immunostaining and in situ hybridization are now used to map brain metabolism under different physiological and non-physiological conditions. Here we review the variety of inducible patterns of c-fos expression in the brain.

Dopamine neurons implanted into people with Parkinson's disease survive without pathology for 14 years

Postmortem analysis of five subjects with Parkinsons disease 9–14 years after transplantation of fetal midbrain cell suspensions revealed surviving grafts that included dopamine and serotonin neurons without pathology. These findings are important for the understanding of the etiopathogenesis of midbrain dopamine neuron degeneration and future use of cell replacement therapies.

D1-dopamine receptor agonists selectively activate striatal c-fos independent of rotational behaviour.

L-Dopa and dopaminergic agonists selective for the D1- or D2-dopamine receptor subtype induce contraversive rotation in rats which have been unilaterally lesioned with injections of 6-hydroxydopamine (6-OHDA) into the substantia nigra. D-Amphetamine, which releases dopamine from neurones on the unlesioned side of the animal, causes ipsiversive rotation. These increases in rotational behaviour are mediated, at least in part, by dopamine receptors in the striatum. In unilaterally lesioned animals, L-dopa and the D1-selective agonists SKF 38393 and CY 208-243 produce contralateral rotation and induction of the nuclear proto-oncogene c-fos in the lesioned striatum. D-Amphetamine induces both ipsilateral rotation and c-fos activation in the intact striatum. Three lines of evidence, however, dissociate fos induction and rotation. First, LY 171555, a selective D2-dopamine receptor agonist, also induces contraversive rotation but this rotation is not accompanied by c-fos activation in striatum. Second, D1-dopamine agonists produce activation of striatal c-fos even if rotation is prevented by an anaesthetic. Third, rotation induced by injection of SKF 38393 into substantia nigra is not accompanied by c-fos induction. These results suggest a mechanism by which D1-dopamine receptor mechanisms may regulate long-term changes in dopaminergic systems.

Brain injury induces c-fos protein(s) in nerve and glial-like cells in adult mammalian brain

Recent studies have shown that the c-fos protein(s) exists in low basal levels in adult mammalian neurons, but not in glial cells. Here we report that c-fos-protein-like immunoreactivity is induced in glial cells following cortical injury. Glial cells in white matter regions around the wound margin express the c-fos protein maximally at 12-24 h post-insult. Injury is also associated with a massive induction of c-fos proteins in nerve cells in the damaged cerebral cortex. Injections of [3H]thymidine into mice and autoradiographic analysis of [3H]thymidine incorporation showed that the increase in c-fos preceded glial cell division following injury. These results show that c-fos protein is induced in glial and nerve cells after injury.

Generalized seizures induce c-fos protein(s) in mammalian neurons

We have recently detected low basal levels of c-fos protein-like immunoreactivity in adult mammalian neurons. Here we report that generalized tonic-clonic seizures in mice are associated with a massive increase in c-fos protein-like immunoreactivity in the cingulate and piriform cortices and the dentate gyrus 1 h after injection of pentylenetetrazol. Midazolam, which prevented the pentylenetetrazol seizures also prevented the increase in c-fos protein-like immunoreactivity. These results suggest that seizure activity induces the formation of c-fos proteins in selective brain regions, and raise the possibility that c-fos proteins play as yet undetermined physiological and/or pathological roles in the mature brain.

Synergistic effects of D1 and D2 dopamine agonists on turning behaviour in rats

In rats with unilateral 6-hydroxydopamine lesions of the substantia nigra, a specific D1 dopamine receptor agonist, SKF 38393A, at a dose that does not itself produce turning, significantly increased the contralateral rotation observed following a low dose of the specific D2 agonist LY 171555. Doses of SKF 38393A or the D2 agonist bromocriptine, which would themselves not induce turning, in combination produced a high rate of turning. These results suggest a synergistic interaction between D1 and D2 dopamine receptors in this system.

Long-term potentiation and the induction of c-fos mRNA and proteins in the dentate gyrus of unanesthetized rats.

We tested the hypothesis that the nuclear proto-oncogene c-fos is involved in long-term potentiation (LTP) of the perforant path-dentate gyrus synapse in awake freely moving rats. High-frequency stimulation that produced LTP induced c-fos mRNA and protein in the dentate granule cells but not in CA1, CA3, or the entorhinal cortex. However, the degree of LTP induction did not correlate with the degree of c-fos induction. Agents that interfered with the production of LTP (e.g. NMDA antagonists) also prevented c-fos induction. Low-frequency stimulation did not lead to either LTP or c-fos induction. However, c-fos induction did not necessarily follow LTP production because some high-frequency stimulation protocols that produced good LTP did not lead to c-fos induction. Thus, c-fos induction is clearly not related to LTP production in unanaesthetized rats, but it remains to be determined if it plays some role in LTP maintenance.

Antisense oligonucleotide eliminates in vivo expression of c-fos in mammalian brain

Immediate-early genes such as c-fos and NGFI-A are rapidly and transiently expressed in the striatum following amphetamine administration in vivo. Here we show that direct infusion of an antisense oligodeoxynucleotide to c-fos into striatum will reduce amphetamine-induced production of Fos-like immunoreactivity without affecting NGFI-A expression. These results suggest that it is possible to use antisense technology to study the role of immediate-early genes in specific sites in the brain in vivo.

Photic induction of Fos protein in the suprachiasmatic nucleus is inhibited by the NMDA receptor antagonist MK-801.

Exposure of rodents to light can induce expression of a number of immediate-early genes, including c-fos, in cells of the suprachiasmatic nucleus (SCN), a dominant pacemaker in the mammalian circadian system. We examined the effects of pre-treatment with the non-competitive N-methyl-D-aspartate (NMDA) receptor antagonist MK-801, on the induction of Fos-like immunoreactivity (Fos-lir) in cells in the hamster SCN. At doses of 3 and 5 mg/kg, MK-801 treatment blocked photic induction of Fos-lir in the rostral SCN and ventrolateral portions of the caudal SCN but failed to block induction of Fos-lir in a discrete region of the dorsolateral SCN. These results suggest that photic induction of Fos-lir in most of the SCN depends on activation of an NMDA-type receptor which is sensitive to MK-801, but that Fos-lir in one portion of the SCN is induced by a mechanism which is not antagonized by MK-801.

Cannabinoid receptor messenger RNA levels decrease in a subset of neurons of the lateral striatum, cortex and hippocampus of transgenic Huntington’s disease mice

One of the earliest changes, at the molecular level, that occurs in human Huntingtons disease patients is reduction in cannabinoid receptor ligand binding in the substantia nigra pars reticulata compared to neurologically normal controls. The loss of cannabinoid receptor binding is thought to occur early in or prior to the development of Huntingtons disease neuropathology. We wish to determine whether cannabinoid receptor messenger RNA levels were altered in a mouse model of Huntingtons disease. Transgenic mice hemizygous for the promoter sequence and exon 1 of the human Huntingtons disease gene exhibit a progressive neurological phenotype with many of the features of Huntingtons disease. This neurological phenotype develops in the absence of neural degeneration making these mice a model system to dissociate changes related to cell dysfunction from changes related to cell loss. We examine the steady-state levels and cellular distribution of the brain-specific cannabinoid receptor messenger RNA by northern blot and in situ hybridization. The cannabinoid receptor messenger RNA was expressed throughout the striatum, cortex and hippocampus of wild-type mice. At four and five weeks of age, there was no difference in the distribution of the cannabinoid receptor messenger RNA between the wild-type and transgenic Huntingtons disease mice. At six, seven, eight and 10 weeks of age, however, the Huntingtons disease mice exhibit reduced levels of cannabinoid receptor messenger RNA in the lateral striatum compared to age-matched controls. The Huntingtons disease mice also showed a loss of cannabinoid receptor messenger RNA within a subset of neurons in the cortex and hippocampus. We did not observe any difference in the expression of cannabinoid receptor between the wild-type and Huntingtons disease mice throughout Ammons horn of the hippocampus or in the medial striatum. The decrease in cannabinoid receptor messenger RNA levels preceded the development of the Huntingtons disease phenotype and neuronal degeneration and, therefore, these transgenic mice model early cellular changes observed in human patients. Our results demonstrate that the single copy cannabinoid receptor gene is subjected to cell-specific and time-dependent regulation of the steady-state level of its gene product as a result of the expression of the Huntingtons disease gene. As the endogenous cannabinoid receptor agonist, anandimide, has been shown to modulate dopamine neurotransmission within the basal ganglia, the loss of cannabinoid receptors may contribute to the development of motor symptoms or cognitive decline or both seen in Huntingtons disease patients.