Divalent ions in blood and cerebrospinal fluid: effect of hypercalcemia, hyperphosphatemia, renal failure and parathyroid hormone

Human cerebrospinal fluid increases the excitability of pyramidal neurons in the in vitro brain slice

KEY POINTS

The cerebrospinal fluid contains numerous neuromodulators at ambient levels but whether, and how, they affect the activity of central neurons is unknown. This study provides experimental evidence that human cerebrospinal fluid (hCSF) increases the excitability of hippocampal and neocortical pyramidal neurons. Hippocampal CA1 pyramidal neurons in hCSF displayed lowered firing thresholds, depolarized resting membrane potentials and reduced input resistance, mimicking properties of pyramidal neurons recorded in vivo. The excitability-increasing effect of hCSF on CA1 pyramidal neurons was entirely occluded by intracellular application of GTPγS, suggesting that neuromodulatory effects were mediated by G-protein coupled receptors. These results indicate that the CSF promotes spontaneous excitatory neuronal activity, and may help to explain observed differences in the activity of pyramidal neurons recorded in vivo and in vitro. The composition of brain extracellular fluid is shaped by a continuous exchange of substances between the cerebrospinal fluid (CSF) and interstitial fluid. The CSF is known to contain a wide range of endogenous neuromodulatory substances, but their collective influence on neuronal activity has been poorly investigated. We show here that replacing artificial CSF (aCSF), routinely used for perfusion of brain slices in vitro, with human CSF (hCSF) powerfully boosts spontaneous firing of CA1, CA3 and layer 5 pyramidal neurons in the rat brain slice. CA1 pyramidal neurons in hCSF display lowered firing thresholds, more depolarized resting membrane potentials and reduced input resistance, mimicking properties of pyramidal neurons recorded in vivo. The increased excitability of CA1 pyramidal neurons was completely occluded by intracellular application of GTPγS, suggesting that endogenous neuromodulators in hCSF act on G-protein coupled receptors to enhance excitability. We found no increase in spontaneous inhibitory synaptic transmission by hCSF, indicating a differential effect on glutamatergic and GABAergic neurons. Our findings highlight a previously unknown function of the CSF in promoting spontaneous excitatory activity, and may help to explain differences observed in the activity of pyramidal neurons recorded in vivo and in vitro.

Psychiatric symptoms and cerebrospinal fluid monoamine metabolites in primary hyperparathyroidism

This prospective study included 32 patients with primary hyperparathyroidism (HPT). As compared with a healthy reference group, the patients had pronounced psychiatric symptomatology [CPRS score 17.2 +/- 9.0 (SD) versus 4.4 +/- 2.0], which was mainly affective in character. The severity of symptoms was not related to the serum calcium or parathyroid hormone concentrations. The majority of the patients had low CSF concentrations of monoamine metabolites (5-HIAA, HVA, and MHPG) and, in particular, those with the most severe psychiatric symptoms had low values for 5-HIAA. At follow-up, 1 year after parathyroid surgery, the patients displayed a clear improvement in mental health (CPRS score 4.4 +/- 3.0) together with an increase in CSF concentrations of 5-HIAA and HVA. The study demonstrates that significant psychiatric disturbances, which can be improved/normalized by surgery, are common in patients with HPT and are possibly related to changes in the central nervous system turnover of monoamines.