Pathways involved in somatosensory electrical modulation of dorsal cochlear nucleus activity.

Our recent study has shown that somatosensory electrical stimulation may be useful to modulate sound-induced hyperactivity in the dorsal cochlear nucleus (DCN), a neural correlate of certain forms of tinnitus. Somatosensory electrical stimulation induced both suppressive and excitatory effects on neural activity in the DCN of both control and tone-exposed animals. However, it is unclear what neural pathways underlie the somatosensory electrical stimulation-induced effects on DCN activity. To address this issue, we conducted c-fos immunocytochemistry using hamsters and mapped neural activation in both auditory and non-auditory structures following transcutaneous electrical stimulation of the basal part of the pinna. We also conducted tracing experiments to investigate the anatomical relations between the DCN and structures that showed a significant increase in the number of Fos-positive neurons as a result of electrical stimulation. Electrical stimulation of the pinna induced significant increases in the number of Fos-positive neurons in the DCN, spinal trigeminal nucleus (Sp5), dorsal raphe nucleus (DR) and locus coeruleus (LC). Results of tracing experiments indicate that the DCN received inputs from the Sp5, DR and LC. The above results suggest that modulation of DCN activity through somatosensory electrical stimulation may involve both direct pathways via the Sp5 and indirect pathways via the DR and LC. Therefore, relieving tinnitus through somatosensory electrical stimulation may require manipulations of both auditory and non-auditory functions.

Glutamate and GABA(B) transmissions in lateral amygdala are involved in startle-like electromyographic (EMG) potentiation caused by activation of auditory thalamus.

The lateral amygdala nucleus (LA) receives auditory inputs from both the auditory thalamus (medial geniculate nucleus, MGN) and auditory association cortex (AAC). These auditory inputs are closely linked with glutamate and GABA(B) receptors in the LA. The LA has intra-amygdaloid connections with the central amygdala nucleus, which mediates auditory fear potentiation of startle (AFPS) via pathways to the startle circuits. The purpose of the present study was to establish an electromyographic (EMG) model for studying AFPS-related neural transmissions in the LA. Hind-limb startle-like EMG responses to single-pulse electrical stimulation of the trigeminal nucleus (TN) were recorded in anesthetized rats. These EMG responses were enhanced by single-pulse sub-threshold electrical stimulation of the MGN when the MGN stimulus led the TN stimulus at short inter-stimulus intervals (ISI). However, the EMG responses were not affected by single-pulse sub-threshold electrical stimulation of the AAC. Bilateral injection of the glutamate antagonist, kynurenic acid, into the LA decreased both the EMG enhancement caused by MGN stimulation at short ISIs and EMG responses to combined TN and AAC stimulation across various ISIs. Moreover, bilateral injection of the GABA(B) antagonist, phaclofen, into the LA increased both EMG responses to combined TN and MGN stimulation across various ISIs, and EMG responses to combined TN and AAC stimulation at short ISIs. These results suggest that the auditory inputs to the LA from the MGN and those from the AAC are affected differently by glutamate and GABA(B) receptors in the LA, and play differential roles in modulating startle responses.

[Action of high and superhigh doses of fission neutrons and gamma quanta on the central noradrenergic formation of the brain--on the locus coeruleus (the blue spot)]. / Deistvie vysokikh i sverkhvysokikh doz neitronov deleniia i gamma-kvantov na tsentral'noe noradrenergicheskoe obrazovanie golovnogo mozga--locus coeruleus (goluboe piatno).

Most of the blue spot neurons of Wistar rats exhibited a pronounced central chromatolysis 24 h following irradiation with fission neutrons (above 100 Gy) and gamma-quanta (above 200 Gy). The changes in the mesencephalic nucleus of the trigeminal nerve were distinct on day 2 after 200 Gy gamma-irradiation. The number of the modified nervous cells in these regions was higher than that in other brain parts.