Pars intermedia: unitary electrical activity regulated by light

In the pars intermedia of frogs in the dark two types of spontaneously firing neuronal units have been found; one can be inhibited by and the other is indifferent to increases in illumination. The receptor for the light-inhibited units appears to be the pineal organ. Transection experiments indicate that the axons to the two kinds of units in the pars intermedia are separately grouped in the floor.

Modification by sex hormones of the spontaneous and evoked bulbar electrical activity in goldfish

Young adult goldfish treated for 4 weeks with oestradiol, progesterone, or with a synthetic oestrogen or progestogen were used in a variety of tests designed to characterize olfactory function, using electroneurophysiological methods. The following observations were made:

1. The olfactory bulb appeared to be among the most responsive to hormone among the tested regions of the brain.

2. In oestrogenized goldfish and in fish given higher dosages of progesterone, there was a spontaneous slow pattern in the olfactory bulbar EEG. This slow pattern is changed to a desynchronized fast pattern after section at the midbrain—hindbrain level (cerveau isolé). On the other hand, the spontaneous 'normal' desynchronized pattern of progestogen-treated fish is converted to a synchronized slow pattern after similar brain stem transection.

3. Centrifugal modification of afferent-evoked bulbar electrical responses produced by NaCl infusion into the ipsilateral olfactory sac was augmented by hormones in lower doses in the cerveau isolé preparation. Oestradiol and progesterone in higher doses inhibit the centrifugal influence on bulbar responses while the synthetic progestational steroid continued to augment this control even when given at higher doses.

These results suggest that sex steroids alter olfactory function through their stimulatory or inhibitory actions on the goldfish central nervous system, but the nature of their action depends upon dosage level and the particular steroid.