50
J. N. BALL AND BRIDGET I. BAKER
lower rate of- secretion in seawater related to the greater availability of
iodine in this medium. However, Knowles and Vollrath (1966~) reported
that TSH cells in some eels caught at sea were more numerous than in
river eels although in some seawater eels they could find no typical TSH
cells (Knowles and Vollrath, 1966d). Silver eels during the downstream
migration displayed very active TSH cells, judging by their extremely
prominent endoplasmic reticulum ( Knowles and Vollrath, 1966b). Thus,
even in the one species, the relationship between TSH cell activity and
external salinity is unclear. The eel TSH cells possibly tend to be less
active in deionized water than in freshwater, although this was not a
very marked reaction ( Olivereau, 1967b).
Reference was made earlier to the fact that in both eel and trout
pituitaries, the TSH cells retain their activity in vitro, the trout cells actually degranulating and becoming apparently more active than in uiuo
( Baker, 1963a, 1965a, 1967a). Comparable data comes from ectopic pituitary homotransplants in Poecilia formosa which secreted TSH at normal
levels, or in some individuals perhaps higher than normal levels, associated with the retention of very active TSH cells in the transplants, often
degranulated but with very active nuclei (Ball et al., 1965; Olivereau and
Ball, 1966). Comparable retention of TSH function and of active TSH
cells has been observed in ectopic pituitary autotransplants in P. latipinnu. The implications of these findings for the analysis of hypothalamic
control of TSH function in teleosts are obvious (see Ball et al., 1963,
1965).
6. PARS INTERMEDIA
The pars intermedia partially or completely surrounds the distal and
largest region of the neurohypophysial core and is usually extensively
invaded by neurohypophysial tracts ( exception: Lepidogobius, Kobayashi
et al., 1959). Its relative size varies in different species. It may be the
smallest region of the adenohypophysis, as in PoeciZia and other cypModonts, or, together with the enclosed neurohypophysis, it may form as
much as two-thirds the volume of the whole pituitary, as in salmonids.
Cells from other regions of the adenohypophysis may invade the pars
intermedia in small numbers (e.g., Hippocampus, Da Lage, 1958), and
pars intermedia cells are sometimes found in the pars distalis (Olivereau
and Ball, 1964).
Two cell types may usually be distinguished by their staining reactions and often also by differences in shape and position. Staining characteristics vary with species; pars intermedia cells have been described
as basophilic, staining for example with Aniline blue, or acidophilic (with
J. N. BALL AND BRIDGET I. BAKER
lower rate of- secretion in seawater related to the greater availability of
iodine in this medium. However, Knowles and Vollrath (1966~) reported
that TSH cells in some eels caught at sea were more numerous than in
river eels although in some seawater eels they could find no typical TSH
cells (Knowles and Vollrath, 1966d). Silver eels during the downstream
migration displayed very active TSH cells, judging by their extremely
prominent endoplasmic reticulum ( Knowles and Vollrath, 1966b). Thus,
even in the one species, the relationship between TSH cell activity and
external salinity is unclear. The eel TSH cells possibly tend to be less
active in deionized water than in freshwater, although this was not a
very marked reaction ( Olivereau, 1967b).
Reference was made earlier to the fact that in both eel and trout
pituitaries, the TSH cells retain their activity in vitro, the trout cells actually degranulating and becoming apparently more active than in uiuo
( Baker, 1963a, 1965a, 1967a). Comparable data comes from ectopic pituitary homotransplants in Poecilia formosa which secreted TSH at normal
levels, or in some individuals perhaps higher than normal levels, associated with the retention of very active TSH cells in the transplants, often
degranulated but with very active nuclei (Ball et al., 1965; Olivereau and
Ball, 1966). Comparable retention of TSH function and of active TSH
cells has been observed in ectopic pituitary autotransplants in P. latipinnu. The implications of these findings for the analysis of hypothalamic
control of TSH function in teleosts are obvious (see Ball et al., 1963,
1965).
6. PARS INTERMEDIA
The pars intermedia partially or completely surrounds the distal and
largest region of the neurohypophysial core and is usually extensively
invaded by neurohypophysial tracts ( exception: Lepidogobius, Kobayashi
et al., 1959). Its relative size varies in different species. It may be the
smallest region of the adenohypophysis, as in PoeciZia and other cypModonts, or, together with the enclosed neurohypophysis, it may form as
much as two-thirds the volume of the whole pituitary, as in salmonids.
Cells from other regions of the adenohypophysis may invade the pars
intermedia in small numbers (e.g., Hippocampus, Da Lage, 1958), and
pars intermedia cells are sometimes found in the pars distalis (Olivereau
and Ball, 1964).
Two cell types may usually be distinguished by their staining reactions and often also by differences in shape and position. Staining characteristics vary with species; pars intermedia cells have been described
as basophilic, staining for example with Aniline blue, or acidophilic (with