Rise of the Animal Kingdom and Epigenetic Mechanisms of Evolution - Building the Most Complex Structure on Earth - page 285

B r a i n

Hypothalamus

Releasing hormones:

GHRH TRH GnRH CRH

Prolactin

Pituitary

Stimulating hormones

GH TSHACTH FSH

+LH

Liver Thyroid Adrenal Gonads

IGF-1 Thyroxine Gluco+mineral

corticoids

Estrogens+
androgens

B o n e

Figure 5.17 Simplified diagram of the central neural control and regulation of osteogenesis
in vertebrates via the hypothalamic-pituitary-terminal endocrine gland (i.e., thyroid, gonads,
and adrenals) axes and via the hypothalamic-pituitary axis (i.e., prolactin). Note that the
orders for activation/inactivation of the five-signal cascades or central regulatory axes for
bone homeostasis ultimately originate in the brain. Abbreviations : ACTH, adrenocorticotropic
hormone; CRH, corticotropin-releasing hormone; FSH, follicle-stimulating hormone; GH,
growth hormone; GHRH, growth hormone-releasing hormone; GnRH, gonadotropin-releasing
hormone; IGF-1, insulin-like growth factor-1; TRH, thyrotropin-releasing hormone; TSH,
thyroid-stimulating hormone (thyrotropin); LH, luteinizing hormone (lutropin).

One of the most important neuropeptides involved in the regulation of bone
homeostasis is the hypothalamic neuropeptide Y (NPY) and one of its receptors, Y2
( Baldock et al., 2002; Reid et al., 2005 ).
Let us see several other examples of the spatial restriction and fine-tuning by the
binary neural control system in animals.
In insects, production of ecdysteroids in the prothoracic gland is regulated by
the combined action of two groups of neuropeptides: ecdysteroid-inducing PTTH
(prothoracicotropic hormone), released by brain neurons, and three ecdysteroid-
inhibiting neuropeptides released by central and peripheral secretory neurons
( Yamanaka et al., 2006, 2010 ).